Increased Airborne Bacterial Survival as a Function of Particle Content and Size

ABSTRACT

Two test vegetative bacteria, Pseudomonas syringae and Erwinia herbicola, and a physical aerosol decay indicator, Bacillus subtilis var. niger spores, were sprayed into a particle size fractionating wind tunnel. Test bacterial survival significantly increased directly with droplet size for varying test cell to spore ratios and temperature. However, survival varied inversely with relative humidity.     

Gradient‐Direction‐Pattern Transform for Automated Measurement of Oil Drops in Images of Multiphase Dispersions

The automated detection and measurement of oil drops in multiphase fermentation systems are important for mass transfer analysis. A novel computer technique for automated detection of oil drops in images is presented in the context of a stirred tank containing a three‐phase water‐oil‐air dispersion. The technique is an original feature extraction transform designed for the detection of objects with a characteristic appearance. The proposed transform, denominated gradient‐direction‐pattern (GDP) transform, utilizes naturally occurring patterns in the orientation of the local gradient appearing in test images. The GDP transform was used to demonstrate the feasibility of automatically estimating oil drop‐size unbiased distributions which is an important task in the chemical and other related industries.     

Accurate measurement of aerosol electric mobility moments

A procedure for the accurate determination of moments of aerosol electric mobility distributions was developed. The main apparatus required is a carefully constructed Hewitt (differential) electric mobility analyzer. The method does not require vanishingly small aerosol flow rates to obtain accuracy. The procedure may be considered a primary standard measurement technique, since no calibration with particles of known characteristics is required.

One application of the procedure is the determination of the mean and standard deviation of particle size for near-monodisperse aerosols. As an illustration, a Dow LS- 1117-B polystyrene latex aerosol was analyzed. The mean and standard deviation of the particle diameter were found to be 0·80 and 0·018 μm, respectively. The accuracy of the mean dia. determination is estimated to be 2 per cent.     

Performance of Two Fluorescence-Based Real-Time Bioaerosol Detectors: BioScout vs. UVAPS

A 405 nm diode laser-based on-line bioaerosol detector, BioScout, was tested and compared with the Ultraviolet Aerodynamic Particle Sizer (UVAPS). Both instruments are based on laser-induced fluorescence of particles. Only a fraction of microbial particles produce enough fluorescence light to be detected by the instruments. This fluorescent particle fraction (FPF) is aerosol and instrument specific. The FPF values for common bacterial and fungal spores and biochemical particles were experimentally determined for both instruments. The BioScout exhibited higher FPF values for all the test aerosols except coenzyme NADH. The difference was higher for smaller particles. The FPF values of fungal spores and bacteria varied between 0.34 to 0.77 and 0.13 to 0.54 for the BioScout and the UVAPS, respectively. The results indicate that the 405 nm diode laser is a useful excitation source for fluorescence-based real-time detection of microbial aerosols. The FPF results of this study can be utilized to estimate the actual concentrations of bacterial and fungal spores in fluorescence-based ambient measurements.

Copyright 2014 American Association for Aerosol Research     

Performance assessment of UVAPS: Influence of fungal spore age and air exposure

This work focused on two main outcomes. The first was the assessment of the response of the Ultraviolet Aerodynamic Particle Sizer Spectrometer (UVAPS) for two different fungal spore species. The UVAPS response was investigated as a function of fungal age and the frequency of air current that their colonies exposure to. This outcome was achieved through the measurement of fungal spore fluorescent percentage and fluorescent intensity throughout a period of culturing time (three weeks), and the study of their fluorescent percentage as a function of exposure to air currents. The second objective was to investigate the change of fungal spore size during this period, which may be of use as a co-factor in this differentiation. Fungal spores were released by blowing the surface of the culture colonies with continuous filtered flow air. The UVAPS was used to detect and measure auto-fluorescing biomolecules such as riboflavin and nicotinamide adenine dinucleotide phosphate (NAD(P)H) present in the released fungal spores.The study demonstrated an increase in aerodynamic diameter for fungal spores under investigation (Aspergillus niger and Penicillium species) over a period of time. The fluorescent percentage of spores was found to decrease for both fungal genera as they aged. It was also found that the fluorescent percentage for tested fungi decreased with frequency of air exposure. The results showed that, while the UVAPS could discriminate between Aspergillus and Penicillium species under well-controlled laboratory conditions, it is unlikely to be able to do so in the field.     

