Effect of Penicillin Resistance on Presentation and Outcome of Nonenterococcal Streptococcal Infective Endocarditis

Background and Aims: Most cases of infective endocarditis are caused by nonenterococcal streptococci. The emergence of strains resistant to penicillin is increasingly recognized worldwide. This study sought to assess the effect of penicillin resistance on presentation and outcome of streptococcal endocarditis. Methods: A retrospective study was conducted in a single tertiary care hospital. Results: Between August 1996 and December 2004, patients infected with nonenterococcal streptococcal endocarditis and known minimal inhibitory concentrations (MICs) to penicillin were included in this study. A total of 62 cases were identified: 48 (77%) cases of the streptococcal endocarditis were caused by viridans streptococci. The most common species groups identified were Streptococcus mitis in 12 (19%) cases, Streptococcus oralis in 9 (15%) cases, Streptococcus sanguis in 7 (11%) cases and Streptococcus mutans in 7 (11%) cases. There were 36 male and 26 female patients with a median age of 46 years (range: 1–85). Twenty-two patients (35%) had peripheral embolization and 10 patients (16%) died in hospital. Twenty-eight (45%) of the 62 patients were infected with streptococcal strains of MICs ≧0.125 µg/ml to penicillin. Infection with streptococcal strains of MICs ≧0.125 µg/ml to penicillin was associated with a lower incidence of all-site embolization, but was not associated with higher mortality or increased frequency of surgery. Conclusions: High-level penicillin resistance of the streptococci responsible for endocarditis was increasingly common and medical therapy with vancomycin had a good response. Penicillin resistance was associated with a decreased risk of embolization, but was not associated with higher mortality.