MRSA is mediated by hydrolysis enzyme abd degrading the drug .

The origin of resistance in MRSA is chromosomal mediated by the acquisition of mec A gene which encodes for the alteration of Penicillin-binding protein (target of B lactam) into PBP2a, with very low affinity for traditional B-lactams.

This bacterium has become resistant to synthetic or semisynthetic B-lactam such as methicillin, due to their acquisition of the Mec A gene from non-pathological bacteria present in the environment such as S. epidermis and vancomycin-resistant Enterococci, either by conjugation or by bacteriophages (conduction) by the mechanisms of genetic transfer between bacteria. Here, this gene worked to produce a new type of PBPs ( a group of enzymatic proteins necessary for cell wall formation in bacteria, without these proteins the cell wall, become fragile and easily lysis) which is considered to be the binding site to beta-lactam. When Mec A gen found it encode the production of modified proteins called PBPs 2a, so it changing binding sites or modified these sites to inhibit synthetic or semisynthetic B-lactam such as methicillin. Currently, strains of them have begun to appear that are negative for the presence of the gene, that is, they do not contain it, but they show moderate resistance against cloxacillin. Studies have shown that these strains are characterized by high secretion of the beta-lactamase enzyme, which gives them more resistance than the normal Staphylococcus aureus against these antibiotics.

Antimicrobial resistance of S. aureus - history

here is the resistance rate in my country :

Deleted research item The research item mentioned here has been deleted

How MRSA acquired resistance to methicillin

Beta lactam antibiotics (e.g. penicillins and cephalosporins) damage bacteria by inactivating penicillin binding proteins (PBPs), enzymes that are essential in the assembly of the bacterial cell wall. Four native PBPs are found in Staphylococci; all four can be inactivated by these antibiotics. As a result of the weakened cell wall, treated bacteria become osmotically fragile and are easily lysed. The Staphylococcal beta-lactamase protein, which cleaves the beta-lactam ring structure, confers resistance to penicillin but not to semi-synthetic penicillins such as methicillin, oxacillin, or cloxacillin. Acquisition of the mecA gene, which codes for the penicillin binding protein PBP2a, confers virtually complete resistance to all beta-lactam antibiotics including the semi-synthetic penicillins. PBP2a has a very low affinity for beta-lactam antibiotics, and is thought to aid cell wall assembly when the normal PBPs are inactivated. The mecA gene is found on a large mobile genetic element called the Staphylococcal chromosomal cassette mec (SCCmec) and is expressed by the regulator genes mecR1 and mecI. At least 8 SCCmec types (SCCmec I through SCCmec VIII) have been identified, although some are more common than others. Some SCCmec types contain genetic elements for other antibiotic resistance, such as Tn554, a transposon responsible for resistance to macrolides, clindamycin and streptogramin-B, while the pT181 plasmid accounts for resistance to tetracyclines. These types have been used to classify and distinguish between HA-MRSA and CA-MRSA strains.

Please see the following RG link:

Thesis Isolation and identification of methicillin resistant staphy...

By acquisition of Mec A gene from other bacterial spp. which encode the production of PBP 2a so ith changing the binding sites with Beta-lactam antibiotics, or through hyperproduction of beta-lactamase enzymes that cleave the ring of these AB.

Nick Gante

please check

Methicillin resistance in Staphylococcus aureus - NCBI

www.ncbi.nlm.nih.gov › pmc › articles › PMC2065735

www.ncbi.nlm.nih.gov › pmc › articles › PMC6148192

In common S. aureus, beta lactam antibiotics kills the bacteria by inhibiting enzymes responsible for cell wall synthesis (PBP1,2,3,4).

However, MRSA also produce another enzyme namely PBP2a (encoded by mecA gene). PBP2a posses a gate-like structure to prevent beta lactam to bind it's active site but favor to bind cell wall components.