Transport efficiency and deposition velocity of fluidized spores in ventilation ducts

Experiments with dry, fluidized spores were conducted in a test apparatus to delineate the extent of spore contamination and deposition behavior under normal airflow conditions within a ventilation system. The surrogate biological warfare agent used in experiments was the spore-forming bacterium Bacillus atrophaeus. Viable-spore-counting methods were used in the study because they provide the most important number for estimating human health effects. Three common ventilation duct materials were evaluated: flexible plastic, galvanized steel, and internally insulated fiberglass. Transport efficiency ranged from 9 to 13% in steel and fiberglass ducts; transport efficiency was far less (0.1–4%) in plastic duct. Results showed that the deposition of surrogate biological warfare agent was significantly different in the three duct materials evaluated. All experimentally determined, dimensionless deposition velocities were in the range of theoretical predictions for dimensionless roughness, k ⁺=10. All were 10–100 times greater than the velocities predicted for ducts with smoother surfaces, k ⁺=0.1. For plastic duct, greater dimensionless deposition velocities were likely the result of charge forces between spores and surface. However, for the steel duct, a relatively large dimensionless deposition velocity was unexpected. These findings imply that building contamination will likely vary, depending on the specific type of duct material used throughout an affected area. Results of this study may aid in refining existing particle-transport models and remediation activities.     

Reaerosolization of Fluidized Spores in Ventilation Systems

This project examined dry, fluidized spore reaerosolization in a heating, ventilating, and air conditioning duct system. Experiments using spores of Bacillus atrophaeus, a nonpathogenic surrogate for Bacillus anthracis, were conducted to delineate the extent of spore reaerosolization behavior under normal indoor airflow conditions. Short-term (five air-volume exchanges), long-term (up to 21,000 air-volume exchanges), and cycled (on-off) reaerosolization tests were conducted using two common duct materials. Spores were released into the test apparatus in turbulent airflow (Reynolds number, 26,000). After the initial pulse of spores (approximately 10¹⁰ to 10¹¹ viable spores) was released, high-efficiency particulate air filters were added to the air intake. Airflow was again used to perturb the spores that had previously deposited onto the duct. Resuspension rates on both steel and plastic duct materials were between 10⁻³ and 10⁻⁵ per second, which decreased to 10 times less than initial rates within 30 min. Pulsed flow caused an initial spike in spore resuspension concentration that rapidly decreased. The resuspension rates were greater than those predicted by resuspension models for contamination in the environment, a result attributed to surface roughness differences. There was no difference between spore reaerosolization from metal and that from plastic duct surfaces over 5 hours of constant airflow. The spores that deposited onto the duct remained a persistent source of contamination over a period of several hours.     

Compartmentation of metabolic systems in the regulation of dormancy in fungus spores

Dormancy in fungus spores can be due to a variety of causes relating to structural, physiological, or biochemical functions. Based on data reported here and earlier, compartmentation of endogenous reserves or of enzymes is proposed as the mechanism controlling dormancy in spores ofMyrothecium verrucaria andTrichoderma reesei. Spores of both organisms contain a pool(s) of reserves composed of trehalose, amino acids, as well as unidentified compounds. Addition of hot water extracts of these reserves to spores results in rapid increases in respiratory activity and germination. This observation coupled with other data showing the stimulation of endogenous respiration by heat, freezing, or azide demonstrates that dormancy is due primarily, if not entirely, to sequestering or compartmentation of the endogenous reserves and not of the enzymatic systems involved in utilization of metabolites for germination. Presumably these reserves are contained within the vacuoles. Data on the interactions of treatments that stimulate endogenous respiration and on the effects of metabolism of exogenous substrates indicate that the transport pathways within the cell, from the pools or from the plasma membrane, to the loci of initial metabolism are not identical and that the total regulatory system is composed of a number of separable processes. It appears probable that examination of the spores of other fungi will show that compartmentation of reserves is not of uncommon occurrence and is not an unusual cause of dormancy.     

