Potentiation of the in vitro activity of some antimicrobial agents against selected gram-negative bacteria by EDTA-tromethamine.

The in vitro synergistic effects of combinations of EDTA-tromethamine and six antimicrobial agents (ampicillin, chloramphenicol, oxytetracycline, streptomycin, nalidixic acid and sulphadimethoxine) on clinically isolated strains of Pseudomonas aeruginosa, Proteus mirabilis and Escherichia coli were investigated. The antibacterial activity was assessed from the minimal inhibitory concentration for the antibiotics alone or in combination with EDTA-tromethamine. EDTA-tromethamine potentiated the antibacterial activity of ampicillin, chloramphenicol, oxytetracycline and streptomycin up to four-fold. There were no significant or consistent synergistic effects with nalidixic acid or sulphadimethoxine.