ISOLATION OF LEGIONELLA FROM WATER SAMPLES USING VARIOUS CULTURE METHODS

The efficacy of a non-selective medium and two selective media were co mpared for the isolation of legionellas from water samples. The effect of acid wash treatment for decontamination of the water samples on th e isolation frequency of legionellas was also studied. The 236 samples were taken from cooling, humidifying and drinking water systems; 21% were legionella-positive when inoculated directly on modified Wadowsky -Yee (MWY) medium and 26% were positive when concentrated (x 200) befo re cultivation on MWY or CCVC media. Inoculation on MWY medium after c oncentration followed by decontamination by the acid-wash technique ga ve the highest isolation frequency (31%). The lowest frequency (8%) wa s found with the non-selective BCYE alpha medium. An isolation frequen cy of 28% was achieved with the BCYE alpha medium after concentration and acid-wash treatment of the samples. Forty per cent of the samples were positive for legionellas when the results from all the culture me thods were combined. Not all the legionella-positive samples were iden tified by a single culture method. Ninety-three of the 95 positive sam ples were detected with the two best combinations of three culture met hods. The best culture method for detecting legionellas depended on th e source of the water sample. Some water quality characteristics, like temperature and organic matter content, affected the isolation freque ncy of Legionella spp.