RHYTHMIC RESPONSE OF SERRATIA MARCESCENS TO ELEVATED TEMPERATURE

Survival of Burkholderia pseudomallei on Environmental Surfaces

The survival of the biothreat agent Burkholderia pseudomallei on the surfaces of four materials was measured by culture and esterase activity analyses. The culture results demonstrated that this organism persisted for <24 h to <7 days depending on the material, bacterial isolate, and suspension medium. The persistence determined by analysis of esterase activity, as measured with a ScanRDI solid-phase cytometer, was always longer than the persistence determined by culture analysis.

Factors affecting catalase level and sensitivity to hydrogen peroxide in Escherichia coli

Composition of the culture medium, growth phase, and temperature play important roles in the sensitivity of Escherichia coli to H2O2. The medium and growth phase affected the sensitivity of the cells to H2O2 by modifying the amount of catalase synthesized by them, whereas the effect of temperature was due to the thermolability of the enzyme. Since catalase is unstable in the presence of its substrate, the correlation between the catalase level in the cells and their sensitivity to H2O2 could be observed only when the H2O2 concentration was not excessive in proportion to the amount of catalase.

Rhythmic changes in dry heat resistance of Bacillus subtilis spores after rapid changes in pH

Heat resistance of freeze-dried Bacillus subtilis spores varied in a rhythmic manner as a function of time between acidification to about pH 1.5 and freezing. A comparable rapid shift to pH 11 produced little change in resistance to heat.

Selective increase in hydrogen peroxide resistance of a coagulase-positive staphylococcus

Staphylococcus culture 105B was serially treated with 0.05% hydrogen peroxide at 54.4 C or without hydrogen peroxide at this temperature to determine changes in resistance to these conditions and in catalase activity of the surviving populations. Resistance of the final surviving populations to H(2)O(2) treatment and to heat treatment without H(2)O(2) was 5.6 and 4.5 times greater, respectively, than the parent culture. Catalase activities of the cell-free extracts of survivors of the H(2)O(2) treatments and of the heat treatments were 33.56 and 2.69 times greater, respectively, than the control. The untreated control cultures grew in Peptonized Milk (Difco), but addition of sodium pyruvate to the medium was necessary to support growth of survivors.

Studies on survival of bacteria: rhythmic response of microorganisms to freeze-drying additives

Various materials were mixed with suspensions of Serratia marcescens and other organisms. Samples were removed and frozen at intervals after mixing; the number of cells that survived both freeze-drying and exposure to air varied rhythmically as a function of time between mixing and freezing. When assayed before or immediately after drying there were essentially no fluctuations. The response was evident only when these dried samples were exposed to air. In a typical experiment, the number of cells surviving in the sample frozen 30 sec after adding propyl gallate was at least 10 times that in samples frozen either 20 sec earlier or 20 sec later. Other "peaks" in survival were observed at approximately 125 and 450 sec, but the times at which the peaks were observed were not consistent from one experiment to the next. Although we have been unable to control or predict the time at which maxima in resistance occur, we have shown that the phenomenon does occur with Escherichia coli and Saccharomyces cerevisiae as well as with S. marcescens. Furthermore, a rhythmic response also was obtained after a change in pH or cell concentration. It appears that microorganisms respond physiologically and synchronously to changes in their environment, and some of these responses have survival value.

Physiological responses of airborne bacteria to shifts in relative humidity

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Survival of bacteria on metal surfaces

Survivor curves were determined for Serratia marcescens, Sarcina lutea, Pasteurella tularensis, and P. pestis deposited from the airborne state onto metallic surfaces and subsequently stored at various humidities and temperatures. Cells of all species tested remained alive longest in a dry atmosphere, except that cells of S. marcescens survived best in a saturated atmosphere. Survival decreased most rapidly at the intermediate humidity level for three of the test organisms, yet P. tularensis died most rapidly in a saturated atmosphere. An increase in temperature decreased survival of P. pestis and P. tularensis.

Effect of 3 percent hydrogen peroxide on the viability of Serratia marcescens

Campbell, Jack E. (University of California, Berkeley), and R. L. Dimmick. Effect of 3% hydrogen peroxide on the viability of Serratia marcescens. J. Bacteriol. 91:925-929. 1966.-Populations of Serratia marcescens were exposed to 3% H(2)O(2) at temperatures from 0 to 20 C. The reaction appeared to follow an Arrhenius plot, but variable numbers of diminutive colonies were found after cell numbers started to decrease. Colony numbers varied on different sampling media and increased when additional incubation was imposed. The overall reaction was sensitive to age of culture, and growth capabilities of treated samples varied with time of treatment, especially during times when no loss of viability was noted. Catalase activity per cell did not correlate with changes in sensitivity; iron added to growth medium increased catalase activity and decreased sensitivity, but not in the same manner. Although the fundamental reaction is presumably molecular in nature, present methods of viability assay measure more than single events and are not suitable for these studies.

Injury and growth of Serratia marcescens studied in a thermal gradient incubator

An incubator capable of producing a controlled thermal gradient of 0 to 40 C is described. Serratia marcescens was incubated in small tubes held in the gradient. When turbidity in the tubes was assayed and recorded by a semiautomatic photometer, growth-temperature patterns were obtained. The shape of these patterns was influenced by age of inoculum or by pretreatment of the culture. Cultures incubated for short times at 52 C, treated with hydrogen peroxide, or lyophilized before being incubated tended to grow at higher mean temperatures than untreated cultures. These findings illustrate the general utility of the instrument for studies of microbial growth.