• Ayed A Dera, Irfan Ahmad, Prasanna Rajagopalan, Mesfer Al Shahrani, Ahmed Saif, Mohammad Y Alshahrani, Yasser Alraey, Ahmad M Alamri, Sultan Alasmari, Mohammed Makkawi, Ali G Alkhathami, Gaffar Zaman, Abdulrahim Hakami, Razan Alhefzi, and Mohammad A Alfhili.
• From the Department of Clinical Laboratory Sciences, Central Research Laboratory (Dera, Ahmad, Rajagopalan, Al Shahrani, Alshahrani, Alraey, Alamri, Alasmari, Makkawi, Alkhathami, Zaman, Hakami, Alhefzi), College of Applied Medical Sciences, King Khalid University, and From the Department of Clinical Laboratory Sciences, Central Research Laboratory (AlAmri), College of Applied Medical Sciences, and Cancer Research Unit, King Khalid University, Abha; from the Department of Clinical Laboratory Sciences (Saif), College of Applied Medical Sciences, Najran University, Najran; and the Chair of Medical and Molecular Genetics Research, Department of Clinical Laboratory Sciences (Alfhili), College of Applied Medical Sciences, King Saud University, Riyadh, Kingdom of Saudi Arabia.
• Saudi Med J. 2021 Feb 1; 42 (2): 196-204.

ObjectivesTo explore the antibacterial activity of thymoquinone (TQ), a quinone extracted from Nigella sativa.MethodsThis study was conducted from May 2019 to March 2020 at the Department of Clinical Laboratory Sciences, College of Applied Medical Sciences, King Khalid University, Abha, Saudi Arabia. The antimicrobial activity, minimum inhibitory concentration (MIC), and minimum bactericidal concentration (MBC) of TQ were determined using an agar well diffusion method and broth microdilution assays, and the synergistic effect was evaluated using antibiotics in parallel. The disruptive effect of TQ on bacterial cell membranes was determined using scanning electron microscopy. The antivirulence properties of TQ, which include adherence and biofilm formation, were also investigated using adherence and biofilm formation assays, respectively.ResultsThymoquinone demonstrated bactericidal efficacy against 4/14 bacterial strains, with MIC range of 1.04-8.3 µg/mL and and MBC range of 10.41-66.66 µg/mL. Thymoquinone showed synergism against Klebsiella pneumoniae, Staphylococcus epidermidis (American Type Culture Collection 12228), Staphylococcus aureus, and Staphylococcus epidermidis in combination with the tested antibiotics. Thymoquinone inhibited bacterial adhesion by 39%-54%, 48%-68%, and 61%-81% at 0.5 × MIC, 1 × MIC, and 2 × MIC, respectively. The tested bacterial strains significantly inhibited biofilm formation after treatment with various concentrations of TQ for 24 and 48 hours.ConclusionThe combinatory effect of TQ with antimicrobials should be considered when developing new antimicrobial therapy regimens to overcome multidrug-resistant.Copyright: © Saudi Medical Journal.

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