Development of a method for the quantitative assessment of microorganism sensitivity to antibiotics using discs. The study of different nutrient media for determining microorganism sensitivity to antibiotics

Five nutrient media used for determination of microbial sensitivity to antibiotics, i.e. beaf-peptone agar, Hottinger pancreatic beaf infusion agar, sprat hydrolysate nutrient agar of the Dagestan Research Institute of Nutrient Media, Muller-Chintone agar from Bulgaria and "Oxoid" agar for determination of microbial sensitivity were studied comparatively. The media were compared with respect to the growth density with the use of different test-cultures and the clearance of the inhibition growth zones around the discs containing different antibiotics. The best results were obtained with the use of sprat hydrolysate nutrient agar. Further studies on the medium standardization are necessary.     

Determination of the sensitivity of bacteria to barium ions,a taxonomic marker of the genus <Emphasis Type="Italic">Pseudomonas</Emphasis>

Comparative efficacy of the determination of the sensitivity of bacterial cells to barium ions was evaluated on a synthetic nutrient medium, FMH agar, Mueller-Hinton agar, and AGV agar. The synthetic nutrient medium developed for this study contained L-proline and L-glutamine as the sole nitrogen and carbon source, which promoted growth of all Pseudomonas strains and ensured the minimal level of barium binding. The sensitivity of 80 strains belonging to 11 Pseudomonas species, including the type strains, as well as of 80 strains of 22 other bacterial species, was studied. The sensitivity of bacteria to barium ions was determined by using serial dilutions of barium chloride in the nutrient medium. The highest level of analytical sensitivity of pseudomonads to barium ions was determined on the synthetic nutrient medium: the minimal inhibitory concentration (MIC) values of barium chloride ranged from 0.5 to 6 g/L, the MIC₉₀ value was 2 g/L. At the same time, 86.1% of all strains of fluorescent Pseudomonas species produced fluorescein on the control BaCl₂-free synthetic nutrient medium. For representatives of other genera grown on all the studied nutrient media, the MIC values of barium chloride ranged from 20 to 50 g/L. The proposed method for determination of the sensitivity of bacteria to barium ions using the synthetic nutrient medium with 6 g/L of barium chloride as a criterion for the classification of barium-sensitive strains to the genus Pseudomonas is suitable for standardization.     

5-Fluoroorotate-resistant mutants of Salmonella typhimurium.

Spontaneously occurring mutants of Salmonella typhimurium resistant to 5-fluoroorotate (5-FOA) were isolated. One class of mutant showed marked derepression of pyrimidine biosynthetic enzymes and had the unusual property of being unable to grow on nutrient agar. However, when the osmotic strength of nutrient agar was increased, the mutants were able to grow. The genetic basis for the osmotic fragility and elevated pyr enzyme synthesis was the result of mutations affecting pyrH, encoding the enzyme uridine 5'-monophosphate kinase.     

Development of an accelerated method of determining the antibiotic sensitivity of Cl. perfringens type A]

An express method for determination of antibiotic sensitivity in the strains of Cl. perfringens of type A using Soviet dry nutrient media and antibiotics is proposed. The criteria for estimation of the level of the antibiotic sensitivity of the causative agent of gas gangrene in short periods on the basis of comparison of the data of the antibiotic agar diffusion procedure and the antibiotic MIC were worked out. Twelve antibiotics and 45 collection strains of Cl. perfringens of type A were used in the experiment. The antibiotic agar diffusion method with the use of the nutrient media, microbial load and cultivation conditions developed by the authors is recommended for tentative determination of the antibiotic sensitivity in Cl. perfringens of type A for 4 hours. The use of the agar diffusion method and determination of the antibiotic MIC provided complete estimation of tha antibiotic sensitivity of Cl. perfringens of type A within not more than 24 hours.     

Postirradiation recovery dependent on the uvr-1 locus in Bacillus subtilis.

A mutant (uvr-1) of Bacillus subtilis that is deficient in excision of ultraviolet (UV)-induced pyrimidine dimers from deoxyribonucleic acid (DNA) shows a marked increase in ability to survive UV irradiation when plated on amino acid-supplemented agar medium compared with its survival ability when plated on nutrient plating medium, the effect is considered to be one of growth-dependent lethality. Irradiated stationary phase uvr-1 cells, incubated in liquid medium lacking amino acids required for growth, recover from this sensitivity to rich medium within 3 to 4 h after irradiation. Recovery is greatly reduced in the absence of glucose oiminated. Exponentially growing cells have a limited ability to recover from sensitivity to rich medium. Growth-dependent lethality can also occur in liquid medium. In nutrient broth the ability of irradiated stationary-phase uvr-1 cells to form colonies on defined agar medium decreases during postirradiation incubation, but treatmeth with chloramphenicol inhibits the loss of colony-forming ability. Recovery from sensitivity to rich media is inhibited by caffeine but not by 6-(p-hydroxyphenylazo)-uracil, and inhibitor of DNA replication. Alkaline sucrose gradient profiles show that conditions allowing recovery also favor maintaining intact DNA strands, whereas DNA strand breakage or degradation is associated with loss of viability. Recovery from sensitivity to rich medium has not been observed in the Ur+ parent or in strains carrying the mutations uvs-42 (another deficiency in dimer excision), recA1, or polA59. A uvr-1 recA1 mutants shows a higher level of recovery than does the recA1 single mutant, but a much lower level than the uvr-1 single mutant. Apparently, both the uvr-1 defect and Rec+ and PoII+ functions are essential for recovery from sensitivity to rich medium. For optimal recovery, growth immediately after irradiation must be delayed. The process requires energy, apparently involves recombination, and probably results in rejoining of DNA strands in which incision but not excision has occurred.     

