Comparative study of selective media for isolation of Legionella pneumophila from potable water.

A total of 100 water samples, 95% of which were taken from hospital potable water fixtures, were cultured on three different media used for the isolation of Legionella pneumophila. The media used were buffered charcoal-yeast extract medium (BCYE alpha medium), BCYE alpha medium with antimicrobial agents (BMPA alpha medium), and BCYE alpha medium with antimicrobial agents, glycine, and differential dyes (MWY medium). An acid wash procedure was also used for specimens plated on BCYE alpha and BMPA alpha media. A total of 24 samples were culture positive for L. pneumophila by one or more techniques. MWY medium detected 92% of positive cultures, BCYE alpha medium with the acid wash detected 83% of positive cultures, BMPA alpha medium detected 79% of positive cultures. BCYE alpha medium detected 71% of positive cultures, and BMPA alpha medium with the acid wash detected 62% of positive cultures. MWY medium was the best medium for isolating L. pneumophila from potable water specimens and can probably be depended upon as the sole medium for this type of testing.