[Bacteria species and antibiotic resistance in bovine mastitis within the framework of the «ReLait» project].

Introduction: This sub-study describes the results of mastitis milk samples collected in the canton of Fribourg. In the «ReLait» project, a total of 2,441 milk samples were submitted from 123 different farms, from which 3,028 pathogens were isolated. Three pathogens were isolated from 26 milk samples, and two from 535 milk samples. Milk samples could be submitted for subclinical mastitis, clinical mastitis, or before dry period. Most milk samples (n=1,524) were collected and analyzed for subclinical mastitis or before the dry period (n=463). Only a few milk samples came from cows with clinical mastitis (n=123). The most frequently diagnosed pathogens were non-aureus staphylococci (NAS) at 37,4 %. In addition, frequently diagnosed bacteria were aesculin-positive streptococci, of which 67,3 % were Streptococcus uberis, coliform and coryneform bacteria, and mixed flora. This distribution largely corresponds to the results of other studies, which also show a predominance of NAS, Corynebacterium bovis, and Staphylococcus uberis. Fewer Staphylococcus aureus (S. aureus)-positive samples were found in our study compared to studies outside Switzerland. The resistance situation among NAS was particularly striking with 73,6 % NAS showing a penicillin resistance. This rate has increased compared to previous Swiss studies where penicillin-resistant isolates of 31 % and 54,2 % in 2013 and 2014 respectively were found. Increased antimicrobial resistance to aminopenicillins (90,3 %) and amoxicillin/clavulanic acid (20,8 %) was found among coliform bacteria. However, due to the geographically limited sampling area, this increased resistance development cannot be extrapolated to the whole of Switzerland. The results, however, show that the resistance situation of some bacteria is alarming regionally. To counteract this, the use of antibiotics for the treatment of subclinical or clinical mastitis should be reconsidered. Bacterial milk culture is always indicated to ensure specific bacterial treatment with or without antibiotics.