Two copies of the ail gene found in Yersinia enterocolitica and Yersinia kristensenii.

Yersinia enterocolitica is the most common Yersinia species causing foodborne infections in humans. Pathogenic strains carry the chromosomal ail gene, which is essential for bacterial attachment to and invasion into host cells and for serum resistance. This gene is commonly amplified in several PCR assays detecting pathogenic Y. enterocolitica in food samples and discriminating pathogenic isolates from non-pathogenic ones. We have isolated several non-pathogenic ail-positive Yersinia strains from various sources in Finland. For this study, we selected 16 ail-positive Yersinia strains, which were phenotypically and genotypically characterised. Eleven strains were confirmed to belong to Y. enterocolitica and five strains to Yersinia kristensenii using whole-genome alignment, Parsnp and the SNP phylogenetic tree. All Y. enterocolitica strains belonged to non-pathogenic biotype 1A. We found two copies of the ail gene (ail1 and ail2) in all five Y. kristensenii strains and in one Y. enterocolitica biotype 1A strain. All 16 Yersinia strains carried the ail1 gene consisting of three different sequence patterns (A6-A8), which were highly similar with the ail gene found in high-pathogenic Y. enterocolitica biotype 1B strains (A2). The Ail protein encoded by the ail1 gene was highly conserved compared to the Ail protein encoded by the ail2 gene. Multiple sequence alignment of the ail gene and Ail protein were conducted with MAFF. In total, 10 ail sequence variations have been identified, of which 8 conserved ones belonged to the ail1 gene. According to our results, the detection of ail alone is not sufficient to predict the pathogenicity of Yersinia isolates.