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K Willeke

Publications and source records attributed to K Willeke.

At least 19 recordsLinked to original sources
PubMed2005

Evaluation of ionic air purifiers for reducing aerosol exposure in confined indoor spaces.

UNLABELLED: Numerous techniques have been developed over the years for reducing aerosol exposure in indoor air environments. Among indoor air purifiers of different types, ionic emitters have gained increasing attention and are presently used for removing dust particles, aeroallergens and airborne microorganisms from indoor air. In this study, five ionic air purifiers (two wearable and three stationary) that produce unipolar air ions were evaluated with respect to their ability to reduce aerosol exposure in confined indoor spaces. The concentration decay of respirable particles of different properties was monitored in real time inside the breathing zone of a human manikin, which was placed in a relatively small (2.6 m3) walk-in chamber during the operation of an ionic air purifier in calm air and under mixing air condition. The particle removal efficiency as a function of particle size was determined using the data collected with a size-selective optical particle counter. The removal efficiency of the more powerful of the two wearable ionic purifiers reached about 50% after 15 min and almost 100% after 1.5 h of continuous operation in the chamber under calm air conditions. In the absence of external ventilation, air mixing, especially vigorous one (900 CFM), enhanced the air cleaning effect. Similar results were obtained when the manikin was placed inside a partial enclosure that simulated an aircraft seating configuration. All three stationary ionic air purifiers tested in this study were found capable of reducing the aerosol concentration in a confined indoor space. The most powerful stationary unit demonstrated an extremely high particle removal efficiency that increased sharply to almost 90% within 5-6 min, reaching about 100% within 10-12 min for all particle sizes (0.3-3 microm) tested in the chamber. For the units of the same emission rate, the data suggest that the ion polarity per se (negative vs. positive) does not affect the performance but the ion emission rate does. The effects of particle size (within the tested range) and properties (NaCl, PSL, Pseudomonas fluorescens bacteria) as well as the effects of the manikin's body temperature and its breathing on the ionic purifier performance were either small or insignificant. The data suggest that the unipolar ionic air purifiers are particularly efficient in reducing aerosol exposure in the breathing zone when used inside confined spaces with a relatively high surface-to-volume ratio. PRACTICAL IMPLICATIONS: Ionic air purifiers have become increasingly popular for removing dust particles, aeroallergens and airborne microorganisms from indoor air in various settings. While the indoor air cleaning effect, resulting from unipolar and bipolar ion emission, has been tested by several investigators, there are still controversial claims (favorable and unfavorable) about the performance of commercially available ionic air purifiers. Among the five tested ionic air purifiers (two wearable and three stationary) producing unipolar air ions, the units with a higher ion emission rate provided higher particle removal efficiency. The ion polarity (negative vs. positive), the particle size (0.3-3 microm) and properties (NaCl, PSL, Pseudomonas fluorescens bacteria), as well as the body temperature and breathing did not considerable affected the ionization-driven particle removal. The data suggest that the unipolar ionic air purifiers are particularly efficient in reducing aerosol exposure in the breathing zone when they are used inside confined spaces with a relatively high surface-to-volume ratio (such as automobile cabins, aircraft seating areas, bathrooms, cellular offices, small residential rooms, and animal confinements). Based on our experiments, we proposed that purifiers with a very high ion emission rate be operated in an intermittent mode if used indoors for extended time periods. As the particles migrate to and deposit on indoor surfaces during the operation of ionic air purifiers, some excessive surface contamination may occur, which introduces the need of periodic cleaning these surfaces.

Aerosols↗
PubMed2001

Pathogenomic mechanisms for particulate matter induction of acute lung injury and inflammation in mice.

