Characterization of clinical Escherichia coli isolates from China containing transferable quinolone resistance determinants.

BACKGROUND The categories of recognized transferable quinolone resistance determinants have been increasing sharply. The rapid horizontal transfer of these quinolone resistance genes has caused concern since they bring new dissemination possibilities for quinolone resistance. METHODS In total, 579 clinical Escherichia coli isolates were subjected to antimicrobial susceptibility testing, screening for qnr alleles, qepA and aac-(6')-Ib-cr by PCR amplification and DNA sequence analysis. Isolates containing transferable quinolone resistance determinants were further characterized by mutation analysis in the quinolone resistance determining regions (QRDRs) of GyrA and ParC, phylogenetic typing and PFGE to determine their genetic relatedness. RESULTS After PCR screening and sequence analysis, transferable quinolone resistance determinants were identified in 74 of 579 E. coli isolates (12.8%). The antimicrobial resistance profiles and phylogenetic groups differed between isolates containing different categories of transferable quinolone resistance determinant. Most of the isolates containing qepA alone were highly resistant to ciprofloxacin (MIC >or= 512 mg/L) and belonged to phylogenetic group D (22/25), while most of the isolates containing aac-(6')-Ib-cr alone belonged to phylogenetic group A (17/35) or D (16/35). Of 74 E. coli isolates containing transferable quinolone resistance determinants, 69 PFGE patterns and 19 clusters were identified. CONCLUSIONS The great genetic variation of E. coli hosts containing transferable quinolone resistance determinants demonstrated the high transmission capacity of these mechanisms. It is urgent to characterize and block their transmission routes in order that the utility of quinolones is preserved.