Experimental bacterial endocarditis. I. Colonization of a sterile vegetation.

Quantitative cultures were made to determine the sites of lodgement and the early fate of streptococci injected intravenously into rabbits with pre-existing non-bacterial thrombotic endocarditis, produced by prior placement of a polythene catheter in the right side of the heart. Serial blood cultures in normal animals showed rapid clearance of injected bacteria, whereas in animals with a pre-existing vegetation a persisting bacteraemia ensued. In such animals substantial numbers of injected bacteria adhered to the vegetation, and in this site they multiplied rapidly in a manner resembling the growth curve associated with favourable conditions Within 2 days the organisms attained a comparatively stationary phase in the vegetation; and this appeared to be the source of the continued bacteraemia. The morphology of the developing lesion was studied in sections taken at various intervals after inoculation. A notable feature was the abrupt appearance of a superficial layer of fibrin between 18 and 24 hr, which may offer protection to the growing colonies.