Sequence analysis reveals genetic exchanges and intraspecific spread of SaPI2, a pathogenicity island involved in menstrual toxic shock.

SaPIs are a family of homologous phage-related pathogenicity islands in staphylococci that carry superantigen and other virulence genes, and are responsible for a wide variety of superantigen-related diseases. SaPIs are induced to excise and replicate by particular staphylococcal phages and are encapsidated in infectious, small-headed, phage-like particles, which are transmitted at very high frequency among staphylococcal strains and species. SaPI2 is a prototypical member of this family that was identified in a typical menstrual toxic shock syndrome (TSS) strain of Staphylococcus aureus, the so-called Harrisburg strain, and found to be mobilizable by typing phage 80. Most menstrual TSS strains belong to a highly uniform agr group III clone of electrophoretic type (ET) 41, and this study was undertaken to determine whether such strains typically carry SaPI2, and whether it has spread beyond the ET41 clone. We report here the complete sequence of SaPI2, describe its relation to other known SaPIs, and show that it, or a very similar element, is carried by most ET41 strains but that it has disseminated to other strains that have also been implicated in TSS. We show additionally, that SaPIs are widespread among the staphylococci and that most TSS strains carry two or more, including SaPI2.