Prevalence of Plasmid-Mediated Determinants With Decreased Susceptibility to Azithromycin Among Isolates in Anhui, China.

OBJECTIVE

The aims of this study were to describe azithromycin (AZM) susceptibility patterns among isolates in Anhui, China and identify predictors of resistance with mobile element-mediated genes.

METHODS

A total of 517 non-duplicate isolates (449 and 68 ) were collected in the Anhui Province of China from September 2011-September 2015, and screened for the plasmid-mediated genes of decreased susceptibility to AZM (DSA), using polymerase chain reaction amplification and sequencing. Conjugation experiments and pulsed-field gel electrophoresis were conducted for all positive DSA isolates.

RESULTS

The DSA rate for 449 isolates was 33.6%, compared with 39.7% for 68 isolates. Among 161 DSA isolates, 93 (57.8%) carried the gene. Among 27 DSA isolates, 11 (40.7%) carried the gene. However, other plasmid-mediated DSA genes were not found in these isolates. A total of 89 transconjugants (95.7%) were obtained from 93 -positive isolates through conjugation, and 10 transconjugants (90.9%) were obtained from 11 -positive isolates. Furthermore, the minimum inhibitory concentrations (MICs) of AZM among 89 transconjugants ranged from 4 to 128 μg/mL, with an MIC of 8 μg/mL and MIC of 32 μg/mL. The MICs of AZM among 10 transconjugants ranged from 4 to 256 μg/mL, with an MIC of 8 μg/mL and MIC of 64 μg/mL. Thirteen clusters were found for -positive , and five clusters were found for -positive . Furthermore, 10 homologous isolates among 13 -positive isolates with high-level DSA were from Sixian county and were multidrug-resistant strains. Of the 10 homologous isolates, eight were from children (≤5 years old), and two from the elderly (>60 years old).

CONCLUSION

Our study demonstrates that the DSA for isolates was severe, and the plasmid-mediated gene was the most common macrolide resistance gene detected in isolates collected in Anhui, China. The -positive isolates with high-level DSA facilitated clonal spread in children and the elderly. This finding is noteworthy and warrants further study.