Occurence of Yersinia pseudotuberculosis in Iceberg Lettuce and Environment

Conclusions

The virF-positive Y. pseudotuberculosis serotype O:2 strain was isolated from food in Finland for the first time. Y. pseudotuberculosis is considered to be a food-borne pathogen, but it has rarely been isolated from foods. Iceberg lettuce are grown on open fields and irrigated with water from lakes, rivers, and ponds on Ahvenanmaa Island. Y. pseudotuberculosis is frequently isolated from many domestic and wild animals (Fukushima and Gomyoda, 1991; Sanford et al., 1995; Niskanen et al., 2001). There is a large population of deers and hares on Ahvenanmaa Island. These animals can be asymptomatic carriers and reservoirs of Y. pseudotuberculosis (Griffin et al., 1992). Wildlife had access to lettuce fields and the ponds used to collect irrigation water. It is possible, that wild animals contaminate water, soil, and lettuce on the fields with their feces containing Y. pseudotuberculosis (Inoue et al., 1991; Fukushima et al., 1995). Contamination of iceberg lettuce was likely resulted from use of irrigation water contaminated with animal feces. Also nontypable Y. pseudotuberculosis strains without the virulence plasmid were recovered from environmental samples and a lettuce sample. Non-pathogenic Y. pseudotuberculosis serotypes O:7-O:14 have been previously recovered in environment (Nagano et al., 1996). Lettuce produced on open fields irrigated with water from natural water systems may contain pathogenic microbes, and should be concern as a possible source of Y. pseudotuberculosis infections.