Antimicrobial Susceptibility Testing........... ppt...pptx

Bacteriology notes in Antimicrobial Susceptibility Testing

1. VIVEKANANDHA ARTS AND SCIENCE COLLEGE FOR WOMEN VEERACHIPALAYAM,SANKAGIRI,SALEM DEPARTMENT OF MICROBIOLOGY ANTIMICROBIAL SUSCEPTIBILITY TESTING SUBJECT : BACTERIOLOGY SUBMITTED BY : K.SHANMUGAPRIYA 1'ST M.SC MICROBIOLOGY

2. Introduction : Antimicrobial susceptibility testing (AST) is  a laboratory procedure performed by medical technologists (clinical laboratory scientists) to identify which antimicrobial regimen is specifically effective for individual patients .

3. Antibiotic Sensitivity Testing Antibiotic sensitivity testing is carried out to determine the appropriate antibiotic agent to be used for a particular bacte-rial strain isolated from clinical specimens. Antibiotic sensitiv-ity testing can be carried out by two broad methods, as follows: a)        Disc diffusion tests b)       Dilution tests

4. Disc diffusion tests :

5. Method :

6. Testing : Four steps :

7. Types of disc diffusion tests Disc diffusion tests are of the following types: a)        Kirby–Bauer disc diffusion method b)       Stokes disc diffusion method c)        Primary disc diffusion test

8. Kirby–Bauer disc diffusion method: Kirby–Bauer discdiffusion method is the most common method used routinely for determination of antibiotic sensitivity of bacteria isolated from clinical specimens. In this method, both the test strains and the control strains are tested in separate plates. Kirby Bauer Disc Diffusion Method

9. Dilution tests : Dilution tests are performed to determine the minimum inhib-itory concentration (MIC) of an antimicrobial agent. MIC is defined as the lowest concentration of an antimicrobial agent that inhibits the growth of organisms. Estimation of the MIC is useful to: ·            Regulate the therapeutic dose of the antibiotic accurately in the treatment of many life-threatening situations, such as bacterial endocarditis.

10. Following methods are carried out to determine the MIC: a)        Broth dilution method b)       Agar dilution method c)         Epsilometer test (E-test)

11. Broth dilution method The broth dilution method is a quantitative method for deter-mining the MIC of an antimicrobial agent that inhibits the growth of organisms in vitro. In this method, the antimicrobial agent is serially diluted in Mueller–Hinton broth by doubling dilution in tubes and then a standard suspension of the broth culture of test organism is added to each of the antibiotic dilu-tions and control tube. This is mixed gently and incubated at 37°C for 16–18 hours.

12. Agar dilution method Agar dilution method is a quantitative method for determining the MIC of antimicrobial agent against the test organism. Mueller–Hinton agar is used in this method. Serial dilution of the antibiotic are made in agar and poured onto Petri dishes. 

13. Epsilometer test (E test) Epsilometer test (E test), based on the principle of disc diffu-sion , is an automated system for measuring MIC of a bacterial isolate. In this method, an absorbent plastic strip with a con- tinuous gradient of antibiotic is immobilized on one side. MIC interpretative scale corresponding to 15 twofold MIC dilu-tions is used on the other side.

14. Table :

15. Description :

16. Antibiotic discs ◍ Antibiotic discs are made from premium quality paper towels impregnated with antimicrobial agents in precise concentrations. They are clearly identified by an  acronym , comprising 1 to 3 letters, printed on each side of the disc

17. ◍ The disc cartridges must be stored in their container between +2 and +8°C in a dry place. The discs must be brought to room temperature. Any opened cartridge must be used within five days.

18. Indications/Applications Antimicrobial susceptibility tests are used  to determine which specific antibiotics a particular bacteria or fungus is sensitive to . Most often, this testing complements a Gram stain and culture, the results of which are obtained much sooner.

19. Conclusion Although a variety of methods exist, the goal of in-vitro antimicrobial susceptibility testing is the same:  to provide a reliable predictor of how a microorganism is likely to respond to antimicrobial therapy in the infected host .

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