Abstract
Colonic contents and mucosal scrapings from pigs inoculated with Brachyspira hyodysenteriae or Brachyspira hampsonii were collected at necropsy and classified as either positive (n = 29) or negative (n = 7) for swine dysentery (SD) based upon lesions and positive culture from the source pig. The microbiota in each sample was analyzed by bacterial census taking (16S rRNA gene sequencing). Procrustes analysis revealed similar clustering by disease classification with a relatively high M2 value (0.44) suggesting differences in the microbiota between mucosal and luminal samples from the same pig. In both sample types, differences in richness and beta diversity were observed between disease statuses (P ≤ 0.014). The relative abundance of Brachyspirales, Campylobacterales, Desulfovibrionales, and Enterobacteriales was higher in pigs with dysentery for both mucosal scrapings and luminal samples while Clostridiales, Erysipelotrichales, and Fusobacteriales were significantly more abundant in the luminal contents only. For inoculated pigs that did not develop dysentery, Burkholderiales were more abundant in both sample types, Bacteroidales and Synergistales were more abundant in mucosal scrapings, and Lactobacillales and Bifidobacteriales were more abundant in luminal contents when compared with diseased pigs. Linear discriminant analysis of effect size revealed Brachyspira, Campylobacter, Mogibacterium, and multiple Desulfovibrio spp. as differential features in mucosal scrapings from pigs with dysentery while Lactobacillus and a Bifidobacterium spp. were differential in pigs without disease. These differential features were not observed in luminal samples. In summary, microbial profiles in both sample types differ significantly between disease states; however, evaluation of the mucosal microbiome specifically may be of higher value in elucidating bacterial mechanisms underlying development of SD.
Highlights
Swine dysentery (SD) is characterized by severe mucohemorrhagic diarrhea and is associated with infection by strongly beta-hemolytic strains of Brachyspira hyodysenteriae, Brachyspira hampsonii, and Brachyspira suanatina [1]
The relative abundance of Firmicutes was greater in the luminal samples of pigs with SD whereas Proteobacteria and Fusobacteria were more abundant in the mucosal scrapings of diseased pigs relative to those not developing disease (Figure 2)
The relative abundance of Brachyspirales, Campylobacterales, Desulfovibrionales, and Enterobacteriales was higher in pigs with SD for both mucosal scrapings (Figure 3) and luminal samples while Clostridiales, Erysipelotrichales, and Fusobacteriales were more abundant in the luminal contents only
Summary
Swine dysentery (SD) is characterized by severe mucohemorrhagic diarrhea and is associated with infection by strongly beta-hemolytic strains of Brachyspira hyodysenteriae, Brachyspira hampsonii, and Brachyspira suanatina [1]. While these spirochetes are required for disease expression, SD only develops in pigs when one or more specific anaerobes are present in the microbiota [2, 3]. In the case of SD, where there are profound changes in the colonic mucosa and where the etiologic agent can be readily visualized microscopically within the mucus layer, crypts, goblet cells, and epithelium [7], it seems logical to explore the microbiome directly associated with this biological niche in efforts to identify potential microbial biomarkers associated with disease susceptibility
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