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Staphylococcus aureus is the most common mastitis-related pathogen in dairy cattle, goats, and sheep worldwide. However, the population structure and genomic characteristics of mastitis-associated S. aureus in small ruminants are limited. Furthermore, the genotypic and phenotypic characteristics involved in the pathogenicity of S. aureus have been thoroughly defined, yet their association with the severity of mastitis is not fully established. Here, we performed genotyping by pulsed-field gel electrophoresis (PFGE) and spa analyses to assess the genetic diversity and relatedness of 162 S. aureus strains recovered from clinical mastitis (CM) and subclinical mastitis (SCM) cases from goats, sheep, and bovines. PFGE analysis revealed 108 distinguishable pulsotypes and 3 main clusters that comprised isolates from the three host species, while according to spa typing, 32 different spa types were identified. Genotypic analysis revealed a spreading of genetically related or indistinguishable S. aureus strains among ovine, caprine, and bovine farms of distant geographical regions. In total, 28 different staphylococcal enterotoxin (SE) gene profiles were observed, revealing a diverse range of SE genes among isolates. By evaluating the antimicrobial resistance, we found low phenotypic antimicrobial resistance among all ruminant isolates. We also performed multiple correspondence analysis, which indicated that the presence of the sec gene, biofilm production, and high autoaggregation ability are associated with CM cases. [ABSTRACT FROM AUTHOR]

Three hundred forty two milk bulk samples were tested for the presence of Staphylococcus aureus ( S. aureus ) originating from 114 ovine farms in Greece that followed ‘transhumant breeding system’. The contamination of farms was low and was recorded at the level of 25.4%, 23.7% and 20.2% during the three sampling periods showing no significant difference. Eighty six out of 106 isolates (81%) were pansusceptible to the 16 antimicrobials tested, strongly suggesting that antibiotics are not used in a routine basis in this breeding system. Resistance was mainly to penicillin and found only at the rate of 6.6%. PFGE revealed 89 distinct pulsotypes, among 106 different isolates, clustering the majority of them into 6 main groups (80% similarity). PFGE showed that predominant clusters were circulating in this region during the study period and also that antimicrobial resistance didn’t affect the predominance of these clusters. Basic biochemical tests can be used only as screening methods to identify S. aureus in raw ewe's milk, additional tests are needed such as STAPH-ID or PCR for confirmation. The findings of this work underscore the value of traditional ovine farming systems in food safety and antimicrobial resistance evolution. These traditional farming systems do not have high rates of antimicrobial agent consumption and subsequently low rates of antimicrobial resistance. [ABSTRACT FROM AUTHOR]