AUTHOR=Liu Yanyan , Li Hongru , Lv Na , Zhang Yalong , Xu Xihai , Ye Ying , Gao Yufeng , Li Jiabin 

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

JOURNAL=Frontiers in Microbiology

VOLUME=11

YEAR=2020

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2020.01181

DOI=10.3389/fmicb.2020.01181

ISSN=1664-302X

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