One of a group of bacteria of the genus Staphylococcus that causes a multitude of diseases: Staphylococci are facultative anaerobes (those which can grow without oxygen) and do not form spores. Many species are parasites or pathogens of animals and some cause wound infections, abscesses, and a type of food poisoning.

Under a microscope, staphylococcus bacteria are round and bunched together. They can cause an illness directly by infection, or indirectly through products they make, such as the toxins responsible for food poisoning and toxic shock syndrome.

The best known member of the Staphylococcus family is the staphylococcus aureus (potentially pathogenic bacteria found in nasal membranes, skin, hair follicles, and perineum [region between the thighs] of warm-blooded animals). They may cause a wide range of infections and intoxications. Staphylococci are the main culprits in hospital-acquired infections, and cause thousands of deaths every year.

Staphylococci are killed by pasteurization and many common disinfectants.