Comparison of different agars used in the formulation of buffered charcoal yeast extract medium.

The effect of agar type used for buffered charcoal yeast extract medium supplemented with 0.1% alpha-ketoglutarate was tested based on the growth and size of Legionella pneumophila. Oxoid Agar no. 1, Difco Bacto and Bitek agars, and BBL Granulated, Grade A, and Select agars were tested. For colony size the agars were ranked in the following order: Oxoid agar no. 1 much greater than Bacto greater than Bitek approximately Granulated approximately Grade A greater than Select. Colony yield per plate was similar for all agars except for Grade A, which gave significantly fewer colonies after 3 days, but not 4 days, of incubation. Agar type significantly influences L. pneumophila growth on buffered charcoal yeast extract medium supplemented with 0.1% alpha-ketoglutarate.