<prompt> Which of the following is not mechanism for resistance to MRSA?Resistance is chromosomally mediatedProduced mainly by alteration in PBPsMRSA resistance is absolutely beta-lactamase independentIntrinsic resistance is known  <response>: Ans. is c i.e., MRSA resistance is absolutely beta-lactamase independentMechanism of Resistance of MRSA There are three known mechanisms for which staphylococcus aureus become resistant to methicillin:i Presence of an acquired penicillin binding protein PBP2a, Most cases.ii Modification of normal Intrinsic penicillin binding proteins.iii Hyperproduction of b-lactamase - Rare. S. aureus strains have four intrinsic penicillin binding proteins PBPs which have high affinity for b-lactam antibiotics. PBP2a is an inducible acquired protein that is produced only by MRSA. It is not an intrinsic PBP. PBP2a has very low affinity for b-lactam antibiotics - staph, aureus strains containing PBP2a, i.e., MRSA are resistant to all b-lactam antibiotics. Production of PB2a is by chromosomally coded mec A gene which alters PBP to PBP-2a. Drug resistance can be transferred between S. aureus strain by Transduction.About the other options: Resistance to MRSA is chromosomally mediated and involves production of an altered penicillin-binding protein PBP2a. MRSA resistance is not absolutely b-lactamase independent. Though altered penicillin binding protein is involved in most strains, b-lactamase production is also involved, rarely. 