Profiling bacterial communities in feedlot cattle affected with bovine foot rot and bovine digital dermatitis lesions using 16S rRNA gene sequencing and quantitative real-time PCR.

Background: The primary infectious foot diseases in cattle, bovine foot rot (BFR) and bovine digital dermatitis (BDD), commonly associated with Fusobacterium necrophorum and Treponema spp., respectively, are considered polybacterial in etiology with several additional bacteria involved such as Porphyromonas levii, Bacteroides pyogenes, and Fusobacterium mortiferum. BDD is further classified into several M-stages (M2: active and ulcerative; M4: chronic proliferative). Using quantitative real-time PCR and 16S rRNA gene (V3-V4 region) sequencing, we quantified several specific bacteria and analyzed bacterial communities present in biopsies of visually diagnosed cases of BFR (n = 32), M2 (n = 17), and M4 (n = 12) stages of BDD in feedlot cattle in contrast to inconclusive (n = 14) clinical cases and healthy (n = 25) cattle.

Results: Bacterial composition of healthy skin differed significantly from that of skin lesions, and between BFR and both lesion stages of BDD, which also differed from each other. All animal groups had generally the same bacterial species, albeit in distinct ratios. Differential abundance analysis relative to the healthy group identified a higher abundance of Fusobacterium spp. in BFR and Treponema spp. in both BDD-M2 and BDD-M4. P. levii had the highest absolute abundance in all animal groups. A significantly higher abundance of F. necrophorum was observed in BFR compared to BDD-M2, and F. mortiferum in both stages of BDD compared to the inconclusive group. Both BDD M-stages had a significantly higher abundance of Treponema phagedenis and Treponema pedis. Treponema medium was significantly more abundant in BDD-M4 compared to BDD-M2.

Conclusion: These results further the evidence of the involvement of Treponema spp., in BDD in feedlot cattle. However, it suggests further exploration of the role of Fusobacterium spp. in BFR and BDD. Importantly, a discriminating polybacterial involvement in these infections was evident demonstrated by changes in the population of multiple bacteria when compared to healthy animals.