A novel antimicrobial colloidal system based on (+)-usnic acid, an important natural antimicrobial molecule, and poly(vinylbenzyl chloride) (PVBC) colloids was synthesized. The chloromethyl functionality on poly(vinylbenzyl chloride) was utilized to bind (+)-usnic acid. To achieve this, the resultant polymer colloids were treated with (+)-usnic acid in triethylamine. The (+)-usnic acid bound particles (PVBC/Us and PVBC/Us/Us) had positive zeta potential values in the range of pH 3-12. The antimicrobial activity of the (+)-usnic acid loaded colloidal particles (PVBC/Us and PVBC/Us/Us) was tested against various microorganisms such as Listeria monocytogenes, Staphylococcus aureus, Enterococcus faecalis, Escherichia coli, Pseudomonas aeruginosa, Salmonella typhimurium, and Klebsiella pneumonia, Candida albicans and Candida glabrata. P. aeruginosa and E. coli appeared to be the most sensitive microorganism compared to the others. The minimum inhibitory concentration (MIC) was determined using different colloid concentrations. The resultant (+)-usnic acid loaded colloids showed high antimicrobial activity against many microorganisms with MIC values down to 0.12 mg colloid/mL. While PVBC/Us/Us colloids had bacteriostatic effect against all the tested microorganisms, PVBC/Us colloids had against only four of them. Furthermore, PVBC/Us/Us colloids showed bactericidal effect against P. aeruginosa and E. coli with minimum bactericidal concentration (MBC) values of 0.94 and 3.75 mg colloid/mL, respectively. In contrast, (+)-usnic acid had no activity on its own. Owing to the small and uniform sizes and high surface areas, (+)-usnic acid loaded colloids afforded greater contact area with the bacterial cell. (C) 2014 Elsevier B.V. All rights reserved.