CHARACTERIZATION AND BIOLOGICAL PROPERTIES OF A NEW STAPHYLOCOCCAL EXOTOXIN

Staphylococcus aureus strain D4508 is a toxic shock syndrome toxin 1-n egative clinical isolate from a nonmenstrual case of toxic shock syndr ome (TSS). In the present study, we have purified and characterized a new exotoxin from the extracellular products of this strain. This toxi n was found to have a molecular mass of 25.14 kD by mass spectrometry and an isoelectric point of 5.65 by isoelectric focusing. We have also cloned and sequenced its corresponding genomic determinant. The DNA s equence encoding the mature protein was found to be 654 base pairs and is predicted to encode a polypeptide of 218 amino acids. The deduced protein contains an NH2-terminal sequence identical to that of the nat ive protein. The calculated molecular weight (25.21 kD) of the recombi nant mature protein is also consistent with that of the native molecul es. When injected intravenously into rabbits, both the native and reco mbinant toxins induce an acute TSS-like illness characterized by high fever, hypotension, diarrhea, shock, and in some cases death, with cla ssical histological findings of TSS. Furthermore, the activity of the toxin is specifically enhanced by low quantities of endotoxins. The to xicity can be blocked by rabbit immunoglobulin G antibody specific for the toxin. Western blotting and DNA sequencing data confirm that the protein is a unique staphylococcal exotoxin, yet shares significant se quence homology with known staphylococcal enterotoxins, especially the SEA, SED, and SEE toxins. We conclude therefore that this 25-kD prote in belongs to the staphylococcal enterotoxin gene family that is capab le of inducing a TSS-like illness in rabbits.