Characterisation of Dichelobacter nodosus isolates from Norway

An outbreak of ovine footrot in Norway in 2008, the first reported since 1948, prompted action to investigate Norwegian isolates of Dichelobacter nodosus. A total of 579 isolates from 124 different farms were characterised. These included 519 isolates from sheep, 52 isolates from cattle and 8 isolates from goats. The potential virulence of the isolates was assessed by the gelatin gel test (GG-test) and the elastin agar test, that test the heat stability and elastase activity of bacterial proteases, respectively. The isolates were also tested for the presence of intA by PCR, and allocated to serogroups by differentiation of fimA variants using multiplex PCR or sequencing. Thirty of the isolates were also serogrouped by slide agglutination. Three hundred and five isolates were defined as virulent by the GG-test. All these were from sheep from 52 farms located in the county of Rogaland in the south west of Norway. All isolates from cattle and goats were defined as benign by the GG-test. IntA was only detected in 6 (2.0%) of the virulent isolates. All serogroups except D and F were detected. Three hundred and seventy-two (64.3%) of the isolates belonged to serogroup A, and 96% of the virulent isolates belonged to this serogroup. On the grounds that virulent isolates were only found in one county, and that the majority belonged to the same serogroup (A), it is believed that a virulent D. nodosus strain was introduced to Norway relatively recently and that so far it has only spread locally.