A note on the use of 3-section plates for the estimation of the numbers of bacteria and to obtain isolated colonies in 1 day

By streaking with an open loop and then swabbing a 4-5 cm2 area on 3-section agar plates, it is possible to obtain isolated colonies and to estimate bacterial densities from 100 to 10(7)/ml on the swabbed area.     

A note on the estimation of allele frequencies

A new method of obtaining allele frequency estimates is described. The method may prove useful when maximum likelihood estimates are not available. No assumptions regarding the absence of alleles are required. Errors of estimates have not been obtained, but the process seems to converge to maximum likelihood.     

A note on the estimation of evoked response

The traditional average evoked response is compared and contrasted with several alternate estimates, derived from frequency domain considerations, for a model of evoked responses superimposed upon a stationary noise series. Further, a means of constructing approximate confidence intervals for the values of an evoked response is indicated. The case of several simultaneously recorded series is also considered.Prepared with the support of the National Science Foundation Grant MCS 76-06117     

A note on the use of microwaves in an improved non-radioactive DNA hybridization procedure for the detection of bacteria in foodstuffs

Foodstuffs were artificially contaminated with Escherichia coli carrying plasmid pBR322, dot blotted onto nylon membranes and briefly subjected to microwaves in the presence of 1·5 mol/l NaC1/0·5 mol/l NaOH. Subsequent hybridization with a biotin-labelled probe specific for pBR322 enabled the detection of cell concentrations > 10⁴ cells/dot blot, equivalent to 2 × 10⁷ cells/g food tested. This shortened and simplified method was effective for all ten foods tested, generated low background levels and should be applicable to a wide range of bacteria.     

A Most Probable Number method (MPN) for the estimation of cell numbers of heterotrophic nitrifying bacteria in soil

A Most Probable Number (MPN) method was developed allowing for the first time estimation of populations of bacteria capable of heterotrophic nitrification. The method was applied to an acidic soil of a coniferous forest exhibiting nitrate production. In this soil nitrate production was unlikely to be catalyzed by autotrophic nitrifiers, since autotrophic ammonia oxidizers never could be detected, and autotrophic nitrite oxidizers were usually not found in appreciable cell numbers. The developed MPN method is based on the demonstration of the presence/absence of nitrite/nitrate produced by heterotrophic nitrifying bacteria during growth in a complex medium (peptone-meat-extract softagar medium) containing low concentrations of agar (0.1%). Both the supply of the growing cultures in MPN test tubes with sufficient oxygen and the presence of low agar concentrations in the medium were found to be favourable for sustainable nitrite/nitrate production. The results demonstrate that in the acidic forest soil the microbial population capable of heterotrophic nitrifcation represents a significant part of the total aerobic heterotrophic population. By applying the developed MPN method, several bacterial strains of different genera not previously described to perform heterotrophic nitrification have been isolated from the soil and have been identified by bacterio-diagnostic tests.     

A note on the conditional approach to interval estimation in the calibration problem.

In the calibration problem, the need to construct a confidence interval to estimate the unknown chi 0 arises when the null hypothesis of zero slope is rejected. Otherwise, the resulting confidence interval will be infinite to reflect the fact that the slope of the regression line may be zero. Under the condition of rejecting the hypothesis of zero slope, we study the properties of the conditional coverage rate of the calibration confidence interval. The conditional coverage rate (P1) is a function of the slope, distance between chi 0 and the mean of the trailing sample means, the sum of squares of chi, and n. When the true slope is close to 0 and chi 0 is away from means, P1 can go down to 0. On the other hand, as the power of testing zero slope reaches 1, with or without chi 0 close to means, P1 will tend to the desired nominal coverage rate. In summary, one should choose a reasonably small alpha in testing zero slope to avoid constructing a confidence interval for chi 0 when the true slope is 0. In addition, it is desirable to have high power in testing zero slope so that the resulting confidence interval will maintain the desired coverage rate when using the conditional approach in the calibration problem.     

A note on adhesion of bacteria to chicken muscle connective tissue

Laboratory cultures of bacteria were tested for the ability to attach to collagen fibres of intact chicken muscle connective tissue. All salmonellas, fimbriate strains of Escherichia coli and a strain of Campylobacter coli were able to attach to tissue only when suspended in distilled water. Prior immersion of tissue in sterile water for 20 min or extended immersion in these bacterial suspensions was a prerequisite for adhesion. Attachment could be prevented by the addition of physiological levels of sodium chloride to the attachment medium.     

