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Course Number: ENVR 430, Fall 2006

College/University: UNC

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, ..~ , .. . "" ~ . *' tIfIII" f .' ~ ~. .. , '~ ~ , .-. ~ , '#itMI ~I I , <F ~ .J" ,.. \ "'* ,.f" , ." , '", " ~ " , . y ;; , w , ? # '" .,p , ~ III' J... ,. ,\' , . "+8,"""' 'to 29.1 . MICROBIAL GROWTH AND FOOD SPOILAGE. 951 .,;. 'iotillism food poisoning due to ingestion I,Ciffood containing botulinum toxin pro!t",duced by Clostridium botulinum tCanning the process of sealing food in a ~ slosed container and heating to destroy ~" living organisms rOOd infection disease caused by active 0 fection resulting from ingestion inof : Ii pathogen-contaminated food 'ilifood poisoning (food intoxication) disease caused by the ingestion of food L "', hat contains preformed microbialtoxins t ~()ol(lspoilage a change in the appearance, ", smell, or taste of a food that makes it unacceptable to the consumer Irradiation the exposure of food to ionizing radiation for the purpose of inhibiting growth of microorganisms and insect pests, or to retard growth or ripening Listeriosis gastrointestinal food infection caused by Listeria monocytogenes that may lead to bacteremia and meningitis Lyophilization (freeze-drying) the proc.ess of removing all water from frozen fooc! under vacuum Nonperishable (stable) foods foods of low water activity that have an extended shelf life and are resistant to spoilage by microorganisms Perishable foods fresh foods generally of high water activity, that have a very short shelf life due to potential for spoilage by growth of microorganisms Pickling the process of acidifying food to prevent microbial growth and spoilage Salmonellosis enterocolitis caused by any of 1400 serotypes of Salmonella spp. Semiperishable foods foods of intermediate water activity that have a limited shelf life due to potential for spoilage by growth of microorganisms Water activity (awJ the availablity of water for use in metabolic processes icroorganisms are important factors in our food supply. A variety of foods that we con~ume are produced or enhanced by microbial action. For IXffillple, dairy products such as cheese, buttermilk, sour "ream, and yogurt are all produced by microbial ferjonentation. Sauerkraut is a fermented vegetable food. i1~qt products including certain sausages, pates, and ~ver spreads are produced using microbial fermentation Jechniques. Cider vinegar is produced by lactic acid bac~~r!a (~ Section 30.10), and alcoholic beverages are ..roduced by fermentation processes using yeast (001::) ~i)ection30.13). We discuss the use of microorganisms to _1i9sluce edible foods on an industrial scale in Chapter 30. .. spoilage agents in foods and we then present a variety of methods used to control their growth and preserve the food supply. Microbial Growth and Food Spoilage A wide variety of microorganisms colonize and grow on common foods. Many foods provide a suitable medium for the growth of microorganisms, and microbial growth usually reduces food quality and availability. Food Spoilage Food spoilage is any change in the appearance, smell, or taste of a food product that makes it unacceptable to the consumer. Spoiled food is not necessarily food unsafe to eat, but in some cases pathogenic organisms may cause spoilage. Spoiled food is generally regarded as unpalatable and will not be purchased or consumed. Food spoilage causes economic loss to producers, distributors, and even consumers in the form of higher prices and constricted supply. Since foods are organic materiat they provide nutrients for the growth of a wide variety of chemoorganotrophic bacteria. The physical and chemical characteristics of the food determine its degree of susceptibility to microbial activity. With respect to spoilage, foods can be classified into three major categories: (1) perishable foods, including many &esh foods; (2) semiperishable foods, such as potatoes and nuts; and (3)stable or nonperishable foods such as flour and sugar (Table29.1).These food categories differ largely with regard to moisturecontent,which is related, as we saw in Section 6.12, to water activity, aw. Nonperishable foods have low water activity and can " In this chapter, we will concentrate on the negative ~.spects of microbial growth in food. Uncontrolled and ~\N'anted microbial growth destroys vast quantities of ~ood, causing significant economic loss as well as a ~:jjremendousloss of nutrients. Consumption of food con'~J.Ilinated with particular microorganisms or microbial 1roducts can also cause serious illnesses such as food 'ections or food poisoning. , FOOD PRESERVATION AND MICROBIAL GROWTH !,;~"(:ticroorganisms ubiquitous in our environment and are ~;~nbe found in water, air, and especially in food. Fresh lood, most prepared foods, and sometimes even pre~erved foods are contaminated with microorganisms. ~~irstwe discuss the microorganisms that are important [I Ii I' 11 952 . Chapter 29 . FOOD PRESERVATION AND FOODBORNE MICROBIAL DISEASES Ii I' II I il Highly perishable Semiperishable Nonperishable Meats, fish, poultry, eggs, milk, most fruits and vegetables Potatoes, some apples, and nuts Sugar, flour, rice, and dry beans 11 II il Ii II i i I :!1 !I, ii Ii II :11 il :1 11 1 ij :1 11 11 iJ jl 'j " j : generally be stored for considerable lengths of time without deterioration. Perishable and semiperishable foods are those with higher water activity. These foods must be stored under conditions that slow or stop microbial growth. Fresh foods are spoiled by a variety of bacteria and fungi, and each type of fresh food is typically colonized by particular microorganisms (Table 29.2). Because the chemical properties of foods vary widely, different foods are colonized by the indigenous spoilage organisms that are best able to use the available nutrients. For example, enteric bacteria such as Salmonella, Shigella, and Escherichia,all potential pathogens that live in the gut of animals, are rarely implicated in fruit or vegetable spoilage, but often contaminate and spoil meat. At slaughter, intestinal contents, including the living bacteria, can leak and contaminate the meat. Likewise, lactic acid bacteria, the most common microorganisms in dairy products, are the major spoilers of milk and milk products. Pseudomonas species are found in both soil and animals and are thus widely involved in the spoilage of fresh foods. Microbial growth in foods follows the standard pattern for bacterial growth (~ Sections 6.3 and 6.4). The lag phase may be of variable duration in a food, depending on the contaminating organism and its previous growth history. The rate of growth during the exponential phase depends on the temperature,the nutrient value of the food, and other conditions of growth. The time required for the population density to reach a significant level in a given food product depends on both the size of the initial inoculum and the rate of growth during the exponential phase. Only when the microbial population density reaches a substantial level are spoilage effects usually observed. Throughout much of the exponential growth phase, population densities may be so low that no effect can be observed. Only the last doubling or two leads to observable spoilage (~ Section 6.4).Thus, for much of the period of microbial growth in a food, there is no visible or easily detectable change in food quality. te g P tl fr IT al w fr of fa m In su teJ se, ./ 29.1 Concept Check Foods often spoil due to contamination by microorganisms. Foods vary considerably in their sensitivity to microbial growth, depending on their nutrient content and water content. Individual categories of food have specific spoilage patterns and spoilage organisms. Many food spoilage microorganisms are also potential pathogens. .I .I List the major categories of food and define them with respect to water content. Identify at least three bacterial genera that cause both food spoilage and human disease. Ell Food Preservation Ac Al is an ity pIisn foe wIlin aCE We now examine a number of food storage and preservation processes that inhibit or stop microbial growth in food, stopping the growth of spoilage microorganisms and human pathogens. Temperature Besides moisture, one of the most crucial factors affecting microbial growth in food is temperature (OC!:) Section 6.9). In general, a lower storage temperature results in a retarded spoilage rate. A number of psychrotolerant (cold cm me of~ ane foo pel de\ the kra cro, the pro bel{ itin; Wa' Waf byr croc acti' bee. the j a so alOl darr proc are f 1 Fruits and vegetables Bacteria Fungi Erwinia, Pseudomonas, Corynebacterium (mainly vegetable pathogens; rarely spoil fruit) Aspergillus, Botrytis, Geotrichium, Rhizopus, Penicillium, Cladosporium, Alternaria, Phytophora, various yeasts Acinetobacter, Aeromonas, Pseudomonas, Micrococcus, AchrorilObacter, ;i " I] Fresh meat, poultry, and seafood Bacteria Fungi Flavobacterium, Proteus, Salmonella, Escherichia, Campylobacter, Listeria Cladosporium, Mucor, Rhizopus, Penicillium, Geotrichium, Sporotrichium, Candida, Torula, Rhodotorula Streptococcus, Leuconostoc, Lactococcus, Lactobacillus, Pseudomonas, Clostridium, Bacillus, Flavobacterium Saccharomyces, Torula, Penicillium Proteus Milk High-sugar foods Bacteria Bacteria Fungi I Ii a The organisms listed are the most commonly observed spoilage agents of fresh, perishable foods. Genera in bold face include possible human pathogens, " II [ 29.2 . FOOD PRESERVATION. 