Veterinary dermatology2026; doi: 10.1111/vde.70099

Screening Equine Skin and Mucous Membranes for Carriage of Coagulase-Positive Staphylococci.

Dierkes, CM
·
Morris, DO
·
Cain, CL
·
Redding, LE
·
Okumura, M
·
Gore, A
·
Cole, SD

Abstract: Commensal populations of coagulase-positive Staphylococcus spp. (CoPS) in healthy horses are not well-defined. Objective: To determine the point prevalence, anatomical distribution, antimicrobial susceptibility and genomic characteristics of CoPS in healthy horses. Methods: One-hundred and fifty privately owned, systemically healthy horses from seven facilities were enrolled in this study. Methods: Horses were sampled from the nares, buccal mucosa and three skin sites. Isolates were identified using matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry, and antimicrobial susceptibility testing was performed by gradient diffusion. Whole-genome sequencing with multilocus sequence typing (MLST) characterised Staphylococcus aureus lineages. In silico PCR differentiated Group A and Group B Staphylococcus delphini. Sampling site sensitivity was calculated using a multisite composite reference. Mixed-effects logistic regression evaluated associations between demographic factors and carriage. Results: Carriage of any staphylococcal species occurred in 111 of 150 (74%) horses: S. aureus 28 of 150 horses (18.7%) and S. delphini 23 of 150 horses (15.3%). Increasing age was associated with decreased odds of CoPS isolation (odds ratio 0.92/year; 95% confidence interval 0.86-0.98). The nares were the most sensitive single sampling site, whereas multisite sampling improved detection. Meticillin-resistance was absent in all CoPS isolates, and S. delphini isolates were fully susceptible to all antimicrobials tested. MLST revealed multiple S. aureus sequence types, some of which were shared across multiple horses at some boarding facilities. Both groups of S. delphini lineage were identified, although many isolates were nontypable. Conclusions: Healthy horses harbour S. aureus and S. delphini, with minimal antimicrobial resistance. Shared S. aureus sequence types within facilities suggest possible lateral transmission.

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Publication Date: 2026-06-25 PubMed ID: 42358087DOI: 10.1111/vde.70099Google Scholar: Lookup

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Summary

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Overview

This study aimed to examine the presence, distribution, antibiotic resistance, and genetic characteristics of coagulase-positive Staphylococcus species (CoPS) in healthy horses.
It found that many healthy horses carry S. aureus and S. delphini without antibiotic resistance, and evidence suggests transmission within boarding facilities.

Background and Purpose

Coagulase-positive Staphylococcus species (CoPS) such as Staphylococcus aureus and Staphylococcus delphini are bacteria often found on animals and can sometimes cause infections.
The commensal populations (natural bacterial residents) of CoPS in healthy horses were not well characterized prior to this study.
The study’s objective was to clarify:

The prevalence (how common) of CoPS in healthy horses.
Anatomical distribution of CoPS carriage on horses’ bodies.
The antimicrobial susceptibility (resistance or sensitivity to antibiotics) of these bacteria.
Genomic traits to understand bacterial lineages and possible transmission.

Methods

Participants: 150 systemically healthy horses from 7 different facilities were enrolled.
Sampling sites: Each horse was sampled from multiple locations including:

Nares (nostrils)
Buccal mucosa (inside of the mouth)
Three separate skin sites

Identification of bacteria: Utilized matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF MS) for precise species identification.
Antimicrobial susceptibility testing: Gradient diffusion method was employed to test bacterial sensitivity to antibiotics.
Genomic characterization: Whole-genome sequencing and multilocus sequence typing (MLST) were performed on Staphylococcus aureus isolates to identify their genetic lineages.
For Staphylococcus delphini, in silico PCR was used to differentiate between Group A and Group B lineages.
Statistical analysis: Mixed-effects logistic regression was used to find associations between horse demographics (e.g., age) and bacterial carriage.

Key Results

Overall carriage: 74% (111/150) of horses carried some form of staphylococcal species.
Specific species carriage:

S. aureus was found in 18.7% (28/150) of horses.
S. delphini was found in 15.3% (23/150) of horses.

Age effect: Older horses had a lower probability of carrying CoPS (odds ratio 0.92 per year increase, meaning a gradual decrease with age).
Sampling sites: The nares were the most sensitive individual sampling site for detecting CoPS.
Use of multiple sampling sites improved the detection rate overall, supporting a multisite approach for screening.
Antimicrobial resistance:

No meticillin-resistant CoPS isolates were identified, indicating absence of MRSA or similar resistant strains.
All S. delphini isolates were fully susceptible to tested antibiotics, indicating no evident resistance.

Genetic diversity:

Multiple genetic sequence types of S. aureus were identified, some shared between horses in the same facilities, suggesting possible transmission within those environments.
Both Group A and Group B S. delphini lineages were found, although many isolates could not be typed.

Conclusions and Significance

Healthy horses commonly carry coagulase-positive staphylococci such as S. aureus and S. delphini on their skin and mucous membranes.
The lack of antibiotic resistance in these isolates is reassuring for equine and human health.
The presence of shared S. aureus sequence types within some boarding facilities suggests potential lateral transmission among horses housed together.
Multisite sampling, especially including the nares, is important for accurate detection of CoPS carriage.
Understanding these carriage patterns has implications for disease control, antimicrobial stewardship, and monitoring of zoonotic risks in equine environments.

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APA

Dierkes CM, Morris DO, Cain CL, Redding LE, Okumura M, Gore A, Cole SD. (2026). Screening Equine Skin and Mucous Membranes for Carriage of Coagulase-Positive Staphylococci. Vet Dermatol. https://doi.org/10.1111/vde.70099

Publication

Veterinary dermatology

ISSN: 1365-3164

NlmUniqueID: 9426187

Country: England

Language: English

Researcher Affiliations

Dierkes, Christina M

Department of Clinical Sciences & Advanced Medicine, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA.

Morris, Daniel O

Department of Clinical Sciences & Advanced Medicine, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA.

Cain, Christine L

Department of Clinical Sciences & Advanced Medicine, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA.

Redding, Laurel E

Department of Clinical Studies - New Bolton Center, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA.

Okumura, Maho

Department of Pathobiology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA.

Gore, Alison

Department of Pathobiology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA.

Cole, Stephen D

Department of Pathobiology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA.

Grant Funding

american college of veterinary dermatology
animal dermatology group

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This article includes 23 references

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