Prevalence and characterization of cefotaxime and ciprofloxacin co-resistant Escherichia coli isolates in retail pork

Objective To investigate the prevalence and characteristics of cefotaxime and ciprofloxacin co-resistant Escherichia coli(E.coli) isolates in retail pork samples.Methods Retail pork samples were collected from 12 supermarkets and 7 farmer's markets in Beijing(n=37)and Hanzhong(n=81);cefotaxime and ciprofloxacin co-resistant E.coli isolates were recovered and subjected to antimicrobial susceptibility testing and resistant mechanism analysis.Results Cefotaxime and ciprofloxacin co-resistant E.coli isolates were recovered in 22.0%(26/118)of retail pork samples.E.coli isolates of phylogenetic group A were dominant(12 isolates).The dominant resistant profiles were ampicillin(AMP)-ceftazidime(CAZ)-cefotaxime(CTX)-ciprofloxacin(CIP)-chloramphenicol(CHL)-gentamicin(GEN)-trimethoprim-sulfamethoxazole(SXT)-tetracycline(TET)(n=14) and AMP-CAZ-CTX-CIP-CHL-SXT-TET(n=7).Point mutations in quinolone resistance determination regions of topoisomerases were identified in all the isolates.Plasmid mediated quinolone resistant determinants were identified in 12 isolates.Four subtypes of bla_CTX-M were identified in 24 extended spectrum β-lactamases producing E.coli isolates and bla_CTX-M-55(n=22)was dominant.Conclusion This study highlights that retail pork could serve as an important reservoir of cefotaxime and ciprofloxacin co-resistant E.coli.The dominant β-lactam resistant mechanism is bla_CTX-M-55(n=22).