CHARACTERISTICS OF AIRBORNE ACTINOMYCETE SPORES

Airborne actinomycete spores, important contaminants in occupational a nd residential environments, were studied with respect to their (i) re lease into the air, (ii) aerodynamic and physical size while airborne, and (iii) survival after collection onto agar,vith an impactor. Three actinomycete species were selected for the tests to exemplify the thr ee main spore types: Streptomyces albus for arthrospores, Micromonospo ra halophytica for aleuriospores, and Thermoactinomyces vulgaris for e ndospores. The results show that the incubation conditions (temperatur e, time, and nutrients) needed for the development of spores for their release into air are different from the conditions that are needed fo r colony growth only. Additional drying of M. halophytica and T. vulga ris cultures was needed before spores could be released from the cultu re. The aerodynamic sizes of the spores, measured with an aerodynamic particle sizer, ranged from 0.57 (T. vulgaris) to 1.28 mu m (M. haloph ytica). The physical sizes of the spores, when measured with a microsc ope and an image analysis system, were found to be smaller than previo usly reported in the literature. The relative recovery of the spores o n agar media ranged from 0.5 (T. vulgaris) to 35% (S. albus). The resu lts indicate that the culturability of the collected airborne actinomy cete spores varies widely and is affected by several variables, such a s the species and the sampling flow rate. Therefore, alternatives to c ommonly used cultivation methods need to be developed for the enumerat ion of actinomycete spores.