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

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.

antibiotic resistance; bovine mastitis; penicillins

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