Enterotoxigenic Escherichia coli as a modulator of the entero-pulmonary axis in piglets : impacts on the microbiota and immune responses

The high prevalence of enterotoxigenic Escherichia coli (ETEC) in nondiarrheic piglets contributes to its rapid spread; however, few studies have explored the effects of latent gastrointestinal pathogens on animal health. Therefore, using high-throughput sequencing approaches, we explored changes in entero-pulmonary microbiota and immune gene expression in healthy, asymptomatic, and diarrheic piglets. As expected, bacterial communities were less diverse in the respiratory tract than in the gut, with a site-specific composition that was more stable in the gut and highly variable in the lung among the investigated animals. Although no significant changes in diversity rates were seen based on ETEC-carrier state, our findings suggest that ETEC’s presence can cause dysbiosis in the gut and lung in asymptomatic and diarrheic piglets, reinforcing the crosstalk in the entero-pulmonary axis. We also identified potential bacterial biomarkers that can be used to monitor piglet health: Sphaerochaeta, Bacteroides, Butyricoccus, and Blautia were highly represented in the gut, while Streptococcus and Prevotellaceae NK3B31 group were enriched in the lungs of healthy piglets. In addition, most metabolic pathways predicted in the bacterial communities were shared despite the ETEC-carrier state, with differences observed only in the gut microbiota, suggesting that ETEC’s presence may impact substrate utilization. Finally, we observed shifts in the intestinal expression of tff2 and cd36 immune markers between healthy and diarrheic piglets, which might suggest their use as prognostic markers for postweaning diarrhea (PWD). Although the effect remains unclear, the ETEC-carrier state also altered the transcription of other markers locally (in the gut and lung) and systemically, which corroborates the shared mucosal immunity in the entero-pulmonary axis in piglets. Overall, despite limitations regarding sample size, our findings give clues about the entero-pulmonary dynamics in piglets in the presence of a gastrointestinal pathogen, representing a starting point for future research on this axis for veterinary purposes.