Strain differentiation in methicillin-resistant Staphylococcus aureus.

Three different systems were used to test 236 isolates of methicillin-resistant Staphylococcus aureus in an attempt to ascertain if more than one strain is responsible for the current problem of cross-infection by this organism in N.S.W. hospitals. The biochemical tests used were of little assistance. Phage typing, using the Basic International Set of typing phages at 100 x routine test dilution (RTD), provided evidence of the presence of several different strains. Phage type 83A/85/95/90/88 was the typing pattern of the predominant strain and the nest most frequent group was not typable. These results were often difficult to read. Five new phages were therefore isolated and found to be valuable as they produced easily identifiable patterns at RTD.