Footrot is a complex endemic infectious disease of sheep feet. Virulent D. nodosus, the causative agent, is essential for the progression of the initial inflammation and the separation of skin from the hoof capsule. A range of different bacterial genera have been identified in the interdigital skin that may also play a role in the disease. Very little information is available on the host response in footrot.
We used post slaughter biopsies of the interdigital space from footrot affected and matched healthy feet. Using metatranscriptomics enabled quantification of the transcriptional differences of the host during a natural footrot infection and identify the bacterial species present within the tissue.
Initial assessment of the taxonomic diversity agrees with control metagenomic sequencing of swabs taken in conjunction with tissue collection, indicating a robust and reproducible approach to assessing the in-tissue bacterial population. As expected, the causative agent of footrot, Dichelobacter nodosus was significantly more abundant in footrot samples. In addition, in footrot affected samples, the abundance of Mycoplasma fermentans, Porphyromonas spp, Corynebacterium aurimucosum and Treponema_spp were significant increased, suggesting a role for these bacteria in the infection.
Most differentially expressed genes in footrot affected feet are associated with an increase in transcripts associated with the wound healing (metalloproteases and their regulators) and inflammation. This is accompanied by a decrease in transcripts associated with skin barrier functions (collagen turnover, long chain fatty acid synthesis) and immunesurveillance.
In conclusion metatranscriptomics allows a comprehensive analysis not only of the host response but also identification of in tissue microbial community to species level.