Lecture 24 Clostridium-ELMS

Lecture 24 Clostridium-ELMS - Clostridium Lecture 24...

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Unformatted text preview: Clostridium Lecture 24 Classification Classification Family Genera Species >177 Bacillaceae Bacillus/Clostridium C. difficile C. perfringens C. septicum C. botulinum C. tetani C. tertium Common Common Uncommon Uncommon Uncommon Uncommon General Characteristics General Characteristics Anaerobic! Spore forming Gram­positive Motile, peritrichous flagella (except C. perfringens!) Ubiquitous in soil, water and sewage Most are saprophytes Produce volatile fatty acids Ferment wide variety of organic compounds and produce large amounts of gas (CO2 and H2) Characteristics Characteristics C. perfringens Large, rectangular rods (2­19µ m long) Gram­positive Nonmotile (exception in Clostridia) Spore formation (but seldom observed) Hemolytic Rapid growth in culture and tissues (8­10min doubling time) Morphology Morphology C. perfringens Heterogenous gram­staining Large array of toxins produced (table 40­3) Classified into five groups (A­E) according to expression of alpha, beta, epsilon and iota toxins (table 40­2) Most common in human infections is Type A Alpha toxin (expressed by all five types): Phospholipase C (Lecithinase); hemolysis, necrotizing activity Enterotoxin: mostly in type A strains; alters membrane permeability in ileum and is superantigen; leads to watery diarrhea; heat­labile Pathogenicity C. perfringens Epidemiology Epidemiology C. perfringens Type A is distributed in soil and water, and found in intestinal microflora Type A is responsible for most human infections Common cause of foodborne illness in US (cooked beef) Clinical Manifestations Soft tissue infections Subdivided into 1) Cellulitis 2) suppurative myositis 3) myonecrosis/gas gangrene Clinical Manifestations Cellulitis Bacteria introduced during surgery or trauma Localized edema with gas formation, necrosis of epithelia but not muscles Usually nonpainful and benign after antibiotic treatment Clinical Manifestations Suppurative myositis Pus accumulation in muscle tissues No necrosis of muscles and no systemic manifestation Must be treated aggressively Clinical Manifestations Myonecrosis/Gas gangrene Onset after about one week Intense pain, muscle necrosis, shock , renal failure, death Production of gas due to metabolic activity of bacteria Abundant growth of bacteria in tissues, without presence of inflammatory cells (lysed by bacterial toxins) Mortality rate (even with treatment) 40­100% Clinical Manifestations Clinical Manifestations Myonecrosis/Gas Gangrene Rare in the US; 2000­3000 cases per year But a major problem in pre­antibiotic era Wound Infections/Gas Gangrene History More than two and a half million men fought in the Civil War. At least 620 000 died, and at least 60% of these deaths were from disease. pamphlet produced for the Confederate army in 1862 Of the many limb wounds which did receive surgical attention, about three out of four led to amputation and as many as 50% died as a result of blood loss or subsequent infection Wound Infections/Gas Gangrene History INGAZ SEMMELWEIS First link of hygiene with decrease in infectious disease in hospitals (puerperal fever) in 1840s Mortality dropped from 18% ot 1% after adoption of hand washing protocol (Chlorine solution) by doctors. During the Franco­Prussian War (1870–1872) many new observations were made on wound infections. Having espoused the principle of antisepsis, and acknowledging the work of Louis Pasteur, Joseph Lister wrote a treatise entitled "A methodof antiseptic treatment applicable to wounded soldiers in the present war", which led to the immediate acceptance of his techniques by German surgeons Wound Infections/Gas Gangrene History The discovery of sulfonamides greatly affected the mortality rate during World War II. American soldiers were taught to immediately sprinkle sulfa powder on any open wound to prevent infection. Every soldier was issued a first aid pouch that was designed to be attached to the soldier’s waist belt. The first aid pouch contained a package of sulfa powder and a bandage to dress the wound. One of the main components carried by a combat medic during World