| Summary: | In the present study, we aimed to determine the antimicrobial resistance and molecular typing of <i>Staphylococcus aureus</i> recovered from transient and persistent intramammary infections and nares/muzzles in dairy cows. We investigated the antimicrobial resistance of 189 <i>S. aureus</i> strains using a broad antimicrobial susceptibility profile. Furthermore, 107 <i>S. aureus</i> isolates were strain-typed using staphylococcal protein-A (spa) typing. A large proportion of strains exhibited multidrug resistance to antimicrobials, including resistance to critically important antimicrobials, although no methicillin-resistant <i>S. aureus</i> strains were found. Our study did not strengthen the idea that extramammary niches (i.e., nares/muzzles) are an important source of <i>S. aureus</i> for bovine mastitis. A discrepancy in the antimicrobial resistance between <i>S. aureus</i> strains isolated from nares/muzzles and milk samples was observed. Furthermore, <i>S. aureus</i> isolates from transient and persistent intramammary infections (IMIs) did not differ by spa typing, suggesting that the persistence of bovine IMIs was determined by cow factors. Thus, the high level of multidrug-resistant <i>S. aureus</i> found in the two herds, considered together with the predominance of a well udder-adapted <i>S. aureus</i> strain, may contribute to our knowledge of the history of the high prevalence of mastitis caused by <i>S. aureus</i>, which is of great concern for animal and public health.
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