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20 terms

Enterobacteriaceae

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Enterobacteria
Gram-negative
If motile, have peritrichous flagella
Main cell wall component = heat-stable lipopolysaccharide (LPS)
Low-maintenance, rapid growth
Biochemical characteristics of enterobacteria
1. Ferment glucose (anaerobes)
2. Oxidase-negative
3. Catalase-positive
4. Reduces nitrates to nitrites or nitric acid
Morphological features of enterobacteria
1. Lactose-fermenting (E. coli, Klebsiella, enterobacter, citrobacter)
2. Non-lactose fermenting (proteus, salmonella, shigella, yersinia)
3. High resistance to detergents from bile salts
4. Prominent capsule (Klebsiella) or diffusible slime layer
3 main antigens in enterobacteria
1. Somatic O antigen (LPS polysaccharides)
2. K antigens (glycocalyx)
Flagellar H antigens (can undergo antigen variation)
Pathogenic features of enterobacteria
1. Endotoxin
2. Glycocalyx
3. Iron sequestration
4. Antibiotic resistance
Endotoxins from enterobacteria
1. Depends on Lipid A (beta-hydroxy myristic acid) part of LPS
2. Released at cell lysis
3. Systemic manifestations
Systemic manifestations of enterobacteria
1. Complement activation
2. Leukocytosis, thrombocytopenia
3. Disseminated intravascular coagulation (DIC)
4. Fever, shock, death
Glycocalyces of enterobacteria
1. Antiphagocytic
2. Interferes with antibody binding
3. Poor immunogen
Iron sequestration
Produce siderophores that bind competitively to iron against host heme/non-chelating proteins
Antibiotic resistance
1. Klebsiella - chromosomal beta-lactamase
2. Resistance (via plasmids or extra-chromosomally)
3. Exchange among species, genera, families
Escherichia coli (epidemiology)
-Part of the normal flora in GI
-At least 95% community-acquired UTI's
-Gastroenteritis in developing countries
-Most infections are endogenous
E. coli urinary tract infections
1. Comes from urethral contamination to bladder colonization --> then can go to kidney
2. Specific serotypes: adhesins (prevent flushing) and hemolysins (cytokine release)
E. coli neonatal meningitis
Infections with maternal GI bacteria
75% strains involved are K1 glycocalyx
E. coli septicemia
Bacteria in bloodstream with shock symptoms
Originate from UTI's or intra-abdominal perforations
Gastroenteritis pathogenic mechanisms (6)
1. ETEC - enterotoxigenic E. coli
2. EPEC - enteropathogenic E. coli
3. EIEC - enteroinvasive E. coli
4. EHEC - enterohemorrhagic E. coli
5. EAEC - enteroaggregative E. coli
6. DAEC - diffuse adherent E. coli
EHEC Gastroenteritis
1. Enterohemorrhagic E. coli (Verotoxin, VTEC)
2. Acid-tolerant, low infective dose
3. 2 toxins = Stx1 (~Shiga), Stx2 (HUS)
4. Normal flora of cows
5. Most common strain = O157:H7
6. Stx2 - Hemolytic uremic syndrome
EPEC Gastroenteritis
1. Enteropathogenic E. coli
2. Major cause of infant diarrhea
3. Characterized by bacterial attachment to cells of small intestine, then effacement (destruction) of microvilli, resulting in diarrhea
EAEC Gastroenteritis
1. Enteroaggressive E. coli
2. Persistent watery diarrhea
EAEC mechanism of action
"Stacked brick" autoagglutinization, mediated by bundle-forming fimbriae, that then adhere to intestinal mucsa.
Mannose-resistant aggregative adherence factor
Blockage of fluid and nutrient absorption
ETEC
Also called "Traveler's diarrhea", "Tourista", "Montezuma's revenge"
Hypersecretion through small intestine = fluid and electrolyte loss