Analysis Of Phenotypic And Genetic Diversity Of Atypical Shigella Flexneri Strains In China

In the present study, we collected1719Shigella flexneri strains from different ares of mainland China during2003-2013. We can see that, the most prevalent Shigella flexneri serotype is2a, followed by2v、lb、Y variant、3a、4s、4y、lc、6、4a、5b and3b. Notablely, Shigella flexneri can be popular for a long time by changing its serotype, so epidemic monitoring and control of infectious diseases of atypical Shigella flexneri are a big challenge in our country. Due to the lack of relative research, the present study was to evaluate the phenotypic and genetic diversity of atypical Shigella flexneri strains in China so as to understand the biological characteristics, evolutionary relationships and epidemiological characteristics, which would provide a solid foundation for the prevention and control of bacillary dysentery strategy.The biochemical test showed that all the149atypical strains (F2v、Flc、F4y、F4s and F1b) can ferment glucose and some of them can ferment mannitol, sucrose, melibiose and so on. It was worth noting that the indole test for certain serotype4y and4s strains were positive. Antimicrobial susceptibility test showed that92.6%of the strains were multidrug-resistant strains. Besides, by the comparison of antibiotic susceptibility profiles of different serotypes in various loations and time, we can see that, the resistance rate of F2v after2009was much higher than that before2009, while F1b from Yunnan were far more resistant than that from Xinjiang. The result showed that the resistance rate of the same serotype would changed significantly over time and space, thus, more highlights should be paid on the significance of real-time monitoring of antibiotics, especially cephalosporins and quinolones. Among54cephalosporin-resistant isolates,blaatem1, blaoxAi, bla CTX-M-14, bla CTX-M-3, bla CTX-M-79, intll and the following gene casttles blaOXA-30+aadA1; aacA4+cmlAl, intI2and the following gene casttles dfrA1+sat1+aadA1were positive. Among28fluoroquinolone-resistant isolates, all carried mutations in ParC(Ser80Ile) and GyrA (His211Tyr and Ser83Leu). Strains contained Asp87Asn mutantion, were not only resistant to norfloxacin, but also resistant to levofloxacin, so we speculate that the mutation Asp87Asn in GyrA probably mediated high levels of quinolones resistance. In addition,24strains contained aac (6’)-Ib-cr genes, and2strains contained the qnrSl genes. The genotype analysis against all the strains were performed by using these three methods MLS、 PFGE and MLVA in combination, as a result, we found that, all the strains of F1b belonged to ST104:all the strains of F2v belonged to ST100; all the strains of Flc belonged to ST104and ST100; all the strains of F4s belonged to ST99and ST100; all the strains of F4y belonged to ST99、ST104、ST107and ST108.Among the149strains, the most popular sequence type is ST100, followed by ST104, ST99, ST108, ST107and ST105. ST100is the dominant type, which is closely related to ST86, followed by ST104. There was only one locus difference between ST107and ST99or ST108, implying a near relationship. The new subtype F2v, is closely related to F2a and F2b, which preliminarily showed that F2v is evolved from F2a and F2b. The genetic polymorphisms of Flc、F4s and F4y varied greatly, which may be derived from multiple clones, In general, the resolution of the MLVA method is basically identical to PFGE, and is much higher than MLST method. The combination of the3methods can be effectively used in traceability of bacterial dysentery outbreak, and provide technical support for the prevention and early warning of bacterial dysentery.