The Etiology of Bioaerosols in Food Environments

The past two decades have been characterised by a significant increase in the worldwide scientific database on bioaerosols in indoor and outdoor environments. Recently, the threats of bioterrorism as well as issues such as SARS and avian influenza have gained more public attention. New techniques and analytical methods have been used towards the precise identification of the sources of microbial contamination, as well as in the evaluation and assessment of potential hazards. In spite of the tremendous scientific progress made by developed countries, the state of knowledge about the biological origin of indoor air pollution in food processing environments remains relatively narrow and insufficient in developing countries. Airborne microorganisms, when they appear at the centre of interest, they are usually related to occupational studies, health complaints, and/or bioterrorism. This passive attitude towards bioaerosols in developing countries, especially in food processing environments, has increased as a result of lack of internationally recognised assessment criteria, unavailability of approved standards, and diminutive interest in bioaerosols.     

Airborne bacterial assemblage in a zero carbon building: A case study

Currently, there is little information pertaining to the airborne bacterial communities of green buildings. In this case study, the air bacterial community of a zero carbon building (ZCB) in Hong Kong was characterized by targeting the bacterial 16S rRNA gene. Bacteria associated with the outdoor environment dominated the indoor airborne bacterial assemblage, with a modest contribution from bacteria associated with human skin. Differences in overall community diversity, membership, and composition associated with short (day‐to‐day) and long‐term temporal properties were detected, which may have been driven by specific environmental genera and taxa. Furthermore, time‐decay relationships in community membership (based on unweighted UniFrac distances) and composition (based on weighted UniFrac distances) differed depending on the season and sampling location. A Bayesian source‐tracking approach further supported the importance of adjacent outdoor air bacterial assemblage in sourcing the ZCB indoor bioaerosol. Despite the unique building attributes, the ZCB microbial assemblage detected and its temporal characteristics were not dissimilar to that of conventional built environments investigated previously. Future controlled experiments and microbial assemblage investigations of other ZCBs will undoubtedly uncover additional knowledge related to how airborne bacteria in green buildings may be influenced by their distinctive architectural attributes.     

Indoor air quality assessment in dwellings with different ventilation strategies in Nunavik and impacts on bacterial and fungal microbiota

Indoor air quality is a major issue for public health, particularly in northern communities. In this extreme environment, adequate ventilation is crucial to provide a healthier indoor environment, especially in airtight dwellings. The main objective of the study is to assess the impact of ventilation systems and their optimization on microbial communities in bioaerosols and dust in 54 dwellings in Nunavik. Dwellings with three ventilation strategies (without mechanical ventilators, with heat recovery ventilators, and with energy recovery ventilators) were investigated before and after optimization of the ventilation systems. Indoor environmental conditions (temperature, relative humidity) and microbiological parameters (total bacteria, Aspergillus/Penicillium, endotoxin, and microbial biodiversity) were measured. Dust samples were collected in closed face cassettes with a polycarbonate filter using a micro-vacuum while a volume of 20 m³ of bioaerosols were collected on filters using a SASS3100 (airflow of 300 L/min). In bioaerosols, the median number of copies was 4.01 × 10³ copies/m³ of air for total bacteria and 1.45 × 10¹ copies/m³ for Aspergillus/Penicillium. Median concentrations were 5.13 × 10⁴ copies/mg of dust, 5.07 × 10¹ copies/mg, 9.98 EU/mg for total bacteria, Aspergillus/Penicillium and endotoxin concentrations, respectively. The main microorganisms were associated with human occupancy such as skin-related bacteria or yeasts, regardless of the type of ventilation.     

生物气溶胶的激光光谱识别研究

生物气溶胶对人类的健康、动植物的生长可构成很大的威胁。生物气溶胶的激光光谱识别和荧光雷达探测研究有利于人类与传染疾病作斗争。有条件采样单位于生物气溶胶荧光光谱分析仪在荧光收集系统之后巧妙地把粒子的弹性散射光和未经色散的荧光按产生的时间先后分成两个部分。光谱仪有条件采样过程可降低数据采集和数据处理速率，提高信噪比。有条件触发单粒子生物气溶胶荧光光谱分析仪的光源为一台连续的Ar＋激光器和一台四倍频Nd：YAG激光器，可得到紫外荧光信息，扩大了应用范围。该仪器必须满足严格的时序条件和逻辑条件。利用紫外激光诱导荧光雷达探测技术可进行生物气溶胶及生物战剂的识别研究。一台紫外－荧光雷达系统，当探测距离为3000m时，浓度探测极限为500mg／m3。一种长距离生物传感探测系统可对正在运动中的气溶胶云团进行测距、探测和跟踪，跟踪高度可达30km。     

