Control of Bacterial Growth l Antibiotics / Chemotherapy –History –Properties –Testing –Spectrum of Antimicrobial Action –Modes of Action –Survey of Drugs

Antibiotics l 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

Antibiotics l Peruvian Indians - treat fevers and reduce shivering with cinchona bark l Use " Peruvian bark" was first recorded by the Jesuits in 1633 l Countess Anna del Chinchón. was cured of the ague (a name for malaria the time) in 1638 l 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. l A formal chemical synthesis was accomplished in 1944 by American chemists Woodward and W.E. DoeringWoodwardW.E. Doering l 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. l Malaria resistant to synthetic but less so to natural l The first synthetic organic dye, mauveine, was discovered by William Henry Perkin in 1856 while he was attempting to synthesize quinine.organicdyemauveine William Henry Perkin

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

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

Antibiotics l Testing –Broth dilution –Agar dilution –Disc diffusion

Antibiotics l 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

Antibiotics l Agar dilution –Dilute drug into agar at varying concentrations –Can test multiple species of bacteria –Not very quantitative

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

Antibiotics l 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

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

Antibiotics l Bactericidal vs. Bacteriostatic –Bactericidal - kills –Bacteriostatic - inhibits growth but once removed growth can resume

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

Antibiotics l 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)

Antibiotics l 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)

Antibiotics l 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

Antibiotics l 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

Antibiotics l 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

Antibiotics l Survey of Drugs - Protein Synthesis –Amyloglycosides (Streptomycin, neomycin Gentamicin) –Tetracyclines - Bacteriostatic –Chloramphenicol –Macrolides - Erythromycin - Bacteriostatic

Antibiotics l Survey of Drugs - Plasma Membrane –Polymyxin B - topical; works against G-

Antibiotics l Survey of Drugs - Nucleic Acids –Rifampin –Quinolones –Fluorquinolones

Antibiotics l Survey of Drugs - Essential Metabolites –Sulfonamides