Egg yolk agar showing a precipitate around the colony indicates which activity?

Egg yolk agar showing a precipitate around the colony indicates which activity?

• A. Lecithinase production
• B. Lipase production
• C. Protease activity
• D. Starch hydrolysis

Answer: (A)

Egg yolk agar tests for the ability to break down lipids present in the yolk. A precipitate around the colony signals lecithinase production, an extracellular phospholipase that hydrolyzes lecithin (phosphatidylcholine) in the egg yolk. When lecithin is split, the products form insoluble complexes that precipitate, creating a visible cloudy zone around the colony. This pattern is a hallmark of lecithinase activity. Lipase would act on triglycerides and is detected by different media or patterns, not the precipitate seen with lecithinase. Protease activity would affect protein components and typically shows clearing in protein-rich media, not the specific precipitate around the colony on egg yolk. Starch hydrolysis is assessed on starch-containing media with iodine and involves clearing after iodine staining, not on egg yolk agar.

Egg yolk agar tests for the ability to break down lipids present in the yolk. A precipitate around the colony signals lecithinase production, an extracellular phospholipase that hydrolyzes lecithin (phosphatidylcholine) in the egg yolk. When lecithin is split, the products form insoluble complexes that precipitate, creating a visible cloudy zone around the colony. This pattern is a hallmark of lecithinase activity. Lipase would act on triglycerides and is detected by different media or patterns, not the precipitate seen with lecithinase. Protease activity would affect protein components and typically shows clearing in protein-rich media, not the specific precipitate around the colony on egg yolk. Starch hydrolysis is assessed on starch-containing media with iodine and involves clearing after iodine staining, not on egg yolk agar.