Antimicrobial drug susceptibility of Staphylococcus aureus isolated from subclinical bovine mastitis in Italy

The antimicrobial susceptibility of 68 Staphylococcus aureus isolates collected during 2004 from milk of cows affected by subclinical mastitis was examined. The anti- microbial agents tested were the β-lactams, penicillin G, amoxicillin, ampicillin, cloxacillin, amoxicillin + cla- vulanate, cephalonium, and cefoperazone; and other drugs including lincomycin, oxytetracycline, doxycy- cline, and kanamycin. Minimum inhibitory concentra- tions recorded show that only certain β-lactamase–re- sistant penicillins (specifically cloxacillin) or penicillin combinations (amoxicillin + clavulanate) were consis- tently effective against Staph. aureus, whereas the other β-lactam derivatives and drugs from other phar- macological groups were either moderately effective or ineffective. Thus, β-lactamase–resistant penicillins are to be considered the antimicrobial agents of choice for treatment of bovine mastitis resulting from infection by Staph. aureus. Key words: Staphylococcus aureus, bovine, minimum inhibitory concentration