War II was sulfa powder and sulfa tablets Clinical Manifestations Gastroenteritis Most common manifestation of C.perfringens infections Self­limiting Caused by contaminated food (meat products) which have been inadequately stored Short incubation period (8­24h) Abdominal cramps, watery diarrhea (no fever or vomiting, most of the time) Lasts 24­48h Caused by enterotoxin Detection of alpha­toxin of C.perfringens Detection of alpha­toxin of Nadler’s reaction A Nagler agar plate, containing 5­10% egg yolk, is used to presumptively identify strains which produce α­toxin (phospholipase C/lecithinase) which interacts with the lipids in egg yolk to produce a characteristic precipitate around the colonies. One half of the plate is inoculated with anti­toxin antibodies to act as a control in the identification Treatment/Prevention Treatment/Prevention C. perfringens Gastroenteritis is self limiting Localized cellulitis: Penicillin treatment Suppurative myositis and Gas Gangrene: surgical removal of necrotic tissue; amputation; high­dose penicillin therapy No vaccine available Use proper wound care C. difficile C. difficile Extremely sensitive to oxygen Terminal spore formation Antibiotic­associated diarrhea and colitis well established since introduction of treatment Until mid­70s Staph. aureus was implicated Since then C. difficile has been established as the main cause of Antibiotic­associated diarrhea 1978­1983 most common cause was clindamycin; treatment was the replacement of clindamycin with vancomycin; 25% relapse after withdrawal of vancomycin (2nd round of treatment) 1984­2003: most common cause cephalosporins; treatment was metronidazole Since 2003: higher frequency, more resistance, hospital AND community acquired disease C. difficile C. difficile History Pathogenicity Pathogenicity C. difficile Two important toxins: Toxin A and Toxin B Mechanism of toxin function Mechanism of toxin function Mechanism of toxin function Mechanism of toxin function both toxins are glycosyltransferase that modify small GTPases (Rho, Rac, CDC42) to remain inactive Clinical Manifestation Clinical Manifestation Wide range; mild diarrhea to colitis and pseudomembranous colitis Risk factors: ­elderly and immunocompromised ­prolonged antibiotic treatments ­anti­acids (anti­ulcer) medication C. difficile C. difficile AAC­Pseudomembranous Colitis Sever inflammation of the lumen of the colon; pseudomembrane formation Cross section of colon epithelium Epidemiology Epidemiology Ubiquitous in environment (anaerobic) 5% asymptomatic carrier (20% in hospitals) Mortality can be up to 25% in elderly, but usually treatments are successful Diagnosis Diagnosis Stool culture Enzyme linked immunoassay for Toxin A and B Prevention/Treatment Prevention/Treatment Avoid prolonged antibiotic treatments No vaccine available Treatment: stop current antibiotic and replace with metronidazole ; if not successful use vancomycin (both orally) 2nd round of treatment may be necessary (~25% of cases) (spores are not killed by antibiotics!) Probiotics may be useful (bifidobacteria, lactobacilli) Metronidazole Metronidazole Metronidazole: is a nitroimidazole anti­infective drug used mainly in the treatment of infections caused by susceptible organisms, particularly anaerobic bacteria and protozoa. Metronidazole is selectively taken up by anaerobic bacteria and sensitive protozoal organisms because of the ability of these organisms to reduce metronidazole to its active form intracellularly. The nitro group of metronidazole is chemically reduced by ferredoxin (or ferredoxin­linked metabolic process) and the products are responsible for disrupting the DNA helical structure, thus inhibiting nucleic acid synthesis (Replication). C. tetani C. tetani Spore forming Motile 11 strains, differentiated by flagellar antigen Pathogenesis Pathogenesis Tetanus Toxin/Tetanospasmin Large A­B toxin (150kDA) Light chain (A­subunit) inhibits release of inhibitory neurotransmitter glycine and GABA Leads to unregulated excitatory synaptic activity (Spastic Paralysis) Clinical Manifestation Clinical Manifestation Neonatal Tetanus Generalized tetanus Occurs in infants without passive immunity (mother is not vaccinated) Caused by cutting umbilical cord with