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Antibiotic Susceptibility Testing

Antibiotic Susceptibility Testing. Tube dilution tests.

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Antibiotic Susceptibility Testing

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  1. Antibiotic Susceptibility Testing

  2. Tube dilution tests A series of culture tubes are prepared, each containing a liquid medium and a different concentration of a chemotherapeutic agent. The tubes are then inoculated with the test organism and incubated for 16-20 hours at 35C. After incubation, the tubes are examined for turbidity (growth). • Minimum Inhibitory Concentration (MIC): • Is the lowest concentration of chemotherapeutic agent capable of preventing growth of the test organism. • Minimum Bactericidal Concentration (MBC): • Is the lowest concentration of the chemotherapeutic agent that results in no growth (turbidity) of the subcultures.

  3. The agar diffusion test (Bauer-Kirby test): In this test, the in vitro response of bacteria to a standardized antibiotic-containing disc has been correlated with the clinical response of patients given that drug. • The MIC for each agent was then compared to the usually-attained blood level in the patient with adequate dosage. Categories of "Resistant,“ "Intermediate," and "Sensitive" were then established.

  4. Disk-Diffusion Test

  5. Epsilo-meter test • It’s a new technique for direct detection of MIC, a graduated increasing concentration of the antibiotic is fixed along a rectangular plastic test strip which is applied to the surface of an inoculated agar plate, after over night incubation a tear drop shaped inhibition zone is seen. • The zone edge intersect the graded test strip at the MIC of the antimicrobial.

  6. E Test

  7. E Test

  8. Effects of Combinations of Drugs • Synergism occurs when the effect of two drugs together is greater than the effect of either alone. • Antagonism occurs when the effect of two drugs together is less than the effect of either alone.

  9. Kirby-Bauer animation

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