Efficacy of beta-lactams against experimental pneumococcal endocarditis caused by strains with different susceptibilities to penicillin

Abstract

Objectives: To compare the in vitro and in vivo activity of penicillin, cefotaxime and ceftriaxone, using three strains of Streptococcus pneumoniae with different susceptibilities to penicillin (MICs of 0.015, 0.25 and 2 mg/L, respectively).

Methods: Time-kill curves and an experimental model of endocarditis in rabbits.

Results: Penicillin was efficacious in clearing bacteria from vegetations and blood irrespective of whether infections were caused by penicillin-susceptible or penicillin-resistant strains (P < 0.01 with respect to control groups). The same efficacy was shown with cefotaxime and ceftriaxone. Comparing the results of the in vivo model with those obtained in time-kill curves, penicillin showed the best results.

Conclusions: These results confirm that penicillin is efficacious in the treatment of pneumococcal infections, including those produced by strains with MICs < or = 2 mg/L (with the exception of pneumococcal meningitis). These results also suggest that the breakpoints to define susceptibility and resistance of S. pneumoniae to penicillin must be reviewed, as has been done with amoxicillin and third-generation cephalosporins.