A novel method for measuring the charge distribution of airborne microbes

Abstract

A novel method for measuring bioaerosol charge distribution was investigated using electrostatic sampling and quantitative polymerase chain reaction (qPCR). Here, Bacillus subtilis var niger and Pseudomonas fluorescens were aerosolized and precipitated into different regions of two 96-well plates placed inside an electrostatic sampler. The concentrations of negatively charged bacteria in the air samples collected were quantified using qPCR, and the relevant bioaerosol charge levels were calculated using an equation developed in this study. Experimental results showed that B. subtilis var niger bioaerosols had wider charge distribution than P. fluorescens. For B. subtilis var niger, 93% of them carried a charge level of 13-42 units, 2% carried a charge level of 8-13 or lower, and 5% carried a charge level of 42-195 or higher. While for P. fluorescens, 99% of P. fluorescens aerosols carried a charge level of 14-34 elementary units. The indicative charge levels of bioaerosols collected at a certain point in the electrostatic sampling line largely depends on the particle size, bacterial species, electrostatic field strength, and the sampling flow rates for a given electrostatic sampler. In general, the trends for the charge levels here were similar to those obtained in previous studies. Use of qPCR technology in this study can distinguish between biological and non-biological particles collected. Thus, this avoided counting the non-biological particles in traditional bioaerosol charge measurements in which an optical particle counter is used. The developed technique here can be also used to analyze the charge levels for other types of bioaerosols.

Measurement of electrical charges carried by airborne bacteria laboratory-generated using a single-pass bubbling aerosolizer

“…For example, Mainelis et al (2001) showed that some bacteria aerosolized using a nebulizer could carry more than 10,000 elementary charge units; however, less than 1% of the aerosolized bacteria were found to carry more than 2000 negative units. This was confirmed by Xie, Shen, and Yao (2011), who showed that most of the bacterial cells contained in a nebulized aerosol carry less than 200 elementary charge units. Mainelis et al (2001) also showed that aerosolized bacterial cells carry higher levels of electrical charge than inert non-biological airborne particles (e.g.…”

Negatively and positively charged bacterial aerosol concentration and diversity in natural environments

“…These findings suggest that different species might carry different levels of natural charges under atmospheric conditions. In our previous study, we have found that most of aerosolized B. subtilis var niger and P. fluorescens were collected into numbers 2, 3, 4 regions of the two square agar plates [10]. Previous studies indicated that for aerosolized bacterial species, the charge consists two components: natural charge and the charge imparted by mechanical dispersion [18].…”

“…In this study, the electrostatic sampler was operated at a sampling flow rate), our sampler should have more than 40% collection efficiency for the particles of 0.3 µm and bigger [10], and complete collection efficiency profile can be obtained from Xie et al [10]. It can be inferred from a previous study [25] that the tested electrostatic field strength and conditions caused little damage to the bacteria including airborne and agar-surface borne.…”

“…Due to its lower deposition velocity and less desiccation, the electrostatic sampling has been shown to be a less stress causing collection method for culturable bioaerosols [15][16][17][18]. It has been shown that airborne biological agents carry certain amount of electrical charges in both charge polarities [10,18,19]. The electrostatic sampling technique is a collection method which utilizes the electrostatic field to collect the charged bioaerosols.…”

“…Accordingly, a variety of sampling techniques including filtration, liquid impingement, and impaction have been investigated in monitoring bioaerosols [4][5][6][7][8]. Recently, electrostatic sampling techniques for bioaerosols have also increasingly been studied [9][10][11][12][13][14][15][16][17][18]. Previous studies have shown that the electrostatic sampling performed better than the BioStage impactor [15] and the BioSampler [12] when sampling airborne culturable bacteria and fungi, endotoxin and allergens, respectively, under certain conditions.…”