Characterization of a Yersinia enterocolitica biotype 1A strain harbouring an ail gene

The chromosomal ail gene (attachment and invasion locus) is commonly used as target gene for the detection of pathogenic Y. enterocolitica strains in food testing. The ail PCR does not detect strains of biotype 1A (BT1A), which are regarded as non-pathogenic because BT1A strains lack the virulence plasmid and chromosomally encoded virulence genes. In some recent reports, however, BT1A strains were discovered that harboured the ail gene. We isolated an ail-positive strain and characterized this strain with phenotypic and genotypic methods to study its possible relation to pathogenic Y. enterocolitica strains.

The ail region of the BT1A strain was sequenced and compared with the corresponding region of nonpathogenic BT1A strains and pathogenic strains. Pulsed field gel electrophoresis (PFGE) analysis was applied revealing no similarity of the PFGE pattern of this strain to the patterns of pathogenic strains. Virulence-gene-based PCR analyses showed the strain to be positive for ystB, but negative for virulence genes ystA, virF and yadA. Whole-cell MALDI-TOF MS combined with a shrinkage discriminant analysis approach was applied and clearly classified the ail-positive biotype 1A strain within the cluster of BT1A strains.

PCR detection of ail sequences in food matrices should be followed by the isolation of the responsible strain and its characterization using phenotypic or genotypic methods.

The ail gene may be present in Y. enterocolitica BT1A strains, which are commonly considered as nonpathogenic. Efficient methods such as PCR typing of other virulence genes or rapid MALDI-TOF MS-based bacterial profiling allow a more comprehensive assessment of the pathogenicity potential of Yersinia strains.