Association of toxin-producing Clostridioides difficile with piglet diarrhea and potential transmission to humans.

The pathogenicity of Clostridioides difficile in piglets remains controversial. It is unknown whether C. difficile control helps protect piglet health. To clarify the association between C. difficile presence and piglet diarrhea, isolates were obtained from piglets with and without diarrhea. In addition, to determine the genetic relationship of C. difficile from pigs and humans, we performed whole-genome sequencing (WGS) of C. difficile isolates. Diarrheal and non-diarrheal stool samples were collected from neonatal piglets from five farms in Japan in 2021. To clarify the relationship between C. difficile derived from pigs and those from human clinical cases, WGS of C. difficile isolates was performed. Toxin-positive C. difficile were significantly more prevalent in piglets with diarrhea, although the overall frequency of C. difficile did not differ between piglets with and without diarrhea. This observation indicates an association between toxin-positive C. difficile and diarrhea in piglets. However, further studies are needed to establish a direct causal relationship and to explore other contributing factors to diarrhea in piglets. WGS results showed that C. difficile sequence type (ST) 11 including the hypervirulent PCR ribotype 078 isolates derived from Japanese pigs were closely related to ST11 of overseas strains (human clinical and animal-derived) and a Japanese human clinical strain. Toxin-positive C. difficile may cause diarrhea in piglets and hypervirulent C. difficile are spreading among pigs and human populations worldwide.