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At least 631 records · Page 35Linked to original sources
PubMed1989

The killing action of fleroxacin upon Bacteroides fragilis.

The killing kinetics of fleroxacin against four strains of Bacteroides fragilis were investigated. Viable counts were determined from 0 to 24 h after exposure to fleroxacin at multiples of the MIC. A one to three log reduction in viable count was observed after 2 h at 8 mg/l fleroxacin, and a more rapid rate of killing was seen at greater concentrations of the antimicrobial agent. An increase in cell length was observed at concentrations at and above the MIC from 2 h after exposure. The presence of a bacteriostatic concentration of chloramphenicol had negligible influence on viability but inhibited cell elongation.

Anti-Bacterial Agents↗
PubMed1972

Storage of conidia of Penicillium chrysogenum in liquid nitrogen.

Conidiated slope cultures of derivative of Penicillium chrysogenum Wis 54-1255 were stored at -196 or +4 C for a period of 3.5 years. After this time, the viability fell to 68% in the former case and to 4% in the latter. At the end of the experiment, 65 single conidial isolates from each series were tested for penicillin yield. Among those from conidia stored at -196 C, the spread of penicillin yields did not differ markedly from that of 65 single conidial isolates made as controls prior to storage. However, 18% of those from conidia stored at +4 C formed a subpopulation with substantially lower penicillin titers than those of control isolates. Storage at -196 C may reduce or prevent a possible source of penicillin yield decay, namely, the selection of spontaneous mutants of low titer present in small numbers in the original culture and selected, as viability decreased, by virtue of their increased longevity relative to that of the parental culture.

Cell Survival↗
PubMed1983

Effects of culture age on symbiotic infectivity of Rhizobium japonicum.

The infectivity of the soybean symbiont Rhizobium japonicum changed two- to fivefold with culture age for strains 110 ARS, 138 Str Spc, and 123 Spc, whereas culture age had relatively little effect on the infectivity of strains 83 Str and 61A76 Str. Infectivity was measured by determining the number of nodules which developed on soybean primary roots in the zone which contained developing and preemergent root hairs at the time of inoculation. Root cells in this region of the host root are susceptible to Rhizobium infection, but this susceptibility is lost during acropetal development and maturation of the root cells within a period of 4 to 6 h (T. V. Bhuvaneswari, B. G. Turgeon, and W. D. Bauer, Plant Physiol. 66:1027-1031, 1980). Profiles of nodulation frequency at different locations on the root were not affected by the age of the R. japonicum cultures, indicating that culture age affected the efficiency of Rhizobium infection rather than how soon infections were initiated after inoculation. Inoculum dose-response experiments also indicated that culture age affected the efficiency of infection. Two strains, 61A76 Str and 83 Str, were relatively inefficient at all culture ages, particularly at low inoculum doses. Changes in infectivity with culture age were reasonably well correlated with changes in the proportion of cells in a culture capable of binding soybean lectin. Suspensions of R. japonicum in water were found to retain their viability and infectivity.

Anti-Bacterial Agents↗
PubMed2001

Identification and characterization of a second superoxide dismutase gene (sodM) from Staphylococcus aureus.

A gene encoding superoxide dismutase (SOD), sodM, from S. aureus was cloned and characterized. The deduced amino acid sequence specifies a 187-amino-acid protein with 75% identity to the S. aureus SodA protein. Amino acid sequence comparisons with known SODs and relative insensitivity to hydrogen peroxide and potassium cyanide indicate that SodM most likely uses manganese (Mn) as a cofactor. The sodM gene expressed from a plasmid rescued an Escherichia coli double mutant (sodA sodB) under conditions that are otherwise lethal. SOD activity gels of S. aureus RN6390 whole-cell lysates revealed three closely migrating bands of activity. The two upper bands were absent in a sodM mutant, while the two lower bands were absent in a sodA mutant. Thus, the middle band of activity most likely represents a SodM-SodA hybrid protein. All three bands of activity increased as highly aerated cultures entered the late exponential phase of growth, SodM more so than SodA. Viability of the sodA and sodM sodA mutants but not the sodM mutant was drastically reduced under oxidative stress conditions generated by methyl viologen (MV) added during the early exponential phase of growth. However, only the viability of the sodM sodA mutant was reduced when MV was added during the late exponential and stationary phases of growth. These data indicate that while SodA may be the major SOD activity in S. aureus throughout all stages of growth, SodM, under oxidative stress, becomes a major source of activity during the late exponential and stationary phases of growth such that viability and growth of an S. aureus sodA mutant are maintained.

Amino Acid Sequence↗
PubMed1998

Growth and survival of Helicobacter pylori in defined medium and susceptibility to Brij 78.

