Actinomyces israelii colony morphology on solid media resembles which description?

• A. Medusa head
• B. Fried egg
• C. Ground glass
• D. Molar tooth

Answer: (D)

Actinomyces israelii is a filamentous, anaerobic gram-positive bacterium from the oral flora. When it grows on solid media, its colonies develop a large, wrinkled, yellowish-white surface with irregular lobes and grooves that resemble a molar tooth. That molar-tooth appearance comes from the dense, radiating filaments and the way the colony expands, giving it the characteristic tooth-like look. This description is the classic, well-established clue for recognizing Actinomyces israelii in culture. Other terms like medusa head, fried egg, or ground glass describe different organisms or growth contexts and don’t match this organism’s typical colony form.