Free Access
Vet. Res.
Volume 40, Number 6, November-December 2009
Number of page(s) 11
Published online 07 July 2009
How to cite this article Vet. Res. (2009) 40:56
How to cite this article: Vet. Res. (2009) 40:56
DOI: 10.1051/vetres/2009039

Difference in virulence between Staphylococcus aureus isolates causing gangrenous mastitis versus subclinical mastitis in a dairy sheep flock

Eric Vautor1, Joshua Cockfield2, Caroline Le Marechal3, Yves Le Loir3, Marlène Chevalier1, D. Ashley Robinson4, Richard Thiery1 and Jodi Lindsay2

1  Agence Française de Sécurité Sanitaire des Aliments (AFSSA), Unité Pathologie des Ruminants, 105 route des Chappes, 06902 Sophia-Antipolis, France
2  Centre of Infection, Department of Cellular and Molecular Medicine, St. Georgés, University of London, Cranmer Terrace, London, SW17 0RE, United Kingdom
3  INRA, UMR1253 STLO, 85 rue de Saint Brieuc, 35042 Rennes, France
4  Department of Microbiology and Immunology, New York Medical College, Valhalla, 10595 NY, USA

Received 12 November 2008; accepted 2 July 2009; published online 7 July 2009

Abstract - Staphylococcus aureus mastitis in dairy sheep ranges from subclinical mastitis to lethal gangrenous mastitis. Neither the S. aureus virulence factors nor the host-factors or the epidemiological events contributing to the different outcomes are known. In a field study in a dairy sheep farm over 21 months, 16 natural isolates of S. aureus were collected from six subclinical mastitis cases, one lethal gangrenous mastitis case, nasal carriage from eight ewes and one isolate from ambient air in the milking room. A genomic comparison of two strains, one responsible for subclinical mastitis and one for lethal gangrenous mastitis, was performed using multi-strain DNA microarrays. Multiple typing techniques (pulsed-field-gel-electrophoresis, multiple-locus variable-number, single-nucleotide polymorphisms, randomly amplified polymorphic DNA, spa typing and sas typing) were used to characterise the remaining isolates and to follow the persistence of the gangrenous isolate in ewes' nares. Our results showed that the two strains were genetically closely related and they shared 3 615 identical predicted open reading frames. However, the gangrenous mastitis isolate carried variant versions of several genes (sdrD, clfA-B, sasA, sasB, sasD, sasI and splE) and was missing fibrinogen binding protein B (fnbB) and a prophage. The typing results showed that this gangrenous strain emerged after the initial subclinical mastitis screening, but then persisted in the flock in the nares of four ewes. Although we cannot dismiss the role of host susceptibility in the clinical events in this flock, our data support the hypothesis that S. aureus populations had evolved in the sheep flock and that S. aureus genetic variations could have contributed to enhanced virulence.

Key words: subclinical mastitis / gangrenous mastitis / dairy sheep / Staphylococcus aureus / microarray

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© INRA, EDP Sciences 2009