The gastrointestinal pathogen Helicobacter pylori requires supplementation with either fetal calf serum (FCS), bovine serum albumin (BSA), or (2,6-dimethyl)-beta-cyclodextrin (CD) for growth in a complex or defined medium. Because the availability of medium in which all components were chemically defined would facilitate metabolic studies of H. pylori, growth of the type strain, ATCC 43504, was compared in a defined medium with different growth additives. The dependency of H. pylori growth on FCS or BSA in a defined medium could partially be replaced by dependency on CD and cholesterol when the last two components were both added to the defined medium. Growth and cell yield were not affected by the addition of glucose, but the culture viability (numbers of CFU per milliliter was extended. Because therapeutic antifoams are used to relieve gastrointestinal symptoms we studied whether the unique susceptibility of H. pylori to the emulsifier polyoxyethylene-20-stearylether (Brij 78) was growth dependent or medium specific. The bactericidal activity exerted in buffer at pH 5 was independent of the preculture medium, and a 5-h exposure of the bacteria to 1.28 to 2.56 microg of Brij 78 per ml reduced the numbers of viable bacteria by >5 log10. The MICs (0.16 to 0.32 microg/ml) were lower than the corresponding minimal bactericidal concentrations in different growth media and were affected by FCS or BSA. In conclusion, CD plus cholesterol promotes the growth of H. pylori in a serum-free defined medium in which glucose enhances cell viability. The antibacterial activity exerted by Brij 78 is neither growth dependent nor medium specific.

Colony Count, Microbial↗
PubMed1990

[The problems of microbial indication of water quality].

In three experimental series the reliability of contemporary microbial indicators has been verified. It was shown that about 30% colonies growing on the Endomedium belongs not to family Enterobacteriaceae. The share of the so-called faecal coliforms growing at 44 degrees C is 54.6%. In comparison with the initial cultivations at the second passage this part increasing at about 126%. In waters of various quality is the viability of E. coli the smallest. Also on the Mc Conkey medium at 44 degrees C disappeared the colonies in order: E. coli (3-14 days), K. pneumoniae (3-21 days) C. freundii (21-28 days). This results brings an evidence that the existing indicator system for water quality should be revised.

Citrobacter↗
PubMed2001

Improved methods for the enumeration of heterotrophic bacteria in bottled mineral waters.

At this time the European Union regulations require that the heterotrophic plate counts (HPC) of mineral waters be assessed at two recovery temperatures: 22 degrees C for 72 h and 37 degrees C for 24 h. This procedure is time consuming and expensive. Development of new rapid methods for microbiological assessment of the microbial flora in the bottled water is an industry-driven need. The objectives of this work were to develop a method for the HPC that utilises only one recovery temperature and one incubation period and evaluate the use of, the LIVE/DEAD(R) BacLight Bacterial Viability Kit, 5-cyano-2,3-ditotyl tetrazolium chloride (CTC) and impedance methods to enumerate viable bacteria in bottled mineral water. Results showed that incubation at 30 degrees C could be used instead of incubation at 22 degrees C and 37 degrees C. Good correlation exists between counts at 30 degrees C and counts at 22 degrees C (r>0.90) and all the pathogens important in mineral water analyses grow similarly at 30 degrees C and 37 degrees C during 24 h. It was demonstrated that impedance methods might be useful to the mineral water industry as a rapid indicator of microbiological quality of the water. Results obtained with BacLight and CTC were similar to those obtained with plate counts.

Bacteria↗
PubMed2000

Nucleic acid-based fluorescent probes in microbial ecology: application of flow cytometry.

Microorganisms in natural environments have often been treated as 'black box' systems. Researchers have measured the inputs and outputs of the box, and have made bulk measurements on cell behaviour. However, unravelling the details of the diversity and interactions that exist within these microbial populations has proven exceptionally difficult. The information gained from the black box approach has been invaluable, and has allowed models of global foodwebs to be generated and tested. However, there is still little information about the interactions of individual microbial cells within natural populations. Such studies are essential to fully understand the integrated functioning of ecosystems. To achieve this goal, researchers need to be able to identify individual cells within a population, enumerate them, estimate both viability and activity, and monitor changes in response to relevant parameters. Due to the diversity, heterogeneity and numbers of cells that make up these populations, these measurements require automation and speed. At present, the use of flow cytometry in conjunction with nucleic acid probes provides an excellent method with which to pursue such studies.

Bacteria↗
PubMed2005

Application of a microplate scale fluorochrome staining assay for the assessment of viability of probiotic preparations.

