Cercarial infection is associated with shifts in culturable gut bacterial communities of Bithynia siamensis goniomphalos.

This study investigated the diversity of culturable bacteria in the gut of Bithynia siamensis goniomphalos, the first intermediate host of trematode parasites. It examined the relationship between bacterial communities and trematode infection. Snails were collected from freshwater habitats in Udon Thani and Khon Kaen provinces, Thailand, and classified as infected or uninfected using the cercarial shedding method. A total of 132 bacterial isolates were obtained and identified based on 16S rRNA gene sequencing. Bacterial abundance differed significantly between the two groups, with higher counts observed in uninfected snails (2.06-8.60 × 103 CFU/ml) than in infected snails (1.06-1.60 × 103 CFU/ml) (p < 0.05). Bacterial composition also varied according to infection status. Bacterial isolates from infected snails were predominantly associated with Acinetobacter, Vogesella, and Stenotrophomonas, whereas Exiguobacterium spp. were mainly found in uninfected snails. Several taxa, including Bacillus spp., Chryseobacterium spp., and Micrococcus spp., were detected in both groups. These findings suggest that parasite infection is associated with shifts in both the abundance and composition of gut bacterial communities in B. siamensis goniomphalos. The results provide new insights into host-microbe-parasite interactions and may contribute to a better understanding of parasite transmission dynamics in freshwater ecosystems.