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Antimicrobial Drugs: Chemotherapy and Antibiotic Resistance

Explore the use of antimicrobial drugs to treat diseases and their impact on microbial growth. Learn about antibiotics, selective toxicity, and the emergence of antibiotic resistance.

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Antimicrobial Drugs: Chemotherapy and Antibiotic Resistance

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  1. Chapter 15: Antimicrobial Drugs • Chemotherapy The use of drugs to treat a disease • Antimicrobial drugs Interfere with the growth of microbes within a host • Antibiotic Inhibits “bacterial” growth; usually produced by bacteria or fungi • Selective toxicity Kills harmful microbes without damaging the host

  2. Broad-spectrum antibiotic • Superinfection • Bactericidal antibiotic • Bacteriostatic antibiotic

  3. The First Antibiotic • 1928 – Fleming discovered penicillin;produced by Penicillium (a fungus). • 1940 – First clinical trials of penicillin. Figure 20.1

  4. Table 20.2

  5. Antimicrobials and Modes of Action • Prevents cell wall synthesis • Prevents protein synthesis • Plasma membrane attack • Prevents nucleic acid synthesis • Disrupts biochemical pathways

  6. Antibacterial Antibiotics: Inhibitors of Cell Wall Synthesis • Penicillin • Natural penicillins • Narrow spectrum • Use for Staphylococci, Streptococci, Spirochetes • Vulnerable to penicillinases (beta lactamases)

  7. Some bacteria can disrupt the functioning of penicillin Figure 20.8

  8. Penicillins Figure 20.6

  9. Semisynthetic penicillins • Penicillinase-resistant penicillins • First was methicillin • Extended-spectrum penicillins • Effective against many Gram negatives • Some effective against Pseudomonas aeruginosa • Penicillins + -lactamase inhibitors

  10. Cephalosporins: • more effective against gram-negatives than natural penicillins • Vancomycin: • Used against antibiotic resistant S. aureus (i.e. MRSA) • VRE have emerged Figure 20.9

  11. Antiviral DrugsNucleoside and Nucleotide Analogs Figure 20.16a

  12. Antiviral DrugsNucleoside and Nucleotide Analogs Figure 20.16b, c

  13. Antiviral Drugs • Protease inhibitors • Entry and Uncoating inhibitors • Viral release inhibitors • i.e. Tamiflu • Interferons, prevent spread of viruses to new cells • Common treatment for Hepatitis C infection

  14. Kirby-Bauer (Disk-Diffusion) Test • Antibiotic soaked disks are placed on cultured plate • Zone of inhibition is measured and compared to table with known results

  15. E test • Antibiotic gradient strip is placed on cultured plate • Minimal inhibitory concentration (MIC) is determined

  16. E Test Figure 20.18

  17. Broth Dilution Test • Can distinguish between MIC and MBC (minimal bactericidal concentration)

  18. Antibiotic Resistance • Mechanisms of antibiotic resistance • Alteration of drug's target site • Rapid ejection of the drug • Enzymatic destruction of drug • Prevention of penetration of drug

  19. Antibiotic Resistance • A variety of mutations can lead to antibiotic resistance. • Resistance genes are often on plasmids or transposons that can be transferred between bacteria.

  20. Antibiotic Resistance • Misuse of antibiotics selects for resistant mutants. Misuse includes: • Using outdated, weakened antibiotics • Using antibiotics for the common cold and other inappropriate conditions • Use of antibiotics in animal feed • Failure to complete the prescribed regimen • Using someone else's leftover prescription

  21. Effects of Drug Combinations • 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.

  22. Effects of Combinations of Drugs Figure 20.22

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