nonsterile equipment 14% of all neonatal death in underdeveloped countries (extremely rare in developed countries) Clinical Manifestation Neonatal Tetanus Clinical Manifestation Generalized Tetanus Soldier dying of tetanus; painting by Sir C. Bell 1809 Lockjaw and Risus sardonicus Clinical Manifestation Generalized Tetanus Onset after 2­14 days Mostly due to wound infections First signs are lockjaw, then stiffness of neck and finally generalized muscle spasms Heart muscle not affected Spasm may last for several minutes and interfere with breathing Epidemiology Epidemiology Worldwide Tetanus cases reported worldwide (1990­2004). Ranging from strongly prevalent (in dark red) to very few cases (in light yellow) (gray, no data). About 1 million cases, 300­500 thousand deaths! Mainly neonatal tetanus Epidemiology Epidemiology About 5 deaths per year Mainly affects unvaccinated (or elapsed) individuals Diagnosis Diagnosis Made upon clinical manifestations Treatment /Prevention Treatment /Prevention Efficient vaccine exists (toxoid vaccine)! Requires booster shot every 10 years Treatment: ­anti­toxin antibodies ­metronidazole ­tetanus vaccination (potentially tracheostomy and mechanical ventilation) General Characteristics General Characteristics C. botulinum Large 3­20um Fastidious Divided into four groups Seven different variants of botulinum toxin (A­G) Pathogenesis Pathogenesis Botulinum toxin , large A­B toxin A­ subunit (light chain) has endopeptidase activity A­subunit cleaves proteins important for releasing acetylcholine No stimulation of muscles Clinical manifestation is “Flaccid paralysis” B­subunit, binds to receptor on neurons Clinical Manifestation Clinical Manifestation Overview Foodborne botulism: mostly associated with home­canned food (<30cases per year) Infant botulism: consumption of food contaminated with spores (Honey) (<100cases per year) Wound botulism: very rare Inhalation botulism: only a concern as bioweapon (aerosolized BoTox) Kerner’s Disease Kerner’s Disease “Sausage­Kerner” First report on “sausage”poisoning; in 1815 ,7 cases due to consumption of liver sausage Food­borne Botulism Food­borne Botulism Caused by toxin ingested with food (Intoxication) similar to Staph food poisoning Spores survive heating of food before canning, germinate and produce toxin Symptoms begin 18­36h after ingestion Weakness, blurred vision, dry mouth Descending weakness of skeletal muscles and finally respiratory paralysis Artist's rendition of an adult patient with mild botulism. Note ptosis (abnormal dropping of eyelids) and facial paralysis, manifesting as youthful, unlined, and seemingly inexpressive facies. The patient is fully alert. Localized Outbreak Localized Outbreak Infant Botulism Infant Botulism Most common form of botulism in US Occurs in infants between 5­20 weeks of age Solid food contaminated with spores (honey!) Bacteria can colonize intestines (Infection) because regular microflora not yet established Characterized by constipation, weak sucking ability and generalized weakness; can progress to more serious paralysis Most infants recover (mortality 1­2%) Potential link to Sudden­Infant­Death­ Syndrome Adequate ventilatory support! Penicillin/Metronidazole treatment Anti­toxin antibody treatment (only effective against unbound toxin) Proper care resulted in decrease of mortality from 60% to 4% Prevention Vaccine available but not applied Proper food handling Children under 1year should not eat honey Treatment/Prevention Treatment/Prevention Epidemiology Epidemiology Botulinum and Tetanus Toxin Botulinum and Tetanus Toxin Two of the most potent biological toxins! Especially BoT; 10g is lethal dose for population of LA! Implications for Bio warfare! Similar mechanism of action Tetanus and Botulism toxins Tetanus and Botulism toxins A­B subunit toxins A (light chain) subunit Enzymatic activity Mediates neurotoxicity B (heavy chain) subunit Translocation from vesicle to cytosol B (heavy chain) subunit Binding to cell surface receptor ...
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This note was uploaded on 01/24/2011 for the course BSCI 424 taught by Professor Staff during the Fall '08 term at Maryland.

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