A note on adhesion of bacteria to chicken muscle connective tissue

Laboratory cultures of bacteria were tested for the ability to attach to collagen fibres of intact chicken muscle connective tissue. All salmonellas, fimbriate strains of Escherichia coli and a strain of Campylobacter coli were able to attach to tissue only when suspended in distilled water. Prior immersion of tissue in sterile water for 20 min or extended immersion in these bacterial suspensions was a prerequisite for adhesion. Attachment could be prevented by the addition of physiological levels of sodium chloride to the attachment medium. Furthermore, attached bacteria could be removed by rinsing tissues in saline media.     

微囊藻群体细胞数量估算的一种简单方法

采用加酸水解和人工计数的方法,对巢湖铜绿微囊藻、放射微囊藻、惠氏微囊藻、坚实微囊藻、绿色微囊藻、挪氏微囊藻、水华微囊藻、鱼害微囊藻所含细胞数进行了估算.通过统计分析,建立了微囊藻群体最大投影面积与所含细胞数的回归方程模型,通过这些模型可以估算群体微囊藻所含的细胞数.     

Most-probable-number procedures for enumerating ruminal bacteria, including the simultaneous estimation of total and cellulolytic numbers in one medium

Based on results from eight experiments, no overall difference was found between roll tube and three- and five-tube most-probable-number (MPN) methods for estimating total numbers of ruminal bacteria. However, standard errors for the replicate means within an experiment were higher with the MPN procedures. Visual growth and pH were the criteria used for scoring the MPN tubes. Total numbers were significantly higher in MPN medium containing 40% ruminal fluid, as compared with a complete medium without ruminal fluid. By using a broth medium containing ball-milled cellulose and soluble carbohydrates as energy sources, it was possible to estimate both total and cellulolytic ruminal bacterial numbers in the same MPN series. Disappearance of cellulose and decrease in pH were used to determine growth. Values did not differ from those obtained in separate MPN assays. By using this method, diurnal changes in total and cellulolytic bacterial numbers were estimated in sheep fed forage or a concentrate-type diet.     

A note on the increased permeability of opsonized luminous bacteria

B arak , M., M erzbach D. & U litzur , S. 1985. A note on the increased permeability of opsonized luminous bacteria. Journal of Applied Bacteriology 59 , 57–59.
Opsonization of a dark variant of the luminous bacterium Photobacterium leiog-nathi by pooled human serum caused an increase in the permeability of the organism to actinomycin D, as judged by the inhibition of the proflavin-induced synthesis of its luminescence system.     

Septage treatments to reduce the numbers of bacteria and polioviruses

Disposal of the pumped contents of septic tanks (septage) represents a possible means of dissemination of enteric pathogens including viruses, since persistence of enteroviruses in septic tank sludge for greater than 100 days has been demonstrated. The risk of exposure to potentially infectious agents can be reduced by disinfecting septages before their disposal. Of the septage disinfectants examined (technical and analytical grade glutaraldehyde, hydrogen peroxide, heat treatments, and a combination of heat and hydrogen peroxide), the treatment including hydrogen peroxide (5 mg, plus 0.33 mg of trichloroacetic acid, per ml of septage) and 55 degrees C killed virtually all the bacteria in septage within 1 h, whereas 55 degrees C alone inactivated inoculated polioviruses within 30 min. Virus was the most sensitive to heat, whereas fecal coliforms appeared to be the most sensitive to all chemical treatments. The responses of fecal streptococci and virus to both grades of glutaraldehyde (each at 1 mg/ml) were similar. Virus was more resistant than either fecal streptococci or total bacteria to low concentrations of hydrogen peroxide (1 to 5 mg/ml); however, virus and fecal streptococci were more labile than total bacteria to the highest peroxide concentration (10 mg/ml) examined. It is possible that the treatment combining heat and hydrogen peroxide was the most effective in reducing the concentrations of all bacteria, because catalase and peroxidases as well as other enzymes were heat inactivated, although catalase seems the most likely cause of damage. However, this most effective treatment does not appear to be practical for on-site use as performed, so further work on septage disinfection is recommended.