A 28-year-old woman presents with acute meningitis (CSF: pleocytosis with PMN predominance, low glucose, elevated protein). Blood cultures grow Gram-negative diplococci that are oxidase-positive. A second patient, a 22-year-old man, presents with acute urethritis (purulent discharge, dysuria). Urethral smear shows Gram-negative diplococci within neutrophils. Both organisms are oxidase-positive. Which clinical and microbiological feature BEST distinguishes the meningitis isolate from the urethritis isolate?