Reaerosolization of Bacillus spp. in Outdoor Environments: A Review of the Experimental Literature

Reaerosolization or resuspension-that is, the reintroduction of previously airborne particles into the atmosphere-is a complex phenomenon. Microbial reaerosolization is particularly poorly understood because few studies have been done in this area, and many of the studies that have been performed are not in the peer-reviewed literature. The reaerosolization of Bacillus anthracis in outdoor environments is of particular concern because of its stability and potential for use as a biological weapon. This review pulls together data from more than 30 publications, spanning field and laboratory experiments, to summarize the current state of our understanding of Bacillus spp. reaerosolization in outdoor environments.     

Protein synthesizing systems from spores and vegetative cells of Bacillus cereus

A system of polyphenylalanine synthesis was optimized for a comparison of the polymerizing activities of ribosomes from spores and vegetative cells of Bacillus cereus T. Ribosomes of both types react similarly, showing a magnesium optimum of about 6 mM and spermidine optima of about 5 mM and 4 mM for vegetative and spore ribosomes, respectively. These lead to optimum mono- to multivalent cation rations of 9 and 10 respectively at 100 mM ammonium ion. A comparison of the response of these ribosomes to suboptimal concentrations of magnesium and spermidine show that they differ qualitatively from each other, suggesting that they possess different structure, macromolecular or ionic components.Abbreviations DFP diisopropylfluorophosphate - HEPES N-2-hydroxyethylpiperazine-N-ethanesulfonic acid     

Inactivation of bacillus spores in dry systems at low and high temperatures.

A plot of the thermal resistance of Bacillus subtilis var. niger spores (log D value) against temperature was linear between 37 and 190 degrees C (z = 23 degrees C), provided that the relative humidity of the spore environment was kept below a certain critical level. The corresponding plot for Bacillus stearothermophilus spores was linear in the range 150 to 180 degrees C (z = 29 degrees C) but departed from linearity at lower temperatures (decreasing z value). However, the z value of 29 degrees C was decreased to 23 degrees C if spores were dried before heat treatment. The straight line corresponding to this new z value was consistent with the inactivation rate at a lower temperature (60 degrees C). The data indicate that bacterial spores which are treated in dry heat at an environmental relative humidity near zero are inactivated mainly by a drying process. By extrapolation of the thermal resistance plot obtained under these conditions for B. subtilis var. niger spores, the D value at 0 degrees C would be about 4 years.     

An evaluation of intra-cage ventilation in three animal caging systems

Although temperature and relative humidity have been quantitated and their effects on research data studied, few studies have measured the air turnover rates at cage level. We evaluated the air distribution and air turnover rates in unoccupied shoe-box mouse cages, filter-top covered cages and shoe-box mouse cages housed in a flexible film isolator by using discontinuous gas chromatography/mass spectrometry and smoke. Results showed that air turnover was most rapid in the unoccupied shoe-box mouse cage and slowest in the filter-top covered cage. Placing mice in the filter-top covered cage did not significantly improve the air turnover rate. Although filter-top covered cages reduce cage-to-cage transmission of disease, the poor airflow observed within these cages could lead to a buildup of gaseous pollutants that may adversely affect the animal's health.     

Comparison of three granular support materials for anaerobic fluidized bed systems

Summary Three different materials, kaolin, pozzolana and biolite (a material used in a commercial anaerobic fluidized bed treatment process) when tested as supports for an anaerobic fluidized bed system had similar physical and fluidization properties but behaved differently towards the biomass hold-up. However, all three systems attained similar removal efficiency rates.Nomenclature U Fluidization velocity (m/s) - U₁ Terminal fluidization velocity (m/s) - g Local acceleration due to gravity (m/s²) - _s Solid density (kg/m³) - _f Fluid density (kg/m³) - P Pressure drop (Pa) - HRT Hydraulic retention time (days) - H_mf Height of bed at minimum fluidization (m) - H Height of bed (m) - C_d Drag coefficient (dimensionless) - W Mass of solids in bed (kg) - dp Particle diameter (m) - A Cross-sectional area of column (m²) - h column height (m) - Rc_t Terminal Reynolds no. - Voidagc (fractional free volume, dimensionless) - _mf Voidage (fractional free volume) at minimum of fluidization (dimensionless)     

