Cloning and sequencing the endocarditis immunodominant antigen of Streptococcus sobrinus strain MUCOB 263

Immunoblotting sera from cases of Streptococcus mutans or S. sobrinus endocarditis against an extract from S. sobrinus strain MUCOB 263 had identified three immunodominant antigenic bands at 190, 200 and 220 kDa. A lambda ZAPII DNA library was produced from the sheared genomic DNA of S. sobrinus MUCOB 263 and six identical positive clones were identified when this library was screened with serum from a patient with endocarditis caused by a bacterium from the mutans group of streptococci. On subcloning and sequencing, a protein containing 1548 amino acids was identified with a 99.2% homology to the SpaA antigen of S. sobrinus and 68.4% homology to the PAc antigen of S. mutans.