Genetics and evolution of Yersinia pseudotuberculosis O-specific polysaccharides: a novel pattern of O-antigen diversity
Yersinia pestis is a very recently evolved clone of Yersinia pseudotuberculosis serotype O:1b. This close relationship causes potential difficulties in DNA-based diagnostic methods. Analysis of the O-antigen gene clusters in these two organisms identified two regions that were used to specifically identify Y. pestis-Y. pseudotuberculosis as a group or Y. pestis alone. Both PCR assays were found to be 100% specific when tested on a large collection of Yersinia species and other Enterobacteriaceae. Furthermore, advantage was taken of the different setups of the O-antigen gene clusters of the 21 known Y. pseudotuberculosis serotypes to develop a multiplex PCR assay to replace the conventional serotyping method of Y. pseudotuberculosis by O-genotyping. The multiplex PCR assay contained nine sets of specific PCRs in a single tube and when used on Y. pseudotuberculosis reference strains allowed the distinction of 14 individual serotypes and two duplex serotypes (O:4a-O:8 and O:12-O:13). Serotype O:7, O:9, and O:10 strains required additional PCRs for O-genotyping. Once applied to Y. pseudotuberculosis strains of various origins, a very good correlation between classical serotypes and O-genotypes was observed, although some discrepancies were found. O-genotyping also proved useful to correct misidentification of some strains and to type Y. pseudotuberculosis isolates that had lost the expression of the O-antigen. The PCR-based O-genotyping can easily be applied in conventional laboratories, without the need for tedious preparation of a large set of specific antisera.