Decline In Viable Numbers Research Articles

Survival of Campylobacter jejuni during stationary phase: evidence for the absence of a phenotypic stationary-phase response.

When Campylobacter jejuni NCTC 11351 was grown microaerobically in rich medium at 39 degrees C, entry into stationary phase was followed by a rapid decline in viable numbers to leave a residual population of 1% of the maximum number or less. Loss of viability was preceded by sublethal injury, which was seen as a loss of the ability to grow on media containing 0.1% sodium deoxycholate or 1% sodium chloride. Resistance of cells to mild heat stress (50 degrees C) or aeration was greatest in exponential phase and declined during early stationary phase. These results show that C. jejuni does not mount the normal phenotypic stationary-phase response which results in enhanced stress resistance. This conclusion is consistent with the absence of rpoS homologues in the recently reported genome sequence of this species and their probable absence from strain NCTC 11351. During prolonged incubation of C. jejuni NCTC 11351 in stationary phase, an unusual pattern of decreasing and increasing heat resistance was observed that coincided with fluctuations in the viable count. During stationary phase of Campylobacter coli UA585, nonmotile variants and those with impaired ability to form coccoid cells were isolated at high frequency. Taken together, these observations suggest that stationary-phase cultures of campylobacters are dynamic populations and that this may be a strategy to promote survival in at least some strains. Investigation of two spontaneously arising variants (NM3 and SC4) of C. coli UA585 showed that a reduced ability to form coccoid cells did not affect survival under nongrowth conditions.

The effect of slurry storage and anaerobic digestion on survival of pathogenic bacteria

The decline in viable numbers of Salmonella typhimurium, Yersinia enterocolitica and Listeria monocytogene in beef cattle slurry is temperature-dependent; they decline more rapidly at 17 degrees C than at 4 degrees C. Mesophilic anaerobic digestion caused an initial rapid decline in the viable numbers of Escherichia coli, Salm. typhimurium, Y. enterocolitica and L. monocytogenes. This was followed by a period in which the viable numbers were not reduced by 90%. The T90 values of E. coli, Salm. typhimurium and Y. enterocolitica ranged from 0.7 to 0.9 d during batch digestion and 1.1 to 2.5 d during semi-continuous digestion. Listeria monocytogenes had a significantly higher mean T90 value during semi-continuous digestion (35.7 d) than batch digestion (12.3 d). Anaerobic digestion had little effect in reducing the viable numbers of Campylobacter jejuni.

Effect of temperature and pH on survival of Listeria monocytogenes in coleslaw

The survival and growth of Listeria monocytogenes in fresh coleslaw, pH3.9, and in coleslaw adjusted to pH 4.0, 5.0, 6.0 or 7.0 before inoculation was studied at three temperature (4, 15 and 25°C). L. monocytogenes was not detectable after 5 days incubation in fresh coleslaw nor in coleslaw adjusted to pH 4.0. Coleslaw at pH 5.0 was also inhibitory to L. monocytogenes at all three temperatures studied. A decline in viable numbers of L. monocytogenes in coleslaw at pH 6.0 occurred at 4°C and at 15°C, whereas at 25°C the viable count of L. monocytogenes increased initially and remained high after incubation for 25 days. L. monocytogenes grew rapidly in coleslaw at pH 7.0 at all the three temperatures studied, followed by an equally rapid decline in viable count.

Synchronized division of avian pleuropneumonialike organisms.

Kelton, William H. (University of Massachusetts, Amherst). Synchronized division of avian pleuropneumonia-like organisms. J. Bacteriol. 83:948-955. 1962.-Evidence indicates that phosphate-buffered 0.85% saline (pH 7.0) is toxic when used for diluting cultures of pleuropneumonia-like organisms (PPLO). A technique for picking single PPLO colonies and streaking on agar medium is described. Growth curves of eight strains of PPLO of avian origin are described. Strain S-6 showed a typical growth curve. The other strains presented the lag and logarithmic phases of growth, followed by a rapid decline in viable numbers and peaks of growth later. Additional studies showed that growth was logarithmic in young cultures of all strains. Synchronization of division of two avian strains of PPLO appeared to have been induced by starvation for horse serum. Studies of small populations of PPLO were also made. The results of these experiments, along with the logarithmic growth, favor binary fission as the mode of reproduction.

Studies in the dynamics of disinfection: XII. The effect of variation in pH on the rate of disinfection at 51°C. of standard cultures of Bact. coli.

1. Standard Bact. coli cultures have been heated at 51° C. in phosphate buffered media having pH values ranging from 2·8 to 8·8, and survivor curves obtained.2. Except at pH 3·9, the first continuous decline in viable numbers was followed by the establishment of a small fluctuating residual population which was apparently permanent.3. The colony counts showed a moderate excess of unduly high values of x2, the bulk of which were encountered when the mortality was between 95 and 99·999%.4. Prolonged incubation of the plates led to increased colony counts, but the rise was confined to the active disinfection phase. It occurred chiefly in the 95–99·999% mortality range and was moderate in degree. The x2 values were little affected.5. The log survivors-time graphs of the disinfection phase were convex in type but approached linearity in the faster reactions. The logarithmic death-rate became maximal at about 90 % mortality and thereafter remained constant, though under the more acid conditions a somewhat lower rate was maintained. At pH 7·0 and 6·4 the curves were exceptionally straight.6. Standardization of all the curves revealed a continuous change in shape with pH but, nevertheless, they could be placed in three closely knit overlapping groups which were best revealed by the variation in maximum death-rate.7. The 50–99·99% mortality times were obtained either from the calculated regressions of log survivors on time over the linear portions of the curves or, outside that range, from the freehand curves. Maximum survival at all mortality levels occurred at about pH 6·5–6·6, i.e. close to the neutral point of pure water at 51° C. On both sides of this point sensitivity increased regularly but was abnormally high at pH 7·0 and 6·4.8. Within these zones of abnormally high sensitivity the assessment of the effect of a given change in pH varied in amount and direction according to the mortality level chosen.9. The enhanced resistance of a culture regenerated from the survivors of a disinfection at 51° C. and pH 7.0, as previously reported, could possibly have been largely due to a small increase in acidity but not to a slight shift towards alkalinity.