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SUMMARY: The survival characteristics of washed stationary phase Aerobacter aerogenes organisms suspended in buffered sodium chloride solution and stored at room temperature, or at 37° with aeration, depended on the medium used for growing the bacteria. Populations of bacteria harvested from tryptic meat broth or tryptone glucose medium remained almost completely viable for longer periods than bacteria from a simple ammonium salt + mannitol medium in which carbon was limiting. Analyses of washed freeze-dried preparations of freshly harvested bacteria showed that the amounts of protein, carbohydrate and ribonucleic acid present varied according to which of the above media was used for growth. During the initial stages of storage at 37°, when the viability of the population remained apparently unchanged, a progressive loss in bacterial dry weight occurred, due to degradation of these cell constituents. Endogenous glycogen was degraded and oxidized; bacteria which contained glycogen survived well. However, the addition of glucose to suspensions stored under aerobic or anaerobic conditions did not favour survival. Utilization of substances made available by degradation of various endogenous macromolecular constituents may be an important factor concerned with the survival of bacteria in unfavourable environments.

SUMMARY: Small numbers of several bacterial species were rapidly and specifically detected with the 125I-labelled antibody method described previously. Multibacterial species detection was achieved in one operation with 125I-labelled mixtures of type-specific anti-bacterial globulins but the level and variability of the blank value increased, and sensitivity decreased, with the number of globulin components in the mixture. An indirect radio-assay that involved successive treatments of bacteria with unlabelled rabbit anti-bacterial serum and 125I-labelled immunopurified goat anti-rabbit globulin was less sensitive and reproducible than the direct radio-assay. A modified assay, developed to detect and determine bacteria filtered on to a membrane filter, allowed the detection of small numbers of bacteria in large volumes of aqueous sample. The feasibility of rapidly and specifically detecting small numbers of virus particles with 125I-labelled anti-viral globulin was investigated with bacteriophage T7 as a model particle. Methods for the rapid separation of phage-125I-labelled globulin complex were developed and a minimum of about 5 × 105 total phage particles was detected.

‘Substrate-accelerated death’ (Postgate & Hunter, 1963a, 1964) was observed with carbon-limited but not ammonium-, phosphate- or sulphate-limited Aerobacter aerogenes grown at 37° in defined medium and starved at 37° in aerated saline buffers containing the growth-limiting substrate. Carbon sources besides the one limiting growth increased the death-rate of starved mannitol-, glycerol-, galactose- and ribose-limited bacteria. Glycerol-accelerated death depended on the rate of oxidation of glycerol and the bacterial concentration; with bacteria fully adapted to glycerol, populations of less than 1-2 x 109 organisms/ml. died at a faster rate the denser the population and above this concentration the death-rate decreased with increasing bacterial concentration. Death was delayed when aerated bacterial suspensions containing glycerol were dialysed at 37° against saline buffer containing the substrate. Bacteria-free filtrates, from populations dying in the presence of glycerol, accelerated the death of fresh bacteria to a greater extent than did glycerol alone. In contrast, bacteria-free filtrates from dense populations surviving in the presence of glycerol partially protected fresh bacteria exposed to glycerol. Mg2+ abolished glycerol-accelerated death but not the lethal effect of filtrates from dying populations. Compared with its influence on glycerol-accelerated death, population density had much less influence on the death-rate of glycerol- or mannitol-limited organisms starved in the presence of glucose or mannitol. Irrespective of bacterial concentration, α-ketoglutarate had no effect and pyruvate, citrate, malate, succinate and oxalacetate had less effect than glycerol on the death-rate of starved glycerol-limited bacteria.

SUMMARY: Aqueous extracts of disintegrated spores of Bacillus cereus and non-virulent B. anthracis contained an enzyme which produced visible lysis of the isolated cell walls of vegetative B. cereus. Optimum activity occurred at pH 7-8 in the presence of cobalt or manganese ions (10 p.p.m.) at 58°. Activity was destroyed during heating at 100° for 15 min. The lytic preparation released non-dialysable components containing αe-diaminopimelic acid (DAP), glutamic acid, alanine, amino sugars and glucose. Although lysis was less obvious, the enzyme preparation released similar material from cell walls of other Bacillus species, spore coats of B. megaterium and coats of autoclaved B. cereus spores. Extracts of freshly harvested B. cereus spores were more active than those from spores which had been stored for several weeks at 2°. Extracts from disintegrated spores of B. megaterium had no enzymic activity; the enzyme system was associated with the insoluble spore coat fraction. The action of the enzyme differed from that of lysozyme or glucosaminidase; the reaction products did not give a significant reaction for N-acetylhexosamine and visible lysis proceeded more rapidly with cell walls of B. cereus than with B. megaterium. Possible functions of the enzyme may be to release ‘spore peptide’ from the spore coat during germination and to lyse the sporangium and free the spore during sporulation.

