This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Microbiology
All of the following statement are true about Staphylococci except : 
Select and explain. 
A. A majority of infection caused by coagulase (-) ve Staph. are due to staph epidermidis, B. β -Lactmase production is under plasmid control, C. Expression of methicillin resistance in Staphylococcus aureus increases when it is incubated at 37 degree C on blood agar, D. Methicillin resistance in Staph. aureus is independent of b-Lactmase production
C: Expression of methicillin resistance in Staphylococcus aureus increases when it is incubated at 37 degree C on blood agar
Answer: C: Expression of methicillin resistance in Staphylococcus aureus increases when it is incubated at 37 degree C on blood agar 
Explanation: “Methicillin resistance is expressed more when Staph. is incubated at 30 0 C than at 37 0 C.”
Penicillin resistance in Staphylococcus is by following ways :
1. Production of β lactmase :

Plasmid mediated inducible enzyme which is transmitted by transduction (more commonly) or conjugation.

Now only <5% of strains of staph are sensitive to penicillin.

Hospital strains mostly form type A penicillinase.
Same plasmid carry genes for resistance to tetracycline, Erythromycin, Aminolgycoside too.

2.  Altered penicillin binding protein :

Due to production of novel penicillin binding protein PBP2a. The protein is synthesized by mecAgene.
Chromosomally mediated expressed more at 30 0 C than at 37 0 C.
Responsible for resistance against penicillinase resistant penicillin such as methicilin, cloxacillin. Strains are called MRSA (Methicillin resistant Staph. aureus).

3. Tolerance to pencillin :

Bacteria only inhibited not killed.