The skin microbiota in equine pastern dermatitis: a case‐control study of horses in Switzerland

Abstract

Background Equine pastern dermatitis (EPD), a multifactorial syndrome, manifests as skin lesions of variable severity in the pastern area. Despite the widespread use of antibacterial therapy for treating this condition, little is known about the contributing bacteria. Hypothesis/Objectives To investigate the bacterial skin microbiota in EPD‐affected and unaffected (control) pasterns. Animals Case‐control study with 80 client‐owned horses; each with at least one EPD‐affected and one control pastern. Methods and materials Horses were grouped by the form of EPD (mild, exudative or proliferative), the assigned severity grade and type of pretreatment (disinfectant, topical antibacterial or no antibacterial pretreatment). Skin swabs were obtained, and the microbiota composition was compared between the groups. Results Bacterial alpha diversity was reduced in affected pasterns (P < 0.001) and this reduction was significantly associated with the EPD forms (P < 0.001), and not with the type of pretreatment (P > 0.14). Analyses of beta‐diversity confirmed a disordering of the skin microbiota (P = 0.004) in affected versus control pasterns, that was particularly profound in more severe lesions. The type of pretreatment was not significantly associated with this disordering. Four differentially abundant families were detected, of which Staphylococcaceae was the most distinct. The relative abundance of staphylococci was significantly increased in affected pasterns (P = 0.011), particularly in those that had received antibacterial treatment previously. Conclusions and clinical relevance Changes in the microbiota are associated with the EPD form or severity of lesions. The role of bacteria in the pathogenesis of EPD as well as the propriety and consequences of antibacterial treatment should therefore be further investigated.

The relationship between equine pastern dermatitis, meteorological factors, and the skin microbiota

“…For completeness, an overview of the abundances of the most frequent bacterial families in both affected and unaffected horses is provided in Appendix . In a recent study, the proportion of staphylococci was increased in EPD, particularly in the more severe forms and in pasterns treated with antibacterial agents 22 . However, as mentioned already, the horses in the present study were only mildly to moderately affected by EPD and limited observations did not permit any statistical analyses.…”

“…Horses were sampled once a month for 12 consecutive months, starting from October 2017 through September 2018. At each visit, all four pasterns of each horse were thoroughly inspected for signs of EPD and graded for lesion severity using a standardised scoring system as described previously 22 . (see Supporting information Appendix ).…”

“…The laboratory work was conducted in the same way as described in previous studies 22,23 . In brief, the QIAmp DNA Mini Kit (Qiagen; Hilden, Germany) was utilised for DNA extraction, followed by the amplification of the V4 region of the bacterial 16S rRNA gene through a 35 cycle PCR.…”

“…At each visit, all four pasterns of each horse were thoroughly inspected for signs of EPD and graded for lesion severity using a standardised scoring system as described previously. 22 (see Supporting information Appendix S1 ). Briefly, the score accounts for dermal lesions commonly associated with EPD, including scales, crusts, ulceration and formation of skin folds, 1 , 2 , 5 and the cumulative value of each pastern can range between 0 (not affected) and 21 (severely affected).…”

“…The laboratory work was conducted in the same way as described in previous studies. 22 , 23 In brief, the QIAmp DNA Mini Kit (Qiagen; Hilden, Germany) was utilised for DNA extraction, followed by the amplification of the V4 region of the bacterial 16S rRNA gene through a 35 cycle PCR. After subsequent purification, PCR products were quantified via gel electrophoresis to confirm a minimum concentration of 1 ng/µL that was considered compulsory to release the samples for sequencing.…”