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Abstract:The re-emergence of swine dysentery (Brachyspira-associated muco-haemorrhagic colitis) since the late 2000s has illuminated diagnostic challenges associated with this genus. The methods used to detect, identify, and characterize Brachyspira from clinical samples have not been standardized, and laboratories frequently rely heavily on in-house techniques. Particularly concerning is the lack of standardized methods for determining and interpreting the antimicrobial susceptibility of Brachyspira spp. The integration of laboratory data into a treatment plan is a critical component of prudent antimicrobial usage. Therefore, the lack of standardized methods is an important limitation to the evidence-based use of antimicrobials. This review will focus on describing the methodological limitations and inconsistencies between current susceptibility testing schemes employed for Brachyspira, provide an overview of what we do know about the susceptibility of these organisms, and suggest future directions to improve and standardize diagnostic strategies.Key words: Brachyspira, susceptibility test, method standardization, veterinary diagnostics, swine dysentery.Résumé : La réémergence de la dysenterie porcine (colite muco-hémorragique associée à Brachyspira) depuis la fin des années 2000 a mis en lumière les défis diagnostiques associés à ce genre. Les méthodes utilisées pour détecter, identifier et caractériser Brachyspira à partir d'échantillons cliniques n'ont jamais été standardisées et les laboratoires dépendent fréquemment et fortement de méthodes maison. L'absence de méthodes standardisées pour déterminer et interpréter la susceptibilité antimicrobienne de Brachyspira spp. est particulièrement inquiétante. L'intégration de données expérimentales à un plan de traitement est une composante importante de l'utilisation avisée d'antimicrobiens, et l'absence de méthodes standardisées constitue conséquemment une limite importante à l'utilisation d'antimicrobiens fondée sur des données probantes. Cette synthèse se concentrera sur la description des limites méthodologiques et des incohérences actuelles qui existent entre les programmes de tests utilisés pour Brachyspira, fournira un exposé général de ce que les auteurs connaissent de la susceptibilité de ces organismes et suggérera des orientations afin d'améliorer et standardiser les stratégies diagnostiques. [Traduit par la Rédaction] Mots-clés : Brachyspira, test de susceptibilité, standardisation de méthodes, diagnostics vétérinaires, dysenterie porcine.

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Objective The Gram‐negative bacterium Actinobacillus suis is an agent of global importance to the swine industry and the cause of lethal respiratory or septicaemic disease in pigs of different ages. Between 2018 and 2019, seven commercial farms in western Canada experienced episodes of increased mortality due to A. suis infection in grower pigs. The goal of this work was to profile, with molecular methods, A. suis isolated from diseased pigs and to compare them to other isolates. Design This inferential observational study used nine western Canadian strains obtained from diseased lungs ( n = 6), heart ( n = 2) and brain ( n = 1) and whole genome sequencing was performed. Comparative genomic analyses were performed to characterise the genetic variability, antimicrobial resistance and the virulence genes present. Results Compared to the reference strain (ATCC 33415), an increased number of RTX (repeats in the structural toxin) gene copies were identified in strains isolated from organs without a mucosal surface, thus theoretically harder to invade. Western Canadian strains did not harbour genes associated with resistance to antimicrobial agents used in swine production. Novel regions were also identified in the genomes of five of nine strains demonstrating recombination and emergence of novel strains. Conclusions The results obtained in this study were associated with the emergence of new lineages. An increased number of RTX toxin gene copies is suggested to be associated with increased virulence. This study will contribute to improve our understanding regarding A. suis and may help guide vaccine development and agent control measures.