Cell viability in probiotic preparations is traditionally assessed by the plate count technique. Additionally, fluorescent staining combined with epifluorescence microscopy or flow cytometry has been developed for the viability assessment, but the currently available assays are either laborious or require highly sophisticated equipment. The aim of this study was to investigate the applicability of a microplate scale fluorochrome assay for predicting the cell state of freeze-dried Lactobacillus rhamnosus and Bifidobacterium animalis subsp. lactis preparations. In addition to viability assessment with LIVE/DEAD BacLight Bacterial Viability Kit, DiBAC(4)3 stain was used for the kinetic measurement of changes in bifidobacterial cell membrane functions during exposure to low pH. The microplate scale fluorochrome assay results on the viability and cell numbers of probiotic preparations correlated well with the results obtained with the culture-based technique and (with few exceptions) with epifluorescence microscopy. The assay was applicable also for the viability assessment of stressed (acid-treated) cells provided that the cell density in treatments was adjusted to the optimal measurement level of the fluorometer. The microplate scale fluorochrome assay offers a rapid and robust tool for the viability assessment of probiotic preparations, and enables also kinetic measurements.

Bifidobacterium↗
PubMed2006

A simple viability-maintaining method produces homogenic cell suspensions of autoaggregating wild-type Actinobacillus actinomycetemcomitans.

Tenacious adherence and autoaggregation of wild-type Actinobacillus actinomycetemcomitans strains jeopardize reliability of determined cell concentrations, e.g. for studies on bacteria-host interactions. We first compared the efficacy of two methods, an indirect and a direct method, for homogenizing cell suspensions of a wild-type, autoaggregating (SA269) strain and of a non-autoaggregating laboratory variant (ATCC 43718) used as a reference. Since the direct method left visible clumps in SA269 suspension, only the indirect method was further tested. In serial dilutions of the homogenized cell suspensions of strains SA269 and ATCC 43718, the OD600 values (R2=0.99, R2=0.99, respectively) and protein concentrations (R2=0.93, R2=0.95, respectively) correlated significantly (all P<0.002) with the dilution factor. There were no differences (P>0.05) in the bacterial viable counts between the two strains or between suspending solutions, i.e., PBS and water, the cell concentrations demonstrating 1x10(9) cells/ml at OD600=1. Repeated microscopic cell counts did not differ (P>0.05) from each other. Large aggregates occurred as 1% of cell units counted. Dispersing bacterial mass indirectly to solution leads to homogeneous cell suspensions with repeatable cell concentrations. Viability of A. actinomycetemcomitans was also maintained when cells were suspended in water.

Aggregatibacter actinomycetemcomitans↗
PubMed2004

Monitoring the cell number and viability of Lactobacillus helveticus GCL1001 in human feces by PCR methods.

Real-time polymerase chain reaction (PCR) and nested reverse transcription (RT) PCR were applied to demonstrate the viability of lactobacilli in the feces of volunteers fed fermented milk containing lactobacilli. Two sets of specific primers and a TaqMan probe for real-time PCR were constructed using the S-layer gene as a target. After fermented milk ingestion, Lactobacillus helveticus GCL1001 was detected in the feces of 12 volunteers over a few days, with the maximum number being between 10(4.5) and 10(7.8) cells g(-1) of feces. Moreover, mRNA from this strain was detected in the feces of all volunteers by nested RT-PCR. The results show that these methods are applicable to the demonstration of bacterial viability in feces, and that ingested L. helveticus GCL1001 can survive through the gastrointestinal tract.

Colony Count, Microbial↗
PubMed2000

Mitotic viability and metabolic competence in UV-irradiated yeast cells.

Colony formation is the classic method for measuring survival of yeast cells. This method measures mitotic viability and can underestimate the fraction of cells capable of carrying out other DNA processing events. Here, we report an alternative method, based on cell metabolism, to determine the fraction of surviving cells after ultraviolet (UV) irradiation. The reduction of 2,3,5-triphenyl tetrazolium chloride (or TTC) to formazan in mitochondria was compared with cell colony formation and DNA repair capacity in wt cells and two repair-deficient strains (rad1Delta and rad7Delta). Both TTC reduction and cell colony formation gave a linear response with different ratios of mitotically viable cells and heat-inactivated cells. However, monitoring the formation of formazan in non-dividing yeast cells that are partially (rad7Delta) or totally (wt) proficient at DNA repair is a more accurate measure of cell survival after UV irradiation. Before repair of UV photoproducts (cis-syn cyclobutane pyrimidine dimers or CPDs) is complete, these two assays give very different results, implying that many damaged cells are metabolically competent but cannot replicate. For example, only 25% of the rad7Delta cells are mitotically viable after a UV dose of 12 J/m(2)75% of these cells are metabolically competent and remove over 55% of the CPDs from their genomic DNA. Moreover, repair of CPDs in wt cells dramatically decreases after the first few hours of liquid holding (L.H.; incubation in water) and correlates with a substantial decrease in cell metabolism over the same time period. In contrast, cell colony formation may be the more accurate indicator of cell survival after UV irradiation of rad1Delta cells (i.e., cells with little DNA repair activity). These results indicate that the metabolic competence of UV-irradiated, non-dividing yeast cells is a much better indicator of cell survival than mitotic viability in partially (or totally) repair proficient yeast cultures.

