To confirm whether incubation with EB can inhibit acid-fast bacteria contamination on membrane filters, we used GVPC agar plates supplemented with EB. GVPC agar plates containing 100 µg/mL of EB were prepared. Bathwater samples were examined; 50 mL of acid-phosphate buffer was added to 50 mL of bathwater. After 10 min, the bathwater-acid-phosphate buffer sample was filtered through a mixed cellulose ester membrane filter with a pore size of 0.45 µm (ADVANTEC, Tokyo, Japan) . After filtering the were filtered through a cellulose acetate membrane filter with pore size of 0.2 µm for sterilization. ETH was dissolved in ethanol. et al., 2004 ) at a concentration of 30 mg/mL (as ethambutol dihydrochloride) . Cell suspensions of L. pneumophila (10 3 CFU/mL) and Mycobacterium spp. (10 6 CFU/ mL) were mixed, and an equal volume of EB-acid-phosphate buffer was added. After 5 min, 0.2 mL of the mixture was inoculated on a GVPC agar plate (where the final concentration of EB in the agar plates was approximately 160 µg/mL) and incubated at 36℃ for 6 d. The agar plates were visually observed for the growth of Mycobacterium spp. and L. pneumophila, and the colonies were enumerated.