One Health genomic insights into environmental and animal reservoirs of community-associated in Japan.

is a well-recognized cause of antibiotic-associated colitis. The highly pathogenic PCR ribotype(RT)027/sequence type(ST)1 strain has been prevalent since 2002, particularly in Europe and the United States, whereas strains detected in Japan primarily comprise RT018/ST17, RT369/ST81, and RT002/ST8. Community-associated infection (CA-CDI) has increased in recent years, and an association with livestock, food, and companion animals has been suggested. This study investigated the molecular epidemiology of in Japan, focusing on isolates from diarrheal outpatients in comparison with animal and environmental sources. A total of 401 samples were collected, including park soil and fecal samples from livestock, companion animals, wild animals, and outpatients. Overall, 63 strains were isolated. High isolation rates were observed in soil samples (19/37, 51%) and companion animals (19/64, 30%), of which 68% and 37% were toxigenic, respectively. Whole-genome sequencing revealed ST2 as the most common sequence type, followed by ST42 and ST15. No single sequence type predominated among isolates from diarrheal outpatients, and six patients met the epidemiological definition of CA-CDI. Core-genome single-nucleotide polymorphism (SNP) analysis identified close genetic relationships in two pairs of ST42 strains-one between a patient-derived isolate and park soil, and another between a canine-derived isolate and soil from a different park-using a hypothetical transmission-exclusion cutoff of