The hemolysin/bacteriocin produced by enterococci is a marker of pathogenicity

The hemolysin/bacteriocin produced by some strains of Enterococcus faecalis is active in the lysis of human, rabbit, and horse erythrocytes, but not those from sheep. In this study, we determined that 20% of clinical enterococcal isolates tested in the clinical microbiology laboratory produced hemolysin and that pathogenic human E. faecalis were more likely to be hemolysin-producing isolates. Among the organisms isolated from different anatomic sites, variability in the degree of hemolysin production existed. We used an isogenic pair of E. faecalis organisms to demonstrate that hemolysin production was due to a hemolysin/bacteriocin determinant transmissible by a plasmid and was not strain dependent. This determinant may be linked to antibiotic resistance genes in some instances. Also, the erythrocyte lysis occurred only when hemolysin was in the presence of E. faecalis organisms, suggesting a bacterial cell dependency for activity of the hemolysin.