Multiple cases of methicillin-resistant CC130 Staphylococcus aureus harboring mecC in milk and swab samples from a Bavarian dairy herd.

The discovery of a new mecA homolog, mecC, necessitates a modification of diagnostic procedures for the identification of methicillin-resistant Staphylococcus aureus (MRSA), as most assays used for the genotypic and phenotypic mecA detection cannot currently recognize mecC. Although the prevalence, distribution, and importance of mecC are not yet completely understood, an exchange of mecC-MRSA between humans and animals seems possible. All previously reported observations of mecC-positive strains have been sporadic. To the best of our knowledge, this is the first report about multiple cases of mecC-positive Staph. aureus in 1 dairy herd. Clonal complex 130 Staph. aureus harboring mecC were found in milk samples from 16 of 56 lactating cows kept in a herd in Bavaria, Germany. Almost all quarter milk samples positive for mecC-MRSA had the lowest possible California Mastitis Test score; composite somatic cell counts obtained from monthly milk recordings showed a mean of 51,600 cells/mL in mecC-MRSA affected cows. Additionally, mecC-positive clonal complex 130 Staph. aureus were detected in swab samples from the mammary skin and a teat lesion of 1 cow from this herd. This report suggests that mecC-carrying strains are able to spread among livestock, and that they have the ability to cause multiple cases in single herds. Therefore, future studies targeting MRSA in dairy cows need to consider mecC.