Inactivation of bacteria and fungus aerosols using microwave irradiation

Abstract

This study investigated the survivals of both lab-generated and environmental bioaerosols when exposed to the microwave irradiation (2450 MHz) for ∼2 min at different output powers (700, 385 and 119 W). Control and exposed bioaerosols were collected by a BioSampler or a mixed cellulose ester (MCE) filter, and the air samples were further cultured. As a comparison, liquid-borne exposure for one species was also conducted. Environmental scanning electron microscope (ESEM) and transmission electron microscope (TEM) were used to study the membrane surface morphologies and intracellular components of the microwave-treated and untreated microbes. The survival rates of airborne Bacillus subtilis var niger spores were shown to be about 35%, 44% and 35% when exposed to the microwave irradiation for 1.5 min with high, medium and low power applied, respectively ( p-value=0.37). In contrast, the airborne Pseudomonas fluorescens were shown to have lower survival rates of 5.8%, 12.2% and 21% ( p-value=0.0045). Similar patterns but higher survival rates at respective powers were observed for airborne Aspergillus versicolor exposure ( p-value<.0001). For environmental bacterial and fungal bioaerosols, 30–40% of them were shown to survive the high power microwave irradiation for 1.7 min. Outdoor bioaerosols were shown to have stronger survival than the indoor bioaerosols when exposed to the microwave irradiation. ESEM and TEM images showed visible damages to the microwave-irradiated microbes. The results obtained here can be used to develop microwave-based air sterilization technologies especially targeted for biological aerosols.