ULTRAVIOLET EXPOSURE STUDIES ON A GAMMA RADIATION RESISTANT MICROCOCCUS ISOLATED FROM FOOD^a,b,c,

Abstract

During laboratory studies on noiisporeforming food spoilage microorganisms which are difficult to destroy by high level gamma radiation ( l ) , it was observed that such species also were resistant to ultraviolet light (UVL) irradiation. Their resistance when irradiated in phosphate buffer was greater than other nonsporeformers or the spores of Bacillus globigii when treated under identical conditions. The response of these microorganisms to ultraviolet light is similar in some respects to their response to gamma radiation. Mechanisms of resistance to UVL and to gamma rays may have some factors in common. It has been shown that both forms of radiation cause the formation of peroxides in the medium (5,7). If similar resistance mechanisms were indicated it was anticipated that by using UVL in place of gamma radiation perhaps some answers to problems associated with radiation sterilization could be obtained without the difficulties associated with the use of gamma rays. The ultimate objective in these experiments was to obtain information on the response of such microorganisms to irradiation under various physical and chemical environments. This paper describes the apparatus and techniques used, together with some completed studies on a UVL and gamma resistant micrococcus. MATERIALS AND METHODS Cultures subjected to irradiation included: a radiation resistant micrococcus, Micrococcits pyogenes var. aureus, Sarcina lutea ATCC 9341, Bacillus subtilis morphotype globigii ATCC 9372 and Escltrrichia coli FDA strain 198.Cultures to be irradiated were grown at 32' C. on a rotary shaker in 50 ml. quantities of tryptone-glucose-yeast extract (TGY) broth contained in 8 02. prescription bottles. A 2% inoculum from a 24 hour old cdture was used. Twenty-four hour cultures (except where stated) were centrifuged and resuspended in 0.05 M phosphate buffer. This resuspended cell stock on adjustment to 90% transmittance at 550 mp with a Bausch and Lomb Spectronic-20 spectrophotometer, gave a viable plate count of 2-5 X 1V per ml. A 25 ml. aliquot of this suspension was placed in a 1 X 8 in. tube of UVL-transmitting glass (Vycor 7910) and irradiated in a specially constructed tank.The irradiation tank (Figure 1) consists of a 3-chambered plastic box with a

Carbohydrate Metabolism in Micrococcus Radiodurans

“…In view of the unique resistance displayed towards high doses of radiation (1,3 ) , it appeared desirable to examine in detail the nature of the pathways of carbohydrate catabolism functio~li~lg in this organism.…”

Sensitization to Radiation by Loss of Recombination Ability in a Temperature-sensitive DNA Mutant of Micrococcus radiodurans Held at Its Restrictive Temperature

“…) and ionizing radiation (Anderson et al 1956;Duggan, Anderson, Elliker & Cain, 1959) because it is able to repair radiation damage to its DNA very efficiently. It possesses a mechanism for the removal of u.v.-induced pyrimidine dimers from its DNA (Boling & Setlow, 1966) and on the basis of the isolation of a u.v.-sensitive mutant, M .…”

Inactivation of the Radiation-Resistant Spoilage Bacterium Micrococcus radiodurans

“…A micrococcus species, which was the only viable aerobic organism isolated from spoiled canned meats previously irradiated to 2 and 3 megarep, has been previously described (Anderson, Rash, and Elliker, 1961;Raj et al, 1960). It was shown to be highly resistant to gamma radiation (Anderson et al, 1956) and to ultraviolet light (Duggan et al, 1959).…”