Question

Antimicrobial Sensitivity

At the conclusion of this exercise you should be able to:

• describe the purpose of using the Kirby-Bauer method of testing sensitivity of bacteria to antibiotics.
• interpret the results of antimicrobial sensitivity using a selection of antibiotic discs.
• compare selected organisms that are susceptible or resistant to antibiotics.

Questions

7.1       Complete the table to record R (resistant), I (intermediate) and S (susceptible) of bacteria to antibiotics tested.

	Organisms
Antibiotic	E.coli	S.aureus	Ps.aeruginosa
Amoxicillin
Cephalothin
Chloramphenicol
Ciprofloxacin
Clindamycin
Erythromycin
Oxacillin
Penicillin G
Streptomycin
Tetracycline
Tobramycin
Trimethoprin sulfa
Vancomycin

7.2       For the results above, discuss your observations for the following characteristics:

            a.         How do the 3 organisms compare in their susceptibility profiles?  

b.         What susceptibility differences do you observe between the Gram positive and Gram negative organisms?

c.         What are the differences in susceptibility between the two Gram negative organisms?

Answer 1

a) The following table recorded R (resistant), I (intermediate) and S (susceptible) of bacteria to antibiotics tested.

b) Amoxicillin, penicillin G, Streptomycin was found to be resistant to both gram positive and gram negative. Cephalothin, chloramphenicol,trimethoprin sulpha(except Ps.aeruginosa) was found to be sensitive to both gram positive and gram negative (Refer the table)

c) Both the gram negative organism showed resistance to most of the antibiotics except few. (Refer the table)

Table:

	Organisms
Antibiotic E.coli S.aureus Ps.aeruginosa Amoxicillin R R R Cephalothin S S R Chloramphenicol S S R Ciprofloxacin R I S Clindamycin R S R Erythromycin R S R Oxacillin R S R Penicillin G R R I Streptomycin R R R Tetracycline R R S Tobramycin R R S Trimethoprin sulfa S S R Vancomycin R S R