Staphylococcal and Streptococcal Superantigens: Basic Biology of Conserved Protein Toxins

Staphylococcus aureus and Streptococcus pyogenes are gram-positive bacteria that possess great pathogenic potential in humans, causing numerous maladies such as arthritis, cutaneous infections, endocarditis, enterocolitis, food poisoning, pharyngitis, pneumonia, rheumatic fever, surgical site infections, and toxic shock. These prevalent pathogens produce various virulence factors that include the staphylococcal enterotoxins (SEs), toxic shock syndrome toxin-1 (TSST-1), and streptococcal pyrogenic exotoxins (SPEs). Minute (picomolar) amounts of these structurally-similar "superantigens" (SAgs) elicit high levels of proinflammatory cytokines and chemokines that can induce fever, hypotension, and lethal shock. In vitro and in vivo models have provided important tools for studying the biological effects of, and potential vaccines plus therapeutics against, these related protein toxins. This review will delve into the known physical and biological properties of the SEs, TSST-1, and SPEs. The reader will hopefully derive a general appreciation of these wonderfully-complex, structurally-similar toxins produced by S. aureus and S. pyogenes.