Evaluation of airborne microbial densities and assemblages following extended impaction onto a modified collection surface

摘要

To account for the heterogeneous distribution of airborne microbes, we tested a modified impaction sampling protocol to facilitate repeated samplings throughout an extended sampling duration and flexibility in downstream analyses. Tests of the ability of four buffered agars showed that peptone-phosphate agar most effectively supported bacteria viability for multiple days. A novel, periodic sampling protocol (10 min h(-1) for 6 h) was developed and included placing a nitrocellulose membrane onto the buffered agar prior to the sampling, which was processed for bacteria enumeration (cell extraction and dilution plating) and assemblage analyses (deoxyribonucleic acid extraction, polymerase chain reaction, and denaturing gradient gel electrophoresis analysis (DGGE)). Among three indoor locations, a significantly greater density of bacteria was detected following periodic sampling (81 CFU m(-3)) than traditional, continuous sampling onto tryptic soy agar (54 CFU m(-3); p = 0.037). The temporal dynamics of bacteria densities were assessed and showed that densities ranged from 34 to 86 CFU m(-3) air and varied significantly throughout the three corridor locations (p = 0.0006) and through time (p < 0.05). DGGE fingerprinting revealed that periodic and continuous samplings resulted in an average of 30 and 19 bands per fingerprint, respectively (p < 0.040), indicating that periodic sampling revealed a greater portion of the overall airborne bacteria assemblage than continuous sampling. Overall, compared with traditional sampling, modifications to the impaction protocol allowed detection of a significantly greater number of bacteria, as well as the potential for simultaneous culture-dependent and culture-independent analyses.