Question

How does MRSA develop antibiotic resistance? What genetic elements does it have and what resistance mechanisms do these confer?

Answer 1

MRSA stands for Methicillin resistant Staphylococcus aureus.

It is a bacteria resistant to many antibiotics.It is resistant to methicillin,amoxicillin,penicillin,oxacillin, and many other antibiotics.

Staphylococcus species have been be treated with antibiotics over the decades, some strains of Staphylococcus like MRSA , have developed resistantance to many antibiotics.

Methicillin resistance in Staphylococcus aureus is mediated by the mecA gene which encodes for a novel penicillin-binding protein (PBP)- PBP-2a. and other genes involved are mecR1 and mecl.

Methicillin inactivates the high binding affinity PBPs.

PBP-2a has a low affinity for Methicillin and takes over the functions of these PBPs permitting the cell to grow in presence of antibiotics. Regulation of the methicillin resistant phenotype and production of PBP-2a are influenced by the action of other two genes those are located upstream from mecA--mecR1 and mecI , these two genes control the expression of PBP-2a.

Development of resistance to other antibiotics :

Enzymatic inactivation of antibiotics by penicillinase synthesis resulting resistance to penicillins.

Aminoglycoside modifying enzymes make MRSA resistant to aminiglycoside antibiotics.

Resistance to other antibiotics including fluoroquinolones, linezolid, have developed through spontaneous mutations.

Drug of choice for treatment of MRSA infections :Now a days, vancomycin remains the drug of choice for the treatment of infections caused by MRSA, eventhough it is intrinsically less active than the anti-staphylococcal penicillins.