Perfis de resistência de Staphylococcus aureus isolados no leite de vacas com mastite subclínica

Staphylococus aureus is considered the most important infectious agent of bovine mastitis. Milk production is reduced and the ill mammary quarters are the most important reservoirs of the pathogen. The objective of this study was to verify the resistance profiles of S. aureus isolated from 66 quarters with bovine mastitis to ampicillin (10 μ g), clindamycin (2 μ g ), erythromycin (15 μ g), gentamicin (30 μ g), oxacillin (1 μ g), penicillin (10 UI), sulfa plus trimethoprim (25 μ g) and tetracycline (30 μ g). The isolates were classified in groups: “A”, resistant to ampicillin and/or penicillin; “B”, resistant to ampicillin and/or penicillin and/or oxacillin; “C”, resistant to sulfa plus trimethoprim; “D”, sensitivity to all antimicrobials tested. Among 66 isolates, 87.9% showed resistance to b-lactams and 40.9% were resistant to oxacillin. Among isolates of mammary quarters with new cases of mastitis, four classified in the group “A” changed to the group “B”, one classified in the group “A” changed to the group “D”, one of the group “B” changed to the group “A”, while three isolates continued in the same group, two in the group “A” and other in the group “D”. The S. aureus isolates showed higher resistance to b-lactams antimicrobials, as penicillin, ampicillin and oxacillin (77.3%, 68.2%, 40.9%, respectively), while the higher sensitivities registers were to gentamicin, sulfa plus trimethoprim, clindamycin and erythromycin (97.0%, 96.3%, 95.6% and 94.4%, respectively).