Occurrence of different strains of Dichelobacter nodosus in new clinical lesions in sheep exposed to footrot associated with multi-strain infections.
OBJECTIVE
To investigate the occurrence of S1, U1 and T strains of Dichelobacter nodosus in new clinical lesions in sheep exposed to footrot associated with multi-strain infections.


METHODS
Seventy-seven donor sheep were grazed with 84 recipients for 33 weeks. The donor sheep were Merinos with a history of clinically virulent footrot associated with protease type S1, U1 and T strains of D nodosus that hybridised with gene sequences pJIR314B, pJIR318 and/or pB645-335. The recipient sheep were Merinos with no history of footrot.


METHODS
Each fortnight, all feet were examined, their lesion scores were recorded and samples of lesion material were taken for laboratory tests.


RESULTS
Eighty-nine percent (299 of 336) of feet of recipient sheep developed new clinical lesions. S1, U1 and T strains of D nodosus were recovered from 58%, 22% and 18%, respectively, of these lesions at a ratio that remained constant during two apparent peaks in footrot transmission. Gene sequences homologous to pJIR314B and pB645-335 were detected in 56% (93 of 166) and 29% (48 of 166), respectively, of S1 strains of D nodosus at a ratio that was not constant during the experiment.


CONCLUSIONS
S1 was the dominant protease type of D nodosus in new clinical lesions. The occurrence of S1 strains did not increase relative to U1 and T strains of D nodosus during the experiment. S1, U1 and T strains of D nodosus remained in equilibrium despite changes in environment, genetic types in the population of S1 strains, and host resistance to footrot.
Jelinek
P D
PD
Agriculture Western Australia, Bunbury, Western Australia.
Depiazzi
L J
LJ
Galvin
D A
DA
Spicer
I T
IT
Palmer
M A
MA
Pitman
D R
DR
D000818:Animals; D020376:Dichelobacter nodosus / Q000145:classification* / Q000235:genetics; D005260:Female; D005535:Foot Rot / Q000453:epidemiology / Q000382:microbiology* / Q000635:transmission; D016905:Gram-Negative Bacterial Infections / Q000453:epidemiology / Q000635:transmission / Q000662:veterinary*; D008297:Male; D016133:Polymerase Chain Reaction / Q000662:veterinary; D012756:Sheep; D012757:Sheep Diseases / Q000453:epidemiology / Q000382:microbiology* / Q000635:transmission; D014904:Western Australia / Q000453:epidemiology