Long-term viable bioaerosol sampling using a temperature- and humidity-controlled filtration apparatus,a laboratory investigation using culturable E. coli.

Sampling for culturable (e.g., viable) aerosolized microbes (bioaerosols) is a useful means to provide information for public health monitoring and studies. However, it is challenging to maintain microbe culturability when sampling at high flow rates (>12 L/min) and extended periods of time (≥4 h). We developed a first-generation, viable bioaerosol collection system (VBCS) utilizing temperature (T) and relative humidity (RH)–conditioned filtration at a flow rate of 25 L/min. A two-stage system of tube-in-shell Nafion? exchange units provides cooling to ≤10°C and RH conditioning to 80–95%. Aerosol particles are collected on a polyurethane nanofiber filter providing a physical collection efficiency of >95% for sizes 0.06–10 µm. The T and RH conditions at the collection filter are maintained, despite changes to ambient conditions. The initial testing of the VBCS was done under indoor, laboratory conditions with aerosolized, vegetative E. coli. A scenario of a 30-min challenge of bioaerosol followed by continued sampling of clean air for various times was used to judge culturability maintenance under extended-term sampling. An initial loss of culturability upon collection onto the filter was observed; 23 ± 13% relative to 4-mm all-glass impinger. However once collected, 98% of culturability was maintained for an additional 4.5 h of sampling. An exponential decay in culturability was observed from 8 h to 15 h of sampling. Also, 24-h cold storage of the filters collected was studied. The VBCS is based on the use of dry filter cassettes, needs minimal maintenance, and preserves culturability of vegetative bacteria for >4 h.

© 2017 RTI International and Aerosol Dynamics Inc.     

Germicidal UV Sensitivity of Bacteria in Aerosols and on Contaminated Surfaces

We compared the UV sensitivity of Bacillus atrophaeus (a surrogate for B. anthracis), Pantoea agglomerans (a bacterial simulant frequently used in biodefense studies), and Yersinia ruckeri (a surrogate for Yersinia pestis) either airborne or deposited on a semisolid (wet) agar surface. Bacterial vegetative cells were aerosolized into an exposure chamber and exposed for various lengths of time to an ultraviolet (UV) light source emitting at 254 nanometer (nm) (in the UVC region also known as UVGI). Aerosols were collected onto gelatin filters, which were dissolved, diluted, plated, and incubated to enumerate colony formation. In darkness (with the UV light switched off), it took between 170 and 330 s airborne (depending on the bacterial species) to decrease by 90% of the original load (i.e., by 1 Log₁₀) the number of viable organisms originally present. The fluence of UVC required to inactivate 90% (F_{–1 Log10}) of bacteria aerosolized into an atmosphere with 80–90% relative humidity corresponded to 70.3 J.m^?2, 73.3 J.m^?2 and 18.3 J.m^?2 for vegetative cells of B. atrophaeus, P. agglomerans, and Y. ruckeri cells, respectively. Additionally, the UV sensitivity of bacteria deposited directly on agar nutrient plates was determined after exposure to 254-nm UV with the F_–1Log10 for the same bacteria on surfaces corresponding to 128 J.m^?2, 28.1 J.m^?2, and 16.3 J.m^?2, respectively. These comparative results among different bacterial species, either airborne or on contaminated surfaces, should assist in predicting the survival of bacterial cells after transmission from infected patients or after an intentional release into the environment.     

Field Evaluation of Sampling Bias with Plastic Petri Dishes for Size-Fractionated Bioaerosol Sampling

Reusable glass dishes are recommended for use with the six-stage viable impactor for size-fractionated bioaerosol sampling. However, it is not convenient to use glass dishes because they are fragile and heavy, not to mention the time-consuming preparation process prior to bioaerosol sampling. On the other hand, disposable plastic dishes have been widely used in microbiology laboratories. However, plastic materials can retain electrostatic charges and may lead to sampling bias. The objective of this study was to evaluate the sampling bias with the use of plastic dishes when a multistage viable impactor is used for airborne fungi and bacteria sampling for field sampling. Two six-stage viable impactors were placed side-by-side 1 m apart in a 147-m³ room. One was used with plastic dishes and the other with glass dishes. Compared with the concentration data obtained with glass dishes, those collected with the plastic dishes demonstrated a significant difference for both fungi and bacteria. However, there was a strong correlation between the data obtained using glass and plastic dishes, which can be estimated by C_plastic = 0.88 C_glass for airborne fungi and C_plastic = 0.86 C_glass for airborne bacteria. When using plastic dishes fungi and bacteria counts were underestimated by 12% and 14%, respectively.

