Methicillin
resistant Staphylococcal aureus (MRSA) is a major pathogen
of nosocomial and community acquired infections associating with
significant morbidity and mortality rates of 15-60%.
Resistance to
methicillin is conferred by the expression of PBP 2a protein which is encoded
by the methicillin resistance gene, mecA gene, which is situated on a unique
mobile genetic element known as the “staphylococcal cassette chromosome mec”
(SCCmec).
The emergence of
MRSA from methicillin susceptible S. aureus (MSSA) is due to site-specific
integration of SCCmec into the orfX locus in the chromosome of a susceptible
isolate. This type of resistance was termed “intrinsic resistance” because it
was not due to destruction of the antibiotic by β-lactamase
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