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NAJRAN UNIVERSITY College of Applied Medical Sciences

NAJRAN UNIVERSITY College of Applied Medical Sciences. General Microbiology Course Lecture No. 11. By. Dr. Ahmed Morad Asaad Associate Professor of Microbiology. Choice of antimicrobial agent 1- In vitro tests of bacterial sensitivity to antibiotics 2- Emprical use of antibiotics

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NAJRAN UNIVERSITY College of Applied Medical Sciences

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  1. NAJRAN UNIVERSITY College of Applied Medical Sciences General Microbiology Course Lecture No. 11 By Dr. Ahmed MoradAsaad Associate Professor of Microbiology

  2. Choice of antimicrobial agent 1- In vitro tests of bacterial sensitivity to antibiotics 2- Emprical use of antibiotics 1- In vitro tests A- Disc diffusion method - A culture medium is inoculated with the organism - Discs impregnated with different antibiotics are placed and the plate is incubated at 37ºC - The degree of inhibition by antibiotic is measured by the diameter of the inhibition zone

  3. B- Dilution method • Serial dilutions of the antibiotics are inoculated with the organism to determine: • Minimum inhibitory concentration (MIC): The lowest concentration of the antibiotic that inhibit the growth of the organism • Minimum bactericidal concentration (MBC): The lowest concentration of the antibiotic that kill the organism • C- E test • Strips with antibiotic gradients • D- Automated systems

  4. Antibiograms: periodic reports that indicate the susceptibility of clinically isolated organisms to the antibiotics in current local use.

  5. Empirical use of antibiotics: Use of antibiotics without in vitro tests is indicated in: 1- In closed lesions with no available samples (brain abscess) 2- While waiting for the results of in vitro sensitivity tests 3- Drug combination: *- Sever infection *- To avoid microbial resistance *- Synergism: The combined effect of a pair of antibiotics is greater than the sum of their independant activities

  6. Factors affecting antimicrobial activity in-vitro: 1- pH of the environment 2- components of the medium 3- Size of the inoculum 4- Stability of the drug 5- Duration of incubation

  7. Complications of antimicrobial chemotherapy: 1- Toxicity: Streptomycin is toxic to 8th cranial nerve Aminoglycosides are nephrotoxic Tetracycline causes teeth deformity and liver damage 2- Hypersensitivity Penicillin (anaphylaxis) 3- Superinfection An infection on top of antibiotic adminstration 4- Masking the diagnosis 5- Development of resistance (TUTORIAL) Non-genetic OR genetic drug resistance

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