Methicillin-resistant staphylococci: genetics and mechanisms of resistance

Beta-lactam antibiotics act by inhibiting enzymes involved in assembling the bacterial cell wall. These enzymes are found in the membrane and catalyze the cross-linking reaction between the peptidoglycan polymers. This cross-linking gives the wall additional rigidity, which is essential to the cell. Many of these enzymes covalently bind beta-lactam antibiotics at their active site (46, 55) and have been termed penicillin-binding proteins (PBPs). The fundamental difference between susceptible staphylococci and methicillin-resistant staphylococci is in their PBPs. The genetic determinant which confers methicillin resistance is termed mec. It is chromosomal and not plasmid derived.