Antimicrobial activity and toxicological evaluation of didecyldimethyl- ammonium chloride complexed with fatty alcohol ethoxylate

Background and Aim: Effective disinfection is critical for controlling pathogenic and opportunistic microorganisms in livestock environments. Didecyldimethylammonium chloride (DDAC), a quaternary ammonium compound, is widely used due to its strong antimicrobial properties; however, improving its efficacy without increasing toxicity remains a key challenge. This study aimed to evaluate the antimicrobial activity of DDAC in combination with fatty alcohol ethoxylate (FAEO8) and to assess the toxicological safety of the resulting complex preparation. Materials and Methods: The antimicrobial activity of DDAC, FAEO8, and DDAC–FAEO8 was evaluated against Staphylococcus aureus, Escherichia coli, and Salmonella Typhimurium using minimum inhibitory concentration (MIC) determination, inhibition zone diameter assays, scanning electron microscopy, potassium ion (K⁺) leakage analysis, and membrane potential assays. Toxicological evaluation included acute and sub-acute oral toxicity studies in rats and dermal irritation/corrosion tests in rabbits, conducted in accordance with international and national guidelines. Results: The DDAC–FAEO8 complex exhibited significantly enhanced antimicrobial activity compared to DDAC alone, with MIC reductions of 44.4%, 30.8%, and 26.7% against S. aureus, E. coli, and S. Typhimurium, respectively. At concentrations ≥2× MIC, the complex inhibited >99% of microbial growth and demonstrated prolonged bacteriostatic effects. Microscopic analysis revealed pronounced structural damage and cell lysis, while K⁺ leakage and membrane depolarization assays confirmed disruption of bacterial membrane integrity. FAEO8 alone showed no bactericidal activity but did contribute to changes in membrane permeability. Toxicological assessment indicated that the complex preparation was non-lethal at doses up to 2000 mg/kg, with no significant pathological alterations observed. Subacute exposure showed minimal physiological changes, and dermal testing confirmed that the diluted formulation (40 mg/mL) was non-corrosive, with only mild, reversible irritation. Conclusion: The combination of DDAC with FAEO8 enhances antimicrobial efficacy through membrane disruption mechanisms while maintaining low toxicity. This additive interaction highlights the potential of DDAC–FAEO8 as an effective and safe disinfectant for veterinary applications.