Microbiology of causative bacteria of Bovine Digital Dermatitis

Bovine digital dermatitis (BDD) is an infectious foot disease in cattle which was first reported in Italy in 1974 and is now recognized throughout the world. In Japan, BDD in dairy cattle is now found in most regions since the first case was reported in 1992. BDD begins as a superficial dermatitis with an erosive lesion and later forms a hyperkeratotic papillomatous lesion with long hair-like projections. These lesions are usually located on the rear of the foot between the bulbs of the heel. BDD often leads to lameness and decreases in body weight and milk production, causing economic loss and animal welfare problems. 

It is suspected that BDD is caused by bacteria, since treatment with antibiotics such as oxytetracycline and penicillin G results in rapid resolution of the lesions. Microscopic examinations of biopsies or direct stamp preparations of the lesions show various bacterial morphotypes, including long filaments, rods, coccoids, and helices. Although several culturable bacteria have been isolated from BDD lesions, it remains unclear whether all are involved in the etiology. 

Among the bacteria detected in BDD lesions, a large number of spirochetes are observed. Choi et al. detected five spirochetal phylotypes using 16S rRNA gene sequence analysis. Similarly, Moter et al. detected four spirochetal phylotypes by using in situ hybridization with oligonucleotide probes of the 16S rRNA gene from treponemes. Indeed, several Treponema species have been isolated from dairy cattle with BDD, and are closely related to oral Treponema species in humans, including T. phagedenis, T. denticola, T. vincentii, and T. medium. Furthermore, Schrank et al. isolated and characterized the newly proposed species Treponema brennaborense. These reports suggest that multiple Treponema species are present in BDD lesions. Their presence in both superficial lesions and deeper layers of the dermis suggests that they play an important role in the infection. However, it has not been proved that these organisms satisfy Koch’s postulates. […]