Relationship between sampling duration and concentration of culturable airborne mould and bacteria on selected culture media

Aims: This study was designed to evaluate potential effects of sampling duration on observed concentrations of airborne culturable mould and bacteria on selected media. Methods and Results: Airborne culturable mould and bacteria from lightly to moderately contaminated environments were collected on selected culture media using two co-located, concurrently operated, Andersen N-6 samplers for five sampling durations in the range of 1-10 min. Differences in mean concentrations, as well as linear relationships between sampling duration and both concentration and variability, were evaluated using nonparametric procedures. For the five sampling durations, there were no significant differences in mean concentrations of mould; for bacteria, there were significant differences, with a trend of decreasing concentrations as sampling duration increased. Data variability decreased with increasing sampling duration for both mould and bacteria. Conclusions: Airborne culturable mould concentrations were similar for sampling durations in the range of 1-10 min. Airborne bacteria concentrations tended to trend downwards with sampling durations exceeding 3 min. Significance and Impact of the Study: This study has shown that sampling durations of 1-10 min are appropriate for collection of airborne culturable mould on malt extract agar (MEA) and dichloran glycerol agar (DG-18); based on the apparent trend of decreasing bacterial sample concentrations associated with increasing sampling duration, sampling durations of <= 3 min may be more appropriate than 5 or 10 min for bacteria on trypticase soy agar (TSA).