Enteric Bacteria 3 Flashcards
(29 cards)
v. cholerae bacteriology
curved, comma shaped gram negative oxidase positive. aerobic and facultatively anaerobic. 2 reservoirs: humans and plankton ecosystem of indian ocean. O cell wall antigen indicates pathogenicity: O1 and O139 are epidemic. Non-O1 cause sporadic or no disease, occasionally cause shellfish food poisoning
v. cholerae pathogenesis
fecal-oral. shed by asymptomatic carriers in incubation or convalescence. travels to untreated water or undercooked shellfish. usually killed by stomach acid. survivors reach small intestine and sccrete mucinase to get into brush border, attach by toxin coregulated pilus, growing bacteria secrete cholera toxin
where does the B subunit of cholerae bind?
B binds the ganglioside receptor GM1 on intestinal lining
what does the A subunit of cholerae cause?
persistent activation of adenylate cyclase, leading to loss of water and ions. Massive watery diarrhea
v. cholerae exam
mild cases don’t present. 5% proced to rice water stool. no pain, blood, or neutrophils in stool. some vomiting, no fever. acidosis and hypokalemia. dehydration.
pediatric symptoms of cholerae
drowsy, coma. fever. hypoglycemic convulsions
cholerae lab
isolate on buffered media. find oxidase positive, only slightly lactose fermenting. ferments sucrose. gives acid reaction on triple sugar iron agar. specific antisera will halt motility. darkfield microscopy of stool sample reveals motile vibrios
cholerae treatment
rehydrate and rebalance electrolytes. can treat with short course of tetra, doxy cycline or furazolidone or ciprofloxacin after IV rehydration
v. parahaemolyticus bacteriology
oxidase pos, gram neg curved rod. saltwater borne. halophile.
v. parahaemolyticus pathogenesis
leading cause of gastroenteritis in those who eat undercooked seafood, mainly shellfish. secretes a hemolysin and an enterotoxin similar to choleragen.
v. parahaemoltyticus exam
N/V, cramps, fever. usually self limited. predisposing factors: immunodeficiency, liver disease, iron overload, kidney disease
v. parahaemolyticus lab
bloodwork for DIC, HBV, HCV, iron. culture in 8% NaCl. ideally culture from stool on thiosulfate-citrate-bile salts-sucrose media.
v. parahaemolyticus treatment
in a previously healthy patient, will be self limited. oral rehydration needed. if complicating factors or high fever, doxycycline or quinolone, IV rehydration
v. vulnificus bacteriology
oxidase + gram - curved motile rod. some encapsulated. saltwater borne. halophile.
v. vulnificus pathogenesis
infects shellfish contaminated wounds. cellulitis progressing to necrotizing fasciitis in shellfish market workers. can also infect wounds exposed to seawater. causes septicemia in immunocompromised people. pre-existing liver disease predisposes to poor outcome
what toxins does v. vulnificus make?
hemolysin and protease exotoxons. also makes siderophores, infection exacerbated by iron overload
v. vulnificus exam
cellulitis with history of handling raw shellfish. foot injuries from stepping on seashells. severe pain -> numbness. things predisposing to complication: immunodeficiency, liver disease, iron overload, kidney disease
v. vulnificus lab
bloodwork for DIC, HBV, HCV, iron. gram stain and culture from aspirate of wound site and adjacent blood. biopsy demonstrates gram negative bacilli, acute inflammation, tissue necrosis and fat infarction
v. vulnificus treatment
surgical care at the wound site. ceftazidime + doxycycline or antipseudomonal penicillin. alts: cefotaxime or fluoroquinolones
campylobacter bacteriology
comma or S shaped gram neg rods. motile. oxidase and catalase pos. microaerophilic. grows well at 42C. reservoir in guts of domestic animals. transmitted fecal-oral, sexual contact, sick pets.
campylobacter pathogenesis
low infectious dose. both intestines are colonized and invaded. bloody diarrhea with pus, crypt abscesses and ulceration. some strains produce a choleralike enterotoxin -> watery diarrhea.
c. jejuni pathogenesis
infection strongly predisposing for Guillain Barre syndrome. can alternatively rtrigger reactive arthritis. rarely causes hemolytic uremic syndrome
campylobacter exam
common in kids. initially watery, foul smelling diarrhea. progresses to bloody stools with fever and ab pain. Sigmoidoscopy: focal mucosal edema, hyperemia, patchy petechiae, ulceration.
campylobacter lab
stool sample culture: blood agar plates with antibiotics. 42C +25C (fails at low temp). 5% oxygen, 10% CO2. grows slow in culture, may have seagull appearance. microscopic exam of fecal smear for darting motility, leukocytes, erythrocytes. gram stain of fecal smear.
