Staphylococcus aureus is a common type of bacteria found on the skin in the nose, armpit, groin or vagina. Since it's one of the body's normal bacteria, most people develop antibodies to prevent it from causing an infection. In rare cases, however, certain strains produce toxins (poisons) that cause TSS.
The other bacteria, Streptococcus pyogenes, usually causes strep throat but it can also set off a TSS related infection called streptococcal toxic shock syndrome, or STSS.