Antimicrobial drug susceptibility of Staphylococcus aureus 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 antimicrobial agents tested were the β-lactams, penicillin G, amoxicillin, ampicillin, cloxacillin, amoxicillin + clavulanate, cephalonium, and cefoperazone; and other drugs including lincomycin, oxytetracycline, doxycycline, and kanamycin. Minimum inhibitory concentrations recorded show that only certain β-lactamase-resistant penicillins (specifically cloxacillin) or penicillin combinations (amoxicillin + clavulanate) were consistently effective against Staph. aureus, whereas the other β-lactam derivatives and drugs from other pharmacological 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.