Virulence Gene ail Present in Yersinia enterocolitica Biotype 1A Strains

Introduction: The pathogenicity of Yersinia enterocolitica strains varies widely: biotypes 1B and 2-5 are pathogenic, whereas biotype 1A strains are considered as nonpathogenic due to the lack of important chromosomal virulence genes, like ail gene coding for adhesion to epithelial cells, and the virulence plasmid. The virulence gene ail is also commonly used target for PCR detection of pathogenic Y. enterocolitica.

Purpose: The carriage of virulence gene ail in Y. enterocolitica biotype 1A strains isolated from various sources was studied to evaluate the prevalence of the gene in nonpathogenic Y. enterocolitica strains and the usefulness of this gene in PCR detection of the pathogenic strains.  

Methods: Total of 420 Y. enterocolitica 1A strains isolated from samples originating from packaged leafy vegetables (11), raw milk (34), sheep feces (17) and feces of wild rodents (358) were investigated. The presence of gene ail was studied with real-time PCR method based on SYBRGreen. The ail genes from six strains isolated from rodents were also partly sequenced.  

Results: From 420 Y. enterocolitica biotype 1A isolates studied, 94 (22.4 %) were carrying the virulence gene ail. Isolates of sheep origin were most commonly ail-positive (58.8%). Total of 82 (22.9 %) isolates of rodent and two (18.2 %) of salad origin were ail-positive. None of Y. enterocolitica 1A isolates from raw milk samples were carrying the ail gene. All six partially sequenced ail genes were identical to each other and with 98.8 % similarity to previously sequenced Y. enterocolitica 1A ailgenes. 

Significance: The virulence gene ail of Y. enterocolitica is frequently carried by biotype 1A strains regarded as nonpathogenic. The presence of ail gene in nonpathogenic Y. enterocolitica strains questions the usefulness of this gene alone in the PCR detection.