Antimicrobial susceptibility
                      testing - methods
                                   nd
                                  2 seminar
   Methods for antimicrobial kvalitatívne 
   susceptibility testing 
   qvalitative
   • Disk diffusion method
   kvantitatívne
   • Dilution method 
   • E test
      Disk diffusion test (Kirby-Bauer Test)
    • wafers containing antibiotics are placed on an agar plate where 
     bacteria have been placed. Antibiotics defund to the agar plate and 
     inhibits bacterial growth.
    • If an antibiotic stops the bacteria from growing or kills the bacteria, 
     there will be an area around the wafer where the bacteria have not 
     grown enough to be visible. This is called a zone of inhibition.
    • More sensitive bacteria give larger zone of inhibition.
                                 c ATB
       Factors influencing susceptibility to antibiotics
       • Cultivation media composition – Mueller Hinton agar No 2 (standardized 
                      2+        2+
         content of Ca  and Mg )
       • Agar should have depth  4 mm. The surface of the agar should be dry 
         before use. No drops of water should be visible on the surface of the agar 
         or inside the lid. 
       • Density of inoculum is 0,5 McFarland for most species.
       • The suspension should optimally be used within 15 min1 and always within 
         60 min of preparation.
       • Plates can be inoculated either by swabbing in three directions or by using 
         an automatic plate rotator. 
       • Incubation 16-20 h (35-37 °C)