A curved appearance on Gram stain is characteristic of which organism?

A curved appearance on Gram stain is characteristic of which organism?

• A. Actinomyces israelii
• B. Clostridium septicum
• C. Fusobacterium nucleatum
• D. Propionibacterium acnes

Answer: (C)

A curved, slender Gram-negative rod describes Fusobacterium nucleatum. This organism is classically seen as fusiform (curved) rods on Gram stain, often in anaerobic specimens. The other options do not have this curved morphology: Actinomyces israelii forms long, branching Gram-positive filaments; Clostridium septicum appears as straight Gram-positive rods (often with spores); Propionibacterium acnes is a small, Gram-positive, pleomorphic rod. So the curved appearance on Gram stain is a hallmark of Fusobacterium nucleatum.

A curved, slender Gram-negative rod describes Fusobacterium nucleatum. This organism is classically seen as fusiform (curved) rods on Gram stain, often in anaerobic specimens. The other options do not have this curved morphology: Actinomyces israelii forms long, branching Gram-positive filaments; Clostridium septicum appears as straight Gram-positive rods (often with spores); Propionibacterium acnes is a small, Gram-positive, pleomorphic rod. So the curved appearance on Gram stain is a hallmark of Fusobacterium nucleatum.