Abstract: Objective: To investigate the effect of culture in the presence of organic acids on inducing acid resistance in Salmonella typhimurium CGMCC 1.1190. Methods: The effects of acidification of the culture medium to different pH levels with citric, lactic, acetic or malic acid on the growth, cellular morphology and subsequent acid resistance in medium at pH 2.5 of this microorganism were studied. The Baranyi model was used to fit the growth data of S. typhimurium CGMCC 1.1190 in trypticase soy broth (TSB) acidified with the four organic acids, and the Weibull model was used to fit the inactivation data of stationary-phase cells in medium at pH 2.5. Results: This strain had different tolerances to the four organic acids. Analysis of the inactivation curves showed that all the organic acids could induce increased acid tolerance and their effects decreased in the order of citric acid > lactic acid > acetic acid > malic acid under the same pH condition. For each organic acid, lower pH resulted in stronger acid resistance. The acid resistance parameter δ-value resulting from citric acid was significantly greater than that of the control group (P < 0.05). Furthermore, the cellular morphology of CGMCC 1.1190 cultured in the presence of citric acid was significantly different from that of the control non-acid adapted cells, and the cell aggregation was more obvious with decreasing induction pH. Conclusion: S. typhimurium CGMCC 1.1190 cells exhibited enhanced acid resistance and altered aggregation state upon being cultured in medium acidified with organic acids.

Key words: Salmonella typhimurium; acid stress; Baranyi model; Weibull model; acid resistance