This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Microbiology
[{'content': 'A female presents with symptoms and signs suggestive of meningitis. MRI reveals a ring enhancing lesion in the frontotemporal region while CSF grows Gram positive bacilli. Other findings are minimally abnormal. Which of the following organisms is the most likely etiological agent ? \nSelect and explain. \nA. Listeria monocytogenes, B. Hemophilus influenza, C. Pneumococcus, D. Staphylococcal aureus', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. is \'a\' i.e., Listeria monocytogenes . Amongst the given options only Listeria is Gram positive bacilli. - Listeria monocytogenes --> Gram positive bacilli - H. influnzae --> Gram negative bacilli - Pneumococcus, Staphylococcus aureus --> Gram positive cocci . MRI feature of ring enhancing lesion with other findings are minimally abnormal also suggests the diagnosis of Listeria monocytogenes. " The subacute course and often minimally abnormal CSF findings may delay the diagnosis which may be suggested by the MRI images showing a\' ring enhancing lesion \'after gadolinium contrast. "-', 'role': 'assistant'}]