scope:

This guideline provides veterinary and aquatic animal disease diagnostic laboratories with currently recommended antimicrobial broth dilution and disk diffusion susceptibility testing methods for nonfastidious bacteria isolated from aquatic animals, including criteria for QC testing with two QC strains. It also provides suggestions as to the testing conditions for other fastidious aquatic animal bacterial pathogens. To avoid confusion, organisms relevant to aquaculture have been grouped (ie, Groups 1 through 5), and the organisms in each group and their corresponding numbers have not changed from previous editions of this guideline. This guideline also provides appendixes and tables describing media and disk preparation, methods for preparing stock solutions and dilutions of antimicrobial agents, and antimicrobial agents used in global aquaculture.

Clinical breakpoints and epidemiological cutoff values (ECVs) are included in VET04.¹ Clinical breakpoints must be established using pharmacokinetic (PK) and pharmacodynamic (PD) data, in vitro antimicrobial susceptibility testing (AST) data, and clinical efficacy data. ECVs can be established from susceptibility data distributions alone. For information on how to develop these interpretive categories, consult CLSI document VET02.¹⁰ As more aquatic animal-specific information becomes available, this guideline and VET04¹ will be updated accordingly.

This guideline and its supplement (VET04¹) are not intended to guide the use of antimicrobial agents that are used for disease prevention or production uses.

¹ CLSI. Performance Standards for Antimicrobial Susceptibility Testing of Bacteria Isolated From Aquatic Animals. 3rd ed. CLSI supplement VET04. Wayne, PA: Clinical and Laboratory Standards Institute; 2020.

¹⁰ CLSI. Development of In Vitro Susceptibility Testing Criteria and Quality Control Parameters for Veterinary Antimicrobial Agents; Approved Guideline-Third Edition. CLSI document VET02-A3. Wayne, PA: Clinical and Laboratory Standards Institute; 2008.