Micro Chapter 20(1).ppt - Chapter 20 Antimicrobial Drugs Antimicrobial Drugs \u2022 Chemotherapy use of drugs to treat disease \u2022 Antimicrobial drugs

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

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Chapter 20: Antimicrobial Drugs
Antimicrobial Drugs Chemotherapy: use of drugs to treat disease Antimicrobial drugs: interfere with growth of microbes within host Antibiotic: substance produced by microbe that, in small amounts, inhibits another microbe Selective toxicity: selectively finding & destroying pathogens without damaging the host
History of Chemotherapy Paul Ehrlich speculated about “magic bullet” that would destroy microbes but not host; coined term chemotherapy 1928: Fleming discovered penicillin, produced by Penicillium 1932, Prontonsil Red was found to control streptococcal infections; sulfa drugs were used during WWII 1940: first clinical trials of penicillin Today there is a growing problem of antibiotic resistance
History of Chemotherapy Antibiotic are easy to discover; few are medically or commercially relevant More then half of antibiotics are produced by Streptomyces Few antibiotics are produced by Bacillus , Penicillum & Cephalosporium Practically all antibiotic- producing microbes have sporulation process
Spectrum of Antimicrobial Activity Harder to find drugs effective against eukaryotic microbes because their cells resemble human cells Viruses are even harder to target because they are inside the host’s cells & viral genetic material forces cells to make viruses
Spectrum of Antimicrobial Activity Narrow spectrum of microbial activity: drugs that affect a narrow range of microbial types Broad-spectrum antibiotics: affect a broad range of gram-positive or gram-negative bacteria Superinfection: overgrowth of normal microbiota that is resistant to antibiotics
Action of Antimicrobial Drugs Bactericidal: kill microbes directly Bacteriostatic: prevent microbes from growing & host’s defenses kills microbes
Major Modes of Antimicrobial Actions
Action of Antimicrobial Drugs Inhibiting Cell Wall Synthesis Ex. Penicillin Prevent the synthesis of intact peptidoglycans which weakens cell walls & cells lyse Only targets actively growing cells Does not effect human cells because human cell wall’s do not have peptidoglycans
Action of Antimicrobial Drugs Inhibiting protein synthesis Target bacterial 70S ribosomes Eukaryotes have 80S ribosome Gives antibiotics selective target Ex. Chloramphenicol, erythromycin, streptomycin & tetracyclines
Action of Antimicrobial Drugs Injuring the plasma membrane Polypeptide antibiotics change membrane permeability Antifungal drugs combine with membrane sterols in fungal plasma membrane to disrupt membrane
Action of Antimicrobial Drugs Inhibiting nucleic acid synthesis Interfere with DNA replication & transcription Limited usefulness because they can interfere with mammalian DNA & RNA Inhibiting the synthesis of essential metabolites Antimetabolites compete with normal substrates for an enzyme Sulfanilamide 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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