Genomic Analysis of Clostridioides difficile Recovered from Horses in Western Australia

Clostridioides difficile poses an ongoing threat as a cause of gastrointestinal disease in humans and animals. Traditionally considered a human healthcare-related disease, increases in community-associated C. difficile infection (CDI) and growing evidence of inter-species transmission suggest a wider perspective is required for CDI control. In horses, C. difficile is a major cause of diarrhoea and life-threatening colitis. This study aimed to better understand the epidemiology of CDI in Australian horses and provide insights into the relationships between horse, human and environmental strains. A total of 752 faecal samples from 387 Western Australian horses were collected. C. difficile was isolated from 104 (30.9%) horses without gastrointestinal signs and 19 (37.8%) with gastrointestinal signs. Of these, 68 (55.3%) harboured one or more toxigenic strains, including C. difficile PCR ribotypes (RTs) 012 (n = 14), 014/020 (n = 10) and 087 (n = 7), all prominent in human infection. Whole-genome analysis of 45 strains identified a phylogenetic cluster of 10 closely related C. difficile RT 012 strains of equine, human and environmental origin (0-62 SNP differences; average 23), indicating recent shared ancestry. Evidence of possible clonal inter-species transmission or common-source exposure was identified for a subgroup of three horse and one human isolates, highlighting the need for a One Health approach to C. difficile surveillance.