Bacteriophages associated with multiresistant Staphylococcus aureus in Australia.

Nineteen multiresistant strains of Staphylococcus aureus from Australian hospitals were examined for lysogenic bacteriophage. Thirteen strains contained prophage inducible with mitomycin C. Three of these lysed completely on induction producing a phage referred to as type 1; this phage plated on S. aureus propagating strains 6, 53 and 77, which are hosts for phages of serogroup-lysogroup A III, B III and F III respectively. Type-1 phage did not plate on other propagating strains representative of the other serogroup-lysogroup combinations in the International Typing Set for S. aureus. Ten strains of S. aureus lysed incompletely when treated with mitomycin C, yielding phage type 2, that plated only on propagating strain 6. The virions of phage types 1 and 2 had isometric heads and flexible tails, and the genome consisted of c. 40 kilobases of double stranded DNA. The DNA from the two phage types was different, as shown by endonuclease digestion and by hybridisation to reference phage DNAs. The remaining six S. aureus strains contained no phage inducible with either mitomycin C or ultraviolet irradiation. However, all contained type 2 DNA, as shown by Southern blotting, present presumably in a defective prophage state. Moreover, the three strains yielding type-1 phage on induction also contained type-2 DNA. Thus, type-2 DNA was found in all 19 strains of multiresistant S. aureus from geographically diverse Australian hospitals.