Buffered Charcoal Yeast Extract (BCYE) Agar: Composition, Uses and Colony characteristics

Buffered Charcoal Yeast Extract Agar (BCYE) was developed by Feeley et al and then further modified by Edelstein for selective cultivation of Legionella species. BCYE Agar is an enrichment medium which is used for the isolation and cultivation of Legionella species from environmental samples and clinical specimens.

BCYE agar provides L-Cysteine and other nutrients required for the growth of Legionella pneumophila, the causative agents of Legionnaires’ disease.

Composition of BCYE Agar and functions of each ingredient

  1. Yeast extract : Yeast extract supplies the protein and other nutrients necessary to support growth
  2. L-Cysteine HCl : L-Cysteine is an essential amino acid, incorporated to satisfy specific nutritional requirements of Legionella species
  3. Charcoal activated : Activated charcoal decomposes hydrogen peroxide, a metabolic product toxic to Legionella species, and may also collect carbon dioxide and modify surface tension
  4. Ferric Pyrophosphate : used as an Iron supplement; iron source
  5. ACES buffer: ACES buffer is added to maintain the proper pH for optimal growth.
  6. Ketoglutarate monopotassium salt : Alpha-ketoglutarate is added to stimulate growth
  7. Agar

Final pH ( at 25°C) 6.9±0.2

Procedure for the preparation of Buffered Charcoal Yeast Extract (BCYE) Agar

  1. Suspend 20 grams in 500 ml distilled water
  2. Heat to boiling to dissolve the medium completely
  3. Sterilize by autoclaving at 15 lbs pressure (121°C) for 15 minutes.
  4. Cool to 50°C.
  5. Aseptically add sterile rehydrated contents of 1 vial each of Legionella Supplement.
  6. Mix well and pour with constant stirring to ensure that charcoal particles get evenly distributed.

 Quality control:  Legionella pneumophila ATCC 33153 grows well on BCYE agar and gives white grey to blue grey colonies.