Responses of acid-stressed Salmonella Typhimurium in broth and chicken patties to subsequent antimicrobial stress with ɛ-polylysine and combined potassium lactate and sodium diacetate

We investigated the growth kinetics and morphological changes in acid-stressed Salmonella Typhimurium as well as the antimicrobial effects of ɛ-polylysine (SAVE-ORY™ GL610) and combined potassium lactate (PL) and sodium diacetate (SDA) (PURASAL® Opti.Form® PD Plus) on acid-stressed S. Typhimurium. Exposure to 0.5% acetic or lactic acid injured over 90% of the S. Typhimurium population. Although the lag time of the injured S. Typhimurium was extended, the injured cells were recovered at 10 °C and 24 °C, indicating a risk of using 10 °C as a storage temperature. Additionally, 4.5% PL/SDA mixture or 2% ɛ-polylysine completely inhibited the growth of acid-stressed S. Typhimurium in broth at 10, 24, or 35 °C. Although 3% PL/SDA mixture inhibited the growth of lactic acid-stressed S. Typhimurium at 10 °C, it did not inhibit the growth of unstressed S. Typhimurium at the same temperature. This finding indicates a different antimicrobial effect due to the physiological status of the pathogen. Furthermore, acid-stressed S. Typhimurium was not resistant to ɛ-polylysine or the PL/SDA mixture, although the antimicrobial effect of these compounds was enhanced at a lower storage temperature. TEM analysis revealed that most of the stressed cells lost their cellular integrity and membranes partially. Both dead and doubling cells were observed after recovery at 30 °C for 12 h. The addition of 2% ɛ-polylysine or 4.5% PL/SDA mixture resulted in the collapse of the structure of S. Typhimurium cells and cytoplasmic materials being released. These results provide valuable information regarding the morphological and physiological responses of acid-stressed S. Typhimurium cells in broth and chicken patties followed by antimicrobial stress with ɛ-polylysine or PL/SDA mixture.