Assessing the cytotoxicity and apoptosis-inducing ability of solar irradiated Salmonella Typhimurium in RAW264.7 cell line in vitro

Abstract

The consumption of solar disinfected (SODIS) water has reduced diarrhoeal incidences in resource-poor regions of the world. Thus, this study assessed the effects of solar radiation on the viability and on three virulence characteristics (invasion, cytotoxicity, and apoptosis) of S. Typhimurium on macrophages. Samples of S. Typhimurium were treated in three ways: (i) suspended in water and exposed to solar ultra-violet radiation (SUVR), (ii) exposed to SUVR but in a non- transparent flask, and (iii) heat and chemically attenuated by treating the bacteria with 0.5% phenol at 65°C for one hour. Salmonella Typhimurium samples were pipetted out from the three treatments after 4 and 8 h and used to infect macrophage RAW264.7 cells. The intracellular growth of S. Typhimurium was assessed by using the gentamicin protection assay. Cytotoxicity assays were carried out using the Lactate Dehydrogenase Assay (LDH). Apoptosis of infected macrophages was analysed using flow cytometry. The results showed that S. Typhimurium was inactivated after 4 and 8 h of solar irradiation. The solar irradiated S. Typhimurium exhibited no intracellular growth, and produced lower cytotoxicity and fewer necrotic cells in RAW 264.7 cells. The non-irradiated S. Typhimurium survived within the macrophages, were highly toxic to the cells and caused a significant increase (p<0.01) in necrotic cells when compared to the solar irradiated samples. In conclusion, solar irradiated S. Typhimurium impacts the viability and virulence properties especially the survival of RAW264.7 cells and also reduces their ability to induce cytotoxicity and necrotic cell death in the macrophages