Download Controlling Microbial Growth in the Body

Controlling Microbial
Growth in the Body
Antimicrobial Drugs
Antimicrobial Drugs

History of Antimicrobial Agents
 Chemotherapy
 Paul
Ehrlich 1854-1915- Magic Bullets
 Alexander
Fleming 1881-1955- Antibiotics
Antimicrobial Drugs
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Mechanisms of Antimicrobial Action
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Selective Toxicity
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Drugs that Inhibit Cell Wall Synthesis
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Prevent synthesis of the polysaccharide, Peptidoglycan that
makes up the bacterial cell wall
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e.g. penicilins, cephalosporins, vancomycin
All penicillins consist of 3 parts

Thiazolidin
 Beta-lactams
 Variable side chain- group

Antimicrobial Drugs

Drugs that Inhibit Protein Synthesis

Differences in the ribosomes of prokaryotes and
eukaryotes
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Prokaryotes have 70S ribosomes and Eukaryotes have 80S
ribosomes
Drugs selectively targets bacterial protein synthesis without
significantly affecting eukaryotes
Examples of drugs include: tetracyclines and the
aminiglycosides such as streptomycin and gentamycin
Aminiglycosides are composed of amino sugars that change
the shape of 30S subunits of prokaryotic ribosomes
Antimicrobial Drugs

Disruption of Cytoplasmic Membranes
 Agent
becomes incorporated into prokaryotic
membranes and damage integrity
 E.g. Amphotericin B
Antimicrobial Drugs

Inhibition of Metabolic Pathways
 Metabolism
is sum total of all chemical
reactions within an organism
 Similarities and differences between
prokaryotic and eukaryotic cells
 Exploit differences
 e.g., Heavy Metals inactivate enzymes, certain
agents paralyze worms, and some prevent
attachment of viruses
Antimicrobial Drugs

Sulfonamides are structural analogs of
PABA (Para Amino Benzoic Acid)
 Paba
is crucial in synthesis of nucleotides
 Analogs of paba such as sulfonamides are
used to compete with paba.
Antimicrobial Drugs

Inhibition of Nucleic Acid Synthesis
 Nucleotide
Analogs
 e.g., Quinolones act against prokaryotic DNA
and Rifampin inhibit RNA Polymerases
Antimicrobial Drugs

Determining Efficacy of Drugs

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1. Diffusion Susceptibility Test
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Variety of Tests Used
Called Kirby-Bauer Test
Measure zone of Inhibition
2. Minimum Inhibitory Concentration (MIC)

Quantitative Expression of Drug Potency


Smallest amount of drug to inhibit growth and reproduction
of pathogen
Determined by Broth Dilution Test
Antimicrobial Drugs

Minimum Bacteriocidal Concentration
(MBC)
 Subculture
into drug-free media
 Growth- bacteriostatic
 No Growth- bacteriocidal
 Lowest concentration of drug for which no
growth occurs is MBC.