Effective disinfection of airborne microbial contamination in hospital wards using a zero‐valent nano‐silver/TiO2‐chitosan composite

A novel antimicrobial composite of zero‐valent silver nanoparticles (AgNPs), titania (TiO₂), and chitosan (CS) was prepared via photochemical deposition of AgNPs on a CS‐TiO₂ matrix (AgNPs@CS‐TiO₂). Electron microscopy showed that the AgNPs were well dispersed on the CS‐TiO₂, with diameters of 6.69‐8.84 nm. X‐ray photoelectron spectra indicated that most of the AgNPs were reduced to metallic Ag. Fourier‐transform infrared spectroscopy indicated that some AgNPs formed a chelate with CS through coordination of Ag⁺ with the CS amide II groups. The zones of inhibition of AgNPs@CS‐TiO₂ for bacteria (Escherichia coli and Staphylococcus epidermidis) and fungi (Aspergillus niger and Penicillium spinulosum) were 6.72‐11.08 and 5.45‐5.77 mm, respectively, and the minimum (critical) concentrations of AgNPs required to inhibit the growth of bacteria and fungi were 7.57 and 16.51 µg‐Ag/mm², respectively. The removal efficiency of a AgNPs@TiO₂‐CS bed filter for bioaerosols (η) increased with the packing depth, and the optimal filter quality (qF) occurred for packing depths of 2‐4 cm (qF = 0.0285‐0.103 Pa^?1; η = 57.6%‐98.2%). When AgNPs@TiO₂‐CS bed filters were installed in the ventilation systems of hospital wards, up to 88% of bacteria and 97% of fungi were removed within 30 minutes. Consequently, AgNPs@TiO₂‐CS has promising potentials in bioaerosol purification.     

Comparison of disinfection performance of UVC-LED and conventional upper-room UVGI systems

We developed a novel, compact upper-room ultraviolet germicidal irradiation system with light-emitting diode sources (UR-UVGI-LED) to enhance the disinfection of bioaerosols in an enclosed room space. Its effectiveness was evaluated and compared with the conventional upper-room ultraviolet germicidal irradiation system with mercury vapor sources (UR-UVGI-MV). Escherichia coli, Serratia marcescens, and Staphylococcus epidermidis were atomized under the well-mixed condition and exposed to UR-UVGI-LED (or UR-UVGI-MV) device. The intensity output of the UR-UVGI-LED was also varied from 0% (no LED), 25%, 50% to 100% to further evaluate the UR-UVGI-LED disinfection effectiveness under different power levels. The decay rates for UR-UVGI-LED ranged from −0.1420 ± 0.04 min⁻¹ to −0.3331 ± 0.07 min⁻¹ for Escherichia coli, −0.1288 ± 0.01 min⁻¹ to −0.3583 ± 0.02 min⁻¹ for Serratia marcescens, and −0.0330 ± 0.01 min⁻¹ to −0.0487 ± 0.01 min⁻¹ for Staphylococcus epidermidis. It was noticed that the intensity level had a non-linear influence on the UR-UVGI-LED’s performance. The decay rates achieved by the UR-UVGI-MV system were −0.3867 ± 0.08 min⁻¹, −0.4745 ± 0.002 min⁻¹, and −0.1624 ± 0.02 min⁻¹ for Escherichia coli, Serratia marcescens, and Staphylococcus epidermidis, respectively. Hence, the disinfection performance of both UR-UVGI-LED and UR-UVGI-MV systems was comparable for Escherichia coli and Serratia marcescens. These results demonstrate that the UR-UVGI-LED system has a high potential to be used as a safe and effective irradiated light source to disinfect indoor airborne pathogens.     

利用近场多波长激光雷达对生物气溶胶的偏振测量

基于非球形粒子偏振特性,设计并试制了近场偏振激光雷达。该系统包含二个激光光源和退偏组件,激光束的线偏振度为1/500,偏振和弹性散射信号由孔径200 mm的卡塞格林望远镜接收。在一个半封闭的生物气溶胶腔里,对10种生物气溶胶,按355, 532, 1064 nm的顺次进行线偏振测量。数据分析结果表明,退偏比表现出较强的波长依赖性; 利用欧氏相关度和马哈拉诺比斯距离,可以确定多波长线偏数据的差异,并对生物气溶胶进行分辨。     

Size-resolved dynamics of indoor and outdoor fluorescent biological aerosol particles in a bedroom: A one-month case study in Singapore

