Question

why is Staphylococcus aureus resistant to many antibiotics

Answer 1

Staphylococcus aureus

• more resistant non sporing bacteria.
• They are remain vaible for 3-6 months.
• From the pus this organism can be isolated after 2-3 months.
• They can survive for 60 degree celcius for 30 minutes and thrie thermal death point is 62 degree celcius for 30 minutes.
• They can grow on salt concentration (15 % NaCl)
• They shows the resistant to 1 % mercuric perchloride solution for 15 minutes and 1 % phenol solution for 10 minutes.
• They shows resistance to many antibiotics due to several reasons:

Penicillin resistance: Mainly due to 3 reasons

1. They have the ability to produce penicillinase (beta lactamase) this split the beta lactam ring and inactivates penicillin. They are produce mainly 4 types penicillinase (A - D). Type A strain are usually seen in hospital. Penicillinase is an inducible enzyme which production is controlled by the plasmid trasmitted by conjugation or transduction. This plasmid carry resistance against a lot of antibiotics.

2. Reduce the binding of the beta lactamase to the antibiotic cell by changes in bacterial surface receptors. A the temperature range between 30 - 37 degree celcius the changes are visiblr otherwise they are chromosomal in nature. There resistance is extended to other antibiotics such as cloxacillin and methicillin. And some strain show resistance to heavy metal and other antibiotics, may leads to hospital outbreaks. The strain which resistant to multiple drugs are called EMRSA (Epidemic Methicillin Resistance Staphylococcus aureus).

3. The tolerance developed to penicillin which means they are not killed but inhibited their growth.

The antiobiotic sucha as erythromycine, aminoglycosides, tetracyclines and other clinically used antibiotics except vacomycine they possess a plasmid borne resistance.