Abstract
Staphylococcus aureus is a major cause of mastitis in ruminants. In ewe mastitis, symptoms range from subclinical to gangrenous mastitis. S. aureus factors or host-factors contributing to the different outcomes are not completely elucidated. In this study, experimental mastitis was induced on primiparous ewes using two S. aureus strains, isolated from gangrenous (strain O11) or subclinical (strain O46) mastitis. Strains induced drastically distinct clinical symptoms when tested in ewe and mice experimental mastitis. Notably, they reproduced mild (O46) or severe (O11) mastitis in ewes. Ewe sera were used to identify staphylococcal immunoreactive proteins commonly or differentially produced during infections of variable severity and to define core and accessory seroproteomes. Such SERological Proteome Analysis (SERPA) allowed the identification of 89 immunoreactive proteins, of which only 52 (58.4%) were previously identified as immunogenic proteins in other staphylococcal infections. Among the 89 proteins identified, 74 appear to constitute the core seroproteome. Among the 15 remaining proteins defining the accessory seroproteome, 12 were specific for strain O11, 3 were specific for O46. Distribution of one protein specific for each mastitis severity was investigated in ten other strains isolated from subclinical or clinical mastitis. We report here for the first time the identification of staphylococcal immunogenic proteins common or specific to S. aureus strains responsible for mild or severe mastitis. These findings open avenues in S. aureus mastitis studies as some of these proteins, expressed in vivo, are likely to account for the success of S. aureus as a pathogen of the ruminant mammary gland.
Highlights
Mastitis is the first cause of economical loss in milk production worldwide [1] and is a major concern in milk transformation [2]
Ewes infected with O11 or O46 S. aureus strains developed mastitis with different severities O11 and O46 strains share the same genotype and are highly genetically similar [10], they were isolated from dramatically different ewe mastitis episodes
In group O11, five out of six ewes developed a gangrenous mastitis, the last one developed a pyogenic mastitis according the criteria defined in Additional file 1, Table S1
Summary
Mastitis is the first cause of economical loss in milk production worldwide [1] and is a major concern in milk transformation [2]. S. aureus is well-known to produce a large variety of virulence factors (including numerous proteins like toxins or adhesins). It induces a large panel of infections, and the clinical acuteness of each infection type may be variable. S. aureus mastitis in dairy sheep ranges from subclinical mastitis to lethal gangrenous mastitis. Such variability relies on staphylococcal virulence factors as well as host factors. No study has been performed to identify the transcripts and proteins commonly or produced in vivo by S. aureus strains during mastitis. To obtain such information using direct transcriptomic or proteomic approaches upon S. aureus samples collected within the infection site stumbles on technical bottlenecks such as the low amounts of S. aureus cells and the difficulty to localize the infection site within the udder
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