Triboelectric charging of fungal spores during resuspension and rebound

The triboelectric charging of fungal spores was experimentally characterized during rebound and resuspension. A fungal spore source strength tester (FSSST) was used as a primary aerosol generator for spores of three fungal species and two powders (silicon carbide and silver). The critical velocity of rebound was determined using a variable nozzle area impactor (VNAI), and the charging state of particles after resuspension and rebound was measured using the FSSST, different impactor setups, electrometers, and optical particle counters. In the impactor setups and the FSSST, five different surface materials relevant for indoor environments were used (steel, glass, polystyrene, paper, and polytetrafluoroethylene). The critical velocity of rebound was determined to be 0.57 m/s for fungal spores, which is relatively low compared to silicon carbide and previous results for micron-sized aerosol particles. Based on the rebound impactor measurements, we were able to define the crucial parameters of charge transfer for different particle–surface material pairs. A contact charge parameter, which describes the triboelectric charging during rebound, was found to have a negative correlation with the charging state of the particles after the resuspension from an impactor. This connects the triboelectric charging during rebound and resuspension to each other. Based on the contact charge parameter values, quantified triboelectric series could be formed. The results of this work show that fungal spores can be charged both positively and negatively during rebound and resuspension depending on the fungal species and surface material.

Copyright © 2016 American Association for Aerosol Research     

Detection and Analysis of Aerosol Particles by Laser-Induced Breakdown Spectroscopy

Laser-induced breakdown spectroscopy (LIBS) was evaluated as a means for quantitative analysis of the size, mass, and composition of individual micron-to submicron-sized aerosol particles over a range of well-characterized experimental conditions. Conditional data analysis was used to identify LIBS spectra that correspond to discrete aerosol particles under low aerosol particle loadings. The size distributions of monodisperse particle source flows were measured using the LIBS technique for calcium- and magnesium-based aerosols. The resulting size distributions were in good agreement with independently measured size distribution data. A lower size detection limit of 175 nm was determined for the calcium- and magnesium-based particles, which corresponds to a detectable mass of approximately 3 femtograms. In addition, the accuracy of the LIBS technique for the interference-free analysis of different particle types was verified using a binary aerosol system of calcium-based and chromium particles.     

Profile and Morphology of Fungal Aerosols Characterized by Field Emission Scanning Electron Microscopy (FESEM)

Fungal aerosols consist of spores and fragments with diverse array of morphologies; however, the size, shape, and origin of the constituents require further characterization. In this study, we characterize the profile of aerosols generated from Aspergillus fumigatus, A. versicolor, and Penicillium chrysogenum grown for 8 weeks on gypsum boards. Fungal particles were aerosolized at 12 and 20 L min^?1 using the Fungal Spore Source Strength Tester (FSSST) and the Stami particle generator (SPG). Collected particles were analyzed with field emission scanning electron microscopy (FESEM). We observed spore particle fraction consisting of single spores and spore aggregates in four size categories, and a fragment fraction that contained submicronic fragments and three size categories of larger fragments. Single spores dominated the aerosols from A. fumigatus (median: 53%), while the submicronic fragment fraction was the highest in the aerosols collected from A. versicolor (median: 34%) and P. chrysogenum (median: 31%). Morphological characteristics showed near spherical particles that were only single spores, oblong particles that comprise some spore aggregates and fragments (<3.5 μm), and fiber-like particles that regroup chained spore aggregates and fragments (>3.5 μm). Further, the near spherical particles dominated the aerosols from A. fumigatus (median: 53%), while oblong particles were dominant in the aerosols from A. versicolor (68%) and P. chrysogenum (55%). Fiber-like particles represented 21% and 24% of the aerosols from A. versicolor and P. chrysogenum, respectively. This study shows that fungal particles of various size, shape, and origin are aerosolized, and supports the need to include a broader range of particle types in fungal exposure assessment.     

