Antibiotics are essential for the treatment of bacterial intramammary infections (IMI) of cows and are the most important drugs in this field (Barkema et al., 2006). They are widely used for curing and preventing IMI (Erskine et al., 2003; Thomson et al., 2008), but AMR emerges to all classes of antibiotics when they are in use (EFSA, 2015; Landers et al., 2012; McEwen and Fedorka-Cray, 2002; Saini et al., 2013). Mastitis remains an important cause of antimicrobial use on Swiss dairy farms. Indeed, in 2015 a total of 3’193 kg of antibiotics (active substance) were sold for intramammary treatment, whereby 1’064 kg were destined for dry cow therapy, and 2’129 kg for lactational therapy (Swiss Administration, 2016). Although there was some decrease during the last years (Swiss Administration, 2016), still large amounts of AB are used in this field. Surprisingly, however, no attention has been paid to how antibiotic use in mastitic cows contributes to the overall problem of AMR in IMI-associated pathogens. To minimize and prevent the pending threat of ending up in a situation where the common mastitis pathogens show AMR against most AB available for veterinary use, understanding the origins, changes and transfer of AMR in these microbes is vital.
During the GTB-sanitation project in Tessin, the use of antibiotics (AB) in general and per farm will be considerably increased in order to cure the infected cows. This results in a high antimicrobial pressure which may lead to increased AMR in Staph. aureus GTB but also in all the other IMI related microbes. This is an optimal setting to study the changes and transfer of AMR in IMI-associated bacteria enabled by a resistome approach.
