In vitro Susceptibility Study of Salmonella typhimurium Mutant to Stress Factors

Background and Objective: In this study, we compared the susceptibility of Salmonella typhimurium phoP mutant and its parent to stress conditions that the pathogen may encounter in a host. Methods: For this purpose, we used the phoP deletion mutant constructed in our previous study. In order to test the in vitro susceptibility of the mutant to stress factors, the effect of acidic pH, heat, bile salts and polymyxin on growth of the mutant was examined. Then, minimum inhibitory concentration and minimum bactericidal concentration of bile salts and polymyxin were determined. Salmonella typhimurium 14028 was used as the parent strain. Results: The mutant was highly susceptible to bile salts and polymyxin in comparison with the parent strain, but no difference was observed in their susceptibility to acid and heat. Conclusion: This study confirms the role of the phoP in resistance of Salmonella to polymyxin and bile salts. Mutation in the phoP leads to susceptibility of the mutant to bile and cationic antimicrobial peptides.