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At least 55 records · Page 3Linked to original sources
PubMed2000

Modeling UV-induced inactivation of microorganisms on surfaces.

A model is presented to account for inactivation by UV light of microorganisms on the surfaces of solid materials. In the model, the surface is divided into a discrete number of zones, each having a characteristic exposure factor (alpha). This is the ratio of UV intensity actually "seen" by the microorganism to that incident on the surface. Application of the model requires inactivation data obtained under conditions where the surface microorganisms are fully exposed to incident UV (alpha = 1) as well as kinetic inactivation data for the same microorganisms actually present on the surface of interest during UV irradiation. The kinetics in question may apply either to a single species or to the characteristic microflora associated with a particular material. Standard nonlinear programming techniques were used to determine the number of zones among which the microorganisms are distributed, the alpha for each zone, and the fraction of the microbial population present in each zone. The model was applied to data previously published by Gardner and Shama for UV inactivation of Bacillus subtilis spores on the surfaces of filter papers and also to the data of Stermer et al. for UV irradiation of beef. Good representation of the kinetics was obtained, and a maximum of three zones was required to adequately represent the experimental data. One direct application of the model is that it yields quantitative information about the UV fluences necessary to achieve specified reductions in microbial viability.

Animals↗
PubMed1982

Effect of incremental doses of radiation on viability of the microbial population on synthetic operating room gowns.

A total of 700 25-cm2 samples of surgical gown material were exposed to doses of cobalt-60 radiation of 0.0 to 0.6 Mrad in 0.1-Mrad increments. Pour plates were made, and the microbial colonies that arose were enumerated, isolated, and identified as to species. The death rate of the microbial population was calculated, and the mean D10 value of 0.269 Mrad was obtained. Analysis showed that the initial population on unirradiated material had been underestimated; when the counts obtained by homogenization of unirradiated material were substituted, a corrected mean D10 value of 0.249 Mrad was obtained. The isolates obtained were identified, and 70.7% were found to be Bacillus spp. with 12 different species identified, 16.2% were Micrococcus spp. with 6 different species identified, and 8.2% were fungi with 10 different species identified. Calculations were made for appropriate doses of radiation to sterilize gowns with this contaminating microbial population. These calculations gave an estimated dose of radiation of 1.98 to 1.81 Mrad to reduce the observed population to 0.001, a standard where 1 gown in 1,000 might contain a living organism. Comparison of the radiation resistance of this population with that of others reported in the literature showed good agreement.

Bacteria↗
PubMed1999

In vitro viability of external eye microbial flora in hydroxy-propyl-methylcellulose.

The aim of this study was to verify the in vitro influence of various dilutions of a viscoelastic substance containing 2% hydroxy-propyl-methylcellulose (HPMC) on the viability of some microbial strains representative of the normal flora of the external eye. Pure reference strain cultures of Candida albicans, Pseudomonas aeruginosa, Propionibacterium acnes, Staphylococcus aureus, Staphylococcus epidermidis and a fresh clinical isolate of Proteus mirabilis were selected for this study. Serial twofold dilutions of 2% HPMC, prepared so as to obtain a final concentration ranging from 50 to 0.78% of the product in sterile saline solution (0.85% NaCl), were taken out with a pipette that delivered 1.0 ml per tube. One hundred microliters of the abovementioned microbial inocula, used for the evaluation of the positive control of the test organism, were dispensed into each tube. After 24 h of incubation, 100 microl of samples were taken from each tube and plated into the specific medium for the growth of the test organism. After 24-48 h of incubation, these agar plates were examined and the colony-forming-unit count of each test organism was compared to the corresponding total colony count, acting as a positive control, in order to determine the quantitative variation of the test organism grown in the presence of the viscoelastic compounds. C. albicans and P. aeruginosa showed a statistically significant increase in growth with HPMC dilutions varying from 1:2 to 1:16. P. acnes and P. mirabilis growth was significantly reduced by all dilutions except for the 1:128 one. S. epidermidis growth was also significantly reduced in the presence of HPMC dilutions varying from 1:2 to 1:64. S. aureus growth was not significantly influenced. The viability of P. aeruginosa in HPMC dilutions needs to be carefully considered because of the ability of this organism to induce endophthalmitis, and the possibility that during cataract surgery, a small amount of HPMC may be left in the eye, trapped behind the intraocular lens optic.

Bacteria↗
PubMed2006

Preservation of micro-organisms by drying; a review.

The preservation of micro-organisms by different drying methodologies has been used for decades. Freeze drying in particular is the preferred method for transporting and storing vast culture collections of micro-organism strain types. The literature on drying and preserving micro-organisms is extensive, but is often specific to one particular strain. This review attempts to draw some similar concepts and findings together in one paper, to compare different drying techniques, with specific reference to microorganisms. The main topics covered are cell growth phases and concentration, inducing drying tolerance in microbial cells, drying methods, rehydration of dried cells and packaging and storage conditions. Also, particular attention has been paid to the use of freeze drying and the protective matrices used to improve microbial cell viability after drying.

Bacteria↗
PubMed1987

Myeloperoxidase-mediated damage to the succinate oxidase system of Escherichia coli. Evidence for selective inactivation of the dehydrogenase component.

