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.     

Associations of Fungal Aerosols,Air Pollutants,and Meteorological Factors

The relationships between fungal aerosols and air pollutants meteorological factors were investigated in the Taipei urban area. In summer, it was observed that geometric mean (GM) concentrations of airborne fungal aerosols were 2,835 CFU m^-3 and 2,651 CFU m^-3 at Kuting and Hsichih stations, respectively. In winter, GM levels of airborne fungi were 1,107 CFU m I 3 and 2,248 CFU m^-3 at Kuting and Hsichih stations, respectively. Moreover, fungal aerosol concentrations were observed to highly depend on weather conditions, and the highest concentration of total colony counts appeared when the temperature was 25-30 C, the RH was 60-70% , and the wind speed was > 1 m s^-1 and from the S-SE wind direction. In addition, total fungal concentrations were negatively correlated with ozone concentrations, and concentration of Cladosporium spp. was positively correlated with hydrocarbons. PM₁₀ were positively correlated with Penicillium and the yeasts in Hsichih station. Our results demonstrated that airborne fungal aerosols are definitely correlated with air pollutants and meteoro logical factors. The complex dynamic interactions were indicated to occur among bioaerosols, air pollutants, and meteorological factors.     

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     

Adsorption and antibacterial activity of silver‐dispersed carbon aerogels

Silver‐dispersed carbon aerogels (Ag/CAs) were obtained by the direct immersion of organic aerogels in aqueous AgNO₃ solutions and then carbonization of the resulting material under a nitrogen atmosphere. The adsorption and antibacterial activity of Escherichia coli and Staphylococcus aureus on Ag/CAs were studied by the measurement of the amount of viable bacteria in suspensions and scanning electron microscopy (SEM) observations. The adsorbed amount of bacteria on samples without silver increased with an increase in the carbonization temperature and contact time. SEM studies showed that the adsorption capacity of Ag/CAs decreased with an increase in the silver content; this was considered to be mainly due to the dissolution behavior of bacteria by silver ions. The antibacterial test showed that 2.5 mg of Ag/CAs with more than 3.6% Ag could inhibit the growth of 10⁵ cfu/mL E. coli in 10 mL of a Mueller–Hinton broth culture, but in the case of S. aureus, 10‐mg samples just got the same antibacterial effect. An antibacterial persistency test showed that 25 mg of Ag/CAs with 6.5% Ag could kill 50 mL of 10⁵ cfu/mL E. coli eight times. These results indicate that Ag/CAs possess strong and long‐term antibacterial activity. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1030–1037, 2006     

Dairy biofilm: an investigation of the impact on the surface chemistry of two materials: silicone and stainless steel

Biofilms are the most common mode of bacterial growth in nature and the formation will occur on organic or inorganic solid surfaces in contact with a liquid. The aims of this study were, by combining numeration and sessile drop technique, (i) to characterize the structural dynamics of dairy biofilm growth and the physico chemical properties on silicone and stainless steel and (ii) to evaluate the impact of bio-adhesion on chemistry of surfaces at different times of contact (2, 7, 9 and 24?h). Significantly, greater biofilm volumes were observed after 48?h on two materials. Gram-positive bacteria and fungal population exhibited a significantly higher biofilm organization than gram-negative (43–64%). Elsewhere, after 48?h, results showed a slight difference on gram-negative adhered cells on stainless steel than silicone (2.6?×?10⁷?cfu/cm² and 4.7?×?10⁵?cfu/cm², respectively). Moreover, the physico chemical properties of the surfaces showed that the silicone and stainless steel have a hydrophobic character (Giwi?=??68.28?mJ/m² and ?57.6?mJ/m², respectively). Also, both the surfaces present a weak electron donor character (γ ^??=?2.2?mJ/m² and 4.1?mJ/m², respectively). The real-time investigation of the impact of dairy biofilm on the physico chemical properties of the materials has shown a decrease of hydrophobicity degree of the silicone surface that becomes hydrophilic (ΔGiwi?=?11.47?mJ/m²) after 7?h and the increase of electron donor character (γ ^??=?75.8?mJ/m²). Elsewhere, bio-adhesion on stainless steel was accompanied with a decrease of hydrophobicity degree of the surface, which becomes hydrophilic after 7?h of contact (ΔGiwi?=?6.62?mJ/m²) and the increase of the electron donor character (γ ^??=?44.8?mJ/m²). While, after 24?h of contact, results showed a decrease of the hydrophilicity degree and surface energy components of silicone and stainless steel that become hydrophobic (ΔGiwi?=??21.2?mJ/m² and ΔGiwi?=??56.51?mJ/m², respectively) and weak electron donor (γ ^??=?14.0 and 2.3?mJ/m², respectively).     

