Control of Bacterial Growth

1. Control of Bacterial Growth • Antibiotics / Chemotherapy • History • Properties • Testing • Spectrum of Antimicrobial Action • Modes of Action • Survey of Drugs

2. Antibiotics • History • Quinine for malaria • Willow bark for treating fever • Paul Ehrlich - staining of bacteria led to ideas for chemotherapy • Fleming (1928) observed the effect of Penicillium of on Staphylococcus • Flory & Chain (1940) developed penicillin and clinically tested it

3. Antibiotics • Peruvian Indians - treat fevers and reduce shivering with cinchona bark • Use " Peruvian bark" was first recorded by the Jesuits in 1633 • Countess Anna del Chinchón. was cured of the ague (a name for malaria the time) in 1638 • The Dutch bought the Bolivian seeds from Charles Ledger, a British botanist, planted them in Java, and came to monopolize the world's supply of quinine for close to 100 years. • A formal chemical synthesis was accomplished in 1944 by American chemists Woodward and W.E. Doering • Since then, several more efficient quinine syntheses have been achieved, but none of them can compete in economic terms with isolation of the alkaloid from natural sources. • Malaria resistant to synthetic but less so to natural • The first synthetic organicdye, mauveine, was discovered by William Henry Perkin in 1856 while he was attempting to synthesize quinine.

5. Antibiotics • 1928 – Fleming discovers penicillin and isolates a crude form of the chemical • 1930’s - Florey and Chain further refine chemical methods for isolation of penicillin from culture filtrates • WWII – work transferred to Peoria IL – development of submerged culture processes • Post WWII – additional markets for penicillin leads to resistance

6. Antibiotics • Properties • Selective toxicity (e.g. sulfanilamide mimics PABA in folic acid synthesis) • Sources • Microorganisms • Synthetic agents • Plants

7. Antibiotics • Testing • Broth dilution • Agar dilution • Disc diffusion

8. Antibiotics • Broth dilution • MIC - minimal inhibitory concentration • smallest concentration that stops growth • Successive dilutions inoculated with same number bacteria • Turbidity measure when compared to control (could also do dilutions & plate counts) • MBC - minimal bactericidal concentration • Concentration of antibiotic where cell number is reduced significantly • Will typically be a higher concentration than MIC

9. Antibiotics • Agar dilution • Dilute drug into agar at varying concentrations • Can test multiple species of bacteria • Not very quantitative

10. Antibiotics • Disc-Diffusion • Discs with known concentrations of antibiotics seeded onto “lawn” of bacteria • Zone of clearing around disk a measure of effectiveness of antibiotic

11. Antibiotics • Spectrum of Antimicrobial Activity • Selectively toxic drugs; uses differences between prokaryotic and eukaryotic cells • Broad spectrum – affect both G+ and G- • Antibiotic effect, e.g. penicillin and Candida albicans

12. Antibiotics • Modes of Action • Bactericidal vs. Bacteriostatic • Cell Wall • Protein Synthesis • Plasma membrane • Nucleic Acid Synthesis • Essential Metabolites

14. Antibiotics • Bactericidal vs. Bacteriostatic • Bactericidal - kills • Bacteriostatic - inhibits growth but once removed growth can resume

15. Antibiotics • Inhibition of Cell Wall Synthesis • Uniqueness of bacterial cell wall • Prevent peptidoglycan synthesis or peptide cross-linking from forming • Penicillins & cephalosporins

16. Antibiotics • Inhibition of Protein Synthesis • Bacterial protein synthesis significantly different than eukaryotic e.g. 70S vs. 80S ribosome or elongation & termination factors • Amyloglycosides (streptomycin and gentamicin)

17. Antibiotics • Injury of Plasma Membrane • Alteration in permeability • Interference with required consituents, e.g. sterols in fungal lipid membranes • Polymixin B (bacteria) • Amphotericin B or miconazole (fungal)

18. Antibiotics • Essential Metabolites • Para-aminobenzoic acid is an essential cofactor used by bacteria to synthesize folic acid (a vitamin that functions as a coenzyme in the synthesis of nucleic acid precursors) • animals ingest folic acid • Sulfanilamide is an analog of PABA

19. Antibiotics • Inhibition of Nucleic Acid Synthesis • Nucleic acid synthesis especially mRNA and DNA • Rifampin and quinolones • Limited utility because of RNA’s and DNA’s essential role in both prokaryotic and eukaryotic cells

20. Antibiotics • Survey of Drugs - Cell Wall Synthesis • Penicillins (G, V) • Semisynthetic penicillins (Ampicillin) • Monobactams • Vancomycin - Glycopeptide topical • Cephalosporins • Bacitracin - bacterial origin; topical use • Isoniazid - tuberculosis • Ethambutol - tuberculosis

22. Antibiotics • Survey of Drugs - Protein Synthesis • Amyloglycosides (Streptomycin, neomycin Gentamicin) • Tetracyclines - Bacteriostatic • Chloramphenicol • Macrolides - Erythromycin - Bacteriostatic

24. Antibiotics • Survey of Drugs - Plasma Membrane • Polymyxin B - topical; works against G-

25. Antibiotics • Survey of Drugs - Nucleic Acids • Rifampin • Quinolones • Fluorquinolones

26. Antibiotics • Survey of Drugs - Essential Metabolites • Sulfonamides