Synergistic hemolysis exhibited by species of staphylococci

The synergistic hemolysis reactions of 61 reference strains and 189 clinical isolates representing 17 species of staphylococci were examined on plates of Trypticase soy blood agar (BBL Microbiology Systems, Cockeysville, Md.). Some or all of the strains of Staphylococcus aureus, S. epidermidis, S. capitis, S. cohnii, S. haemolyticus, S. hyicus, S. simulans, S. warneri, and S. xylosus produced a delta-hemolysin that gave synergistic, complete hemolysis of washed human, sheep, and ox blood cells in an area of beta-lysin activity from strains of S. aureus and S. intermedius. Strains of the same nine species were positive with a commercial beta-lysin paper disk designed for presumptive identification of group B streptococci; most of these strains also gave synergistic, complete hemolysis with exotoxin from a strain of Corynebacterium pseudotuberculosis. None of the strains of S. auricularis, S. carnosus, S. caseolyticus, S. hominis, S. intermedius, S. saprophyticus, S. sciuri, or S. lentus were positive by any of these tests for synergistic hemolysis. These results indicate that a synergistic hemolysis test could prove very useful for differentiating these species; they also suggest that one role of some of these organisms in human infections could be that of a synergist. Further studies of synergism may clarify the clinical significance of these results.