To begin identifying genes controlling individual susceptibility to particulate matter, responses of inbred mouse strains exposed to nickel sulfate (NiSO4*) were compared with those of mice exposed to ozone (O3) or polytetrafluoroethylene (PTFE). The A strain was sensitive to NiSO4-induced lung injury (quantified by survival time), the C3H/He (C3) strain and several other strains were intermediate in their responses, and the C57BL/6 (B6) strain was resistant. The strains showed a pattern of response similar to the patterns of response to O3 and PTFE. The phenotype of A x B6 offspring (B6AF1) resembled that of the resistant B6 parental strain, with strains exhibiting sensitivity in the order A > C3 > B6 = B6AF1. Pathology was comparable for the A and B6 mice, and exposure to NiSO4 at 15 microg/m3 produced 20% mortality in A mice. Strain sensitivity for the presence of protein or neutrophils in lavage fluid differed from strain sensitivity for survival time, suggesting that they are not causally linked but are controlled by an independent gene or genes. In the B6 strain, exposure to nickel oxide (NiO) by instillation (40 to 1000 nm) or inhalation (50 nm) produced no changes, whereas inhalation of NiSO4 (60 or 250 nm) increased lavage proteins and neutrophils. Complementary DNA (cDNA) microarray analysis with 8,734 sequence-verified clones revealed a temporal pattern of increased oxidative stress, extracellular matrix repair, cell proliferation, and hypoxia, followed by a decrease in surfactant-associated proteins (SPs). Certain expressed sequence tags (ESTs), clustered with known genes, suggest possible coregulation and novel roles in pulmonary injury. Finally, locus number estimation (Wright equation) and a genomewide analysis suggested 5 genes could explain the survival time and identified significant linkage for a quantitative trait locus (QTL) on chromosome 6, Aliq4 (acute lung injury QTL4). Haplotype analysis identified an allelic combination of 5 QTLs that could explain the difference in sensitivity to acute lung injury between parental strains. Positional candidate genes for Aliq4 include aquaporin-1 (Aqp1), SP-B, and transforming growth factor-alpha (TGF-alpha). Transgenic mice expressing TGF-alpha were rescued from NiSO4 injury (that is, they had diminished SP-B loss and increased survival time). These findings suggest that NiSO4-induced acute lung injury is a complex trait controlled by at least 5 genes (all possibly involved in cell proliferation and surfactant function). Future assessment of these susceptibility genes (including evaluations of human synteny and function) could provide valuable insights into individual susceptibility to the adverse effects of particulate matter.

Air Pollutants↗
PubMed2000

Metal exposure among abrasive blasting workers at four U.S. Air Force facilities.

Button Aerosol Samplers were used to monitor the personal exposure of workers performing abrasive blasting operations at four U.S. Air Force facilities. Inhalable aerosols containing 25 metals, including cadmium, lead, and chromium, were investigated. The Button Aerosol Sampler was chosen because of its ability to successfully withstand mechanical stress, prevent very large particles from collection, and protect the filter from overloading and shredding by rebound particles. In addition, previous studies have shown that the sampling efficiency of this personal Aerosol Sampler exhibits low sensitivity to the ambient air conditions and that it adequately follows the inhalability convention. Inductively coupled plasma (ICP) was used to analyze the collected samples for all 25 metals. In addition, visual absorption spectrophotometry (VAS) was used to analyze for hexavalent chromium because of the presence of strontium chromate. The collected samples yielded 8-hr time-weighted average (TWA) concentrations that were up to 250, 6, and 5 times higher than the permissible exposure limits (PELs) for cadmium, lead, and hexavalent chromium, respectively. Also, the chromium levels measured by the ICP and VAS exceeded the strontium chromate threshold limit value (TLV) by up to 640 and 950 times, respectively. No correlation was found between the ICP and VAS hexavalent chromium concentrations. The likely reasons of this were the presence of Cr (II) and (III) that cannot be detected by the VAS, and the chemical interference from iron and some other metals in the samples. The Button Aerosol Sampler was shown to be useful for the monitoring of workers' exposure to heavy metals during abrasive blasting operations.

Aerosols↗
PubMed2000

Genetic susceptibility to irritant-induced acute lung injury in mice.

