Eikenella corrodens often exhibits which characteristic on agar?

• A. Pitting of the agar
• B. Pigmentation
• C. Hemolysis
• D. Rapid growth in pure culture

Answer: (A)

Eikenella corrodens is best recognized by how it interacts with agar: it corrodes or pits the medium around its colonies. This pit formation is a visible cigarette-like “etching” of the agar, caused by the organism’s metabolic activity, and it’s such a distinctive feature that the species’ name reflects this behavior. In practice, when cultured on routine media like blood agar, you’ll see small pits around colonies rather than smooth, spreading growth. This organism is part of the normal oral flora and is associated with bite wounds and periodontal disease, and it tends to grow slowly and be fastidious, so rapid growth in pure culture isn’t typical. It also doesn’t typically produce pigment or cause strong hemolysis, so those features aren’t characteristic, making agar pit formation the best clue for identification.