Copyright 2015 American Association for Aerosol Research     

Optimization of Propidium Monoazide Quantitative PCR for Evaluating Performances of Bioaerosol Samplers for Sampling Airborne Staphylococcus aureus

Airborne Staphylococcus aureus causes a significant proportion of nosocomial infections. The purpose of this study was to combine real-time quantitative polymerase chain reaction with the DNA-binding agent propidium monoazide (PMA-qPCR) to assess exposures to airborne S. aureus. In this work, we generated a S. aureus aerosol and used our assay to detect viable, airborne S. aureus in a study chamber. The biological collection efficiencies of three samplers (the AGI-30 impinger, BioSampler, and Nuclepore filter sampler) were evaluated using the S. aureus aerosols. The effects of storage in collection fluid on S. aureus sampled by the AGI-30 impinger and BioSampler were evaluated. Furthermore, air samples from an intensive care unit (ICU) and a gymnasium (GYM) were subsequently used to test the performance of a BioSampler combined with our PMA-qPCR technique. The BioSampler was more effective than the AGI-30 and Nuclepore filter samplers for preserving the culturability and viability of S. aureus aerosol samples. After sampling by impingement, the loss of viable S. aureus was minimized by treating the cells with PMA prior to storage at ?20°C and analyzing the samples by qPCR within 3 weeks. In field applications, we noted that traditional culture assays tended to underestimate the viable concentrations of S. aureus by approximately one order of magnitude. Overall, combining qPCR with and without PMA staining may be useful for assessing exposure to airborne S. aureus. However, a complex set of parameters that may affect the efficiency of PMA-qPCR must be taken into account before applying PMA-qPCR to bioaerosol detection.

Copyright 2014 American Association for Aerosol Research     

Investigation of the Efficiencies of Bioaerosol Samplers for Collecting Aerosolized Bacteria Using a Fluorescent Tracer. I: Effects of Non-sampling Processes on Bacterial Culturability

By sampling aerosolized microorganisms, the efficiency of a bioaerosol sampler can be calculated depending on its ability both to collect microorganisms and to preserve their culturability during a sampling process. However, those culturability losses in the non-sampling processes should not be counted toward the sampling efficiency. Prior to the efficiency assessment, this study was designed to investigate the culturability losses in three non-sampling processes: (1) the tracer uranine induced loss; (2) the loss during aerosolization (pre-sampling process); and (3) the bacteria and uranine recovery in air sample handling procedures for the samples of the Andersen 6-stage impactor and the Airport MD8 (post-sampling process). The results indicated that uranine had no significant effect on the culturability of Enterococcus faecalis, Escherichia coli, and Mycoplasma synoviae in suspensions (P > 0.05), but negatively affected the culturability of Campylobacter jejuni (P = 0.01). The culturability of E. faecalis, E. coli, and M. synoviae was not affected by stresses caused by aerosolization (P > 0.05). Only 29% of C. jejuni were still culturable during aerosolization (P = 0.02). In the air sample handling procedures, the four species of bacteria were recovered without significant losses from the samples of the Andersen impactor, but only 33–60% uranine was recovered. E. faecalis, E. coli, and M. synoviae were recovered without significant losses from the samples of the Airport MD8. More C. jejuni was recovered (172%), probably due to multiplication or counting variation. It is suggested that tracer and bacteria should be aerosolized separately when the tracer negatively affects the bacterial culturability. In both pre- and post-sampling processes, losses of bacterial culturability (or multiplication) may occur, which should be taken into account when assessing the efficiencies of bioaerosol samplers.     

