In addition to salts with bromide or amino acid anion, the antimicrobial activity of quinine in the form of hydrochloride and free base was also examined. All tested microorganisms were susceptible to QAS-type disinfectants and none of the bacterial strains selected contained any genes determining resistance to the antimicrobial activity of this group of compounds (e.g., qacE or qacEΔ1 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 - 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 - 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 ).