AbstractsMedical & Health Science

Yersinia pseudotuberculosis infections derive from ingestion of contaminated food or water. Typical symptoms of yersiniosis are fever and abdominal pain resulting from mesenteric lymphadenitis, and immunological sequelae are possible. The pathogen has recently caused several epidemics in Finland through fresh produce. However, the slow growth rate and poor competition of Y. pseudotuberculosis make its detection and isolation demanding. Polymerase chain reaction with primers targeted to virulence genes inv, virF, and yadA is thus often used in detection, although the sequence variability of the virulence genes is unknown. To study genetic variability of the virulence genes, inv, virF, and yadA of 18 Y. pseudotuberculosis strains, and two Yersinia similis strains originating from 12 different countries were sequenced. The greatest sequence variability was detected in yadA, while the variability of inv and virF was limited. The observed variability in yadA may hinder detection using PCR and also impact functional properties of YadA. Furthermore, the commonly used primers targeted to inv can, in addition to Y. pseudotuberculosis, detect Y. similis. Y. pseudotuberculosis tolerates well low temperature and other stressful conditions in the environment and in the food chain. However, information on the stress tolerance mechanisms used by this pathogen is limited. Here, the roles of two-component systems (TCSs), alternative sigma factor σE, and RNA helicase CsdA of Y. pseudotuberculosis IP32953 under stress conditions were studied. The relative expression levels of 54 genes encoding putative TCSs in Y. pseudotuberculosis IP32953 were determined at 3°C and at the optimum growth temperature of 28°C. The relative expression levels of most of the genes were higher at 3°C than at 28°C, and TCS CheA/CheY encoding genes cheA and cheY had the highest relative expression levels at 3°C. Mutational analysis demonstrated the demand for cheA for optimal growth at 3°C. In addition, both cheA and cheY were required for motility. Increased expression of several TCS encoding genes demonstrate that probably in Y. pseudotuberculosis many TCSs play a role in adaptation to low temperatures. In addition, motility seems to be associated with cold tolerance. The role of alternative sigma factor σE under stress conditions was studied by determining relative expression levels of rpoE encoding σE and using mutational analysis. Expression of rpoE was induced under low and high temperatures, acid and alkaline conditions, and osmotic and ethanol stress. Mutation of rpoE impaired or abolished growth at pH 5.0, at 3°C, at 37°C, at 42°C, and at 3% ethanol, demonstrating that functional σE is essential under several stress conditions in Y. pseudotuberculosis IP32953. In addition, the rpoE mutant had a higher minimum and a lower maximum growth temperature than the wild-type strain. Thus, in this pathogen, σE has a significant role in stress tolerance, and it contributes to survival during food processing and storage. The function of a cold-induced RNA…