Which organism forms molar tooth colonies and branching Gram-positive bacilli?

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Multiple Choice

Which organism forms molar tooth colonies and branching Gram-positive bacilli?

Recognition of distinctive colony morphology and branching filamentous Gram-positive bacilli points to Actinomyces israelii. This organism is an anaerobic, non-spore-forming, filamentous bacterium that resides in the oral cavity and dental flora. In actinomycosis, it forms sulfur granules in draining sinus tracts and produces colonies described as “molar tooth” due to their irregular, tooth-like appearance. The branching, filamentous nature on microscopic exam is a key clue that sets it apart from other bacteria. Pseudomonas aeruginosa is a Gram-negative rod and does not display branching filaments. Streptococcus viridans are Gram-positive cocci in chains and are non-branching; they don’t form molar tooth colonies. Alcaligenes faecalis is also a Gram-negative rod, not branching.

Recognition of distinctive colony morphology and branching filamentous Gram-positive bacilli points to Actinomyces israelii. This organism is an anaerobic, non-spore-forming, filamentous bacterium that resides in the oral cavity and dental flora. In actinomycosis, it forms sulfur granules in draining sinus tracts and produces colonies described as “molar tooth” due to their irregular, tooth-like appearance. The branching, filamentous nature on microscopic exam is a key clue that sets it apart from other bacteria.

Pseudomonas aeruginosa is a Gram-negative rod and does not display branching filaments. Streptococcus viridans are Gram-positive cocci in chains and are non-branching; they don’t form molar tooth colonies. Alcaligenes faecalis is also a Gram-negative rod, not branching.

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