Effect of radiation and freezing on [3H]DNA of Yersinia enterocolitica

Abstract

Freezing of the enteropathogenic bacterium Yersinia enterocolitica to-18 and-75°C caused 7 and 42% cell death, respectively, and 0.329 and 0.588 single-strand breaks per 108 daltons of DNA, respectively, while radiation to one D1o dose (10% cell survival) combined with freezing to 2 to 0,-18, and-75°C induced 0.05, 0.75, and 5.04 single-strand breaks, respectively. The increase in the effectiveness of radiation with respect to the yield of single-strand breaks at-18 and-75°C is contrary to expectation and seems to be due to arrest of repair of single-strand breaks by these low temperatures. Yersinia enterocolitica has been isolated throughout the world from such products as beef, pork, ice cream, mussels, oysters, and drinking water (9, 15, 18). As a foodborne pathogen Y. enterocolitica presents a worldwide public health hazard. The dangerous nature of Y. enterocolitica is magnified by its ability to survive and multiply in refrigerated foods at 0 to 4°C (18, 19). Since Y. enterocolitica does not form spores, it is fairly sensitive to radiation (8). It is also sensitive to freezing (7). Radiation doses of <1 Mrad may be used to eliminate foodborne Y. enterocolitica (8) as well as Salmonella (14, 22), Shigella (8), and Staphylococcus (8) spp. During food irradiation it is a common practice to cool or freeze the food product to protect it against undesirable microbiological and organoleptic changes. Freezing by itself or in combination with radiation causes cell inactivation as well as cell injury. Cell injury is defined as increased sensitivity of surviving cells to deleterious agents. In practice, cell injury is measured as the fraction of cells unable to grow in the presence of 2.5% NaCl in the recovery medium (8). In gram-negative bacteria ionizing radiation induces DNA strand breaks detected by the alkaline sucrose gradient sedimentation technique (5, 11, 23, 24). Freezing similarly induces DNA breakage in the gram-negative species Escherichia coli (1, 2, 3). A causal relationship of DNA breakage to cell inactivation has been reported for both radiation (12, 17) and freezing (1, 2, 3); however, in the present study no simple relation could be seen between these two parameters when radiation was compared with freezing or with the combination of radiation and freezing, a common practice in food irradiation. Although the study of DNA injury by radiation and freezing in gram-negative organisms is not new, the enteropathogen Y. enterocolitica has, to our knowledge, not been investigated. Furthermore, the combined action of freezing and radiation is also poorly understood. In the present study we investigated these two points. MATERIALS AND METHODS Growth and labeling of Y. enterocolitica. A clinical strain of Y. enterocolitica, strain WA, kindly provided by W. H. Lee,

Freezing shortens the lifetime of DNA molecules under tension

“…In low ionic strength buffer, a pulling force is conducive to breathing/peeling in dsDNA [ 39 , 40 ] and accelerates the breaking process near closely spaced nicks. Our data indicate that the frozen DNA specimens had lower mechanical strength levels, which is consistent with previous findings for DNA at low temperatures [ 10 ].…”

“…The structural stability of nucleotide probes can also influence hybridization efficiency for molecular detection. Various factors, such as ionic strength, can influence the integrity of molecular structures, and several technologies have been developed to probe the integrity of polynucleotides [ 9 , 10 ]. However, to probe the integrity of DNA at a single molecular level is still challenging for most current technologies.…”

Reduced virulence of Yersinia enterocolitica by copper-induced injury

“…Low levels of copper in a chlorine-free distribution system have been reported to cause substantial injury to coliform populations (12). However, copper injury of Y. enterocolitica has not been described previously, although injury from exposure to heat (34), radiation (16), and radiation and freezing (15,19) has been recently reported.…”