Escherichia coli

MICROBIOLOGY

• Gram negative rod, Enterobacteriaceae w/ human strains as (1) commensal bowel flora, (2) intestinal pathogenic (enteric/diarrheogenic), (3) extraintestinal pathogenic.
• Predominant facultative anaerobe 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% (+).
• E. coli producing CTX-M enzymes now worldwide concern in community-acquired UTIs and also blood stream 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.