Thilini Keerthirathne
Flinders University, Australia
Title: Investigation into the effect of pH and temperature on the survival of Salmonella enterica serovar Typhimurium
Biography
Biography: Thilini Keerthirathne
Abstract
In Australia the incidence of salmonellosis is increasing with Salmonella Typhimurium linked to eggs and raw egg products identified as the main cause. Australian guidelines recommend raw egg mayonnaise is prepared and stored under 50C and adjusted to a pH of 4.6. This study investigated the combined effect of pH and temperature on the survival of S. Typhimurium. Nutrient broths with a pH of either 4.2, 4.4, 4.6, or 7.0 (adjusted with acetic acid) were inoculated with 1 mL log phase S. Typhimurium (105 CFU/ mL) and were incubated at either 370C, 230C or 40C. All experiments were conducted in triplicate. The survival of Salmonella over time was determined using the drop plate method on X.L.D. agar, also conducted in triplicate. Survival was significantly (P<0.05) improved when cultures were incubated at 40C compared to 230C and 370C for all pH conditions tested. After 24 hours of incubation at 370C, there were no viable Salmonella at pH 4.2 and 4.4 but there was survival at 230C and 40C for the same pH conditions. The maximum survival was at 4 0C. In conclusion, lower temperatures protected S. Typhimurium from the bactericidal effect of low pH.