Investigating the virulence of Treponema phagedenis strains isolated from digital dermatitis lesions in a murine abscess model
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2023-07
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Abstract
Digital Dermatitis (DD) is an ulcerative foot lesion in the heel bulbs of dairy cattle. DD is a polymicrobial disease with no precise etiology, although key pathogenic genera have been consistently found disproportional and abundant in diseased tissue as opposed to healthy skin. One such genera is Treponema, a member genus of the phylum Spirochaetes. Within Treponema, many different phylotypes are found in DD, however the species Treponema phagedenis is uniformly found in copious quantities and deep within the skin layers in the active, ulcerative stages of disease. The pathogenic mechanisms these bacteria use to persist in the skin and the role they play in the larger pathology of DD is widely unknown. To explore the pathogenesis and virulence of Treponema phagedenis, isolates of this species were investigated in a subcutaneous murine abscess model. For this purpose, mice were subcutaneously inoculated with T. phagedenis in two infection trials. In the first trial, a dosage study was conducted to elucidate the pathogenicity of strains across three different spirochete per inoculum (SPI) doses, based on abscess volumes. In the second trial, isolates were inoculated with the dose of 5 x 109 SPI selected based on trial 1 results, to determine the expression level of 11 putative virulence genes and gain insight into the virulence of strains. To do this, abscesses were harvested for RNA extraction followed by RT-qPCR. From the RT-qPCR assay, the relative fold change of these genes was surmised by comparing the expression levels of in vitro culture samples against in vivo murine samples. During this analysis, it was determined that genes encoding for two metal-ion import lipoproteins, were found highly upregulated during infection. In addition, two genes involved in the adherence of treponemes to the host were found moderately expressed versus the in vitro samples. Conversely, two genes involved in motility and chemotaxis were found to not be significantly upregulated or utilized during infection. This gene expression analysis highlights the preference in strategy for T. phagedenis to persist and adhere in the host rather than engage motility and disseminate.
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Scott, C. (2023). Investigating the virulence of Treponema phagedenis strains isolated from digital dermatitis lesions in a murine abscess model (Master's thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.