Resistência a antimicrobianos em Staphylococcus aureus isolados de mastite em bovinos leiteiros de Minas Gerais, Brasil Antimicrobial resistance in Staphylococcus aureus isolated from mastitis in dairy herds from the state of Minas Gerais, Brazil

Staphylococcus aureus (S. aureus) stands out as one of the most common etiological agents of bovine mastitis, currently causing major economic losses to dairy farming. In order to evaluate the sensitivity of this micro-organism to antimicrobials, 352 isolates from 35 dairy herds located in the state of Minas Gerais were submitted to antibiogram tests, using the disc diffusion technique. Nitrofurantoin and the associations of neomycin, bacitracin and tetracycline (NBT), as well as penicillin, nafcillin and dihydrostreptomycin (PND), showed 100% efficiency in vitro. There were low resistance rates in the group of cephalosporins, with values of 0, 0.28 and 0.40% for cefquimona, cephalothin, and ceftiofur, respectively. Among the aminoglycosides, there was 1.69% resistance to gentamicin and 3.35% for neomycin. The highest resistance was observed for polymyxin B (82%), followed by betalactams, ampicillin and penicillin, with resistance rates of 80.92 and 80.45%, respectively. Moderate levels of resistance were observed for tetracycline, lincomycin, cefoperazone and sulfazotrim. Among the tested isolates, 65 (18.15%), coming from 24 of the 35 herds studied, showed multidrug resistance (MAR index ≥ 0.2). The results pointed out to high variation in antimicrobial resistance profiles and the occurrence of multidrug resistance among some studied strains, highlighting the importance of antibiogram tests for the choice of an appropriate drug to be used for the treatment or prevention of mastitis caused by