Effects of osmotic and high pressure stress on expression of virulence factors among Enterococcus spp. isolated from food of animal origin.

The aim of study was to determine the occurrence of virulence factors and virulence-related genes among enterococci isolated from food of animal origin and effects of osmotic and high pressure stress on expression of virulence-related genes. The number of 78 isolates were analyzed. None of them showed a strong ability to form biofilm, 38.5% (n = 30) had the slime production ability, 41% (n = 32) had gelatinase activity, γ -type hemolysis was observed in 55% of isolates, and α-type hemolysis in 45%. All of the isolates carried 1-13 virulence-related genes. The most common genes were gelE (85.9%), sprE (78.2%) and asa1 (75.6%). There were also observed changes in the expression of the gelE, esp, asa1 and cylL genes in response to various NaCl concentration and high pressure processing. Results obtained in this study indicate that enterococci isolated from food may act as reservoirs of virulence genes. The presence of virulence factors among enterococci, especially the ability to biofilm formation is important for food safety and the protection of public health. The results presented in our work demonstrate that stress that can occur during food preservation and food processing can induce the changes in the virulence-related genes expression.