A Comparison of Replicate Field Samples Collected with the Bi-Air,Air-O-Cell,and Graesby-Andersen N6 Bioaerosol Samplers

The Bi-Air (BA) and Air-O-Cell (AOC) cassettes have been compared for the collection of Aspergillus/Penicillium (Asp/Pen) and Chaetomium spores based on replicate and/or duplicate samples collected under typical field conditions. Total culturable Asp and Pen concentrations were also compared for the BA and the N6 impactor based on duplicate field samples. When single Asp/Pen spores or small chains were dominant, the average BA:AOC concentration ratio was 2.1 (11,260 spores/m³ v 5,400 spores/m³) for six duplicate samples collected in a well-mixed room. This ratio was consistent with previous studies performed under controlled conditions. However, the average BA:AOC concentration ratio was 54 (765,00 spores/m³ v 36,800 spores/m³) for four replicate samples in which small Asp/Pen spores and clusters of Asp/Pen spores were dominant. The average BA:AOC concentration ratio for Chaetomium was typically 8.6, with a high of 100 for the four replicate samples in which Asp/Pen clusters were dominant. It was concluded that the performance of the BA and the AOC, except for a reasonably constant 2:1 ratio of concentrations, were similar for the detection of single Asp/Pen spores or small chains. However, the BA generally detected higher concentrations of Asp/Pen spores when clusters were dominant; and detected Chaetomium spores in more of the replicate field samples and at a higher average concentration.

The average concentrations of culturable Aspergillus and Penicillium were not statistically different for six duplicate N6 and BA samples collected in a well-mixed room. For nine duplicate field samples with N6 concentrations of total culturable fungi greater than 1,000 cfu/m³, the N6 and BA were moderately correlated (r = 0.76). It was concluded that the ability of the BA to collect culturable fungi was similar to that of the N6 for short-term samples.     

Evaluation of a Methodology for Quantifying the Effect of Room Air Ultraviolet Germicidal Irradiation on Airborne Bacteria

As a result of the recent resurgence in tuberculosis (TB) and the increasing incidence of multidrug-resistant TB, there has been renewed interest in engineering controls to reduce the spread of TB and other airborne infectious diseases in high-risk settings. Techniques such as the use of lamps that produce ultraviolet germicidal radiation may reduce exposure to infectious agents by inactivating or killing microorganisms while they are airborne. We designed and evaluated a test method to quantitatively estimate the efficacy of germicidal lamps, in conjunction with dilution ventilation, for reducing the concentration of viable airborne bacteria. Bacterial particles were generated in a 36m³ room and collected with midget impingers at 5-7 locations. The effectiveness of the control technique was determined by comparing concentrations of culturable airborne bacteria with and without the control in operation. Results for a single, 15 W germicidal lamp showed reductions of 50% for Bacillus subtilis (B. subtilis) and Micrococcus luteus (M. luteus); tests with Escherichia coli (E. coli) showed nearly 100% reduction (E. coli were isolated only from the sampler nearest the aerosol source when the lamp was operating). The addition of louvers to a lamp greatly reduced its efficacy. Decay experiments showed that roughly 4-6 equivalent air changes per hour were achieved for B. subtilis with one or two lamps operating. These preliminary experiments demonstrated that this methodology was well suited for these evaluations and identified factors that could be modified to refine the study design for future work.     

ALIPHATIC,POLYCYCLIC AROMATIC HYDROCARBONS AND NITRATED-POLYCYCLIC AROMATIC HYDROCARBONS IN PM 10 IN SOUTHWESTERN MEXICO CITY

