MCQ of the Day: 12 November 2026

Answer: C. Listeria monocytogenes. Listeriosis is a foodborne infection linked with unpasteurised dairy products, soft cheeses and chilled ready-to-eat foods, because the organism can grow at refrigeration temperatures. Pregnant women often have only a mild febrile illness, but transplacental infection can cause miscarriage, preterm delivery and neonatal sepsis or meningitis. L. monocytogenes is a small, non-spore-forming Gram-positive rod that is catalase positive, aesculin positive and gives a narrow zone of beta-haemolysis. Its flagella are expressed at 20 to 25 °C, not at 37 °C, which explains tumbling motility in a wet mount and umbrella-shaped growth in semi-solid agar at room temperature only.

A. Erysipelothrix rhusiopathiae is catalase negative, non-motile and produces H2S; it causes erysipeloid in fish and meat handlers.

B. Corynebacterium diphtheriae is non-motile and aesculin negative, with club-shaped rods and metachromatic granules on Albert stain.

D. Bacillus cereus forms large spore-bearing rods with a wide zone of beta-haemolysis; it is linked with reheated rice, and it does not show tumbling motility.