Clostridioides difficile is a Gram-positive, spore-forming anaerobic bacillus that has been recognized as an important enteropathogen in both humans and animals [1,2]. In humans, it can colonize and proliferate in the gut, especially in cases of an imbalance of the intestinal microbiota, such as the use of broad-spectrum antibiotics, which leads to diarrhea and pseudomembranous colitis [3]. Most pathogenic isolates of C. difficile are associated with three major toxins, TcdA, TcdB, and CDT, which are the main virulence factors and promote, among other things, detachment of the epithelial surface, extravasation of plasma proteins, and alteration of hydroelectrolytic transportation [4,5]. The consequence is an enteric disease known as Clostridioides difficile infection (CDI).

In humans, CDI was initially associated with the use of antibiotic therapy [6] in immunocompromised and hospitalized patients [3,7]. Nevertheless, the epidemiology of C. difficile has changed in recent decades, growing in the community environment with different risk factors in greater frequency and geographical locations not yet described [8,9]. This new pattern associated with genotypic similarity, sometimes indistinguishable, recovered from human and animal isolates suggests a zoonotic possibility [10]. The One Health concept raises concerns about transmission sources beyond the hospital environment, such as nature, food, and animals [11]. There are substantial community reservoirs and evidence of long-range interspecies transmission, probably linked to anthropomorphic factors such as intensive animal husbandry, increased travel, international trade, and indiscriminate use of antibiotics in farm animals [11]. Surveillance focused on the One Health concept of C. difficile from diverse human, animal, and environmental sources, and that considered the specificities of each geographic region, which is critical for developing a better understanding of the epidemiological and genetic factors that contribute to the emergence, evolution, and spread of C. difficile [12].

As for dogs, close contact should increase an even greater risk for transmission, especially if the pet stays indoors. Studies show different rates of isolation for C. difficile, ranging from 0 to 18% for diarrheal [1,2,[13], [14], [15]] and non-diarrheal dogs [8,[16], [17], [18], [19]], reaching 58% in association with specific groups, such as age [[20], [21], [22]] and contact with human or veterinary health facilities [[23], [24], [25], [26]]. Due to the presence of toxigenic C. difficile strains in asymptomatic animals and the failure to reproduce the CDI in healthy dogs with or without antibiotic treatment [27], the role of C. difficile in canine enteric disease remains unknown [28,29]. There have been some reports of toxigenic strains of C. difficile being associated with diarrhea in dogs [1,2,4,[13], [14], [15], [16],[30], [31], [32], [33]], including an outbreak in a veterinary hospital [34]. It is still unknown whether C. difficile represents an opportunistic pathogen or is simply a fortuitous finding in this animal species.

Few reports of C. difficile in dogs have been published in Brazil [15,19,35,36] and none have linked the pathological findings in positive animals to diarrheal disorders. The purpose of this study was to isolate and characterize the clinical, epidemiological and pathological findings associated with C. difficile strains in dogs with disorders with lower gastrointestinal tract in Rio de Janeiro. C. difficile were also characterized according to their ribotype, antimicrobial resistance pattern, biofilm production, and motility assay.