A novel radiation-resistant Deinobacter sp. isolated from irradiated pork

Abstract

A red-pigmented, radiation-resistant, Gram-negative, rod-shaped bacterium isolated from irradiated pork is described. The D,, values in buffer solution and on pork mince are 3. 45 and 5.05 kGy respectively. The strain has been identified as a Deinobacter species.The sensitivity of micro-organisms to ionizing radiation can vary with genus, species or strain. The relative sensitivity of bacteria to gamma irradiation is compared by calculating D,, values where the D,, is the dose required to inactivate 90% of the population. Gramnegative bacteria tend to be more sensitive than Gram-positive to irradiation (have lower D,, values) and rod-shaped bacteria tend to be more sensitive than cocci (Ingram & Farkas 1977). The range of sensitivity of bacteria commonly found in foods is large, for example, the D,, value of a Pseudomonas juorescens strain irradiated in a low fat beef at 5°C was 0.13kGy compared to 0.58 kGy for Staphylococcus aureus irradiated under the same conditions (Maxcy & Tiwari 1973). Clostridium botulinum type A spores were found to have D,, values ranging from 3.4 to 3.6 kGy in cooked beef irradiated at 25°C (Grecz et al. 1971).In addition to these more common food contaminants non-spore-forming, extremely radiation-resistant bacteria are known to occur naturally in foods. Deinococcus radiodurans, formerly Micrococcus radiodurans, was first isolated by Anderson et al. (1956) This report describes a similar radiationresistant, Gram-negative rod isolated from irradiated pork. Materials and Methods ISOLATION A N D M A I N T E N A N C E OF T H E O R G A N I S MThe organism was isolated on glucose nutrient agar (Oxoid CM3 + 0.5% D-ghCOSe), incubated at 25°C for 3d, from a pork chop which had 22Irene R. Grant and Margaret F. Patterson been irradiated to a dose of 1.75kGy. Better growth was observed on Yeast extract peptone (YP) agar (Oyaizu & Komagata 1981) and subsequently the organism, which produces a bright red pigment, was cultured on YP broth or agar at 25"C, unless otherwise stated. DETERMINATION OF R A D I A T I O N RESISTANCEThe organism was grown in 500ml YP broth for 24h at 25"C, harvested by centrifugation and resuspended in phosphate buffered saline (PBS, Oxoid BR14a) to give approximately 10' cells/ml. Aliquots (1 ml) of inoculum were dispensed into sterile stoppered plastic tubes (Sterilin, Middlesex, England) and irradiated using a 6oCo Gammabeam 650 facility (Atomic Energy of Canada Limited) with a dose rate of 0.85 kGy/h and a temperature of 15°C. Samples were irradiated in triplicate at doses of 0, 2, 4, 6, 8 and 10 kGy. The number of survivors in each sample was determined by the Miles & Misra (1938) technique on YP agar at 25°C for 3d.The logarithm of the bacterial count was plotted against radiation dose to determine death rate and the D,, value calculated as the reciprocal of the slope of the best fit line (Ley 1983). A similar procedure was used to determine the D,, value in sterile pork. Samples (25 g) of irradiation-sterilized (dose of 25 kGy) minced pork were inoculated with l m ...

Extensive Diversity of Ionizing-Radiation-Resistant Bacteria Recovered from Sonoran Desert Soil and Description of Nine New Species of the Genus Deinococcus Obtained from a Single Soil Sample

“…Species of these two genera made up 82% of the isolates recovered from the soil sample after exposure to doses of ionizing radiation of 17 kGy or more. At the highest doses (23,25, and 30 kGy), Deinococcus species accounted for more than 72% of the isolates recovered, and Geodermatophilus and Hymenobacter species accounted for 23 and 5%, respectively. Of the 126 isolates recovered and identified from the soil sample exposed to various levels of ionizing radiation in this study, 106 belonged to these three genera (Deinococcus, 60 strains; Geodermatophilus, 40 strains; and Hymenobacter, 6 strains).…”

“…Of the genera containing ionizing-radiation-resistant organisms, Deinococcus and Rubrobacter show the highest levels of resistance, and all species of these genera have been shown to be either gamma radiation resistant or UV radiation resistant or both (2,6,19,20,22,47,61,62,73 (5,19,26,52,61). Other ionizing-radiationresistant bacteria have been isolated and described; these include some species of the genera Acinetobacter, Chroococcidiopsis, Hymenobacter, Kineococcus, Kocuria, and Methylobacterium (4,5,11,23,24,30,49,50,53). Hyperthermophilic euryarchaeote species of the genera Thermococcus and Pyrococcus also contain ionizing-radiation-resistant strains (15,32,33).…”

“…Species of the genera Deinococcus and Rubrobacter have been shown to survive exposure to doses greater than 25 kGy (3,6,19,20,47,73), while species of the genus Chroococcidiopsis survive exposure to 15 kGy (4). Strains of the species Acinetobacter radioresistens, Hymenobacter actinosclerus, Kineococcus radiotolerans, Methylobacterium radiotolerans, Pyrococcus furiosus, Pyrococcus abyssi, Thermococcus gammatolerans, Thermococcus marinus, and Thermococcus radiotolerans are less resistant and have been shown to survive after exposure to much lower levels of radiation (15,23,30,32,33,53).…”

“…Ionizing-radiation-resistant organisms have been isolated from a wide range of environments, including sawdust (29), sewage (31), paper mill machinery (36,66), animal feeds (31), processed meat (69), dried food (39,42), feather pillows (67), room dust (8), textiles (37), irradiated meat and fish (13,23,69), high-level nuclear waste sites at Savannah River in South Carolina (53) and at Hanford in Washington (22), thermally polluted water (6), and irradiated rice (28). Other environments from which radiation-resistant isolates have been obtained include soil (5,47), feces (5,52), warm freshwater geothermal springs (19,20), and shallow and abyssal marine thermal springs (15,21,32,33).…”

Antioxidant, antibacterial, and ultraviolet-protective properties of carotenoids isolated from Micrococcus spp.

“…[2] Several researchers have reported that some pigmented bacteria, which are rich in carotenoids have been resistant to radiation when subjected to sub-lethal and lethal doses of ionizing radiations, due to the accumulation of the radio-protective pigments in the outer membrane. [3][4][5][6] Carotenoids are the terpenoid pigments produced by a wide variety of plants and microbes, which are reported to have radio-protective property. [7] Carotenoid pigments of bacterial origin have been reported to have radio-protective and antioxidant properties, and as natural coloring agents.…”