Long-Term Sampling of Viable Airborne Viruses

A novel bioaerosol sampling technique, which utilizes the bubbling process in the collection fluid, has recently been developed and found feasible for a long-term personal sampling of airborne bacteria and fungal spores as it maintained high physical collection efficiency and high microbial recovery rate for robust and stress-sensitive microorganisms. Further tests have shown that the new technique also has potential to collect viable airborne viruses, particularly when utilized for a short-term sampling of robust strains. As the short-term sampling has a limited application for assessing personal exposure in bioaerosol-contaminated environments, the present study was undertaken to investigate the feasibility of the “bubbler” for a long-term monitoring of viable airborne viruses. Liquid droplets containing Vaccinia virions (that simulate Variola, a causative agent of smallpox) were aerosolized with a Collison nebulizer into a 400-liter test chamber, from which the droplets were collected by three identical prototype personal samplers in the liquid medium during different time periods ranging from 1 to 6 hours. The viral content was measured in the collection fluid of the sampler and in the initial suspension of the nebulizer using the fluorescence-based method and by enumerating plaque-forming units per milliliter of the fluids. The relative recovery of viruses after the sampling act was determined. The results show that the “bubbling” technique has consistent collection efficiency over time and is capable of maintaining the viability of Vaccinia, for at least 6 hours, with a loss in recovery rate of about 10%. The data demonstrate a good potential of the new technique for measuring personal exposure to robust airborne viruses over a long period.     

A Temperature-Controlled AGI-30 Impinger for Sampling of Bioaerosols

AGI-30 impingers are widely applied for the efficient collection of bioaerosols. However, these glass vessels are not protected against solar radiation and changing ambient temperature during sampling, which may impair the sampling efficiency by too high or low temperatures of the sampling liquid leading to early proliferation of microorganisms or ice formation. In order to reduce such disadvantages, an impinger holder was developed and tested under laboratory and field conditions, which insulates and controls the temperature of the impinger and the sampling liquid by means of a Peltier element. The influence of various ambient temperatures and relative humidities on the temperatures of tempered and untempered impinger liquids such as mineral oil, peptone water, and phosphate-buffered saline (PBS) during sampling periods of 30 min was investigated and compared. The type of sampling liquid greatly influenced the amount of residual liquid after sampling and the temperature in both the tempered and untempered impingers depended on the type of sample liquid, ambient temperature, and humidity. Mineral oil showed the lowest losses, followed by PBS and peptone water. Tempering of the impingers had some influence on the amount of losses. Tempering also strongly influenced the number of culturable bacteria (colony-forming unit [CFU]) in the sampling liquids. In the tempered impingers, three times higher CFU/m³ were found than in the untempered impingers. A great advantage of tempering was that sampling at ambient temperatures as low as ?5°C was possible. However, in spite of insulation and tempering the impinger to a fixed value, the variance was rather high due to varying ambient temperature and relative humidity, which always have a strong influence on condensation and evaporation and therefore on the amount of sample liquid and the resulting number of CFU. Nevertheless, the temperature-controlled AGI-30 impinger is a step forward to more stable results.     

Assessment of Bioaerosol Sampling Techniques for Viable Legionella pneumophila by Ethidium Monoazide Quantitative PCR

Legionella pneumophila causes severe pneumonia and Pontiac fever in humans. Rapid and sensitive bioaerosol monitoring techniques for viable L. pneumophila are unavailable. Coupled with a newly developed viable assay called ethidium monoazide with quantitative PCR (EMA-qPCR), this study applies EMA-qPCR to aerobiology for the first time to evaluate the effects of the method of sampling (all-glass impinger (AGI-30), BioSampler, and MAS-100 sampler) and sampling time (3, 30, 60 min) on the collection of viable L. pneumophila. The effects of the collection fluid (deionized water (DW) and Tween mixture) and the replenishment of DW every 15 min during 60-min sampling were also assessed. Escherichia coli, as a model microorganism in bioaerosol research, was also tested. Using the Tween mixture (DW containing 1% peptone, 0.01% Tween 80, and 0.005% antifoam), the AGI-30 and BioSampler performed significantly better than the MAS-100 sampler for collecting viable L. pneumophila and viable E. coli (P < 0.05). An increase in sampling time adversely affected the quantification of both bacterial species (P < 0.05). The collection with DW yielded greater recovery of viable L. pneumophila than the Tween mixture in both AGI-30 and BioSampler, regardless of sampling time, by a factor of 1.4–6.9 (P < 0.05). The replenishment of DW every 15 min further improved the collection of viable L. pneumophila. This study demonstrates that viable L. pneumophila can be efficiently sampled by the AGI-30 and BioSampler and successfully quantified by EMA-qPCR.     

