Antibiotic sensitivity test: in vitro testing of bacterial cultures with antibiotics to determine susceptibility of bacteria to antibiotic therapy. A laboratory test which determines how effective antibiotic therapy is against a bacterial infections. Antibiotic sensitivity testing will control the use of Antibiotics in clinical practice Testing will assist the clinicians in the choice of drugs for the treatment of infections. Helps to guide the Physician in choosing Antibiotics The accumulated results on different pathogens their sensitivity will guide the physician in choosing empirical treatment in serious patients before the individual’s laboratory results are analyzed in the Microbiology laboratory. Reveals the changing trends in the local isolates. Helps the local pattern of antibiotic prescribing. PPT Prepared by Dr.Prince.C.P Department of Microbiology Mother Theresa PG&RIHS Pondicherry

1. Antibiotic
Sensitivity Testing
DR.PRINCE C P
HOD & Associate Professor
Department of Microbiology
Mother Theresa Post Graduate & Research Institute of Health Sciences
(Government of Puducherry Institution)
Pondicherry

2. Alexander Fleming

3. Antibiotic sensitivity test
• Antibiotic sensitivity test: in vitro testing of
bacterial cultures with antibiotics to
determine susceptibility of bacteria to
antibiotic therapy.

4. Antibiotic sensitivity test
• A laboratory test which determines how
effective antibiotic therapy is against a
bacterial infections.
• Antibiotic sensitivity testing will control the
use of Antibiotics in clinical practice
• Testing will assist the clinicians in the choice of
drugs for the treatment of infections.

5. • MIC: Minimum inhibitory concentration
• MBC: Minimum bactericidal concentration
• SENSITIVE: the antibiotic can prevent the
growth of Bacteria.
• RESISTANT: the antibiotic fails to prevent the
growth of Bacteria

6. MIC
• Minimum inhibitory concentration in
microbiology, is the lowest concentration of an
antimicrobial that will inhibit the visible growth of
a micro organism after overnight incubation.
• Minimum inhibitory concentrations are
important in diagnostic laboratories to confirm
resistance of micro organisms to an antimicrobial
agent and also to monitor the activity of new
antimicrobial agent

7. 1. The identification of relevant pathogens in
exudates and body fluids collected from patients
2. Sensitivity tests done to determine the degree
of sensitivity or resistance of pathogens isolated
from patient to an appropriate range of
antimicrobial drugs
3. Assay of the concentration of an administered
drug in the blood or body fluid of patient
required to control the schedule of dosage

8. • Antibiotic Sensitivity Testing is Essential of
selection of Antibiotics
• Isolation and Identification of Bacteria
precedes the selection of Antibiotic Testing
Methods

10. Uses of Antibiotic Sensitivity Testing
• Helps to guide the Physician in choosing
Antibiotics
• The accumulated results on different pathogens
their sensitivity will guide the physician in
choosing empirical treatment in serious patients
before the individual’s laboratory results are
analyzed in the Microbiology laboratory.
• Reveals the changing trends in the local isolates.
• Helps the local pattern of antibiotic prescribing

11. Why Need continues for testing
for Antibiotic Sensitivity
• Bacteria have the ability to develop resistance
following repeated or subclinical (insufficient)
doses, so more advanced antibiotics and
synthetic antimicrobials are continually
required to overcome them.
• Resistance implies that the infection is not
treatable with the tested Antibiotic because
its MIC exceeds achievable safe tissue or urine
levels.

12. METHODS
• Diffusion test
• Dilution test

13. Diffusion test
• Disc diffusion
• Well diffusion
• Cup plate diffusion
• Patch diffusion

14. Dilution test
• Used to detect MIC and MBC
• Agar dilution
• Broth dilution

15. Disc diffusion
• Kirby-Bauer antibiotic testing
• Stokes comparative method
• E-test

16. Kirby-Bauer
• Kirby-Bauer methods A commonly used
method in basic laboratories
• uses antibiotic-impregnated paper discs to
test whether particular bacteria are
susceptible to specific antibiotics

17. Procedure
• The bacterium is swabbed on the agar( Lawn
culture method) and the antibiotic discs are
placed on top. The antibiotic diffuses from the
disc into the agar in decreasing amounts the
further it is away from the disc. If the
organism is killed or inhibited by the
concentration of the antibiotic, there will be
NO growth in the immediate area around the
disc: This is called the zone of inhibition .

19. Lawn culture

20. Placing antibiotic discs

21. Zone of inhibition

22. Zone of inhibition- measurement

23. Sensitivity plate reading

24. Stokes comparative method
• In the Stokes controlled sensitivity test, a
control organism is inoculated on part of a
plate and the test organism is plated on the
remainder. Disks are placed at the interface
and the zones of inhibition are compared. The
use of a sensitive control shows that the
antibiotic is active, so that if the test organism
grows up to the disk it may safely be assumed
that the test organism is resistant to that drug.

25. Stokes comparative method

26. Multidisc

27. The Antibiotics are diluted to various dilution to test
the minimum inhibitory concentration

28. Epsilometer test
• E test is an antimicrobial gradient technique in
which 15 reference MIC dilutions of an
antibiotic have been repackaged with
innovative dry chemistry technology onto a
plastic strip.
• The predefined gradient provides precise and
accurate assessment of antimicrobial activity
against both fastidious and non-fastidious
microorganisms.

29. E test The strips are impregnated with various
concentration of Antibiotics

30. automation

31. automation

32. Thank you