Procedures for the characterisation of bioaerosol particles. Part II: Effects of environment on culturability

Abstract

The behaviour of bioaerosol particles in industrial and health-careapplications may be most effectively understood once they have beenquantitatively assessed using well-characterised sampling and assaytechniques. However, the large number of different conditions possiblein this wide range of applications makes the assessment of bioaerosolparticles very difficult. In addition to the effects of differentsampling and assay technologies, the mechanism of aerosolisation andenvironmental conditions can influence bioaerosol behaviour. The effectsof sampler selection and suspension aerosolisation on bioaerosolviability were reported earlier as ``Part I'' of two papers, and theeffects of the environment on the culturability of three different typesof microorganism are reported here as ``Part II''. The environmentalrelative factors considered in the present study are: relativehumidity (RH), aerosol-age, and a number of gaseous pollutants. A smallnumber of additional tests, examining the effects of aerosolisationmethod on culturability, are also reported. A combination of anenvironmentally controlled Bioaerosol Test Chamber and Goldberg RotatingDrum were shown to be an appropriate facility to carry out the study.Changing RH was shown to have a considerable effect on the culturablefraction of aerosolised Sacharomyces cerevisiae cells but notPenicillium expansum spores or Bacillus subtilis var.niger spores. In this text, ``culturable fraction'' is definedas the fraction of the total number of microorganisms in a sample thatwill form colonies (i.e. grow and reproduce) on a suitably preparedculture plate under optimum conditions for the species of microorganismunder consideration. After the initial shock of aerosolisation, theculturable fraction of S. cerevisiae cells and P.expansum spores is not further affected by increasing aerosol age.Results from an earlier study have shown spray suspension and collectedaerosol age also have no effect on culturability of P. expansumspores. The effects of gaseous pollutants are reflected in the reductionin culturability of P. expansum spores following exposure tosulphur dioxide, ozone and ozone hydrocarbon cocktail. This reductionwas never to less than 30% of the unpolluted control. All thetests show that P. expansum spores are fairly robust andbiologically stable. Examination of the effects of aerosolisationtechnique on the culturability of S. cerevisiae shows theCollison nebuliser produces aerosols with the highest culturabilitycompared with either a plain glass atomiser or a Unimed nebuliser usedin these tests.