Typing of methicillin-resistant Staphylococcus aureus by antibiotic resistance phenotypes.

The identification of new epidemic strains of methicillin-resistant Staphylococcus aureus is essential for rapid, effective infection control. We have developed a typing method which uses antibiotic sensitivity patterns to differentiate methicillin-resistant S. aureus and which is faster and more cost-effective than biochemical analysis or bacteriophage typing. Characterisation of phenotypes which are chromosomally-encoded, plasmid- or chromosomally-encoded or exclusively plasmid-mediated has enabled us to separate Australian strains of methicillin-resistant S. aureus into 11 classes, representatives of which were indistinguishable by bacteriophage type, or plasmid profile alone. The value of this procedure is thus clearly shown.