Pseudomonas fluorescens tolerance to benzyldimethyldodecyl ammonium chloride: Altered phenotype and cross-resistance

Benzyldimethyldodecyl ammonium chloride (BDMDAC) is a quaternary ammonium compound (QAC) with bactericidal action that is used as an active molecule in detergent formulations. Pseudomonas fluorescens is a Gram-negative bacterium with versatile metabolism that is frequently present in biofilms on industrial surfaces. This work reports P. fluorescens adaptation to BDMDAC and subsequent concurrent reduced susceptibility to the QAC benzalkonium chloride (BAC) and the antimicrobial ciprofloxacin (CIP).

Stepwise adaptation to increasing concentrations of BDMDAC was easily achieved and caused changes in the bacterial phenotype of P. fluorescens. Adaptation was evaluated through minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) determination and was subsequently confirmed by time-kill curves. Biofilm phenotype (biomass and number of cells) was characterised for the adapted and reference strains after treatment with BDMDAC, BAC and CIP.

Susceptibility to BAC and CIP was reduced in adapted P. fluorescens. Biofilms developed by the adapted strain had 20% more mass and a higher number of bacteria (2 log).

This study revealed that exposure to sublethal concentrations of BDMDAC may select tolerant strains to that product as well as to related products and unrelated antimicrobial agents.