Method to Determine the Number of Bacterial Spores Within Aerosol Particles

We describe methodology to reveal the number of microbial spores within aerosol particles. The procedure involves visualization under differential- interference-contrast microscopy enhanced by high-resolution photography and further analysis by computer-assisted imaging. The method was used to analyze spore of Bacillus globigii in aerosols generated by a small (pressured metered-dose inhaler type) generator. Particles consisting in 1 or 2 spores accounted for 85% of all generated particles. This percentage rose to 91% when the same aerosol was collected on an Andersen cascade impactor that collected particles larger than 0.65 μm and was even higher (96%) when particles larger than 3.3 μm were also eliminated. These results demonstrate that the imaging analysis of aerosol particles collected on glass slides is sensitive to even relatively small changes in aerosol particle composition. The accuracy of the enhanced microscopic method described herein (differences between visual and computer analysis were approximately 3% of the total particle counts) seems adequate to determine the spore composition of aerosols of interest in biodefense.     

A diethylene glycol condensation particle counter for rapid sizing of sub-3 nm atmospheric clusters

Abstract

This article describes the modification of a laminar flow, thermally diffusive universal-fluid condensation particle counter (standard operation: 50% detection efficiency at 5?nm) to rapidly measure the size distribution of sub 3?nm aerosol. Sub 3?nm detection was achieved by using diethylene glycol as the working fluid, which enabled high instrument super-saturations while minimizing homogenous nucleation of the working fluid; a detection efficiency of 50% was achieved at 1.6?nm with laboratory-generated ammonium sulfate (AS) aerosol. Rapid aerosol sizing beneath 3?nm was achieved by inverting the measured grown droplet size distribution (1?s sampling) to recover the sampled aerosol size distribution. The developed inversion algorithm utilizes analytical kernel functions determined from the instrument response to pseudo-monodisperse AS aerosol from 1.5?nm to 20?nm, generated by a high-resolution DMA and a nano DMA. The inversion algorithm was tested numerically with assumed, idealized aerosol size distributions consistent with observed new particle formation events, yielding a reasonable agreement between inverted and assumed aerosol size distributions below 3?nm. This technique provides a measure of the aerosol size assuming an aerosol composition identical to that of the aerosol used to generate the experimentally determined kernel function.

Copyright © 2018 American Association for Aerosol Research     

Design of an instrument for real-time detection of bioaerosols using simultaneous measurement of particle aerodynamic size and intrinsic fluorescence

A prototype instrument has been constructed to measure individual airborne particles based on their aerodynamic size and their intrinsic fluorescence at selected excitation and emission wavelength bands. The instrument combines features of an aerodynamic particle sizing device with capabilities similar to those of a liquid flow cytometer. The goal of the instrument is to provide real-time data indicative of particle characteristics, and it is especially targeted to respond to bioaerosols from 0.5 to 10 micrometers (aerodynamic diameter) with intrinsic fluorescence exited at a wavelength of 325 nm and emitting from 420 to 580 nm. This size range covers individual airborne bacteria and bacteria clusters, and the fluorescence sensitivity is selected for biological molecules commonly found in cellular systems, for example, reduced nicotinamide adenine dinucleotide phosphate [NAD(P)H] and riboflavin. Initial tests with nebulised Bacillus subtilis var. niger (BG, ATCC 9372) spores have shown that, for both individual spores and spore clumps, a low level of fluorescence is detected from 17% of the particles. This detection percentage is on the same order as previous experiments that have measured viability of about 12% for mechanically dispersed BG spores (Ho and Fisher (1993) Defense Research Establishment Suffield Memorandum 1421) and suggests a need for further investigation into the possible relationship between the detected fluorescence and viability of bacterial spores.     

The structure of fossil fungal spores based on the results of ion etching

New data on the structure of fossil fungal spores in coal beds were obtained with the use of the previously developed method of ionic etching (sputtering). The multilayer structure of spore shells was found for the first time, and considerations of the biochemical composition of layers were presented. The morphology of spores and their internal cytochemical elements was characterized. The reasonability of a further petrographic study of the spores of fungi in the coal beds is discussed.     

