Influence of pH and temperature on growth characteristics of leading foodborne pathogens in a laboratory medium and select food beverages

Accurate prediction of bacterial growth responsiveness over a range of processing environments is important for food processors to ensure proper food safety. Therefore, the aim of the current study was to evaluate growth characteristics of leading foodborne pathogens subjected to a range of pH levels (3 to 10) in a laboratory medium incubated at a range of temperatures (25 to 45°C). Bacterial lag times and growth rates were quantified at 620 nm for 48 hours via microtiter plate reader. This study was also validated by subjecting these pathogens into food beverages with different pH levels at 25°C. Results revealed that the densities of all species when subjected to pH 3 and 4 of laboratory medium at any tested temperature and all pH at 45°C, were limited to ≤ 3 log CFU/ml (inoculums level). The overall optimal levels for bacterial growth rate were pH 9 and 35°C. All species generally demonstrated lower growth rates in acidic environments than in alkaline environments. Data from studies with food beverages showed that all tested bacterial species with few exceptions were either maintained at inoculum level or increased no more than 1 log CFU/ ml at pH ≤ 4.0, which further confirmed our laboratory medium findings. This study clearly demonstrates different responses by bacterial species to pH and temperature and will help inform decisions about the stringency of environments needed to reduce or control bacterial pathogen growth in foods.