Bactericidal activity of 5 beta-lactam antibiotics againstStreptococcus pneumoniae

Assays were performed to determine bactericidal activity as a function of time (1, 3, 5, and 7 hours) and of the concentration (1, 2, 4, and 8 MIC) of antibiotics for 2 penicillin-sensitive strains ofStreptococcus pneumoniae (MIC<0.06 mg/L), 2 strains with moderate penicillin sensitivity (MIC=0.125 mg/L) and 2 penicillin-resistant strains (MIC-2 mg/L). The beta-lactam antibiotics studied were penicillin, amoxicillin, cefotaxime, imipenem and cefpirome. Imipenem was the antibiotic with the greatest antibacterial activity, followed by amoxicillin. The bactericidal activity of all the antibiotics was greater against the penicillin-sensitive strains than against those strains with some degree of resistance. However, the bactericidal activity observed for cefpirome suggests that further studies are necessary to determine the value of this antibiotic in the treatment of severeS. pneumoniae infections.