Thymoquinone inhibits biofilm formation and has selective antibacterial activity due to ROS generation

Abstract

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 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 IC value was found to be 50 μg/ml. This IC value was higher than that of MIC (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.

An updated knowledge of Black seed (Nigella sativa Linn.): Review of phytochemical constituents and pharmacological properties

“…There have been many studies to find out the chemical nature of N. sativa and it was found that the medicinal value of N. sativa is mainly due to the presence of its quinone constituent which is also known as thymoquinone (TQ) ( Sahak et al, 2016 ). TQ is the main constituent of the volatile oil and has a variety of pharmacological properties such as hepatoprotective ( Hassanein et al, 2016 ; Laskar et al, 2016 ; Saheb et al, 2016 ), anti-inflammatory ( Abd-Elbaset et al, 2017 ; Shaarani et al, 2017 ), antibacterial ( Goel and Mishra, 2018 ), antioxidant ( Erol et al, 2017 ), fungicidal ( Almshawit and Macreadie, 2017 ), nephroprotective ( Kotb et al, 2018 ) and anticancer ( Almoyad, 2018 ; Majdalawieh et al, 2017 ; Shaarani et al, 2017 ). There is also literature showing evidence for the molecular mechanism of this molecule ( Gholamnezhad et al, 2016 ).…”

MoS2/TiO2 Hybrid Nanostructure‐Based Field‐Effect Transistor for Highly Sensitive, Selective, and Rapid Detection of Gram‐Positive Bacteria

“…The cells were then centrifuged at 1073 × g for 10 min. Next, the cells were re‐suspended in 10 mL of PBS or FBS to obtain a concentration of 10 8 cfu mL −1 . The cells were diluted with PBS or FBS to get the desired cell concentrations (10 2 –10 8 cfu mL −1 ) for further experiments.…”

Therapeutic effects of antibiotics loaded cellulose nanofiber and κ-carrageenan oligosaccharide composite hydrogels for periodontitis treatment

“…150 µl of samples were incubated with 350 µl bacterial solution at 37 °C for 24 h. After centrifugation (3000 rpm, 3 min) and the bacteria were stained with acridine orange (1 mg/ml) for 15 min. Later, the cells were observed under a microscope 105 .…”