EFFECT OF SELECTED SOLUTES ON GROWTH AND RECOVERY OF A RADIATION‐RESISTANT Moraxella SP.

Abstract

A highly radiation‐resistant Moraxella sp. from beef was more resistant to gamma radiation in frozen beef than Clostridium botulinum 33A spores. Even though the Moraxella sp. was extremely radiation‐resistant, its recovery after irradiation was markedly influenced by the plating medium. Fewer colony‐forming units were recovered in Tryptic Soy Agar (TSA) than in Plate Count Agar (PCA), and differences in recovery became more pronounced with increasing radiation dose. Growth studies of the nonirradiated Moraxella sp. suggested the presence of dialyzable inhibitory factor(s) in Trypticase Soy Broth (TSB) and TSA. The low (0.5%) concentration of NaCl in TSA was shown to be mainly responsible for the slow growth and reduced recovery after irradiation. Reduced recovery was also obtained by plating the Moraxella sp. in PCA plus 0.5% NaCl or PCA plus 6% glucose after irradiation. It was noted that 2 other highly radiation‐resistant isolates identified as Moraxella sp. gave similar results. Sensitivity to low solute concentrations, therefore, appeared to be a general phenomenon for this group.

Factors Influencing Radiation Resistance of Vegetative Bacteria and Spores Associated with Radappertization of Meat

“…and Acinetobacter sp. were frequently found in irradiated beef (Tiwari and Maxcy, 1972) and were shown to be more resistant than C. botulinum spores to radiation destruction (Bruns and Maxcy, 1978). Furthermore, these bacteria were extremely resistant to drying (Sanders and Maxcy, 1979), and their unique characteristics were highly influenced by the microenvironment.…”

SIGNIFICANCE OF RESIDUAL ORGANISMS IN FOODS AFTER SUBSTERILIZING DOSES OF GAMMA RADIATION: A REVIEW1

“…The nature of menstruum with such factors as water availability, ionic concentration, and available oxygen influence the rate of destruction as well as recovery from radiation (Bruns and Maxcy 1978). Vacuum packaging affords some protection to bacteria.…”

“…The injured bacteria are sensitive to similar osmolar concentrations of other solutes such as glucose (Bruns and Maxcy 1978). This equivalent concentration of dissolved substances is common in foods and a factor to be considered in evaluating the outgrowth of injured cells.…”