The majority of recent isolates of Staphylococcus aureus can be separated into two varieties and these may correspond to the original antigenic forms of Cowan’s serotypes I and III.
The most common variety has antigen 17 or I as a surface antigen and is lysed by serological group B phages; it may contain serological group A prophages and is usually tetracycline sensitive. It is probably more virulent (particularly in the 17+ form) than the second variety which possesses antigen 13 or 3, and is lysed by serological group A phages and may contain B prophages. It is usually tetracycline resistant.
Torres PereiraA.1962; Relation between virulence and sensitivity to antibiotics in Staphylococcus aureus (A selective action of the animal on tetracycline-sensitive strains of Staphylococcus aureus). Bol. Clin. Hosp. Civis Lisboa 26:313