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 ?

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. "-