Calibration Correction of an Active Scattering Spectrometer Probe to Account for Refractive Index of Stratospheric Aerosols: Comparison of Results with Inertial Impaction

Real-time particle size spectra are being acquired on our research aircraft with relative ease and speed by techniques that make use of the real-time interaction of laser light with aerosols and cloud droplets. The results are, however, sometimes ambiguous, because the optical “signatures” of the particles depend on their refractive indices in addition to physical dimensions. The calibration supplied by the manufacturer is based on instrument response to a specific test aerosol, e.g., latex spheres (refractive index = 1.59). Such a calibration is strictly valid only for sample aerosols of refractive index and shape similar to the test aerosol. Whenever the sample aerosol differs from the test aerosol, a calibration correction is in order. Of concern here is the use of an active scattering spectrometer probe (ASAS-X), to measure sulfuric acid aerosols on high-flying U-2 and ER-2 research aircraft. Correcting the calibration of the ASAS-X for dilute sulfuric acid droplets (refractive index = 1.44) that predominate the stratospheric aerosol changes the inferred sizes by up to 32% per size interval from that determined from the nominal calibration. This results in an average increase in particle surface area and volume of 42 ± 10% and 71 ± 19%, respectively. The calibration correction of the optical spectrometer probe for stratospheric aerosol is validated by independent and simultaneous sampling of the particles with impactors. Sizing and counting of particles on microphotographs of scanning electron microscope images give results on total particle surface areas and volumes. After the calibration correction, the optical spectrometer data (averaged over four size distributions) agree with the impactor results (similarly averaged) to within a few percent. We conclude that the optical properties, or chemical makeup, of the sample aerosol must be known for accurate size analysis by optical aerosol spectrometers.     

Submicrometer Aerosol Mass Distributions of Emissions from Boilers,Fireplaces, Automobiles,Diesel Trucks,and Meat-Cooking Operations

The predominant peak in the mass distribution emitted from each source measured in this study occurs at or below about 0.2 μm in particle diameter, whereas the Los Angeles atmospheric aerosol contains peaks at a variety of sizes in the range between 0.1 and 1.0 μm in particle diameter, including peaks at sizes larger than 0.2 μm. This suggests that considerable modification of the primary aerosol size distribution occurs because of subsequent processes in the atmosphere. The data presented here are intended for use in defining the size distribution of the primary combustion source effluent for use with mathematical models of the evolution of the atmospheric aerosol size distribution.     

Filtration efficiency for bacterial aerosol through breathing filters

Tests determining the filtration efficiency for a bacterial test aerosol of Bacillus subtilis spores through filter cartridges of domestic materials and through filter cartridges where the principal filtering layer was an electrostatic material from Freudenberg company were carried out to determine the efficiency of purifying air from microorganisms using breathing filters. Tests of the breathing filters were prepared and carried out according to a procedure developed at the SRC FMBA of Russia. Spores of B. subtilis were elliptical and small (0.7 × 1.3 μm). Their concentration in the aerosol was (2.76-5.00)⋅10⁷ spore/m³. The tests were carried out with linear filtration rate 17 cm/s.     

UV-C Decontamination of Aerosolized and Surface-Bound Single Spores and Bioclusters

Biological particles are rarely individual organisms, but are clusters of organisms physically bound to one another, or bound to other material present in the environment. The size and composition of these bioclusters contribute to the protection of the organisms within the core of cluster from the harmful effects of ambient UV light. The use of ultraviolet irradiation has been evaluated in the past as an option for decontaminating surfaces and air; however, previous studies were conducted with single spores, or poorly characterized polydispersed aerosols making comparisons between studies difficult. This study is intended to evaluate the effect of UV-C irradiation on monodispersed particles of spore clusters with mean diameters of 2.8 μm and 4.4 μm, and single spores of Bacillus atrophaeus var. globigii on fixed surfaces and as aerosol. The D₉₀, the UV-C irradiation doses at which 90% of the colony forming units were rendered nonculturable, for single spores and spore clusters of 2.8 and 4.4 μm on surfaces were 138, 725, and 1128 J/m², respectively. The respective values for airborne spores were 27, 42, and 86–94 J/m². The first-stage decay rate constant for the surface exposure ranged from 0.012 for single spores to 0.003 for 4.4 μm clusters. Similarly, the aerosol decay rate constant ranged from 0.12 for single spores to 0.04 for 4.4 μm clusters. The results of this study demonstrate that the decay rate of spores contained in clusters is proportional to the overall particle size, and that it is harder to inactivate large clusters on surfaces.

