Lab 8: Approach to Identification -

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Lab 8 Approach to Identification - API System
and Antimicrobial Susceptibility Testing
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Microorganism Identification
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Recall how many tests are done to identify Gram
Negative Rods (below). Wouldnt it be convenient
if there was a one-step system for all of these
tests?
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Rapid Identification Systems API 20E

• The API 20E system is a multiple test system
  allowing the determination of 20 different
  biochemical tests simultaneously.
• Most commonly used to identify gram-negative
  bacteria like E.coli, Salmonella, and Shigella.

See pgs 105-111
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Antimicrobial Susceptibility TestingThe
Kirby-Bauer Method

• Antimicrobial is a general term for something
  that inhibits or kills microbes.
• An antibiotic is a type of antimicrobial that is
  made by microbes to kill or inhibit other
  microbes.
• Very few antibiotics are effective against all
  types of bacteria (most are effective against
  either gram positive OR gram negative bacteria).

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Antimicrobial Susceptibility TestingThe
Kirby-Bauer Method

• Antibiotics are produced by metabolic reactions
  of bacteria and fungi.
• Most antibiotics produced come from 2 bacterial
  strains, Streptomyces and Bacillus, and the fungi
  Penicillium.

Penicillium
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Antimicrobial Susceptibility TestingThe
Kirby-Bauer Method

• This lab technique asks the question Which of
  these drugs stops the spread of this particular
  strain of bacteria?
• The procedure is designed to evaluate the
  susceptibility of a pathogen to assorted
  antibiotics.
• Disk diffusion test uses a Petri plate of agar
  (Mueller-Hinton) inoculated with bacteria over
  entire surface. Paper disks with standard
  concentration of antibiotic is placed on the
  agar.
• Zone of inhibition inhibition of bacterial
  growth around the antibiotic disk.

Zone of inhibition
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Antimicrobial Susceptibility TestingThe
Kirby-Bauer Method

• Minimum inhibitory concentration (MIC) the
  concentration of antibiotic at the edge of the
  disk zone of inhibition. MIC is determined by
  comparing the zone of inhibition to MIC standards
  in a table (pg 116).
• Susceptible zone size indicates antibiotic is
  effective for treatment.
• Intermediate zone size indicates antibiotic is
  moderately effective for treatment.
• Resistant zone size indicates antibiotic is
  ineffective for treatment.

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Antibiotic Susceptibility Test Part 1Pages
114-116
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Antibiotic Susceptibility Test Part 1
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Antibiotic Susceptibility Test Part 1
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Assignments for this week

• Lab Reports
• API PRE-LAB questions 1-3
• Kirby Bauer Lab chart and questions 1-4
• Lab Smart (reminder)
• Identification of Unknown Bacteria
• Available Oct 21st, Due Nov 17th

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Antibiotic Susceptibility Test Part 2
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Antibiotic Susceptibility Test Part 2
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Antibiotic Susceptibility Test Part 2