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RADIATION RESISTANCE OF A HEMOLYTIC MICROCOCCUS ISOLATED FROM CHICKEN MEAT
Abstract
The effects of environmental factors on a highly radiation-resistant hemolytic micrococcus isolated from chicken meat were studied. NaCl tolerance and gamma radiation resistance of the cells were growth phase-related. The cells were resistant to injury from drying or freezing/thawing. Under certain conditions, cells in the frozen state required approximately 5 Mrad to inactivate 90% of the population; 0.2 Mrad injured an equivalent proportion. Survival curve of the cells heated at 60(DEGREES)C showed a unique pattern which was in three distinct phases. Heat-stressed cells were much more sensitive to radiation inactivation than unheated cells. When suspended in fresh m-Plate Count Broth (PCB), the injured cells repaired without multiplication during incubation at 32(DEGREES)C. The repair process in this bacterium, however, was slower compared to thermally injured organisms studied by other workers. An improved replica-plating technique, utilizing filter paper discs as replicators, was devised for isolation of radiation-sensitive mutants of pigmented bacteria. Compared to the conventional Lederberg and Lederberg procedure, this filter paper replication (FPR) system was better in reliability and much less time-consuming. A simple method to demonstrate radiation-inducible radiation resistance in microbial cells was developed. Cells under investigation were "fixed" on agar plates throughout the successive steps, which included induction-irradiation, post-induction incubation, challenging irradiation, and final incubation for the survivors to form a visible cell "mass." Thus, the new method required neither washing/centrifugation nor procedures for cell enumeration. Mutagenesis treatment of the radiation-resistant micrococcal bacterium with N-methyl-N'-nitro-N-nitrosoguanidine (NTG) followed by FPR and screening steps resulted in isolation of two radiation-sensitive mutants. The more sensitive mutant strain, designated as 702, was seven times as sensitive to gamma or UV radiation as the wild type. No apparent difference was observed between 702 and the wild type in (1) cell morphology, colonial morphology, and pigment production or (2) tolerance to NaCl, drying/storage, freezing/thawing, and heating. The 702 had a slower growth rate than the wild type in PCB. Under certain conditions, the wild type showed an inducible mechanism for radiation resistance, while 702 failed. Sodium dodecyl sulfate treatment (for curing) of the wild type did not result in isolation of a radiation-sensitive mutant.
Subject Area
Food science|Microbiology|Biophysics
Recommended Citation
TAN, SHIEH-TE, "RADIATION RESISTANCE OF A HEMOLYTIC MICROCOCCUS ISOLATED FROM CHICKEN MEAT" (1982). ETD collection for University of Nebraska-Lincoln. AAI8306515.
https://digitalcommons.unl.edu/dissertations/AAI8306515