Recent studies suggest that genetic variability can influence irritant-induced lung injury and inflammation. To begin identifying genes controlling susceptibility to inhaled irritants, seven inbred mouse strains were continuously exposed to nickel sulfate (NiSO(4)), polytetrafluoroethylene, or ozone (O(3)), and survival time was recorded. The A/J (A) mouse strain was sensitive, the C3H/He (C3) strain was intermediate, and the C57BL/6 (B6) strain was resistant to NiSO(4)-induced acute lung injury. The B6AF(1) offspring were also resistant. The strain sensitivity pattern for NiSO(4) exposure was similar to that of polytetrafluoroethylene or ozone (O(3)). Pulmonary pathology was comparable for A and B6 mice. In the A strain, 15 microg/m(3) of NiSO(4) produced 20% mortality. The strain sensitivity patterns for lavage fluid proteins (B6 > C3 > A) and neutrophils (A >/= B6 > C3) differed from those for acute lung injury. This phenotype discordance suggests that these traits are not causally linked (i.e., controlled by independent arrays of genes). As in acute lung injury, B6C3F(1) offspring exhibited phenotypes (lavage fluid proteins and neutrophils) resembling those of the resistant parental strain. Agreement of acute lung injury strain sensitivity patterns among irritants suggested a common mechanism, possibly oxidative stress, and offspring resistance suggested that sensitivity is inherited as a recessive trait.

Acute Disease↗
PubMed1999

Survival of mycobacteria on N95 personal respirators.

OBJECTIVES: The overall aim of this study was to investigate the survival and possible growth of Mycobacterium tuberculosis simulant bacteria on respirator filters. METHODS: Mycobacterium smegmatis was used as a biochemical simulant for M tuberculosis. Bacterial survival was tested on National Institute for Occupational Safety and Health-certified N95 respirators from three manufacturers. The first experiments simulated one-time respirator use and subsequent storage for 1 to 9 days under ideal conditions for the growth of mycobacteria: 37 degrees C and 85% relative humidity. The bacteria were loaded on the respirator filters under three different nutritional conditions: in the absence of nutrients; in the presence of human saliva (simulating conditions when the respirator is worn); and in the presence of nutrient broth (for ideal growth potential). The subsequent experiments simulated respirator wear for 2 hours under medium work-load conditions at a breathing rate of 56 L/min. RESULTS: It was found that M smegmatis did not grow on the tested respirators, even when the respirators were stored at temperature, humidity, and nutrition conditions most favorable for microbial growth. However, these bacteria could survive on respirators for up to 3 days during storage. The culturability of M smegmatis was not affected by airflow that simulated the breathing rate associated with medium work-load conditions for 2 hours. CONCLUSIONS: This study shows that M tuberculosis surrogate bacteria collected on a respirator are not able to grow and are able to survive only in ideal (ie, not clinically relevant) conditions. Based on these experiments, we conclude that M tuberculosis is unlikely ever to become an infectious problem in the air again, once it is removed by a respirator.

Colony Count, Microbial↗
PubMed1998

Tuberculosis control through respirator wear: performance of National Institute for Occupational Safety and Health-regulated respirators.

BACKGROUND: In 1995 the National Institute for Occupational Safety and Health issued new rules for personal respirators. All nine new respirator categories are authorized in health care facilities for the prevention of the transmission of tuberculosis (TB). The new N95 respirator category is the most frequently used for this purpose. Data are presented on their efficiency for collecting TB-size bacteria and their potential for reaerosolizing collected bacteria. METHODS: All measurements of bacterial penetration were performed with dynamic aerosol size spectrometers at flow conditions corresponding to normal wear and respirator certification conditions. The reaerosolization tests were performed at conditions ranging from normal breathing to violent coughing or sneezing. RESULTS: The tested N95 respirators collected 0.1 to 0.3 microm particles with efficiencies of 95% or higher, as specified by the regulations. TB-size bacteria of 0.8 microm and larger, however, were collected with 99.5% or higher efficiencies; that is, the penetration of these bacteria through the filter material was 0.5% or less, much less than the required maximum penetration of 5% for the smaller particle sizes. No bacteria were reaerosolized during normal exhalation. Some reaerosolization (0.1% or less) was observed only at low humidity and extremely high air flow through the respirator, corresponding to violent coughing or sneezing. CONCLUSIONS: The filter materials of N95 respirators provide good protection against TB bacteria. Thus, a significant number of bacteria can enter the respirator-wearer's breathing space only through spaces where the respirator inadequately seals to the wearer's face. Reentrainment and reaerosolization of mycobacteria is not a problem when normal work practices are observed in health care facilities.