SUMMARY: When washed sporulating cells of Bacillus cereus were incubated in buffer at 37°G in the presence of toluene, a partial autolysis occurred resulting in the freeing of mature and immature spores. The autolysate contained lytie enzymes which attacked vegetative cells and cell-wall preparations, releasing hexosaminecontaining peptides of characteristic constitution. The most active enzyme preparations were obtained from sporulating cells incubated for 1-2 hr. in buffer at pH 5-0-6-0. Two water-soluble lytic systems, enzyme V and enzyme S with pH optima near 4-5 and 8-0 respectively, were separated from the autolysate. Enzyme S is probably identical with the lytic system present in spores of B. cereus and other Bacillus species and further observations on this system are described. When non-sporulating cells of B. cereus were incubated under similar conditions no obvious lysis or sporulation occurred and no cell-wall lytic activity could be demonstrated. In growing cultures of Bacillus cereus, considerable amounts of hexosamine-containing peptides were released into the medium during the period between the appearance of intracellular spores and free spores. It is suggested that enzyme V may be mainly concerned with the release of free spores from sporangia and enzyme S with the lytic processes which accompany spore germination.

SUMMARY: An assay for rapidly detecting and determining sparse populations of vegetative bacteria or bacterial spores (minimum number about 500; 2 to 4 x 10-10g. equivalent bacterial dry weight) is described. A sample is treated with 125I-labelled purified homologous antibody, filtered and washed on a Millipore membrane filter, and the radioactivity of the separated labelled immune complex is measured. The assay is specific, accurate and completed within 8 to 10 min. Sensitivity and accuracy decrease if the assay is applied to samples that contain particulate matter that non-specifically attaches antibody and is retained by a membrane filter. This type of interference is decreased by pretreating samples with clarified normal rabbit serum for a few minutes before assay.

SUMMARY: The death-rate of washed exponential phase Aerobacter aerogenes chilled in saline phosphate buffer (pH 6.5) at 0° was increased by ribonuclease (RNase) but not by deoxyribonuclease, trypsin, pepsin or lysozyme; none of these enzymes had any immediate effect on the viability of similar bacterial suspensions at 20°. Leakage products from chilled A. aerogenes, Mg2+ and, to a smaller extent, 0.3M-sucrose, antagonized the lethal effect of RNase on chilled organisms. RNA degradation occurred when bacteria were chilled and then incubated in fresh diluent at 37°; organisms exposed to RNase during chilling degraded RNA at 20-25° when the rate of auto-degradation of RNA was low. As the salt content of the environment was decreased, the amount of RNase adsorbed by the bacteria and its lethal effect increased at both 0° and 20°; in distilled water RNase was more lethal at 20° than at 0°. Anilino-naphthalene-8-sulphonate penetrated into bacteria chilled in buffer containing this dye. Acid or alkali accelerated the death rate of bacteria to greater extents at 0° than at 20°. RNase increased the lethal effect of freezing and thawing on a population from a continuous culture and augmented subsequent degradation of RNA.

SUMMARY: The lethal effect of cold shock on Aerobacter aerogenes suspensions depended on the time of exposure to low temperature, the growth phase, the concentration of bacteria, the diluent. No death occurred when weak suspensions of susceptible bacteria (about 108/ml.) in buffered saline (pH 6.5) were rapidly cooled to 0° and immediately warmed to 20°, but loss of viability was progressive during 1 hr. at 0°. Bacteria harvested from defined medium at intervals during the exponential growth phase varied in sensitivity to chilling but were more susceptible than stationary phase organisms. While growing in partially synchronized culture the sensitivity of bacteria did not increase significantly during the division lag phase. The viability of dense suspensions (about 1010 bacteria/ml.) in buffered saline was little affected by chilling for 1 hr. at 0°, irrespective of the growth phase. A bacteria-free filtrate from a chilled concentrated suspension of exponential-phase organisms substantially protected a dilute suspension from the lethal effect of chilling. Substances found in protective filtrates were amino acids, adenosine triphosphate and nucleic acid constituents. When added to the diluent in which susceptible bacteria were chilled, a mixture of amino acids afforded some protection; small amounts of adenosine triphosphate had no effect. Other substances found to protect susceptible bacteria were sucrose (0.3 M), magnesium or calcium ions (5 x 10−3M) and, to a much smaller extent, spermine (10−5M). The present results support the suggestion that the lethal effect of chilling is at least partly due to interference with the functioning of a bacterial permeability control mechanism.

SUMMARY: The viability of microbial populations recovered from aerosols was determined by a slide culture technique and/or the radioactively labelled antibody method and the results were compared with those obtained by the more widely used Bacillus subtilis var. niger spore tracer technique. With Escherichia coli MRE 162, results with the three methods were in good agreement. Slide culture gave inaccurate results with Pasteurella tularensis, live vaccine strain (LVS) and E. coli MRE 160. Results with the spore tracer and radio-antibody methods in conjunction with determinations of viable numbers were in fair agreement when P. tularensis, E. coli MRE 160 and coliphage T 7 were tested.

