A 3-week-old neonate presents with poor feeding, lethargy and seizures. CSF examination reveals a Gram-positive rod that shows end-over-end 'tumbling' motility on wet mount. The mother had consumed unpasteurised cheese in the third trimester. Which property of this organism is most characteristic?
- A It grows well at refrigeration temperatures of 4 degrees Celsius ✓
- B It requires intracellular calcium for growth
- C It is an obligate anaerobe producing double zones of haemolysis
- D It cannot be cultured on routine blood agar
Correct answer: A. It grows well at refrigeration temperatures of 4 degrees Celsius
Explanation
Listeria monocytogenes is a facultative intracellular Gram-positive rod that characteristically multiplies even at 4 degrees Celsius, allowing enrichment in contaminated refrigerated dairy products. This property explains outbreaks linked to soft cheeses and cold-stored foods. It shows tumbling motility at 25 degrees Celsius, produces a narrow zone of beta-haemolysis on blood agar, and is treated with ampicillin. The other options describe features of organisms such as Legionella and Clostridium, not Listeria.
Reference: Ananthanarayan and Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.