A sampling campaign of airborne particles ≤ 10 μ m (PM ₁₀ ) was carried out from February to April of 2004 at the Universidad Nacional Autónoma de México in southwestern Mexico City. The average PM ₁₀ mass concentration was 51 ± 14 μ g m^?3. Extracted organic matter was determined, with a mean of 6.5 ± 1.7 μ g m^?3, which represents 12.9% of PM ₁₀ mass concentration. The standard additions method was used on real samples at four concentration levels for 13 n-alkanes, 14 PAHs and 5 nitro-PAHs. The average concentration for the sum was 99.04 ng m^{? 3} for n-alkanes, 4.9 ng m^?3 for PAHs and 710 pg m^{? 3} for nitro-PAHs. Higher concentrations of n-alkanes > C ₂₄ were found, indicating biogenic emissions as the dominant source. Coronene, benzo[ghi]perylene, benzo[b+j+k]fluoranthenes and indeno[1,2,3-cd]pyrene were the most abundant PAHs, suggesting a strong contribution from incomplete combustion of gasoline. The PAHs considered for calculating BaPE represented 52% of the total PAHs analyzed. The presence of 9-nitroanthracene indicates direct emission from diesel combustion and heterogeneous nitrating reactions on sorbed particles, while 2-nitrofluoranthene, indicates gas-phase reactions with fluoranthene, hydroxyl (OH^?) and/or nitrate (NO ₃ ^?) radicals in the presence of nitrogen oxides (NOx).     

Experimental and numerical study of the performance of upper-room ultraviolet germicidal irradiation with the effective Z-value of airborne bacteria

Upper-room ultraviolet germicidal irradiation (UR-UVGI) is recommended for the defense against airborne pathogens in poorly ventilated rooms in public buildings or high risk environments, such as hospitals. Currently, there are few studies on the performance of UR-UVGI with the effective bacteria susceptibility constant (eZ-value) obtained from UR-UVGI experiment. In this study, the Eulerian model for the inactivation of UVGI was improved to consider the difference between exposure time and computational time, and was validated by our previous experiments. The method was applied to study numerically the performance of the UR-UVGI for 3, 6, and 10 air changes per hour (ACH) with the application of the eZ-value of airborne bacteria. Moreover, the eZ-values of commonly found bacteria, including Serratia marcescens, Staphylococcus epidermidis, Pseudomonas alcaligenes, and Micrococcus luteus, were obtained from a series of experiments in a full-scale environmental chamber equipped with a UR-UVGI fixture. The eZ-values were 0.0983, 0.0586, 0.0476, and 0.0115 m²/J, respectively. Compared with the data in the literature, these eZ-values of the tested bacteria are different from the Z-values obtained from single-pass UVGI. The simulation results show that UR-UVGI exhibited the highest inactivation efficiency on S. marcescens among the tested bacteria in this study. The percentage of bacteria inactivated by UR-UVGI decreased as the ventilation rate increased. The bacteria concentration in the breathing zone under low ventilation rate could be decreased using UR-UVGI. The findings demonstrate that high indoor air quality can be achieved with the application of UR-UVGI without the need to maintain high ventilation rate.

Copyright © 2017 American Association for Aerosol Research     

New Ammonium- and 1,2,4-Triazolium-Based Ionic Liquids for Wood Preservation

Biological activity of new potential wood preservatives—ammonium- and triazolium-based ionic liquids—was determined employing screening agar-plate, agar-block, and perlite-block methods. Experiments were carried out on Scots pine (Pinus sylvestris L.) and beech (Fagus sylvatica L.) wood. This study examined the effect of the ionic liquid structure on anti-fungal efficacy, depth of penetration, and fixation in wood. It was stated that the fungicidal value of new ammonium compounds depended, above all, upon the cation structure; for Coniophora puteana, it ranged from 2.7 kg m^?3 to 4.6 kg m^?3. These compounds effectively protected Scots pine wood against the action of mold fungi. Ammonium ionic liquids with a nitrite anion were characterized by strong fungitoxic properties, stronger than ammonium nitrates. The application in the amount of 15 g m^?2 caused an insignificant growth of mold fungi on the surface of Scots pine wood. For the mixture of 7.5% tebuconazole and 7.5% propiconazole dissolved in ionic liquids, the synergistic effect against mold fungi at the application of 15 g m^?2 was found. Dissolving tebuconazole in didecyldimethylammonium nitrate repeatedly lowered the fungicidal value against brown-rot fungi, as well as increased penetration of the ionic liquids in wood. This was associated with reduced viscosity of this ionic liquid caused by the addition of 1,2,4-triazole derivatives. Quaternary derivatives of 1,2,4-triazoles showed very high activity against blue stain and wood-decaying fungi. Additionally, most of the test compounds were well-fixed in Scots pine wood. The spectral study in infrared confirmed that nitrite, nitrate anions, and didecyldimethylammonium cation were retained in the treated wood.     

