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Objective  The aims of this study were to describe azithromycin (AZM) susceptibility patterns among  Shigella  isolates in Anhui, China and identify predictors of resistance with mobile element-mediated genes.    Methods  A total of 517 non-duplicate  Shigella  isolates (449  S. flexneri  and 68  S. sonnei ) 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  mphA- positive DSA isolates.    Results  The DSA rate for 449  S. flexneri  isolates was 33.6%, compared with 39.7% for 68  S. sonnei  isolates. Among 161 DSA  S. flexneri  isolates, 93 (57.8%) carried the  mphA  gene. Among 27 DSA  S. sonnei  isolates, 11 (40.7%) carried the  mphA  gene. However, other plasmid-mediated DSA genes were not found in these isolates. A total of 89 transconjugants (95.7%) were obtained from 93  mphA -positive  S. flexneri  isolates through conjugation, and 10 transconjugants (90.9%) were obtained from 11  mphA -positive  S. sonnei  isolates. Furthermore, the minimum inhibitory concentrations (MICs) of AZM among 89  S. flexneri  transconjugants ranged from 4 to 128 μg/mL, with an MIC 50  of 8 μg/mL and MIC 90  of 32 μg/mL. The MICs of AZM among 10  S. sonnei  transconjugants ranged from 4 to 256 μg/mL, with an MIC 50  of 8 μg/mL and MIC 90  of 64 μg/mL. Thirteen clusters were found for  mphA -positive  S. flexneri , and five clusters were found for  mphA -positive  S. sonnei . Furthermore, 10 homologous isolates among 13  mphA -positive  S. flexneri  isolates with high-level DSA were from Sixian county and were multidrug-resistant strains. Of the 10 homologous  S. flexneri  isolates, eight were from children (≤5 years old), and two from the elderly (>60 years old).    Conclusion  Our study demonstrates that the DSA for  Shigella  isolates was severe, and the plasmid-mediated  mphA  gene was the most common macrolide resistance gene detected in  Shigella  isolates collected in Anhui, China. The  mphA -positive  S. flexneri  isolates with high-level DSA facilitated clonal spread in children and the elderly. This finding is noteworthy and warrants further study.

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