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Biomedical subjects

B Lighthart

Publications and source records attributed to B Lighthart.

12 recordsLinked to original sources
PubMed1995

Trehalose and sucrose protect both membranes and proteins in intact bacteria during drying.

The microorganisms Escherichia coli DH5 alpha and Bacillus thuringiensis HD-1 show an increased tolerance to freeze-drying when dried in the presence of the disaccharides trehalose and sucrose. When the bacteria were dried with 100 mM trehalose, 70% of the E. coli and 57% of the B. thuringiensis organisms survived, compared with 56 and 44%, respectively, when they were dried with sucrose. Only 8% of the E. coli and 14% of the B. thuringiensis organisms survived drying without the sugars. Fourier transform infrared spectroscopy was used to investigate the role of membrane phase transitions in the survival of the organisms during drying and rehydration. Both E. coli and B. thuringiensis showed an increase of 30 to 40 degrees C in the temperature of their phospholipid phase transition when dried without the sugars, while phase transition temperatures of those dried with the sugars remained near those of the hydrated cells. A Fourier transform infrared spectroscopy microscope made it possible to investigate the effects of drying on the protein structure in the intact cells. The amide II peak shifts from 1,543 cm-1 in the hydrated cells to about 1,533 cm-1 in the cells dried without sugar. There is no shift in the amide II peak when the cells are dried with trehalose or sucrose. We attribute the increased survival to the sugars' ability to lower the membrane phase transition temperature and to protect protein structure in the dry state.(ABSTRACT TRUNCATED AT 250 WORDS)

Bacillus thuringiensis↗
PubMed1991

Trajectory of aerosol droplets from a sprayed bacterial suspension.

Simulated droplet trajectories of a polydispersed microbial aerosol in a laminar air flow regimen were compared with observed dispersal patterns of aerosolized Bacillus subtilis subsp. niger spores in quasilaminar airflow. Simulated dispersal patterns could be explained in terms of initial droplet sizes and whether the droplets evaporated to residual aeroplanktonic size before settling to the ground. For droplets that evaporated prior to settling out, a vertical downwind size fractionation is predicted in which the microbial residue of the smallest droplets settles the least, and is found in the airstream at about sprayer height, and progressively larger droplet residues settle to progressively lower heights. Observations of spore particle size distributions downwind from a spray source support the simulation. Droplet and particle size distributions near the source had three size fractions: one containing large, presumably nonevaporated droplets of greater than or equal to 7 microns in diameter, and two smaller fractions, with diameters of 2 to 3 microns (probably the residue of droplets containing more than one spore) and 1 to 2 microns (probably the residue from single-spore droplets). As predicted by the simulation, the aerosol settled and progressed downwind, with the number of small droplets and particles increasing in proportion to the height and distance downwind.

Aerosols↗
PubMed1991

Resuscitation effects of catalase on airborne bacteria.

Catalase incorporation into enumeration media caused a significant increase (greater than 63%) in the colony-forming abilities of airborne bacteria. Incubation for 30 to 60 min of airborne bacteria in collection fluid containing catalase caused a greater than 95% increase in colony-forming ability. However, catalase did not have any effects on enumeration at high relative humidities (80 to 90%).

Air Microbiology↗
PubMed1990

Effects of betaine on enumeration of airborne bacteria.

The osmoprotectant betaine was incorporated into collection fluid and enumeration medium to determine its effects on the colony-forming abilities of airborne bacteria, which were collected from three separate locations: a wastewater treatment plant, the roof of a laboratory building, and an unobstructed farmland. At all locations, addition of 2 to 5 mM betaine caused a significant increase (from 21.6 to 61.3%) in colonial outgrowth, compared with the growth rate of controls without betaine. The presence of betaine in both the collection fluid and the enumeration medium had an additive effect on the colony-forming ability of airborne bacteria compared with the presence of betaine in either one alone. The effect of various betaine concentrations on the enumeration of aerosolized Pseudomonas syringae was determined. Betaine showed a threshold for maximum effect at a concentration of 2 to 5 mM. At higher concentrations (10 to 20 mM), the effects of betaine were negligible or possibly inhibitory. The significance of these results with respect to the development of protocols for monitoring airborne microorganisms, including genetically engineered microorganisms, is discussed.

Air Microbiology↗
PubMed1987

Estimating downwind concentrations of viable airborne microorganisms in dynamic atmospheric conditions.

