Andrographolide Inhibits Biofilm and Virulence in Listeria monocytogenes as a Quorum-Sensing Inhibitor

Abstract

Listeria monocytogenes is a major foodborne pathogen that can cause listeriosis in humans and animals. Andrographolide is known as a natural antibiotic and exhibits good antibacterial activity. We aimed to investigate the effect of andrographolide on two quorum-sensing (QS) systems, LuxS/AI-2 and Agr/AIP of L. monocytogenes, as well as QS-controlled phenotypes in this study. Our results showed that neither luxS expression nor AI-2 production was affected by andrographolide. Nevertheless, andrographolide significantly reduced the expression levels of the agr genes and the activity of the agr promoter P2. Results from the crystal violet staining method, confocal laser scanning microscopy (CLSM), and field emission scanning electron microscopy (FE-SEM) demonstrated that andrographolide remarkably inhibited the biofilm-forming ability of L. monocytogenes 10403S. The preformed biofilms were eradicated when exposed to andrographolide, and reduced surviving cells were also observed in treated biofilms. L. monocytogenes treated with andrographolide exhibited decreased ability to secrete LLO and adhere to and invade Caco-2 cells. Therefore, andrographolide is a potential QS inhibitor by targeting the Agr QS system to reduce biofilm formation and virulence of L. monocytogenes.

DNase inhibits early biofilm formation in Pseudomonas aeruginosa- or Staphylococcus aureus-induced empyema models

“…We used a previously described biofilm CLSM method ( Yu et al., 2022 ). Briefly, biofilms were grown on confocal Petri dishes for 24 h in the absence or presence of DNase I (final concentration, 66.7 U/L).…”

Recent advances on the regulation of bacterial biofilm formation by herbal medicines

“…They found that andrographolide significantly decrease the lactate dehydrogenase release, F-actin cytoskeleton polymerization, and bacterial adhesion to chicken type II pneumocytes by inhibiting the expression of QS signaling molecule AI-2 and virulence factors ( Guo et al, 2014 ). However, study also showed that andrographolide had no effect on the production of AI-2, but significantly decreased the expression level of arg gene and the activity of arg promoter P 2 , leading to inhibition of the biofilm formation and virulence of L. monocytogenes ( Yu et al, 2022 ).…”

Physicochemical Characteristics and Antibacterial Activities of Freeze-Thawed Polyvinyl Alcohol/Andrographolide Hydrogels

“…Specifically, AG can hinder the growth of bacterial biofilms, inhibit the virulence factors, separate the adhesion between bacteria, and destroy the bacterial integrity in direct bacteriostatic action. 24 Nevertheless, the clinical application of AG is still difficult due to its poor solubility. Hence, there is a thorough effort to increase the clinical effectiveness of AG by modifying the structure to increase the solubility or by improving the delivery system.…”

“…Specifically, AG can hinder the growth of bacterial biofilms, inhibit the virulence factors, separate the adhesion between bacteria, and destroy the bacterial integrity in direct bacteriostatic action. 24 …”