DISPARATE FINDINGS ON THE ROLE OF VIRULENCE FACTORS OF ENTEROCOCCUS-FAECALIS IN MOUSE AND RAT MODELS OF PERITONITIS

The role of Enterococcus faecalis in polymicrobial peritonitis is stil l debated, Virulence factors expressed in some enterococcal strains mi ght be involved in the pathogenicity of these organisms, To clarify th eir role, three of these virulence factors (cytolysin, gelatinase, and aggregation substance) were studied in six isogenic strains of E. fae calis expressing various combinations of these factors. Since the path ogenic effects of enterococci are only moderate, the expression of the ir virulence might vary from one animal species to another and from on e type of infection to another. Therefore, we evaluated these effects in two animal models, i.e.,, a systemic infection in mice in which we assessed the virulence of the strains in 50% lethal dose studies and a model of compartmentalized infection in rats in which the microbiolog ic and inflammatory effects of the strains were evaluated in monomicro bial or polymicrobial infection. In mice, significant differences were observed in the cumulative survival curves depending on the virulence factors (P < 0.0001 [log rank test]). In rats, monomicrobial infectio n induced only mild changes, In polymicrobial peritonitis, the virulen ce factors mainly increased the inflammatory response while the change s observed in the microbiologic response were minimal, The combination of two virulence factors did not significantly increase the severity of infection either in the mice model or the polymicrobial rat model. These data argue for species and model dependence of the role of the v irulence factors studied here and suggest that other important factors may be involved in the pathogenicity of enterococci.