Diagnostics and epidemiology of Yersinia pseudotuberculosis

Taina Niskanen

Tutkimustuotos: OpinnäyteVäitöskirjaArtikkelikokoelma


Yersinia pseudotuberculosis is an animal pathogen widespread in nature. The bacterium has caused infections in humans occasionally. Most of the reported Y. pseudotuberculosis -infections are sporadic, and the sources and vehicles of Y. pseudotuberculosis remain obscure. Y. pseudotuberculosis has emerged as an outbreak -associated pathogen in Finland since 1997. Indirect evidence has indicated that Y. pseudotuberculosis is a potential food borne pathogen, but no specific food has been previously confirmed as a source of the human infections.

The aim of this thesis was to determine the prevalence of Y. pseudotuberculosis in different animal species and to evaluate them as a possible source of Y. pseudotuberculosis. Clinically healthy pigs were found to carry Y. pseudotuberculosis. The prevalence of Y. pseudotuberculosis was 4 % and 14 % in fattening pigs at slaughterhouse and at farm level, respectively. All Y. pseudotuberculosis isolates from pigs were pathogenic. Migratory birds representing 57 different bird species were studied for pathogenic Y. pseudotuberculosis during spring and autumn migration. Pathogenic Y. pseudotuberculosis was recovered from two species of birds during spring migration.

Y. pseudotuberculosis was first time confirmed to be the cause of a food borne outbreak through domestically produced iceberg lettuce in epidemiological study. Contamination of iceberg lettuce was investigated on farm level in a two-year survey. Several factors predisposing to Y. pseudotuberculosis contamination of lettuce were found on the farms, including a large population of deers and free access of wild animals to unfenced lettuce fields and to irrigation water sources.

Pulsed-field gel electrophoresis (PFGE) analysis was optimized for efficient molecular typing method for Y. pseudotuberculosis isolates. PFGE was used to compare Y. pseudotuberculosis isolates from different origin. Y. pseudotuberculosis isolates of different sources showed high genetic diversity, while Y. pseudotuberculosis isolates found in same animal species representing the same serotype showed limited genetic diversity. Identification of environmental Y. pseudotuberculosis isolates was found to be incorrect based solely on biochemical tests. Commercial test kits misidentified some environmental Yersinia spp. isolates as Y. pseudotuberculosis. However, no specific virulence genes of Y. pseudotuberculosis were found in these isolates by polymerase chain reaction (PCR) targeting these gene areas.
Painoksen ISBN978-952-92-6589-3
Sähköinen ISBN978-952-10-5921-6
TilaJulkaistu - 2010
OKM-julkaisutyyppiG5 Tohtorinväitöskirja (artikkeli)


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