Escherichia coli

Gram Stain

• Gram negative bacilli - fermenter

Clinical Significance

E. coli colonizes the large intestine of humans. 

It is the most common pathogen of urinary tract infections and is associated with pneumonia, bacteremia (typically secondary to urinary tract infections), endocarditis, meningitis (typically in neonates), hepatic abscesses, peritonitis, endophthalmitis, sinusitis, brain abscesses, skin/soft tissue, bone and joint infections.  

Certain strains of E coli (enterotoxigenic, enteropathogenic, enteroinvasive, enterohemorrhagic) cause diarrhea.

Usual Susceptibility Pattern

E. coli has variable susceptibility to ampicillin, cephalexin, TMP/SMX, and quinolones.

Note: Cefazolin susceptibility does not predict cephalexin susceptibility. 

The number of strains producing extended spectrum beta-lactamases (ESBL) or AmpC cephalosporinases is increasing resulting in resistance to penicillins, cephalosporins, and beta-lactamase inhibitor combinations.

Most isolates (including ESBL / AmpC producers) remain susceptible to nitrofurantoin and fosfomycin.