Prevalence and transmission of plasmid-mediated quinolone resistance qnrS gene among Escherichia coli isolates in a poultry farm

Abstract:

Abstract:［Objective］To investigate the prevalence and transmission of plasmid-mediated quinolone resistance qnrS gene among Escherichia coli isolates in a poultry farm and its environment.［Methods］E.coli isolates from fecal samples in a poultry farm and its environment from February to June 2010 were screened for the prevalence and dynamic changes of qnrS gene． Susceptibility testing，conjugant experiments，and pulsed field gel electrophoresis of qnrS-positive isolates were also performed.［Results］A total of 379 isolates were randomly obtained from feces samples of chickens，ducks and geese in a poultry farm and its environment. The qnrS positive strains were detected in all sources of isolates and two alleles of qnrS were prevalent on this farm．The positive rate of qnrS gene in environmental strains was 29.2%，which was significantly higher than that in the avian strains (13.4%). Chicken can quickly acquire qnrS gene after they live on this farm．Transconjugants of the qnrS gene can elevate ciprofloxacin Minimun inhibitory concentrations (MICs) by 16－32 fold compared with the recipient. Various determinants for resistance to other antimicrobial agents were also transferred with the qnrS plasmid. The XbaⅠ PFGE analysis of the qnrS positive strains showed that the dissemination of qnrS was not mainly due to the clonal dissemination of positive strains. However，qnrS-positive strains with indistinguishable PFGE patterns were found in ducks and environment.［Conclusion］Both horizontal gene transfer and clonal spread could be responsible for the dissemination of the qnrS gene in the poultry farm and its environment，but it is mainly disseminated by horizontal transmission.