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

ABSTRACTQuinolone- and fluoroquinolone-resistant Escherichia colistrains 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 IIJ96-associated), fimA, iss, and iutAgenes, and the presence of type 1 fimbriae, P fimbriae, and hemolysin in 243 urinary E. coliisolates 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]). hlyand cnf1were 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 cnf1than their susceptible counterparts (P< 0.001). In contrast, the incidence of iutAappeared 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 fimAgenes. 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.