Question

1. How you will determine the antibiotic sensitivities of Staphylococcus aureus to ampicillin, chloramphenicol and tetracycline; then predict the expected results based on what you know about this organism. Assume it has not acquired any new antibiotic resistance.

Answer 1

Antibiotic sensitivity of staphylococcus aureus is done by using Kirby Bauer test or disk diffusion method. In this method antibiotic of particular concentration are used to determine sensitivity.

Steps include

1) Take a sterile agar plate and spread suspension of S. aureus over it in aseptic condition.

2) Make wells of particular diameter on agar by using cork borrer and pour antibiotic of particular concentration. Or place disc of antibiotic

3) Incubate plate at defined temperature for 24 hrs.

4) After incubation if zone of inhibition occure around well or disc that means organism is sensitive. If no inhibition , organism is resistant.

(Use above mentioned antibiotic in same process)

Results

1) zone of inhibition observed around chloramphenicol antibiotic. Means S. aureus is sensitive to this antibiotic

2) zone of antibiotic does not observed around ampicillin and tetracycline. I.e organism is resistant. There is no effect of these 2 antibiotic on growth of organism.