What organism is Nagler agar selective medium for?

Nagler agar is a specialized selective medium primarily used to isolate and identify Clostridium perfringens. This organism is known for its role in gas gangrene and food poisoning, and it produces α-toxin that causes the characteristic lecithinase activity detectable on this medium.

The formulation of Nagler agar contains egg yolk, which provides lecithin, a substrate for the enzyme produced by Clostridium perfringens. When colonies of this organism grow on the medium, they produce a zone of opacity around them, indicating positive lecithinase activity. This makes Nagler agar a valuable tool in differentiating Clostridium perfringens from other species of Clostridia and other bacteria.

In contrast, the other organisms listed do not exhibit the same selective growth characteristics on Nagler agar. While Clostridium difficile and Bacteroides fragilis are important pathogens, they do not produce the same enzymatic reactions that would allow for their identification using this medium. Escherichia coli, a common enteric bacterium, is also not associated with Nagler agar and does not grow under the same conditions. Thus, Clostridium perfringens is the correct answer as it is specifically selected for