953 )lerant) microorganisms, however, can survive and row at refrigerator temperatures. Therefore, storage of erishable food products for long periods of time (greater lan several days) is possible only at temperatures below :eezing. Freezing and thawing alter the physical strucHe of many foods. Therefore, freezing is not an acceptble preservation method for many fresh foods, but is ridely used for the preservation of meats and many ~uitsand vegetables. Freezers providing a temperature f -20C are most commonly used. At -20C, storage )r weeks or months is possible, but microbial growth lay still occur in pockets of liquid water trapped with1the frozen mass. For long-term storage, temperatures llch as -80C (dry ice temperature) are necessary. Main~nance of such low temperatures is expensive and conequently is not used for routine food storage. lcidity ,nother major factor affecting microbial growth in food ; pH or acidity. Foods vary somewhat in pH, but most re neutral or acidic. Microorganisms differ in their abil:y to grow under acidic conditions, but conditions of H 5 or less inhibit the growth of most spoilage organ,ms (~ Section 6.11). Therefore, acid is often used in )od preservation, a process called pickling. Vinegar, rhich is dilute acetic acid, is usually added in the pickng process (vinegar is a fermentation product of the cetic acid bacteria; its industrial production will be disussed in Section 30.10). In addition to vinegar, pickling 1ethods usually include the addition of large amounts ,fsalt or sugar to decrease water availability (see below) nd further inhibit microbial growth. Common pickled )ods include cucumbers (sweet, sour, and dill pickles), 'eppers, meats, fish, and fruits. In some cases, acid can levelop in the food as a result of microbial action, and he product is called a fermented food, such as in sauer:raut (cabbage), yogurt, cheese, and sour cream. The miroorganisms involved in food fermentations include he lactic acid bacteria, the acetic acid bacteria, and the lropionic acid bacteria. These bacteria do not grow 'elow about pH 4, so the food fermentation is a self-limting process. Vater activity Vater activity (aw) is the availability of water for use 'y microorganisms in metabolic processes. Because miroorganisms do not grow under condition of low water ctivity (low water availability), microbial growth can 'e controlled by lowering the available water content of he food by drying or by adding high concentrations of ,solute such as salt or sugar (~Section 6.12). NaturIIor artificial heat is often used for drying, but the least lamaging physical method used to dry foods is the >rocess of lyophilization (freeze-drying), where foods lIe frozen and water is removed under vacuum. Milk, meat, fish, vegetables, fruit, eggs, and other economically important foods are commonly preserved by some form of drying. A number of foods are preserved by addition of salt or sugar to reduce water activity. Foods preserved by addition of sugar are mainly fruits (jams, jellies, and preserves). Salted products are primarily meats and fish. Sausage and ham are preserved by salt, although individual products vary in water activity depending on how much salt is added and how much the meat has been dried. Canning Canning is a process in which a food is sealed in a container such as a can or glass jar and heated to kill allliving organisms, or at least to ensure that there will be no growth of residual organisms. When the can is properly sealed and heated, the food should remain stable and unspoiled indefinitely, even when stored in the absence of refrigeration. The temperature-time relationships for canning depend on the type of food, its pH, the size of the container, and the consistency or density of the food. Because heat must penetrate completely to the center of the food within the can, heating times must be longer for large cans or very dense foods. Acid foods can often be canned effectively by heating just to boiling, 100C, whereas nonacid foods must be heated to autoclave temperatures (121C). Unfortunately, heating times long enough to guarantee absolute sterility of every can (~ Section 20.1) would change the food so greatly that it would likely be unpalatable and lose nutritional value. Therefore, properly canned foods may not be sterile. The environment inside a can is anoxic, and microbial growth in a canned food is frequently the result of the growth of organisms that produce extensive amounts of gas. This can cause pressure build-up inside the can, resulting in bulges or, in severe cases, even an explosion of the can (Figure 29.1). Because some of the anoxic bacteria that grow in canned foods are toxin producers of the genus Clostridium (OCt)Sections 21.10 and 29.5), food from a can that is visibly altered should never be eaten'oHowever, the lack of obvious gas production is not an absolute guarantee that the food is safe to consume. Chemical Food Preservation A number of chemicals are used commercially to control microbial growth in food. These are classified by the U.S. Food and Drug Administration as "generally recognized as safe" and find wide application in the food industry (Table 29.3). Many of these chemicals, like sodium propionate, have been used for many years with no evidence of human toxicity. Others, like nitrites (carcinogen precursor), ethylene or propylene oxides (mutagens; ,,~ 954 . Chapter 29 . FOOD PRESERVATION AND FOODBORNE MICROBIAL DISEASES ~ Section 10.4), or antibiotics (development of antibiotic-resistant pathogens; ~ Section 20.12), are more controversial food additives because of evidence that these compounds may be detrimental to human health. Because of lengthy and costly testing programs for any new chemical proposed as a food preservative today, it is unlikely that new compounds will be added to the list of chemical food preservatives in Table 29.3 in the near future. Irradiation Irradiation of food using ionizing irradiation is now a standard method for reducing contamination by bacteria, fungi, and even insects (~Section 20.2). Table 29.4 lists some foods for which radiation treatment has been approved. Foods such as spices are routinely irradiated. In the United States, fresh meat products such as hamburger and poultry can now be irradiated to limit contamination by Escherichiacoli0157:H7 and other enteric pathogens (hamburger) and Campylobacterjejuni (poultry). For food irradiation, gamma rays are generated from 60Coor 137Cssources. The food products receive a controlled radiation dose. This dose varies considerably by each food category and purpose. For example, a dose of 44 kilo Grays (kGys) is used to sterilize meat products used on United States NASA space flights and is nearly 10 times higher than the 4.5-kGy dose used for control of pathogens in hamburger (Table 29.4). In the United States, a consumer product information label must be affixed to foods that are irradiated. I ~1 Fn Fn Dr Re Pa, Dr Fre nc, liar (a) (b) at a nun I A SL and Tabl, two ized late 1 ~ u OJ 0 I-' e (c) (d) ./ 29.2 Concept Check IIim!EII Changes in cans as a result of microbial spoilage. (a) Normal can; the top of the can is slightly indented due to negative pressure (vacuum) inside. (b) Swelling resulting from minimal gas-production. Note that the top is slightly distended. (c) Severe swelling due to extensive gas production. (d) The can shown in (c) was dropped and the gas pressure resulted in a violent explosion, tearing the lid apart. Food microbiology deals with methods for limiting spoilage and the growth of disease-causing microorganisms in food during processing and storage. Foods vary considerably in their sensitivity to microbial growth, depending on their nutrient content, water availability, and pH. The growth of microorganisms in perishable foods can be controlled by refrigeration, freezing, canning, pickling, dehydration, chemical preservation, or irradiation. ,/' ,/' Outline at least four methods of food preservation. How does each method limit growth of microorganisms? Are-food spoilage microorganisms also pathogens? Give examples to support your answer. FOOt Fooe suIts crobi toxin alive Thei prefe some botul1 ins oj Fooci Food gestic the pc suffic tion a mont food Many disea~ Micrc As di~ pr~~~r Sodium or calcium propionate Sodium benzoate Bread Carbonated beverages, fruit, fruit juices, pickles, margarine, preserves Citrus products, cheese, pickles, salads Dried fruits and vegetables; wine Meat, fish Spices, dried fruits, nuts Smoked ham, bacon Sorbic acid Sulfur dioxide, sulfites, bisulfites Formaldehyde (from food-smoking process) Ethylene and propylene oxides Sodium nitrite II FOOD BORNE DISEASES Failure to adequately decontaminate and preserve food may allow the growth of pathogens, resulting in diseases with significant morbidity and mortality. Like waterborne diseases, foodborne diseases are common-source diseases; a single contaminated food 50urceJ for instal1\:e 29.4 . STAPHYLOCOCCAL FOOD POISONING. 