The Effect of X-Rays on the Survival of Bacteria and Yeast

Abstract

The variety of metabolic and morphologic characteristics found in microorganisms offers an opportunity to study the influence of these factors on cellular sensitivity to X-rays that has not been fully utilized. A review of the literature for bacteria showed that the survival curve and LDs0 had been determined accurately for members of only nine genera: Achromobacter, Aerobacter, Escherichia, Micrococcus, Pseudomonas, SalmoneUa, Sarcina, Serratia, and Shigella. Seven of these are gram-negative rods MATERI AND METHODS Microbiological. The strains employed and their sources were as follows: Azotobacter agile strain M.B.4.4, Rhodopseudomonas spheroides strain ATH 2.4.1 (C. B. van Niel, Stanford Univ.), Escherichia coli strain W-1485 (E. M. Lederberg, Univ. of Wisconsin), Pseudomonas fluorescens strain A.3.12 (R. Y. Stanier, Univ. of California, Berkeley), Saccharomyces cerevisae, haploid, strain 93.1C (a) and diploid strain 93 (C. A. Tobias, Univ. of California, Berkeley). In the case of Saccharomyce8, the original Lindegren strain numbers are used. Zirkle and Tobias (1953) called the haploid and diploid strains SC-7 and SC-6, respectively. E. coli, P. fluorescens, and R. spheroides were routinely grown and plated on yeast agar containing NH4Cl, 0.1 per cent; K2HP04, 0.1 per cent; MgSO4.7H20, 0.05 per cent; yeast extract 571

CULTURAL CONDITIONS AS DETERMINANTS OF SENSITIVITY OF ESCHERICHIA COLI TO DAMAGING AGENTS

“…The radiation effect investigated was inactiva-544 on September 22, 2020 by guest http://jb.asm.org/ Downloaded from tion or loss of ability of the exposed cells to produce a macroscopically visible colony after 24 to 48 hr incubation at 37 C. The composition of the plating medium for all experiments was as follows (per liter): peptone, 10 g; glucose, 2 g; KH2PO4, 4.5 g; K2HPO4-3H20, 7.6 g; and agar, 20 g. In the present studies, as in those of Gunter and Kohn (1956), no more colonies developed with incubation for longer periods of time. Stationary-phase cultures were diluted 100-fold in 0.066 M P04 buffer (pH 6.8) at room temperature and irradiated immediately at this temperature.…”

“…The difference in sensitivity of types A and B cultures seems to involve a slope change, whereas types B and C cultures seem to show survival curves that differ chiefly in the magnitude of the shoulder. Sigmoid survival curves of the type obtained for the type C culture are often referred to as multihit, multitarget, or multiunit curves and suggest a multiplicity of events required to bring about inactivation (Atwood and Norman, 1949;Gunter and Kohn, 1956;Tobias, 1952). The best fit of the final slope of curve C as shown in figure 1 extrapolates at zero dose to a hit or target number of between 10 and 100.…”

Microbiological Quality Control of Sterilized Products: Evaluation of a Model Relating Frequency of Contaminated Items with Increasing Radiation Treatment

“…The kinetics of inactivation of microbial populations vary with strain and species of organism under test and with the conditions under which measurements are made. Four general types of dose/ln survival curve have been recognized (Gunter & Kohn, 1956;Alper, 1961) and for each a mathematical expression has been derived that describes wholly the reduction in numbers of survivors with increasing radiation dose. Unquestionably, the expression which has found most general application for noninterpretive descriptions of inactivation is that termed 'multiple hit', usually written as…”

Radiation Sterilization and the Anaesthetist

“…When these results are plotted semilogarithmically, curve shapes are produced as indicated in Figure 2. Gunter and Kohn (1956) designated the curves A, B, Cl and C2, and experience suggests that most micro-organisms give either a straight line type A curve or a type Cl curve with a small shoulder at very low doses. These essentially straight line curves allow a numerical measure of the radiation sensitivity of micro-organisms, and the usual one is known as the DI0 value.…”