Phage conversion of exfoliative toxin A in Staphylococcus aureus isolated from cows with mastitis

An exfoliative toxin produced by Staphylococcus aureus is the causative agent of staphylococcal scalded-skin syndrome (SSSS) in young children. Recently, we reported that only few isolates of S. aureus from bovine mastitis contained the eta gene encoding exfoliative toxin A (ETA) and produced ETA in vitro. In this study, we isolated temperate phages from two ETA-positive bovine isolates of S. aureus by treatment with mitomycin C. Polymerase chain reaction (PCR) assay of the phage genomes suggested that the temperate phages carried the structural gene for ETA. Moreover, the nucleotide sequence analysis of the PCR products revealed that the eta gene was located very close to an amidase gene on the phage genomes. The nucleotide sequence for the amidase gene of the bovine phage (bovine phi ETA) differed at nine positions from that of the amidase gene of phi ETA from a human isolate reported by Yamaguchi et al. [Mol. Microbiol. 38 (2000) 694], suggesting that eta-converting phages are heterogeneous. Bovine phi ETA had a head with a hexagonal outline and a non-contractile and flexible tail. Bovine phi ETA was able to lysogenize ETA-negative bovine isolates of S. aureus, and the lysogenized S. aureus isolates had the ability to produce ETA. These results suggest the possibility of horizontal transmission of the eta gene by temperate bacteriophages among bovine isolates of S. aureus.