Antimicrobial

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Antimicrobial Drugs
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Action of Antibiotics
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Discovery of Antibiotics

• Penicillin from Penicillium mold.
• Half of antibiotics come from genus Streptomyces.
• A few come from bacteria themselves (bacitracin,
  polymixin).

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Spectrum of Antibiotic Activity

• Spectrum- the range of susceptible organisms.
• Narrow spectrum- a few species or Genus.
• Broad spectrum - many organisms

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Action of Antibiotics
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Survey of Antibiotics

• Active against Cell Wall Synthesis
• Penicillins
• Natural (G, V)

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Survey of Antibiotics

• Penicillins
• Inhinbit cell wall peptide cross linking
• MOST effective with growing organisms.

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Survey of Antibiotics

• Penicillins
• Synthetic
• Extend spectrum
• Combat Antibiotic Resistance

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Survey of Antibiotics

• Penicillins
• Effective Dose - depends upon susceptibility of
  pathogen and concentration in tissues.

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Survey of Antibiotics

• Penicillin Resistance
• Penicillinase - PPNG
• Altered CW enzymes
• Antibiotic pumps

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Survey of Antibiotics

• Cephalosporins
• Resemble penicillin
• Resistant to penicillinase
• Many penicillin resistant pathogens are
  susceptible

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Survey of Antibiotics

• Bacitracin
• Made by B. subtilis
• Topical
• Bactericidal to Gram
• Vancomycin
• Used for resistant S. aureus
• Isoniazid
• Effective against M. tuberculosis
• Inhibits mycolic acid synthesis

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Inhibition of Protein Synthesis

• Aminoiglycosides
• Streptomycin
• Gentamicin
• Neomycin
• Active against Gram esp Pseudomonas
• Broad spectrum
• Bactericidal
• Binds to 30S subunit in ribosome and causes mRNA
  to be misread

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Inhibition of Protein Synthesis

• Tetracyclines
• made by Streptomyces
• Broad spectrum
• Gram and
• Bacteriostatic
• Penetrates tissues affects intracellular bacteria
  like Chlamydia, Mycoplasma
• Prevents t-RNA from binding

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Inhibition of Protein Synthesis

• Chloramphenicol
• made by Streptomyces
• Broad spectrum
• Gram and
• Bacteriostatic
• Serious side effects.
• Binds to 50S subunit inhibits peptide bond
  formation

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Inhibition of Protein Synthesis

• Macrolides
• made by Streptomyces
• Narrow spectrum
• Gram , Mycoplasma, T. pallidum
• Bacteriostatic
• Binds to 50S subunit prevents ribosome from
  moving

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Damage of Cell Membrane

• Polymixin B
• Bacillus polymyxa
• Narrow spectrum
• Pseudomonas
• Bacteriocidal
• Topical

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Inhibition of Transcription

• Rifamycins
• made by Streptomyces
• Narrow spectrum
• Mycobacteria
• Bacteriostatic
• Ability to penetrate neural tissues
• Inhibit mRNA synthesis (transcription)

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Inhibition of Replication

• Quinolones
• synthetic
• Broad spectrum
• Gram
• Bactericidal
• Binds to DNA gyrase
• prevents DNA from being copied.

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Inhibition of Metabolism

• Sulfonamides
• synthetic
• Broad spectrum
• Gram
• Bacteriostatic
• Similar to PABA, inhibits folic acid formation.

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Antifungal Drugs

• Polyenes
• Amphotericin B
• Toxic
• Imidazole
• Yeasts, Tinea
• Griseofulvin
• Binds to keratin
• Tolnaftate
• Tinea- athletes foot, ringworm

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Anti-Viral Drugs

• Nucleic acid analogs
• Acyclovir
• Substitutes for nucleic acid base - G
• Anti-Herpes
• AZT
• Anti-HIV

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Anti-Protozoan Drugs

• Quinine
• Anti-malarian
• Metronidazole
• Trichamonas vaginalis

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Measuring Effectiveness

• Diffusion Methods Kirby Bauer
• Zone of Inhibition
• MICs
• Broth Dilution Tests
• MBC

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Mechanism of Antibiotic Resistance

• Alteration of Receptors Mutation of bacterial
  DNA produces r-RNA that works, but no allosteric
  site for streptomycin or erythromycin, therefore
  no inhibition of translation
• Altration of membrane permeability Mutation in
  bacterial DNA changes character of receptor sites
  or pores, therefore entry way for antibiotic
  blocked

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Antibiotic Resistance in Bacteria

• Development of enzymes that destroy antibiotics
  Beta lactamases, plasmids containing genes for
  enzymes to destroy chloramphenicol and various
  aminoglycosides
• Alteration of bacterial enzymes that prevent
  competetive inhibition from occurring enzyme
  might be slightly altered to exclude
  antimetabolite and have high affinity for proper
  substrate. Therefore no competitive inhibition

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Antibiotic Resistance in Bacteria

• Alteration of a Bacterial Metabolic Pathway By
  pass a reaction that would be inhibited by an
  antimetabolite. Bacterial cell could become
  permeable to folic acid by passing blockage by
  Sulfanilamide and still produce nucleotides.

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