Antimicrobial Therapy

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Antimicrobial Therapy
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Sir Alexander Fleming(1881 1955)
One sometimes finds what one is not looking
forPenicillin
He observed inhibition of staphylococci on an
agar plate contaminated by a Penicillium mold
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Antimicrobial Therapy
Natural antibiotic agents Metabolic products
produced by microorganisms Penicillium notatum
penicillin Streptomyces spp.
streptomycin Semi-synthetic antibiotic agents
chemically modified natural agents (large group
of modern antibiotics) synthetic antibiotic
agents Chemically related to natural antibiotics
but completely industrially manufactured
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Antimicrobial Therapy
Criteria that determine the effectiveness of
antimicrobial agents

• selective destruction of the microorganism
• no or rare side effects on the host
• antimicrobial substances should have a specific
  action against molecules or enzymes or metabolism
  of the microorganism only

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Antibiotics and ChemotherapeuticsModes of Action
cell-wall
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Antibiotics Modes of Action
bacteriostatic
bactericidal
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Bacteriostatic vs. Bactericidal

• bacteriostatic - stop growth (don't kill)
• bactericidal kill cells

bacteriostatic
bacteriocidal
log viable count
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Disadvantages of Antimicrobial Therapy

• Allergic reactions
• Toxic effects on normal tissue
• Disturbs host normal flora secondary
  infections
• Development of resistant strains(producing
  enzymes that can destroy antibiotics resistance
  genes e.g. in plasmids, transferred from
• to one bacterial cell to the other,
  mutation of the target)

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Antibiotic Resistance

• innate (natural) resistance primary
  resistance, is based on a genetically caused
  insensitivity of a type of bacteria to a
• certain antibiotic e.g. inefficacy of
  penicillin to Ps. aeruginosa
• acquired resistance secondary resistance,
  after or during antibiotic treatment, activation
  of enzymes or genes

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Avoid disadvantages by

• avoiding indiscriminate use of antibiotics
• maintain proper levels
• for sufficient (prescribed) length of time
• use a combination of 2 or more antibiotics in
  severe infections to prevent resistance
  synergistic effects of the antibiotics
• perform antibiotic sensitivity test to determine
  the most effective antibiotics

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Antibiotic Sensitivity Test
Measurement of the sensitivity of microorganisms
to antibiotics and chemotherapeutics is of great
importance in the rational use of chemotherapy
Methods a) agar diffusion - Kirby-Bauer test (
disc test) - Etest ( strip test) b) broth
dilution
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Antibiotic Sensitivity Test
Kirby-Bauer Test (disc diffusion test)
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Antibiotic Sensitivity Test
Etest (strip test)
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Antibiotic Sensitivity TestBroth Dilution Method
antibiotic (dilution series)
bacterial suspension growth ?

(standard amount)
MIC minimal inhibitory concentration