Equipment Contamination↗
PubMed1998

Intranasal angiotensin II directly influences central nervous regulation of blood pressure.

Intranasal administration of some peptides has been shown to directly influence central nervous functions, thus pointing to a nose-brain pathway for these substances in humans. The present study investigated whether intranasal administration of angiotensin II (ANG II) affects central nervous functions of cardiovascular control in a different way from intravenously administered ANG II. In a balanced cross-over design 12 healthy men were treated with ANG II intravenously (2.5 microg), ANG II intranasally (400 microg), and placebo. Angiotensin II, vasopressin, norepinephrine, and epinephrine plasma levels were assessed every 10 min; blood pressure, heart rate, and systemic vascular resistance were measured by a Dinamap, and by continuous, noninvasive body plethysmography. Also, feelings of activation and mood were measured. Intranasal and intravenous administration invoked equivalent increases in plasma levels of ANG II, and induced an acute rise in blood pressure of comparable size and duration. However, subsequent blood pressure profiles differed dependent on intravenous and intranasal ANG II administration; after intravenous ANG II administration blood pressure remained enhanced at an intermediate level, but it returned to normal or even decreased below normal levels after intranasal ANG II administration. Intranasal ANG II also counteracted the decrease in norepinephrine levels observed after intravenous administration of ANG II. Intranasal but not intravenous ANG II enhanced plasma concentrations of vasopressin. This diverging pattern of effects bears similarities with effects of intracerebroventricular administration of ANG II in animals, suggesting that the effects after intranasal administration reflect a direct central nervous action of ANG II.

Administration, Intranasal↗
PubMed1998

Method for measuring the spatial variability of aerosol penetration through respirator filters.

Fibrous filter media are widely used in respirators to remove airborne particulate matter from the inhaled airflow of workers. The N95 half-mask particulate respirator appears to be the most frequently used respirator under the new NIOSH regulation, 42 CFR 84. Considerable spatial variability in light penetration through the fibrous filter medium of an N95 respirator can be seen by visual observation when it is held to the light. This variability is due to the way in which the fibers are manufactured and laid down to form the filter medium. Similar spatial variability is expected in the aerosol penetration through the filters. Therefore, a test method has been developed for measuring the spatial variability in aerosol penetration. The main components of this method are an aerosol generator, a filter test stand with a movable sampling inlet, an aerosol size spectrometer, and an aerosol photometer. Measurements with the filter media of N95 respirators, tested at average filtration velocities corresponding to light, moderate, and heavy work loads, have shown spatial variations in aerosol penetration in excess of 100% relative to the average aerosol penetration for the entire respirator. N95 respirators are required to be at least 95% efficient (i.e., less than 5% penetrating) at the most penetrating particle size, when tested at 85 L/min. Tests with the new method have shown that the aerosol penetration of the most penetrating particles of about 0.1 micron diameter may locally be higher than 5%, while the average aerosol penetration of 0.1 micron particles is less than 5%.

Aerosols↗
PubMed1998

Performance of N95 respirators: filtration efficiency for airborne microbial and inert particles.

