The antimicrobial activity of the tested compounds was determined in relation to Rhodotorula mucilaginosa (PUEB collection) and filamentous fungi Fusarium graminearum (PUEB collection). Minimal inhibitory concentration (MIC) and minimal bactericidal/fungicidal concentration (MBC/MFC) of the tested substances was determined using the microdilution method based on methodology described previously with some modifications. First, a series of two-fold dilutions of the tested substances in the concentration range of 0.48-1000 mg dm -3 were prepared in 96-well microplates in MH broth (for S. aureus, P. aeruginosa and E. coli), TSB (for S. marcescens, M. catarrhalis and M. luteus), BHI (for L. monocytogenes and E. faecalis), YPD (for C. albicans and R. mucilaginosa) or PDB (for F. graminearum). Then, suspensions prepared from 24-hour cultures of indicator microorganisms in broth media at a final concentration of 10 5 CFU cm -3 , were inoculated into the microplates with diluted substances. Incubation was carried out for 24 hours at 30 or 37 °C, depending on the indicator microorganism. The inoculate of F. graminearum was prepared in liquid PDB medium from a fresh culture, setting the final spore concentration at 10 4 CFU cm - 3 , introduced into the prepared microplates and incubated for 5-7 days at 25 °C. After incubation the optical density of microorganisms culturewas determined at 600 nm using BioTek Epoch 2 microplate reader (Agilent, USA). The results are expressed as the average of three replicates. The MIC value was defined as the concentration of tested substances, inhibiting the growth of the microorganism by at least 90%. MBC/MFC values were determined by spot inoculation of 10 mm 3 of cultures from wells with no growth observed in the MIC assay on an agar medium and incubation for 24-48 h at 30 or 37 °C. The lowest concentration of the tested substances supporting no microorganisms growth was defined as the MBC/MFC. In case of F. graminearum the MIC and MFC value was evaluated by spotting of 100 mm 3 of cultures from wells on PDA and incubation for 5-7 days at 25 °C. The lowest concentration of the tested substances supporting no fungal growth was defined as the MIC and MFC. The tested compounds were applied in the form of aqueous solutions at the defined concentration, with the exception of 1-alkylquininium bromides and free base quinine, which were applied in the form of solutions in water-DMSO mixture with volumetric ratio of 7:3. Water-DMSO mixture was used as a control.