Standardization of the methods of determining microorganism sensitivity to antibiotics. The effect of the size of the inoculate on the results of determining microorganism sensitivity to antibiotics and its standardization

The literature data and personal observations of the authors on the effect of the inoculate amount on the results of determination of microbial sensitivity to antibiotics by the methods of serial dilutions in the liquid and solid nutrient media and agar diffusion are discussed. It was shown that the inoculate of the density of 3.6.10(7) to 4.25.10(7) microbial bodies per 1 ml was optimal for the methods of agar diffusion and serial dilutions in agar. Recommendations for simplifying standardization and dilution of the inoculate are presented.     

Peroxide sensitivity and catalase activity in Campylobacter jejuni after injury and during recovery

Cells of Campylobacter jejuni damaged by freezing or mild heat showed increased sensitivity to hydrogen peroxide and also required the addition of catalase for growth on nutrient agar. These phenomena, which could have important practical consequences, were not associated, however, with changes in total catalase activity and may be due to alterations in outer membrane permeability.     

Peroxide sensitivity and catalase activity in Campylobacter jejuni after injury and during recovery

Cells of Campylobacter jejuni damaged by freezing or mild heat showed increased sensitivity to hydrogen peroxide and also required the addition of catalase for growth on nutrient agar. These phenomena, which could have important practical consequences, were not associated, however, with changes in total catalase activity and may be due to alterations in outer membrane permeability.     

Selection in yeast II: The fitness distribution of new mutations inSaccharomyces cerevisiae and its use in a computer simulation

Summary The fitness distribution of new mutations inSaccharomyces cerevisiae strain Montrachet was determined for cells on agar irradiated for four periods of time with ultraviolet light. The fitness distributions were obtained by converting a large number of colony diameters into relative fitnesses. The distributions were then used to perform a computer simulation with the purpose of predicting the potential of a stock culture to increase in general fitness through selection, given a frequency and magnitude of mutations.     

Agarose/agar assay system for the selection of bacteriocin-producing lactic fermentation bacteria

The direct selection of bacteriocin-producing lactic fermentation bacteria was possible by plating diluted cultures of Pediococcus acidilactici on mixed agarose agar layers with the amount of each component incrementally adjusted to 1.2% (w/v). Between 0.5 and 1% agarose, the increased flexibility of the solidified support layer allowed its removal from Petri dishes without tearing and its smooth layering on the surface of 1.5% (w/v) standard agar medium seeded with Listeria innocua as the test organism. Selection of bacteriocin-producing clones was based on the size of inhibition zones visible in the bottom agar layer under colonies growing on the agarose/agar top layer. The lack of contact with the test organism permitted the transfer of superior clones from the surface of the agarose/agar layer directly into an appropriate nutrient medium.     

磷酸盐对V族大肠杆菌素形成的影响

含ColV质粒的大肠杆菌在含有磷酸盐的牛肉膏蛋白胨培养基上形成的菌落,当覆盖敏感菌后可以形成较大的抑菌圈。说明磷酸盐对ColV质粒所编码的V族大肠杆菌素的形成有促进作用。在培养基中加入二价离子螯合剂——EDTA对大肠杆菌素形成同样有促进作用,而增加二价阳离子Ca++或Mg++却起到相反的作用。磷酸盐的这种促进作用是由于它降低了牛肉膏蛋白胨培养基中二价阳离子的浓度而引起的。因此,在培养基中添加磷酸盐有助于分离ColV质粒含有菌和对V族大肠杆菌素的研究。     

Mutation induction in haploid yeast after split-dose radiation-exposure

Summary Mutation induction was investigated in wild-type haploid yeastSacchaomyces cerevisiae after split-dose UV-irradiation. Cells were exposed to fractionated 254 nm-UV-doses separated by intervals from 0 to 6 h with incubation either on non-nutrient or nutrient agar between. The test parameter was resistance to canavanine. If modifications of sensitivity due to incubation are appropriately taken into account there is no change of mutation frequency.     

Direct quantitative method for evaluating the effect of biocides on Pseudomonas fluorescens in different culture media

A method for quantitative evaluation of the effects of biocides is presented. The method was tested in experiments with Pseudomonas fluorescens grown on various agar nutrient media. The effective concentrations of biocides that decreased the maximum specific rate of the colony biomass growth (mu'm) were called S (suppressing) concentrations, and concentrations that decreased the number of colony-forming units (CFU) were taken as L (sublethal) concentrations. The efficiency of the reported approach was demonstrated in experiments with three biocides tested in four nutrient media. It was found that the biocide sensitivity of Pseudomonas fluorescens varied by a factor of 30, depending on the amount and the type of the nutrient substrate.     