955 Fresh pork Fresh fruits and vegetables Dried spices, herbs, and flavoring mixtures Refrigerated or frozen uncooked meat products, including ground meat Packaged frozen meats used in the National Aeronautics and Space Administration (NASA) flight program Dry or dehydrated enzyme preparations (e.g., meat tenderizer) Frozen, uncooked poultry and poultry products Control of Trichinellaspiralis parasite Inhibition of growth and maturation (ripening) Microbial disinfection Control of foodbome pathogens Extension of shelf life Sterilization Microbial disinfection Control of foodborne pathogens aConsumer labeling laws in the United States require that all irradiated foods must be conspicuously labeled "Treated with radiation" or "Treated by irradiation" in addition to information required by other regulations. [at a food-processing plant or a restaurant, may affect a !'number of individuals. Foodborne Diseases and Microbial Sampling A summary of the most prevalent foodborne diseases and the microorganisms that cause them is shown in [Table29.5. These common diseases can be separated into '.two categories, food poisoningand foodinfection.Special'ized microbial sampling techniques are necessary to isolate the pathogens responsible for foodborne diseases. ,Food Poisoning "Food poisoning or food intoxication is disease that retsults from ingestion of foods containing preformed mi~crobial toxins. The microorganisms that produced the !toxins do not have to grow in the host and are often not 'alive at the time the contaminated food is consumed. ; "The illness is due to ingestion and subsequent action of ~preformed bioactive toxin. We previously discussed "some of these toxins, notably the exotoxin of Clostridium '"botulinum(000 Section 21.10) and the superantigen toxins of Staphylococcus aureus (~ Section 22.14). !Food Infection tFood infections are active infections resulting from in1'gestion of pathogen-contaminated food. In addition to the passive transfer of microbial toxins, food may contain ;sufficient numbers of viable pathogens to cause infec,bon and disease in the host. Food infection is a very com':montype of foodborne illness (Table 29.5), and Salmonella 'food infection is a typical example (see Section 29.6). 'Many of these infectious agents also cause waterborne 'diseases (~ Chapter 28). Microbial Sampling of Foods [Asdiscussed in Section 29.1, microorganisms are always !presentin fresh foods. Because pathogens may be present along with many harmless organisms, methods have been developed to detect important pathogens such as Escherichiacoli 0157:H7, Salmonella, Staphylococcus, and Clostridium botulinum. We discussed in Section 24.13 the use of nucleic acid probes for the detection of specific foodborne pathogens. For growth studies of nonliquid foods, preliminary treatment is usually required to suspend microorganisms embedded or entrapped within the food. The most suitable method is high-speed blending. The food should be examined as soon after sampling as possible; if examination cannot begin within 1h of sampling, the food should be refrigerated. A frozen food should be thawed in its original container in a refrigerator and examined or cultured as soon as thawing is complete. Samples can be inoculated onto emiched media, followed by transfer to differential or selective media for isolation and identification, as we described for human pathogens (~ Section 24.1), or probed directly for pathogen presence using nucleic acid-based methods such as the polymerase chain reaction (PCR) (0Ci::I Section 24.13). ./ 29.3 ConcepfCheck Foodbome diseases include food poisoning resulting from the action of microbial toxins and food infections due to the growth and invasion of microorganisms in the body. Specialized techniques are used to sample microorganisms in food. ./' ./' Distinguish between food infection and food poisoning. Describe the sampling of a solid food such as meat for the presence of microorganisms. Ell Staphylococcal Food Poisoning A very common food poisoning is caused by the grampositive coccus, Staphylococcus aureus. Biology and Epidemiology Staphylococcus ureusand other members of the genus a are small, gram-positive cocci (0;10Section12.19). s we A 956 . Chapter 29 . FOOD PRESERVATION AND FOOD BORNE MICROBIAL DISEASES or ar. fOI fir tht da ba co lit! Of Bacteria Bacillus cereus Campylobacter jejuni Clostridium perfringens Escherichia coli 0157:H7 Other enteropathogenic Listeria monocytogenes Salmonella spp. Staphylococcus aureus Streptococcus Yersinia enterocolitica All other bacteria Total bacterial Escherichia coli FP Fl FP Fl Fl Fl Fl FP Fl Fl FP and Fl 27,000 1,963,000 248,000 63,000 110,000 2,500 1,340,000 185,000 50,000 87,000 102,000 4,177,500 30,000 16,000 200,000 113,000 359,000 9,200,000 82,000 9,282,000 13,818,500 Rice and starchy foods, high-sugar foods Poultry, dairy Cooked and reheated meats and meat products Meat, especially ground meat Meat, especially ground meat Meat and dairy Poultry, meat, dairy, eggs Meat, desserts Dairy, meat Pork, milk on se! Se' Tn diE inf cal du foe Fo( for she Parasites Cryptosporidiumparvum Cyclospora cayetanensis Giardialamblia Toxoplasma ondii g Total parasites Viruses Norwalk-like viruses All other viruses Total viruses Total Annual Foodborne Diseases Fl Fl Fl Fl Raw and undercooked meat Fresh produce Contaminated or infected meat Raw and undercooked meat Fl Fl Shellfish, many other foods app, food poisoning: PI, food infection. Estimates are based on data provided by the Centers for Disease Control and Prevention, Atlanta, GA, USA. ./ StaJ pre DeDe can if if discussed in Section 26.9, staphylococci are found on the skin and in the respiratory tract of nearly all humans, and are often opportunistic pathogens. Staphylococcus aureus is frequently associated with food poisoning because, as it grows, this organism produces several heatstable protein enterotoxins (~ Section 21.11). The enterotoxins are released into the surrounding medium or food; if food that contains toxin is ingested, gastroenteritis characterized by nausea, vomiting, and diarrhea, occurs within 1-6 h. Each year, an estimated 185,000 cases of staphylococcal food poisoning occur in the United States (Table 29.5). The foods most commonly involved are custardand cream-filled baked goods, poultry, meat and meat products, gravies, egg and meat salads, puddings, and creamy salad dressings. If such foods are kept refrigerated after preparation, they usually remain safe, because S. aureus growth is significantly reduced at low temperatures. Foods of this type, however, are often kept in kitchens at room temperature or outdoors at picnics. The food, if inoculated with S. aureus from an infected food handler, supports rapid bacterial growth and enterotoxin production. Even if the toxin-containing foods are reheated again before eating, the toxin is relatively heatstable and may remain active. Pathogenesis Staphylococcusaureusproduces seven different enterotoxins: A, B,C1, C2, C3, D, and E. Enterotoxin A, a super antigen, is most frequently associated with staphylococcal food poisoning (~Section 22.14). Superantigens work by stimulating large numbers of T cells, which in turn release intercellular mediators called cytokines, activating a general inflammatory response in the intestine that results in gastroenteritis, including massive loss of fluids from the intestine. S. aureus enterotoxin A is a small single peptide of 30,000 molecular weight that is encoded by a chromosomal gene. Cloning and sequencing of this gene, the entA gene, and of several other S. aureus enterotoxin genes, show that the toxins are genetically related. Although the entA gene is on the bacterial chromosome, type Band C S. aureusenterotoxins may be encoded on plasmids, transposons, or lysogenic bacteriophages. We discussed the importance of accessory genetic elements such as plasmids and bacteriophages as vectors for toxin production in Sections 21.10 and 21.11. Diagnosis, Treatment, and Prevention Several assays based on the detection of either enterotoxin (ELISAdetection of enterotoxin; ~ Section 24.11) E Bot cau diU! coo spo spo Clo ClOf sPO] It a! mar Sect port an e 29.5 . CLOSTRIDIAL FOOD POISONING. 957 or S. aureus exonuclease (an enzyme that degrades DNA) ,. are available to detect dangerous levels of S. aureus in food. However, these rapid tests are qualitative, confirming only the presence or absence of S. aureus above the detection limits of the assay. To obtain quantitative ." data and determine the extent ofbacterialcontamination, ",. \ \ " f. \ .. '" ... \ .." ... .