Characterization and biological properties of a new staphylococcal exotoxin.

Abstract

SummaryStaphylococcus aureus strain D4508 is a toxic shock syndrome toxin 1-negative clinical isolate from a nonmenstrual case of toxic shock syndrome (TSS). In the present study, we have purified and characterized a new exotoxin from the extracellular products of this strain. This toxin 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 sequence 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 native protein. The calculated molecular weight (25.21 kD) of the recombinant mature protein is also consistent with that of the native molecules. When injected intravenously into rabbits, both the native and recombinant toxins induce an acute TSSlike illness characterized by high fever, hypotension, diarrhea, shock, and in some cases death, with classical histological findings of TSS. Furthermore, the activity of the toxin is specifically enhanced by low quantities of endotoxins. The toxicity 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 sequence homology with known staphylococcal enterotoxins, especially the SEA, SED, and SEE toxins. We conclude therefore that this 25-kD protein belongs to the staphylococcal enterotoxin gene family that is capable of inducing a TSS-like illness in rabbits.

Characterization and Distribution of a New Enterotoxin‐Related Superantigen Produced by Staphylococcus aureus

“…By comparing the deduced amino acid sequence of SEGv with those of the GenBank database, the highest homology was observed with SSA (46.4%), followed by SEB, SEC2, and SPEA (45.2, 43.1, and 42.7%, respectively). These amino acid sequence similarities seem to be reflected in their TCR-Vf3 specificity, because the Vr3 families of T cells stimulated with SEGv were partly overlapped with SSA, SEB, SEC2, and SPEA (1,15,22,26). On the other hand, SEGv had little overlap in vo specificity with SEA or SEE, to which SEGv had less amino acid similarity, 32.6 and 28.9%, respectively.…”

“…These findings prompted us and other groups to look for yet uncharacterized superantigen toxins produced by the organisms. Recently, several groups have reported the cloning of new enterotoxin genes such as SEG, SEH and SEI (23,26).…”

“…Staphylococcus aureus (S. aureus) produces several enterotoxins (SEs) which are responsible for food poisoning in humans and for shock symptoms in some cases of toxic shock syndrome (TSS) (6,7,9,12,23,26,32,33). SEs are also characterized as superantigens activating a large proportion of T cells bearing particular TCR V13 elements.…”

Quantitative Analysis of Staphylococcus aureus in Skimmed Milk Powder by Real-Time PCR

“…Although 18 major antigenic types of SEs or SE-like putative toxins have been reported, SEA is the major cause of food poisoning [1,6,10,11,14,[16][17][18][19][20][21]. In an outbreak caused by SEA present in chocolate milk in the United States, twelve cartons each containing half pint (approx 0.28 l) contained SEA at a concentration of 94-184 ng, and SEA of 200 ng or less was presumed to have caused food poisoning [3].…”

Analysis of the Epitopes on Staphylococcal Enterotoxin A Responsible for Emetic Activity.

“…They are serologically classified into eight distinct types such as A (SEA), B (SEB), C (SEC), D (SED), E (SEE), G (SEG), H (SEH) and I (SEI) with varying molecular mass ranging from 25 to 30 kDa [14,15,18,25]. Genes encoding for SEA through SEI have been cloned and their nucleotide sequences and amino acid sequences have been analyzed [2,15,25].…”