In 1995 the National Institute for Occupational Safety and Health issued new regulations for nonpowered particulate respirators (42 CFR Part 84). A new filter certification system also was created. Among the new particulate respirators that have entered the market, the N95 respirator is the most commonly used in industrial and health care environments. The filtration efficiencies of unloaded N95 particulate respirators have been compared with those of dust/mist (DM) and dust/fume/mist (DFM) respirators certified under the former regulations (30 CFR Part 11). Through laboratory tests with NaCl certification aerosols and measurements with particle-size spectrometers, N95 respirators were found to have higher filtration efficiencies than DM and DFM respirators and noncertified surgical masks. N95 respirators made by different companies were found to have different filtration efficiencies for the most penetrating particle size (0.1 to 0.3 micron), but all were at least 95% efficient at that size for NaCl particles. Above the most penetrating particle size the filtration efficiency increases with size; it reaches approximately 99.5% or higher at about 0.75 micron. Tests with bacteria of size and shape similar to Mycobacterium tuberculosis also showed filtration efficiencies of 99.5% or higher. Experimental data were used to calculate the aerosol mass concentrations inside the respirator when worn in representative work environments. The penetrated mass fractions, in the absence of face leakage, ranged from 0.02% for large particle distributions to 1.8% for submicrometer-size welding fumes. Thus, N95 respirators provide excellent protection against airborne particles when there is a good face seal.

Aerosols↗
PubMed1998

Characteristics of airborne actinomycete spores.

Airborne actinomycete spores, important contaminants in occupational and residential environments, were studied with respect to their (i) release into the air, (ii) aerodynamic and physical size while airborne, and (iii) survival after collection onto agar with an impactor. Three actinomycete species were selected for the tests to exemplify the three main spore types: Streptomyces albus for arthrospores, Micromonospora halophytica for aleuriospores, and Thermoactinomyces vulgaris for endospores. The results show that the incubation conditions (temperature, time, and nutrients) needed for the development of spores for their release into air are different from the conditions that are needed for colony growth only. Additional drying of M. halophytica and T. vulgaris cultures was needed before spores could be released from the culture. The aerodynamic sizes of the spores, measured with an aerodynamic particle sizer, ranged from 0.57 (T. vulgaris) to 1.28 micron (M. halophytica). The physical sizes of the spores, when measured with a microscope and an image analysis system, were found to be smaller than previously reported in the literature. The relative recovery of the spores on agar media ranged from 0.5 (T. vulgaris) to 35% (S. albus). The results indicate that the culturability of the collected airborne actinomycete spores varies widely and is affected by several variables, such as the species and the sampling flow rate. Therefore, alternatives to commonly used cultivation methods need to be developed for the enumeration of actinomycete spores.

Actinomyces↗
PubMed1998

Analysis of airborne actinomycete spores with fluorogenic substrates.

The reactions between seven fluorogenic substrates and different groups of enzymes, esterases, lipases, phosphatases, and dehydrogenases, were studied in a search for a new method for the detection of actinomycete spores. Fluorescence measurement was chosen as a fast and sensitive method for microbial analysis. The focus of the research was on the spores of important air contaminants: Streptomyces albus and Thermoactinomyces vulgaris. For the measurement of the enzymatic activity, the chosen fluorogenic substrate was added to a mixture of spores and nutrient media, and the resulting fluorescence was measured with a spectrofluorometer. Fluorogenic substrates were found to show enzymatic activities even for dormant spores. Comparison of the enzymatic activities of dormant spores with those of vegetative cells showed similarity of the enzymatic profiles but higher activity for vegetative cells. The increase of enzymatic activity from dormant spores to vegetative cells was not linear but fluctuating. The largest fluctuations were found after 4 to 5 h of incubation. The enzymatic activities of S. albus were 10 to 50 times lower than those of T. vulgaris, except for the dehydrogenase activity, which was seven times higher. These results indicate that analysis with fluorogenic substrates has the potential for becoming a fast and sensitive method for the enumeration and identification of airborne actinomycete spores.

Actinomycetales↗
PubMed1997

Performance of N95 respirators: reaerosolization of bacteria and solid particles.

