Chlorine-stressed Salmonella cells are significantly more engulfed by Acanthamoeba trophozoites and have a longer intracystic survival than the non-stressed cells

Abstract

In the present study, the effect of sublethal chlorine-induced oxidative stress on the subsequent interaction of Salmonella enterica serovars Enteritidis and Typhimurium with Acanthamoeba castellanii and A. polyphaga was evaluated. Sublethal chlorine concentration was determined using the lag phase extension information and used to prepare chlorine-stressed Salmonella cells. Coculture experiments of Acanthamoeba and Salmonella cells were performed in Page's amoeba saline (PAS) at 25 °C for 2 h. The results showed that the chlorine-stressed Salmonella cells were significantly more engulfed by A. castellanii and A. polyphaga trophozoites than the non-stressed cells. The uptake rates of the chlorine-stressed and non-stressed Salmonella cells were in the range of 14.17-27.34 and 6.51-11.52% for A. castellanii, and in the range of 8.32-17.76 and 2.28-6.12% for A. polyphaga trophozoites, respectively. Moreover, intracystic survival time of chlorine-stressed cells of S. Enteritidis and S. Typhimurium was significantly longer than that of non-stressed cells. While, non-stressed Salmonella cells survived within A. castellanii and A. polyphaga cysts for 13-20 and 8-15 days, chlorine-stressed cells were recovered from A. castellanii and A. polyphaga cysts after 22-32 and 15-24 days, respectively. These results underscore the importance of bacterial exposure to sublethal chlorine concentrations in their interaction with free-living amoebae, and may lead to a better understanding of the parameters affecting the persistence of Salmonella enterica serovars in food-related environments.

Keywords: Acanthamoeba; Chlorine; Salmonella enteritidis; Salmonella typhimurium; Stress.