Toward Understanding Prevalence of Airborne Microorganisms in a Hot-Arid Environment

摘要

This study aims to determine prevalence of microorganisms in the air state and those associated particulate matter (PM) in a hot arid environment (Makkah city, Saudi Arabia) in relation to time of the day, PM concentration and meteorological conditions during the period between July and September 2014. PM and black smoke samples were collected on cellulose nitrate membrane filters during the daytime (8.00 am - 20.00 pm) and the nighttime (20.00 pm - 8.00 am). PMs, filters were eluted in buffer phosphate and aliquots were spread plated onto the surfaces of trypticase soya agar, malt extract agar, and starch casein agar media for counting bacteria, fungi and actinomycetes associated PM, respectively. Airborne microorganisms were collected using an Andersen two stage impactor sampler equipped with Petri plates containing the previously mentioned agar media. The Andersen two-stage viable cascade impactor sampler separates particles into coarse (≥8 μm) and fine (≤8 μm) size fractions. Airborne microorganisms were taken at three day time-scales: in the morning (8 am - 10 am), at the afternoon (13.00 pm - 16.00 pm) and in the evening (22.00 pm - 1.00 am). The average concentrations of PM (149.5 μg/m3) and smoke (57.03 μg/m3) were higher in the daytime and nighttime, respectively. The greatest concentrations of microorganisms associated PM were found in the daytime, however the peak concentration of airborne microorganisms was found in the evening time. Fine microbial fraction constituted ~60% - 75.9% of the total microbial concentrations. Positive correlations were found between bacteria with PM concentration in the daytime and meteorological conditions at the nighttime. Temperature and relative humidity positively affected survivability of microorganisms associated PM at the nighttime and airborne fungi as well. This study helps understand distribution pattern of microorganisms in the atmosphere of a hot-arid environment.