Investigation into the effect of pH and temperature on the survival of Salmonella enterica serovar typhimurium
Thilini Piushani Keerthirathne, Kirstin Ross, Howard Fallowfield and Harriet Whiley
Flinders University, Australia
Scientific Tracks Abstracts: J Nutr Food Sci
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 5 oC 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 37, 23 or 4 oC. 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 4 oC compared to 23 oC and 37 oC for all pH conditions tested. After 24 hours of incubation at 37 oC, there were no viable Salmonella at pH 4.2 and 4.4 but there was survival at 23 oC and 4 oC for the same pH conditions. The maximum survival was at 4 oC. In conclusion, lower temperatures protected S. typhimurium from the bactericidal effect of low pH.
Thilini Piushani Keerthirathne is currently pursuing PhD from the College of Science and Engineering, Flinders University, Australia. She has obtained her BSc in Genetics from the University of Bangalore, India in 2010 and completed her Postgraduate studies in Biochemistry and Molecular Biology at the University of Colombo, Sri Lanka. She was working as a Research Assistant at the National Institute of Fundamental Studies, Kandy, Sri Lanka before coming to Australia. She has published four peer-reviewed journal articles to her credit.
Email:keer0004@flinders.edu.au
