Antimicrobial Susceptibility Testing for Respiratory Pathogens in Large Animals

Antimicrobials are some of the most frequently used pharmaceutical agents in large animal practice. In recent years, the emergence of multi-drug (MDR) or extensively-drug resistant (XDR) strains of bacteria has limited the therapeutic choices available to practitioners. Furthermore, there is increased pressure on veterinarians to limit the use of certain antimicrobial agents in food-producing animals. Therefore, selection of the most appropriate antimicrobial agent for the purposes of disease prevention and treatment is essential to ensuring antimicrobial efficacy and availability. Antimicrobial susceptibility testing (AST) is a means by which veterinarians can obtain information that will guide them in selecting the most appropriate antimicrobial for a specific situation and is an essential component of antimicrobial stewardship programs. Unfortunately, the results of AST are often misunderstood and used in ways inconsistent with their intended clinical application. The purpose of this presentation is to familiarize veterinary practitioners with the terminology associated with AST, provide guidelines for the appropriate use of AST, and demonstrate how the results of testing might be applied to clinical practice, with a particular focus on food animals.