Antimicrobial Susceptibility Testing Methods and Interpretation of Results

The veterinary diagnostic microbiology laboratory plays a key role in the practice of evidence-based antimicrobial therapy by providing culture and susceptibility information to practitioners. Susceptibility testing is vital for effective therapeutic decision making. In the clinical setting, the goal of antimicrobial susceptibility testing is to help clinicians choose the optimal antimicrobial therapy. Testing methods can be divided into two distinct categories: diffusion-based methods and dilution-based methods. In recent years, whole-genome sequencing has revolutionized microbiology with the ability to analyze bacterial isolates at the highest possible resolution, namely at deoxyribonucleic acid level. By considering the pharmacokinetic/pharmacodynamic properties of the antimicrobials in conjunction with interpretive reading of in vitro susceptibility test results, clinical success can be maximized. While categorical susceptibility data can provide vital information to clinicians, minimum inhibitory concentration data are superior for allowing pharmacokinetic principles to be applied directly.