If a respirator does not contain an exhalation value, and the respirator wearer sneezes or coughs, one may expect previously collected particles to be reaerosolized. This may be of special concern in environments contaminated with airborne microorganisms. The percentages of reaerosolization were measured in a test setup where the number of reaerosolized particles were registered by dynamic aerosol size spectrometry relative to the number of previously collected particles or bacteria. Experiments at low relative humidity have shown that the reaerosolization of particles below 1 micron, including Mycobacterium tuberculosis surrogate bacteria, does not exceed 0.025%, even if the re-entrainment air velocity is as high as 300 cm/sec (i.e., 37 times the air velocity through the respirator during breathing under heavy workload conditions). The reaerosolization of larger particles into dry air was significant at the highest re-entrainment velocity of 300 cm/sec, which simulates violent sneezing or coughing: 0.1% for 3 microns and about 6% for 5-micron test particles. No reaerosolization was detected at relative humidity levels exceeding 35% at these conditions. Thus, it is concluded that the reaerosolization of particles and bacteria, collected on the fibrous filters of N95 respirators, is insignificant at conditions encountered in respirator wear.

Aerosols↗
PubMed1997

Field testing of new aerosol sampling method with a porous curved surface as inlet.

A new aerosol sampling method, utilizing a porous curved surface as the sampling inlet, has recently been developed. Previous laboratory evaluations of this method have demonstrated its important features, such as low wind sensitivity and good filter collection uniformity. In this study a prototype incorporating the new method was evaluated in the field as a stationary and personal sampling device. The small sampler, utilizing a 25-mm filter is called the button aerosol sampler and was evaluated for collecting total airborne dust and fungal spores. The study was performed in nine poorly maintained inner-city houses during environmental cleanups at different cleanliness levels. The button sampler was used in parallel with the standard 37-mm closed-face filter cassette. Four collocated samplers of each type were tested at all sites as stationary samplers, and three samplers of each type were tested at two sites as personal samplers. Aerosol samples were collected on filters and analyzed using the gravimetric method for total dust and epifluorescence microscopy for fungal spores. The average particle concentration values measured with the button sampler and with the standard sampling cassette were found to correlate well within ranges of 10(1)-10(3) micrograms/m3 for total dust and 10(3)-10(5) spores/m3 for airborne fungi. The measurement results obtained with the new button sampler showed lower intersample variations of the measured concentration levels and higher uniformity of the particle deposits on the filters than those obtained with the standard cassette.

Aerosols↗
PubMed1997

Quantitative fit testing techniques and regulations for tight-fitting respirators: current methods measuring aerosol or air leakage, and new developments.

Until a few years ago, only two quantitative fit testing (QNFT) techniques were available and accepted by U.S. Occupational Safety and Health Administration (OSHA) regulations. In the 1980s and 1990s, several new and fundamentally different QNFT methods were developed. Two of the newer methods are commercially available and are accepted by OSHA as suitable alternatives. In this article the principles of operation of the OSHA-accepted and of some newly developed but not yet approved QNFT techniques are explained, and each technique's major advantages and disadvantages are pointed out. Emphasis is given to negative-pressure air-purifying respirators, as they are in most frequent use today. The requirements and recommendations for fit testing positive-pressure respirators are discussed as well. Finally, the presently available QNFT standards and regulations are summarized to assist the user in making fit testing decisions.

Aerosols↗
PubMed1996

Penetration of airborne microorganisms through a surgical mask and a dust/mist respirator.

