BSCI 424 Pathogenic Microbiology -- Escherichia

BSCI 424 — PATHOGENIC MICROBIOLOGY — Fall 2000

Escherichia coli Summary

Morphology & Physiology:

Gram-negative bacilli (see WebLinked image)

Cultural Characteristics: grow as fermenting colonies, some beta-hemolysis upon initial isolation; motile, non-pigmented

Antigenic Structure: O, K, H antigens typed serologically as an epidemiologic tool

Taxonomy:

Family Enterobacteriaceae

Escherichia coli

Opportunistic Escherichia coli

ETEC = enterotoxigenic E. coli

EIEC = enteroinvasive E. coli

EPEC = enteropathogenic E. coli

EHEC = enterohemorrhagic E. coli

EaggEC = enteroaggregative E. coli

UPEC = uropathogenic E. coli

Clinical Syndromes:

85% of urinary tract infections

50% of primary nosocomial pneumonia in some hospitals

Major cause of neonatal meningitis with up to 80% mortality

Gastroenteritis (see above and Summary Table below for specific syndromes and virulence factors associated with specific strains)

Wound infections

Peritonitis: sepsis

Epidemiology:

Most predominant organism of the large intestine

Ordinarily non-pathogenic but may be opportunistic or true pathogens (see above and Summary Table below for specific syndromes and virulence factors associated with specific strains)

Pathogenesis & Immunity:

Fimbriae (formerly pili): important for colonization of host tissues

Some strains have adhesins and exotoxins (enterotoxins) as virulence factors and are true pathogens (see above and Summary Table below for specific syndromes and virulence factors associated with specific strains)

Other invasive factors

Laboratory Identification:

Mere isolation of E. coli from specimens is not definitive diagnosis

Treatment, Prevention & Control:

Diarrhea: fluid and electrolyte replacement; trimethoprim-sulfamethoxazole prophylactically

Other Conditions: treatment varies depending upon site of infection and antibiogram of isolate

Summary of Clinical Syndromes and Virulence Factors of Escherichia coli
	SITE AFFECTED	CLINICAL SYNDROME	ADHESINS	EXOTOXINS	PATHOGENESIS
Opportunistic E. coli	Various sites	See above and Enterobacteriaceae	??	??	Urinary tract infections; Primary nosocomial pneumonia; neonatal meningitis; Wound infections; Peritonitis; septicemia
Enterotoxigenic E. coli (ETEC)	Small intestine	Traveller's diarrhea	Type 1 pili; Colonization factor antigens (CFA/I; CFA/II)	Heat stable toxins (STa; STb); Heat labile toxins (LT-I; LT-II)	Hypersecretion of fluids and electrolytes stimulated by plasmid-mediated enterotoxins
Enteroinvasive E. coli (EIEC)	Large intestine	Shigellosis-like disease in developing countries	??	??	Plasmid-mediated invasion and destruction of enterocytes
Enteropathogenic E. coli (EPEC)	Small intestine	Infant diarrhea	Bundle-forming pili (Bfp); Intimin	??	Plasmid-mediated adherence and destruction of enterocytes
Enterohemorrhagic E. coli (EHEC)	Large intestine	Hemmorrhagic colitis possible leading to hemolytic uremic syndrome (HUS)	Intimin	Shiga-like toxins (SLT-I; SLT-II)	Inhibition of protein synthesis by lysogenic bacteriophage-encoded cytotoxic enterotoxins
Enteroaggregative E. coli (EaggEC)	Small intestine	Infant diarrhea in developing countries	GVVPQ fimbriae	Enteroaggregative heat stable toxin	Inhibition of fluid absorption by plasmid-mediated aggregative adherence
Uropathogenic E. coli (UPEC)	Urinary tract	Urinary tract infections	P pili; Afimbrial adhesins (AFA-I; AFA-III); Dr adhesin	HlyA (hemolysin)	Adherence to specific receptors on epithelial cells of the bladder and upper urinary tract with HlyA cell lysis leading to cytokine release and inflammatory responses

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