Colony Count, Microbial↗
PubMedDate not supplied

Determination of viable yeast cells by gravitational field-flow fractionation with fluorescence detection.

Vinification processing is largely related to yeast performance and depends on the initial cell viability. To optimize the quality of wine fermentation, control of the yeast quality is mandatory. The present paper describes a new method using gravitational field flow fractionation (GrFFF) with fluorescence detection for the determination of yeast cell viability before the fermentation process. A GrFFF calibration procedure was developed using commercial yeast to prepare standards of viable cells and propidium iodide (PI) as fluorescent probe for nonviable cells. The suitability of the new method was tested with several commercial yeast strains with a g/L content ranging from 1 to 3. The validation of the method was performed by comparing GrFFF viability values with those obtained using Coulter counter and flow cytometry techniques.

Cell Separation↗
PubMed2005

Antibacterial screening of anthocyanic and proanthocyanic fractions from cranberry juice.

The effect of anthocyanin- and proanthocyanidin-rich fractions isolated from cranberry juice was studied for their antibacterial activity against nine bacterial strains. Activity was assessed by the agar diffusion assay. Staphylococcus aureus ATCC 6538 was the only strain to exhibit some susceptibility to four out of 10 anthocyanin-rich fractions tested. A variable susceptibility of S. aureus, Enterococcus faecalis ATCC 10541, and Micrococcus luteus ATCC 9341 to proanthocyanidin- rich fractions was also observed. Streptococcus mutans strains as well as Escherichia coli ATCC 10538 and Pseudomonas aeruginosa ATCC 27853 were not susceptible to any of the cranberry juice samples or fractions at the tested concentrations. There was no clear correlation between Gram-positive or Gram-negative bacterial susceptibility to cranberry juice. In this work, the role of cranberry juice anthocyanic and proanthocyanic fractions upon bacterial viability is discussed.

Anthocyanins↗
PubMed1986

Uptake of gentamicin by Staphylococcus aureus possessing gentamicin-modifying enzymes: enhancement of uptake by puromycin and N,N'-dicyclohexylcarbodiimide.

Uptake of gentamicin by a gentamicin-resistant strain of Staphylococcus aureus possessing the aminoglycoside-modifying phosphotransferase enzyme APH(2") was enhanced by the protein synthesis inhibitor, puromycin or by the proton-translocating ATPase inhibitor, N,N'-dicylohexylcarbodiimide. Such enhanced uptake was inhibited by carbonyl cyanide p trifluoromethoxyphenylhydrazone or by valinomycin in the presence of potassium ions, suggesting a role for the transmembrane proton motive force in the process. The accumulated gentamicin did not cause loss of cell viability and exhibited altered chromatographic mobility compared with a control (unmodified) preparation of gentamicin.

Carbodiimides↗
PubMed2003

Survival of Yersinia pestis on environmental surfaces.

The survival of two strains of Yersinia pestis (avirulent A1122 and virulent Harbin) on the surfaces of four materials was investigated. Viability was evaluated with epifluorescence microscopy by using the metabolic stain cyanoditolyl tetrazolium chloride and plate counts. Small numbers of cells suspended in phosphate buffer survived 2 to 4 h after visible drying on stainless steel, polyethylene, or glass and beyond 48 h on paper. Cells suspended in brain heart infusion broth (BHI) persisted more than 72 h on stainless steel, polyethylene, and glass. Small numbers of cells suspended in BHI were still viable at 120 h on paper. These data suggest that Y. pestis maintains viability for extended periods (last measured at 5 days) under controlled conditions.

Colony Count, Microbial↗
PubMed1970

Growth of mouse L cells in shaken culture and mengovirus plaque formation on L cells suspended in agar.

Procedures are described that require a minimum of equipment and maintenance for growing mouse L cells suspended in liquid medium and for plaquing mengovirus on L cells suspended in agar. Viability of L cells during storage for 1 to 2 hr at relatively high concentrations was better in media at 30 C than at 0 C, as measured by viable counts after growth for 24 hr at 35 C. The number and size of plaques increased with increasing concentration of NaHCO(3) in the agar layers, but the relative difference in plaque size was maintained. Large- and small-plaque-size variants had similar virulence as determined by the rates of viability loss of L cells in liquid suspension cultures.

Agar↗