Which statement describes a distinguishing growth characteristic of Listeria monocytogenes?

• A. Is non-motile at room temperature.
• B. Requires aerobic conditions.
• C. Grows at refrigeration temperatures (4°C); tumbling motility at room temperature; facultative intracellular organism.
• D. Does not grow at 4°C.

Answer: (C)

Listeria monocytogenes is notable for its growth pattern that includes thriving at refrigeration temperatures and moving actively at room temperature, along with the ability to invade and replicate inside host cells. It can grow in foods stored in the fridge because it multiplies at 4°C, which is unusual for many pathogens. At room temperature, it shows tumbling motility, a rapid, irregular movement that reflects its flagellar activity outside cells. It’s also a facultative intracellular organism, meaning it can survive and multiply outside cells but can invade and replicate within host cells when it encounters them. This trio of traits—growth at 4°C, tumbling motility at room temperature, and facultative intracellular growth—best describes its distinguishing growth characteristics. Non-motility at room temperature isn’t correct because it is motile; it does not require strictly aerobic conditions since it is facultative and can grow with or without oxygen; and it does grow at 4°C, so a statement saying it does not would be inaccurate.