~ I ,It '\ "" .. ... , '" ,. , \ -II bacterial plate counts are required. For staphylococcal counts, a high-salt medium (either sodium chloride or lithium chloride at a final concentration of 7.5%) is used. Of the organisms present in foods, staphylococci are the only common ones tolerant of such levels of salt. S. aureus food poisoning can be quite severe, but is self-limiting, usually resolving within 48 h after onset. Severe cases may require treatment for dehydration. Treatment with antibiotics is not useful because the disease is caused by a preformed toxin, not an active infection. Staphylococcal food poisoning can be prevented by ,. .- , .. , . <l '1 " \. 4f1 ~ ." ,,'" !." \. \ "- , ~ .,. ..' .. - H ., ... ...' .,"""" , ~. >Ii ~ Gramstain of Clostridium perfringens.The individual gram-positive bacilli are about 1 J.lmin diameter. careful sanitation and hygiene measures both in pro- ~. uction and food preparation steps and by storage of d foods at low temperatures to inhibit bacterial growth. Foods susceptible to colonization by S. aureus and kept rfor several hours above 4C (refrigerator temperature) should be discarded rather than eaten. 29.4 Concept Check r preformed enterotoxinA, Staphylococcal food poisoning results from the ingestion of a superantigen produced by Staphylococcus ureuswhen growing in foods. In many cases, S.aureus a cannot be cultured from the contaminated food. ,f ,f Explain the symptoms of staphylococcal food poisoning and the action of enterotoxin A. Will antibiotics effect the outcome or the severity of staphylococcal food poisoning? Explain. The disease results from the ingestion of a large dose of Clostridium perfringens (> 108 cells) in contaminated cooked and uncooked foods, especially meat, poultry, and fish. Large numbers of C. perfringens can grow in meat dishes cooked in bulk (heat penetration in these situations is often slow and insufficient) and then left at 20-40C for short time periods. Spores of C. perfringens germinate under anoxic conditions, such as in a sealed container, and grow quickly in the meat. However, the toxin is not yet present. After consumption of the contaminated food, the living C. perfringens begins to sporulate in the intestine, triggering production of the perfringens enterotoxin (OQ:)Table 21.4). The enterotoxin alters the permeability of the intestinal epithelium, leading to diarrhea and intestinal cramps, usually with no fever or vomiting. The onset of perfringens food poisoning begins about 7-15 h after consumption of the contaminated food, but usually resolves within 24 h, and fatalities are rare. Diagnosis, Treatment, and Prevention Diagnosis of perfringens food poisoning is made by isolation of C. perfringens from the gut or, more reliably, by a direct enzyme-linked immunosorbent (ELISA) assay to detect C. perfringens enterotoxin in feces (~ Section 24.11). Because C. perfringens food poisoning is selflimiting, treatment is usually not necessary, although antitoxins are available (~ Section 22.11). Prevention of perfringens food poisoning requires measures to prevent contamination of raw and cooked foods and control of cooking and canning procedures to ensure proper heat treatment of all foods. Botulism Botulism is a severe food poisoning; it is often fatal and occurs following the consumption of food containing the exotoxin produced by the anaerobic, gram-positive !i Clostridial FoodPoisoning Both Clostridium perfringens and Clostridium botulinum cause serious food poisoning. Members of the Clostri,odium genus are anaerobic spore formers. Canning and cooking procedures kill living organisms but do not kill tspores. Under appropriate anaerobic conditions, the spores germinate and toxin is produced. Clostridium perfringens Food Poisoning iClostridium perfringens is an anaerobic, gram-positive ';spore-forming rod commonly found in soil (Figure 29.2). IJtalso lives in small numbers in the intestinal tract of :many animals and is therefore found in sewage (00::1 Section 12.21). C. perfringens is the most prevalent reorted cause of food poisoning in the United States, with .an estimated 248,000 annual cases (Table 29.5). i L 958 . Chapter 29 . FOOD PRESERVATION AND FOODBORNE MICROBIAL DISEASES ,j' ,j' rod Clostridium botulinum. This bacterium normally inhabits soil or water, but its spores may contaminate raw foods before harvest or slaughter. If the foods are properly processed so that the C. botulinum spores are removed or killed, no problem arises; but if viable spores are present, they may initiate growth and toxin production. Even a small amount of the resultant neurotoxin can be poisonous. We discussed the nature and action of botulinum toxin in Section 21.10 (~ Figure 21.19).Botulinum toxin is a neurotoxin that causes flacid paralysis, usually affecting the autonomic nerves that control body functions such as respiration and heart beat. At least seven distinct types of botulinum toxin are known. The toxins are destroyed by high heat (80DCfor 10 min), and so thoroughly cooked food, even if contaminated with toxin, may be harmless. Most cases of botulism occur as a result of eating foods that are not cooked after processing (Figure 29.3a). For example, nonacid, home-canned vegetables (e.g., home-canned corn and beans) are often used without cooking when making cold salads. Similarly, smoked and fresh fish, vacuum packed in plastic, are often eaten without cooking. Under such conditions, C. botulinum spores germinate, and the resulting cells produce toxin. If these foods are consumed, then ingestion of even a small amount will result in this severe and highly dangerous type of food poisoning. Infant botulism occurs when spores of Clostridium botulinum are ingested, often from raw honey (Figure 29.3b). If the infant's normal flora is not well developed or if the infant is undergoing antibiotic therapy, the spores may germinate and C. botulinum cells may grow and release toxin. Most cases of infant botulism occur between the first week of life and 2 months of age; infant botulism is rare in children older than 6 months when the normal intestinal flora is more developed (~ Section 21.4). All forms of botulism are quite rare and usually less than 150 total cases occur each year in the United States, but up to 25% are fatal. Death occurs from respiratory paralysis or cardiac arrest due to the paralyzing action of the botulinum neurotoxin (~Section 21.10). Diagnosis, Treatment, and Prevention Diagnosis is by demonstrating toxin in patient serum, or by finding toxin or Clostridium botulinum in suspected food products. Laboratory findings are coupled with clinical observations including neurological signs of localized paralysis (impaired vision and speech) beginning 18-24 h after ingestion of contaminated food. Treatment involves administration of antitoxin (~ Section 22.11) and mechanical ventilation. Prevention requires maintaining careful controls over canning and preservation methods and heating susceptible foods to destroy spores, or boiling for 20 minutes to destroy the toxins. en Q) en cu u -0 Q) t 0 Q. Q) Laboratory-confirmedcases NationalNotifiableDiseases Surveillance System (NNDSS) data a: 110 Outbr~ak caused by 100 sauteed onions, IL 90 Outbreak caused Outbreak caused by 80 baked potatoes, TX by fermented 70 60 + 50 "hit'" Pi"C'" AK 40 30 20 10 0 1994 1989 1984 1999 1979 I Al1 sis nel. col Sic Sah rod entl inh, Virt S. t}j but mos cOuJ caus type oger caus prev. over cases the b 3C c 0 "3 j Year (a) Foodborne botulism 110 100 90 en en cu u -0 Q) t 0 Q. Q) Q) 80 70 60 50 40 30 20 10 0 1979 1984 1989 Year 1994 1999 a: (b) Infant botulism ~e incidence of botulism in the United States. (a) Foodborne botulism. In years with high numbers of cases, major outbreaks that account for the increase are indicated. (b) Infant botulism. More than half of the cases of infant botulism Prevention, Atlanta, GA, USA. in the United States occur in California. Data are from the Centers for Disease Control and ' 25 20 a. 0 a. 0 0 0 :: In infant botulism, a 0 C. botulism and toxin are often found in bowel contents. Infant botulism is usually sellimiting and most infants recover with only supportive therapy, such as assisted ventilation. Occasional deaths may occur due to respiratory failure. Honey may be a source of C. botulinum spores. Therefore, feeding honey to children under 2 years of age is generally discouraged. () '" (J.) ~ 10 (J.) a. 15 "0 (J.) J 51 0 19 ./ 29.5 Concept Check Clostridiumfood poisoning resultsfrom ingestionof toxinsproduced by microbial growth in foods or due to microbial growth and toxin production in the body. Perfringens food poisoning is quite common, and is usually a self-limiting gastrointestinal disease. Botulism is a rare but very serious disease, with significant mortality. ~ in the Ur 40,000 al onlyabot reported. lion, At/al - __n--- ___n-_n_n-__n-- 29.6 . SALMONELLOSIS. 