From predisposition to recovery: field evidence of interactions between the gut microbiota and Brachyspira hyodysenteriae infection.

Restrictions on antibiotics use have increased interest in the gut microbiota relationship to host health, particularly in enteric infections. The present field study, performed on two farms with endemic swine dysentery (SD) infection, characterises the faecal microbiota in 102 faecal samples from 13 diseased and 13 non-diseased pigs by shotgun metagenomic sequencing. The samples were collected during four samplings, which allowed us to monitor the animals before, during and after the clinical disease to investigate the role of the gut microbiota in disease outcome, assess the impact of infection on microbial composition and evaluate the microbiota evolution following recovery. Samples collected before disease demonstrated that SD susceptible pigs had lower microbial diversity, with significantly lower abundance of Treponema rectale, Prevotella spp. or Ruminiclostridium E compared with SD resistant pigs, which remained healthy. Marked alterations in microbial species composition and their functional profiles were evident during clinical disease. Brachyspira hyodysenteriae, Dysosmobacter sp. BX15, Acetivibrio ethanolgignens and Mucispirillum sp. 910586745 were significantly increased in abundance, which was associated with an increase of functions such as Bacteroides capsular polysaccharide transcription antitermination proteins or pterin carbinolamine dehydratase. No changes in the microbiota were observed after the disease when compared with non-diseased pigs, thus evidencing a restoration of the microbiota composition after therapeutic treatment and recovery. The study demonstrates that the microbiota may play a relevant role in SD disease outcome and evidences the changes that occur during clinical disease do not persist over time after pig therapeutic treatment.