Abstract:

The aim of this study was to evaluate the antimicrobial susceptibility of Staphylococcus aureus isolates originated from bovine mastitis belonging to 37 herds in the northwest of Portugal. Moreover, genes encoding resistance markers in Staphylococcus aureus isolates were also evaluated. Antimicrobial susceptibility tests were performed for aminosides (gentamicin, tobramycin, amikacin, and kanamycin), penicillins (methicillin), tetracyclines (tetracycline), macrolides (erythromycin), lincosamides (clindamycin and trimethoprim-sulfamethoxazole), and glycopeptides (vancomycin) families of antibiotics by the disk diffusion method. The detection of aph(3′)-IIIa-, ant(4′)-Ia- and aac(6′)-aph(2″)-, mecA-, tet(M)-, tet(K)-, erm(T)-, van(A)-, lnu(C)-, sal(A)-, vga(C)-, and dfrK-associated resistance genes were performed by polymerase chain reaction. In this study, a higher phenotypic resistance to tetracycline (75.0%), erythromycin (67.3%), and amikacin (42.3%) antibiotics were observed for the tested antibiotics. Moreover, the higher percentages of antibiotic resistance were detected for the ant(4′)-Ia- (63.5%), tet(M)- (57.7%), and aph(3′)-IIIa (30.8%)-related tested genes. Globally, obtained results suggest an alarming situation in Staphylococcus aureus bovine mastitis therapy in the northwest region of Portugal and could contribute for designing a new more specific Staphylococcus aureus therapy program supporting bovine mastitis disease control in this region.  

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