Killing Rate and Growth Rate Comparison for Newer Beta-lactamase-stable Oral Beta-lactams Against Streptococcus Pneumoniae, Haemophilus Influenzae and Moraxella Catarrhalis

A new method of data presentation that takes into account the relationship between growth and killing rate was used to evaluate the comparative in vitro bactericidal activity of cefpodoxime, cefuroxime, cefixime and an amoxicillin/clavulanic acid combination against Streptococcus pneumoniae and beta-lactamase-producing strains of Haemophilus influenzae and Moraxella catarrhalis. For each strain, the viable count decrease (log CFU/ml) after 6 h of exposure to different antibiotic concentrations was plotted against the viable count increase in the control culture, over the same time. Higher killing rates than those predicted by growth rates were defined as a positive balance; lower rates than those predicted by growth rates were defined as a negative balance. The activity of the 4 drugs against S. pneumoniae and M. catarrhalis was characterized by a positive balance. Conversely, the 3 cephalosporins showed a negative balance for H. influenzae.