AGGREGATION AND BINDING SUBSTANCES ENHANCE PATHOGENICITY IN RABBIT MODELS OF ENTEROCOCCUS-FAECALIS ENDOCARDITIS

We investigated the importance of enterococcal aggregation substance ( AS) and enterococcal binding substance (EBS) in rabbit models of Enter ococcus faecalis cardiac infections. First, American Dutch belted rabb its were injected intraventricularly with 10(8) CFU and observed for 2 days. No clinical signs of illness developed in animals given AS(-) E BS- organisms, and all survived. All rabbits given AS(-) EBS+ organism s developed signs of illness, including significant pericardial inflam mation, but only one of six died, All animals given AS(+) EBS- organis ms developed signs of illness, including pericardial inflammation, and survived. All rabbits given AS(+) EBS+ organisms developed signs of i llness and died. None of the rabbits receiving AS(+) EBS+ organisms sh owed gross pericardial inflammation. The lethality and lack of inflamm ation are consistent with the presence of a superantigen. Rabbit and h uman lymphocytes were highly stimulated in vitro by cell extracts, but not cell-free culture fluids, of AS(+) EBS+ organisms. In contrast, c ell extracts from AS(-) EBS- organisms weakly stimulated lymphocyte pr oliferation. Culture fluids from human lymphocytes stimulated with AS( +)/EBS+ enterococci contained high levels of gamma interferon and tumo r necrosis factor alpha (TNF-alpha) and TNF-beta, which is consistent with functional stimulation of T-lymphocyte proliferation and macropha ge activation. Subsequent experiments examined the abilities of the sa me strains to cause endocarditis in a catheterization model. New Zeala nd White rabbits underwent transaortic catheterization for 2 h, at whi ch time catheters were removed and animals were injected with 2 x 10(9 ) CFU of test organisms, None of the animals given AS(-) EBS- organism s developed vegetations or showed autopsy evidence of tissue damage. R abbits given AS(-) EBS+ or AS(+) EBS- organisms developed small vegeta tions and had splenomegaly at autopsy. All rabbits given AS(+) EBS+ or ganisms developed large vegetations and had splenomegaly and lung cong estion at autopsy. Similar experiments that left catheters in place fo r 3 days revealed that all rabbits given AS(-) EBS- or AS(+) EBS+ orga nisms developed vegetations, but animals given AS(+) EBS+ organisms ha d larger vegetations and autopsy evidence of lung congestion. These ex periments provide direct evidence that these two cell wall components play an important role in the pathogenesis of endocarditis as well as in conjugative plasmid transfer.