Association of unique, isolated treponemes with bovine digital dermatitis lesions

This study used a PCR-based approach targeting 16S rRNA gene fragments to determine the occurrence and association of the three bovine digital dermatitis (BDD) treponeme phylogroups within lesions found in cattle from the United Kingdom. Examination of 51 BDD lesions collected from infected cattle across the United Kingdom revealed that BDD treponeme group 1 (Treponema medium/Treponema vincentii-like), group 2 (Treponema phagedenis-like), and group 3 (Treponema putidum/Treponema denticola-like) were present in 96.1%, 98%, and 76.5% of BDD lesions, respectively. The three phylogroups were present together in 74.5% of lesions. The PCR assays enabled the isolation of further treponeme strains from previously mixed primary BDD lesion cultures. Here a representative from each of the three distinct treponeme phylogroups was isolated from a single BDD lesion for the first time. These data highlight the extent to which this disease is polytreponemal. Immunohistochemistry and electron microscopy were used to investigate lesional hoof tissues, resulting in treponemes being identified copiously in hair follicles and sebaceous glands, suggesting a potential route of exit and/or entry for these pathogens. This study gives further evidence for the importance of the three treponeme groups in BDD pathogenesis and reiterates the value of molecular genetic approaches for isolating and identifying fastidious anaerobes.