Bacterial concentration correlations in experimental endocarditis caused by Staphylococcus epidermidis

Abstract

Using 13 strains of Staphylococcus epidermidis to produce catheter-induced experimental endocarditis in rats, we found that bacterial concentrations in blood cultures obtained at the time of sacrifice correlated significantly with the number of organisms per gram of endocardial vegetation (P < 0.001) and the total number of organisms per vegetation (P < 0.001). Furthermore, blood culture concentrations correlated with vegetation weights (P < 0.001) and sizes of infecting inocula (P < 0.0001). Mean bacterial concentrations in vegetations more than doubled as bacterial concentrations in blood rose from less than 10 to greater than 100 CFU/ml. Mean values for vegetation weights, total organisms per vegetation, and sizes of infecting inocula were also reflected by the intensity of bacteremia. Moreover, intracardiac catheters were more likely colonized as bacterial concentrations in blood cultures increased, with all catheters culture positive in the 25 animals that exhibited high-grade bacteremia (≥ 100 CFU/ml). Slime production by the bacteria did not influence the above-mentioned correlations. These data indicate that the blood concentration of bacteria reflects the microbiologic status of infected vegetations in experimental infective endocarditis.