Quinolone/fluoroquinolone susceptibility in Escherichia coli correlates with human polymicrobial bacteriuria and with in vitro interleukine-8 suppression

Urinary tract infections (UTIs) are frequently polymicrobial diseases mainly sustained by Escherichia coli in association with other opportunistic pathogens. Cystitis and pyelonephritis are usually accompanied by an inflammatory response, which includes neutrophil recruitment. Uropathogenic E. coli possess the ability to evade host defenses, modulating the innate immune response. The aim of this study was to determine whether particular E. coli strains correlate with polymicrobial bacteriuria and whether escape from the early host defenses and microbial synergy could lead to mixed UTIs. We evaluated 188 E. coli-positive urine samples and assessed the relationships among polymicrobism, neutrophil presence and several traits of E. coli isolates (virulence factors such as hlyA, fimA, papC and their relative products, i.e. hemolysin, type 1 and P fimbriae, and cnf1, their phylogenetic group) and their ability to suppress cytokine response in 5637 bladder epithelial cells. Escherichia coli susceptibility toward quinolones and fluoroquinolones, known to be linked to the pathogenicity of this species, was also considered. We found significant correlations among polymicrobial bacteriuria, absence of pyuria and quinolone/fluoroquinolone susceptibility of E. coli isolates and their enhanced capability to suppress interleukin-8 urothelial production when compared with the patterns induced by the resistant strains.