Quinolone resistance and correlation to other antimicrobial resistances in faecal isolates of Escherichia coli in Hong Kong.

In an attempt to assess the level of quinolone resistance and its association with other antimicrobial resistance in faecal Escherichia coli isolated from routine outpatient specimens in Hong Kong, ciprofloxacin-supplemented MacConkey agar was used to screen for resistant isolates. Antimicrobial susceptibility testing of the isolates was done by VITEK 2 and previous amplification-based methods were employed to characterize the genetic determinants behind some of the resistance phenotypes. One hundred and seventy-six (43%) of 409 specimens had quinolone-resistant E. coli isolated (199 isolates). Quinolone resistance was found to be associated with resistances to penicillins (>80%) and co-trimoxazole (69%). Nonsusceptibility to combinations of penicillins and clavulanic acid was above 20% and up to 50% for the aminoglycosides gentamicin and tobramycin. CTX-M-type extended-spectrum beta-lactamases were found responsible for most cephalosporin resistances but the transferable quinolone resistance determinant qnrA was not detected. Our data suggested that a high percentage of E. coli isolates as part of the alleged normal intestinal microflora in humans appeared to be resistant to quinolones. Co-resistance to various other frequently used antimicrobials was also observed. Transferable genetic determinants were found to be involved in some cases.