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Microbiology and Immunology
Microbiology and Immunology 2500A/B

Clostridia • G+ rod shaped endospore formers Endospores are critical in the development of the diseases that clostridia causes Strict anaerobes, vegetative cells killed by oxygen • • Generally found in soil & intestinal tracts of animals • responsible for several unrelated diseases • There are over 80 species of clostridia • Important human pathogens :  C. difficile - pseudomembranous colitis  C. tetani - tetanus  C. botulinum - botulism  C. perfringens - food-borne illness & gas gangrene • can cause life threatening diseases mediated by exotoxins Endospore Formation • endo = within • Endospores are highly resistant to heat & harsh chemicals, drying & nutrient depletion function as ‘survival structures’ • • used for dispersal through air, water & intestinal tracts • Clostridia produce terminal endospores o The endospores form at end of cells • The endospore formation is best studied in Bacillus & Clostridium species Sporulation occurs due to lack of nutrients or stress (developing spore) • • A dormant stage in bacterial life cycle • Can remain dormant for years but as the spore matures, it reverts back to being a vegetative cell rapidly (within minutes via germination) Occurs through a complex series of events • • Exosporium & spore coat are composed of protein Core wall is peptidoglycan • • Cortex contains DNA, cytoplasm, ribosomes etc • Main thing :  dipicolonic acid complex with calcium helps to hydrate the cortex - consistency of a gel but very resistant to heat, chemicals, etc • Pasteurization (63-72 degrees) will not kill them  can germinate from this • Autoclaving @ 121 degrees will kill The Pathogen : C. difficile • cause of pseudomembranous colitis aka antibiotic associated diarrhea • can exist as: • asymptomatic carrier state • cause of mild-moderate diarrhea • cause of life threatening pseudomembranous colitis • C. difficile can be harbored in the large intestine in low numbers approx 3% of healthy adults are colonized • • found in nursing homes & hospital environments • nosocomial • under harsh conditions - reverts to the highly resistant spore • spores can be very difficult to eradicate from the environment • mode of transportation is through the spore: fecal-oral route • C. Difficile Toxins produces A:B toxins called large clostridial cytotoxins • • A:B serves to designate two domains • A- active portion of toxin that carries enzymatic activity - responsible for damage • B- responsible for binding & uptake by the host cell A domain inactivates key regulatory proteins (called G proteins) of host cell • • can’t regulate cells - cells die - induces inflammation • causes disregulation of multiple cell processes including cytoskeletal rearrangements - cell death, inflammation • Pseudomembranous Colitis most symptomatic patients have recently received antibiotic agent • • single most important risk factor • antibiotic used to kill infections but also kill normal microbiota • suppression of normal flora & persistence of C. difficile endospores • in response to the antibiotic, C. diff enters the endospore state • after antibiotic stopped, spores germinate, overgrowth of C. diff occurs with production of toxins C. diff does not invade, but the toxins damage the intestinal lining of large • intestine • Symptoms & Diagnosis • inflammatory condition of large intestine • offensive smelling diarrhea, abdominal pain, fever, nausea, dehydration patients usually have “constitutional” symptoms • • symptoms may occur 1-2 days after antibiotics or several weeks after antibiotic is discontinued • in serious cases can lead to low blood pressure, kidney failure, perforated colon, toxic megacolon endoscopy shows characteristic yellow lesions • • lesions can be stripped off - the pseudomembrane • Diagnosis & Treatment • history (antibiotic use), symptoms & lab tests to confirm C. difficile • tests can detect these toxins in the stool • endoscopy & toxin detection assays • discontinue inciting antibiotics if still used • fluids • antibiotic more specific for C. difficile - usually metronidazol • avoid antidiarrheal agents, don’t want colonic stasis - decreased toxin clearance Fecal Microbiota Transplantation • take someones microbiota & implant it into someone elses intestine to restore it • extremely effective Problem: if g
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