959 '" ./ ./ Describe the events that lead to perfringens food poisoning. What is the likely outcome of the poisoning? Describe the events that lead to botulism. What is the likely outcome of botulism? Ell Salmonellosis Although sometimes called food poisoning, salmonellosis is a gastrointestinal disease due to foodbome Salmonellainfection. Symptoms begin only after the pathogen colonizes the intestinal epithelium. Biology and Epidemiology Salmonella spp. are gram-negative facultative aerobic rods related to Escherichia coli, Shigella spp., and other enteric Bacteria (~ Section 12.11). Salmonella normally inhabit the gut of animals and are thus found in sewage. Virtually all Salmonella are pathogenic for humans: One, S. typhi, causes the serious human disease typhoid fever, ~. ut b and estimates place the actual number at over 1,300,000 cases of salmonellosis every year (Table 29.5). The ultimate sources of the foodbome salmonellas are the intestinal tracts of humans and warm-blooded animals. The organism may reach food by fecal contamination from food handlers. Food production animals such as chickens and cattle may also harbor Salmonella strains that are pathogenic to humans and may pass the bacteria to finished fresh foods such as eggs, meat, and dairy products. Salmonellafood infections are often traced to products such as custards, cream cakes, meringues, pies, and eggnog made with uncooked eggs. Other foods commonly implicated in salmonellosis outbreaks are meats and meat products such as meat pies, cured but uncooked sausages and meats, poultry, milk, and milk products. Pathogenesis The most common salmonellosis is a Salmonella-induced enterocolitis.Ingestion of food containing 105-108 viable Salmonella results in colonization of the small and large intestine. Onset of the disease occurs 8-48 h after ingestion. Symptoms include the sudden onset of headache, chills, vomiting, and diarrhea, followed by a fever that lasts a few days. The disease normally resolves without intervention in 2 to 3 days. However, even after recovery, patients shed Salmonellain feces for several weeks. Some patients recover and remain asymptomatic, but shed organisms for months or even years, resulting in a chronic carrier condition (~ the box, the Tragic Case of Typhoid Mary, Chapter 25). Salmonellosis may also cause septicemia, a blood infection, enteric fever, or typhoidfever, a disease characrterized by systemic infection and high fever lasting several weeks. Mortality can approach 15% in untreated typhoid fever. Diagnosis, Treatment, and Prevention Diagnosis is made by observation of clinical symptoms, history of recent food consumption, and by culture of the organism from feces. Several selective media are available (~ Section 24.2), and tests for the presence of Salmonella are commonly done on animal food products, such as raw meat, poultry, eggs, and powdered milk, because Salmonella from production animals is the usual source of food contamination. For enterocolitis, treatment is usually unnecessary, and antibiotic treatment does not shorten the course of the disease or eliminate the carrier state. Antibiotic treatment, however, significantly reduces the length and severity of septicemia and typhoid fever. Mortality due to typhoid fever can be reduced to less than 1% with appropriate antibiotic therapy. Cooked foods heated to 70C for at least 10 minutes are considered safe if consumed immediately, or if held is fortunately very rare in the United States, with . most of the 500 foodbome cases imported from other countries. However, a number of Salmonella species cause foodbome gastroenteritis. In all, over 1400 serotypes of various Salmonellaspecies are known to be path- , ogenic for humans. S. typhimuriumis the most common cause of salmonellosis in humans. The incidence and prevalence of reportedsalmonellosis has been very steady ! over the last decade, with about 45,000 documented leases each year (Figure 29.4). However, less than 4% of ithe total cases of salmonellosis are probably reported, 30 0 c: 25 .- Outbreak caused by contaminated pasteurized milk, IL 1'5 a. 0 a. 0 0 0 1'0 '.0 ~ 20 ~:: Q) a. m Q) 15 it) gj 10 n~ '.t Q) a: 8. 5 0 1969 1974 1979 1984 Year 1989 1994 1999 The prevalence of reported cases of salmonellosis in the United States. The total number of reported cases is between 40,000 and 45,000 per year. Epidemiologic investigations suggest that 10nlyabout 3% of all cases of salmonellosis are properly identified and reported. Data are from the Centers for Disease Control and Prevention, Atlanta. GA, USA. .~ .. 960 . Chapter 29 . FOOD PRESERVATION AND FOODBORNE MICROBIAL DISEASES at 50C or stored at lOoCor less. Cooked or canned foods that become contaminated by an infected food handler can support the growth of Salmonellaif the foods are held for long periods of time without heating or refrigeration. Salmonella infections are more common in summer than in winter, probably because warm environmental conditions are more favorable for growth of microorganisms in foods (Figure 29.4). Although local laws and enforcement vary, because of the lengthy carrier state, infected individuals are often banned from work as food handlers until their feces are negative for Salmonella in three successive cultures. ,/ 29.6 Concept Check Salmonellosis, an extremely common foodborne infection, results from infection with ingested Salmonella spp. Salmonella can enter the food chain via production animals or food handlers. ./ ./ Describe the three kinds of salmonellosis food infection. Which is most common? How might Salmonella contamination of production animals be contained? Ell Pathogenic Escherichia coli Several strains of Escherichiacoliare potential foodborne pathogens. All pathogenic strains act first on the intestine and several are characterized by their ability to produce potent enterotoxins (~Section 21.11). Biology, Epidemiology, and Pathogenesis Escherichiacoliis a common inhabitant of the animal gut. The short, gram-negative rods are classified as enteric Bacteria (GQ::;, Section 12.11). There are about 200 known pathogenic E. coli that can cause life-threatening diarrheal disease and urinary tract infections. The pathogenic strains are divided into several categories, based primarily on the toxins they produce and the diseases they cause. Enterohemorrhagic E. coli(EHEC) produce verotoxin, an enterotoxin similar to one produced by Shigelladysenteriae, the Shiga toxin (0fJt:\Table 21.4). After ingestion of food or water containing one particular EHEC strain, E. coli 0157:H7, the organism grows in the small intestine and produces the verotoxin. Verotoxin causes both hemorrhagic (bloody) diarrhea and kidney failure. E. coli 0157:H7 causes at least 60,000 infections and 50 deaths each year from foodborne disease (Table 29.5) and is a leading cause of kidney failure in children. The most common cause of this infection is the consumption of contaminated uncooked or undercooked meat, particularly mass-processed ground meat. In several major outbreaks involving E. coli 0157;H7-infected ground beef, regional distribution centers were the source of the contaminated meat and the infected product caused disease in several states. Another outbreak involved processed, cured, but uncooked beef in ready-to-eat sausages. The major source of contamination was the beef, and the E. coli 0157:H7 probably originated from the slaughtered beef carcasses. Since E. coli O.157:H7 grows in the intestines and is found in fecal material, it is also a potential source of waterborne disease. There have been several cases of serious E. coli 0157:H7 infections from fecally contaminated public swimming areas. Diarrheal disease often occurs in children in developing countries. It also occurs as "traveler's diarrhea," an extremely common enteric infection causing watery diarrhea in travelers to developing countries. The primary causal agents are the enterotoxigenicEscherichiaoli (ETEC). he c T ETEC strains make two heat-labile diarrhea-producing enterotoxins. In studies done with U.S. citizens traveling in Mexico, the infection rate with ETEC is often greater than 50%. The prime vehicles are foods such as fresh vegetables (for example, lettuce in salads) and water. The very high infection rate in travelers is due to contamination of local public water supplies. The local population is usually resistant to the infecting strains, undoubtedly because they have lived with the agent for a long period of time. Secretory antibodies (~ Section 22.8)present in the bowel may prevent successful colonization of the pathogen in local residents, but the organism readily colonizes the intestine of a nonimmune person, causing disease. Enteropathogenic .coli (EPEC)cause diarrheal disE eases in infants and small children, but does not cause invasive disease or produce toxins. Enteroinvasive E. coli (EIEC) strains cause invasive disease in the colon, producing watery to bloody diarrhea. The cells are taken up by phagocytes, where they escape lysis in the phagolysosomes (~ Section 22.2), grow in the cytoplasm, and move into other cells. This invasive disease causes diarrhea and is common in developing countries. Diagnosis, Treatment, and Prevention The general pattern