Determination of DB10B values of single and mixed cultures of bacteria after gamma irradiation

Abstract

The DB10B value of bacteria represents the absorbed radiation dose required to inactivate 90 % of a viable populati-on or reduce the population by a factor of 10. DB10B values of 3 bacterial isolates (Escherichia coli, Staphylococ-cus aureus and Salmonella parathyphi B) were determined using single and mixed cultures to assess the effect of microbial competition on radiosensitivity. The isolates were inoculated into wakye substrate and exposed to γ-radiation doses of 0, 100, 300, 450, 600, 750, 850 Gy from a P60PCo source at a dose rate of 2.20 kGy/h in air. Enumeration of survivors of the isolates was carried out using serial dilution and pour plate methods. The survi-ving fraction of isolates decreased with increased irradiation doses. DB10B values of E. coli, S. aureus and S. parat-hyphi B were respectively 0.27, 0.33 and 0.44 kGy when inoculated as single cultures, and 0.24, 0.28 and 0.32 kGy respectively when inoculated as mixed cultures. DB10B values were lower for mixed cultures compared to single cultures, which might indicate reduced resistance to γ-radiation as a result of competition among the isolates. Microbiological challenge tests based on the DB10B values may result in delivery of higher irradiation doses, but the extra dose could serve as safety margin to enhance the food preservative capacity of radiation processing.