[Staphylococcus aureus and its genotypes as a mastitis pathogen in dairy cattles - a review]

In the last decade the knowledge on Staphylococcus aureus as the etiologic agent of chronic mastitis in dairy cattle has increased. Molecular biology and increasingly whole genome sequencing provide an advanced technology far beyond the classical, phenotypic bacteriology. Staphylococcus aureus has different characteristics, thus clinical and epidemiological properties are massively dependent on the genotypes. In Switzerland, Staphylococcus aureus genotype B (GTB) is a common genotype that causes infectious mastitis. Often, half and more cows of the herd are infected. Conversely, genotype C (GTC) and some of the other Staphylococcus aureus genotypes are classified less problematic because they affect individual cows and only one mammary gland quarter. Since Staphylococcus aureus GTB causes herd problems, the associated costs are high in the dairy industry. This applies in particular in the alpine region, because GTB-positive and -negative cows are not separated during milking and the infectious pathogen can spread rapidly. The pathogen is transferred by contaminated milking liners. Staphylococcus aureus GTB is highly associated with the mammary gland. In contrast, the skin and the udder are identified as the reservoir for Staphylococcus aureus GTC and the other genotypes. Staphylococcus aureus GTC is a classic infectious pathogen in wounds and occasionally in mammary glands.