Yeast and mould enumeration: Which culture medium is specifically recommended for determining yeast and mould counts in foods (after suitable dilution)?

Introduction / Context:
Yeasts and moulds are significant spoilers in acidic, low-aw, or refrigerated foods. Enumeration guides shelf-life predictions, sanitation decisions, and ingredient acceptance.

Given Data / Assumptions:

• Fungal counts require media that favor yeasts/moulds and suppress bacteria.
• Acidification (e.g., to pH ~3.5–4.0) inhibits many bacteria while allowing fungi to grow.
• Potato-based media support robust fungal growth.

Concept / Approach:
Acidified potato glucose/dextrose agar (APGA/APDA) or other acidified fungal media are standard for YM counts. The potato infusion provides nutrients, glucose supports growth, and low pH suppresses bacterial background. Some protocols add antibiotics as further bacterial inhibitors when needed.

Step-by-Step Solution:
Select a medium formulated for fungi and acidified to inhibit bacteria. Recognize APGA/APDA as widely used for YM counts. Exclude bacterial-selective media (MacConkey, VRBA, XLD) and general nutrient agar. Choose acidified potato glucose agar.

Verification / Alternative check:
Compendial methods list acidified PDA or Dichloran Rose Bengal Chloramphenicol agar for YM enumeration, both designed to suppress bacterial growth and limit mould spread.

Why Other Options Are Wrong:
Nutrient agar favors bacteria; MacConkey/VRBA/XLD are for enteric bacteria and coliforms, not fungi.

Common Pitfalls:
Failing to acidify or add antibiotics leads to bacterial overgrowth and underestimation of fungal counts.

Final Answer:
Acidified potato glucose (dextrose) agar.