Abstract
This study aimed to determine the antimicrobial activity of thymoquinone (TQ) against Listeria monocytogenes, and to examine its inhibitory effects on biofilm formation, motility, hemolysin production, and attachment-invasion of host cells. The minimum inhibitory concentrations (MICs) of TQ against eight different L. monocytogenes strains ranged from 6.25—12.50 μg/mL. Crystal violet staining showed that TQ clearly reduced biofilm biomass at sub-MICs in a dose-dependent manner. Scanning electron microscopy suggested that TQ inhibited biofilm formation on glass slides and induced an apparent collapse of biofilm architecture. At sub-MICs, TQ effectively inhibited the motility of L. monocytogenes ATCC 19115, and significantly impacted adhesion to and invasion of human colon adenocarcinoma cells as well as the secretion of listeriolysin O. Supporting these findings, real-time quantitative polymerase chain reaction analysis revealed that TQ down-regulated the transcription of genes associated with motility, biofilm formation, hemolysin secretion, and attachment-invasion in host cells. Overall, these findings confirm that TQ has the potential to be used to combat L. monocytogenes infection.
Highlights
Listeria monocytogenes is a Gram-positive, non-spore-forming bacterium ubiquitously found in nature
The minimum inhibitory concentrations (MICs) of TQ against several L. monocytogenes strains were determined for the first time
With MICs ranging from 6.25—12.5 μg/mL, TQ exhibited significant antimicrobial activity against the tested L. monocytogenes strains
Summary
Listeria monocytogenes is a Gram-positive, non-spore-forming bacterium ubiquitously found in nature. It is a frequent cause of food-borne illness, with the most common sources of infection being processed foods, including raw milk products and ready-to-eat chilled foods (Farber and Peterkin, 1991; Allerberger and Wagner, 2010). Within the European Union, a statistically-significant increase in cases of listeriosis was noted between 2009 and 2015. The number of confirmed human cases of listeriosis increased from 1,331 in 2009 to 2,206 in 2015 (EFSA, 2016). Based on the susceptibility of the host, the severity of disease ranges from mild gastroenteritis to life-threatening infections such as septicemia, encephalitis, and meningitis (Zhu et al, 2017)
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