Overview of the development of quinolone resistance in species in China, 2005-2016.

PURPOSE

Several factors contribute to the complexity of quinolone resistance in , including >2000 different serotypes, a variety of hosts for , and wide use of quinolones in human beings and animals. We thus aimed to obtain an overview of the development of quinolone resistance and relevant molecular mechanisms of such a resistance in species.

MATERIALS AND METHODS

A total of 1,776 isolates were collected in Ningbo, China, between 2005 and 2016. Antimicrobial susceptibility to quinolone and relevant genetic mechanisms in these isolates were retrospectively analyzed.

RESULTS

The ratio for ciprofloxacin (CIP) resistant:reduced CIP susceptible:CIP susceptible was 26:522:1,228. CIP resistance was found in nine of 51 serotypes: Derby, London, Kentucky, Indiana, Corvallis, Rissen, Hadar, Typhimurium, and Agona. Of 26 CIP-resistant isolates, all were concurrently resistant to ampicillin and 21 were also concurrently resistant to cefotaxime and produced extended-spectrum β-lactamase (ESBL). The minimal inhibitory concentration values were at three levels: 2-4 μg/mL (serotypes except for Kentucky and Indiana), 16 μg/mL (one Kentucky isolate), and >32 μg/mL (Indiana isolates). As with the three most common serotypes, Typhi showed quickly increased prevalence of reduced CIP susceptibility in recent years, Enteritidis remained at a high prevalence of reduced CIP susceptibility throughout the study period, and several isolates of Typhimurium were resistant to CIP. Transferable plasmid-mediated quinolone resistance gene was only found in all CIP-resistant isolates. In contrast, mutations were often found in reduced CIP-susceptible isolates and were not necessarily found in all CIP-resistant isolates.

CONCLUSION

We conclude that in , there exists a high prevalence of reduced CIP susceptibility and a low prevalence of CIP resistance, which focuses on several serotypes. Our study also demonstrates that, rather than mutations, is the most common indicator for CIP resistance.