This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Microbiology
A young female presents with symptoms and signs of meningitis. CSF shows gram-positive bacilli. The most likely causative agent is? 
Select and explain. 
A. Listeria monocytogenes, B. Haemophilus influenzae, C. Pneumococcus, D. Pseudomonas
A: Listeria monocytogenes
Answer: A: Listeria monocytogenes 
Explanation: Listeria monocytogens are gram-positive bacilli.Haemophilus influenzae and Pseudomonas are Gram negative.Pneumococcus is capsulated gram-positive cocci in pairs.