Organisms Commonly Co-Isolated with E. coli in UTIs
E. coli is most commonly co-isolated with Klebsiella pneumoniae, Proteus mirabilis, Enterococcus faecalis, and Staphylococcus saprophyticus in urinary tract infections. 1
Primary Co-Pathogens
The bacterial landscape of UTIs shows a consistent pattern of organisms that accompany E. coli:
Klebsiella pneumoniae is the second most common uropathogen found alongside E. coli, particularly in complicated UTIs and healthcare-associated infections 1, 2
Proteus mirabilis frequently co-exists with E. coli, especially in patients with structural urinary tract abnormalities or catheter-associated infections 1
Enterococcus faecalis represents another common co-pathogen, particularly in polymicrobial infections and in patients with instrumentation or recent antibiotic exposure 1
Staphylococcus saprophyticus is commonly identified alongside E. coli, particularly in young sexually active women with uncomplicated cystitis 1
Clinical Context
While E. coli accounts for up to 90% of all UTIs in ambulatory populations as a single pathogen 3, when polymicrobial infections occur, the organisms listed above represent the most frequent co-isolates 1.
Important Considerations:
E. coli dominance: In most UTI cases, E. coli is the predominant organism even when other bacteria are present, with uropathogenic E. coli (UPEC) being the primary driver of infection 1
Antimicrobial resistance patterns: Co-infections with these organisms increasingly involve multidrug-resistant strains, particularly ESBL-producing Enterobacterales (E. coli and Klebsiella) 2
Treatment implications: When treating suspected polymicrobial UTIs, empiric coverage must account for both E. coli and these common co-pathogens, with consideration of local resistance patterns 2