Two novel mutations in parE among Shigella flexneri isolated from Jiangsu Province of China, 2016.

Background: The study was conducted to assess the resistance capacity of quinolone against Shigella flexneri , and to investigate the involved quinolone resistance mechanism. The data were collected from Jiangsu Province, China in 2016.
Methods: The number of 81 S. flexneri was obtained from 12 cities in Jiangsu Province of China during 2016. Slide agglutination was taken for serotyping, and susceptibility test was identified by the disc diffusion method. PCR aimed to amplify the quinolone resistance-determining region ( QRDR ) genes and screen for plasmid-mediated quinolone resistance (PMQR) determinants. Chromosomal mutation was confirmed by sequencing and Blast comparison.
Results: 2a was the commonest serotype, accounting for 40.7% (33/81) of the 81 S. flexneri . 70.4% (57/81) isolates expressed resistance against nalidixic acid, and the resistance against ciprofloxacin even reached up to a high proportion of 58.0% (47/81). A total of 8 point mutations were identified, including 2 novel mutations discovered in parE (Ser458Leu and Gly408Asp). The common mutation Ser83Leu in gyrA was still the most prevalent here with a percentage of 70.4% (57/81), followed by the approximate mutation of 69.1% (56/81) in parC (Ser80Ile) and His211Tyr in gyrA . Meanwhile, 35.8% (29/81) isolates were confirmed with mutation of Gln517Arg in gyrB . In addition, qnrS positive isolates occupied a proportion of 7.4% (6/81), but only 1 strain was observed with aac ( 6' )- Ib-cr . All PMQR positive isolates were resistant to nalidixic acid. However, 5 of them didn't stay susceptible to ciprofloxacin any more.
Conclusions: This is the first time that a study researches the occurrence of mutations in parE among S. flexneri , Ser458Leu and Gly408Asp included. The study indicates that the high resistance to fluoroquinolone remains a serious problem in Jiangsu, China. Thus, the prevention and control of current infection urge for a comprehensive and systematic surveillance based on persistent surveys.
Competing Interests: Conflicts of Interest: The authors have no conflicts of interest to declare.