Fluorochrome in Monitoring Indoor Bioaerosols

In this study total concentration, viability, culturability of indoor and outdoor bioaerosols in ten residential environments were studied by using a cultivating method and an epifluorescence microscopy method with fluorochrome (EFM/FL) using four different dyes (AO, DAPI, PI, and YOPRO-1). Results from the EFM/FL were then compared with those from the traditional cultivating method. The total indoor microbial cell concentrations measured by EFM/FL was 630 to 5200 times higher than that measured by the cultivating method; ranging from 1.38 × 10⁶ to 4.48 × 10⁶cells/m³ (microbial cells per cubic meter) with AO staining, and from 7.84 × 10⁵ to 2.75 × 10⁶ cells/m³ with DAPI staining, compared with the average concentration of 721 CFU/m³ for bacteria and 587 CFU/m³ for fungi by the cultivating methods. The viability of bioaerosols ranged from 0.63 to 0.92 by EFM/FL with PI staining, from 0.19 to 0.72 by EFM/FL with YOPRO-1 staining, and from 0.0002 to 0.0015 by the cultivating method. The viability determined by EFM/FL was much higher than the culturability. In summary, the total microbial cell concentration and viability were highly underestimated by the cultivating method. In conclusion, EFM/FL method can effectively assess the total concentration and viability of bioaerosols in indoor samples.     

Dominant Mechanisms that Shape the Airborne Particle Size and Composition Distribution in Central California

The size and composition of ambient airborne particulate matter is reported for winter conditions at five locations in (or near) the San Joaquin Valley in central California. Two distinct types of airborne particles were identified based on diurnal patterns and size distribution similarity: hygroscopic sulfate/ammonium/nitrate particles and less hygroscopic particles composed of mostly organic carbon with smaller amounts of elemental carbon. Daytime PM₁₀ concentrations for sulfate/ammonium/nitrate particles were measured to be 10.1 μ g m^?3, 28.3 μ g m^?3, and 52.8 μ g m^?3 at Sacramento, Modesto and Bakersfield, California, respectively. Nighttime concentrations were 10–30% lower, suggesting that these particles are dominated by secondary production. Simulation of the data with a box model suggests that these particles were formed by the condensation of ammonia and nitric acid onto background or primary sulfate particles. These hygroscopic particles had a mass distribution peak in the accumulation mode (0.56–1.0 μ m) at all times. Daytime PM₁₀ carbon particle concentrations were measured to be 9.5 μ g m^?3, 15.1 μ g m^?3, and 16.2 μ g m^?3 at Sacramento, Modesto, and Bakersfield, respectively. Corresponding nighttime concentrations were 200–300% higher, suggesting that these particles are dominated by primary emissions. The peak in the carbon particle mass distribution varied between 0.2–1.0 μ m. Carbon particles emitted directly from combustion sources typically have a mass distribution peak diameter between 0.1–0.32 μ m. Box model calculations suggest that the formation of secondary organic aerosol is negligible under cool winter conditions, and that the observed shift in the carbon particle mass distribution results from coagulation in the heavily polluted concentrations experienced during the current study. The analysis suggests that carbon particles and sulfate/ammonium/nitrate particles exist separately in the atmosphere of the San Joaquin Valley until coagulation mixes them in the accumulation mode.     

Real-time measurement of bacterial aerosols with the UVAPS: performance evaluation

This paper presents the results of the laboratory evaluation of the Ultraviolet Aerodynamic Particle Size Spectrometer, the novel instrument for real-time continues monitoring of bioaerosols. The main focus of this study was on evaluating selectivity, sensitivity, counting efficiency, and the detection limits of the UVAPS. The tests were performed with two types of aerosols, bacterial (e.g., Bacillus subtilis spores or vegetative cells, and Pseudomonas fluorescens) and non-bacterial (e.g., NaCl, latex, peptone water, and nutrient agar/broth). To control viability of airborne bacteria, the bioaerosols were simultaneously sampled with the AGI-30 impingers. The study has demonstrated the UVAPS cross-sensitivity to the non-bacterial organic materials and the need for careful preparation (washing) of test bacteria, in order to avoid the interference with the fluorescence signals of nutrient media used to grow bacteria. The results were indicative of strong sensitivity of the UVAPS to the type of airborne bacteria. The limitations in the capability of the UVAPS to measure bacterial spores were also found. Counting efficiency of the fluorescent particles was shown to depend on particle concentration with the upper limit of detection of the UVAPS approximately 6×10⁷ particles/m³.     

