Quaternary ammonium salts (QASs) are commonly used in medicine, agriculture and industry and their wide usage caused the development of microbial resistance, thus there is still a need for new effective antimicrobial agents. Present work describes the biological activity of alanine- (DMALM-n) and glycine-derived (DMGM-n) QASs against planktonic and biofilm forms of micro-organisms. The antimicrobial activity was dependent mainly on the hydrocarbon chain length and surfactants with 12-16 atoms of carbon in the alkyl chain were the most active ones. The lowest MIC value was determined for DMALM-14 against Rhodotorula rubra and Saccharomyces cerevisiae (2·5 µmol l^- ¹ ). Generally, alanine derivatives showed stronger effects against micro-organisms than glycine-derived QASs. Alanine-derived surfactants with 12-16 carbons in the alkyl chain had antiadhesive properties on the polystyrene surface, preventing cell attachment (about 70% of inhibition for C. albicans and 40% for S. epidermidis). Strong adhesion reduction was also observed on the stainless steel surface and the highest reduction was observed for C. albicans cells incubated on surface pretreated with DMGM-16. Moreover, DMGM-16 and DMALM-16 prevented C. albicans filamentation, one of the determinants of cell adhesion. Surfactants with C₁₆ alkyl chain (DMGM-16 and DMALM-16) eradicated bacterial and yeast biofilm (from 60 to 90% of reduction observed after incubation of the previously grown biofilm in the presence of the highest tested concentration of the surfactant - 400 µmol l^- ¹ ) and reduced its viability. Strong antimicrobial activity as well as antiadhesive properties make alanine- and glycine-derived QASs the potential candidates for future application as disinfectants. SIGNIFICANCE AND IMPACT OF THE STUDY: Cationic surfactants are used in many fields, among others in medicine, cosmetic and pharmaceutical industry. Their usage on a large scale caused the development of microbial resistance mechanisms to such compounds. Thus, there is a need to synthesize new surfactants with potential application as effective disinfectants to combat both planktonic and biofilm forms of micro-organisms. Present work focuses on the antimicrobial activity of chosen quaternary ammonium salts.

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