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Recovery of culturable Escherichia coli O157:H7 during operation of a liquid-based bioaerosol sampler

Robert S. Dungan, April B. Leytem
Aerosol science and technology 2016 v.50 no.1 pp. 71-75
Escherichia coli O157, ambient temperature, betaine, bioaerosols, evaporation, microorganisms, osmotolerance, peptones, probability, samplers, viability, viscosity
Collection fluids used in liquid-based bioaerosol samplers can influence the viability of microorganisms. In this study we determined the recovery efficiency of vegetative E. coli O157:H7 cells that were spiked into low viscosity evaporating collection fluids during operation of a BioSampler™ for up to 90 min at room temperature. The collection fluids tested were distilled (DI) water, phosphate-buffered saline (PBS) and osmoprotectants consisting of peptone and/or antifoam or betaine at 0.1% (w/w) in DI water. Using DI water, there was a rapid decline in the recovery of culturable E. coli, with only 11, 3, and 0% being recovered after 30, 60, and 90 min, respectively. Recoveries were substantially greater with use of PBS (53, 25, and 16%, respectively) but not as high as with use of the osmoprotectants. Peptone solutions, which are commonly used in liquid-based bioaerosol samplers, allowed for the recovery of 87% of the E. coli after 90 min. However, the control data indicate that some cellular growth did occur, which could be offsetting the recovery of culturable E. coli towards slightly higher values. When an antifoaming agent was added to the peptone solution there was little overall change in the amount of E. coli recovered. Betaine was also determined to be an effective osmoprotectant, with 101, 77, and 41% of E. coli recovered from the impingers at 30, 60, and 90 min, respectively. The results from this study support the incorporation of osmoprotectants in collection fluids, but not use of DI water and PBS, when BioSampler runtimes up to 90 min will be utilized. Runtimes longer than 30 min are sometimes necessary when the airborne concentration of a target organism is low and one is trying to increase the probability of detection.