1. Antibiotic sensitivity
PHT 381
Lab # 7
Antibiotic sensitivity
Testing

2. Antibiotic Sensitivity Testing
Antibiotic sensitivity testing is used to determine the susceptibility of the microorganism to various antimicrobial agents.

3. Sensitivity testing techniques:
Disc Diffusion Method.
Serial Dilution Method (Minimum inhibitory concentration).

4. Disc Diffusion Method
The effectiveness of an antibiotic in this technique is based on the size of the zone of inhibition that surrounds a disc that has been impregnated with a specific concentration of the agent.
Advantages:
Rapid
Accurate
Inexpensive

5. The recommended medium →
Mueller Hinton agar
** The pH of the medium ( )
**5% defibrinated sheep blood is added to the medium for certain fastidious organisms.

6. “0.5 McFarland” (a barium sulphate standard)
The inoculum:
The turbidity of a broth culture / saline suspension of the test organism has to match a defined standard
“0.5 McFarland” (a barium sulphate standard)
( the matched inoculum should give confluent growth).

7. Types of antibiotic:-
Narrow spectrum antibiotic active against either Gram +ve bacteria only or gram –ve bacteria only
Broad spectrum antibiotic active against both Gram’s +ve and -ve bacteria

8. Disc Diffusion method Materials: Cultures of Staph. aureus, E. coli
Pseudomonas aeruginosa
Filter paper disc
Antibiotic solutions (Vancomycin, Augmentin, Ceftazidime, Azactam)
20 ml melted nutrient agar
Petri-dish
Sterile 1ml pipette

9. Procedure incubate Don’t invert 0.1ml inoculate 45°c Aug Cef 24 h
m.o
0.1ml Az
inoculate
45°c
Aug
Cef
incubate
24 h
at 37°c Az
Van
Don’t invert

10. Results: Measure the diameter of each inhibition zone
* The diameter of the inhibition zones are directly proportional to the susceptibility of the microorganism to the antibiotics.
Van
Aug
Cef Az

11. Results: Mo AB S E Ps 1 2 3 4

12. Thank You