Diversification of H-Antigens and Development of H-Genotyping PCR.

is a recently recognized human enteropathogen that is closely related to . As sometimes causes outbreaks of gastroenteritis, rapid strain typing systems, such as the O- and H-serotyping systems widely used for , will be useful for outbreak investigation and surveillance. Although an O-genotyping system has recently been developed, the diversity of H-antigens (flagellins) encoded by genes remains to be systematically investigated, and no H-serotyping or genotyping system is currently available. Here, we analyzed the genes of 243 genome-sequenced strains and identified 73 sequence types, which were grouped into four clearly distinguishable types designated H-genotypes 1-4 (EAHg1-EAHg4). Although there was a clear sign of intraspecies transfer of genes in , none of the four H-genotypes (EAHgs) were closely related to any of the 53 known H-antigens, indicating the absence or rare occurrence of interspecies transfer of genes between the two species. Although the analysis of more strains will be required to confirm the low level of variation in their genes, this finding suggests that may exist in limited natural hosts or environments and/or that the flagella of may function in a limited stage(s) in their life cycle. Based on the sequences of the four EAHgs, we developed a multiplex PCR-based H-genotyping system for (EAH-genotyping PCR), which will be useful for epidemiological studies of infections.