Abstract:

Purpose: To investigate the low pH acid adaptability of Salmonella heidelberg and the effect of acid adaptation
on its response to different environment stresses. Methods: S. heidelberg was exposed to TSB at pH 5.5 for 2 h for acid
adaptation. Comparison of the responses of acid adapted and unadapted cells to different temperature, high osmosis, bile
salt, and disinfectant stresses was conducted by calculating their survival rate. Results: pH 5.5 acid adaptation enabled
S. heidelberg to survive better in pH 3.0 acid challenge medium. Acid adaptation also provided S. heidelberg with increased
tolerance to thermal stress at 45 and 50 ℃, and made it more susceptable to 4 ℃ cold environment, but did not affect its
survival at −20 ℃. pH 5.5 acid adaptation also increased high osmotic and bile salt tolerance, and 60% of S. heidelberg
survived after 1 h treatment in 5?10 g/100 mL NaCl solution. It survival rate in 1?10 g/100 mL bile salt was 3.8 times higher
than that of the control group. Acid adaptation also changed S. heidelberg response to disinfectants, showing a significant
increase (3.1 times at most) in survival rate under H2O2 stress in the concentration range of 10?25 mmol/L when compared
to the control group. On the other hand, acid adapted Salmonella had enhanced sensitivity to NaClO and ethanol, with no
significant difference noted between the two disinfectants at high concentrations. Conclusion: Salmonella heidelberg could
develop acid tolerance response (ATR) after being inoculated in low pH medium. Low pH acid exposure induced crosstolerance
of S. heidelberg cells to thermal, high osmotic, bile salt and H2O2 stresses. However, the tolerance to 4 and −20 ℃
low temperatures, and NaClO and ethanol disinfectants was reduced due to acid adaptation.

Key words: Salmonella heidelberg, acid adaptation, environmental stresses