Charcoal-yeast extract agar: primary isolation medium for Legionella pneumophila

TLDR

Charcoal‑yeast extract agar is a new bacteriological medium that supports excellent growth of Legionella pneumophila. It is derived from F‑G agar by replacing casein hydrolysate with yeast extract, omitting beef extractives and starch, and adding 0.20 % activated charcoal. Compared with F‑G agar, charcoal‑yeast extract agar yields 4.35 × 10⁶ CFU from a standardized inoculum versus 4.85 × 10⁴ CFU and produces visible colonies in 3 days instead of 4 days.

Abstract

Charcoal-yeast extract agar is a new bacteriological medium that supports excellent growth of the Legionella pneumophila. It results from modifications made in an existing L. pneumophila medium, F-G agar. Yeast extract, instead of an acid hydrolysate of casein, serves as the protein source. Beef extractives and starch are not added. Activated charcoal (Norit A or Norit SG) is included at 0.20% (wt/vol). Comparison of charcoal-yeast extract and F-G agars showed that a greater number of colony-forming units of L. pneumophila was recovered from a standardized tissue inoculum on charcoal-yeast extract agar (4.35 x 10(6) colony-forming units) than on F-G agar (4.85 x 10(4) colony-forming units). Macroscopic colonies of L. pneumophila were visible on the new medium within 3 days, whereas 4 days of growth was required on F-G agar.