Non-specificity of primers used for PCR based serogrouping of Dichelobacter nodosus and identification of a novel D. nodosus strain

• Study records the first case of non-specificity of typing primers developed by Dhungyel et al. (2002).
• Identification of a novel strain which may qualify for a new serotype G3 within serogroup G of Dichelobacter nodosus.
• Indicates the evolution of new serotypes of D. nodosus with serious diagnostic and prophylactic consequences.

The present study records the first case of non-specificity of typing primers developed by Dhungyel et al. [1]. A strain of Dichelobacter nodosus (JKS-20G) isolated from ovine footrot in Kashmir, India, showed specificity for serogroup C and G primers. The fimA sequence of the strain turned out to be closer to serogroup G than C. The nucleotide sequence showed maximum homology of 92% with that of serotype G1 strain 238 and 95% with partial sequence available for serotype G2 strain VCS 1004. However, the deduced amino acid sequence of the fimbrial subunit gene of JKS-20G differed from strain 238 by 16 amino acids and by four amino acids from that of partial sequence of strain VCS 1004. This variation indicates towards declaring this isolate as a new serotype (G3) but just insufficient to classify this into a new serogroup. Some of the amino acid substitutions were located within three hypervariable regions a characteristic of different serogroups. However, to ascertain whether this isolate deserves a new serotype status, there is a need to go for antigenic characterisation of this isolate using the tube and cross tube agglutination test.