SUMMARY: “Substrate-accelerated death” (Postgate & Hunter, 1963a; 1964) occurred when a nitrogen-limited variant of Aerobacter aerogenes NCTC 418 (Postgate & Hunter, 1962) was starved at growth temperature (37° or 40°) in aerated saline buffers containing ammonium ion; it was not observed when the parent strain of A. aerogenes or Escherichia coli (MRE 162) was grown and starved under similar conditions. Sulphate ion increased the lethal effect of ammonium ion on the variant and magnesium did not abolish either the effect of ammonium or ammonium + sulphate ions. The A. aerogenes variant differed from the parent strain in morphology, colonial appearance on nutrient agar, biochemical and immunological reactions and ability to synthesize polysaccharide. In ammonium-limited medium at 37° or 40° at a dilution rate near 0·25 hr−1 the variant contained 3-5% and the parent strain 12-16% of dry weight as polysacharide; in spent medium or phosphate buffer at 37° with added glycerol the rate of polysaccharide synthesis by the variant was about 25% that of the parent strain. When grown in nitrogen-deficient medium with excess glycerol in batch culture, populations of the variant containing 25% polysaccharide were obtained; the survival of the polysaccharide-rich variant was not affected by ammonium ion.

SUMMARY: The death-rate of washed Aerobacter aerogenes in aqueous suspension at 47° depended on the nature of the growth medium, the composition of the liquid used to wash and resuspend the bacteria, the bacterial growth phase, the bacterial concentration in heated suspensions, the pH value, the oxygen tension and the composition of the diluent in which bacteria were heated. The relative resistance of bacteria in different growth phases differed according to the growth medium and the washing fluid; stationary phase bacteria were not more resistant than exponential phase organisms under all conditions. Starvation increased the thermal resistance of exponential and stationary phase bacteria. High bacterial concentration favoured survival at 47° under most conditions; cell-free filtrate from a heated dense suspension (1010 bacteria/ml.) protected a sparser population of fresh bacteria (107-109/ml.) heated in it. Protective material in filtrate was heat-stable (100°/15 min.) and diffused through cellophan. The optimum pH value for survival at 47° was near pH 6·5. Aerobic conditions favoured survival in distilled water but not in salt solutions or phosphate saline (pH 6·5). The effects of various concentrations of NaCl and KCl on the survival of bacteria at 47° under aerobic conditions were different, K+ concentrations above 0·1 m being more lethal than equivalent concentrations of Na+; the lethal effect of heating in mixtures of these salts (total m > 0·1) increased with K+ concentration. Growth medium, Mg2+ (0·01–5 mm) and, to a lesser extent, Mn2+ (0·5 mm) or Co2+ (5 mm) decreased the death-rate, whereas ethylenediamine tetraacetic acid (mm), or various sugars, increased it. Mg2+ but not Mn2+ reversed the lethal effect of sugars. Generally, conditions which accelerated the death-rate of Aerobacter aerogenes at 47° also increased the rate of degradation of endogenous RNA. This was accompanied by an increase in the ultraviolet absorption of cold acid-extracts of bacteria and of the suspending fluid. Bacterial protein was degraded to a smaller extent. Depletion of RNA is probably not the primary cause of death at 47° but the effect on bacterial metabolism of a rapid increase in endogenous pool constituents resulting from RNA degradation may contribute to the lethal effect.

SUMMARY: The magnesium and RNA contents of Aerobacter aerogenes, growth-limited by Mg2+, K+, NH4+ or carbon source, in defined media at 35° increased with growth rate. The results support the view that the amounts of these constituents are functions of the growth rate and are inter-dependent. Up to 26% of the total Mg2+ of bacteria freshly harvested from cultures containing excess magnesium was loosely bound to the bacterial surface; this adsorbed Mg2+ was removed by washing with 0·85% (w/v) NaCl but was unaffected by distilled water. Mg2+-limited bacteria had no surface-adsorbed magnesium. Surface-adsorbed Mg2+ stimulated polysaccharide synthesis, and affected the response of bacteria in saline buffer to stresses including starvation, heat-accelerated and substrate-accelerated death, and cold shock.

SUMMARY: Aerosolization decreased the accumulation of methyl-[α-D-gluco]pyranoside (αMG) in two strains of Escherichia coli. The inactivation was apparently not due to damaged permeases but to detachment from the bacteria of components involved in the transport of substrates through bacterial membranes. Transport activity was partially restored when aerosolized bacteria were incubated with leaked components. Aerosolization also decreased accumulation of isopropyl-thio-β-D-galactopyranoside (IPTG) by E. coli but increased permeability to O-nitrophenyl-β-D-galactopyranoside (ONPG). Loss in viability of airborne bacterial populations correlated with the decrease in αMG accumulation by bacteria recovered from aerosols one second after generation of the cloud.