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- Gram-negative (GN) rod, E. coli member of Enterobacteriaceae: human strains may be: (1) commensal bowel flora, (2) intestinal pathogenic (enteric/diarrheogenic), (3) extraintestinal pathogenic.
- Predominant GN in composition of normal human colonic flora.
- E. coli easy to grow from sterile specimens.
- Stool cx: only if chronic diarrhea (need reference lab to ID) or suspect O157:H7 (cx all bloody diarrhea) use sorbitol-MacConkey agar or perform Shiga toxin EIA.
- ~ 90% strains ferment lactose; some diarrheogenic E. coli strains, including many of the EIEC strains, typically lactose negative. Indole test 99% (+).
- Major resistance concerns :
- Plasmid-mediated AmpC β-lactamases (e.g., CMY)
- Extended-spectrum β-lactamases (e.g., CTX-M)
- Now worldwide concern in community-acquired UTIs and also bloodstream infections
- In some Asian countries rates of ESBL E. coli have been reported as high as 55-79%.
- Rates are lower in North America but rising.
- Carbapenemases (e.g., New Delhi metallo-β-lactamase, Klebsiella pneumonaie carbapenemase and OXA-48)