Copyright 2014 American Association for Aerosol Research     

Estimating aerosol hazards from an anthrax letter

Events following the anthrax letter incidences in 2001 changed many previously held assumptions regarding biological aerosol hazards. As there were significant fatalities resulting from the sorting of a single anthrax letter, it suggests there is a need to reevaluate how best to measure biological aerosols and to use the information to make accurate predictions. This paper describes the biological aerosol created from manipulating envelopes containing Bacillus subtilis globigii spores (a simulant for anthrax). In addition, the measurements on dispersion of spores from an envelope processed by a mail sorter provide important dynamic aerosol characteristics, information previously unavailable for health risk assessment. The findings produced a number of significant aerosol dosage estimates related to spore contaminated letters. Graphic presentations show significant hazard in handling anthrax-laced letters. Aerosol particle dynamics are described and specific lethal dosage values are listed for a range of activities; these will be useful in assisting the modeling community to create more realistic predictions in hazard assessment studies.     

Identification of single microbial particles using electro-dynamic balance assisted laser-induced breakdown and fluorescence spectroscopy

Online characterization of fungal and bacterial spores is important in various applications due to their health and climatic relevance. The aim of this study was to demonstrate the capability of the combination of electro-dynamic balance assisted laser-induced breakdown spectroscopy (LIBS) and laser-induced fluorescence (LIF) techniques for the online detection of single fungal spores (Aspergillus versicolor and Penicillium brevicompactum) and bacteria (Bacillus aureus). The method enabled sensitive and repeatable LIBS analysis of common elemental components (Ca, Na, and K) from single microbial particles for the first time. Significant differences in the concentrations of these elements were observed between the species, e.g., bacterial spores had over three orders of magnitude higher Ca concentration (2 × 10^?12 g/particle) compared to fungal spores (3–5 × 10^?16 g/particle). The LIF analysis has previously been used to distinguish bioaerosols from other aerosols due to their fluorescence ability. This study showed that combination of LIF and LIBS analysis is a promising tool for identification of different bioaerosol particle types.

Copyright © 2016 American Association for Aerosol Research     

Adaptation of the Twomey Algorithm to the Inversion of Cascade Impactor Data

The Twomey nonlinear iterative algorithm for inverting aerosol size distribution data has been adapted for use with the Berner cascade impactor. Key factors affecting the performance of the algorithm have been identified. A procedure producing accurate inversions without artifacts includes establishing a set of continuous and smooth kernel functions based on measurements of the impactor cutoff characteristics, using modified weighting functions, placing constraints on the first-guess distribution, treating zero values and the ends of the distribution, and setting stopping criteria based on experimental errors. This general approach should be useful in solving inversion problems for other cascade impactors. The routine was extensively tested with numerically created test distributions and a large data base of ambient aerosol samples. An extended version of the program separates the inverted size distribution into a spectrum of lognormal distributions. Lognormal parameters from 44 ambient nitrate size distributions have been compared to the results of the inversion program of Dzubay and Hasan.     

Remote detection and mapping of bioaerosols

A rapidly scanning lidar system, the Laser Cloud Mapper (LCM), was operated to determine and assess its sensitivity as well as its mapping capability for the remote characterization of airborne biological organisms. Both field and aerosol chamber experiments were conducted. The test bioaerosol was produced by aerosolization of aqueous suspensions of Bacillus subtilis var. niger sp. globiggi (BG) in spore form; the relative concentration (by volume) of BG spores in tap water was varied from 0.001 to 100%. In a few additional trials, other biological simulants were studied. The statistical procedures formulated to analyze the linear depolarization ratios derived from the lidar data, and the results of this analysis are described with the objective of characterizing the biodetection capabilities and limitations (e.g., lower limits of detection, minimum mean time to detection for a given mean time between false alarms, etc.) of the LCM.