Antibiofilm activity of shikonin against Listeria monocytogenes and inhibition of key virulence factors

Shikonin is a bioactive compound found in the roots of Lithospermum erythrorhizon and has demonstrated antibacterial activity. In the current study, we aimed to examine the antibiofilm activity of shikonin against Listeria monocytogenes, and to investigate its effects on key L. monocytogenes virulence factors associated with human infection. Present results showed that the minimum inhibitory concentration of shikonin against L. monocytogenes ranged from 25 to 100 μg/mL. Crystal violet staining confirmed that sub-inhibitory concentrations (SICs) of shikonin significantly reduced biofilm biomass in as little as 24 h. Decreased biofilm adhesion, altered biofilm morphology, and disruption of biofilm architecture following treatment with SICs of shikonin were also confirmed by light microscopy and field-emission scanning electron microscopy. Further, at SICs, shikonin effectively reduced the ability of L. monocytogenes to adhere to and invade HT-29 cells and prevented the secretion of listeriolysin O. Moreover, the transcription of biofilm-associated genes and key virulence genes that contribute to infection was also suppressed by shikonin at SICs. Therefore, present results suggest that shikonin could be used as an alternative antibacterial agent to combat L. monocytogenes biofilm formation and infection.