Antimicrobial Susceptibility Test of an Isolate from a Clinical Specimen



Diagnostic Microbiology In Action
  Microbiology of the Respiratory Tract
      Isolation and Identification of Staphylococci
      Staphylococci in the Normal Flora
    Streptococci, Pneumococci, and Enterococci
      Isolation and Identification of Streptococci
      The CAMP Test for Group B Streptococci
      Identification of Pneumococci
      Identification of Enterococci
      Streptococci in the Normal Flora
    Haemophilus, Corynebacteri and Bordetella
    Clinical Specimens from the Respiratory Tract
      Laboratory Diagnosis of a Sore Throat
      Laboratory Diagnosis of Bacterial Pneumonia
      Antimicrobial Susceptibility Test of an Isolate from a Clinical Specimen

Purpose To determine the antimicrobial susceptibility pattern of an organism isolated from a clinical
specimen (in Experiment 23.2)
Materials Nutrient agar plates (Mueller-Hinton if available)
Antimicrobial disks
Sterile swabs
Blood agar plate with pure culture of isolate
Tube of nutrient broth (5.0 ml)
McFarland No. 0.5 turbidity standard

  1. Using a sterile swab, take some of the growth of a pure culture you isolated from the clinical specimen in Experiment 23.2, and emulsify it in 5.0 ml of nutrient broth until the turbidity is equivalent to the McFarland 0.5 standard. Discard the swab.
  2. Take another sterile swab, dip it in the broth suspension, drain off excess fluid against the inner wall of the tube.
  3. Inoculate an agar plate as described in Experiment 15.1.
  4. Follow procedures 4 through 7 of Experiment 15.1.
  5. Incubate the agar plate at 35°C for 24 hours.
  6. Examine plates and record results for each antimicrobial disk as S (susceptible), I (intermediate), or R (resistant).
  7. Prepare a report for the “physician.”

Record results: