Native Medicinal Plants and Their Effects on Anti-biofilm and Anti-quorum Sensing Activity

Background: Pseudomonas aeruginosa is an opportunistic pathogen with a high mortality rate, particularly among immunocompromised patients. The increase in antibiotic resistance in P. aeruginosa isolates from clinical samples has prompted researchers to seek alternative ways to reduce the pathogenicity of this microorganism. Targeting quorum sensing (QS) presents a promising approach for limiting infections caused by this bacterium. Objectives: This study aimed to evaluate mechanisms for reducing QS and controlling bacterial growth using various medicinal plants. Methods: In this study, the anti-QS effects of seven plant extracts—thyme (Thymus vulgaris), chamomile (Matricaria chamomilla), sumac (Rhus coriaria), ginger (Zingiber officinale), lemon balm (Melissa officinalis), rosehip (Echinacea angustifolia), and marshmallow (Althaea officinalis)—were investigated against P. aeruginosa. A total of 180 P. aeruginosa clinical isolates were examined. High-performance liquid chromatography (HPLC) was then used to detect phenolic compounds and flavonoids in the seven extracts. The presence of quorum-sensing genes (lasR, rhlR, and rhlI) was also evaluated. In addition, pyocyanin quantification, swarming motility assays, and biofilm formation assays were conducted with the herbal extracts. Results: The HPLC analysis results were determined based on relative times and peak areas, revealing specific peaks at different points. Molecular methods confirmed the presence of QS genes, including LasI (54%), lasR (34%), rhlR (12%), and rhlI (4%), which were used in anti-QS screening. Expression of the LasI gene decreased in P. aeruginosa strains treated with herbal extracts compared to untreated strains. Notably, Thymus vulgaris extract demonstrated the strongest inhibition, reducing violacein production by 70.5%, suppressing pyocyanin by 94%, and inhibiting swarming motility and biofilm formation by 80.3%. Conclusions: This study demonstrated that herbal extracts influence virulence factors and gene expression, particularly targeting the las gene, in P. aeruginosa isolates. We recommend further research on the extraction and identification of active ingredients, which may hold potential as therapeutic agents.