Which organism is actively motile at room temperature and is known to cause meningitis in newborns?

• A. Listeria monocytogenes
• B. Streptococcus agalactiae
• C. Bacillus cereus
• D. Staphylococcus aureus

Answer: (A)

Motility at room temperature points to Listeria monocytogenes because this organism has flagella and is actively motile in environmental, cooler conditions, unlike many other bacteria that are nonmotile outside the host. Listeria is a facultative intracellular pathogen that can grow in refrigerated foods and is a well-known cause of meningitis in newborns, typically acquired by vertical transmission from the mother during birth or late in pregnancy. Once inside the host, Listeria invades cells, escapes phagosomes, and can spread cell-to-cell, contributing to CNS invasion and meningitis in neonates. The other organisms either lack this room-temperature motility or are not characteristically associated with neonatal meningitis in this context, which is why Listeria monocytogenes is the best fit.