Part 5 – Antimicrobial susceptibility testing – Results reporting

Ðurđa Slavić

Animal Health Laboratory, University of Guelph, Guelph, ON

AHL Newsletter 2022;26(4):9

In the series of articles about antimicrobial susceptibility testing, AHL published information about test methods, selection of bacterial organisms, selection of antimicrobials for antimicrobial susceptibility testing (AST) and laboratory results interpretation.  In this fifth and the final article of this series, result reporting is discussed.  The full document is available on the AHL website as  LabNote 64: https://www.uoguelph.ca/ahl/ahl-labnote-64-antimicrobial-susceptibility-testing-ast

As per CLSI: “Veterinarians should understand that the presence of AST results for a drug on a laboratory report does not provide permission or the necessary justification for use of that drug. The presence of the drug on the panel does not indicate that it is legal or appropriate to use.” It is the responsibility of a veterinarian to use the drugs as per their label recommendations, as laboratories do not provide separate panels for different commodity groups (i.e., beef vs dairy), and sometimes, one antimicrobial panel is shared with different animal species (e.g. bovine/porcine panel).

If the drug is excluded from the report, it is likely that:

    1. The bacterial organism is intrinsically resistant to it and there is no need to perform AST (Table 1);
    2. There are no CLSI guidelines available for that particular organism/drug combination; or
    3. The drug is not approved for use in that food animal species.   AHL

Table 1. Examples of intrinsic resistance in Enterobacterales and Enterococcus spp.

Table 1. Examples of intrinsic resistance in Enterobacterales and Enterococcus spp.

References

1. CLSI. Performance standards for antimicrobial disk and dilution susceptibility tests for bacteria isolated from animals. 5th ed. CLSI supplement VET01S. Clinical and Laboratory Standard Institute; 2020.

2. CLSI. Understanding susceptibility test data as a component of antimicrobial stewardship in veterinary settings. 1st ed. CLSI report VET09. Clinical and Laboratory Standard Institute; 2019.

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