A 45 year old woman is brought to the ER complaining of a hi…

A 45 year old woman is brought to the ER complaining of a high fever, headache, neck pain, and nausea. You suspect it is meningitis and therefore you perform a  spinal tap and a gram stain on the CSF. The gram stain shows gram positive diplococci that show an alpha hemolysis on blood agar plate. The most likely agent is: