A seven year old boy presented to the emergency department with high grade fever on the previous day. He complained of headache, was disoriented and had projectile vomiting. On examination, the neck rigidity was seen and kernig's sign was positive. A lumbar puncture was carried out for Gram staining, Culture, complete blood counts and serum biochemistry. Gram staining of CSF showing gram negative cocci, what would be the possible cause of infection?