Chapter 3 : Antimicrobial Susceptibility Testing of Bacteria of Veterinary Origin

Abstract:

Antimicrobial susceptibility tests (ASTs) provide essential information that guides the veterinarian in selecting the most appropriate agent. In 1993 the National Committee for Clinical Laboratory Standards (NCCLS) formed the Subcommittee on Veterinary Antimicrobial Susceptibility Testing (V-AST) with the task of developing veterinary-specific AST standards. This group decided that rather than attempt to address all uses of antimicrobial agents in veterinary medicine, such as growth promotion, prophylaxis, and extralabel usage, it would limit its efforts to therapeutic uses in systemic diseases. The veterinary diagnostic laboratory can select from several different methodologies for antimicrobial susceptibility testing of veterinary pathogens, with most laboratories using either the agar disk diffusion method (ADD) or the broth microdilution MIC method. Regardless of the test method selected, the routine conduct of quality control (QC) testing is an essential component of the AST. In order for AST to be clinically relevant to the clinician, individual test results must be reported in an accurate, timely fashion. The development of test methods for additional veterinary pathogens such as Haemophilus parasuis from swine needs to be addressed, as well as the continued development of veterinary-specific interpretive criteria for older, generic agents. At present, a standardized method for susceptibility testing of Campylobacter spp. has been developed, but no interpretive criteria for these organisms or other enteric pathogens are available.