Evaluation of Antimicrobial and Antibiofilm Effects of Kojic Acid Derivatives against Bacteria and Fungi

Objective: In this study, it was aimed to investigate the antibacterial and antifungal activities of kojic acid derivatives against Gram-negative bacteria (Pseudomonas aeruginosa and Escherichia coli), Gram-positive bacteria (Enterococcus faecalis and Staphylococcus aureus) and fungal strain (Candida albicans). Material and Methods: Antimicrobial activity profiles of the compounds were investigated by microdilution and disk diffusion method. Antibiofilm activities were investigated by spectrophotometric microplate method including crystal violet staining. Moreover, the impact of the compounds on both biofilm and cells was also clarified via scanning electron microscopy (SEM). Results: Minimum inhibitory concentration values were found between 16 μg/mL to 1024 μg/mL. The most potent substance, 3b bearing 3,4- dichlorobenzylpiperazine moiety, has been shown to have inhibitory effects at 16-64 μg/mL concentrations. It was determined that 3a and 3b had stronger inhibitory effects than the other substances against C. albicans. In addition, antibacterial activity was discovered to be greater against Gram-positive strains than Gram-negative. It was also shown by SEM that compound 3b caused significant deformation on the cell wall and membrane of E. faecalis strain and inhibited the biofilm structures of S. aureus and E. coli strains. Conclusion: Kojic acid derivatives were found to inhibit the growth of both bacterial and fungal pathogens at low concentrations. It was also shown that kojic acid derivatives were able to decrease biofilm formation. It is thought that, this will be a favourable scenario for novel therapeutic candidates since more novel compounds will be created, and the inhibitory mechanism will be explored in various research including phenotypic and genotypic experiments.