Used to determine the ability of drug

1. k.rasika
||| B.SC MICROBIOLOGY

2. ❖ Used to determine the ability of drug.
❖ An antibiotic sensitivity or susceptibility test
is done to help choose the antibiotic that will be
most effective against specific type of bacteria
or fungus infecting an individual person.

4. ❖ Disc diffusion was discovered by W. Kirby
and A. Bauer in 1950. So the test is also
called as Kirby bauer test.
❖ To measure the zone of inhibition (ZOI)

6. ❖ Medium containing beef infusion, peptone,
Starch.
❖ It is a loose agar.
❖ Better diffusion of the antibiotic.
❖ Muller hinter agar is considered best for
routine.
❖ Susceptibility test.

7. ❖ A supply of cotton wool
swabs n wooden
applicator sticks should
be prepared.
❖ They can be sterilized in
tins, culture tubes, either
in the autoclave.

8. ❖ An antibiotic disc is
small, circular piece
of filter paper.
❖ Used to test the
effectiveness of
particular antibiotic
against specific target
organisms.

9. 1. Muller hinton sterile agar plates are prepared.
2. A cotton swab is dipped in to the culture and
spread uniformly on the surface of the MHA
plates.
3. Antibiotic disc are placed on the surface of the
media at specific distance.
4. Incubated for 12 – 18 hour.

10. 5. After incubation, the plates are observed for
zone of inhibition around the placed antibiotic
disc.
6. Measure diameter of the zone of inhibition.
7. Based on the diameter of zone of inhibition, we
can determine whether the antibiotic is effective
against the bacteria.

11. RESISTANCE
When there is no zone. Not to respond to a given
antibiotic.
INTERMEDIATE
Medium size zone. To an antibiotic that can be
used for treatment at a higher dosage.
SENSITIVITY
Wide zone. Respond to a given antibiotic.
Can be used for treatment at a lower dosage.

12. Resistance
Intermediate
Sensitivity
Disc diffusion

13. ❖ Used to determine the minimal concentration
of antibiotic to inhibit or kill the microorganisms.
❖ To measure the Minimal Inhibitory Concentration
(MIC)

14. ❖ The lowest concentration of drug that inhibits the
growth of the bacteria.
1. Place nine sterile tubes in a rack.
2. With a 0.5 ml pipette,0.5 ml of sterile broth was
added to each tube.
3. Add 0.5 ml of the amipicillin broth to the first
tube.

15. 4. Continue the dilution process through tube
number 7
5. The eight and ninth tubes receive no antibiotic.
6. Transfer 0.1 ml of the E.coli suspension in to
a tube.
7. Place the tubes in the incubator for 18 to 24 hours.
8. After 24 hours the lowest concentration that is
completely presenting the growth of microbes is
observe.
9. The MIC value of each antibiotic will decide the
dosage schedule.

16. G = Growth control, S= Sterility control
Tube Number
Broth added 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5
initially
1 2 3 4 5 6 7 8 9

17. ❖ Epsilometer test
❖ Quantitative method of antibiotic sensitivity
testing.
E - test
Diffusion Dilution

18. 1. A stripe containing various dosage levels of
antibiotics in an increasing order.
2. E - test stripe is placed on the agar surface of
the media.
3. Incubation of plate
4. The gradation of zone of inhibition is interpreted
along the concentration of the
drug.

19. E - test
Agar plate with growing
organisms
E – test stripe
Zone of inhibition
MIC 0.94 ml