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Appl. Environ. Microbiol., Apr 1995, 1232-1239, Vol 61, No. 4
SL Stewart, SA Grinshpun, K Willeke, S Terzieva, V Ulevicius and J Donnelly
Microbial stress due to the impaction of microorganisms onto an agar
collection surface was studied experimentally. The relative recovery rates
of aerosolized Pseudomonas fluorescens and Micrococcus luteus were
determined as a function of the impaction velocity by using a moving agar
slide impactor operating over a flow rate range from 3.8 to 40 liters/min
yielding impaction velocities from 24 to 250 m/s. As a reference, the sixth
stage of the Andersen Six-Stage Viable Particle Sizing Sampler was used at
its operating flow rate of 28.3 liters/min (24 m/s). At a collection
efficiency of close to 100% for the agar slide impactor, an increase in
sampling flow rate and, therefore, in impaction velocity produced a
significant decline in the percentage of microorganisms recovered.
Conversely, when the collection efficiency was less than 100%, greater
recovery and lower injury rates occurred. The highest relative rate of
recovery (approximately 51% for P. fluorescens and approximately 62% for M.
luteus) was obtained on the complete (Trypticase soy agar) medium at 40 and
24 m/s (6.4 and 3.8 liters/min), respectively. M. luteus demonstrated less
damage than P. fluorescens, suggesting the hardy nature of the
gram-positive strain versus that of the gram-negative microorganism.
Comparison of results from the agar slide and Andersen impactors at the
same sampling velocity showed that recovery and injury due to collection
depends not only on the magnitude of the impaction velocity but also on the
degree to which the microorganisms may be embedded in the collection
medium.(ABSTRACT TRUNCATED AT 250 WORDS)
Copyright © 1995, American Society for Microbiology
Effect of impact stress on microbial recovery on an agar surface
Department of Environmental Health, University of Cincinnati, Ohio 45267-0056, USA.
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