In the context of acquiring multidirectional resistance by strains of pathogenic microorganisms against commonly used disinfectants (e.g., benzalkonium chloride) Piovesan Pereira and Tagkopoulos, 2019; , as well as the risks associated with the penetration of synthetic cationic surfactants into the environment and their high toxicity toward aquatic organisms , it becomes necessary to search for new, safer active ingredients with potent antimicrobial activity among compounds of natural origin. Therefore, the biological activity of the obtained quinine-based QASs against various microbes that pose a serious threat to human health, especially to immunocompromised patients in hospital settings, was investigated. The microorganisms tested included pathogenic foodborne bacteria (L. monocytogenes) and microbes responsible for opportunistic infections with potentially serious consequences (e.g., S. aureus, P. aeruginosa, E. coli, C. albicans).