Chapter 20 - Chapter 20 Antimicrobial Medications...

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Chapter 20 Antimicrobial Medications
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Chemotherapy Antibiotic Synthetic drugs Semi-synthetic drugs
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In 1910, Paul Ehrlich discovered Salvarsan Arsenic derivative used to treat syphilis In 1935, Gerhard Dogmak discovered a red dye that inhibited G+ bacteria Prontosil In 1936, Ernest Fourneau discovered it was the sulfur portion of the dye that was active stimulated the development of sulfa drugs
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In 1928, Alexander Flemming -1st true antibiotic Mold Penicillium notatum secreted compound that inhibited bacterial growth Soon after Selman Waksman isolated streptomycin from the soil bacteria Streptomyces griseus In 1940s, Howard Florey and Ernst Chain performed first clinical trials of penicillin Developed a method for mass production Penicillin G
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More than ½ of antibiotics in use come from bacteria Primarily species of Streptomyces Some are isolated from species of Bacillus Some are isolated from various molds Penicillium and C ephalosporium Most antibiotic producers are spore formers
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Selective Toxicity Magic bullet causes damage to the microorganism without causing significant harm to the host Easier with prokaryotic pathogens Why?
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Therapeutic dosage level eliminates pathogen Toxic dosage Level causes host damage Chemotherapeutic index maximum tolerable dose (per kg body weight) / minimum effective dose (per kg body weight) Higher the index the safer for host
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Spectrum of activity range of different microorganisms against which the drug is effective Narrow-spectrum Example – anti-mycobacterials Broad-spectrum May disturb normal microbiota May lead to superinfection
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Synergism increased effect of two drugs when used together clavulinic acid and amoxicillin Antagonism reduction of a drug’s desirable effect when administered with another penicillin and tetracycline
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Adverse effects of antimicrobials Allergic reactions Toxic effects Suppression of normal flora Microbial resistance
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Modes of Action
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Inhibition of Cell Wall Synthesis Bacterial cell walls are composed of the polysaccharide peptidoglycan Some antibiotics prevent the synthesis of intact peptidoglycan Human cells are unaffected
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Disruption of Cell Membrane changes permeability of the plasma membrane Results in the loss of important metabolites May target specific membrane components Ex. particular sterols in fungi cell membranes Bacteria cells generally lack sterols Animal cells usually have different sterols
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Inhibition of Protein Synthesis Common feature of all cells May target the ribosomes, which are different in prokaryotes Mitochondria also have 70S ribosome there is the potential for damage to the host cell Use is limited
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Inhibition of Nucleic Acid Synthesis Interfere with DNA replication or RNA transcription Some have an extremely limited usefulness
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This note was uploaded on 02/21/2008 for the course BIOLOGY 380 taught by Professor Littlejohn during the Spring '06 term at University Of Southern Mississippi .

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Chapter 20 - Chapter 20 Antimicrobial Medications...

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