as the psm classes are closely related there are many conserved aspects. however each psm class plays a different role, as such there are some distinctive features for each. generally psms are encoded on the core genome of "staphylococcal" species however some, such as psm-mec, are encoded on mobile genetic elements. psms are generally separated into one of two classes α-type psms and β-type psms, which are based upon characteristics of the two most well studied psms psmα and psmβ.