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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


Also called "Traveler's diarrhea", "Tourista", "Montezuma's revenge"
Hypersecretion through small intestine = fluid and electrolyte loss

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