A Gaussian plume model has been modified to include an airborne microbial survival term that is a best-fit function of laboratory experimental data of weather variables. The model has been included in an algorithm using microbial source strength and local hourly mean weather data to drive the model through a summer- and winter-day cycle. For illustrative purposes, a composite airborne "virus" (developed using actual characteristics from two viruses) was used to show how wind speed could have a major modulating effect on near-source viable concentrations. For example, at high wind speeds such as those occurring during the day, or with short travel times, near-source locations experience high viable concentrations because the microorganisms have not had time to become inactivated. As the travel time increases, because of slow wind speed or longer distances, die-off modulation by sunshine, relative humidity, temperature, etc., potentially becomes increasingly predominant.

Air Microbiology↗
PubMed1980

Effects of certain cadmium species on pure and litter populations of microorganisms.

Cadmium inhibition of microorganisms was found to be bacterial and chemical species dependent. E. coli inhibition was a function of the cadmium-ion concentration irregardless of the presence of citrate, a chelator for cadmium that it could not metabolize. Whereas with a Pseudomonas sp. able to metabolize citrate, cadmium inhibition was a function of both the cadmium ion and the presence of citrate. With no citrate, inhibition of this organism occurred only at relatively high cadmium-ion concentrations (above 10(-4) M); when citrate was added to the same cadmium-containing growth medium, inhibition was observed at a 1000 times lower cadmium-ion concentration (i.e., 10(-7) M). This observation is contrary to the classical understanding where a chelate reduces the toxic form of a metal allowing increased growth of the organism. The species of cadmium also differentially inhibited the Douglas fir letter respiration and nitrogen-fixing community activities.

Cadmium↗
PubMed1979

Enrichment of cadmium-mediated antibiotic-resistant bacteria in a Douglas-fir (Pseudotsuga menziesii) litter microcosm.

A set of Douglas-fir needle litter microcosms was amended with cadmium, acid, a combination of both, or neither. After 2 weeks of incubation, bacterial colony counts were made of litter homogenates inoculated onto agar media containing an antibiotic (streptomycin, chloromycetin, ampicillin, or gentamicin), cadmium, both, or neither. In all microcosms bacterial abundance was similar but the quality was very dissimiliar. Cadmium-treated microcosms had populations enriched for cadmium and gentamicin resistance and streptomycin and chloramphenicol sensitivity. Acid amendment had no consistent effect on the microcosm populations except that which could be attributed to the cadmium treatment amendment alone.

Anti-Bacterial Agents↗
PubMed1976

Estimation of viable airborne microbes downwind from a point source.

Modification of the Pasquill atmospheric diffusion equations for estimating viable microbial airborne cell concentrations downwind form a continuous point source is presented. A graphical method is given to estimate the ground level cell concentration given (i) microbial death rate, (ii) mean wind speed, (iii) atmospheric stability class, (iv) downwind sample distance from the source, and (v) source height.

Air Microbiology↗
PubMed1975

A cluster analysis of some bacteria in the water column of Green Lake, Washington.

Mass inoculation and computer clustering techniques were used in an abbreviated procedure to group similar bacteria isolated from four depths in the water column of Green Lake, Washington. Four groups of bacteria were differentiable and were catagorized as orange-yellow Flavobacterium-Cytophaga, yellow Flavobacterium-Cytophaga, Vibrio-Aeromonas-, and Pseudomonas-like. Some of the groups were most prevalent in certain sample depths in the water column.

Aeromonas↗
PubMed1973

Survival of airborne bacteria in a high urban concentration of carbon monoxide.

Vegetative cells of Serratia marcescens 8UK, Sarcina lutea, and spores of Bacillus subtilus var. niger were held in aerosols, with and without an urban concentration of CO (85 muliters per liter or ppm), for up to 6 hr at 15 C and a relative humidity (RH) of approximately 0, 25, 50, 75, and 95%. It was found that CO enhanced the death rate of S. marcescens 8UK at least four- to sevenfold at low RH (ca. 1 to 25%), but protected the cells at high RH (ca. 90%). Death rates of S. lutea, with or without added CO, were comparatively low over the entire RH range. However, in the first hour, airborne S. lutea held in CO-containing air were more stable than those in air without added CO (i.e., CO protection). A marked increase in the death rate (up to 70-fold) occurred in the subsequent 5 hr within the RH range of approximately 0 to 75%. Statistical analysis indicated that aerosol decay rates of B. subtilus var. niger spores decreased significantly, when held in a CO-containing as compared to a non-CO-containing atmosphere, in the 0 to 85% RH range. Thus, the data presented indicate that CO in the urban environment may have a protective or lethal effect on airborne bacteria, dependent upon at least the microbial species, aerosol age, and relative humidity. A mechanism for CO death enhancement and protection of airborne S. marcescens 8UK is suggested to involve CO uncoupling of an energy-requiring death mechanism and an energy-requiring maintenance mechanism at high and low RH, respectively.

Aerosols↗