Severe udder cleft dermatitis lesion transcriptomics points to an impaired skin barrier, defective wound repair and a dysregulated inflammatory response as key elements in the pathogenesis

Invited review: Udder cleft dermatitis in dairy cows

Udder cleft dermatitis (UCD) is a common dermatological condition of the udder skin in dairy cows. It is generally considered to be a multifactorial disease, being described in a rather limited amount of literature. Its cow and within-herd prevalence widely ranges between studies depending on the study characteristics, environment and breed. Known risk factors include husbandry practices and environmental factors, such as freestall housing, the use of mattresses as cubicle bases, and footbathing. Cow-related elements, such as udder conformation, parity, and lactation parameters are well-known risk factors for developing UCD. Despite being associated with a high incidence of veterinary-treated clinical mastitis and culling due to udder disease, the SCC of the milk is not influenced by UCD. Severe UCD lesions are characterized by chronic and persistent, dysregulated inflammation accompanied by hampered skin healing and an impaired skin barrier. There is a decrease in microbial diversity followed by dysbiosis and a concomitant overgrowth of opportunistic bacteria negatively affecting beneficial commensal bacteria. Concurrently, a shift in virulence factors most likely contributes to the creation of an environment favorable to pathogens. Anecdotally, mange mites have been associated with UCD but current literature refutes this. The role of treponemes remains inconclusive. Multiomics analysis of both transcriptomic and metagenomic severe UCD datasets, revealed the negative interaction of the facultative pathogen Streptococcus pyogenes with microbiome-associated virulence factors and the patient's transcriptome. No efficient curative treatments nor prevention strategies have been identified so far, although alginogel products have been described to have a positive effect on the healing process of severe lesions. All in all, UCD is a painful skin disease for which an array of miscellaneous risk factors have been identified. For the first time we assimilate literature on prevalence and risk factors, and results from recent elementary studies that provide insights into the pathogenesis of this challenging disease.

Multi-omics analysis elucidates the host-microbiome interplay in severe udder cleft dermatitis lesions in dairy cows

Udder cleft dermatitis is a skin disease in dairy cattle that is characterized by painful, large open wounds between the udder halves or at the front udder attachment. Its impact on animal welfare and production warrants an in-depth investigation of its pathogenesis. The present study delves into the pathophysiology of severe udder cleft dermatitis, employing a multi-omics approach by integrating transcriptomic and metagenomic data obtained from samples of severe udder cleft dermatitis lesions and healthy udder skin of dairy cattle. All dominant features selected from the virulence factor, taxonomic, and transcriptomic datasets, except for the facultative pathogen Streptococcus pyogenes, form a network that could be associated with the healthy udder skin. The severe udder cleft dermatitis-associated Streptococcus pyogenes exhibited a negative correlation with these virulence factors and genes, but was not correlated with the other commensal bacteria in the analysis. Examining the different components interacting with each other could advance our understanding of the pathogenesis of severe udder cleft dermatitis.

An in-depth investigation of the microbiota and its virulence factors associated with severe udder cleft dermatitis lesions

Udder cleft dermatitis (UCD) is a skin condition affecting the anterior parts of the udder in dairy cattle. In the present study, we aimed to shed light on the microbiota in severe UCD lesions versus healthy udder skin by putting forward a taxonomic and functional profile based on a virulence factor analysis. Through shotgun metagenomic sequencing, we found a high proportion of bacteria in addition to a low abundance of archaea. A distinct clustering of healthy udder skin versus UCD lesion samples was shown by applying principal component analysis and (sparse) partial least squares analysis on the metagenomic data. Proteobacteria, Bacillota, and Actinomycetota were among the most abundant phyla in healthy udder skin samples. In UCD samples, Bacteroidota was the most abundant phylum. At genus level, Bifidobacterium spp. had the highest relative abundance in healthy skin samples, whereas Porphyromonas spp. and Corynebacterium spp. had the highest relative abundance in UCD samples. In the differential abundance analysis, Porphyromonas spp. and Bacteroides spp. were significantly differentially abundant in UCD samples, whereas Bifidobacterium spp., Staphylococcus sp. AntiMn-1, and Staphylococcus equorum were more commonly found in healthy samples. Moreover, the abundance of several treponeme phylotypes was significantly higher in lesion samples. The streptococcal cysteine protease speB was among the most abundant virulence factors present in severe UCD lesions, while a plethora of virulence factors such as the antitoxin relB were downregulated, possibly contributing to creating the ideal wound climate for the dysbiotic community. Network analysis showed healthy lesion samples had a large network ofpositive, correlations between the abundances of beneficial species such as Aerococcus urinaeequi and Bifidobacterium angulatum, indicating that the healthy skin microbiome forms an active protective bacterial network, which is disrupted in case of UCD. In UCD samples, a smaller microbial network mainly consisting of positive correlations between the abundances of Bacteroides fragilis and anaerobic Bacteroidota was exposed. Moreover, a high correlation between the taxonomic data and virulence factors was revealed, concurrently with 2 separate networks of microbes and virulence factors. One network, matching with the taxonomic findings in the healthy udder skin samples, showcased a community of harmless or beneficial bacteria, such as Bifidobacterium spp. and Butyrivibrio proteoclasticus, associated with hcnB, hcnC, relB, glyoxalase, and cupin 2. The other network, corresponding to UCD samples, consisted of pathogenic or facultative pathogenic and mainly anaerobic bacteria such as Treponema spp., Mycoplasmopsis spp., and bovine gammaherpesvirus 4, that correlated with virulence factors SpvB, fhaB, and haemagglutination activity domain-associated factor. Our results point toward a dysbiotic community with a notable decrease in diversity and evenness, with a loss of normal skin inhabitants and innocuous or useful species making way for predominantly anaerobic, facultative pathogens. The shift in the abundance of virulence factors such as fhaB and SpvB could play a role in the manifestation of a local micro-environment favorable to the microbiome associated with udder skin lesions. Lastly, the presence of specific networks between microbial species, and between microbes and virulence factors was shown.