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Infect. Immun., Mar 1997, 994-1002, Vol 65, No. 3
HB Viscount, CL Munro, D Burnette-Curley, DL Peterson and FL Macrina
FimA, a surface-associated protein of Streptococcus parasanguis, is
associated with initial colonization of damaged heart tissue in an
endocarditis model (D. Burnette-Curley, V. Wells, H. Viscount, C. Munro, J.
Fenno, P. Fives-Taylor, and F. Macrina, Infect. Immun. 63:4669-4674, 1995).
We have evaluated the efficacy of recombinant FimA as a vaccine in the rat
model of endocarditis and investigated in vitro the mechanism for the
protective role of immunization. FimA-immunized and nonimmunized control
animals were catheterized to induce heart valve damage and infected
intravenously with 10(7) CFU of wild-type S. parasanguis FW213 bacteria.
The presence of bacteria associated with platelet-fibrin vegetations 24 h
postchallenge was evaluated. Immunized rats were significantly less
susceptible to endocarditis (2 cases among 34 animals) than the control
group (21 cases among 33 animals) (P < 0.001). Incubation of S.
parasanguis FW213 with rabbit anti-FimA immune serum decreased the mean
percent adherence (0.34% of added cells) to platelet-fibrin matrix in vitro
compared with that of preimmune normal serum (5.04% of added cells; P <
0.001). Adsorption of immune serum with FimA-positive S. parasanguis FW213
yielded antiserum that failed to block adherence to the platelet-fibrin
matrix. We assessed the vaccine potential of FimA as a common immunogen
able to provide cross- protection in streptococcal endocarditis by
determining the occurrence and expression of fimA in the viridans group
streptococci and enterococci. We detected the presence of fimA homologs by
Southern hybridization and PCR amplification analyses and determined by
immunoblotting the expression of FimA-like proteins among a variety of
streptococci and enterococci that frequently cause endocarditis. Eighty-
one percent (26 of 32) of streptococcal and enterococcal strains isolated
from bacteremic patients expressed proteins that comigrated with FimA and
were reactive with polyclonal anti-FimA serum. Streptococcal DNA from
strains that were positive by Western blot (immunoblot) analysis hybridized
to the full-length fimA probe. Our studies suggest that FimA immunization
results in antibody-mediated inhibition of bacterial adherence, a critical
early event in the pathogenesis of endocarditis. Our data demonstrate that
a majority of streptococcal strains associated with endocarditis have genes
that encode FimA-like proteins. Taken together, these results suggest that
FimA is a promising candidate for an endocarditis vaccine.
Copyright © 1997, American Society for Microbiology
Immunization with FimA protects against Streptococcus parasanguis endocarditis in rats
Department of Microbiology and Immunology, Virginia Commonwealth University, Richmond 23298, USA.
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