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

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 deionized (DI) water, DI water with 0.1% (w/w) antifoam B (AFB), phosphate-buffered saline (PBS), and osmoprotectants consisting of peptone (with and without AFB) or betaine at .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 or AFB. Peptone and AFB alone or together allowed for the greatest recovery of E. coli, with average values ranging from 87 to 98% at 90 min. Betaine was also determined to be an effective osmoprotectant for runtimes of 30 and 60 min, with respective E. coli recoveries of 101 and 77% from the impingers. The results from this study support the incorporation of peptone, AFB, and betaine in collection fluids for BioSampler runtimes from 30 to 90 min. Runtimes longer than the recommend 30 min with low viscosity collection fluids are sometimes necessary when the airborne concentration of a target microorganism is low and one is trying to increase the probability of detection.