Experimental endocarditis in rabbits. 3. Significance of the proteolytic capacity of the infecting strains of Streptococcus faecalis.

Insertion of a polyethylene catheter into the left ventricle of the heart was used for regular establishment of sterile endocarditis, and bacterial endocarditis was established by injection of approximately 10(8) Streptococcus faecalis into the blood stream at the same time as removal of the catheter which had been in place for 3 days. 100 out of 102 rabbits died spontaneously of bacterial endocarditis. Evidence is produced that the host-parasite interaction is influenced by the proteolytic property of S. faecalis in this experimental model. Two distinct types of clinical course are described: 1) A predominantly acute and damaging illness, characterized by a high level of bacteraemia, small amounts of soft, friable vegetations in the left side of the heart, high frequency of kidney infarcts and shorter survival time in rabbits infected with proteolytic strains. 2) A relatively subacute illness, characterized by a lower level of bacteraemia, large, hard, non-friable vegetations on the aortic valves, less pronounced destructive changes in the substance of valve leaflets, relatively lower frequency of kidney infarcts and longer survival time in rabbits infected with non-proteolytic strains. The results suggest that proteolytic strains of S. faecalis cause partial dissolution of the vegetations resulting in a more severe clinical picture.