Factors affecting microbiological colony count accuracy for bioaerosol sampling and analysis.
Chang-W; Grinshpun-SA; Willeke-K; Macher-JM; Donnelly-J; Clark-S; Juozaitis-A
Am Ind Hyg Assoc J 1995 Oct; 56(10):979-986
The effects of bacterial spore surface density, nutrient concentration in culture medium, sample incubation time and ability of an observation system to identify overlapped colonies on colony masking were investigated using Bacillus-subtilis. A suspension of B-subtilis spores was aerosolized, and the aerosol was sampled using a slit to agar (STA) impactor. Colonies were counted after 12 and 36 hours of incubation. The results indicated that the degree of bacterial colony masking depended on colony density on a collection surface, on colony diameter, and on the ability of an observation system to distinguish overlapped colonies. Colony surface density depended directly on four factors, including bioaerosol concentration in the sampled air, sampler airflow rate, small collection time, and collection surface area. Colony surface density depended indirectly on nutrient concentration and incubation conditions. Colony diameter depended on nutrient concentration, incubation time and temperature, and colony surface density. Colony size was also a function of the specific organism studied and its growth rate and pattern. The occurrence of colony masking for STA impaction samplers, which results in an underestimation of actual colony count, increased with increasing colony surface density and diameter and with decreased ability to distinguish overlapped colonies. The authors offer a method to determine appropriate sample collection time to limit surface density of collected microorganisms and thereby reduce colony masking.
NIOSH-Publication; NIOSH-Grant; Respirators; Bacteria; Sampling-methods; Microorganisms; Air-quality-control; Aerosol-sampling
Environmental Health University of Cincinnati 3223 Eden Avenue Cincinnati, OH 45267-0056
Respirator Research; Respirators
American Industrial Hygiene Association Journal
University of Cincinnati, Cincinnati, Ohio