Toxinogenicity of clinical isolates of coagulase-negative staphylococci towards various animal cells

The toxinogenicity of fifty coagulase-negative staphylococci isolated from various clinical syndromes was compared, using lysis of human erythrocytes, leakage of a radio-active marker from human embryonic lung fibroblasts by culture filtrates, and direct cytotoxicity of growing bacteria towards mouse skin fibroblasts in an agar overlay assay. Good correlation was obtained between those strains which elaborated greater than or equal to 16 HU/ml delta-toxin in culture, measurable also in terms of radioactive nucleotide leakage from tissue culture cells and those strains which caused a direct cytotoxicity effect in the colony overlay test. delta-toxin was implicated in the genesis of such cellular damage. Speciation of the coagulase-negative staphylococci revealed that isolates identified as S. epidermidis, S. saprophyticus and S. haemolyticus were most active in each of these tests. The colony overlay technique is suggested as being a potential screening assay for toxinogenic coagulase-negative staphylococci associated with clinical infections.