In-vitro susceptibility of Nocardia asteroides to 21 beta-lactam antibiotics, in combination with three beta-lactamase inhibitors, and its relationship to the beta-lactamase content.

Twelve strains of Nocardia asteroides were studied for their susceptibility to 21 beta-lactam antibiotics, alone or in combination with clavulanic acid, sulbactam, or BLP 2013, and for their content of beta-lactamase. Eleven strains were shown to have beta-lactamase activities, which gave three different patterns after analytical isoelectric focusing. The only strain with no detectable beta-lactamase was the most susceptible to the antibiotics tested. The other strains containing beta-lactamases showed almost the same susceptibility profile. Clavulanic acid was the only beta-lactamase inhibitor to show a significant synergistic effect when combined with penicillins.