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Bacterial Diseases of the GI Tract
n/a
19
Medical
Professional
09/18/2009

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Cards

Term
Enterobacteriaceae
Definition
  • gram-, non-spore forming rods
  • capsule or slime layer
  • motile or non-motile
  • pili for attachment
  • speciated by carbohydrate fermentation tests
  • cause diarrhea, dysentery, typhoid fever, hemorrhagic colitis, UTIs, septicemia, pneumonia, meningitis
  • Ag structure
    • K Ag - mucopolysaccharide
    • O Ag - LPS
    • H Ag - flagellin protein
  • Determinants of pathology
    • endotoxins - lipid A portion of LPS ---> fever, shock
    • enterotoxins - affect small intestine to cause transduction of fluid into lumen --> diarrhea
  • Laboratory diagnosis
    • grow in air to eliminate anaerobes
    • carbohydrate fermentation tests: MacConkey, Hektoen agar
    • serology: O, H, K Ag
    • PCR
  • Escherichia
  • Shigella
  • Salmonella
  • Proteus
  • Klebsiella
  • Enterobacter
  • Serratia
  • Citrobacter
Term
Vibrionaceae
Definition
  • gram-, halophilic, non-spore forming curved rods
  • highly motile, oxidase+
  • cause cholera, gastroenteritis, septicemia, wound infections, peptic ulcers, diarrhea
  • LPS (O Ag) important
  • Vibrio
  • Campylobacter
  • Helicobacter
Term
ETEC
Definition
  • motile, lactase+, oxidase- no H2S production
  • facultative anaerobe
  • grow on MacConkey agar (bile salts inhibit gram+)
  • pathogenesis (genes carried on plasmids)
    • adhesins
    • heat labile toxin --> binds AC --> ↑ cAMP + fluid loss
    • heat stable toxins --> bind to GC --> ↑cGMP + fluid loss
Term
Vibrio cholerae
Definition
  • gram-, comma shaped, never normal flora
  • found in coastal waters (shellfish)
  • many strains with antigenically different O Ag
  • mode of transmission - contaminated water or food
  • sesntitive to stomach acid - need large innoculum
  • virulence
    • flagella
    • type IV pili
    • ToxR - complex toxin part of filamentous phage ΦCTX genome
      • ADP ribosylates G protein --> activates AC --> ↑ cAMP --> ↑ secretion of Cl, ↓ absorption of Na --> diarrhea
  • clinical picture - severe diarrhea and vomiting
  • diagnosis - TCBS culture (agglutinins in blood, oxidase+, motile, no H2S production
  • Treatment
    • vaccines
    • oral rehydration therapy
Term
EPEC
Definition
  • watery diarrhea in newborns and infants
  • colonizes rapidly --> septicemia, dehydration
  • major cause of pediatric diarrhea and death in underdeveloped nations
  • diagnosis: PCR for virulence factors
  • treatment: neomycin
Term
EAggEC
Definition
  • persistant diarrhea in children and infants
  • non-invasive, heat-labile toxin
  • clumping - adheres to surfaces of specific cell types
  • Diagnosis: tissue culture assays for aggregated adherence
  • treatment: rehydration
Term
DAEC
Definition
  • watery diarrhea in adults and children
  • adheres diffusely to surface of various cell types
  • diagnosis: tissue culture assays for diffuse adherence
  • treatment: rehydration
Term
Shigella spp.
