A 21-year-old male college student who had complained of headache and feeling feverish the night before is brought this morning to the emergency department (ED) when his roommate was unable to rouse him. He had been well until yesterday. Vital signs include fever (39.8°C/103.1°F), tachycardia, and hypotension (BP 70/55). Remarkable on physical examination is petechial rash (purpuric in areas) and nuchal rigidity with positive Kernig and Brudzinski signs. CSF is cloudy with high protein and low glucose. Intracellular, red diplococci are seen on Gram stain. What is the most likely genus?