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Introduction : The preparations based on hydroxyquinoline, in various combinations, are used in medicine, being shown to have an inhibitory effect against bacteria, molds, fungi, parasites, and viruses, but also having other beneficial effects mentioned in other medical conditions (anti-cancer, anti-degenerative, anti-inflammatory). Aims : In vitro susceptibility testing of microorganisms: bacteria (Gram positive and Gram negative), yeast ( Candida spp.,) and unicellular algae ( Prototheca spp.) at the preparations based on hydroxyquinoline (HQ) and its cupric derivatives deposited on hydroxyapatite (HAP). Materials and methods : There were tested microbial strains of the following genera: Escherichia , Staphylococcus , Micrococcus , Bacillus , Candida , and Prototheca . The tested products (developed in the Laboratory for Nanobiomaterials Synthesis, Center of Physical Chemistry, Faculty of Chemistry and Chemical Engineering, UBB Cluj-Napoca) were developed in three versions: 1) HQ–Cu 2+ –HAP 1 ; 2) HQ–Cu 2+ –HAP 2 ; and 3) NHQ–Cu 2+ –HAP 2 , where NHQ stands for nitro hydroxyquinoline. Determination of the inhibitory effect was conducted by diffusion technique in nutrient agar, according to CLSI 2013 standards, with necessary adaptations for testing of products made in the form of suspensions. Results : Following interpretation, it was found that the inhibition zones, arising from the antimicrobial effect of the tested products showed variability in size, depending on the test product and the microbial strain: Escherichia coli (8-10 mm), Staphylococcus sp. (17.6 - 23.2 mm), Micrococcus spp. (24.4 - 27.6 mm), Bacillus spp. (14.0 - 16.0 mm), Candida spp. (20.4 - 25.2 mm), Prototheca spp. (20.8 - 30.0 mm). From the three tested products, the best efficacy was found at the product no. 3 (NHQ – Cu 2+ – HAP 2 ), followed by no. 1 (HQ– Cu 2+ –HAP 1 ) and no. 2 (HQ–Cu 2+ –HAP 2 ). Conclusions : The inhibitory effect was bactericidal, manifested more intensively against Gram-positive bacteria, yeasts, and prototheca. Such products, prepared in the form of suspensions, may have practical application in the prevention and treatment of skin or hooves disorders. No resistance phenomena are recorded. Keywords : copper, hydroxyapatite, hydroxyquinoline, microorganisms, sensitivity.