More than 80% of food poisoning bacteria such asSalmonellaare reported as antibiotic-resistant to at least one type antibiotic, and more than 50% as resistant to two or more. For the decontamination of food poisoning bacteria in foods, radiation resistibility on drug-resistant bacteria were investigated compared with drug-sensitive bacteria. Possibility on induction of drugresistant mutation by radiation treatment was also investigated. For these studies, type strains ofEscherichia coliS2, Salmonella enteritidisYK-2 and Staphylococcus aureusH12 were used to induce drug-resistant strains with penicillin G. From the study of radiation sensitivity on the drug-resistant strain induced fromE. coliS2, D10value was obtained to be 0.20 kGy compared with 0.25 kGy at parent strain. OnS. enteritidisYK-2, D10value was obtained to be 0.14 kGy at drug-resistant strain compared with 0.16 kGy at parent strain. D10value was also obtained to be 0.15 kGy at drug-resistant strain compared with 0.21 kGy at parent strain ofSt. aureusH12. Many isolates ofE. coli0157: H7 or other type ofE. colifrom meats such as beef were resistant to penicillin G, and looked to be no relationship on radiation resistivities between drug-resistant strains and sensitive strains. On the study of radiation sensitivity onE. coliS2 at plate agars containing antibiotics, higher survival fractions were obtained at higher doses compared with normal plate agar. The reason of higher survival fractions at higher doses on plate agar containing antibiotics should be recovery of high rate of injured cells by the relay of cell division, and drug-resistant strains by mutation are hardly induced by irradiation.