Protein recovery from dairy industry wastes with aerobic biofiltration

Experiments were carried out to improve the economics of effluent treatment by the recovery of single cell protein. Field observations showed that acidic strong wastes, such as those from the dairy industry, produced a predominantly fungal biomass. Mixtures of dairy waste and domestic sewage did not produce fungal films. The most common fungi isolated were Fusarium and Geotrichum, but the species was affected by local conditions, i.e. creamery, yoghurt, milk or cheese wastes and the load to the plant. Batch culture was used to determine the growth requirements of Fusarium and Geotrichum and continuous culture, on vertical and horizontal fixed films, to determine growth and sloughing at different organic loads. The fungi grew well on acidic strong wastes which would discourage other organisms. A 1 m³ h^?1 pilot plant was built to treat the wastes from cheese, butter and cream production. The plant was run at pH 4–5 and at between 5 and 10 kg of BOD day^?1 m^?3. BOD removal was between 30 and 50% and biomass production between 0.1 and 0.5 kg of dry solids day^?1. The filamentous fungal growth was separated from the tower effluent by an inclined screen. The amino acid content of the product was similar to other single-cell protein. Feeding trials are being carried out.     

Analysis of Aerosolized Particulates of Feedyards Located in the Southern High Plains of Texas

The objective of this study was to quantify, size, and examine the composition of particulates found in ambient aerosolized dust of four large feedyards in the Southern High Plains. Ambient air samples (concentration of dust) were collected upwind (background) and downwind of the feedyards. Aerosolized particulate samples were collected using high volume sequential reference ambient air samplers, PM ₁₀ and PM _2.5 , laser strategic aerosol monitors, cyclone air samplers, and biological cascade impactors. Weather parameters were monitored at each feedyard. The overall (main effects and estimable interactions) statistical (P < 0.0001) general linear model statement (GLM) for PM ₁₀ data showed more concentration of dust (μg/m ³ of air) downwind than upwind and more concentration of dust in the summer than in the winter. PM _2.5 concentrations of dust were comparable for 3 of 4 feedyards upwind and downwind, and PM _2.5 concentrations of dust were lower in the winter than in the summer. GLM (P < 0.0001) data for cascade impactor (all aerobic bacteria, Enterococcus spp, and fungi) mean respirable and non-respirable colony forming units (CFU) were 676 ± 74 CFU/m ³ , and 880 ± 119 CFU/m ³ , respectively. The PM ₁₀ geometric mean size (±GSD) of particles were analyzed in aerosols of the feedyards (range 1.782 ± 1.7 μm to 2.02 ± 1.74μm) and PM _2.5 geometric mean size particles were determined (range 0.66 ± 1.76 μm to 0.71 ± 1.71 μm). Three of 4 feedyards were non-compliant for the Environmental Protection Agency (EPA) concentration standard (150 μg/m ³ /24 h) for PM ₁₀ particles. This may be significant because excess dust may have a negative impact on respiratory disease.     

Yogurt Starter Obtained from Lactobacillus plantarum by Spray Drying

Probiotics have been known to mankind for many centuries and the quest for its health benefits is increasing in this century through focused research on various food products. Researchers have a growing interest in probiotics starter cultures for fermented milk products. Lactobacillus plantarum MA2 was isolated with good fermentation characteristics from Tibet kefir and identified by morphological, physiological, biochemical, and 16S rDNA sequence analysis. This work focused on the preparation of MA2 starter cultures by spray drying and compared the physiological activity of starter cultures to that of freeze-dried powder. The experimental results showed that the best spray-drying conditions were as follows: inlet air temperature of 148.9°C, raw material flow rate of 61.5 mL/h, and a protectant : cell ratio of 3:1. The viable cells of spray-dried starter cultures was 1.82 × 10⁹ colony-forming units (cfu)/g. The in vivo experiments revealed that after the spray-drying process, starter cultures of MA2 had good milk curdling and cholesterol removal ability (45.5%), which was very close to the fresh bacteria broth (46.8%) and freeze-dried starter cultures (46.1%). Furthermore, the spray-dried starter cultures had good stability during storage at 4°C. These results showed that the modified spray-drying process achieved the intended purpose of efficient preparation of the yogurt starter cultures.     