Definition
  • S. dysenteriae, S. flexneri, S. boydii, S. sonnei (different O Ag)
  • cause bacillary dysentery
  • gram-, oxidase-, lactose-, no H2S, non-motile rods
  • cannot be distinguished readily from E. coli by DNA hybridization --> different virulence properties
  • clinical picture
    • 2-4 day incubation
    • frequent passage of stools w/blood, mucus, pus
    • fever, abdominal pain, tenesmus
  • pathogenesis
    • survive stomach acid
    • enter epithelial cells
    • lyse phagosome and multply in cytosol
    • inflammation and necrosis
  • virulence
    • plasmid borne invasion proteins
    • shiga toxin (S. dysenteriae)
      • irreversibly inactivates host 60S ribosome
      • targes villus cells in colon - ↓ Na absorption - ↑ fluid loss
      • cytotoxic effects on mucosal epithelial cells
  • diagnosis - stool culture
  • treatment - oral rehydration, antibiotics if very severe
Term
EHEC
Definition
  • non febrile bloody diarrhea or hemorrhagic colitis
  • rare serotype O157:H7
  • found in undercooked beef, contaminated ground water
  • pathogenesis
    • colonizes colonic epithelium
    • produces Shiga-like toxins
    • toxins can enter blood→ hemolytic uremic syndrome (kidney failure)
  • diagnosis
    • growth on sorbitol MacConkey
      • most E. coli are sorbitol+
      • EHEC is sorbitol-
    • immunoassay to detect Shiga toxin in stool
  • therapy - rehydration (antibiotics may increase risk of HUS)
Term
Campylobacter jejuni
Definition
  • gram-, oxidase+, single flagellum, rods often in pairs
  • found in contaminated water, undercooked poultry and eggs
  • symptoms - similar to dysentery, usually no dehydration
  • pathogenesis
    • small innoculum
    • produce heat labile Shiga-like toxin
    • colonizes both small and large intestine
  • Diagnosis
    • isolated from rectal and stool specimens
    • cultured at 42° on CampyBAP medium
  • Treatment
    • antibiotics
    • rehydration
    • vaccine under development
Term
Salmonella enterica enteritidis
Definition
  • pili, long wavy flagella, produces H2S oxidase-
  • clinical picture
    • 6-24 hours after ingestion - diarrhea, nausea, vomiting, fever, abdominal pain
    • usually self-limiting
  • pathogenesis
    • often ingested in undercooked meat, poultry, eggs
    • penetrate epithelium, multiply in lymph follicles
    • infection contained to GI tract
    • Type III secretion system delivers proteins to gut that disrupt cell fxn, cause inflammation, and stimulate ↑ cAMP and fluid secretion
    • no known exotoxins
  • treatment - supportive rehydration
Term
Salmonella enterica typhi
Definition
  • typhoid fever
  • normal flora in chicken, cattle, reptiles, but never humans
  • clinical picture - fever, rash, constipation/diarrhea, delerium, rose-colored spots on abdomen
  • pathogenesis
    • systemic infection - can lead to septicemia, kidney, liver, spleen, and bone marrow involvement
    • can remain in gallbladder - carrier state
    • in colon, can cause severe diarrhea, hemorrhage, perforation
  • virulence
    • capsular V Ag
    • flagella (H Ag) - phase variation
    • cell invasion machinery
    • intra-macrophage survival mechanisms
    • endotoxin (LPS) - systemic inflammatory response
    • Type III secretion system
  • Diagnosis
    • IgM, IgG Ab available to various Ags
    • specimens in blood, stool, urine, bone marrow
  • Treatment
    • vaccines
    • variety of antibiotics
    • cholycystectomy if carrier
Term
EIEC
Definition
  • Enteroinvasive E. coli
  • Shigella - like illness
  • treated with antibiotics
Term
Vibrio parahemolyticus
Definition
  • bloody diarrhea, gastroenteritis
  • found in seafood produces enterotoxin
  • treatment: rehydration
Term
Vibrio vulnificus
Definition
  • septicemia, wound infections, gastroenteritis
  • found in raw/undercooked seafood
  • associated w/liver disease (alcohol, viral hepatitis)
  • treated with tetracycline, 3rd generation cephalosporins
Term
Yersinia enterocolytica
Definition
  • causes Yersiniosis, pseudoappendicitis
  • gram- rod found in animals
  • grows in mesenteric lymph nodes
  • makes ST-like toxin - inflammatory
Term
Clostridium difficile
Definition
  • antibiotic-induced diarrhea, pseudomembranous colitis
  • occurs after antibiotic treatment due to destruction of normal flora and overgrown of gram+ rods
  • diagnosis: detection of toxin in stool
  • treatment: vancomycin
Term
Bacillus cereus
Definition
  • emetic and diarrheal forms
  • two toxins → ↑ cAMP levels
Term
Helicobacter pylori
Definition
  • general characteristics
    • gram- curved rod
    • polar tuft of 4 - 7 flagella
    • grows in stomach (normal flora for some)
    • causitive agent of chronic gastritis and peptic ulcers
    • risk factor for gastric adenocarcinoma and non-Hodgkin's lymphoma of stomach
  • virulence
    • flagella - move through mucin layer
    • urease - forms ammonia w/in bacteria --> helps buffer incoming H+ ions
    • adhesins - recognize carbohydrate Ag on surface of epithelial cells
    • cag pathogenicity island
      • type IV secretion system
      • cagA - cytotoxin
      • VacA - vacuolating cytotoxin --> tissue death
  • clinical picture
    • acute gastritis
    • sometimes diarrhea
    • chronic inflammation of gastric mucosa
  • diagnosis
    • gastric biopsy
    • isolate bacteria
    • test urease+
  • treatment - triple therapy
    • amoxicillin
    • clarythromycin or Flagyl
    • Omeprazole (H+ pump inhibitor)
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