In vitro activity of ampicillin alone and in combination with different concentrations of 6 beta-bromopenicillanic acid, clavulanic acid and mecillinam.

The antibacterial activity of ampicillin against Enterobacteriaceae strongly increased when combined with 6 beta-bromopenicillanic acid (BPA) or clavulanic acid (CA). In vitro, the combination ampicillin: BPA in the ratio 1:1 proved to be the most effective one. The antibacterial activity of mecillinam against Enterobacteriaceae was strongly potentiated by the addition of ampicillin. The combination mecillinam:ampicillin in the ratio 4:5 showed an antibacterial activity comparable to that of new beta-lactam compounds such as cefotaxime and ceftazidime.