Bacterial air counts obtained with a centrifugal (RCS) sampler and a slit sampler--the influence of aerosols

Samples of air collected from an air-conditioned hospital room with a 'Biotest RCS' centrifugal air sampler yielded (assuming a sampling rate of 40 l/min) air counts that were approximately twice those obtained with a modified conventional ' Casella ' slit sampler. However, for samples taken during the generation of an aerosol of spores of Bacillus globigii, the slit sampler gave counts that were apparently three- to tenfold higher than those with the centrifugal sampler. For a few minutes after switching off the nebulizer, higher counts were still obtained with the slit sampler, but then the centrifugal sampler again gave consistently higher counts. Our results illustrate that attempts to measure the number of bacteria in air are influenced by the size of the bacterial particles and the sampler that is used.