“In vitro” antimicrobial susceptibility of “Staphylococcus aureus” isolated from bovine subclinical mastitis

Abstract

Eighty-three strains of Staphylococcus aureus isolated from bovine subclinical mastitis were studied in order to evaluate the in vitro antimicrobial sensibility. Using agar diffusion technique, 79 (95%) strains were resistant to penicillin G and 73 (88%) to ampicillin. Against for the others tested drugs 83 (100%) were sensitive to cephalothin, 79 (95%) to enrofloxacin, 77 (93%) to tetracycline, 76 (92%) to erythromycin and clindamycin, and 65 (78%) to gentamicin. samples From those animals with recent intramammary infection, 91 and 87% strains were resistant to penicillin and ampicillin, while from chronic infection 100 and 89% were resistant to those drugs, respectively. There was significant difference among the effectiveness of penicillin and ampicillin (P<0.01) for chronic infection category. Resistance to two antibiotics simultaneously was the most frequent with the profile penicillin+ampicillin observed in 55 (66%) of the studied strains. The results showed that resistance to penicillins frequently occurs in Staphylococcus aureus isolated from subclinical mastitis in dairy cattle herds in the municipality of Garanhuns, PE, Brazil.