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Test Methods in Detecting Antimicrobial Resistance

There are several antimicrobial susceptibility testing methods available today, and each one has their respective advantages and disadvantages. They all have one and the same goal, which is to provide a reliable prediction of whether an infection caused by  a bacterial isolate will respond therapeutically to a particular antibiotict reatment. This data may be utilized as guidelines for chemotherapy, or at the population level as indicators of emergence and spread of resistance based on passive or active surveillance.  Some examples of antibiotic sensitivity tesing methods are:

  • Dilution method (broth and agar dilution method)
  • Disk-diffusion method
  • E-test
  • Automated methods
  • Mechanism-specific tests such as beta-lactamase detection test and chromogenic cephalosporin test
  • Genotypic methods such as PCR and DNA hybridization methods

Selection of  the appropriate method will depend on the intended degree of accuracy, convenience, urgency, availability of resources, availability of technical expertise and cost..    Interpretation should be based on veterinary standards whenever possible, rather than on human medical standards, which may not always be applicable.   Among these available tests, the two most commonly used methods in veterinary laboratories are the agar disk-diffusion method and the broth microdilution method.  



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Organizations Publishing



United States: Clinical and Laboratory Standards institute (CLSI; formerly NCCLS)


European Union: European Committee of Antimicrobial Susceptibility Testing (EUCAST)


European Union: Office International des Èpizooties (OIE)


United Kingdom: British Society for Antimicrobial Chemotherapy


Germany: Deutsches Institut für Normung  


France: Société Française de Microbiologie


Sweden: Swedish Reference Group for antibiotics


Australia: CDS disk diffusion method