S. aureus is a frequent and constant colonizer of the skin and mucosal surfaces of humans. It has the capability of producing a large number of enzymes that contribute to its pathogenic potential. S. aureus is a common cause of nosocomial infections, particularly wound- and IV-catheter-associated infections. Lysogenization of these organisms appears to contribute to a number of properties, the most important of which is the resistance to antimicrobials. Such resistance is an important problem--both clinically and in the microbiology laboratory--where the not infrequent inability to identify such resistant strains may contribute to morbidity and mortality of staphylococcal disease.