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 (φETA) that encodes ETA and determined the complete nucleotide sequence of the φETA genome. φETA has a head with a hexagonal outline and a non-contractile and flexible tail. The genome of φETA 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 φETA genome, including eta, which was found to be located very close to a putative attachment site (attP). φETA converted ETA non-producing strains into ETA producers. Southern blot analysis of chromosomal DNA from clinical isolates suggested that φETA or related phages are responsible for the acquisition of eta genes in S. aureus.