Comparison of methods for detection and enumeration of airborne microorganisms collected by liquid impingement

Abstract

Bacterial agents and cell components can be spread as bioaerosols, producing infections and asthmatic problems. This study compares four methods for the detection and enumeration of aerosolized bacteria collected in an AGI-30 impinger. Changes in the total and viable concentrations of Pseudomonas fluorescens in the collection fluid with respect to time of impingement were determined. Two direct microscopic methods (acridine orange and BacLight) and aerodynamic aerosol-size spectrometry (Aerosizer) were employed to measure the total bacterial cell concentrations in the impinger collection fluid and the air, respectively. These data were compared with plate counts on selective (MacConkey agar) and nonselective (Trypticase soy agar) media, and the percentages of culturable cells in the collection fluid and the bacterial injury response to the impingement process were determined. The bacterial collection rate was found to be relatively unchanged during 60 min of impingement. The aerosol measurements indicated an increased amount of cell fragments upstream of the impinger due to continuous bacterial nebulization. Some of the bacterial clusters, present in the air upstream of the impinger, deagglomerated during impingement, thus increasing the total bacterial count by both direct microscopic methods. The BacLight staining technique was also used to determine the changes in viable bacterial concentration during the impingement process. The percentage of viable bacteria, determined as a ratio of BacLight live to total counts was only 20% after 60 min of sampling. High counts on Trypticase soy agar indicated that most of the injured cells could recover. On the other hand, the counts from the MacConkey agar were very low, indicating that most of the cells were structurally damaged in the impinger. The comparison of data on the percentage of injured bacteria obtained by the traditional plate count with the data on percentage of nonviable bacteria obtained by the BacLight method showed good agreement.

Atmospheric Movement of Microorganisms in Clouds of Desert Dust and Implications for Human Health

“…The drawback of this method is the loss of viability due to impaction stress (257). Impingement of microorganisms into a liquid matrix (via bubbling) is another method of capture used in aeromicrobiology (7,27,227). A widely used liquid impinger is the AGI-30 (Ace Glass Inc., Vineland, NJ), which utilizes a low flow rate to bubble air through a liquid matrix.…”

The Global Dispersion of Pathogenic Microorganisms by Dust Storms and Its Relevance to Agriculture

“…Fluorescence microscopy enables the acquisition of additional data (metabolic state of the cell, direct counts of bacteria and fungi, etc.) through the use of different stains such as acridine orange, SYBR green, LIVE/DEAD staining, or DAPI (Albrecht et al, 2007;Fallschissel et al, 2010;Terzieva et al, 1996). The combined use of microscopy along with immunology or genetic methods allows identification to the species level.…”

Effects of different sampling solutions on the survival of bacteriophages in bubbling aeration

“…And this supposition was proved by the experiment of determination of reaerosolized phages designed as later. Because of extensive evaporation of the collection fluid during operation, which reached 50% of the initial impinger volume per hour at a relative humidity of 30% (Terzieva et al 1996), all plaque count results were corrected by a liquid evaporation factor, which was calculated by use of Eq. 2.…”