Antimicrobial susceptibility of mastitis pathogens of dairy cows in Switzerland

This study evaluates the antimicrobial resistance of pathogens cultured from 3954 quarter milk samples from dairy cows in Switzerland. A total of 1228 Streptococcus (Strep.) uberis, 1107 Staphylococcus (Staph.) spp. other than Staph. aureus, 598 coliform, 490 Staph. aureus, 270 Enterococcus spp. and 213 Strep. dysgalactiae isolates were tested for susceptibility to 9 antimicrobial drugs using agar diffusion. Streptococcus uberis, Strep. dysgalactiae and Staph. aureus had the highest antimicrobial sensitivities to amoxicillin clavulanic acid (99.6%, 100% and 98.8%, respectively). Of all isolated pathogens, only 2.6% were resistant to amoxicillin clavulanic acid and 8.0% to cefoperazone. The overall resistance level to gentamicin was 45.5%, to penicillin 39.2%, and to ampicillin 26.7%. The highest resistance levels occurred with polymyxin (86.0%), oxacillin (64.7%) and lincomycin (53.7%). Our results showed that at least one resistance exists to one antimicrobial agent examined in this study. Ideally the selection of the antibacterial drug for the treatment of intramammary infection should be based on antibiotic susceptibility testing.