Comparison of four media for the isolation of Aspergillus flavus group fungi

Abstract

Four agar media used to isolate aflatoxin producing fungi were compared for utility in isolating fungi in the Aspergillus flavus group from agricultural soils collected in 15 fields and four states in the southern United States. The four media were Aspergillus flavus and parasiticus Agar (AFPA, 14), the rose bengal agar described by Bell and Crawford (BCRB; 3), a modified rose bengal agar (M-RB), and Czapek's-Dox Agar supplemented with the antibiotics in BC-RB (CZ-RB). M-RB was the most useful for studying the population biology of this group because it permitted both identification of the greatest number of A. flavus group strains and growth of the fewest competing fungi. M-RB supported an average of 12% more A. flavus group colonies than the original rose bengal medium while reducing the number of mucorales colonies and the number of total fungi by 99% and 70%, respectively. M-RB was successfully employed to isolate all three aflatoxin producing species, A. flavus, A. parasiticus and A. nomius, and both the S and L strains of A. flavus. M-RB is a defined medium without complex nitrogen and carbon sources (e.g. peptone and yeast extract) present in BC-RB. M-RB should be useful for studies on the population biology of the A. flavus group.