Growth response of Salmonella typhimurium as a function of temperature, pH, organic and inorganic acids, and NaCl concentration

Salmonella is still one of the most important pathogens related with foodborne outbreaks.This study was designed to examine the combined effects of different levels of pH (7.4, 6.4, and 5.4), acids (acetic, citric and hydrochloric acid), temperatures (35 °C and 25 °C), and NaCl concentrations (0.5, 3 and 6%, w/v), on growth of Salmonella typhimurium in brain heart infusion broth. The experiment conducted in triplicate. Growth was monitored by visible turbidity over a 30-day period.To evaluate the effects of explanatory variable on time to detect (TTD) the bacterial growth, parametric survival models based on the weibull distribution was used. According to our results, the growth of S.typhimurium was affected significantly (P <0.05) by selected parameters.TTD for combinations with acetic and citric acid was 6.97 and 1.30 times greater than HCl respectively. TTD for combinations with pH levels of 6.4 and 5.4 was 1.72 and 7.96 times greater than those with pH level of 7.4. This time with 3% and 6% NaCl concentration was 1.38 and 1.82 times greater than with 0.5% NaCl. Furthermore, this period for combinations with incubation temperature of 25°C was 1.30 times greater than combinations with those by incubation temperature of 35°C.The final model showed that all explanatory variables had significant association with time of detection.