Most pneumococci are susceptible to penicillin, amoxicillin, and erythromycin.
Penicillin-resistant strains: Most pneumococci are suscep-tible to penicillin. Strains that are susceptible to penicillin are also susceptible to nearly all other antibiotics. But since 1977, penicillin-resistant pneumococci are being increasingly docu-mented. Penicillin-resistant strains may be moderately resis-tant (minimum inhibitory concentration, or MIC, 0.1 1 g/ mL) or highly resistant (MIC 2 g/mL). The resistance to penicillin and other beta-lactam antibiotics is not mediated by production of beta-lactamase enzymes, but is due to the modi-fications of proteins, such as penicillin-binding proteins (PBPs) found on the cell wall. These penicillin-resistant strains are also resistant to multiple drugs, such as cefotaxime, ceftriaxone, erythromycin, tetracycline, macrolides, and trimethoprim–sul-famethoxazole (TMP–SMX). Resistance is seen most often in S.pneumoniae serotypes 6, 9, 14, 19, and 23.
The success of antibiotic therapy depends on drug con-centrations attained in the affected part of the body, which should be several times higher than the MIC of the organism.
Beta-lactam antibiotics are not used alone for the treatment of meningitis caused by penicillin-resistant pneumococci. This is because, adequate bactericidal levels against penicillin-resistant organisms in the central nervous system (CNS) are difficult to achieve with beta-lactam antibiotics. Ceftriaxone can be used for meningitis caused by ceftriaxone-susceptible pneumo-cocci (MIC 0.5 g/mL). Amoxicillin is the drug of choice for treatment of otitis media, sinusitis, and pneumonia caused by penicillin-resistant pneumococci with intermediate resis-tance. Ceftriaxone is the drug of choice for non-CNS invasive pneumococcal diseases caused by penicillin- and ceftriaxone-resistant pneumococci. Vancomycin is used if the pneumococ-cus is resistant to ceftriaxone (MIC 0.5 g/mL).
Pneumococcal vaccines play an important role in prevention of pneumococcal diseases.