Effect of Low Dose γ-Irradiation on the Fate and Cell Envelope of Bacillus cereus, Escherichia coli, and Salmonella Typhimurium

This study investigated the effect of low dose γ-irradiation on the damage of the cell envelopes and antibiotic sensitivity profiles of Bacillus cereus, Escherichia coli, and Salmonella Typhimurium. The bacteria suspension in tryptic soy broth was exposed to the γ-irradiation doses of 0, 1, 1.5, 3, and 5 kGy, and then stored at 0oC for 24 h. A viability test, an antimicrobial sensitivity profile, and an electron microscopy were performed to observe the effects due to γ-irradiation treatment. B. cereus could survive the γ-irradiation up to 5 kGy while E. coli and S. Typhimurium were all deactivated at 1.5 kGy and 5 kGy, respectively. At 5 kGy, the cell count of B. cereus was significantly reduced, and the survived bacteria cells retained their important features. There were no significant changes observed in the antimicrobial sensitivity profile (p>0.05) for the recovered bacteria after irradiation treatment. Low dose γ-irradiation below 3 kGy was found to be insufficient to achieve decontamination of B. cereus and S. Typhimurium. Cell envelope damage and deactivation of different bacteria did not occur in the same manner; thus, deferent doses of γ-irradiation may be required for deactivation of different bacteria.