Suppression of initiation-negative strains of Escherichia coli by integration of the sex factor F.

Data are presented suggesting that the most critical factor determining whether an Hfr dnaAts strain can synthesize deoxyribonucleic acid and form colonies at temperatures that are nonpermissive for corresponding F- strains is neither the site of insertion of F nor the presence of additional mutations in the F particle or the chromosome; it is whether the particle is capable of autonomous replication at the temperature used. Consequently, suppression of the DnaA phenotype in Hfr strains occurs at 40 C but not, in most of them, at 42 C without the occurrence of additional mutations. The site of insertion of F may also be important since it is shown that in one Hfr dnaA strain partial suppression does occur at 42 C. In addition, it is shown that strains exhibiting suppression by integration of F at 40 C on minimal agar plates do not do so at this temperature on nutrient agar plates.     

A note on a selective agar medium for the enumeration of Flavobacterium species in water

A selective nutrient agar medium containing kanamycin at 50 μg/ml was developed for the isolation and enumeration of yellow-pigmented colonies from the River Sowe, Coventry. Such organisms were shown to be members of the heterogeneous genus Flavobacterium . Typically, yellow pigmented colonies constituted less than 10% of the colonies on nutrient agar alone but up to 70% on nutrient agar plus kanamycin. This medium is a useful addition to the range of media available for the isolation and further ecological study of particular species of this important group of micro-organisms.     

A note on a selective agar medium for the enumeration of Flavobacterium species in water

A selective nutrient agar medium containing kanamycin at 50 micrograms/ml was developed for the isolation and enumeration of yellow-pigmented colonies from the River Sowe, Coventry. Such organisms were shown to be members of the heterogeneous genus Flavobacterium. Typically, yellow pigmented colonies constituted less than 10% of the colonies on nutrient agar alone but up to 70% on nutrient agar plus kanamycin. This medium is a useful addition to the range of media available for the isolation and further ecological study of particular species of this important group of micro-organisms.     

A novel and cost effective methodology for qualitative screening of alkalo-thermophilic cellulase free xylano-pectinolytic microorganisms using agricultural wastes

Qualitative screening of alkalo-thermophilic cellulase free xylano-pectinolytic microorganisms was done on agricultural residues. Since xylan is an expensive substrate for the isolation of xylanase producing microorganisms, the possibility of using wheat bran for screening of these microorganisms was investigated. Screening was carried out on wheat bran for the selection of xylanolytic microorganisms, on waste paper for the evaluation of cellulase free xylanolytic microorganisms, and on citrus peel for screening of pectinolytic microorganisms. Qualitative analysis of xylanase, pectinase and cellulase activities depicted that the zones obtained on nutrient agar medium containing agricultural residues were apparent and comparable with the zones obtained on nutrient agar medium containing commercial substrates. A strategy of using cost effective wheat-bran, wastepaper and citrus-peel for the isolation of cellulase free xylano-pectinolytic microorganisms is a novel and promising method and will ultimately bring down the cost of screening of these enzyme producing microorganisms.     

A comparison of solid and liquid media for measuring the sensitivity of heat-injured Salmonella typhimurium to selenite and tetrathionate media, and the time needed to recover resistance

Sensitivity of heat-injured Salmonella typhimurium to selenite and tetrathionate media was measured by viable counts in liquid and on agar-solidified versions of these media and on nutrient media. All solid media, including the supposedly non-inhibitory nutrient agar, were more inhibitory to injured cells than the corresponding liquid media. Catalase or pyruvate increased counts on nutrient agar to the level obtained in nutrient broth. Therefore nutrient agar plus pyruvate was the most suitable reference medium against which to compare recoveries on other media. Although recoveries of injured cells varied widely depending on the composition and physical state of the medium, this had a minor effect on estimates of repair time because resistance to all selective media was regained by the end of the lag phase.     

WL营养琼脂对葡萄酒相关酵母的鉴定效果验证

利用WL营养琼脂对采自葡萄园和葡萄汁发酵过程中的35株酵母菌进行了分类鉴定,同时进行了5.8S-ITS和26S rDNA D1/D2区的扩增与测序。结果表明利用WL营养琼脂的鉴定结果与测序结果基本符合。WL营养琼脂是一种较为有效的葡萄酒相关酵母菌的分类鉴定培养基。     

THE FAILURE OF PHENOL TREATED ESCHERICHIA COLI TO GROW ON MEMBRANE FILTERS

SUMMARY: Counts of Escherichia coli were done on nutrient agar (control), on membrane filters on nutrient agar and on membrane filters on filter paper pads. With untreated bacteria counts were similar under all conditions, though membrane filters on nutrient agar tended to give slightly low counts. Phenol treated bacteria gave much lower counts when membrane filters were used: the mean counts for 3 strains of the test organism with filters on nutrient agar varied from 35–65% of the control, while counts with filters on filter paper pads were somewhat lower, varying from 30–47% of the control. The low counts on membrane filters on filter paper pads were not due to adsorption of phenol by the filters or to a low concentration of nutrients in the growth medium.