Epidemiologic and clinical utility of typing systems for differentiating among strains of methicillin-resistant Staphylococcus aureus.

Typing systems for differentiating among strains of methicillin-resistant Staphylococcus aureus (MRSA) can be valuable tools for the epidemiologist and the clinician. Specific criteria for evaluating such systems are typeability, reproducibility, and discriminatory power. An ideal typing system also would be rapid, inexpensive, technically simple, and readily available. Systems based on the detection of phenotypic variations include antimicrobial susceptibility testing, bacteriophage typing, multilocus enzyme electrophoresis, and electrophoretic methods such as protein electrophoresis and immunoblotting. Systems that directly detect genotypic variations include plasmid profile analysis, restriction enzyme analysis of plasmid DNA, restriction enzyme analysis of chromosomal DNA, Southern blot analysis of specific restriction fragment length polymorphisms, and pulse field gel electrophoresis. In general, the more widely available typing systems based on phenotypic assays and plasmid analysis have limitations in typeability and/or discriminatory power. The chromosomal DNA-based techniques, although promising, are unproven approaches still under active investigation.