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Digestive System Diseases

Bacterial Infections of the Digestive System

Bacteria cause a wide array of alimentary canal diseases, with severity ranging from inconsequential to life-threatening.
One of the common symptoms produced by bacterial disease is diarrhea. Diarrhea, the occurrence of more than three liquid or very loose bowel movements per day, is a common gastrointestinal disease symptom. Its causes may be bacterial, viral, fungal, or parasitic. An enterotoxin, a toxin released by certain viral and bacterial pathogens that specifically targets the intestines, can frequently be a cause of diarrhea. Acute diarrhea is an occurrence of more than three liquid or very loose bowel movements each day over a period of two days to two weeks. It is often caused by a viral infection such as rotavirus and norovirus or by bacteria such as E. coli, Shigella, Staphylococcus, and Salmonella. Acute diarrhea is commonly referred to as food poisoning. The causative agents of acute diarrhea are often transmitted by food, and disease can occur when the contaminated food transports the virus or bacteria into the body. These diseases can also be transmitted by infected individuals who do not properly wash their hands.
Escherichia coli (scanning electron microscope) is a gram-negative rod-shaped bacteria common in the large intestine. Most E. coli are mutualists, though some strains cause serious food poisoning.
Credit: NIAID
Salmonella is a group of rod-shaped gram-negative bacteria. Serotype Typhi, the causative agent of typhoid fever, is hosted only in humans and is spread through feces-contaminated food or water.
Credit: CDC/James Archer
Shigella, one cause of acute diarrhea, causes a disease called dysentery, which is a condition characterized by severe diarrhea and stomach cramps with blood or mucus in the feces and is often resolved within a few days. Recovery from acute diarrhea typically occurs within a week, even in the absence of medical intervention.
Shigella (light microscope, 1,125x) is a bacterium that causes dysentery, a disease that produces severe diarrhea and stomach cramps.
Credit: CDC/Wallis DeWitt
Chronic diarrhea is an occurrence of more than three liquid or very loose bowel movements each day over a period of two to four weeks or longer. Chronic diarrhea can be caused by an infection or by other inflammatory states, such as irritable bowel syndrome, ulcerative colitis, and food allergy or sensitivity, and as a side effect of some medications. Bacterial causes of chronic diarrhea include Clostridium spp. and Vibrio cholera. Clostridium spp. is a common organism transmitted in hospitals to patients taking antibiotics, while V. cholera is transmitted by contaminated water. Regardless of the cause of diarrhea, dehydration is a major side effect. Dehydration can lead to side effects affecting organs throughout the body that are not receiving adequate amounts of water to function properly. Fluid replacement of water and electrolytes is important in the recovery from acute or chronic diarrhea.
Vibrio cholerae (scanning electron microscope, 13,184x), the causative agent for the disease cholera, is a type of gram-negative vibrio (comma-shaped) bacteria found in contaminated water.
Credit: CDC/James Gathany
Clostridium difficile (scanning electron microscope, 3,006x) is a gram-positive, rod-shaped, spore-forming, anaerobic bacteria that may grow in abundance in individuals taking antibiotics.
Credit: CDC/Lois S. Wiggs
Dental caries, also known as a cavity, is an area of permanent tooth decay and is another common disease of the digestive system. Dental caries can be caused by acid that breaks down the tooth enamel. The acid is formed when bacteria in the mouth attach to the teeth and produce acid, which destroys the enamel and the tooth underneath. Dental caries are repaired by clearing out the diseased area of the tooth and replacing it with a filling, usually a plug made of a silver alloy containing silver, tin, zinc, and copper.

The bacterium Streptococcus mutans is the primary cause of tooth cavities. S. mutans grows rapidly and produces biofilms in the presence of sugar. The biofilm is a protective layer, and if not removed it will harden through the addition of calcium in the process of calcification, producing tartar. Several other bacteria participate in the progression of decay started by S. mutans, including species of Lactobacillus and Actinomyces. When the buildup of tartar is not removed through regular oral hygiene, the gums become irritated and inflamed (gingivitis), resulting in bleeding and a condition known as periodontal disease. The bacteria associated with periodontal diseases are predominantly anaerobic bacteria and cause the erosion of the enamel and bone surrounding the teeth. Proper hygiene is suggested to prevent the development of cavities, including regular dental cleanings, flossing and brushing at least twice per day, and use of a strong antibiotic mouthwash to kill any remaining bacteria.

