Properties of strains of Staphylococcus aureus in the 94, 96 complex.

Strains of Staphylococcus aureus that are lysed by typing phages 94 or 96, or by both phages, are usually resistant to lysis by other basic-set typing phages. They are, however, sensitive to several experimental phages and show a number of different lytic patterns when tested against these phages. These differences in susceptibility are due, in part, to immunity imposed by temperate phages carried by the different strains. Resistance to lysis by other basic-set phages was not due to prophage immunity, but to at least one restriction and modification system in such strains. Restrictionless mutants were isolated from one strain in several experiments. These showed an increased sensitivity to many basic-set phages. However, all of these mutants retained the ability to modify the phages to the characteristic "94, 96" specificity. Strains in the 94, 96 complex showed a remarkable homogeneity in biological traits. The majority were non-pigmented, and produced lipase, fibrinolysin, alpha and delta haemolysins and enterotoxin B. This homogeneity may well be a reflexion of the restriction and modification systems in these strains, that prevent the acquisition of genetic material from strains outside the complex. A new lytic group V is proposed for members of the 94, 96 complex.