Effect of quaternary ammonium salts and amine oxides on Pseudomonas aeruginosa

Two quaternary ammonium salts, viz (1-methyldodecyl) trimethylammonium bromide (ATDBr) and tetramethylammonium bromide (TMABr), as well as two amine oxides, (1-methyldodecyl)dimethylamine oxide (ATDNO) and trimethylamine oxide (TMANO), were tested for their inhibitory activity on a Pseudomonas aeruginosa strain isolated from nosocomial infections. Only those compounds with long alkyl chains in their molecules (ATDBr and ATDNO) showed antimicrobial efficacy. In subinhibitory concentrations both compounds inhibited incorporation of [14C]-adenine and [14C]-leucine as precursors of macromolecular biosynthesis. Endogenous respiration of the cells was more sensitive to both agents than the respiration of various substrates. Among the virulence factors only the production of phospholipase C was inhibited by sub-MICs, while the activities of elastase and proteinase were stimulated until the inhibitory concentrations were reached. The short-chain analogues TMABr and TMANO did not show these effects. It is suggested that the production of virulence factors is affected by amphiphilic compounds due to their antimicrobial activity.