Spatiotemporal distribution and the passive dispersal of fungal spores through HVAC systems

Heating, ventilation and air conditioning (HVAC) systems are widely used to regulate indoor temperature and air quality of modern buildings. The central supply and exhaust system cause the dispersal and removal of bioaerosols. This study presents results from ex situ experiments conducted to a better understanding of the spatiotemporal distribution, passive dispersal and removal of fungal spores through HVAC systems. The study was conducted in a 50 square meters by 3 m high instrument room in a research building with HVAC systems. Plates with Aspergillus flavus colony were attached upside down on the edge of the ceiling vent to imitate the mildew growing. Fungal spores were released for 10 min, collected and counted by the settle plate method in 2 h. Results show that A. flavus spores dispersed to 3.6 m in 2 min and were evenly distributed in the room within 8 min. The concentration of spores decreased from 48 to 3–6 CFU/plate after 60 min and was lower than 1% after 120 min. Our results suggest that airborne fungal spores disperse and remove by HVAC systems efficiently. Without the external and internal source, the HVAC system could greatly reduce the fungal amount in the indoor air to the background level within one hour. This study provided the observed data of the transmission and retention of internal or external biological contaminants through HVAC system.

     

The impact of cage ventilation on rats housed in IVC systems

Today the use of individually ventilated cage systems (IVC systems) is common, especially for housing transgenic rodents. Typically, in each cage a ventilation rate of 40 to 50 air changes per hour is applied, but in some systems even up to 120 air changes per hour is applied. To reach this rate, the air is blown into the cage at a relatively high speed. However, at the animal's level most systems ventilate with an air speed of approximately 0.2 m/s. In the present paper, two studies were conducted, one analysing whether an air speed below 0.2 m/s or just above 0.5 m/s affects the rats, and another study analysing whether air changes of 50, 80 and 120 times per hour affect the rats. In both studies, monitoring of preferences as well as physiological parameters such as heart rate and blood pressure, was used to show the ability of the animals to register the different parameters and to avoid them if possible. Air speeds inside the cage of as high as 0.5 m/s could not be shown to affect the rats, while the number of air changes in each cage should be kept below 80 times per hour to avoid impacts on physiology (heart rate and systolic blood pressure). Also the rats prefer cages with air changes below 80 times per hour if they have the opportunity of choosing, as shown in the preference test.     

Thermal resistance of Bacillus stearothermophilus spores in different heating systems containing some approved food additives

M. LÓPEZ, M. MAZAS, I. GONZÁLEZ, J. GONZALEZ AND A. BERNARDO. 1996. The effects of different heating systems on the heat resistance of Bacillus stearothermophilus spores (ATCC 7953, 12980, 15951 and 15952) were investigated. Spores were heated in distilled water, Sorensen buffer (0.18 moll⁻¹), McIlvaine buffer (0.0025-0.18 moll⁻¹), and several solutions containing sodium chloride (0.0612%), sodium nitrite (125 ppm), potassium sorbate (0.1%) and sodium benzoate (0.1%) over a wide range of temperatures (115-140°C). D-values obtained for McIlvaine and Sorensen buffers, at the same molarities, were not significantly different (P > 0.05), but decimal reduction times increased as phosphate concentrations in the solutions decreased. The concentrations, in which statistically significant differences (P < 0.05) were obtained, varied among strains. Among the additives assayed, only sodium chloride reduced heat resistance, being effective at concentrations as low as 0.06%. The z-values calculated in this study ranged from 6.99 to 8.40 with a mean value of 7.60±0.45. Although z-values observed for salt and buffers (180 moll⁻¹) were slightly higher than those obtained in the other conditions assayed, the difference was not statistically significant (P > 0.05).     

