Development Of A Serotype Specific Pcr Assay For Shigella Flexneri And Analysis Of A Serotype-converting Bacteriophage Sfx

Shigella flexneri is one of the main enteric pathogens in developing countries including China. Based on the differences of O antigen structure, S.flexneri can be divided into 15 serotypes, namely Fx, Fy, F1a, F1b, F1c, F2a, F2b, F3a, F3b, F4a, F4b, F5a, F5b, Fxv, and F6. The 14 serotypes of S.flexneri share a same repeating tetrasacharide unit, of which the glycosylation/acylation on different site could lead to type-specific antigen, such asⅠ,Ⅱ,Ⅲ,Ⅳ,Ⅴand group-specific antigen such as 3,4; 7,8. The genes encoding glycosylation/acylation, such as glycosyltransferase A (gtrA), glycosyltransferase B (gtrB), glycosyltransferase (Ⅰ,Ⅱ,Ⅳ,Ⅴ,Ⅹ) and/or O- acetylase (oac) are on serotype associated phages. In this study, we developed serotype specific PCR assay targeting for gtr genes, which could detect 14 of 15 serotypes of S.flexneri. Mis-diagnosis or mis-identification due to cross reactions of the traditional serological diagnostic agglutination method could be resolved by this PCR methods.We also studied the serotype converting phages of S.flexneri which encodes the glycosyltransferase involved in O-antigen modification. We successfully induced serotype-converting phage SfX from serotype Fx strain 2002017, and analyzed the genome sequence, which were present in 61.9% of S.flexneri isolates collect during 2001 to 2008 in China in our study. When compared with genomes of 402 double strand DNA phages, is was found that the serotype-converting phage SfX of S.flexneri was phylogenetically related to another O antigen modification phage P22, which is widespread in Salmonella. Nine genes were found to be shared only by SfX and P22. Since both of the serotype associated phages related with dominant serotypes, we propose that those genes may associated the epidemic strength of certain serotypes in Salmonella and S.flexneri.