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Antibiotic Sensitivity Testing in Bacterial Cultures

Explore the significance of in vitro antibiotic testing on bacterial cultures to guide treatment decisions & understand resistance patterns. Discover methodologies like Kirby-Bauer & MIC for optimal therapy selection.

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Antibiotic Sensitivity Testing in Bacterial Cultures

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  1. The in vitro testing of bacterial cultures with antibiotics todetermine . K Hari Krishnan TirunelveliMedical College

  2. Antibiotic Sensitivity Testing K Hari Krishnan TirunelveliMedical College

  3. To guide the clinician in selecting the best antibiotic agent for an individualpatient. To control the useof in clinicalpractice. To accumulate epidemiological information on the resistance of microorganisms of public health importance within thecommunity. To reveal the changing trends inthe localisolates. K Hari Krishnan TirunelveliMedical College

  4. Bacteria have the ability to develop resistance following repeated or subclinical (insufficient) doses, so more advanced antibiotics and synthetic antibiotics are continually required to overcomethem. K Hari Krishnan TirunelveliMedical College

  5. AST is essential for the selection ofthe K Hari Krishnan TirunelveliMedical College

  6. For the testing of isolates from “healthy” patientswith intact immunedefenses. • For such asuncomplicated • urinary tractinfections. • In the treatment of serious infections such as endocarditis orosteomyelitis. • For infections in high-risk patient groups such as immunocompromised patients (e.g..transplant patients). – Those who are criticallyill. K Hari Krishnan TirunelveliMedical College

  7. Antibiotic SensitivityTests Diffusion & Dilution Diffusion Dilution Kirby-Bauer Method Stokes Method Tube Dilution Agar Dilution E-Test QualitativeMethods QuantitativeMethods K Hari Krishnan TirunelveliMedical College

  8. Enterobacteriaceae Pseudomonas aeruginosa Staphylococcus Blood& Tissues Intestinal Urinary Benzylpenicillin Oxacillin Erythromycin Tetracycline Chloramphenicol Ampicillin Chloramphenicol Cotrimoxazole Tetracycline Sulfonamides Trimethoprim Cotrimoxazole Ampicillin Nitrofurantoin Tetracycline Ampicillin Chloramphenicol Cotrimoxazole Tetracycline Cefalotin Gentamycin Piperacillin Gentamycin Tobramycin Drugs K Hari Krishnan TirunelveliMedical College

  9. K Hari Krishnan TirunelveliMedical College

  10. – A paper disk with a defined amount of antibiotic is used to generate a dynamically changing gradient of antibiotic concentrations in the agar in the vicinity of thedisk. K Hari Krishnan TirunelveliMedical College

  11. The allowedto contained in a reservoiris and interact in a plate freshly seeded with the test organisms. The disk is applied to the surface of an agar plate inoculated with the test organism. • The • gradient. • The diffuses out of the disk to form starts to divide and growand progresses toward a critical mass ofcells. K Hari Krishnan TirunelveliMedical College

  12. is formed at the critical time where a particular concentration of the antibiotic is just able to inhibit the organism before it reaches an overwhelming cell mass or criticalmass. K Hari Krishnan TirunelveliMedical College

  13. Any commercially available discs with the proper diameter and potency can beused. Stocks of antibiotic discs can be storedat -20 ⁰C for 1month. – On removal from the refrigerator, the containers should be left at room temperature for about 1 hour to allow the temperature toequilibrate. K Hari Krishnan TirunelveliMedical College

  14. K Hari Krishnan TirunelveliMedical College

  15. K Hari Krishnan TirunelveliMedical College

  16. Used to determinethe of antibiotic to inhibit or killthe microorganism. Achieved by dilution of antibiotic in either agar or brothmedia. K Hari Krishnan TirunelveliMedical College

  17. K Hari Krishnan TirunelveliMedical College

  18. The lowest concentration of drugthat of thebacteria isolated from thepatient. The MIC is determined by inoculating the organism isolated from the patient into a series of tubes or cups containing progressive dilutions of thedrug. K Hari Krishnan TirunelveliMedical College

  19. Patient's organism is added to tubes containing decreasing amounts of the antibiotic Incubation At 37°Covernight Lowest concentration of drug that inhibits growth is theMIC K Hari Krishnan TirunelveliMedical College

  20. MIC K Hari Krishnan TirunelveliMedical College

  21. The lowest concentration of drugthat the bacteria isolated from thepatient. K Hari Krishnan TirunelveliMedical College

  22. Serial dilutions of the drug are prepared in agar and poured intoplates. – Many strains can be inoculated on each plate containing an antibioticdilution. K Hari Krishnan TirunelveliMedical College

  23. K Hari Krishnan TirunelveliMedical College

  24.  Broth microdilution platecontains – Eachrow: • standard dilutions ofeight by lettersA-H). • – Eachcolumn in each row(denoted • containsastandard concentration that doubles whenmoving from right toleft. •  The minimum inhibitory concentration (MIC) is determined by the first well where there is no visiblegrowth. K Hari Krishnan TirunelveliMedical College

  25. K Hari Krishnan TirunelveliMedical College

  26. K Hari Krishnan TirunelveliMedical College

  27. EpsilometerTest Quantitative method of antibiotic sensitivity testing. Applies both dilution of antibiotic and diffusion of antibiotic into themedium. K Hari Krishnan TirunelveliMedical College

  28. Combines the principles of disk diffusion and agar dilutionmethods Diffusion E-Test Dilution K Hari Krishnan TirunelveliMedical College

  29. A predefined stable antibiotic gradient is present on a thin inert carrierstrip. Using innovative dry chemistry technology, E-Test is used to determine the on-scale Minimum Inhibitory Concentration(MIC). K Hari Krishnan TirunelveliMedical College

  30. The intersection of the inhibitory zone edge and the calibrated carrier strip indicates the MIC withinherent K Hari Krishnan TirunelveliMedical College precision andaccuracy.

  31. MIC K Hari Krishnan TirunelveliMedical College

  32. K Hari Krishnan TirunelveliMedical College

  33. Over100 are now available in the product range for testing of aerobic bacteria and fastidious organisms suchas • Pneumococci • Haemophilus • Helicobacter pylori • Meningococci • Gonococci • Fungi • Mycobacteria K Hari Krishnan TirunelveliMedical College

  34. K Hari Krishnan TirunelveliMedical College

  35. Antibiotic SensitivityTesting K Hari Krishnan TirunelveliMedical College

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