Serological diversity and virulence determination of Dichelobacter nodosus from footrot in India

One hundred and twenty-eight swab samples from footrot lesions of naturally infected sheep were examined for presence of Dichelobacter nodosus (D. nodosus). The detection of D. nodosus was carried out by polymerase chain reaction (PCR), directly from swabs or after isolation, using 16S rDNA specific primers. The isolation of the bacterium was carried out anaerobically on trypticase-arginine-serine (TAS) agar containing 4% hoof powder. Serogrouping of the D. nodosus was accomplished with multiplex PCR using nine (A-I) serogroup specific primers. The virulent and benign status of the isolates was ascertained by detection of virulence specific integrase A (intA) gene. Out of total 83 D. nodosus isolates, 62 (74.69%) belonged to serogroup B, 18 (21.68%) to serogroup E and three (3.62%) to serogroup I. Serogroup I was detected and isolated for the first time in India. All the positive samples revealed infection by single serogroup of D. nodosus except one which showed mixed infection of serogroups B and E. Sixty (72.28%) isolates possessed intA gene and thus were considered as virulent strains. Serogroupwise intA gene was found in 43 (69.35%) isolates of serogroup B, 14 (77.78%) of E and in all the three (100%) of I.