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 organic dye, mauveine, was
  discovered by William Henry Perkin in 1856 while
  he was attempting to synthesize quinine.

4
(No Transcript)
5
Antibiotics

• 1928 Fleming discovers penicillin and isolates
  a crude form of the chemical
• 1930s - 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

13
(No Transcript)
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 RNAs and DNAs
  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

21
(No Transcript)
22
Antibiotics

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

23
(No Transcript)
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