Effects of temperature on the viability, growth and gene profile of Yersinia pseudotuberculosis and Yersinia enterocolitica inoculated in milk

This study was aimed at deciphering the viability and growth of Yersinia pseudotuberculosis and Yersinia enterocolitica in milk at different temperatures, and at identifying the temperature-dependent changes in gene expression in Yersinia. Fresh Yersinia culture was suspended either in pasteurized or in autoclaved milk and subjected to different temperature ranges. Colony forming units (CFU) were determined from inoculated milk after one and two weeks of storage using direct plating technique. In both one and two weeks of storage, growth of Y. pseudotuberculosis and Y. enterocolitica increased significantly at 4 °C and 24 °C (P < 0.05). Furthermore, gene expression profile and DNA microarray analyses were conducted. After one-week storage, the growths of Y. pseudotuberculosis and Y. enterocolitica were optimal at 4 °C and 24 °C. Remarkably, at 37 °C there was no detectable level of CFU from both Yersinia spp inoculated in pasteurized milk, whereas they grew well at 37 °C in autoclaved milk. The NotI-profile of Y. pseudotuberculosis grown at 24 °C generated different banding patterns from other treatment groups when compared to FseI and XbaI-PFGE pulso-type. Microarray interrogation of 4038 genes of Y. pseudotuberculosis revealed that 38 genes were upregulated by ≥8 fold and 237 genes exhibited ≥2 fold downregulation (at 95% significant level) after temperature shift from 4 °C to 24 °C. The findings of this study highlight the survival potential of Y. pseudotuberculosis and Y. enterocolitica in milk under different temperatures and the associated gene expression patterns, which may be important in the processing and safety of milk and dairy products.