Cyclic fatigue—crack growth along polymer/glass interfaces

Delamination of polymer/glass interfaces was studied under cyclic and monotonic loading using an interfacial, four-point flexure sandwich specimen. Specifically, crack growth rates along epoxy acrylate/glass interfaces were characterized over a range of velocities from 10⁻⁹ to 10⁻⁶ m/s as a function of low (10–20% RH) and high (75–80% RH) humidities. For low humidities, interfacial crack growth rates under cyclic loading are almost two orders of magnitude greater than those under monotonic loading with energy release rates G = G_max of the cyclic loading. At high humidities, interfacial crack growth rates under monotonic loading are approximately equal to cyclic fatigue crack growth rates at low humidity.     

Performance of CHROMagar VRE Medium for the Detection of Airborne Vancomycin-Resistant/Sensitive Enterococcus Species

Vancomycin-sensitive and vancomycin-resistant Enterococcus (VSE and VRE) species have become a significant health problem. CHROMagar medium, which permits direct, color-based identification of target pathogens, could potentially be used to rapidly monitor airborne VSE and VRE. In this study, the efficiency of CHROMagar VRE medium without vancomycin supplementation (CVSE) for collecting airborne vancomycin-sensitive Enterococcus faecalis was evaluated in a chamber study. Subsequently, the performance of bioaerosol samplers combined with CVSE and CHROMagar VRE (CVRE) was evaluated in a hospital environment, a wastewater treatment plant, and a pig-rearing facility. Our results demonstrated that an Andersen impactor was much more effective than a Nuclepore filter for collecting airborne E. faecalis at relative humidity levels of 30% and 55%. In addition, approximately 10% of the isolated environmental Enterococcus strains were vancomycin-resistant. The average sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of the colony identification were 58.5%, 81.3%, 5.5%, and 99.1%, respectively, for CVSE and 100%, 88.3%, 8.4%, and 100%, respectively, for CVRE. These findings indicate that the use of CHROMagar might provide a rapid method for detecting airborne VSE or VRE, shortening the detection time to 24–48 h. However, any mauve-colored colonies recovered on CVSE or CVRE by air sampling should be subjected to further identification tests.

Copyright 2014 American Association for Aerosol Research     

A novel laminar-flow-based bioaerosol test system to determine biological sampling efficiencies of bioaerosol samplers

In this work, we describe a novel type of bioaerosol test system based on a laminar airflow chamber that provides a homogenous aerosol of microbial cells with known concentrations and defined culturability to bioaerosol samplers positioned in the chamber. In the system, three control and monitoring points (CMPs) are implemented in which the number and culturability of microbes can be determined by combining optical particle counting with microscopic and culture-based microbiological analyses. This lineup is designed to quantify the biological sampling efficiency (BSE) of a bioaerosol sampling device. Seven bioaerosol samplers were tested with four fungal and one bacterial species and their BSEs have been determined under optimized standard operating conditions. After executing tests with the appropriate statistical power, this new laminar-flow platform demonstrated the sensitivity necessary to determine significant differences in the recovery efficiency of viable fungal spores and bacterial cells in modern samplers. Under these test conditions, the samplers showed considerable differences in BSEs for the individual fungal and bacterial species. Our data demonstrate that a large number of experimental repetitions and measurements under tightly controlled and monitored conditions are necessary to quantify the BSE of a given sampler and to compare them to each other. Employing this system improves biological evaluation of samplers because natural environments are not suitable for this task due to their high variabilities in homogeneity and distribution of cells as well as fluctuations in culturability ratios.

© 2019 American Association for Aerosol Research     

Concentration and Size Distribution of Culturable Airborne Microorganisms in Outdoor Environments in Beijing,China

