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Veterinary research communications2025; 50(2); 83; doi: 10.1007/s11259-025-11037-8

Characterization of Staphylococci colonizing healthy equine skin: antibiotic resistance, virulence factors, and biofilm formation.

Abstract: In order to develop non-antibiotic therapies to treat dermatological diseases it is urgent to spread knowledge on composition and properties of skin bacteria in healthy animals. Since horses are popular companions of humans, it is necessary to know what risk skin bacteria pose to humans. Therefore the aim of this work was to analyse species composition of staphylococci isolated from skin swabs of 50 healthy horses using MALDI-TOF (Matrix-Assisted Laser Desorption/Ionization Time-of-Flight) spectrometry and to characterize their virulence properties. Swabs were collected from five body areas (neck, dorsal back, abdomen, pastern and muzzle). Among 19 different staphylococcal species identified, the most common species were Staphylococcus succinus, S. xylosus, S. vitulinus and S. warneri. The most frequent antimicrobial resistance in staphylococcal isolates was observed for penicillin G (48%). The blaZ gene was detected in 90% of penicillin resistant isolates while mecA and mecC genes were not observed. Only low level resistance was noted for erythromycin (12%), tetracycline (6%), linezolid (4%) and oxacillin (4%). No multidrug-resistant strain was found, the MAR (multiple antibiotic resistant) index in average was 0.048 ± 0.039. Biofilm production was observed in 90.1% of isolates whereas 62% of them showed strong production. Gelatinase, DNase, protease and lipase activity was found in 50.4%, 41.3%, 22.3% and 46.3% of isolates, respectively. The results of enzyme activities testing using API ZYM kits (BioMérieux) revealed common production of acid and alkaline phosphatase, esterase, esterase lipase and napthtol-AS-BI-phosphohydrolase. The caution when interacting with horses is important especially in the case of injury since their staphylococci showed many virulent characteristics however they were not multi-resistant.
© 2025. The Author(s), under exclusive licence to Springer Nature B.V.
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Publication Date: 2025-12-23 PubMed ID: 41432965PubMed Central: 11938290DOI: 10.1007/s11259-025-11037-8Google Scholar: Lookup
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Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

Overview

  • This study analyzed the types of staphylococcal bacteria present on the skin of healthy horses and examined their antibiotic resistance, virulence factors, and ability to form biofilms, to assess potential risks to horse and human health.
  • The research aimed to better understand these bacteria to inform non-antibiotic treatments for horse skin diseases and evaluate any zoonotic risk posed to humans.

Introduction and Purpose

  • Horses are common companion animals, making the characterization of their skin microbiota important for both veterinary and human health.
  • Understanding the species composition and properties of staphylococci on healthy equine skin helps in developing alternative therapies to antibiotics.
  • The study specifically focused on assessing antibiotic resistance, virulence factors such as enzyme activity, and biofilm-forming ability of these bacteria.

Methods

  • Skin swabs were collected from five distinct body areas of 50 healthy horses: neck, dorsal back, abdomen, pastern (lower leg), and muzzle.
  • Identification of staphylococcal species was performed using MALDI-TOF mass spectrometry, a rapid and accurate technique for bacterial species determination.
  • Antibiotic resistance profiles were examined by testing sensitivity to commonly used antibiotics and detecting resistance genes such as blaZ, mecA, and mecC.
  • Biofilm formation was assessed, as biofilms contribute to bacterial virulence and antibiotic tolerance.
  • Virulence factors were further evaluated by measuring enzyme activities, including gelatinase, DNase, protease, lipase, and others, using API ZYM kits.

Key Findings – Species Diversity

  • A total of 19 different staphylococcal species were identified, indicating a diverse skin microbiota on horses.
  • The most common species isolated were:
    • Staphylococcus succinus
    • Staphylococcus xylosus
    • Staphylococcus vitulinus
    • Staphylococcus warneri

Antibiotic Resistance

  • Nearly half (48%) of the staphylococcal isolates displayed resistance to penicillin G.
  • The blaZ gene, responsible for beta-lactam resistance, was present in 90% of those penicillin-resistant strains.
  • Resistance genes mecA and mecC, typically associated with methicillin resistance, were not found in any isolates.
  • Low levels of resistance were detected for other antibiotics:
    • Erythromycin: 12%
    • Tetracycline: 6%
    • Linezolid: 4%
    • Oxacillin: 4%
  • No multidrug-resistant staphylococcal strains were identified.
  • The Multiple Antibiotic Resistant (MAR) index was low on average (0.048 ± 0.039), indicating limited exposure to antibiotics or resistance pressure.

