450 likes | 481 Views
Antimicrobial Drugs. Chemotherapy : Use of chemicals that do not harm the host yet kills others. Chemotherapeutic agent : substance that is used in medicine. Antimicrobial agents: Chemicals used to treat diseases caused by microbes. Antibiotics: Produced by microbes to inhibit others
E N D
Antimicrobial Drugs • Chemotherapy: Use of chemicals that do not harm the host yet kills others. • Chemotherapeutic agent: substance that is used in medicine. • Antimicrobial agents: Chemicals used to treat diseases caused by microbes.
Antibiotics: Produced by microbes to inhibit others • Synthetic drugs: Antimicrobials made in the lab • Semi Synthetic: synthetic or natural that is modified in the lab.
History of Antibiotics • Paul Ehrlich- Sulfa that stains bacteria may be able to inhibit it as well. Predicted the rise of antimicrobials
1928 Fleming makes his observation • 1940’s production of penicillin • In order to keep up with microbial resistance we must continually discover new antibiotics, but this is getting harder to do
1928 – Fleming discovered penicillin, produced by Penicillium. • 1940 – Howard Florey and Ernst Chain performed first clinical trials of penicillin. Figure 20.1
Drug Discovery Figure 20.1
General Properties of antimicrobials • Selective toxicity: Kills microbes not host • Has a spectrum of activity • Broad • Narrow • Which is better? • Why?
The Action of Antimicrobial Drugs Figure 20.2
Modes of action • Inhibition of cell wall synthesis • Pen • Disruption of cell membrane function • Polymyxins • Inhibition of protein synthesis • Chloramphenicol • Erythromycin • Tetracycline • Streptomycin
The Action of Antimicrobial Drugs Figure 20.4
Inhibition of nucleic acid synthesis • Rifamycin • Inhibitors of enzymatic function of primary metabolism • Competitive inhibition • Noncompetitive inhibition
Competitive Inhibitors • Sulfonamides (sulfa drugs) • Inhibit folic acid synthesis • Broad spectrum Figure 5.7b
Side Effects • Toxicity in host • Allergy in host • Disruption of normal microbiota • Birth defects in pregnancy
Resistance of microbes • When microbes no longer respond to an antibiotic • Resistance is acquired by • Non genetic means, basically evasion, grow in an area not exposed to antibiotic • Tuberculosis • Genetic resistance • A change in the chromosome or gain of a plasmid.
Antibiotic Resistance • A variety of mutations can lead to antibiotic resistance. • Mechanisms of antibiotic resistance 1. Enzymatic destruction of drug 2. Prevention of penetration of drug 3. Alteration of drug's target site 4. Rapid ejection of the drug • Resistance genes are often on plasmids or transposons that can be transferred between bacteria.
We humans will always have to find or create new antibiotics as microbes become resistant
8 Attributes of an ideal antimicrobial agent • Solubility in body fluids • Selectively toxic • Toxicity not easily altered • Not allergenic • Stability in body • Resistance not easily acquired • Long shelf life • Reasonable cost
Inhibitors of cell wall Synthesis • Ampicillin • Cephalosporin • Bacitracin • Vancomycin
Inhibitors of Protein Synthesis • Streptomycin • Tetracycline • Clormphenicol • Erythromycin
Plasma membrane • Polymyxin B
Inhibitors of Nucleic Acid Synthesis • Rifampin • ciprofloxacin
Competitive inhibitors of the Synthesis of Essential Metabolites • Trimethoprim-sulfamethoxozole
Antifungal • Amphotericin B • Griseofulvin • Flucytosine
Antiviral drugs • Acyclovir • Ganciclovir • Indinavir • Alpha interferon
Antiprotozoan Drugs • Chloroquine • Diiodohydroxyquin • Metronidazole
Antihelminthic Drugs • Niclosamide
Nucleoside and Nucleotide Analogs Figure 20.16b ,c
Tests to Guide Chemotherapy • MIC: Minimal inhibitory concentration • MBC: Minimal bactericidal concentration • Antibiogram
Broth Dilution Test Figure 20.19
Resistance to Antibiotics Figure 20.20
From Lab • How do antimicrobials work • How are they tested?
Effects of Combinations of Drugs Figure 20.22
Effects of Combinations of Drugs • Synergism occurs when the effect of two drugs together is greater than the effect of either alone • Antagonism occurs when the effect of two drugs together is less than the effect of either alone
Disk-Diffusion Test Figure 20.17
Future of Chemotherapeutic Agents • Antimicrobial peptides • Broad-spectrum antibiotics • Nisin (lactic acid bacteria) • Magainin (frogs) • Cecropin (moths)
Future of Chemotherapeutic Agents • Antisense agents • Complementary DNA that binds to a pathogen's virulence gene(s) and prevents transcription • Fomivirsen to treat CMV retinitis
Future of Chemotherapeutic Agents • siRNA • Complementary RNA that binds mRNA to inhibit translation Figure 9.14