Possible cause of allergy for the librarians: books manipulation and ventilation as sources of fungus spores spreading

The objective of this study was to investigate the airborne viable spore concentrations and identify the fungal species in all indoor spaces from the lending library at the Technical University “Gheorghe Asachi” Iaşi, Romania. Samples were collected using the settle plate method and swab samples from PC cooler fan grids as well as from the wall in it’s vicinity and from paper/wood fragments. There were no air conditioning systems in the library rooms. The heating systems were standard with an environmental temperature of 20°C in winter, except for the storage area of old/rare books stacks II, where the temperature was below 15°C and the humidity was very high due to water infiltrations in the walls and poor maintenance. More than 296 fungal colonies from over 78 samples were identified, enumerated, and reported. Indoor airborne fungal spore deposition rates were within the range of 419–1,677 CFU/m², with the predominance of genera being Aspergillus spp., Penicillium spp., Cladosporium spp., Alternaria spp. and Chaetomium spp. Approximately ten fungal colonies could not be identified. The PC fans move particles from the low levels (floor) to the air, and are thus responsible for maintaining a constant air velocity and contribute to fungal-spore aerosolization, transport, deposition and resuspension. Book paper and wood furniture are known to be suitable substrates for cellulose degrading fungi.     

Changes in decoated spores of Clostridium perfringens caused by treatment with some enzymatic and non-enzymatic systems

Decoated and Cu²⁺-binding spores of Clostridium perfringens underwent germination-like changes followed by lysis when incubated with the following non-enzymatic and enzymatic systems: ascorbic acid under aerobic conditions, a mixture of NADH and phenazine methosulphate, glucose with glucose oxidase, and NADH with NADH oxidase. Hydrogen peroxide formed from these systems in common is responsible for lysis of treated spores, because catalase strongly inhibited lysis. Superoxide radical is not directly involved in the reaction, because superoxide dismutase did not inhibit lysis.     

Reaerosolization of Spores from Flooring Surfaces To Assess the Risk of Dissemination and Transmission of Infections

The aim of this study was to quantify reaerosolization of microorganisms caused by walking on contaminated flooring to assess the risk to individuals accessing areas contaminated with pathogenic organisms, for example, spores of Bacillus anthracis. Industrial carpet and polyvinyl chloride (PVC) floor coverings were contaminated with aerosolized spores of Bacillus atrophaeus by using an artist airbrush to produce deposition of ∼10³ to 10⁴ CFU · cm⁻². Microbiological air samplers were used to quantify the particle size distribution of the aerosol generated when a person walked over the floorings in an environmental chamber. Results were expressed as reaerosolization factors (percent per square centimeter per liter), to represent the ratio of air concentration to surface concentration generated. Walking on carpet generated a statistically significantly higher reaerosolization factor value than did walking on PVC (t = 20.42; P < 0.001). Heavier walking produced a statistically significantly higher reaerosolization factor value than did lighter walking (t = 12.421; P < 0.001). Height also had a statistically significant effect on the reaerosolization factor, with higher rates of recovery of B. atrophaeus at lower levels, demonstrating a height-dependent gradient of particle reaerosolization. Particles in the respirable size range were recovered in all sampling scenarios (mass mean diameters ranged from 2.6 to 4.1 μm). The results of this study can be used to produce a risk assessment of the potential aerosol exposure of a person accessing areas with contaminated flooring in order to inform the choice of appropriate respiratory protective equipment and may aid in the selection of the most suitable flooring types for use in health care environments, to reduce aerosol transmission in the event of contamination.     

Comprehensive modeling of methanogenic biofilms in fluidized bed systems: Mass transfer limitations and multisubstrate aspects

A cognitive model for anaerobic digestion in fluidized bed reactors is developed. The general pathway of the process is divided into five main reactions performed by different bacterial groups. Molecular diffusion of each substrate involved in the reaction scheme is described. Effectiveness factor calculations are performed in steady state for each bacterial group taken into account in the process. The case of a single substrate removal is discussed, and optimal biofilm sizes are found. Sequential substrate removal is investigated, and different kinetic regimes are characterized. The influence of biofilm size and primary substrate removal is discussed in the case of standard concentrations in the liquid phase. This study shows that, according to the theoretical model the limiting step of the process may be different and depends in a large way on mass transfer effects. Finally, importance of biofilm size is compared for acidogenic and methano-genic steps: each reaction is found to be optimized for different biofilm thicknesses. This result may be of interest for design purposes and further dynamic modeling. Concluding remarks concerning the validation of the model are made, and a comparison to experimental data from the literature is presented. (c) 1995 John Wiley & Sons, Inc.     

