The effect of sampling time on the total efficiency of the Andersen Microbial Sampler: A field study

The Andersen Microbial Sampler (AMS) has been used under varying conditions , bur it has not been fully characterized with respect to the effect of sam pling time on total sampler efficiency. The objective of this study was to characterize the AMS with respect to sampling time on total efficiency, mea sured as colony-forming units per cubic meter (CFU m(-3)) when sampling for total culturable bacteria with Tryptic-soy agar (TSA) at an outdoor compos t center. The sample times ranged from 1 to 6 min. Statistical analysis usi ng multivariate analysis of variance (MANOVA) coupled with mixed model anal ysis of variance showed a parabolic trend between CFU m(-3) and sampling ru n rime. At both sites, the highest average CFU m(-3) occurred at a sampling run time of 2 min. Duplicate samples were taken, and a test of internal va lidity was performed to show that the sampling methodology used was not a s ource of error, The Pearson's correlation coefficient for the two samplers was 0.86 at the first site and 0.90 at the second. The: effect of sampling time on the particles impacting the second stage was also examined and foun d not to be significant. Even though field testing presents uncontrollable variables, optimal sampling run times can still be determined using statist ical analyses. Thus, optimal sampling times based on a complex microflora a nd not a single genus will minimize unsuccessful sampling episodes (e.g. pl ate overloading). (C) 1999 Elsevier Science Ltd. All rights reserved.