Development of a novel expression, ZI MAX/K ZI, for determination of the counter-anion effect on the antimicrobial activity of tetrabutylammonium salts.

Due to the increasing number of strains of drug-resistant bacteria, the development of new antibiotics has become increasingly important. The antibacterial properties of quaternary amines and their derivatives on both Gram-positive and Gram-negative bacteria are well known. However, an encompassing study with specific emphasis on the role of the counter-anion has not been reported in the literature. By monitoring the Zone of Inhibition of various concentrations of tetrabutylammonium (TBA) salts, we observed that the counter anion plays a significant role in activity. We developed a novel method of reporting activity using zone of inhibition tests (ZI(MAX)/K(ZI)) and found it to be strongly correlated with the minimum inhibitory concentration (MIC).