What is the Gram stain appearance of Clostridium tetani on Gram stain?

• A. Gram-positive rods with terminal spores
• B. Tennis racket appearance
• C. Gram-positive cocci in clusters
• D. Filamentous bacteria with branching

Answer: (B)

Clostridium tetani on Gram stain presents as a Gram-positive rod with a terminal endospore, which gives a distinctive tennis-racket shape. The long slender rod forms with a spore at one end creates that handle-and-head look, a visual cue that helps you recognize this organism under the microscope. This endospore at the end is the key feature, setting it apart from other Gram-positive rods, cocci in clusters, or filamentous branching bacteria. While other stains may show a safety-pin appearance due to staining of the spore within the cell, the Gram stain specifically highlights the rod with its terminal spore, producing the tennis-racket appearance.