# Veterinary method evaluation of Vitek-2 compact for antimicrobial susceptibility testing of Staphylococcus spp. and Enterococcus spp

## TL;DR

This study evaluates the Vitek-2 Compact for testing antibiotic resistance in Staphylococcus and Enterococcus bacteria in veterinary medicine, finding it mostly reliable but with some limitations.

## Contribution

The study provides a veterinary-specific evaluation of the Vitek-2 Compact, demonstrating its scalability and utility for antimicrobial susceptibility testing in a One Health context.

## Key findings

- The Vitek-2 Compact showed acceptable overall performance with ≥94% agreement across species.
- Minocycline and clindamycin testing had issues, requiring confirmatory methods or updates.
- Updated antimicrobial offerings and dilution ranges are needed for better test accuracy and quality control.

## Abstract

Quality laboratory data are central to antimicrobial resistance detection in support of good patient care and for use in a One Health surveillance system. Here, we evaluated the Vitek-2 Compact AST-GP81 cards against Sensititre COMGP1F broth microdilution panels. A total of 51 Staphylococcus spp. not aureus/lugdunensis; 30 Staphylococcus aureus and Staphylococcus lugdunensis; and 34 Enterococcus spp. were selected for testing. Overall performance of the Vitek-2 Compact was acceptable, with at least 96% essential agreement and 94% categorical agreement across organism groups, exceeding the minimum performance goal of ≥90% agreement; however, several antimicrobials did not meet minimum performance standards. For Staphylococcus spp. not aureus/lugdunsis, minocycline failed entirely, precluding patient reporting and clindamycin required offline confirmatory testing. We observed unacceptable rates of minor errors if Staphylococcus cephalosporin breakpoints were used, whereas a surrogate agent produced consistent results between methods. Notably, we reaffirm that it is necessary to confirm any susceptible Staphylococcus pseudintermedius penicillin results with an induced nitrocefin β-lactamase test, especially if Sensititre COMPGP1F panels are used. Both test panels require updated antimicrobial offerings and dilution ranges to ensure a full range of test results can be reported. These updates should include consideration for test ranges that allow for on-scale quality control testing and translation across One Health sectors. Because antimicrobial susceptibility test results impact far more than single patient care in veterinary medicine, including human, herd, and environmental health, we advocate for the use of stringent antimicrobial susceptibility test method evaluation procedures in veterinary laboratories.

Antimicrobial resistance is a critical threat to human and animal health globally. While our patient populations are different, we are connected by our shared environments and intertwined existence. As such, our antimicrobial susceptibility testing diagnostic and surveillance tools, as well as methods to evaluate their performance, should be uniform and capable of detecting critical antimicrobial resistance mechanisms. We evaluated the Vitek-2 Compact against our legacy Sensititre system and determined that accurate patient results and quality surveillance data could be produced using the Vitek-2 Compact. We used the evaluation method described in the Clinical Microbiology Procedures Handbook to demonstrate the utility of this method to peer veterinary laboratories. This publication importantly demonstrates that this evaluation procedure is scalable for veterinary applications. Furthermore, there is a need for updates to veterinary test panels as well as investments in and advancement of veterinary diagnostic tools, in support of a One Health approach to antimicrobial resistance detection.