Fecal Pathogenic Bacteria Composition and Community Assembly Mechanisms in Captive Brown Bears and Asiatic Black Bears

Asian black bears (Ursus thibetanus) and brown bears (Ursus arctos) are commonly kept in captivity in zoos, where captive conditions may alter fecal pathogenic bacterial communities and affect host health, although systematic studies remain limited. This study used 16S rRNA sequencing to characterize the composition, diversity, and community assembly mechanisms of fecal pathogenic bacteria in captive brown bears and black bears. Brown bear samples clustered relatively closely, whereas black bear samples were more dispersed, with juveniles and adults clearly separated; the Shannon index of adult black bears was significantly higher than that of brown bears (p < 0.001). Animal pathogenic bacteria (3.37–80.30%) and zoonotic potentially pathogenic bacterial taxa (18.00–96.60%) were the dominant types in both species, with Escherichia coli showing the highest abundance in most samples, and zoonotic potentially pathogenic taxa abundance was higher in adults (83.67%) than in juveniles (74.77%). These findings indicate that captivity and host age shape fecal MBPD-annotated potentially pathogenic bacterial communities in ursids, with enrichment of MBPD-annotated zoonotic potentially pathogenic taxa, including E. coli–assigned sequences, providing a scientific basis for health management of captive bears and potential public health risk assessment.