Identification of immunogenic proteins in Treponema phagedenis-like strain V1 from digital dermatitis lesions by phage display.

Digital dermatitis (DD) is a contagious claw disease causing lameness in cattle, affecting both animal welfare and economics. In this study, shotgun phage display was used to identify immunogenic proteins in a strain (V1) of the Treponema phylotype closely related to Treponema phagedenis, indicated as a key agent in the pathogenesis of DD. A genomic phage library was constructed and selected against antibodies from a rabbit immunized with live strain V1 bacteria. A homolog to the immunogenic protein TmpA of Treponema pallidum subsp. pallidum was identified, as well as a putative phage tail tape measure protein (Ttm), and a putative proline-rich repeat lipoprotein (PrrA). The complete amino acid sequences of these proteins were predicted from a genomic sequence of strain V1 generated by 454 Sequencing™. The presence of these genes in ten Treponema spp. field isolates was investigated by PCR. The tmpA and ttm genes were detected in all T. phagedenis-like isolates while prrA was detected in four out of seven. None of the genes were detected in the three Treponema pedis isolates investigated. Recombinant proteins were produced and used in indirect ELISAs. For all three proteins, a majority of serum samples from cattle with DD (n=8) showed higher optical density values than samples from cattle without DD (n=7).