Wadowsky-Yee-Okuda (WYO) Medium: A New Selective Medium for the Isolation of Legionellae Strains from Environmental Water Specimens

In order to obtain more effective medium for the selective isolation of strains of Legionella species from environmental water specimens, 18 test media were prepared by adding each one of the 5 antifungal agents, amphotericin B, anisomycin, cycloheximide, nystatin, or miconazole, in various concentrations to GVP (glycine-vancomycin-polymyxin B) medium proposed by Wadowsky and Yee.In a comparative study to isolate legionellae from the water specimens of 15 cooling towers in Fukuoka Prefecture, 15 (100%) specimens were positive on the GVP medium added with either amphotericin B or anisomycin in a concentration of 80μg/ml, 14 (93%) on GVP added with 80μg/ml cycloheximide, whereas 11 (73%) on MWY (modification of Wadowsky-Yee) by Edelstein was the highest and only 1 (7%) on BMPA (buffered cefamandole-polymyxin B-anisomycin) medium was the lowest among the 6 previously reported selective media. All these 24 media were used in combination with acid-buffer treatment of the water specimens.Of these 3 effective antifungal agents, amphotericin B is of cheaper cost and of easier availability than anisomycin in Japan, and is less inhibitory to the growth of legionellae and more inhibitory to candidae than cycloheximide. Thus amphotericin B was chosen as antifungal agent to be incorporated to GVP medium in a concentration of 80pg/ml. This medium in herein named as WYO (Wadowsky-Yee-Okuda) medium and recommended for the selective isolation of legionellae in combination with acidbuffer treatment of the specimen.Growth rates of the 13 test strains of 7 Legionella species on WYO medium were almost similar to those on the original GVP medium. Although the inability of the type strain of L. gormanii to grow on WYO medium would suggests a limitation of such selective isolation device, WYO medium would be helpful for both ecological and epidemiological researches on legionellae and human legionellosis.