Browsing by Subject "Yersinia pseudotuberculosis"

In early spring of 2014, a Yersinia pseudotuberculosis strain O:1 caused an outbreak via commercially distributed raw milk in Southern Finland. This was so far the most widespread raw milk outbreak detected in Finland. There are no earlier cases of Y. pseudotuberculosis infecting consumers via raw milk in Finland. Yersinia outbreaks caused by raw milk are also uncommon in other countries, and they are usually caused by Yersinia enterocolitica. Occurrence of pathogenic bacteria in milk is typically caused by fecal contamination during milking process. The contamination routes of Y. pseudotuberculosis in dairy farms have not been studied earlier. The goal of this study was to determine genotypes of the strains collected from the farm during the raw milk outbreak and in a follow-up study. Genotyping was conducted by using pulsed-field gel electrophoresis (PFGE) with two different restriction enzymes (SpeI and NotI). Based on genotyping results, some of the strains were selected to a 21-day cold growth assay in 3 °C. The growth parameters obtained during cold growth assay showed significant differences between strains from fecal or milk-related samples. PFGE genotyping revealed four different genotypes among the examined Y. pseudotuberculosis strains. Two of these strains were extracted only from fecal samples and the other two only from samples from packed milk, bulk tank milk or milk filter. The most prevalent genotype in milk-related samples (S1/N1) was identical to the epidemic strain genotyped by The Institute of Health and Welfare during the outbreak in 2014.The strains genotyped in this study were not uniform with strains collected and genotyped during previous Y. pseudotuberculosis outbreaks or follow-up studies. Strains extracted from cows’ feces were similar with a strain extracted from feces of an alpine ibex, whereas strains collected from milk-related samples formed their own, distinguishable genetic group. The observed differences in fecal and milk-related strains’ genotype and growth suggest their different origin. Yersiniae are known to be a part of normal flora in various small rodents and birds. In the dairy farm, which was the source of the raw milk outbreak, there had been several pest sightings of rats and wild birds during the initial epidemic investigation. The pest animals had had free access to cattle feed and other areas in the farm environment. Also the cows have most probably had some kind of role in the transmission of pathogens, as a Y. pseudotuberculosis strain, identical to patient samples, was prevalent in bulk tank milk and/or milk filters from April to November. The selection of the epidemic strain might have occurred in the milking system or bulk tank due to its cold tolerance properties. Due to partly insufficient sample material, the exact contamination routes of Y. pseudotuberculosis cannot be completely verified. The preservation of cold chain has been regarded as one of the cornerstones of food safety. However, it does not prevent the growth of psychrotropic bacteria, but rather offers them ideal growth environment. Although the Finnish regulation regarding production and microbial screening of raw milk has been defined in the beginning of 2018, it still focuses mainly on mesophilic pathogens. As the popularity of raw milk continues to grow, the microbial screening of this high-risk food should be extended to cover also the species that can thrive in cold storage conditions, such as yersiniae.