Characterization of Escherichia coli isolated from urinary tract infection and association between virulence expression and antimicrobial susceptibility

BACKGROUND: The capacity of antibiotics to modulate bacterial virulence has raised concerns over the appropriateness of antibiotic therapies, including when dosing strategies fall below sub-therapeutic levels. In this work, we investigated the ability of antibiotics to influence virulence in Escherichia coli isolated from urinary tract infection (UTI). RESULTS: Out of 120 isolates, 32.5% carried pap, 21.7% carried hlyA, and 17.5% carried cnf. The predominant B2 phylogroup was significantly associated with the quinolone-resistant isolates. A significant association was seen between the presence of hlyA hemolysin and susceptibility to ceftriaxone and ciprofloxacin (P < 0.05). Sub-inhibitory concentrations of both antibiotics reduced the levels of hlyA expression and hemolysis in isolates treated with antibiotics compared to untreated isolates (P < 0.05). Growth rate assay showed that the decrease in hlyA expression was not an effect of decreased growth rate. CONCLUSION: Our study indicated the inhibitory effect of ciprofloxacin and ceftriaxone on the level of hemolysis, suggesting that the sub-inhibitory concentrations of these antibiotics may affect the outcome of infections. Further studies, including animal models may elucidate the outcome of virulence modulation by these antibiotics in UTI pathogenesis.