Synthesis and Properties of Novel Phenylenediamine Gemini Surfactants

In the present work, a two-step method was adopted to synthesize a series of novel Gemini surfactants using N,N-dimethylalkyl amines (alkyl length = C₁₂, C₁₆ and C₁₈), epichlorohydrin, and n-phenyllenediamine as starting materials. The products were characterized using mass spectroscopy (MS) and nuclear magnetic resonance spectroscopy (¹H NMR). Systematic experiments were conducted to evaluate their surface activity, foaming properties, and antibacterial performance. Results showed the critical micelle concentrations (CMC) of the C₁₂-based, C₁₆-based, and C₁₈-based phenylenediamine surfactants were 3.295 × 10⁻³, 2.532 × 10⁻⁴, and 3.140 × 10⁻⁴ mol L⁻¹ at 298 K, respectively, with corresponding surface tension (γ_cmc) values of 28.24, 31.95, and 35.06 mN m⁻¹ under the same conditions. The Gemini surfactants showed not only good surface activity and foaming properties, but also demonstrated good antimicrobial performance against Gram-positive and Gram-negative bacteria and fungi.     

Aerosolisation of Escherichia coli and associated endotoxin using an improved bubbling bioaerosol generator

Experimental bioaerosol generators are widely used in scientific studies. However, the choice of such a generator for a given application is made difficult by the lack of information on the performances or limits of these systems. In this article, we venture the assumption that a bubbling liquid generator constitutes a promising choice to produce experimental bioaerosols with known and controlled characteristics. A generator inspired by the Liquid Sparging Aerosolizer (LSA) developed by Mainelis et al. (2005) was used to aerosolise microorganisms by bubbling compressed air through a bacterial suspension film.Performances of a modified LSA-type bubbling generator were evaluated. The generated bioaerosols were characterised, in particular in terms of concentrations, stability over time and reproducibility. The possibility to produce controlled airborne endotoxin concentrations from gram-negative bacterial suspensions was also investigated.A test rig to generate and characterise experimental bioaerosols was designed. Tests were performed on standardised Escherichia coli suspensions, stable over time, showing cultivable bacteria concentrations between 1.5×10⁸ and 3.0×10⁸ CFU mL^?1. In the operating conditions evaluated, the generator provided aerosol concentrations in the following ranges: 4.0×10⁵–1.0×10⁹ Cell m^?3 total bacteria, 2.5×10⁴–2.0×10⁷ CFU m^?3 cultivable bacteria and 20–15,000 EU m^?3 endotoxins. Bioaerosol properties were stable throughout generation (180 min) and were satisfactorily reproducible between tests. Bioaerosol generation was controllable, making these experimental bioaerosols appropriate for various laboratory assays, including work requiring the use of airborne endotoxins at known concentrations. Data on both the physical and biological properties of the bioaerosol, and very complete information on the generation system's performance were obtained. The influences of parameters such as airflow rate, height of liquid film or concentration of the bacterial suspension were also evaluated. These parameters can be used to adjust the bioaerosol to the needs of the experiment.     

Fluorochrome and Fluorescent In Situ Hybridization to Monitor Bioaerosols in Swine Buildings

Total microbial cell concentration, viability, and culturability of bioaerosols in swine buildings were monitored by using epifluorescence microscopy with fluorochrome (EFM/FL) with four fluorescent dyes (AO, DAPI, PI, and YOPRO-1) and by using fluorescent in situ hybridization (FISH) with five oligonucleotide probes (fl-Univ, fl-EUB, cy-EUK, fl-PSMg, and fl-NotEUB) probes. Results from these two non-culture-based methods were then compared with those using a commonly used culture method. The total microbial cell concentration measured using the non-culture-based methods was 10 to 200 times higher than that using the culture method; from 5.48 × 10⁶ to 2.18 × 10⁷ cells/m³ with AO staining and from 5.03 × 10⁶ to 2.13 × 10⁷ cells/m³ with DAPI staining, compared with the average concentration of 1.02 × 10⁵ CFU/m³ for bacteria and 1.27 × 10³ CFU/m³ for fungi by the culture method. The viability ranged from 0.27 to 0.76 by EFM/FL with PI staining, from 0.02 to 0.60 with YOPRO-1 staining, from 0.53 to 0.79 by FISH, and from 0.002 to 0.033 by the culture method. The viability by EFM/FL and FISH were much higher than the culturability. In summary, the total microbial cell concentration and viability were highly underestimated by the culture method. Based on the FISH results, eubacteria and eukaryotes were the dominant components of the bioaerosols. In conclusion, EFM/FL and FISH methods can effectively assess the total microbial cell concentration and viability of bioaerosols in environmental samples.