[Sensitivity pattern of Staphylococcus aureus isolated from quarter milk from cattle].

Strains of Staphylococcus aureus (n = 319) from bovine quarter milk were tested for susceptibility to antimicrobial drugs. The minimum inhibitory concentration (MIC), was determined by agar dilution methods, and the diameter of the inhibition area was determined by agar diffusion methods. In addition beta-lactamase production was tested. The strains tested showed resistance to penicillin, (38.4%), oxytetracyclin (21.2%), and streptomycin (11.5%). Little or no resistance was found to the other antimicrobials in this study. A strong correlation between dilution and diffusion methods was calculated for oxytetracyclin: r = 0.88, and for streptomycin: r = -0.90; correlation for penicillin was weaker: r = -0.66. Since 17% of the strains with an MIC for penicillin less than 0.16 mg/L are still able to produce beta-lactamase, we recommend that when antibiotic susceptibility of staphylococci is examined, beta-lactamase production should also be tested. Dapsone, a sulfone compound, formerly not considered a chemotherapeutical drug under Dutch law, had an MIC less than or equal to 0.64 mg/L for 85% of the strains. Therefore, we recommend that sulfone compounds should be registered under the new Veterinary Medicines Act. Since the resistance patterns of S. aureus strains to most antimicrobial drugs were the same as those seen in earlier studies, we find no reason to resort to new generations of broad-spectrum antibiotics in routine prevention and treatment of mastitis.