Classic morphology: Which Clostridium species typically shows a “drumstick” appearance under the microscope due to terminal spore formation with a swollen sporangium?

Introduction / Context:
Spore position and the effect on cell shape are important morphological clues in the identification of clostridia. Certain species produce terminal spores that distend the cell, generating characteristic silhouettes on stained smears.

Given Data / Assumptions:

• “Drumstick” or “tennis-racket” appearance describes a thin rod with a bulbous terminal swelling where the spore resides.
• Clostridium tetani forms terminal spores that markedly swell the sporangium.
• Other clostridia have subterminal or central spores and do not typically produce the drumstick profile.

Concept / Approach:

Correlate spore position with species: C. tetani (terminal, swollen); C. perfringens (subterminal/rare in clinical isolates); C. botulinum (subterminal); C. histolyticum (variable). The unique swelling in C. tetani is a classic exam image.

Step-by-Step Solution:

Verification / Alternative check:

Textbook photomicrographs of C. tetani consistently show the drumstick/tennis-racket outline, reinforcing the association.

Why Other Options Are Wrong:

C. perfringens: rarely shows spores in clinical material; spore position not terminally swollen.

C. botulinum: typically subterminal spores; morphology differs.

C. histolyticum: proteolytic, but no classic drumstick morphology.

Common Pitfalls:

Confusing terminal but non-swelling spores with true drumstick appearance; the swelling is key to the silhouette.

Final Answer:

C tetani