Lack of synergy of erythromycin combined with penicillin or cefotaxime against Streptococcus pneumoniae in vitro.

We investigated a possible synergistic effect of a macrolide and beta-lactams against Streptococcus pneumoniae strains with different resistance profiles. Checkerboard and time-kill assays of erythromycin combined with penicillin or cefotaxime essentially showed indifference, suggesting that these antibiotics in combinations in vitro act substantially as individuals in their activity against S. pneumoniae.