Micro Chapter 20(1).ppt - Chapter 20 Antimicrobial Drugs...

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Chapter 20: Antimicrobial Drugs
Antimicrobial DrugsChemotherapy: use of drugs to treat diseaseAntimicrobial drugs: interfere with growth of microbes within hostAntibiotic: substance produced by microbe that, in small amounts, inhibits another microbeSelective toxicity: selectively finding & destroying pathogens without damaging the host
History of ChemotherapyPaul Ehrlich speculated about “magic bullet” that would destroy microbes but not host; coined term chemotherapy1928: Fleming discovered penicillin, produced by Penicillium1932, Prontonsil Red was found to control streptococcal infections; sulfa drugs were used during WWII1940: first clinical trials of penicillinToday there is a growing problem of antibiotic resistance
History of ChemotherapyAntibiotic are easy to discover; few are medically or commercially relevantMore then half of antibiotics are produced by StreptomycesFew antibiotics are produced by Bacillus, Penicillum& CephalosporiumPractically all antibiotic-producing microbes have sporulation process
Spectrum of Antimicrobial ActivityHarder to find drugs effective against eukaryotic microbes because their cells resemble human cellsViruses are even harder to target because they are inside the host’s cells & viral genetic material forces cells to make viruses
Spectrum of Antimicrobial ActivityNarrow spectrum of microbial activity: drugs that affect a narrow range of microbial typesBroad-spectrum antibiotics: affect a broad range of gram-positive or gram-negative bacteriaSuperinfection: overgrowth of normal microbiota that is resistant to antibiotics
Action of Antimicrobial DrugsBactericidal: kill microbes directlyBacteriostatic: prevent microbes from growing & host’s defenses kills microbes
Major Modes of Antimicrobial Actions
Action of Antimicrobial DrugsInhibiting Cell Wall SynthesisEx. PenicillinPrevent the synthesis of intact peptidoglycans which weakens cell walls & cells lyseOnly targets actively growing cellsDoes not effect human cells because human cell wall’s do not have peptidoglycans
Action of Antimicrobial DrugsInhibiting protein synthesisTarget bacterial 70S ribosomesEukaryotes have 80S ribosomeGives antibiotics selective targetEx. Chloramphenicol, erythromycin, streptomycin & tetracyclines
Action of Antimicrobial DrugsInjuring the plasma membranePolypeptide antibiotics change membrane permeability Antifungal drugs combine with membrane sterols in fungal plasma membrane to disrupt membrane
Action of Antimicrobial DrugsInhibiting nucleic acid synthesisInterfere with DNA replication & transcriptionLimited usefulness because they can interfere with mammalian DNA & RNAInhibiting the synthesis of essential metabolitesAntimetabolites compete with normal substrates for an enzymeSulfanilamide competes with para-aminobenzoic acid (PABA), stopping the synthesis of folic acid which is needed by microbes as a coenzyme for synthesis of nucleic acid bases & amino acids

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