Publication Abstract

Yersinia ruckeri is a Gram-negative bacterium that causes enteric redmouth disease, which commonly infects farmed salmonid fishes often requiring antimicrobial treatment. Studies on antimicrobial susceptibility pattens of Y. ruckeri have found resistance to some antimicrobials but have lacked official criteria that provide consensus on identifying Y. ruckeri with decreased susceptibility. To address the need for criteria, called epidemiological cutoff values (ECVs), we gathered minimal inhibitory concentration testing data generated using the standard broth microdilution testing method published by the Clinical and Laboratory Standard Institute (CLSI) at 22 °C for 24-28 h and/or 44-48 h against nine antimicrobials. The dataset includes minimal inhibitory concentration data from up to 431 isolates from seven independent laboratories, which was analyzed with the program’s normalized resistance interpretation and ECOFFinder to compare mean, standard deviation, and coefficient of variation between the two timepoints for each antimicrobial and to calculate potential ECVs. The data was very similar between the timepoints which confirmed ECVs were only needed for the 24-28 h incubation. Potential ECVs for 8 of the 9 antimicrobials were proposed to CLSI’s Subcommittee on Veterinary Antimicrobial Susceptibility Testing, which voted to accept these values. These new ECVs will be included in the next edition of the VET04 supplement. The approved ECVs for ampicillin, enrofloxacin, florfenicol, gentamicin, oxolinic acid, oxytetracycline, ormetoprim/sulfadimethoxine and trimethoprim/sulfamethoxazole are ≤8, ≤0.03, ≤8, ≤2, ≤0.06, ≤0.25/4.8, and ≤0.5/9.5 µg/mL, respectively. Use of these new interpretive criteria with the standard test method will greatly improve antimicrobial resistance surveillance of this bacterium.

Charles Gieseker, Matthew Saab, Timothy Welch, Trevor Alexander, Kayleigh Carranza, Becca M. Wolking, Sandrine Baron, Andrew W. Joseph*, Edel Light, Athina Papadopoulou*, David Verner – Jeffreys, Amedeo Manfrin, Tina C. Crosby, Elliott Kittel, Peter Smith