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6378134 
Journal Article 
Thymoquinone inhibits biofilm formation and has selective antibacterial activity due to ROS generation 
Goel, SM 
2018 
Yes 
Applied Microbiology and Biotechnology
ISSN: 0175-7598
EISSN: 1432-0614 
102 
4 
1955-1955 
English 
29356869 
WOS:000424053700036 
The present study was aimed to investigate the antibacterial potential and antibiofilm activity of thymoquinone and its mechanism of action. Antibacterial activity of thymoquinone was studied using minimum inhibitory concentration, minimum bactericidal concentration, time-kill assay, and post-antibiotic effect. Thymoquinone exhibited antibacterial activity against both Gram-negative and Gram-positive bacteria. In this study, the minimum inhibitory concentration was found to be in the range of 1.56 to 100&;#xa0;µg/ml. Scanning electron microscopy imaging revealed changes in cell morphology with dents, cell lysis, and reduction in cell size. Live/dead imaging using acridine orange and ethidium bromide confirmed the bactericidal activity as treated bacteria showed selective uptake of ethidium bromide over acridine orange. Cell viability was also studied using HaCaT (human keratinocytes) cell line by MTT assay, and IC90 value was found to be 50&;#xa0;µg/ml. This IC90 value was higher than that of MICbacteria (except for MIC of E. coli), demonstrating that its selectivity is higher towards bacteria than normal human cells. Thymoquinone also showed promising antibiofilm activity against Gram-negative (E. coli and P. aeruginosa) and Gram-positive bacteria (B. subtilis and S. aureus), which was studied by crystal violet assay, CFU method, and SEM. For understanding the mechanism of action of thymoquinone, DiSC3, NPN, and ROS assay was performed. DiSC3 and NPN assay has not shown any membrane damage whereas bacterial cells treated with thymoquinone at MIC showed increased dichlorofluorescin fluorescence, suggesting that the probable mechanism of action of thymoquinone against bacterial cells is due to the production of reactive oxygen species. 
; Bacteria; Scanning electron microscopy; Ethidium bromide; Antibacterial activity; Biofilms; Cytology; Acridine; Gram-positive bacteria; Antibiotics; E coli; Bactericidal activity; Keratinocytes; Electron microscopy; Viability; Fluorescence; Lysis; Assaying; Minimum inhibitory concentration; Cell size; Acridine orange; Cell morphology/