Antimicrobial and Biofilm Inhibition Activity of Novel Biobased Quaternary Ammonium Salts

The growing threat of antibiotic-resistant bacteria continues to be one of the biggest challenges facing public health. As a result, there is an increasing focus on developing new substances with both antimicrobial and biofilm inhibition activities. One such group of compounds is surfactants, particularly quaternary ammonium salts (QASs), which are commonly used as disinfectants in healthcare. In this study, a three-step synthesis was used to prepare a range of QASs, including quaternary esters, hydroxyamides, and dihydroxyamides with alkyl chains of 12-18 carbon atoms. First, the initial step of the synthesis was optimized by testing various catalysts, with CH₃OK showing the highest efficiency and proving to be the most suitable choice for further development. Then, the antimicrobial activity was tested against Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Candida albicans, and Aspergillus brasiliensis, while biofilm inhibition activity was evaluated only for the bacterial strains (S. aureus, E. coli, and P. aeruginosa). The results were compared with those obtained for benzyldimethyldodecylammonium chloride (BDMDAC), which is a commonly used disinfectant. QASs derived from myristic and palmitic acids showed the highest antimicrobial and biofilm inhibition activities, often higher than BDMDAC. Interestingly, some compounds reached maximum biofilm inhibition activity at the lowest concentration testedparticularly stearic acid quaternary hydroxyamide and stearic acid quaternary dihydroxyamide, which reached minimum biofilm inhibitory concentration (MBIC) values as low as 0.016 mmol L^-1. Compounds derived from myristic acid showed higher antimicrobial activity compared with BDMDAC, while both myristic- and palmitic-acid-based compounds demonstrated superior biofilm inhibition activity. These findings highlight the potential of myristic- and palmitic-acid-based QASs as promising candidates for next-generation disinfectant formulations, particularly in applications where strong biofilm inhibition activity is essential.