From the Guidelines
Legionella species, particularly Legionella pneumophila, are the primary organisms that grow on charcoal yeast extract agar. This is based on the most recent evidence from 1, which highlights the importance of specific culture media for detecting diverse pathogens, including Legionella sp. that requires cultivation on buffered charcoal yeast extract agar for 8-10 days.
Key Characteristics of Charcoal Yeast Extract Agar
- The medium contains activated charcoal to detoxify harmful compounds, yeast extract for essential nutrients, and iron and cysteine supplements critical for Legionella growth.
- It is specifically designed for the growth of fastidious organisms like Legionella that have unique nutritional requirements.
- Other organisms such as some Francisella species and certain fastidious gram-negative bacteria may also grow on this medium, albeit less efficiently.
Clinical Significance
- Charcoal yeast extract agar is the gold standard for isolating Legionella from clinical and environmental samples.
- It plays a crucial role in diagnosing Legionnaires' disease and in monitoring water systems for potential contamination, as emphasized in 1.
- The ability to culture Legionella on this medium is vital for confirming the diagnosis and guiding antibiotic therapy, especially given the variable cultivation times required for different pathogens, ranging from 24 hours to 12 weeks as noted in 1.
From the Research
Organisms that Grow on Charcoal Yeast Extract Agar
- Legionella pneumophila, as it is the primary organism that this medium is designed to support 2, 3, 4, 5, 6
- Other Legionella species, although the growth of these species may be less robust than that of L. pneumophila 2, 4
- Specifically, L. adelaidensis and L. londiniensis have been shown to multiply on BCYE agar at elevated pH and temperature 2
- Some species, such as L. anisa, can be present in high numbers on BCYE agar, but may not grow as well on selective media 2
- L. santicrucis, L. rubrilucens, and L. erythra may grow poorly on certain selective BCYE media 4
- L. micdadei and L. bozemanii may not grow on cefamandole-containing media 4
Culture Conditions
- Buffered Charcoal Yeast Extract (BCYE) agar is typically used at a pH of 6.9 ± 0.4 and incubated at 36 ± 1 °C 2
- Elevated pH (7.3 ± 0.1) and temperature (40 ± 0.5 °C) can be used to selectively enumerate L. pneumophila 2
- The use of selective agents, such as polymyxin B, anisomycin, and vancomycin, can help to inhibit the growth of non-Legionella species 4