A one-year (from June 2003 to May 2004) study of airborne microbial concentration and size distribution was conducted systematically at three selected sampling sites in Beijing. Microbial samples were collected in triplicate for 3 min, 3 times per day, for 3 consecutive days of each month using FA-I sampler (imitated Andersen sampler, made by Applied Technical Institute of Liaoyang, China). Results showed that the concentration of total culturable microorganisms ranged from 4.8 × 10 ² colony forming units (CFU)/m ³ to 2.4 × 10 ⁴ CFU/m ³ , with an arithmetic mean of 3.7 × 10 ³ ± 2.1 × 10 ² (standard deviation) CFU/m ³ . As a whole, the percentage of airborne bacteria, accounting for 59.0% of the total culturable microorganisms, was significantly higher than those of airborne fungi (35.2%) and actinomycetes (5.8%). At RCEES (Research Center for Eco-Environmental Sciences—a culture and education area) and XZM (Xizhimen—a main traffic line), significantly higher percentages of airborne bacteria were found as compared to airborne fungi. No significant difference was observed between airborne bacteria and fungi at BBG (Beijing Botanical Garden—a green garden area). The total microbial concentration was significantly higher at RCEES than at XZM and BBG (*P < 0.05), and no significant difference between XZM and BBG was observed (P > 0.05). Total microbial concentrations were higher in summer and autumn, and lower in spring and winter at RCEES and XZM (*P < 0.05). At BBG, higher concentration was observed in summer during the sampling periods (***P < 0.001). The size distribution of airborne bacteria showed a skewed distribution at three sampling sites. The proportion of bacterial particles decreased gradually from Stage 1 ( > 7.0 μm) to Stage 6 (0.65 ～ 1.1 μm), and there was an obvious downtrend on Stage 2 (4.7 ～ 7.0 μm). Bacterial particles were mainly distributed at the first four Stages ( > 2.1 μm), accounting for 78.6% at RCEES, 84.0% at XZM, and 81.5% at BBG. The size distribution pattern of airborne fungi was found with normal logarithmic distribution at three sampling sites. Fungal particles were mainly distributed at Stage 3 (3.0 ～ 6.0 μ m), Stage 4 (2.0 ～ 3.5 μ m) and Stage 5 (1.0 ～ 2.0 μ m), composing 71.6% of the population at RCEES, 74.2% at XZM, and 68.3% at BBG. However, different distribution patterns were found in different dominant fungal genera. Cladosporium, Penicillium, and Aspergillus were present with normal logarithmic distribution, while Alternaria and sterile mycelia were found with skewed distribution. In opposition to the distribution pattern of fungal particles, the actinomycete particles at all sampling sites were primarily collected on Stage 1, Stage 5, and Stage 6, accounting for 61.1% at RCEES, 60.7% at XZM, and 64.8% at BBG.     

Soybean lipoxygenase is active on nonaqueous media at low moisture: a constraint to xerophilic fungi and aflatoxins?

Previous workers have reported that certain products of the lipoxygenase pathway are detrimental either to the development and growth of Aspergillus species or to aflatoxin production by these organisms. Since Aspergillus often thrives on “dry” stored grains, depending on the level of the relative humidity, we sought to determine if lipoxygenase could catalyze the oxidation of linoleic acid on these “dry” substrates equilibrated at various relative humidities. A desiccated model system, previously adjusted to pH 7.5, was composed of soybean extract, linoleic acid, and cellulose carrier. The model system was incubated for up to 24 h at four relative humidities ranging between 52 and 95% to determine the extent of oxidation catalyzed by lipoxygenase, compared with heat-inactivated controls. Oxidation in the active samples was much greater than in the controls at all relative humidities, and oxidation was principally enzymatic as demonstrated by chiral analysis of the linoleate hydroperoxides formed. The main product was 13S-hydroperoxy-9Z,11E-octadecadienoic acid, accompanied by a significant percentage of 9S-hydroperoxy-10E,12Z-octadecadienoic acid. Since the products became more racemic with time of incubation, autoxidation appeared to be initiated by the lipoxygenase reaction in dry media. Additionally, the biological relevance of lipoxygenase activity was tested under these xerophilic conditions. Thus, enzyme-active and heat-inactivated defatted soy flour amended either with or without 3.5% by weight linoleic acid was inoculated with fungal spores and incubated at 95% relative humidity. Although fungal growth occurred on all treatments, samples inoculated with Aspergillus parasiticus showed significantly less aflatoxin in the enzyme-active samples, compared to inactivated flour. Addition of linoleic acid had little effect, possibly because the defatted soy flour was found to contain 1.7% residual linoleic acid as glyceride lipid.     

