Which organism is commonly associated with polymicrobial abscesses of the oral cavity and may produce pitting of the agar?

• A. Eikenella corrodens
• B. Burkholderia cepacia
• C. Pseudomonas aeruginosa
• D. Haemophilus influenzae

Answer: (A)

This question hinges on recognizing a distinctive culture clue tied to a specific oral organism. Eikenella corrodens is a normal inhabitant of the human mouth and is a common player in polymicrobial dental abscesses. What sets it apart in the lab is its ability to corrode the agar, creating pits as it grows. This agar-pitting occurs because the organism produces acidic byproducts that erode the medium, a characteristic behavior that has earned it the name corrodens.

In the clinical context, finding Eikenella in an oral or dental-abscess setting fits well with its usual ecological niche and its involvement in mixed infections of the mouth. The other organisms listed do not typically produce this agar-pitting effect and are associated with different settings (for example, Burkholderia ce­pacia in CF or environmental habitats, Pseudomonas aeruginosa in a variety of infections, Haemophilus influenzae with respiratory contexts and requiring X and V factors).