Unusual properties of Staphylococcus aureus strains of the new epidemic phage type 95.

Three hundred and seventy-one penicillin-resistant Staphylococcus aureus strains of phage type 95 isolated in the years 1977-1983 were investigated. They had characteristic resistance patterns to cadmium (Cd), arsenate (As) and mercury (Hg). Most were susceptible to all three heavy metals; 25 strains were resistant to As only and one to Cd and As. The susceptible strains had a uniform medium level of penicillinase production, whereas the As-resistant strains produced large amounts of penicillinase. In most of the strains, penicillin resistance was located on a very unstable penicillinase plasmid. The combination of rare properties found in Danish type-95 strains seems to point to the spread of one or two clones. Co-reactions with other phage groups or complexes and results of lysogenisation experiments suggest that the Danish type-95 strains are derived from strains of the 52, 52A, 80, 81 complex.