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

This post was most recently updated on December 15th, 2019

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.

The Legionellaceae are aerobic and nutritionally fastidious organism. They require L-cysteine and iron salts for growth. Growth on BCYE agar after 3 or more days of incubation with no growth on blood agar and/or chocolate agar is one of the most useful presumptive clues that an isolate could be a species of Legionella.

Clinician should inform the laboratory if infection with Legionella is suspected so that the appropriate media are set up. 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 (N-(2-Acetamido)-2-aminoethanesulfonic acid) 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

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

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.
Buffered Charcoal Yeast Extract (BCYE) Agar
Legionella colonies in BCYE Agar

Colony characteristics

After 3-4 days of incubation, small white colonies of Legionella appear in BCYE agar which become grey in few days. The colonies are round and covex with entire edges.
The isolate may show typical ground glass (or irridescent) colony appearance.

Colonies may be examined under long-wave UV light (360 nm ± 20nm) to reveal yellow pigment on BCYE or auto-fluorescence of Legionella colonies.

About Acharya Tankeshwar 407 Articles
Hello, thank you for visiting my blog. I am Tankeshwar Acharya. Blogging is my passion. I am working as an Asst. Professor and Microbiologist at Department of Microbiology and Immunology, Patan Academy of Health Sciences, Nepal. If you want me to write about any posts that you found confusing/difficult, please mention in the comments below.

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