Inhibition of Growth of Fungi on Rose Bengal Media by Light

Since 1953, the airborne fungus flora of Kansas has been the subject of considerable study, particularly the numbers and kinds occurring throughout the year. Early work dealt chiefly with fungus spores (13) which were impinged on a silicone-coated slide in a slit sampler (12). In 1956, it was decided to supplement these studies by using nutrient plates to identify by culture those fungi such as Penicillium and Aspergillus which could not be identified on the basis of their spores alone. After testing many media, a rose bengal-streptomycin :(RBS) medium was found to be the best (16) and was used routinely in a two-year study of the seasonal occurrence of the fungi (8, 9, 10) and more recently in studying the fungi in the air during a 24-hour period. In the former study the RBS medium was highly satisfactory but in the latter investigations negative plates were frequently found when exposures were made during midday. It has been determined that the sterile plates were due to a photodynamic action caused by exposure of the rose bengal to sunlight. A preliminary paper is being published (15) while this one presents further information on the reduction of growth of fungi in rose bengal media following exposure to sunlight.