Foodborne Infections of the Digestive System

Causative Agent Description Symptoms Diagnosis and Treatment
Bacillus cereus Soil-dwelling, gram-positive, endospore former; endotoxins released when heated during cooking. There are two forms. In one, abdominal pain and diarrhea are typical; in the other, nausea and vomiting are typical. Culture or isolation of bacteria from the contaminated food;
Self-limiting; rehydration and supportive care
Campylobacter jejuni Native of avian alimentary canal, gram-negative with variable shape (rod to vibrio to spiral and environmentally dependent) and a single flagella Abdominal pain, cramps, diarrhea with dehydration, dysentery in severe infections, fever, vomiting; associated with Guillain-Barré syndrome Not common, culture on selective media and environmental conditions;
Unnecessary, or ciprofloxacin and erythromycin. Resistance to ciprofloxacin is increasing in prevalence.
Clostridium perfringens Widely distributed in nature, endospore- and enterotoxin-forming gram-positive rod Cramps and diarrhea PCR, toxin detection in stool;
Rehydration—intravenous may be necessary.
Listeria monocytogenes Soil-dwelling, food-contaminating, gram-positive rod; along with two closely related species (L. ivanovii, L. grayi), is the causative age of listeriosis Commonly problematic only for the elderly, immunocompromised, pregnant women, and the young. First symptoms are diarrhea or other alimentary canal symptoms. The pathogen may spread from the intestines to the blood, and confusion, convulsions, fever, headache, and muscle aches can occur. Miscarriage may occur in pregnant women. Culture from blood or cerebrospinal fluid following spinal tap;
Ampicillin, gentamicin
Salmonella bongori and Salmonella enterica Commensal in birds and common member of alimentary canal in other vertebrates, gram-negative rod, causative agent of salmonellosis Abdominal cramps, diarrhea, fever, headache, nausea, vomiting. May (particularly Typhi strains) infect epithelial cells and migrate to the blood and lymph, resulting in systemic infection and exacerbating current symptoms, increasing vascular permeability, altering thermal regulation, decreasing blood volume, and causing septic shock. Selective culture, PCR;
Often self-limiting. Rehydration alone and antibiotics in serious cases. Ampicillin, cephalosporins, fluoroquinolones. Some strains carry antibiotic resistance, particularly to ciprofloxacin.
Staphylococcus aureus Gram-positive cocci, forms clumps, typically found in human nasal passages and on skin Nausea, vomiting, stomach cramps Presence of symptoms, blood tests recommended in rare causes;
Plenty of fluids, antibiotics are not effective as toxins are not affected by them

Many bacterial infections are caused by toxins that are ingested when consuming food. Symptoms include diarrhea, cramping, and mild fever. Most are self-limiting with rehydration therapy, though others result in serious life-threatening disorders.

Other Transmitted Infections of the Digestive System

Causative Agent Description Transmission Symptoms Diagnosis and Treatment
Clostridium difficile Commensal of the alimentary canal, endospore-forming gram-positive rod. Overgrowth is common following antibiotic therapy. None or nosocomial Abdominal pain, appetite suppression, colon inflammation, diarrhea with dehydration, fever. If the colon is perforated, septicemia and death can result. Colonoscopy, ELISA to toxins, PCR;
Rehydration in mild cases; fidaxomicin, vancomycin
Vibrio cholerae Found in brackish aquatic environments, gram-negative comma-shaped rod, causative agent of cholera, susceptible to low pH so large doses are necessary for infection of intestines Contaminated food or water Abdominal cramps and vomiting. Extreme diarrhea resulting from enterotoxin-induced osmotic shifts in epithelial cells. Differential culture from stool sample, Immunoassay Self-limiting. Rehydration with electrolytes;
Azithromycin, ciprofloxacin, doxycycline, erythromycin, norfloxacin, tetracycline. Many strains have resistance to one or many antibiotics; of note are ampicillin, co-trimoxazole, and sulfamethoxazole-trimethoprim resistance.
Escherichia coli Commensal of alimentary canal, gram-negative rod; six pathogenic strains with additional virulence factors including enterotoxin, adhesin compounds that aid in colonization Fecal-oral, contaminated food or water Enterohemorrhagic strains: contains verotoxin acquired from Shigella dysenteriae, bloody diarrhea, cramps, may lead to life-threatening hemorrhagic colitis (colon inflammation). Enteroinvasive strains: epithelial cell invasion followed by chills, cramps, diarrhea with dehydration, dysentery, fever. Enteropathogenic strains: diarrhea with dehydration, fever, vomiting. Enterotoxigenic strains: abdominal cramps, diarrhea with dehydration, fever. Culture and serological typing or PCR diagnosis of toxin genes;
Accurate diagnosis of strain is critical. Following antibiotic therapy, cell lysis of toxin-producing strains releases toxins and worsens conditions.
Self-limiting infections best treated with rehydration and supportive therapy. Antibiotic resistance is common in pathogenic and toxigenic strains, which may be treated with doxycycline, fluoroquinolones, or rifamycin. Antibiotics are not recommended for invasive or hemorrhagic strains.
Helicobacter pylori Common resident of the stomach, gram-negative curved rod (helical), causative agent of (peptic) stomach ulcers. Lack of H. pylori increases the risk of some cancers. Person to person by saliva, fecal contamination of food and water Appetite suppression, bloating, nausea, stomach inflammation (gastritis), weight loss. If allowed to develop, hemorrhagic ulcers and life-threatening perforation of the stomach can result. Breath test (detection of radiolabeled CO2 in the breath resulting from treating the stomach with radiolabeled urea), direct detection in stool or stomach biopsy, immunoassay;
Multiple triple treatments are available. Each combines a pair of antibiotics (amoxicillin and clarithromycin, or metronidazole and tetracycline) with an acid-reducing therapy (omeprazole, bismuth subsalicylate, or lansoprazole).
Shigella species Found in primate alimentary canal, gram-negative rod, causative agent of shigellosis Fecal-oral Abdominal cramps, diarrhea (in some cases with blood or mucus), fever, flatulence, nausea, vomiting. In strains carrying Shiga toxin: hemorrhage of colonic epithelial cells and dysentery, hemolytic uremic syndrome, or reactive arthritis. Immunoassay, PCR of stool sample;
Azithromycin, ciprofloxacin. Ciprofloxacin resistance occurs in some strains.
Yersinia enterocolitica Environmentally widespread gram-negative rod, may produce endotoxins and exotoxins Zoonotic, fecal-oral Abdominal cramps, diarrhea, more severe symptoms if spread into blood Detection in stool;
Self-limiting, rehydration. Aminoglycoside, doxycycline, fluoroquinolones, or sulfamethoxazole-trimethoprim in systemic or blood infections.

Some bacterial infections are caused ingesting food or water that has been contaminated with fecal material, or from animals or from person-to-person. Similar to foodborne infections, symptoms include diarrhea, cramping, and mild fever.