Myeloperoxidase, a granule-associated enzyme of neutrophils and monocytes, combines with H2O2 and chloride to form a potent microbicidal system that contributes to phagocyte antimicrobial activity. The nature of the lesion or lesions induced by the myeloperoxidase system which are responsible for the loss of microbial replicative activity (viability) remains unknown. Using Escherichia coli grown to late log or stationary phase under conditions of low aeration with succinate as the sole carbon source, we found that myeloperoxidase-induced loss of microbial viability could be correlated with a decrease in succinate-dependent respiration (succinate oxidase activity). Succinate dehydrogenase activity fell rapidly to undetectable levels during incubation with the myeloperoxidase system, suggesting that damage to the dehydrogenase was a major factor in the loss of oxidase activity. Other components of the succinate oxidase system were resistant to the actions of myeloperoxidase. The ubiquinone-8 and cytochrome components of the respiratory chain remained nearly constant in amount despite reduction of respiration to undetectable levels. However, as expected from the loss of succinate dehydrogenase activity, succinate-ubiquinone reductase and succinate-cytochrome reductase activities were markedly impaired. We propose that the loss of E. coli viability induced by the myeloperoxidase-H2O2-chloride system is due in part to the loss of electron transport function consequent to the oxidation of critical catalytic centers in susceptible dehydrogenases.

Electron Transport↗
PubMed2006

Cryopreservation of Holospora undulata, a bacterial parasite of the ciliate Paramecium caudatum.

We investigated cryopreservation of horizontal transmission stages of Holospora undulata, a micronucleus-specific bacterial parasite of Paramecium caudatum. Unlike in previous studies on related Holospora species, protocols using glycerol as cryoprotectant failed entirely. In contrast, freezing with dimethyl sulfoxide (Me2SO) conserved infectiousness of nearly all replicate inocula, although infection success was considerably lower than that of fresh inocula. Infection probability was enhanced by increasing the Me2SO concentration from 5 to 10%, and by freezing at -196 degrees C rather than -80 degrees C. Prolonged storage of up to 3 months had no significant effect on the viability of the inocula.

Animals↗
PubMed2006

Biofilm development of the polyethylene-degrading bacterium Rhodococcus ruber.

We have recently isolated a biofilm-producing strain (C208) of Rhodococcus ruber that degraded polyethylene at a rate of 0.86% per week (r2=0.98). Strain C208 adheres to polyethylene immediately upon exposure to the polyolefin. This initial biofilm differentiates (in a stepwise process that lasts about 20 h) into cell-aggregation-forming microcolonies. Further organization yields "mushroom-like" three-dimensional structures on the mature biofilm. The ratio between the population densities of the biofilm and the planktonic C208 cells after 10 days of incubation was about 60:1, indicating a high preference for the biofilm mode of growth. Analysis of extracellular polymeric substances (EPS) in the biofilm of C208 revealed that the polysaccharides level was up to 2.5 folds higher than that of the protein. The biofilm showed a high viability even after 60 days of incubation, apparently due to polyethylene biodegradation.

Biodegradation, Environmental↗
PubMed2006

Development of a real-time NASBA assay for the detection of Campylobacter jejuni cells.

The objectives of this study were the development of a real-time NASBA assay for the detection of Campylobacter jejuni mRNA and the evaluation of its potential to determine the viability of the detected C. jejuni cells. A set of specific primers and probes was chosen to amplify the mRNA of the tuf-gene and the GTPase-gene. Only the tuf-assay was able to detect as low as 10(2) cells per NASBA reaction and was specific for Campylobacter. However, as the assay was able to detect dead cells, it cannot be used to demonstrate the viability of C. jejuni cells. The tuf-gene mRNA is no good viability indicator due to its stability.

Base Sequence↗
PubMed2006

New methodology for viability testing in environmental samples.

Environmental samples can be complex and are comprised of microorganisms and a matrix of decaying organic matter as well as an inorganic phase such as sand or precipitated material (waste water, sludge, soils, etc.). Nucleic acid dyes have recently been developed to address the growing need for environmental analyses (cell staining, counting, viability testing and specific organism identification). However, certain dyes may not be ideally suited for testing of environmental samples, because they readily adhere to the substrate material as well as their target molecule, resulting in increased non-specific binding and background fluorescence. The aim of this study was to address the limitations of the widely used and commercially available Live/Dead BacLight Bacterial Viability kit (Molecular Probes, Eugene, OR). A new combination of nucleic acid dyes, i.e. SYTO13 and SYTOX Orange (Molecular Probes, Eugene, OR), was proposed as an alternative. The dyes were carefully chosen for their spectral separation and increase of fluorescence quantum yield. A protocol for this combination was first designed and optimized and the two staining assays were compared against suspensions of live and dead E. coli, mixed in different proportions and it was shown that both protocols performed equally on pure cultures. However, when testing activated sludge samples, the commercial kit showed greater background fluorescence and non-specific binding than the alternate combination. Therefore, the proposed dye combination and its corresponding protocol are deemed more suitable for use on complex environmental samples than the Live/Dead BacLight Bacterial Viability kit.

Environmental Microbiology↗