Enhanced antifungal effect of the selective medium for the detection of Legionella species by a combination of cycloheximide, amphotericin B and thiabendazole

Abstract

The accurate detection of Legionella from environmental water samples using conventional plate culture methods is often made difficult by the overgrowth of non-target microorganisms on the selective agar plates. Acid pretreatment is a very effective pretreatment to decrease the overgrowth of heterotrophic bacteria. However, acid pretreatment would not be expected to eliminate molds. We evaluated the effects of four kinds of antifungal agents, individually and in combination, on the growth of Legionella strains and molds. Consequently, it was demonstrated that the combination of cycloheximide, amphotericin B and thiabendazole was very effective in eliminating molds on agar plates, and resulted in the improved detection of Legionella. Examination of 214 cooling tower water samples using the enhanced antifungal selective medium (CAT α) instead of GVPC α selective medium demonstrated a decrease in contamination by molds from 13.6% to 1.9% without affecting the growth of Legionella.