Salmonella Typhimurium Treated by Gamma Radiation as an Approach for Cancer Management

Abstract
Background: Salmonellae are gram-negative, facultative anaerobes, it can survive and colonize in hypoxic environment of the tumor, leading to a substantial reduction in the tumor size. Bacteria can be attenuated by radiation which resulted in complete loss of replicative ability but remained metabol-ically active.
Aim of the Work: This study was conducted to evaluate the efficiency of y-radiation as a tool to decrease the virulence of Salmonella typhimurium wild type strain ATCC 14028 (S. typhimurium.WT.) capable of tumor regression.
Methods: Exposure of Salmonella typhimurium wild type strain (S.typhimurium.WT.) to different doses of y-radiation, testing S.typhimurium.WT. that exposed to different doses of y radiation for cytotoxic activity in vitro, and its pathogenicity in mice as well as the wild type strain was assessed. The antitumor activity of the y-irradiated Salmonella in vivo was tested as well. Sixty adult male weighty 20-25g were used for this purpose and the mice divided into 6 experimental group, three of these groups were mice bearing EACs solid tumor, after the tumor volume reached approximately 1cm3, the mice were treated with S.typhimurium.WT. parent strain and S.typhimurium.WT. exposed to 1and 4kGy y-irradiation dose histopathological analysis, as well as, proliferation and immunological biomarker, was assessed. The study has been carried out for last three years in the National Center for Radiation Research and technology, Atomic Energy Authority, Egypt.
Results: Results showed a reduction in S.typhimurium.WT. viable count with the increase of y-radiation exposure dose, also a highly significant inhabitation in EAC cells count % was occurred when S.typhimurium.WT. exposed to y radiation at dose of 1 and 4kGy, it was found S.typhimurium y-1kGy give a high inhabitation percentage in cell line and became less virulent to mice than S.typhimurium wild type strain, results revealed that, treatment with S. typhimurium y1kGy caused retardation in tumor growth in mice bearing tumor groups more than the wild type strain do. This was leading to a reduction in tumor volume accompanied with a significant increase in caspase-3 activity. In addition, histopathological analysis revealed that irradiated Salmonella achieve improve-ment of the muscular thigh tissue compared to EAC tumor bearing mice.
Conclusion: The exposure of S.typhimurium.WT. to y-radiation decreases its virulence in mice and increase its antitumor activity in vivo and in vitro.