title: Difference in virulence between Staphylococcus aureus isolates causing gangrenous mastitis versus subclinical mastitis in a dairy sheep flock.
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.
authors: Agence Française de Sécurité Sanitaire des Aliments (AFSSA), Unité Pathologie des Ruminants, 105 route des Chappes, 06902 Sophia-Antipolis, France. e.vautor@afssa.fr
authors: Eric
authors: E
authors: Vautor
authors: Joshua
authors: J
authors: Cockfield
authors: Caroline
authors: C
authors: Le Marechal
authors: Yves
authors: Y
authors: Le Loir
authors: Marlène
authors: M
authors: Chevalier
authors: D Ashley
authors: DA
authors: Robinson
authors: Richard
authors: R
authors: Thiery
authors: Jodi
authors: J
authors: Lindsay
mesh_terms: D000818:Animals; D004269:DNA, Bacterial / Q000145:classification / Q000235:genetics; D005260:Female; D005734:Gangrene / Q000382:microbiology / Q000662:veterinary*; D008413:Mastitis / Q000382:microbiology / Q000662:veterinary*; D020411:Oligonucleotide Array Sequence Analysis; D012756:Sheep; D012757:Sheep Diseases / Q000382:microbiology*; D013203:Staphylococcal Infections / Q000382:microbiology / Q000662:veterinary*; D013211:Staphylococcus aureus / Q000145:classification* / Q000472:pathogenicity*; D014774:Virulence
chemical_list: D004269:DNA, Bacterial