Rapid bactericidal and nematicidal activity of a ternary quaternary ammonium formulation via membrane disruption in bacteria and cuticle damage in Bursaphelenchus xylophilus.

Pine wilt disease, caused by Bursaphelenchus xylophilus and associated bacterial communities, represents a serious biosecurity threat to global forestry. Phytosanitary management of infested wood requires agents that combine rapid, broad-spectrum bactericidal activity with direct nematicidal efficacy. We characterized the antimicrobial and nematicidal properties of AQAS, a multi-component disinfectant comprising a ternary blend of short-, long-, and double-chain quaternary ammonium compounds (QACs) together with ethanol and a dual-chelation buffering system. Against representative bacterial test organisms, AQAS achieved >5.0 log reduction against Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus within 1.0 min at a 1:19 working dilution. Time-kill kinetics showed complete inactivation of S. aureus within 30 s and complete elimination of P. aeruginosa within 3 min at 5% AQAS. Fluorescence probe assays (DiSC3(5), NPN, PI) demonstrated membrane depolarisation within 15 s and progressive loss of cell-envelope barrier function, and scanning electron microscopy revealed severe structural disintegration in both Gram-positive and Gram-negative cells. Against B. xylophilus, AQAS produced dose-dependent lethality with an LC50 of 33.32 ppm, accompanied by rigid paralysis and marked cuticular collapse. Component-level bioassays confirmed that each individual QAC constituent, all pairwise binary combinations, and the ternary combination each exhibited independent nematicidal activity (LC50 range 32.23-61.70 ppm), with the pattern not consistent with formal potency synergy. In a laboratory wood-segment immersion assay, 5% AQAS reduced recoverable live nematode numbers by 97.9% and produced 86.2% mortality among recovered individuals. These findings support AQAS as a candidate formulation for rapid phytosanitary disinfection, while field-scale validation under realistic wood-treatment conditions remains necessary.