Download Chapter 15: Antimicrobial Drugs

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
• Broad-spectrum antibiotic
• Superinfection
• Bactericidal antibiotic
• Bacteriostatic antibiotic
The First Antibiotic
• 1928 – Fleming
discovered
penicillin;
produced by
Penicillium (a
fungus).
• 1940 – First
clinical trials of
penicillin.
Figure 20.1
Table 20.2
Antimicrobials and Modes of Action
• Prevents cell wall synthesis
• Prevents protein synthesis
• Plasma membrane attack
• Prevents nucleic acid synthesis
• Disrupts biochemical pathways
Antibacterial Antibiotics:
Inhibitors of Cell Wall Synthesis
• Penicillin
• Natural penicillins
• Narrow spectrum
• Use for Staphylococci, Streptococci, Spirochetes
• Vulnerable to penicillinases (beta lactamases)
Some bacteria can disrupt the functioning
of penicillin
Figure 20.8
Penicillins
Figure 20.6
• Semisynthetic penicillins
• Penicillinase-resistant penicillins
• First was methicillin
• Extended-spectrum penicillins
• Effective against many Gram negatives
• Some effective against Pseudomonas aeruginosa
• Penicillins + -lactamase inhibitors
• Cephalosporins:
• more effective
against gramnegatives than
natural penicillins
Vancomycin:
• Used against antibiotic resistant S. aureus
(i.e. MRSA)
• VRE have emerged
Figure 20.9
Antiviral Drugs
Nucleoside and Nucleotide Analogs
Figure 20.16a
Antiviral Drugs
Nucleoside and Nucleotide Analogs
Figure 20.16b, c
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
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
E test
• Antibiotic gradient strip is placed on cultured plate
• Minimal inhibitory concentration (MIC) is determined
E Test
Figure 20.18
Broth Dilution Test
• Can distinguish between MIC and MBC (minimal
bactericidal concentration)
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
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.
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
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
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.
Effects of Combinations of Drugs
Figure 20.22