Download Bacterial Classification

Control of Bacterial Growth
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Antibiotics / Chemotherapy
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History
Properties
Testing
Spectrum of Antimicrobial Action
Modes of Action
Survey of Drugs
Antibiotics
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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
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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 organic dye, mauveine, was discovered by
William Henry Perkin in 1856 while he was attempting to
synthesize quinine.
Antibiotics
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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
Antibiotics
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Properties
– Selective toxicity (e.g. sulfanilamide
mimics PABA in folic acid synthesis)
– Sources
» Microorganisms
» Synthetic agents
» Plants
Antibiotics
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Testing
– Broth dilution
– Agar dilution
– Disc diffusion
Antibiotics
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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
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Agar dilution
– Dilute drug into agar at varying
concentrations
– Can test multiple species of bacteria
– Not very quantitative
Antibiotics
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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
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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
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Modes of Action
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Bactericidal vs. Bacteriostatic
Cell Wall
Protein Synthesis
Plasma membrane
Nucleic Acid Synthesis
Essential Metabolites
Antibiotics
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Bactericidal vs. Bacteriostatic
– Bactericidal - kills
– Bacteriostatic - inhibits growth but once
removed growth can resume
Antibiotics
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Inhibition of Cell Wall Synthesis
– Uniqueness of bacterial cell wall
– Prevent peptidoglycan synthesis or peptide
cross-linking from forming
– Penicillins & cephalosporins
Antibiotics
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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
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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
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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
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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
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Survey of Drugs - Cell Wall Synthesis
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Penicillins (G, V)
Semisynthetic penicillins (Ampicillin)
Monobactams
Vancomycin - Glycopeptide topical
Cephalosporins
Bacitracin - bacterial origin; topical use
Isoniazid - tuberculosis
Ethambutol - tuberculosis
Antibiotics
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Survey of Drugs - Protein Synthesis
– Amyloglycosides (Streptomycin, neomycin
Gentamicin)
– Tetracyclines - Bacteriostatic
– Chloramphenicol
– Macrolides - Erythromycin - Bacteriostatic
Antibiotics
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Survey of Drugs - Plasma Membrane
– Polymyxin B - topical; works against G-
Antibiotics
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Survey of Drugs - Nucleic Acids
– Rifampin
– Quinolones
– Fluorquinolones
Antibiotics
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Survey of Drugs - Essential Metabolites
– Sulfonamides