Serotype conversion due to gtrI gene dysfunctional mutation in Shigella flexneri serotype Y strains

Objective To characterize the Shigella flexneri serotype Y strains carrying dysfunctional gtrI gene. Methods Multiple-PCR was conducted to screen S. flexneri strains which carry gtrI gene within genomes, but have antigenic epitope I on cell surface. The gtrⅠ gene clusters in these candidates were sequenced. The genome DNA of these strains were analyzed with PFGE and compared with that of other strains. Results A total of 5 strains were found to carry gtrI gene cluster within genomes, but not to react with typing I antisera, presenting the characteristics of serotype Y. Sequencing analysis suggested that all the strains had dysfunctional mutation in the gtrI gene sequence. The PFGE patterns of the 5 strains were identified, which were similar to that of serotype 1a strains. Conclusion The five serotype Y strains which carried dysfunctional gtrI gene were originated from serotype 1a through gtrI gene mutation.