Virulence Factors and Biofilm Formation

  • A high proportion (90.1%) of isolates produced biofilms, with 62% showing strong biofilm production, which can protect bacteria from the host immune system and antibiotics.
  • Enzyme activities detected among the isolates included:
    • Gelatinase: 50.4% of isolates
    • DNase: 41.3%
    • Protease: 22.3%
    • Lipase: 46.3%
  • The API ZYM enzymatic testing further revealed frequent production of:
    • Acid and alkaline phosphatases
    • Esterase and esterase lipase
    • Napththol-AS-BI-phosphohydrolase

Implications and Conclusions

  • The skin of healthy horses harbors a variety of staphylococcal species with several virulence factors, indicating these bacteria have potential to cause infection if the skin barrier is breached.
  • The presence of virulent bacteria underlines the importance of caution when handling horses, especially in situations where injuries could allow bacterial entry.
  • Although virulence traits are common, the lack of multidrug resistance suggests that current antibiotic therapies remain effective against these skin bacteria.
  • This study’s findings provide crucial knowledge towards developing alternative, non-antibiotic treatments for equine skin diseases and assessing zoonotic risks.

Cite This Article

APA
Strompfová V, Štempelová L, Bujňáková D, Karahutová L, Gondoľová D, Nagyová M, Siegfried L. (2025). Characterization of Staphylococci colonizing healthy equine skin: antibiotic resistance, virulence factors, and biofilm formation. Vet Res Commun, 50(2), 83. https://doi.org/10.1007/s11259-025-11037-8

Publication

Veterinary research communications
ISSN: 1573-7446
NlmUniqueID: 8100520
Country: Switzerland
Language: English
Volume: 50
Issue: 2
Pages: 83

Researcher Affiliations

Strompfová, Viola
  • Centre of Biosciences of the Slovak Academy of Sciences, Institute of Animal Physiology, Šoltésovej 4-6, Košice, 040 01, Slovakia.
Štempelová, Lucia
  • Centre of Biosciences of the Slovak Academy of Sciences, Institute of Animal Physiology, Šoltésovej 4-6, Košice, 040 01, Slovakia. stempelova@saske.sk.
Bujňáková, Dobroslava
  • Centre of Biosciences of the Slovak Academy of Sciences, Institute of Animal Physiology, Šoltésovej 4-6, Košice, 040 01, Slovakia.
Karahutová, Lívia
  • Centre of Biosciences of the Slovak Academy of Sciences, Institute of Animal Physiology, Šoltésovej 4-6, Košice, 040 01, Slovakia.
Gondoľová, Dajana
  • Centre of Biosciences of the Slovak Academy of Sciences, Institute of Animal Physiology, Šoltésovej 4-6, Košice, 040 01, Slovakia.
  • University of Veterinary Medicine and Pharmacy, Komenského 73, Košice, 041 81, Slovakia.
Nagyová, Mária
  • Faculty of Medicine, Department of Medical and Clinical Microbiology, University of P. J. Šafárik in Košice, Trieda SNP 1, Košice, 040 11, Slovakia.
Siegfried, Leonard
  • Faculty of Medicine, Department of Medical and Clinical Microbiology, University of P. J. Šafárik in Košice, Trieda SNP 1, Košice, 040 11, Slovakia.

MeSH Terms

  • Animals
  • Horses / microbiology
  • Biofilms / growth & development
  • Staphylococcus / drug effects
  • Staphylococcus / physiology
  • Staphylococcus / genetics
  • Staphylococcus / pathogenicity
  • Virulence Factors / genetics
  • Virulence Factors / metabolism
  • Skin / microbiology
  • Anti-Bacterial Agents / pharmacology
  • Drug Resistance, Bacterial
  • Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / veterinary

Conflict of Interest Statement

Declarations. Ethics approval: The study involved horses for one-time collection of superficial swab samples. All manipulation was in accordance with standard veterinary practices according Slovak legislation (no. 377/2012 and 436/2012). Competing interests: The authors declare no competing interests.

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