Antimicrobial activities of beta-lactam antibiotics and gentamicin against penicillin-susceptible and penicillin-resistant pneumococci.

The MICs of penicillin and cefotaxime for a range of penicillin-susceptible and penicillin-resistant isolates of Streptococcus pneumoniae were unchanged by the addition of gentamicin. In time-kill studies the rate of killing was greater for 18 of 20 isolates in the presence of gentamicin. However, mean differences in killing after 6 h of incubation were modest, not exceeding 1 log10 unit.