All of the following statement are true about Staphylococci except :
Correct Answer: Expression of methicillin resistance in Staphylococcus aureus increases when it is incubated at 37 degree C on blood agar
Description: “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.
Category:
Microbiology
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