Development of an additive for simple enhanced selectivity of selective agar plates for the detection of <i>Legionella</i>

CAT agar plates, which contain cycloheximide, amphotericin B and thiabendazole as antifungal agents and vancomycin and polymyxin B as antibiotics, are selective agars with enhanced selectivity for Legionella detection, but preparation of these plates is not easy. We have therefore developed a CAT additive that produces CAT agars by simply spreading the additive on GVPC agars. GVPC agars that had been spread with the CAT additive performed as well as or better than CAT agars in detecting Legionella in concentrated stock samples of environmental water. The CAT additive would be effective for Legionella testing such as in cooling tower water samples, which are often contaminated with non-target microorganisms, and for retesting when Legionella cannot be detected due to the effects of contamination by non-target microorganisms.