Colonization of fiberglass insulation used in heating,ventilation and air conditioning systems

Summary The number of fungal species colonizing thermal and acoustic fiberglass insulations used in heating, ventilation, and air conditioning (HVAC) systems was fewer than that obtained from initial direct culture of these insulations. The colonization, determined by the microscopic observation of conidiophores with conidia, was primarily of acrylic-latex-facing material, but eventually the fungi permeated the fiberglass matrix. Isolates ofAspergillus versicolor were most often obtained from non-challenged insulation, whereasAcremonium obclavatum appeared to be the primary colonizing fungus in high-humidity (>90%) challenge chambers. At a lower humidity (about 70%)Aspergillus flavus was one of the more prominent fungi. Not all duct liner samples were equally susceptible to colonization and duct board appeared relatively resistant to colonization.     

三种麻醉机通气系统对患者肺部病原微生态的影响研究

目的分析不同麻醉机通气系统对患者肺部病原微生态的影响情况。方法选择90例全麻插管手术患者作为研究对象,将其随机分为A组(未干预组)、B组(呼吸过滤器组)和C组(麻醉消毒机组),每组30例,比较患者术后肺部感染发生情况。结果三组在麻醉前进行病原菌检测,检出定植菌株,均为条件致病菌:革兰阳性菌、革兰阴性菌和真菌,主要为微球菌、凝固酶阴性葡萄球菌、芽胞杆菌、棒状杆菌、黄杆菌属、酵母样真菌。三组麻醉机各部位病原菌阳性率比较:麻醉前,三组麻醉机不同部位的病原菌阳性率差异无统计学意义(P0.05);结束麻醉后,检查麻醉机各端口病原菌阳性检出率,其中C组显著低于A组(P0.05),A、B两组差异无统计学意义(P0.05)。B、C两组患者术后肺部感染发生率显著低于A组患者(P0.05)。结论经过干预的麻醉机通气系统对患者肺部微生态环境的影响较小,患者术后呼吸道感染的发生率显著降低。     

Conventional vs CO2 demand-controlled ventilation systems

1. 1. The feasibility of controlling the ventilation system using the occupant-generated carbon dioxide as an indicator of ventilation rate and indoor air quality has been investigated in an eleven storey office building.

2. 2. The study compares the indoor environment created by two different types of ventilation control systems.

3. 3. The two ventilation systems tested consisted of: a conventional system controlled by outdoor temperatures, and a demand-controlled system regulated by indoor carbon dioxide concentration.

4. 4. The results show that the CO₂-based demand-controlled ventilation system does not worsen indoor air quality and thermal comfort. It was also noticed that an energy saving of 12% was achieved using the CO₂ control system.

5. 5. The occupants perceived that their productivity is proportional to their perception of the indoor environment; indicating that higher productivity rates can be achieved by better controlling the working environment above satisfactory levels.

Production of flavour ketones in aqueous-organic two-phase systems by using free and microencapsulated fungal spores as biocatalysts

The formation of 2-alkanones by free and microencapsulated P. roquefortii spores in an aqueous-organic two-phase system was investigated by using substrates supplied as a solution in decane. It was shown that the spores remained catalytically active after entrapment within permeable polyamide microcapsules and readily catalyzed the formation of 2-pentanone, 2-heptanone, and 2-undecanone from short-chain alkyl esters of hexanoic, octanoic, and lauric acid, respectively, with the rate of reaction being markedly dependent on the type and concentration of the ester substrate used. In general, the optimal concentration of the esters in decane was found to be much higher than that of the respective fatty acid substrates and, in the case of alkyl dodecanoates, the biotransformation could be carried out efficiently even in the absence of added solvent. Further analysis revealed a significant difference in the reaction rates observed with free and microencapsulated spores at 0.5 but not at 3.0 M methyl dodecanoate, suggesting that at high substrate concentrations the biotransformation was no longer limited by mass transfer.