This study investigated bacterial penetration of different bacterial shapes, aerodynamic sizes, and flow rates through a surgical mask and a dust/mist respirator. The bacterial penetrations were compared with those of spherical corn oil particles of the same aerodynamic diameter tested under the same conditions. The tests were performed at different levels of aerosol penetration. Bacteria, ranging from spherical to rod-shaped with a high aspect (length to width) ratio, were selected as test agents. Among these, Pseudomonas fluorescens physically simulates Mycobacterium tuberculosis by shape and size. The concentrations of bacteria upstream and downstream of the test devices were measured with an aerodynamic size spectrometer. This instrument was found to measure the total viable and nonviable bacterial concentration effectively and dynamically over the entire bacterial size range down to 0.5 microns in aerodynamic size. The results indicate that the spherical corn oil particles and the spherical Streptococcus salivarius bacteria have the same penetration in the size range from 0.9 to 1.7 microns. It has been found that rod-shaped bacteria penetrate less. The penetration difference between the spherical and rod-shaped bacteria depends on the aspect ratio of the bacteria. For an aspect ratio of 4, the penetration of rod-shaped bacteria is about half that of spherical ones. Thus, it is projected that a respirator with 90% efficiency against spherical microorganisms or test particles (10% penetration) will be 95% efficient against rod-shaped microorganisms of the same aerodynamic equivalent diameter with an aspect ratio of 3 to 4, such as Mycobacterium tuberculosis (5% penetration).

Aerosols↗
PubMed1996

Comparison of methods for detection and enumeration of airborne microorganisms collected by liquid impingement.

Bacterial agents and cell components can be spread as bioaerosols, producing infections and asthmatic problems. This study compares four methods for the detection and enumeration of aerosolized bacteria collected in an AGI-30 impinger. Changes in the total and viable concentrations of Pseudomonas fluorescens in the collection fluid with respect to time of impingement were determined. Two direct microscopic methods (acridine orange and BacLight) and aerodynamic aerosol-size spectrometry (Aerosizer) were employed to measure the total bacterial cell concentrations in the impinger collection fluid and the air, respectively. These data were compared with plate counts on selective (MacConkey agar) and nonselective (Trypticase soy agar) media, and the percentages of culturable cells in the collection fluid and the bacterial injury response to the impingement process were determined'. The bacterial collection rate was found to be relatively unchanged during 60 min of impingement. The aerosol measurements indicated an increased amount of cell fragments upstream of the impinger due to continuous bacterial nebulization. Some of the bacterial clusters, present in the air upstream of the impinger, deagglomerated during impingement, thus increasing the total bacterial count by both direct microscopic methods. The BacLight staining technique was also used to determine the changes in viable bacterial concentration during the impingement process. The percentage of viable bacteria, determined as a ratio of BacLight live to total counts was only 20% after 60 min of sampling. High counts on Trypticase soy agar indicated that most of the injured cells could recover. On the other hand, the counts from the MacConkey agar were very low, indicating that most of the cells were structurally damaged in the impinger. The comparison of data on the percentage of injured bacteria obtained by the traditional plate count with the data on percentage of nonviable bacteria obtained by the BacLight method showed good agreement.

Acridine Orange↗
PubMed1995

Factors affecting microbiological colony count accuracy for bioaerosol sampling and analysis.

The effects of the following variables on the occurrence of colony masking (the indistinguishable merging or overlap of sufficiently close colonies) were evaluated experimentally using the bacterium Bacillus subtilis: spore density on a collection surface, concentration of nutrients in the culture medium, sample incubation time, and ability of an observation system to distinguish overlapped colonies. Increasing spore surface density and incubation time increased colony masking, whereas lowering nutrient concentration decreased colony diameter and, therefore, masking but also limited spore germination and growth. Overall, full-strength medium was best for accurate counting of early microcolonies examined with the aid of a microscope, whereas half- or quarter-strength medium was better for counting older readily observable macrocolonies. Masking bias was determined for varying spore surface densities and colony diameters and was applied to two widely used slit-to-agar bioaerosol impactors. Appropriate collection times have been determined for these samplers to minimize colony masking for expected bioaerosol concentrations. It was found, for example, that 6-min samples collected from an environment with an air concentration of 10(3) CFU m-3 would result in colony surface densities, for 3-mm colonies, of 1.5 and 3.9 microorganisms cm-2 for the two samplers with respective masking biases of < 10% and < 20%.

Aerosols↗