Lack of extracellular slime effect on treatment outcome of Staphylococcus epidermidis experimental endocarditis

We studied the response of two slime negative Staphylococcus epidermidis strains (NS1 and NS2) and one slime producing strain (S1) to treatment with vancomycin in the rabbit catheter-induced endocarditis model. All micro-organisms had vancomycin minimal inhibitory concentration and minimal bactericidal concentration of 4 mg/l. Three days after infection, treatment with vancomycin 25 mg/kg every 12 h was begun and continued for 4 days. Cardiac valve vegetations were harvested 12 h after the last dose of vancomycin and cultured quantitatively. In treated animals the mean +/- S.D. log10 colony forming units per g of cardiac valve vegetation were 1.6 +/- 0.1 for NS1, 4.4 +/- 1.9 for NS2, and 2.3 +/- 1.2 for S1. Slime production did not influence the results of vancomycin therapy of S. epidermidis experimental endocarditis. Other factors may cause strain-dependent variability in response to antimicrobial treatment in this model.