Identification of two new Dichelobacter nodosus strains in Germany

The multi-strain anaerobe Dichelobacter nodosus causes footrot, a contagious disease of the digits of ruminants that occurs worldwide. Eleven D. nodosus-like isolates from footrot lesions of sheep in Germany were investigated by PCR amplification of the variable region of the D. nodosus fimbrial (fimA) gene. In six isolates, fimA PCR amplicons of a size suggestive of D. nodosus were generated. Single-strand conformational polymorphism (SSCP) analysis of the amplicons revealed three banding patterns, the cloning and sequencing of which confirmed they represented three different strains of D. nodosus. One strain had a fimA sequence identical to D. nodosus isolate 265 of serotype H1, whilst the other two strains (Bde1 and Hde1) exhibited novel fimA sequences. The Bde1 strain was most similar to D. nodosus serotype B1 isolate AC127, with six nucleotide differences in the fimA gene and four amino acid substitutions at the protein level. However, strain Hde1 was quite different from known strains of D. nodosus having 15 nucleotide differences and a three nucleotide deletion in its fimA gene relative to its closest homologue, isolate 351 of serotype H2. This resulted in 12 amino acid differences and one amino acid deletion at the protein level which suggests that Hde1 represents a new D. nodosus serotype within serogroup H. The identification of novel strains may have implications for current vaccination strategies against the disease.