Phage conversion of exfoliative toxin A production in Staphylococcus aureus

The staphylococcal exfoliative toxins (ETs) are extracellular proteins that cause splitting of human skin at the epidermal layer during infection in infants. Two antigenically distinct toxins possessing identical activity have been isolated from Staphylococcus aureus, ETA and ETB. The gene for ETA (eta) is located on the chromosome, whereas that for ETB is located on a large plasmid, The observation that relatively few clinical isolates produce ETA suggests that the eta gene is acquired by horizontal gene transfer. In this study, we isolated a temperate phage (phi ETA) that encodes ETA and determined the complete nucleotide sequence of the phi ETA genome. phi ETA has a head with a hexagonal outline and a non-contractile and flexible tail. The genome of phi ETA is a circularly permuted linear double-stranded DNA, and the genome size is 43 081 bp. Sixty-six open reading frames (ORFs) were identified on the phi ETA genome, including efa, which was found to be located very close to a putative attachment site (attP). phi ETA converted ETA non-producing strains into ETA producers. Southern blot analysis of chromosomal DNA from clinical isolates suggested that phi ETA or related phages are responsible for the acquisition of efa genes in S. aureus.