Legionella agar was designed for the isolation of Legionella spp. and is used primarily in water and environmental laboratories. Since Legionella spp. are fastidious organisms, the medium contains yeast extract as a source of nitrogen, carbon and vitamins. Charcoal is also included to neutralise growth-inhibiting substances and agar is the solidifying agent.
The medium requires supplementation with ferric pyrophosphate as a source of iron, L-cysteine, an essential amino acid for the growth of Legionella spp. and α-ketoglutaric acid, which acts as a growth stimulant. ACES buffer/potassium hydroxide is also added to maintain the optimal pH of 6.9 for growth of Legionella spp. Omission of the L-cysteine produces a confirmation medium that can be used to test presumptive Legionella spp. as isolates will not be able to grow.
Selective versions of the medium can also be created by the addition of various selective agents. GVPC is the most popular for water testing and BMPA for clinical testing.