Susceptibility of Staphylococcus aureus strains isolated from bovine intramammary infections to different antimicrobial agents

We have shown the results of routine microbiological testing and susceptibility of Staphylococcus aureus isolates that were isolated from cows with inflammation of mammary gland during a five year period. Totally, 2719 strains identified as Staphylococcus aureus were routinely tested to twelve antimicrobial agents by the agar-disc diffusion technique. The strains were isolated from 45, 000 samples of udder secretion on Columbia agar plates containing 5% of defibrinated ovine blood (0.01 ml on a quarter of culture medium). They were identified on the basis of colony morphology, catalase and coagulase tests, a tube coagulase test and the strains from 2002 were identified by the API ID 32 Staph system. Of strains isolated in 2002, 70.77% were penicillin-susceptible, higher than any other year, after that 39.13% of strains in 2007, 37.54% in 2008, 37.96% in 2009, and 44.65% in 2010. Totally, 66.66% of oxacillin-susceptible strains were found in 2007, 67.45% in 2008, 71.52% in 2009 and 88.56% in 2010. For potentiated penicillins like amoxicillin and clavulanic acid 93.85% to 95.65% of susceptible strains were found. For first-generation cephalosporins 36.66%-85.98% of strains demonstrated susceptibility, while for third-generation cephalosporins 100% of strains were susceptible in 2002 and 2007, but 91.07% of isolated strains were susceptible in 2009 and 95.94% in 2010. The strains have shown various susceptibility to tetracyclines, lincosamides, aminoglycosides, fluroquinolone and sulfonamides. The results show the resistance of strains to all groups of antibiotics.