T472C was the only nonsynonymous mutation that accounts for a serotype shift in the Inaba A-1155463 supplier strains in 2005, and we experimentally demonstrated the critical role of a serine at this site for the function of RfbT. The

same single substitution was also reported in the Inaba strains isolated during different years (2005–2008) in Iran [42] and India [41]. Characteristic rfbT mutations occurred in different Inaba serotype dominant epidemics, which may suggest the clonality of the epidemic strains. These mutations can be used as the sequence signatures in the clonal and evolutionary analysis, and even the tracking markers in epidemiological investigations. Serotype conversion and serotype-shifting in cholera epidemics have been thought to be related to the immune response of individuals and the immune status of the overall population, and has also been documented in animal models [20, 22, 26]. Thereby it could be deduced that in the cholera endemic regions rfbT mutation will be an advantage for the spread of Inaba strains following Ogawa serotype epidemic. In general,

the conversion of serotype from Ogawa to Inaba is easy to occur, which is simply a rfbT mutant enrichment procedure [22]. While the reciprocal serotype conversion, from Inaba to Ogawa, is much more difficult considering the requirement AZD5363 research buy of the reversion of the original mutation and the great variety of the rfbT genetic status of Inaba strains. Maybe, the Inaba strains caused by transposase insertion could be relatively liable to reverse to Ogawa phenotype due to the active mobile ability of the insertion element. Some strains were noticed to have accumulated multiple mutations, it remains a puzzle if this represents a transitional state of overcoming the original mutation by introducing the second or third mutation. Conclusion Our study presents the rfbT sequence variations of V. cholerae O1 isolates during the serotype shifts over a 48-year period in China. Different types of mutational events and new mutation sites resulting in abnormal translation

of rfbT are observed, and characteristic rfbT mutations in different Inaba serotype dominant epidemic periods are found. These distinguishable Histamine H2 receptor mutations can be used as the tracing markers in the epidemic clone analysis, and even surveillance for dissemination of specific clones. The rfbT mutation and subsequent serotype shifts of the epidemic strains also could be considered as one type of adaption to population immunity barrier in the cholera endemic regions. Acknowledgements This work was supported by the Project of the National Natural Science Foundation of China (30830008 and 81071410) and the National Basic Research Priorities Program (2009CB522604). Electronic supplementary material CH5424802 research buy Additional file 1: Table S1: Information of O1 V. cholerae strains used in this study. (DOC 218 KB) Additional file 2: Figure S1: The rfbT sequence alignment of the mutation sites between the classical and El Tor biotypes.