In vitro activity of ceftizoxime, ceftazidime, cefuroxime, ceftriaxone, cefotaxime, and penicillin against Streptococcus pneumoniae as determined by three quantitative methods.

E-test, broth microdilution, and agar dilution susceptibility tests were used to evaluate penicillin and five extended-spectrum cephalosporins against 196 strains of Streptococcus pneumoniae with different levels of penicillin resistance. Oxacillin disk tests corresponded to minimum inhibitory concentrations of penicillin determined by the E-test better than those generated by broth microdilution or agar dilution methods. Relative potency of the study drugs was as follows: cefotaxime = ceftriaxone > penicillin > cefuroxime > ceftizoxime > ceftazidime.