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International audience; Background: Clostridioides difficile is a sporulating anaerobe and a major entero-pathogen of both humans and animals. It produces toxins and is responsible for post-antibiotic diarrhoea and colitis that are difficult to treat and can be recurrent. In animals, the importance of C. difficile is not well evaluated. In cases of diarrhoea, its presence is not necessarily tested for. Moreover, diagnosis of C. difficile infection is difficult, because toxinogenic strains can be asymptomatically carried, if they do not produce toxins. They nevertheless remain able, after spread and transmission, to cause new, and notably community-acquired, infections. Objectives: The project aimed to i) build up and characterise a collection of C. difficile strains isolated from necropsied equidae, and ii) evaluate the frequency of C. difficile carriers in this whole equine population, together with its prevalence as a cause of infectious disease. Study design: Post-mortem survey Methods: The presence of C. difficile was systematically monitored in equideae that had been necropsied at Anses since 2019, whatever the cause of their death. Animal data (individual, clinical, epidemiological, cause of death) were registered and intestinal contents sampled to search for C. difficile. C. difficile strains were isolated and stored, forming the CloDifEqui collection. They were characterised by molecular genotyping and phenotyping. The intestinal contents of equideae displaying a toxinogenic strain were analysed for the presence of the toxins, in order to establish a diagnosis of infection. Results: Twenty strains were isolated in 80 necropsies. Conclusions: C difficile is prevalent in equine intestinal contents. Further work on molecular epidemiology and to compare these findings with the animal data is needed.

National audience; Clostridioides difficile est un entéro‐pathogène majeur, anaérobie et sporulant. Il provoque, par sestoxines, des diarrhées post‐antibiotiques difficiles à traiter et des récidives fréquentes dans lesquellesles biofilms pourraient jouer un rôle. Le portage asymptomatique de souches toxinogènes quin’expriment pas les gènes de toxines participe à leur persistence et leur virulence pourra s’exprimerchez un autre hôte. C. difficile pose un problème de santé humaine, à l’hôpital et dans la communauté,mais aussi vétérinaire. Chez les animaux qui peuvent disséminer des spores et contaminer l’homme,l’importance de C. difficile reste mal évaluée : sa recherche n’est pas systématique, et celle de sestoxines encore plus rare..Le projet CloDifEqui de l’Anses et l’INRAe, qui est financé notamment par l’Institut Français du Chevalet de l’Equitation, consiste à évaluer la fréquence de C. difficile chez les équidés autopsiés de 2019 à2021 à l’Anses quelle que soit la cause de la mort.A chaque autopsie, les données de l’animal (individuelles, cliniques, épidémiologiques) sontenregistrées et du contenu intestinal est prélèvé pour rechercher C. difficile. Les souches isoléesd’espèce confirmée constituent la collection CloDifEqui. Leurs principaux caractères génotypiques(gènes des toxines, ribotype …) et phénotypiques (sporulation, mobilité, résistance aux antibiotiques,formation de biofilm …) sont en cours d’étude et seront comparés à ceux de souches d’origine humaineou animale. En parallèle, un diagnostic d’infection est établi en collaboration avec le CNR C. difficile parla recherche des toxines dans les contenus intestinaux présentant C. difficile et provenant d’équidésavec des signes d’infection intestinale. Cela permettra d’établir la fréquence de C. difficile chez leséquidés, à la fois en cas d’infection et de portage asymptomatique. Les résultats de caractérisation dessouches seront croisés avec les données individuelles et cliniques des animaux autopsiés, notammentleurs traitements antibiotiques antérieurs éventuels.Après 80 autopsies, la collection CloDifEqui comprend 20 souches isolées d’animaux différents etcaractériéses. L’analyse croisée de l’ensemble des données et résultats est en cours. Le projet devraitcontribuer à mieux comprendre l’épidémiologie de C. difficile chez les équidés et à évaluer lacirculation des souches, leur potentiel de transmission zoonotique et de persistance.

The accurate identification of Taylorella equigenitalis strains is essential to improve worldwide prevention and control strategies for contagious equine metritis (CEM). This study compared 367 worldwide equine strains using multilocus sequence typing according to the geographical origin, isolation year and equine breed. The strains were divided into 49 sequence types (STs), including 10 described for the first time. Three major and three minor clonal complexes (CCs), and 11 singletons, were identified. The genetic heterogeneity was low (0.13 STs/strain) despite the wide diversity of geographical origins (n = 16), isolation years (1977-2018) and equine breeds (n = 18). It was highest outside Europe and in the 1977-1997 period; current major STs and CCs already existed before 1998. Previous data associated the major CC1 with the first CEM outbreaks in 1977-1978 in the United Kingdom, Australia and the United States, and revealed its circulation in France. Our study confirms its circulation in France over a longer period of time (1992-2018) and its distribution in Spain and Germany but not throughout Europe. In addition to CC1, relationships between non-European and European countries were observed only through ST4, ST17 and ST30. Within Europe, several STs emerged with cross-border circulation, in particular ST16 and ST46 from the major complexes CC2 and CC8. These results constitute a baseline for monitoring the spread of CEM outbreaks. A retrospective analysis of a higher number of strains isolated worldwide between 1977 and the early 2000s would be helpful to obtain an exhaustive picture of the original CEM situation.