established for diagnosis, treatment, and prevention of infection by Escherichia oli 0157:H7 c reflects the current procedures used for all of the various pathogenic strains. Diagnosis of infection by Escherichia coli 0157:H7 involves culture from the feces and identification of the 0 and H antigens and toxins by serology (~ Sections 4.9 and 24.7). Subtyping of strains is also done using molecular methods such as restriction fragment length polymorphism (RFLP) and pulse field gel electrophoresis (~ the box, DNA Fingerprinting, Chapter 31).Escherichia oli 0157:H7 illness is a nationc ally reportable infectious disease (~ Table 25.3). Treatmentof allpathogenic E. coli infectionsinvolves supportive therapy and, in severe cases, antimicrobial drugs to shorten and eliminate infection. fooc sure it s11 cleaJ Stab ana, fecti, imp] radii sure grinE mea! hanc prev. rhea and 1 ./ Enter< tions. beeni ./ D co ./ H ar E Camp! borne Biolo Camp! rods tJ croael specie OgniZE annua bacter j cause, sheep. Ca inated and of chlorir nal tra. carcaSE is rarel mestic arrhea Campyi domes' ', The most effective way to prevent infection with hoodbome enteropathogenic E. coli 0157:H7 is to make ~sure that meat is cooked thoroughly, which means that ~it should app~ar gray or brown a~d juices shoul~ be 'clear. As we dIscussed above (SectIon 29.2), the Umted ~States has approved the irradiation of ground meat as ~an acceptable means of eliminating or reducing food in~fectionbacteria, largely because E. coli0157:H7 has been I'implicated in several foodbome epidemics. Penetrating ~radiation is considered the only effective means to en,sure decontamination after the grinding process because ;grinding may distribute the pathogens throughout the meat, not simply on the surface. In general, proper food I 29.9 . LISTERIOSIS. 961 Pathogenesis After ingesting food contaminated with at least 104 Campylobacter, the organism multiplies in the small intestine, invades the epithelium, and causes inflammation, resulting in disease. The symptoms of Campylobacter infection include a high fever (usually greater than 104F or 40C), headache, malaise, nausea, abdominal cramps, and profuse diarrhea with watery, frequently bloody, stools. The disease subsides in about 1 week, and recovery is complete and spontaneous. Diagnosis, Treatment, and Prevention Diagnosis requires isolation of the organism from stool samples and identification by growth-dependent tests or immunological assays. Because of the frequency with which C.jejuni infections are observed in infants, a variety of selective media and highly specific immunological methods have been developed for positive identification of this organism. Treatment of infections with erythromycin do not shorten the acute diarrhea, but may shorten the time during which patients shed Campylobacter in their feces. Personal hygiene, proper washing of uncooked poultry (and any utensils coming in contact with uncooked poultry), and thorough cooking of the meat eliminate the possibility of Campylobacterinfection. , mhandling, water purification, and hygiene habits will ~prevent the spread of pathogenic E. coli. Traveler's diari;rhea can be prevented by avoiding local water sources and fresh foods. , ,/ 29.7 Concept Check ,Enteropathogenic Escherichiacoli can cause serious food infechions. .Specific measures, such as radiation of ground beef, have , tcbeenlmplemented to curb spread of these pathogens. Describe the pathology of enteropathogenic Escherichia coli food infection. What is the likely outcome? How might Escherichia coli contamination of production animals be prevented? ./ 29.8 Concept Check IEII Campylobacter !Campylobacter spp. cause the most prevalent JJ10rnenfections in the United States. i bacterialfood- Campylabacterinfection is by far the most prevalent foodborne bacterial infection. Though usually self-limiting, this disease affects nearly 2 million people per year. .I ,Describe the pathology of Campylobacter food infection. What is the likely outcome? .I How might Campylabacter contamination of production animals be controlled? !Biology and Epidemiology ~Campylobacterpecies are gram-negative, motile, curved s ~rodsthat grow at reduced oxygen tension, that is, as mi~croaerophiles (~ Section 12.14). Several pathogenic !species, Campylobacterjejuni, C. coli, and C.fetus, are recfpgnized. C. jejuni and C. coliaccount for nearly 2 million ~annual cases of bacterial diarrhea (Table 29.5). Campylo!Pacter fetus is economically important because it is a major [~auseof sterility and spontaneous abortion in cattle and !,sheep. Campylobacteris transmitted to humans via contam~inatedfood, most frequently in poultry, pork, raw clams, land other shellfish, or in surface waters not subjected to " Fhlorination. C. jejuni is a normal resident in the intesti, al tract of poultry, and virtually all chicken and turkey [:arcasses contain this organism. Beef, on the other hand, ~ rarely a vehicle. Campylobacter species also infect dois estic animals such as dogs, causing a milder form of difarrhea than that observed in humans. Infant cases of fFampylobacterinfection are frequently traced to infected " ~domesticanimals, especially dogs. " , . ", ..' , ~ Listeria monocytogenesis emerging as an important foodborne pathogen. L. monocytogenescauses listeriosis,a gastrointestinal food infection that may lead to bacteremia and meningitis. Biology and Epidemiology Listeria monocytogenes is an acid-tolerant, psychrotolerant (cold-tolerant), facultatively anaerobic, and salt-tolerant bacterium. It is a short, gram-positive, nonspore-forming rod (~ Section 12.19) (Figure 29.5). It is found widely in soil and water, and virtually no fresh food source is safe from possible L. monocytogenescontamination. Fresh food can become contaminated at any stage during food growth or processing. Methods such as refrigeration, which ordinarily slow microbial growth, are ineffective I I I .. L.. 962 . Chapter 29 . FOOD PRESERVATION AND FOODBORNE MICROBIAL DISEASES ., ~,\'II ~ ~. \ /.1T .' -. ~~ ,': ... U I !#~- ,}~ .. '1 ... ~ y""" " It."'> ":"~ '" '. . ""'. A' ". ~ , II t' '... \ ;--'-OW" ( f. )~ .. , .~'T /:. ~, - t.. ,-, .. . . .;:q " .' -,. t, ...,. , .. . ",,,,"". . '.' #It ., ,'" t - .'4 , ' / "\ 'I \ \ ';"'". w. ." ~ -o..J 0'.. '-\ .1... ... -z. 'Or'" ~~l\ .,.. '" :,", ~ ~. ~ . '."', ~ t" j, ., .. .. 1 It. , \ 'f:~ ~ ' , ... ,,' .. '< ~ .' r' .' 'I.. .. { ' . ~.. .'" 1; . ~ , ... . tr".. ... . 7 ,. I III. j .. . :' 't< .',,' ,. u.11t \ . :r. ,'". -t"'" . \ I. ~: '# \'." ~ I ) -"'" '" "-- 1J!p' .. r"" . \ ., .,' I . ,. I ~.o .. ~.. ~1f '.I' ,'" #... ::; ' .. .., 1i . ~ t , ';:i ~ Table 24.9). Antibiotic treatment with trimethoprimsulfamethoxazole is effective. Prevention measures include recalling contaminated food and taking steps to limit 1. monocytogenescontamination at the food-processing site. Since 1. monocytogenes is susceptible to heat and radiation, raw food and food handling equipment can be readily decontaminated. However, without sterilizing the finished food product, the risk of food contamination cannot be completely eliminated because of the widespread distribution of the pathogen. Individuals who are immunocompromised should avoid nonpasteurized dairy products and pay careful attention to expiration dates when consuming ready-to-eat processed foods. fooc izec VOIr wit! (~ of it (Tab mate tavil COllE each tranf manwasl food Pari! Impe 29.5. parm food, treate Presl soure crypt 28.6). impo resuli 'fI feces, most mild, fectio: blind} also e ~ gram-positive Gram stain of Listeria monocytogenes. The short, bacilli are about 0.5 IJm in diameter. ./ 29.9 Concept Check in limiting growth of this psychrotolerant organism. Thus, meat, dairy products, and fresh produce can be contaminated with this pathogen. Common sources of listeriosis outbreaks are ready-to-eat processed foods such as meat products and unpasteurized dairy products that are stored for long periods at refrigerator temperature (4C). Pathogenesis Listeria monocytogenesis an intracellular pathogen. It enters the body through the gastrointestinal tract after ingestion of contaminated food. Uptake of the pathogen by phagocytes results in growth and proliferation of the bacterium, lysis of the phagocyte, and spread to surrounding cells. Immunity to 1. monocytogenes is mainly cell-mediated via TH1cells (0Ct:i ection 22.7).IndividuS als having weakened cellular immunity, induding the elderly, neonates, patients undergoing immunosuppressive drug treatment (e.g., steroid treatment), or those who have immunosuppressive diseases such as AIDS, have increased susceptibility to listeriosis (0Ct:iSection 26.14). Although exposure to 1. monocytogenes is undoubtedly very common, acute listeriosis is quite rare. The acute disease is usually characterized by bacteremia and meningitis and has a mortality rate of about 20%. Although there are only about 2500 cases of acute listeriosis each year, about 500 cases end in death. Nearly all require hospitalization. Diagnosis, Treatment, and Prevention The diagnosis