Determined values of minimum inhibitory concentration (MIC), as well as minimum bactericidal/fungicidal concentration (MBC/MFC) are summarized in Table .3 (Supplementary Data). The results indicate that 3Br, 3Asp and 3Ala comprising a dodecyl substituent showed the highest antimicrobial activity. They were characterized by MIC values of <1 mg dm -3 for the tested Gram-positive bacteria and Gram-negative M. catarrhalis, while MIC determined for the other Gram-negative bacteria (P. aeruginosa, E. coli, S. marcescens) and the fungi R. mucilaginosa and F. graminearum ranged from 3.9 to 31.25 mg dm -3 (Fig. ). MBC/MFC values against the mentioned microorganisms were equal or twice as high (<0.48-62.5 mg dm - 3 ). These results indicate that 3Br, 3Asp and 3Ala demonstrate activity against pathogens at the level of benzalkonium chloride, commonly applied as a potent disinfectant . Relatively low susceptibility to the tested dodecyl substituted QASs was noted only in the case of C. albicans (MIC 15.62-62.5 mg dm -3 , MFC 62.5-250 mg dm -3 ).