Bactericidal activity of oxacillin and glycopeptides against Staphylococcus aureus in patients with endocarditis: Looking for a relationship between tolerance and outcome

Minimal bacteriostatic and minimal bactericidal concentrations were determined for Staphylococcus aureus strains isolated from patients with endocarditis following standardized methods. Medical records were reviewed retrospectively to collect data on antimicrobial susceptibility at admission, antimicrobial therapy, need for surgery, embolic events and outcome.Sixty-two Staphylococcus aureus strains were studied in 62 patients with endocarditis. Overall, 91.9% definite, 21% methicillin resistant and 72.6% cured. Surgery was performed in 32.3% and embolic events were documented in 64.5%. Tolerance to oxacillin and teicoplanin was more common than vancomycin tolerance among methicillin susceptible Staphylococcus aureus. Among methicillin resistant Staphylococcus aureus teicoplanin was shown to have a higher rate of tolerance than vancomycin. No statistically significant differences on clinical outcome between oxacillin tolerant and oxacillin non tolerant Staphylococcus aureus infections were observed. Tolerance to oxacillin did not adversely affect clinical outcomes of patients with methicillin susceptible Staphylococcus aureus endocarditis treated with a combination of antimicrobials including oxacillin. The cure rate was significantly lower among patients with methicillin resistant Staphylococcus aureus endocarditis.In vitro bactericidal test results were not valid predictors of clinical outcome. Physicians need to use additional parameters when treating patients with staphylococcal endocarditis.In recently published surveysStaphylococcus aureus (S.aureus) is reported to overstep viridans Streptococci as a cause of endocarditis (IE) and associated morbidities and mortality [1,2]. S.aureus is an extraordinarily adaptable bacterium, developing increasing patterns of resistance which contribute to clinical failures. Penicillin resistance was soon followed by methicillin resistance, which always includes resistance to all beta-lactam antimicrobials and often to several o