1 Paul Ehrlich developed the concept of chemotherapy to treat microbial diseases he predicted the development of chemotherapeutic agents which would kill pathogens without harming the host ID: 1046087
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1. Antimicrobial Drugs
2. The History of Chemotherapy 1. Paul Ehrlich developed the concept of chemotherapy to treat microbial diseases; he predicted the development of chemotherapeutic agents, which would kill pathogens without harming the host (selective toxicity).2. Sulfa drugs came into prominence in the 1930s.3. Alexander Fleming discovered the first antibiotic, penicillin, in 1928; its first clinical trials were done in 1940.
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4. Antibiotic, a substance produced by microorganisms that in small amounts inhibits another microorganism.Antimicrobial drugs, not antibiotics, The wholly synthetic sulfa drugs, for example. Prophylaxis: Use of a drug to prevent the potential for infection in a person at risk.
5. Sources of Antibiotics
6. Spectrum of Antimicrobial ActivityIt’s easy to find or develop drugs that are effective against prokaryotic cells and that do not affect the eukaryotic cells of humans because these two cell types differ in The presence or absence of cell walls, The fine structure of their ribosomes, and Details of their metabolism.Thus, selective toxicity has numerous targets.
7. The problem is more difficult when the pathogen is a eukaryotic cell, such as a fungus, protozoan, or helminth. At the cellular level, these organisms resemble the human cell much more closely than a bacterial cell does. So, a drug that targets these pathogens usually damages the host, too. Viral infections are also particularly difficult to treat because the pathogen is within the human host’s cells and because the genetic information of the virus is directing the human cell to make viruses rather than to synthesize normal cellular materials.
8. Narrow spectrum of microbial activity, act against a limited group of bacteria, either gram positive or gram-negative. Penicillin G, for example, affects gram-positive bacteria but not gram-negative bacteria. Antibiotics that affect a broad range of gram-positive or gram-negative bacteria are therefore called broad-spectrum antibiotics. The disadvantage is that these drugs destroy many normal microbiotas of the host. If the antibiotic does not destroy certain organisms in the normal microbiota but does destroy their competitors, the survivors may flourish and become opportunistic pathogens. An example is overgrowth by the yeastlike fungus Candida albicans, which is not sensitive to bacterial antibiotics. This overgrowth is called a superinfection.
9. The Action of Antimicrobial Drugs Antimicrobial drugs are either bactericidal (they kill microbes directly) or bacteriostatic (they prevent microbes from growing). In bacteriostasis, the host’s own defenses, such as phagocytosis and antibody production, usually destroy the microorganisms.
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11. Inhibiting Cell Wall SynthesisThe cell wall of a bacterium consists of a macromolecular network called peptidoglycan, which found only in bacterial cell walls. Penicillin and certain other antibiotics prevent the synthesis of intact peptidoglycan; consequently, the cell wall is greatly weakened, and the cell undergoes lysis.
12. Inhibiting Protein SynthesisBecause protein synthesis is a common feature of all cells, whether prokaryotic or eukaryotic. One notable difference between prokaryotes and eukaryotes, however, is the structure of their ribosomes.Eukaryotic cells have 80S ribosomes whereas prokaryotic cells have 70S ribosomes. The difference in ribosomal structure accounts for the selective toxicity of antibiotics that affect protein synthesis.
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14. Injuring the Plasma MembraneCertain antibiotics, especially polypeptide antibiotics (ex: polymyxin B), bring about changes in the permeability of the plasma membrane that result in the loss of important metabolites from the microbial cell.Some antifungal drugs, such as amphotericin B, and ketoconazole, are effective against a considerable range of fungal diseases. Such drugs combine with sterols in the fungal plasma membrane to disrupt the membrane. Because bacterial plasma membranes generally lack sterols, these antibiotics do not act on bacteria.
15. Inhibiting Nucleic Acid SynthesisA number of antibiotics, such as quinolones and rifampin, interfere with the processes of DNA replication and transcription in microorganisms. Some drugs with this mode of action have an extremely limited usefulness because they interfere with mammalian DNA and RNA as well.
16. Inhibiting the Synthesis of Essential Metabolites
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