Which clostridial species has a terminal spore that causes the cell to swell?

• A. botulinum
• B. difficile
• C. perfringens
• D. tetani

Answer: (D)

A key way to recognize some Clostridium species under microscopy is where the endospore sits in the cell. When a spore forms at the end, it can push the bacterial body outward, producing a swollen, drumstick- or tennis racket–shaped appearance. Clostridium tetani is classically described as having terminal endospores that cause this swollen cell shape. This distinctive morphology helps differentiate it from other Clostridium species, whose spores are typically subterminal or central and do not produce the same swollen terminal form. So the organism with terminal spores that make the cell swell is Clostridium tetani.