TRANSPOSON MUTANTS OF STAPHYLOCOCCUS-EPIDERMIDIS DEFICIENT IN ELABORATION OF CAPSULAR POLYSACCHARIDE ADHESIN AND SLIME ARE AVIRULENT IN A RABBIT MODEL OF ENDOCARDITIS/

Virulence comparisons were made in a rabbit model of endocarditis betw een wild-type and transposon mutants of Staphylococcus epidermidis def icient in elaboration of the capsular polysaccharide/adhesin (PS/A) an d slime. The parental phenotype grew from 36 (61%) of 59 cultures of b lood. The PS/A-negative phenotype grew in 1 (1%) of 98 cultures of blo od (P < .001). No animals infected with PS/A-negative strains develope d endocarditis compared with 75% of rabbits infected with PS/A-positiv e strains. PS/A-producing strains survived better than did PS/A-defici ent strains in intact, absorbed rabbit or human serum plus human leuko cytes. There was also greater deposition of C3 onto the PS/A-deficient strains than with the PS/A-producing isogenic strains. PS/A functions as an antiphagocytic bacterial capsule preventing C3 deposition and p hagocytosis; loss of this structure increases the strain's susceptibil ity to opsonic killing and decreases its virulence.