New method for isolating antibiotic-producing fungi

A convenient and efficient method was established for isolating antifungal antibiotic-producing fungi from soil samples. In this method, soil samples were diluted and directly plated in agar medium by the standard fungi-isolating method, and the plates were cultured at 27 degrees C for 2-3 days to permit the growth of fungal colonies. Then, the suspension of pathogenic Candida albicans in saline (40 mu l, 5-10 x 10(5) CFU ml(-1)) was overlaid by spraying on the plates under controlled conditions in the safety cabinet. After 1-day incubation, fungal colonies showing an antagonistic effect with the inhibition zone against sprayed C. albicans were selected. Among 151 isolates, 26 strains were found to reproduce anti-C. albicans activity in liquid medium, yielding a higher selection rate (17.2%) than that (3.1%) by the traditional method. This new method can be applied for isolation of microorganisms (fungi and actinomycetes) that produce antibiotics active against pathogenic microorganisms. The Journal of Antibiotics (2013) 66, 17-21; doi: 10.1038/ja.2012.79; published online 14 November 2012