Clinical significance of tolerant strains of streptococci in adults with infective endocarditis

Abstract

To compare the characteristics of patients with endocarditis due to tolerant and non-tolerant Streptococcus strains. A retrospective nine-year study was conducted in a single tertiary-care hospital. The study included 24 cases of streptococcal endocarditis with known beta-lactam minimal inhibitory and bactericidal concentrations. Ten of the 24 patients concerned were infected with tolerant streptococcal strains, and 14 with non-tolerant strains. Bacterial tolerance was not associated with higher mortality or increased frequency of surgery. Fewer patients infected with tolerant than non-tolerant strains had serum bactericidal titers reaching success-predictive levels, and more of these experienced failure of initial antibiotic treatment and needed longer treatment. The results of this study strongly suggest that penicillin tolerance of the streptococci responsible for endocarditis has a clinical impact. Consequently, pending a larger prospective study addressing the problem of tolerance, it is clinically relevant to determine the minimal inhibitory and bactericidal penicillin concentrations for all streptococcal isolates causing endocarditis.