Abstract

MRSA is defined by the presence of staphylococcal cassette chromosome mec
(SCCmec); which is a large mobile genetic element that carries the mecA gene
which codes for an alternative form of penicillin binding protein (PBP2a).
Staphylococcus aureus developed resistance to this type of β-lactam antibiotics by
acquiring the mecA gene which is carried on the SCCmec element described
earlier. Strains which carry this mecA gene are known as methicillin resistant
Staphylococcus aureus (MRSA), even though they are actually resistant to all β-
lactam based antibiotics. Historically, Staphylococcus aureus has been known to
develop antimicrobial resistance to most antimicrobials rapidly. The bacteria
developed resistance to penicillin only a year after the introduction of penicillin into
clinical use. It is now estimated that 90%–95% of Staphylococcus aureus strains
worldwide are resistant to penicillin. The resistance exhibited by MRSA to most
antibiotics imply that treatment for suspected or verified severe Staphylococcus
aureus infections, including common skin and wound infections, must rely on
second line drugs.