What colors are the colonies on Hektoen Enteric Agar?

Hektoen Enteric Agar is a selective and differential medium primarily used to isolate and differentiate enteric Gram-negative pathogens, particularly Salmonella and Shigella species, from fecal samples. The agar contains indicators that react with the metabolic byproducts of the bacteria, leading to distinctive coloration of the colonies.

The correct choice, which identifies the colors of the colonies as orange and blue-green, is based on the behavior of specific bacteria on this medium. For instance, lactose fermenters like some strains of Escherichia coli will produce acid, resulting in colonies that have a blue-green hue due to acidification. In contrast, non-lactose fermenters, such as Salmonella and Shigella, may appear more muted or developing different colors based on hydrogen sulfide production, further contributing to the overall color profile observed on the agar.

The unique coloring of colonies on Hektoen Enteric Agar aids microbiologists in identifying and distinguishing between various enteric bacteria, which is crucial for accurate diagnosis and treatment of gastrointestinal infections.