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

Phylogenetic analysis of Dichelobacter nodosus serogroup-specific fimA gene from ovine footrot in Andhra Pradesh

Aim:

Identification of different serogroups of Dichelobacter nodosus prevailing in the region and to understand the degree of genetic heterogeneities among the different isolates of D. nodosus.

Materials and Methods:

A total of 150 exudate samples of footrot lesions with a lesion score of 2-4 were collected from naturally infected sheep. The samples were screened by polymerase chain reaction (PCR) targeting D. nodosus specific 16srRNA. Of 150 samples screened, 70 samples were found to be positive. The positive samples were attempted for isolation of D. nodosus, out of which 16 isolates were recovered. All the isolates were subjected to serogrouping by multiplex PCR targeting fimA gene using A-I serogroup specific primers.

Results:

Of 16 isolates, 7 (43.75%) isolates were serogroup B, 4 (25.00%) isolates were serogroup A, 3 isolates (18.75%) were serogroup I and 2 (12.5%) isolates yielded both serogroup A and B. phylogenetic analysis was performed using neighbor-joining algorithm of the ClustelX2 software in order to study whether the serogroups isolated in the present investigation differed genetically from other published serogroups. The fimA gene sequence of present isolates of serogroups A, B, and I were segregated into three distinct groups with high bootstrap values. The serogroup B clustered with Australian isolate of serotype B1 suggesting high genetic similarity of the present isolate with serotype B1.

Conclusions:

The clinical samples were collected from suspected outbreaks of footrot and identified the prevalence of D. nodosus by PCR targeting 16srRNA gene. Identified serogroups A, B, and I from different districts of Andhra Pradesh. The phylogenetic analysis will help for the tentative identification of serotypes present in the serogroup and to understand the degree of genetic heterogeneities among the different isolates of D. nodosus.