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?

Table 20.2

The Action of Antimicrobial Drugs Foundation figure 20.2 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

Figure 20.13

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

Drugs with all 8 characteristics are very very rare.

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

What are these drugs, modes of action and side effects?

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