Physiological changes induced by the quaternary ammonium compound benzyldimethyldodecylammonium chloride on Pseudomonas fluorescens

Objectives: Antimicrobial resistance is a major public health concern, particularly in hospitals and other health-care settings. For the rational design of disinfection strategies, it is of utmost importance to understand the mechanisms of action of antimicrobials. In this study, the mechanism of action of benzyldimethyldodecylammonium chloride (BDMDAC) was assessed against Pseudomonas fluorescens. Methods: The targets of antimicrobial action were studied using different bacterial physiological indices. The MIC, MBC, membrane permeabilization, intracellular potassium release, physico-chemical surface properties, surface charge, outer membrane protein (OMP) expression and morphological changes were assessed after BDMDAC exposure. Results: The MIC was found to be 20 mg/L and the MBC was 10 mg/L. BDMDAC led to a significant change in cell surface hydrophobicity and induced propidium iodide uptake. Such results suggest cytoplasmic membrane damage, corroborated by the release of intracellular potassium. The results obtained from the zeta potential measurement demonstrate a -31.2 mV value for untreated cells and -21.0 mV for cells at the MIC. Scanning electron microscopy revealed that cells treated with 20 mg/L were less bulky, and their membrane seemed to be rougher, wrinkled and deformed when compared with untreated cells. The overall bactericidal events occurred without detectable changes in OMP expression. Conclusions: BDMDAC is an effective biocide against P. fluorescens. It binds by ionic and hydrophobic interactions to the cell membrane, causing changes in membrane properties and function, as manifested by phenomena such as cellular disruption and loss of membrane integrity with consequent leakage of essential intracellular constituents.