Plasmid-associated hemolysin and aggregation substance production contribute to virulence in experimental enterococcal endocarditis

A rabbit endocarditis model was utilized to evaluate the virulence conferred by the conjugative plasmid pAD1 with the following strains: Enterococcus faecalis plasmid-free FA2-2 and FA2-2 containing plasmids pAD1 (hemolysin and aggregation substance positive), pAM9058 (insertional inactivation of hemolysin), and pAM944 or pAM947 (insertional inactivation of aggregation substance). All isolates were similar in ability to produce endocarditis. Mean vegetation weight was greater in animals inoculated with strains that produced aggregation substance (P < 0.01). Mortality was significantly increased in animals given FA2-2 containing pAD1 compared with those given all other strains (P < 0.01). These results suggest that the combination of hemolysin and aggregation substance is associated with increased mortality and that vegetation weight is associated with production of aggregation substance in experimental E. faecalis endocarditis.