All of the following statement are true about Staphylococci except :
“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.
A majority of infection caused by coagulase (-) ve Staph. are due to staph epidermidis
β -Lactmase production is under plasmid control
Expression of methicillin resistance in Staphylococcus aureus increases when it is incubated at 37 degree C on blood agar
Methicillin resistance in Staph. aureus is independent of b-Lactmase production