of listeriosis is accomplished by culturing Listeria monocytogenes from the blood or spinal fluid. L. monocytogenes can be identified in food by direct culture or by a variety of molecular methods such as ribotyping (0Ct:i Section 11.9) and the polymerase chain reaction (PCR) (~ Section 10.17, Section 24.13, and Listeriamonocytogenesis ubiquitous in the environment. In normal individuals, Listeria causes no infection. However, in immunocompromised individuals, Listeria can cause serious disease and even death. ,/ ,/ Describe the pathology of Listeria food infection. What is the likely outcome in normal individuals? Why are immunocompromised individuals extremely susceptible to life-threatening Listeria infections? Other Foodborne Diseases Infectious A number of other microorganisms and infectious agents contribute to foodbome diseases. Bacteria Table 29.5 lists several other bacteria that cause human foodbome disease. Yersinia enterocolitica is commonly found in the intestines of domestic animals and causes foodbome infections due to contaminated meat and dairy products. Y.enterocolitica causes enteric fever, a severe life-threatening infection. Bacillus cereus produces an enterotoxin that causes diarrhea and vomiting. B. cereus grows in high-carbohydrate foods such as rice. Spores of this gram-positive rod germinate and, as the organism grows in food that is left at room temperature, pathogenic amounts of toxin are produced. Reheating may kill the B. cereus, but the toxin remains active. Shigellaspp. cause nearly 100,000 cases of severe foodborne invasive gastroenteritis called shigellosis each year. Several members of the Vibrio genus cause food poisoning after consumption of contaminated shellfish. Viruses The largest number of annual foodbome infections are thought to be caused by viruses. In general, viral 1. I f 2. I I r 3. r b 4. C P d 5. II 51 d REVIEW QUESTIONS. 963 oodborne illness consists of gastroenteritis characterzed by diarrhea, often accompanied by nausea and omiting. Recovery is spontaneous and rapid, usually rithin 24-48 h ("24-hour flu"). Norwalk-like viruses ~ Table 25.5 and Section 28.8) are responsible for most )fthe foodborne infectious disease in the United States Table 29.5), accounting for over 9 million of the estinated 13 million cases of food infection per year. Roavirus, astrovirus, and hepatitis A (~ Section 26.11) ollectively cause 100,000 cases of foodborne disease .ach year. These viruses inhabit the gut and are often ransmitted to food or water with fecal matter. As with any foodborne infections, proper food handling, handashing, and a source of clean water to prepare fresh oods are essential to prevent infection. arasites nportant foodborne parasitic diseases are listed in Table 9.5. Parasites including Giardialamblia,Cryptospordium can be spread via arvum, and Cyclosporacayetanensis ood, presumably contaminated by fecal matter in un:reated water used to wash, irrigate, or spray crops. ~resh foods such as fruits are often implicated as the iource of these parasites. We discussed giardiasis and :ryptosporidiosis in the previous chapter (~ Section ~8.6).Cyclosporiasis is an acute gastroenteritis and is an mportant emerging disease. Most cases appear to be the 'esult of eating imported fresh produce. Toxoplasma gondii is a parasite spread through cat eces, but also found in raw or undercooked meat. In .ost individuals, the toxoplasmosis infection causes a ild, self-limiting gastroenteritis. However, prenatal inection can lead to a variety of complications, including Hndness and stillbirth. Immunocompromised patients Iso exhibit signs of acute toxoplasmosis. Prions Prions are proteins, presumably of host origin, that adopt novel conformations, inhibiting normal protein function and causing disruption in neural tissue. The foodborne variety of prion disease in humans is known as "variant Creutzfeldt-Jakob Disease" (vCJD). VCJD is a slow-acting degenerative nervous system disorder and has affected several hundred people in the United Kingdom and other European countries (~Section 9.13). The disease appears to be spread by eating meat products from cattle afflicted with bovine spongiform encephalitis (BSE),a prion disease commonly called mad cow disease. Although the mechanism of replication is not entirely clear, BSE prions consumed in the meat products from affected cattle somehow trigger structurally and functionally related human proteins to assume an altered conformation, resulting in protein dysfunction and disease. BSE has not yet been discovered in cattle nor has vCJD been observed in humans in the United States. In Europe, all cattle known or suspected to have BSE have been destroyed. Bans on feeding cattle with animal meal appear to have stopped the development of new cases of BSE in Europe. ./ 29.10 Concept Check Over 200 different infectious agents cause foodborne disease. Viruses cause the vast majority of foodborne illnesses. A number of other bacteria, parasites, and prions also cause foodborne illnesses. ,/' Identify the viruses most likely to be involved in foodborne illnesses. ,/' How might prion contamination of production animals be prevented in the United States? 964 . Chapter 29 . FOOD PRESERVATION AND FOODBORNE MICROBIAL DISEASES I I I I ! I I I.1 A' I. I !

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Texas A&M - MATH - 308
Solutions to Homework from Section 4.1Problem 2 Given the differential equation y + 2y + 4y = 5 sin(3t) we look for a solution of the form A cos(t) + B sin(t) Substituting this into the differential equation, we get A2 cos(t)B2 sin(t)2A sin(t)+2B co
Texas A&M - MATH - 308
Solutions to Homework from Section 7.3Problem 20 We use the trig identity cos(A + B) = cos(A) cos(B) sin(A) sin(B) cos(A B) = cos(A) cos(B)A + sin(A) sin(B) therefore cos(A B) cos(A + B) = 2 sin(A) sin(B) that is sin(A) sin(B) = (1/2)(cos(A B)
Texas A&M - MATH - 308
Chapter 7. Laplace Transforms. Section 7.4 Inverse Laplace Transform. Denition 1. [0, ) and satises Given a function F (s), if there is a function f (t) that is continuous on L{f }(s) = F (s), then we say that f (t) is the inverse Laplace transform o
Texas A&M - MATH - 308
Chapter 7. Laplace Transforms. Section 7.2 Denition of the Laplace Transform. Denition 1. Let f (x) be a function on [0, ). The Laplace transform of f is the function F dened by the integralF (s) =0f (t)est dt.The domain of F (s) is all the v
Texas A&M - MATH - 308
Math 308, Sections 301, 302, Summer 2008 Lecture 7.06/13/2008Chapter 4. Linear Second Order Equations Chapter 4.1 is skipped. Section 4.2 Linear Differential Operators Definition A linear second order equation is an equation that can be written i
Texas A&M - M - 412
Math. 412(Fulling)29 September 2005 Test A SolutionsCalculators may be used for simple arithmetic operations only! 1. (15 pts.) Classify each equation as linear homogeneous, linear nonhomogeneous, or nonlinear. 2u u 2 (a) + = x2 cos(2x) 2 x t
Texas A&M - M - 311
Math. 311(Fulling)26 October 1998 Test B Solutions1. (18 pts.) For each of these sets, tell whether or not it is a basis for R3 ; and if not, explain briey why not. (a) {(1, 1, 1), (0, 1, 1), (0, 0, 2)}1 Yes From the matrix 0 0 the determina
Texas A&M - M - 311
Chapter 1Vectors1.1 Vectors that You KnowVectors (and things made out of vectors or related to them) are the main subject matter of this book. Instead of starting with a precise mathematical definition of a vector, we give an informal, intuitive
Texas A&M - M - 152
Spring 2006 Math 152/STEPS 2nd-Order Linear Nonhomogeneous Constant Coefcient Differential Equations: The Method of Undetermined Coefcients c 2006, Art Belmonte Fri, 03/MarSummaryA nonhomogeneous second-order linear differential equation with const
Texas A&M - MATH - 151
Math 151Final Exam 105 May 2008Name (print):You are responsible for following the instructions below. 1.) Mark your Math 151 section below. 501 (TR 5:30) 502 (TR 3:55) 503 (TR 2:20)2.) Print your name, section, and exam form (F.1 or F.2) on
Texas A&M - M - 131
MATH 131 Exam II - Form AJuly 25, 2006Printed Name: Signature:(By signing here you acknowledge that all of the work on this test is your own.)Seat#:Instructions: Except for the multiple choice questions where the answer must be circled, you
Texas A&M - M - 151
Math 151Sample Test III QuestionsMon, 21/Nov/2005Short answers to the sample problems for Test 3 (Sorry, I didn't have time to write down long solutions) (Also, I may have made a mistake somewhere in the rush!)4 1. Let f (x) = x(-3/x ) . Find
Texas A&M - M - 131
1 HOMEWORK #1. Solutions of the problems that will be gradedThe ve problems that will be graded (out of the nine problems that you had to turn in) are : Section 1.3, Problem #26; Sec. 1.5, Prob. #24; Sec. 1.6, Prob. #33; Sec. 1.6, Prob. #34; Sec 1.9
Texas A&M - M - 308
Math 308 Quiz 9BDierential EquationsSummer 19991. What is the denition of the Laplace transform of a function f (t) dened on [0, )? Answer: The Laplace transform of f (t) is the function given by L{f }(s) = 0est f (t) dt,and dened for all
