Bacterial meningitis in adults. Bacterial meningitis continues to be an important cause of morbidity and mortality despite the availability of effective bactericidal antibiotics. Penicillin or ampicillin remains the drug of choice for meningitis caused by Streptococcus pneumoniae and Neisseria meningitidis. The third generation cephalosporins have revolutionized the treatment of gram-negative meningitis. Future therapy for bacterial meningitis will use recent developments in the understanding of pathogenic and pathophysiologic mechanisms underlying this disease. 