Performance Standards for Antimicrobial Disk and Dilution Susceptibility Tests for Bacteria Isolated From Animals; Approved Standard
|Publication Date:||1 February 2008|
This document provides veterinary diagnostic laboratories with currently recommended antimicrobial agent disk and dilution susceptibility test methods for bacteria isolated from animals; criteria for quality control (QC) testing; and interpretive criteria. The interpretive criteria are intended only to support therapeutic label claims for animal antimicrobial agent use and do not apply to label claims for disease prevention or performance enhancement. Additionally, the document provides a brief overview of the various antimicrobial classes and mechanisms of resistance to them, including specific tests for antimicrobial resistance.
In order to have a positive impact on clinical outcomes, help maintain antimicrobial effectiveness, assist clinicians in using antimicrobials safely, and minimize selection of resistant pathogens, laboratories must use a standardized, well-defined method for performing antimicrobial susceptibility testing (AST). A critical component of an AST method is the relationship between the test outcome and clinical outcome following treatment of the animal. In other words, an isolate yielding a susceptible AST result would be expected to respond clinically to that agent at the appropriate dosages while an AST result of resistant would imply that the treatment would fail. The purpose of the test method is not to mimic in vivo conditions; rather, it is to establish a method that provides reproducible results. Therefore, to ensure the generation of accurate, reproducible results when performing ASTs on veterinary pathogens, laboratories must adhere to a standard, well-defined method that includes the appropriate QC information. The M31- A3 document is predicated on providing AST methods that give accurate, reproducible, clinically relevant results for veterinary pathogens. It is important to consider that the judicious use of antimicrobials in the veterinary setting is directly related to the interpretive criteria associated with AST in that a given set of interpretive criteria only applies to that specific antimicrobial and disease combination. It is also important to note that the interpretive criteria in M31-A3 apply only if the laboratory has conducted susceptibility testing according to the specific methods found in the documents.
To date, an increasing number of antimicrobial agents have established veterinary-specific interpretive criteria. In most cases where veterinary-specific interpretive criteria are not established, human interpretive criteria are used when appropriate (see CLSI documents M2, M7, and M111-3). The veterinary-specific interpretive criteria have been established following M37, with particular attention given to product label indications and directions as approved by regulatory authorities. As more veterinary-specific information becomes available, changes in the listing of the agents will be incorporated into future revisions of this document and associated supplements. AST of bacteria from aquaculture environments has been advanced with the publication of two CLSI documents: M42 and M49.4,5