Controversy regarding optimal antimicrobial therapy for penicillin-sensitive streptococcal endocarditis persists. Is penicillin alone adequate? Is an aminoglycoside antibiotic such as streptomycin also required? This controversy is readdressed in two reports in this issue of The Journal (pp 1801 and 1807). Their common conclusion is that single-drug therapy with penicillin may be sufficient. In evaluating this conclusion, let us consider (1) the mechanisms of action of the pertinent antibiotics, (2) the results of experimental studies of penicillin-aminoglycoside synergism, (3) similar-clinical reports during the past 35 years, and (4) certain aspects of the natural history of this disease.
Penicillin does not enter the bacterial cell. It inhibits the enzymatic formation of pentapeptide bridges cross-linking the peptide side chains of polysaccharide polymers, which constitute the cell wall. Thus, the final stage in bacterial cell-wall synthesis is impaired, making the bacterium more susceptible to lysis.3 Penicillin does not, however, act on cell-wall—deficient forms