Which medium is commonly used for primary recovery of dermatophytes?

Which medium is commonly used for primary recovery of dermatophytes?

• A. Chromogenic agar
• B. Dermatophyte test medium
• C. Inhibitory mold agar
• D. Potato flake agar

Answer: (B)

Primary recovery of dermatophytes relies on a medium that both supports growth and signals positive isolation. Dermatophyte test medium is designed for this purpose: it contains a pH indicator that changes color as dermatophytes metabolize keratin and raise the pH, typically turning from yellow to red, so the colonies are easy to spot. It also includes an agent like cycloheximide to suppress rapidly growing non-dermatophyte fungi, helping dermatophytes stand out from contaminating flora. Because of these features—selective growth and a clear, visible positive signal—this medium is the standard choice for initial isolation of dermatophytes from clinical specimens. Chromogenic agar and inhibitory mold agar are useful tools in certain workflows or for identification and suppression of contaminants, but they are not the classic primary recovery medium. Potato flake agar is a general growth medium without the targeted selectivity or signaling needed for reliable primary recovery of dermatophytes.

Primary recovery of dermatophytes relies on a medium that both supports growth and signals positive isolation. Dermatophyte test medium is designed for this purpose: it contains a pH indicator that changes color as dermatophytes metabolize keratin and raise the pH, typically turning from yellow to red, so the colonies are easy to spot. It also includes an agent like cycloheximide to suppress rapidly growing non-dermatophyte fungi, helping dermatophytes stand out from contaminating flora. Because of these features—selective growth and a clear, visible positive signal—this medium is the standard choice for initial isolation of dermatophytes from clinical specimens. Chromogenic agar and inhibitory mold agar are useful tools in certain workflows or for identification and suppression of contaminants, but they are not the classic primary recovery medium. Potato flake agar is a general growth medium without the targeted selectivity or signaling needed for reliable primary recovery of dermatophytes.