This study evaluated the interrelations between indoor and outdoor bioaerosols in a bedroom under a living condition. Two wideband integrated bioaerosol sensors were utilized to measure indoor and outdoor particulate matter (PM) and fluorescent biological airborne particles (FBAPs), which were within a size range of 0.5-20 μm. Throughout this one-month case study, the median proportion of FBAPs in PM by number was 19% (5%; the interquartile range, hereafter) and 17% (3%) for indoors and outdoors, respectively, and those by mass were 78% (12%) and 55% (9%). According to the size-resolved data, FBAPs dominated above 2 and 3.5 μm indoors and outdoors, respectively. Comparing indoor upon outdoor ratios among occupancy and window conditions, the indoor FBAPs larger than 3.16 μm were dominated by indoor sources, while non-FBAPs were mainly from outdoors. The occupant dominated the indoor source of both FBAPs and non-FBAPs. Under awake and asleep, count- and mass-based mean emission rates were 45.9 and 18.7 × 10⁶ #/h and 5.02 and 2.83 mg/h, respectively. Based on indoor activities and local outdoor air quality in Singapore, this study recommended opening the window when awake and closing it during sleep to lower indoor bioaerosol exposure.     

Aerosol and bioaerosol particle size and dynamics from defective sanitary plumbing systems

Aerosols are readily transported on airstreams through building sanitary plumbing and sewer systems, and those containing microbial pathogens (known as bioaerosols) are recognized as contributors to infection spread within buildings. When a defect occurs in the sanitary plumbing system that affects the system integrity, a cross-transmission route is created that can enable the emission of bioaerosols from the system into the building. These emission occurrences are characterized as short-burst events (typically <1 min in duration) which make them difficult to detect and predict. The characterization of these emission events is the focus of this research. Two methods were used to characterize bioaerosol emission events in a full-scale test rig: (a) an Aerodynamic Particle Sizer (APS) for particle size distribution and concentrations; and (b) a slit-to-agar sampler to enumerate the ingress of a viable tracer microorganism (Pseudomonas putida). The APS data confirmed that most particles (>99.5%) were <5 μm and were therefore considered aerosols. Particles generated within the sanitary plumbing system as a result of a toilet flush leads to emissions into the building during system defect conditions with an equivalence of someone talking loudly for over 6 and a half minutes. There were no particles detected of a size >11 μm anywhere in the system. Particle count was influenced by toilet flush volume, but it was not possible to determine if there was any direct influence from airflow rate since both particle and biological data showed no correlation with upward airflow rates and velocities. Typical emissions resulting from a 6 L toilet flush were in the range of 280–400 particles per second at a concentration of typically 9–12 number per cm³ and a total particle count in the region of 3000 to 4000 particles, whereas the peak emissions from a 1.2 L toilet flush were 60–80 particles per second at a concentration of 2.4–3 number per cm³ and a total particle count in the region of 886 to 1045 particles. The reduction in particles is in direct proportion to the reduction in toilet flush volume. The slit-to-agar sampler was able to provide viable time course CFU data and confirmed the origin of the particles to be the tracer microorganism flushed into the system. The time course data also have characteristics consistent with the unsteady nature of a toilet flush.     

Thermal effects on bacterial bioaerosols in continuous air flow

Exposure to bacterial bioaerosols can have adverse effects on health, such as infectious diseases, acute toxic effects, and allergies. The search for ways of preventing and curing the harmful effects of bacterial bioaerosols has created a strong demand for the study and development of an efficient method of controlling bioaerosols. We investigated the thermal effects on bacterial bioaerosols of Escherichia coli and Bacillus subtilis by using a thermal electric heating system in continuous air flow. The bacterial bioaerosols were exposed to a surrounding temperature that ranged from 20 °C to 700 °C for about 0.3 s. Both E. coli and B. subtilis vegetative cells were rendered more than 99.9% inactive at 160 °C and 350 °C of wall temperature of the quartz tube, respectively. Although the data on bacterial injury showed that the bacteria tended to sustain greater damage as the surrounding temperature increased, Gram-negative E. coli was highly sensitive to structural injury but Gram-positive B. subtilis was slightly more sensitive to metabolic injury. In addition, the inactivation of E. coli endotoxins was found to range from 9.2% (at 200 °C) to 82.0% (at 700 °C). However, the particle size distribution and morphology of both bacterial bioaerosols were maintained, despite exposure to a surrounding temperature of 700 °C. Our results show that thermal heating in a continuous air flow can be used with short exposure time to control bacterial bioaerosols by rendering the bacteria and endotoxins to a large extent inactive. This result could also be useful for developing more effective thermal treatment strategies for use in air purification or sterilization systems to control bioaerosols.