Staphylococcus aureus characterization in equine pastern dermatitis (PD)

Whether the primary cause of paster dermatitis (PD) or secondary to other skin diseases there is no doubt that Staph plays a major role in PD. The presence of some virulence factors may indicate whether this is a primary or secondary cause.
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Prevalence and WGS-based characteristics of Staphylococcus aureus in the nasal mucosa and pastern of horses with equine pastern dermatitis
BMC Vet Res. 2022 Feb 24;18(1):79. doi: 10.1186/s12917-021-03053-y.
Authors
Sarah Kaiser-Thom 1 , Vinzenz Gerber 1 , Alexandra Collaud 2 , Joel Hurni 1 2 , Vincent Perreten 3
Affiliations

1 Department of Clinical Veterinary Medicine, Vetsuisse Faculty, Swiss Institute of Equine Medicine (ISME), University of Bern, and Agroscope, Bern, Switzerland.
2 Institute of Veterinary Bacteriology, Vetsuisse Faculty, University of Bern, Bern, Switzerland.
3 Institute of Veterinary Bacteriology, Vetsuisse Faculty, University of Bern, Bern, Switzerland. vincent.perreten@vetsuisse.unibe.ch.

PMID: 35209904
DOI: 10.1186/s12917-021-03053-y

Abstract

Background: Many contributing factors are involved in the development of equine pastern dermatitis (EPD). Among the most frequently suspected is Staphylococcus aureus, known for its pathogenic potential in skin and soft tissue infections. We therefore investigated the association between S. aureus carriage and EPD.

Results: One hundred five EPD-affected horses and 95 unaffected controls were examined for the presence of methicillin-resistant and -susceptible Staphylococcus aureus (MRSA and MSSA) on the pastern skin and in the nostrils. S. aureus isolates were cultivated from swab samples on selective MSSA and MRSA chromogenic agar and identified using MALDI-TOF MS. Isolates were analysed by Illumina whole genome sequencing for genetic relatedness (cgMLST, spa typing), and for the presence of antimicrobial resistance and virulence determinants. A markedly higher proportion of samples from EPD-affected horses proved positive for S. aureus, both from the pastern (59.0 % vs. 6.3 % in unaffected horses; P<0.001), and from the nose (59.0 % vs. 8.4 %; P<0.001). Isolates belonged to 20 sequence types (ST) with lineages ST15-t084 (spa) (18 %), ST1-t127 (13 %), and ST1-t1508 (12 %) being predominant. Eight S. aureus were MRSA ST398-t011 and ST6239-t1456, and contained the staphylococcal cassette chromosome SCCmecIVa. Antimicrobial resistance genes were almost equally frequent in pastern and in nasal samples, whereas some virulence factors such as the beta-hemolysin, ESAT-6 secretion system, and some enterotoxins were more abundant in isolates from pastern samples, possibly enhancing their pathogenic potential.

Conclusions: The markedly higher prevalence of S. aureus containing specific virulence factors in affected skin suggests their contribution in the development and course of EPD.

Keywords: Antimicrobial resistance; Dermatology; Equine pastern dermatitis; Frequency; Genotyping; Staphylococcus aureus; Virulence factors; WGS.