This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Bacteria, Subject name: Microbiology
Which of the following is not mechanism for resistance to MRSA? 
Select and explain. 
A. Resistance is chromosomally mediated, B. Produced mainly by alteration in PBPs, C. MRSA resistance is absolutely beta-lactamase independent, D. Intrinsic resistance is known
C: MRSA resistance is absolutely beta-lactamase independent
Answer: C: MRSA resistance is absolutely beta-lactamase independent 
Explanation: 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.