The influence of clinical severity and topical antimicrobial treatment on bacteriological culture and the microbiota of equine pastern dermatitis

Abstract

Background Equine pastern dermatitis (EPD) is a common dermatological problem in horses, yet its aetiology and pathogenesis are poorly understood. Objectives This study aimed to investigate the effects of lesion severity and topical antimicrobial treatment on bacterial flora of EPD‐affected skin. Animals Sixteen horses with EPD were investigated. Methods and materials An observational study was conducted by assigning a clinical severity score ranging from 0 (macroscopically nonlesional) to 21 (severe), and sampling the most and least severely affected limbs of 16 horses (32 limbs) for bacteriological culture and 16S rRNA sequencing. Topical antimicrobial treatment in the month before sampling was recorded. The limbs were allocated to a nonlesional or mildly affected group (Group A, score 0–3) and a moderate to severely affected group (Group B, score 4–21). Results The most commonly cultured bacterial species was Staphylococcus aureus (one of 15 Group A versus nine of 17 Group B). Within Group B, S. aureus was found in three of six limbs treated with topical antimicrobials and in six of 11 untreated limbs. β‐haemolytic streptococci (three of 32) and Trueperella pyogenes (two of 32) also were cultured exclusively in the untreated limbs of Group B. Staphylococci and streptococci were found more often by 16S rRNA sequencing than in culture. Limbs with higher lesion severity and topical antimicrobial treatment appeared to have a lower alpha diversity and different beta diversity compared to milder and untreated lesions. Conclusions and clinical importance Observed differences in microbiota of equine skin are likely to be linked to the presence and severity of EPD and topical antimicrobial treatment. Further research is needed to establish causal bacteria.

Prevalence and WGS-based characteristics of Staphylococcus aureus in the nasal mucosa and pastern of horses with equine pastern dermatitis

“…Specifically, infection with Staphylococcus aureus , which is known for its opportunistic pathogenicity [ 4 ] and association with skin and soft tissue infections [ 5 , 6 ], is frequently suspected in the context of EPD [ 1 , 3 , 7 , 8 ]. S. aureus can be found in a proportion of the normal skin flora of humans, and can also colonize different animals, including horses [ 5 ]; yet, not appearing as a typical commensal on their skin [ 9 , 10 ], but being found rather in the nasal cavities, if present [ 11 , 12 ]. Furthermore, S. aureus is also a major opportunistic pathogen that causes a variety of infections in both humans and animals, with the nasal mucosa often serving as a reservoir for endogenous infection [ 13 , 14 ].…”

Owner reported clinical signs and ­treatment decisions in equine pastern dermatitis

“…11,12 Draft breeds are more frequently and more severely affected than other breeds, 5,11,12,25 but external environmental factors like damp conditions or poor hygiene are also thought to play a role. 19,27 Infectious agents that may be involved in EPD include Chorioptes mites and other parasites, bacterial infections, in particular Staphylococcus spp., 6,18 while a role for Dermatophilus congolensis and dermatophytes in EPD could not be confirmed in one study with this specific focus. 2 These infectious agents may be primary causes for the clinical signs or occur secondarily and act as perpetuating factors.…”

Chronic Progressive Lymphedema in Belgian Draft Horses: Understanding and Managing a Challenging Disease

“…In addition, lymphatic dysfunction results in a lowered skin immunity, facilitating bacterial invasion and infection or pastern dermatitis [ 5 , 57 ]. In horses with CPL, the opportunistic pathogen Staphylococcus aureus is the most prevalent bacterial species isolated from skin samples [ 5 , 58 ], as in warmblood horses with pastern dermatitis [ 59 ]. Affected skin is irritated, red, inflamed, and/or swollen, and will develop a discharge that appears ‘greasy’ or sticky ( Figure 10 ).…”