Evaluation of a procedure to isolate culturable microorganisms from carpet dust

Details of a method to isolate culturable bacteria and fungi from carpet dust were evaluated to isolate the greatest numbers of these agents. Four broad groups were evaluated: mesophilic and thermophilic bacteria and moderately hydrophilic and xerophilic fungi. Features studied included: 1) mixing time; 2) addition of glass beads; 3) length of time dust settled before suspensions were plated; 4) relative concentrations of microorganisms in the fibrous and fine dust fractions; and 5) storage temperature and period. The findings are preliminary because of the small number of samples, but a votexing time of at least 2 min with glass beads gave the best results in terms of the highest estimate of the concentration of culturable bacteria or fungi. Microorganisms were retrievable from the upper portion of a suspending liquid for at least 30 min with little detectable change in concentration. Both bacteria and fungi were more abundant in the fine than the fibrous dust fraction. No significant losses were observed for samples stored up to 25 days at 5 degreesC or 25 degreesC. This procedure optimized measurement of total concentration, but may not identify the range of genera and species in dust if microorganisms present in small numbers and as single units are underrepresented relative to those in clusters and aggregates.