Abstract: The influence of acid induction, two-component regulatory systems and long-term low-temperature storage on the formation of acid tolerance response (ATR) was evaluated, and the mechanism of ATR formation was elucidated by using the λRed recombination system, real-time polymerase chain reaction (real-time PCR) and amino acid addition experiments. The results showed that mild acid induction significantly enhanced the acid tolerance of Salmonella (P < 0.05), and once induced, it could be maintained for at least 1 week at 4 ℃, posing a great threat to food safety. As a mildly acidic incubation medium, beef did not induce ATR at 4 ℃, indicating that low-temperature treatment may be an important method to inhibit ATR in Salmonella typhimurium. Real-time PCR and amino acid addition experiments showed that PhoP/PhoQ and PmrA/PmrB were involved in the perception of the acidic environment, improving bacterial acid resistance by regulating the arginine decarboxylation and lysine decarboxylation systems. This explains the mechanism of ATR formation from the perspective of amino acid metabolism, which may also reveal an explanation of why food substrates can enhance the acid resistance of some bacteria.

Key words: beef; Salmonella; acid tolerance response; two-component regulatory system; PhoP/PhoQ; PmrA/PmrB; food safety