10 BIO 326R chemotherapy

10 BIO 326R chemotherapy - BIO 326R Antibiotics,...

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BIO 326R Antibiotics, chemotherapy
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Terms Therapeutic ratio toxic dose / therapeutic dose higher = better Spectrum Broad spectrum – effective against a wide variety/large number of bacteria Narrow spectrum – effective against a few select bacteria (e.g. isoniazid is effective against mycobacteria, not against others) Bacteriocidal: kills Bacteriostatic: stops growth MBC: Minimum Bacteriocidal Concentration Lowest concentration that kills 99.9% of bacteria in a given time MIC: Minimum Inhibitory Concentration Lowest concentration that inhibits visual growth in plates (colony/lawn formation) or liquid culture (turbidity or OD measurement)
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Therapeutic Ratio All chemotherapeutic agents rely on some form of selective toxicity They must be more toxic to the pathogen than the host Selective toxicity can be represented by the therapeutic ratio Ratio of concentration toxic to host to concentration toxic to pathogen High therapeutic ratios are usually obtained by drugs which target mechanisms (enzymes/structures) that the host does not possess. Penicillin target transpeptida se enzymes which cross-link peptidoglycan. There are no human enzymes which are inhibited by penicillins. Penicillins are thus usually very well tolerated by humans in high amounts. Toxic effects may not be seen until the concentration is so high that it begins to precipitate. High ratio (penicillin) Low ratio (AZT) Even ratio (bleach) Conc. Toxic to host Conc. Toxic to pathogen Effective dose Effective dose
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Bacteria plated at high concentration so they will grow as a “lawn” on plate will cover whole surface of plate, no individual colonies Paper discs with a known concentration of antibiotic are placed on the plate. Bacteria are allowed to grow for given time Bacteria will not grow around discs that have an effective concentration – seen as a clear zone of no growth within the lawn Size of zone of inhibition depends on rate of diffusion of antibiotic, sensitvity and growth rate of bacteria Large molecules diffuse slower. Conditions standardized for antibiotics and bacteria Can check to see what concentration of a specific antibiotic is needed or compare sensitivity to several antibiotics all at once. 1ug
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This note was uploaded on 04/09/2009 for the course BIO 326R taught by Professor Whiteley during the Spring '08 term at University of Texas at Austin.

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10 BIO 326R chemotherapy - BIO 326R Antibiotics,...

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