Phenotypes of Escherichia coli isolated from urine: Differences between extended-spectrum β-lactamase producers and sensitive strains

Escherichia coli is a frequent causative agent of urinary tract infections, and increasing resistance of E. coli to antimicrobials presents a growing challenge.

Here we compare phenotypes of extended-spectrum β-lactamase (ESBL) producers (n = 220) with a control group of sensitive strains (non-ESBL producers; n = 150). For each strain, we assessed the presence of O25 antigen, hemolysis, biofilm production, sensitivity to antibiotics, and biochemical profile.

Compared to the control group, ESBL producers were more frequently O25 positive (6.0% vs. 42.3%) and less frequently hemolytic (34.7% vs. 6.4%). Comparison of biofilm production in brain-heart infusion (BHI) and in BHI with 4% glucose supplementation showed that ESBL-positive strains produced biofilm in BHI with glucose less intensely than the control group (p < 0.05). Most ESBL producers were ciprofloxacin-resistant (91.8%). Biochemical analyses revealed that ESBL producers more frequently utilized inositol, ornithine, sorbitol, melibiose, and saccharose, whereas the control group more frequently used esculin, lysine, arginine, and dulcitol. The control group strains with O25 antigen were more commonly resistant to ciprofloxacin (p < 0.05). Pulsed-field gel electrophoresis results showed higher variability among the control group of sensitive strains.

These findings suggest a potential to detect ESBL strains based on virulence factors and biochemical properties, which could be useful in shaping proper empiric antimicrobial therapy, and for initiating such therapy as soon as possible.