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Title:
Diversity and Evolution of Dichelobacter nodosus, the Causative Agent of Footrot
in Sheep
Authors & affiliations:
E. Smith1*, C. Russell2, L. Calvo-Bado1, L. Green1, E. Wellington1, G. Medley1, et al
1
School of Life Sciences, University of Warwick, England; 2Department of Clinical
Veterinary Sciences, University of Bristol, England
edward.smith@warwick.ac.uk
Abstract: (Your abstract must use Normal style and must fit in this box. Your abstract should be no
longer than 300 words. The box will ‘expand’ over 2 pages as you add text/diagrams into it.)
Dichelobacter nodosus, the causal agent of footrot in sheep is a Gram negative,
anaerobic bacterium. Current molecular and biochemical methods of characterising D.
nodosus include virulence testing and determining isolate serogroup. These tests
provide limited epidemiological information and more detail is required to further our
understanding of disease transmission and pathogen evolution. Multi-locus variable
number tandem repeat (VNTR) analysis (MLVA) involves the identification and
enumeration of polymorphic tandem repeats within the genome of a bacterium. The
aims of this study were to develop a D. nodosus MLVA typing scheme suitable for use
as a molecular typing tool, and apply this to analyse a collection of global isolates.
Four polymorphic VNTR regions (MLVA4) were identified in D. nodosus which, when
combined, had all the attributes required of a typing method for use as an
epidemiological tool: high discriminatory power (D>0.95), typeability and
reproducibility. Analysis of these regions allows the description of potential
evolutionary patterns and speculation on routes of global dissemination.
From the analysis we conclude that Dichelobacter nodosus has evolved through a
balance of recombination and clonal expansion events that define the clonal groups
present today. Stable, globally widespread, major clonal complexes, indicate a core of
D. nodosus MLVA types that are able to survive in a variety of environments; these are
augmented by clonal complexes with MLVA profiles specific to individual countries or
regions. Phylogenetic analyses support this finding as members of localised clonal
complexes form small clusters at the ends of branches rather than appearing around
major nodes (Fig. 1).
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Figure 1. D. nodosus minimum-spanning tree. Numbers indicate the MLVA type;
circle size is proportional to isolate numbers from Australia (green), GB (dark blue),
India (red), Norway (purple) and Sweden (light blue). Single, double and triple locus
variant relationships are represented by solid, dashed and dotted lines respectively.