Virulence Factors in Urinary Escherichia coli Strains: Phylogenetic Background and Quinolone and Fluoroquinolone Resistance

Abstract

Quinolone- and fluoroquinolone-resistant Escherichia coli strains harbor fewer virulence factors than susceptible strains. The reasons underlying this correlation are incompletely understood. We investigated the phylogenetic background, the presence of the papC, hlyA , and cnf1 (pathogenicity island II _J96 -associated), fimA, iss , and iutA genes, and the presence of type 1 fimbriae, P fimbriae, and hemolysin in 243 urinary E. coli isolates resistant only to quinolones (8%), resistant to both quinolones and fluoroquinolones (51%), or susceptible to both drugs (41%). Group B2 accounted for 56% of the isolates, showing a significantly higher prevalence among fluoroquinolone-susceptible strains than among resistant strains (65% versus 50% [ P = 0.03]). hly and cnf1 were significantly more associated with susceptibility ( P < 0.001) and with group B2 ( P < 0.001 for group B2 versus groups A and D). However, within group B2, fluoroquinolone-resistant strains showed lower prevalences of papC, hlyA , and cnf1 than their susceptible counterparts ( P < 0.001). In contrast, the incidence of iutA appeared higher for refractory isolates, including group B2, than for susceptible isolates ( P < 0.001). Only in group B2 did fluoroquinolone-resistant strains reveal a lesser ability to agglutinate Saccharomyces cerevisiae (7%) than quinolone-resistant (87%) and susceptible (80%) isolates, despite uniform possession of fimA genes. No similar contrast emerged for expression of hemolysin and P fimbriae. Mutations conferring quinolone and fluoroquinolone resistance may thus require a particular genetic background, not strictly correlated with phylogenetic groups. More interestingly, the mutational event itself can affect the expression of type 1 fimbriae, at least in the prevalent and complex B2 strains.