New personal sampler for viable airborne viruses: feasibility study

While various sampling methods exist for collecting and enumerating airborne bacteria and fungi, no credible methodology has yet been developed for airborne viruses. A new sampling method for monitoring the personal exposure to bioaerosol particles has recently been developed and evaluated with bacteria and fungi. In this method, bacterial/fungal aerosol is aspirated and transported through a porous medium, which is submerged into a liquid layer. As the air is split into numerous bubbles, the particles are scavenged by these bubbles and effectively removed. The current feasibility study was initiated to evaluate the efficiency of the new personal sampler prototype (“bubbler”) with airborne viable viruses. Two common viral strains, Influenza (stress-sensitive) and Vaccinia (robust), were aerosolized in the test chamber and collected by two identical “bubblers” that operated simultaneously for a duration of upto 5 min. A virus maintenance liquid, proven to be the optimum collecting environment for the test organisms, was used as a collection fluid. After sampling, the collecting fluid was analyzed and the viral recovery rate was determined. The overall recovery (affected not only by the sampling but also by the aerosolization and the aerosol transport) was 20% for Influenza virus and 89% for Vaccinia virus. The new sampling method was found feasible for the collection and enumeration of robust airborne viruses.     

Macromolecular design of novel sulfur‐containing copolyesters with promising mechanical properties

The miscibility of poly(butylene succinate) (PBS)/poly(butylene thiodiglycolate) (PBTDG) blends was investigated by DSC technique. PBS and PBTDG were completely immiscible in as blended‐state, as evidenced by the presence of two T_gs at ?34 and ?48°C, respectively. The miscibility changes upon mixing at elevated temperature: the original two phases merged into a single one because of transesterification reactions. Poly(butylene succinate/thiodiglycolate) block copolymers, prepared by reactive blending of the parent homopolymers, were studied to investigate the effects of transesterification reactions on the molecular structure and solid‐state properties. ¹³C‐NMR analysis evidenced the formation of copolymers whose degree of randomness increased with mixing time. Thermal characterization results showed that all the samples were semicrystalline, with a soft rubbery amorphous phase and a rigid crystal phase whose amount decreased by introducing BTDG units into the PBS chain (20 ≤ χ_c ≤ 41). Lastly, the mechanical properties were found strictly related to crystallinity degree (χ_c), the random copolymer, exhibiting the lowest elastic modulus (E = 61 MPa) and the highest deformation at break (ε_b (%) = 713). © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Drastic Attenuation of Pseudomonas aeruginosa Pathogenicity in a Holoxenic Mouse Experimental Model Induced by Subinhibitory Concentrations of Phenyllactic acid (PLA)

The discovery of communication systems regulating bacterial virulence has afforded a novel opportunity to control infectious bacteria without interfering with growth. In this paper we describe the effect of subinhibitory concentrations of phenyllactic acid (PLA) on the pathogenicity of Pseudomonas aeruginosa in mice. The animals were inoculated by oral (p.o.), intranasal (i.n.), intravenous (i.v.) and intraperitoneal (i.p.) routes with P. aeruginoasa wild and PLA-treated cultures. The mice were followed up during 16 days after infection and the body weight, mortality and morbidity rate were measured every day. The microbial charge was studied by viable cell counts in lungs, spleen, intestinal mucosa and blood. The mice batches infected with wild P. aeruginosa bacterial cultures exhibited high mortality rates (100 % after i.v. and i.p. route) and very high cell counts in blood, lungs, intestine and spleen. In contrast, the animal batches infected with PLA treated bacterial cultures exhibited good survival rates (0 % mortality) and the viable cell counts in the internal organs revealed with one exception the complete abolition of the invasive capacity of the tested strains. In this study, using a mouse infection model we show that D-3-phenyllactic acid (PLA) can act as a potent antagonist of Pseudomonas (P.) aeruginosa pathogenicity, without interfering with the bacterial growth, as demonstrated by the improvement of the survival rates as well as the clearance of bacterial strains from the body.     

Superposition of electrical properties in temperature-sensing wire composed of thermosensitive polyamide–phenol compounds at various temperatures and humidities

The relationship between the DC conductance (G) and the capacitance (C) in temperaturesensing wire composed of thermosensitive polyamide–phenol compounds has been studied. The G–C characteristics at various temperatures and humidities are approximately plotted on a same line, and the log G–log C plots draw a straight line with time. This implies that when the temperature-sensing wire is in equilibrium under the constant temperature and humidity, if either one of them has been known, the other value is determined from the characteristics. These characteristics will be available properties, e.g., for the temperature and humidity sensing material. These also show that the electrical behaviors due to an absorbed water cannot be distinguished from that due to the amide and phenol groups. This is because that both of them constitute the similar dielectric segments composed of hydrogen bonds, and proton carriers for conduction also generate from them. It also shows that the behaviors of protons from amide, phenol group, and absorbed water cannot be electrically distinguished from one another. It is deduced that the absorbed water mainly contributes to the number of proton carriers and the increase in moisture content contributes more to the DC conductance instead of less than the increase of mobility due to thermal activation of the proton carriers generating from amide, phenol, and absorbed water.     

