In this subproject, the occurrence and genotypic characteristics of methicillin-resistant staphylococci from 20 German dairy farms were investigated. In addition to
MRSAshort forMethicillin-resistant Staphylococcus aureus, non-
aureus staphylococci (NAS) were frequently found on the dairy farms investigated in this study. NAS carrying the
mecA gene were found as well as those in which this gene and the
mecC gene were not absent, making it unclear what causes resistance to cefoxitin. Also, different
MRSAshort forMethicillin-resistant Staphylococcus aureus and NAS on the dairy farms often did not carry the same SCC
mec element, so multiple independent resistance events can be assumed. Colonization of nares with methicillin-resistant staphylococci decreased in young animals with increasing age of the animals. Udder quarters colonized with
MRSAshort forMethicillin-resistant Staphylococcus aureus had higher average somatic cell counts in quarter milk samples than
MRSAshort forMethicillin-resistant Staphylococcus aureus-negative quarters, suggesting an inflammatory response. Milking hygiene is inadequate on some farms. Persistence of
MRSAshort forMethicillin-resistant Staphylococcus aureus and MR-NAS in teat cups after ineffective cleaning and/or disinfection could contribute to the spread of these bacteria. If
MRSAshort forMethicillin-resistant Staphylococcus aureus or MR-NAS are detected in quarter milk samples, there is a high probability that they are also present in the bulk tank milk. However, the
MRSAshort forMethicillin-resistant Staphylococcus aureus counts in the BTM were consistently low (<1000
MPNshort forMost Probable Number/
mlshort formillilitre). At these low bacterial counts, colonization or even infection from raw milk consumption is very unlikely. In addition, raw milk is usually heat-treated, so that the risk of transmission is reduced. The detected
MRSAshort forMethicillin-resistant Staphylococcus aureus and MR-NAS from the dairy farms carried resistance genes and showed phenotypic resistances to different classes of antibiotics. In particular, the MR-NAS species
S.
epidermidis,
S.
haemolyticus, and
S.
sciuri partly harbored a higher number of resistance genes than the detected
MRSAshort forMethicillin-resistant Staphylococcus aureus. Several genes associated with pathogenicity mechanisms were also found in
MRSAshort forMethicillin-resistant Staphylococcus aureus and the MR-NAS species
S.
epidermidis and
S.
haemolyticus. However, the detected genes suggest a low human infectious and toxin-producing potential in the isolates studied.