Texas A&M - MATH - 308
Solutions to Homework from Section 1.2Problem 3 The second derivative of y = sin(x) + x2 is y = sin(x) + 2 so y + y = ( sin(x) + 2) + (sin(x) + x2 ) = x2 + 2 so it is a solution. Problem 6 If we subsitute the function (t) = 2e3t e2t into the diffe
Texas A&M - MATH - 308
Solutions to Homework from Section 7.5Problem 17 Given the differential equation y + y - y = t3 , y(0) = 1, y (0) = 0 We can take the Laplace transform of both sides getting s2 Y (s) - sy(0) - y (0) + sY (s) - y(0) - Y (s) = That is, (s2 + s - 1)Y (
Texas A&M - MATH - 308
Solutions to Homework from Section 4.6Problem 28 The solution of y (x) + by (x) + 4y(x) = 0, y(0) = 1, y (0) = 0 is given by y(x) = y (x) = 1/2 With b=5: b+ b2 16 e(1/2 b+1/2 b2 16 b2 16)x1/2bb2 16 e(1/2 b1/2 b2 16b2 16)x10.8
Texas A&M - MATH - 308
Solutions to Homework from Section 4.7Problem 13 a) The difference of any two particular solutions is a homogeneous solution, therefore y1 (x) = x3 - x and y2 (x) = x2 - x are homogeneous solutions. These are linearly independent. b) Using x3 as a p
Texas A&M - MATH - 308
Solutions to Homework from Section 4.10Problem 4 We show that y1 (t) = 1/(1 - t)2 , y2 (t) = 1/(2 - t)2 , and y3 (t) = 1/(3 - t)2 are independent by computing the Wronskian y1 y2 y3 W = y1 y2 y3 y1 y2 y31 (1-t)3 3 (1-t)4 12 (1-t)5 1 (2-t)3 3 (2-t)4
Texas A&M - MATH - 308
Solutions to Homework from Section 1.5Problem 5 Applying Eulers method (euler.m) gives the following results xn 1.0000 1.2000 1.4000 1.6000 1.8000 yn 1.0000 1.4000 1.9600 2.7888 4.1096Problem 12 Given the initial value problem y = y, Eulers meth
Texas A&M - MATH - 696
Submitted to the 5th Rhine Workshop on Computer Algebra]A review of the ODE solvers of Maple, Mathematica, Macsyma and MuPADFrank Postel Paul Zimmermanny 31 October 1995Using a wide set of more than 50 di erent kinds of ordinary di erential equa
Texas A&M - MATH - 308
Solutions to Homework from Section 1.1Problem 15 From the statement of the problem dT (M - T (t) dt which means that dT = k(M - T (t) dtfor some constant k. Problem 16 In a similar fashion to 15, dA A(t)2 dt or dA = kA2 (t) dtfor some constant
Texas A&M - MATH - 308
Solutions to Homework from Section 4.12Problem 5 The general solution of my (t) + ky(t) = F0 cos(t) y(0) = y (0) = 0 is given by y (t) = This can be reduced to m( 2 From the trig identities cos(A + B) = cos(A) cos(B) - sin(A) sin(B) cos(A - B) = cos
Texas A&M - MATH - 308
Solutions to Homework from Section 4.11Problem 3 The general solution of y (t) + by (t) + 16y(t) = 0, y(0) = 1, y (0) = 0 is 1/2 b+ b2 - 64 e(-1/2 b+1/2 b2 - 64 b2 -64)t+1/2-b +b2 - 64 e(-1/2 b-1/2 b2 - 64b2 -64)tThe solutions are
Texas A&M - MATH - 308
Solutions to Homework from Section 2.2Problem 5 Writing the equation as ds s =t s2 dt s+1 you can see that there is no way to fact the right hand side into an expression of the form f (s)g(t). Therefore the equation is not separable! Problem 6 Sinc
UNC - ECON - 410
Chapter 14TaxesChanges in the tax structure also aect the market equilibrium. Were going to devote considerable energy to the analysis of taxes, both because of their importance in real life and because their impact on the market can be quantied:
UNC - ECON - 560
CAN INTEGRATION INTO THE WORLD ECONOMY SUBSTITUTE FOR A DEVELOPMENT STRATEGY? 1 Dani Rodrik Harvard University May 2000 According to The Wall Street Journal, a senior U.S. Treasury official recently &quot;urged Mexico's government to work harder to reduce
UNC - STAT - 4001
RMS 4001Homework Assignment #2 due Thursday, October 18, 2001 1. Use the inverse transform method to generate a random variable X having the distribution (a) P (X = i) =1 i(i+1) , i= 1, 2, .(b) P (X = i) = n+i1 (1 p)i pn , i = 0, 1, 2, ., wh
UNC - STAT - 3008
Statistics 3008Homework Assignment #3 due Thursday, November 19, 2002 Note that each of the following problems may not necessarily carry the same weight. 1. True or False. Answer the following questions. (a) When the errors are highly correlated, th
UNC - STOR - 645
Homework set #10 1. Assume that we have an innite sequence of events A1 , A2 , A3 , A 1 such that P (Ak ) = k(k+1) . (a) Prove or disprove: An n=1 n=1 k=nAk n=1 k=n n=1 k=nAk n=1An(b) What can you say about P (Ak )?(c) Is
UNC - STOR - 645
Homework set #2 1. Write the following function using 1 x f (x) = x 1 indicators: if if if if x &lt; 1, 1 x &lt; 0, 0 x &lt; 1, x 1.2. Prove or disprove: IAB = IA + IB IA IB . 3. A random variable X has a distribution function FX (s). What is the
UNC - OR - 220
CHAPTER 9Markov Regenerative ProcessesDenitions and Examples Markov Renewal Process and Markov Renewal Function Key Renewal Theorem for MRPs Extended Key Renewal theorem Semi-Markov Processes: Further Results Markov Regenerative Processes Applica
Texas A&M - ENERGY - 101
[Ver. 2008.01.14] ENGR 101 - Energy: Resources, Utilization, and Importance to Society Syllabus and Administrative Procedures Spring 2008 Welcome to ENGR 101! We are excited that you have chosen to join this ongoing quest to address issues of energy
Texas A&M - APR - 0507
Endangered and Threatened Species of the Edwards AquiferDr. Mara L. Alexander, Botanist Dr. Catherine T. Phillips, Fish BiologistTexas wild-rice Zizania texanaStatusEndangered TPWD 2006 survey: ~4200 m2 Only in relatively small patches Historica
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ARCH 614S2009abnARCH 614. Cardboard Swing-Couch DesignDates: Part I during class on 2/5/09 in Building B foyer Part II due 4/21/09 Problem Statement for PART I: The design involves the construction of a hanging structure of original design, cons
Texas A&M - ENDS - 231
ENDS 231Su2006abnENDS 231. Cardboard Swing-Chair DesignDate: During class on Tuesday June 13, 2006 Location: classroom (or nearby) Problem Statement: The design involves the construction of a hanging structure of original design, constructed onl
Structure, Vol. 12, 429438, March, 2004, 2004 Elsevier Science Ltd. All rights reserved.DOI 10.1016/j.str.2004.02.005Structural Basis for Allosteric Regulation of the Monomeric Allosteric Enzyme Human GlucokinaseKenji Kamata,* Morihiro Mitsuya,
UNC - COMP - 290
COMP 290-040 Hot Topics in OS Research Software Systems Research is Irrelevant The Rob Pike PolemicKevin JeffayDepartment of Computer Science University of North Carolina at Chapel Hill August 22, 2001http:/
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Texas A&M - CHEM - 642
CHEM 642 - Fall 2006Organo-lithium/alkaliPreparation Structure Reactivity Addition compoundsPart 1, R-LiPreparationDirect synthesisTransmetalationMetal exchangeMetal-halogen exchangeMetalationCarbometallationBuLi + Ph-CC-Ph =&gt; Bu
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University of North CarolinaFall 2006ECONOMICS 586 THE ECONOMICS OF THE FAMILYBoone A. Turchi Gardner Hall 200A 966-5348 email: Office Hours: Tuesday, 4:45-5:45 or by appointment Web Page: http:/
UNC - ECON - 001
Prof. Boone A. TurchiHow to Survive Economics 101hToto Ive a feeling were not in Kansas anymore. This course has the dual task of preparing beginning students for advanced work in economics and exposing others who will never take another economics
UNC - ECON - 586
UNC - ECON - 586
UNC - ECON - 586
Is Making Divorce Easier Bad for Children? The Long-Run Implications of Unila.Jonathan Gruber Journal of Labor Economics; Oct 2004; 22, 4; ABI/INFORM Global pg. 799Reproduced with permission of the copyright owner. Further reproduction prohibited
UNC - ECON - 423
Econ 423: Questions from Previous Versions of Quiz 3 [Fall 2000-present] 1. Diversification can be effective in reducing the riskiness of portfolios of financial assets issued by specific firms, but it is relatively ineffective as a mechanism for red
Texas A&M - CHEM - 634
Assignment 2 Due Tuesday, February 23, 2009 (1) Electronic absorption spectroscopy can be useful for monitoring the course of reactions. In this problem you are asked to read through problem 5-59 in Harris and Bertolucci and to work out for all parts
Texas A&M - CHEM - 462
Classes 7.1-2-3Intro. to Coordination ComplexesMWF. October 25, 27, 29 CHEM 462 T. HughbanksCoordination CompoundsEven in cases where we think of solvated cations, evidence for solventcation interactions shows that more than electrostatics is i
Texas A&M - CHEM - 673
Problem Set 4 Due Thursday, November 8, 2007 (1) (a) Consider the tricyclic radical anion shown below with its EPR spectrum, in which the proton hyperfine splitting is clearly evident. Use a Hckel calculation to help you interpret this spectrum, as w
UNC - ECON - 870
ECON 870 Fall, 2008Midterm October 22, 2008Saraswata Chaudhuri Stanislav KhrapovWarmup Problems: [2.5 4 = 10 points]Consider a sequence of random variables {Xn } . n=1 1. What does it mean when we say that Xn X? - 2. What does it mean when
UNC - ECON - 770
Department of Economics UNC-Chapel Hill ECON 770 Introduction to the Mathematical and Statistical Foundations of Econometrics Homework 1 (for 10/16/2007) Eric RENAULTFall 20071Exercise 1Consider a probability space (, z, P ) and a sequence of