Investigation of the Efficiencies of Bioaerosol Samplers for Collecting Aerosolized Bacteria Using a Fluorescent Tracer. II: Sampling Efficiency and Half-Life Time

Using uranine as a physical tracer, this study assessed the sampling efficiencies of four bioaerosol samplers (Andersen 6-stage impactor, all glass impinger “AGI-30,” OMNI-3000, and Airport MD8 with gelatin filter) for collecting Gram-positive bacteria (Enterococcus faecalis), Gram-negative bacteria (Escherichia coli and Campylobacter jejuni), and bacteria without cell wall (Mycoplasma synoviae) which were aerosolized in a HEPA isolator. In addition, the half-life times of these bacteria in aerosols were estimated. The uranine concentrations collected by the samplers were used for calculating the physical efficiencies, and the bacteria/uranine ratios were used for calculating the biological efficiencies. The results show the Airport MD8 had the highest physical efficiency. Compared with the Airport MD8, the physical efficiencies of the AGI-30 and the OMNI-3000 were 74% and 49%, respectively. A low physical efficiency of the Andersen impactor (18%) was obtained, but it was mainly caused by the incomplete recovery of uranine when handling the air samples, so could not be ascribed to the sampler efficiency. Both the Andersen impactor and the AGI-30 showed high biological efficiencies for all four bacterial species. The biological efficiencies of the OMNI-3000 for C. jejuni (1%) and of the Airport MD8 for E. coli (38%) and C. jejuni (2%) were significantly lower than 100%, indicating that their sampling stresses inactivated the bacterial culturability. The half-life times at 21–23°C temperature and 80–85% relative humidity were 43.3 min for E. faecalis, 26.7 min for M. synoviae, 21.2 min for E. coli, and 4.0 min for C. jejuni in the air.     

Bubble size and radial gas hold‐up distributions in a slurry bubble column using ultrafast electron beam X‐ray tomography

Gas hold‐up and bubble size distribution in a slurry bubble column (SBC) were measured using the advanced noninvasive ultrafast electron beam X‐ray tomography technique. Experiments have been performed in a cylindrical column (D_T = 0.07 m) with air and water as the gas and liquid phase and spherical glass particles (d_P = 100 μm) as solids. The effects of solid concentration (0 ≤ C_s ≤ 0.36) and superficial gas velocity (0.02 ≤ U_G ≤ 0.05 m/s) on the flow structure, radial gas hold‐up profile and approximate bubble size distribution at different column heights in a SBC were studied. Bubble coalescence regime was observed with addition of solid particles; however, at higher solid concentrations, larger bubble slugs were found to break‐up. The approximate bubble size distribution and radial gas hold‐up was found to be dependent on U_G and C_s. The average bubble diameter calculated from the approximate bubble size distribution was increasing with increase of U_G. The average gas hold‐up was calculated as a function of U_G and agrees satisfactorily with previously published findings. The average gas hold‐up was also predicted as a function of C_s and agrees well for low C_s and disagrees for high C_s with findings of previous literature. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1709–1722, 2013     

PCR and gene probes for detecting bioaerosols

Current methods for analyzing bioaerosols are based on maintaining organism viability and quantifying culturability; this can result in underestimation of concentrations. A feasibility study investigated a new analytical technique that only requires intact cellular DNA to identify organisms. This technique uses the polymerase chain reaction (PCR) to amplify specific DNA sequences from an organism, and hybridization of PCR product with DNA probes, to detect and quantify organisms. Legionella pneumophila solutions were aerosolized in a chamber, and air samples were collected using impingers and membrane filters. Samples were analyzed using the PCR-gene probe technique and gel electrophoresis. Results were compared with traditional plate counting and direct microscopic counts of cells stained with acridine orange. Results indicated that the PCR-gene probe technique provides a new way to identify and quantify bioaerosols that does not rely on viability and culturability. Therefore, the method would provide a more reliable estimate of airborne bacterial concentrations compared to traditional plate counts.