What color do colonies appear on Brilliant Green Agar?

Brilliant Green Agar is a selective culture medium primarily used for isolating and differentiating enteric bacteria, particularly Salmonella. The agar contains the dye brilliant green, which inhibits the growth of many other bacteria while allowing certain species to form distinctive colonies.

Colonies on Brilliant Green Agar typically appear whitish to red. The whitish coloration often indicates the presence of non-lactose fermenting organisms, while the red coloration is typically due to the fermentation activity of certain bacteria, which produce acid leading to a color change in the medium. The agar's composition allows differentiation based on metabolic activity related to carbohydrate fermentation.

Understanding this agar's role in bacteriology helps in the identification of various enteric pathogens. It’s also important to note that not all bacteria that grow on this medium will necessarily produce red colonies, which is why observing a combination of typical whitish and red colony colors indicates the potential presence of different bacterial species.