Abstract
Escherichia albertii is a recently recognized human enteropathogen that is closely related to Escherichia coli. As E. albertii sometimes causes outbreaks of gastroenteritis, rapid strain typing systems, such as the O- and H-serotyping systems widely used for E. coli, will be useful for outbreak investigation and surveillance. Although an O-genotyping system has recently been developed, the diversity of E. albertii H-antigens (flagellins) encoded by fliC genes remains to be systematically investigated, and no H-serotyping or genotyping system is currently available. Here, we analyzed the fliC genes of 243 genome-sequenced E. albertii strains and identified 73 sequence types, which were grouped into four clearly distinguishable types designated E. albertii H-genotypes 1–4 (EAHg1–EAHg4). Although there was a clear sign of intraspecies transfer of fliC genes in E. albertii, none of the four E. albertii H-genotypes (EAHgs) were closely related to any of the 53 known E. coli H-antigens, indicating the absence or rare occurrence of interspecies transfer of fliC genes between the two species. Although the analysis of more E. albertii strains will be required to confirm the low level of variation in their fliC genes, this finding suggests that E. albertii may exist in limited natural hosts or environments and/or that the flagella of E. albertii may function in a limited stage(s) in their life cycle. Based on the fliC sequences of the four EAHgs, we developed a multiplex PCR-based H-genotyping system for E. albertii (EAH-genotyping PCR), which will be useful for epidemiological studies of E. albertii infections.
Highlights
Escherichia albertii is a recently recognized human enteropathogen and an avian pathogen (Albert et al, 1992; Huys et al, 2003; Oaks et al, 2010; Ooka et al, 2012)
Through the clustering analysis of the 231 of intact fliC gene sequences, we identified a total of 73 sequence types with one or more SNPs (Supplementary Table 1), among which 42 were singletons, and 31 were composed of sequences from multiple genomes
The phylogenetic analysis of the 73 fliC sequences identified in E. albertii with 53 fliC sequences of known E. coli H-serotypes as references revealed that the fliC genes of E. albertii formed a monophyletic branch, separate from those of E. coli (Figure 1A)
Summary
Escherichia albertii is a recently recognized human enteropathogen and an avian pathogen (Albert et al, 1992; Huys et al, 2003; Oaks et al, 2010; Ooka et al, 2012). In E. albertii, only a genotyping system based on the variation in O-antigen biosynthesis genes has been developed far (Ooka et al, 2019), rapid, and low-cost effective H-genotyping system are useful to increase the discrimination power and to assist epidemiological studies in combination with O-genotyping system. In E. coli, flagellin is encoded by the fliC gene in the fliY-T region on the chromosome or its homologs, such as fliK, fliA, and fimA (Ratiner, 1998; Wang et al, 2003; Tominaga, 2004; Feng et al, 2008; Ratiner et al, 2010), and a total of 53 H-antigens have been identified far. In E. albertii, the gene cluster associated with flagellar biosynthesis and its regulation, including the fliY-T region, is conserved in most strains (Ooka et al, 2015). We attempted to develop a multiplex PCR-based H-genotyping system for E. albertii strains based on the sequence diversity of their fliC genes
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