Listeria monocytogenes is a small, gram-positive bacillus that is actively motile at room temperature. Which option describes its motility temperature range?

• A. Body temperature
• B. Refrigeration temperature
• C. High temperature
• D. Room temperature

Answer: (D)

Listeria monocytogenes uses flagella for movement, and its flagellar system is turned on at cooler, ambient temperatures but turned off at mammalian body temperature. Because it is described as actively motile at room temperature, the temperature range where motility is observed is around room temperature, not at body temperature where motility is repressed. High temperatures suppress motility, and refrigeration temperatures aren’t the commonly cited condition for active flagellar motility in this organism. So the best fit is room temperature, reflecting the temperature-dependent expression of its motility apparatus.