Pseudomonas aeruginosa causes infections in human particularly immunocompromised patients with cystic fibrosis, severe burns and HIV, resulting in high morbidity and mortality. The pathogenic bacteria P. aeruginosa produces virulence factors regulated by the mechanism called quorum sensing system. The aim of this study was to assess the anti-quorum sensing activity of Ageratum conyzoides extracts. Chromobacterium violaceum reporter strain CV026 was used to highlight any interference with bacterium QS and strains derived from P. aeruginosa PAO1 were used to reveal any interference with the expression of quorum sensing genes, and to assess any impact of extract on the kinetics of the production of pyocyanin, elastases and biofilm formation. Chloroform fraction from hydro-methanolic extract at the sub-inhibitory concentration of 100 µg/mL reduced quorum sensing virulence factors production such as, pyocyanin, elastases, and rhamnolipids in P. aeruginosa PAO1 after 8h and 18 hours monitoring. Moreover, a significant inhibition in HSL-mediated violacein production on C. violaceum CV026 were recorded after 24h and 48 hours monitoring without affecting the bacterial growth. The chloroform fraction was rich in polyphenols and triterpenes and was found to interact with QS receptors. The regulatory genes (rhlR and lasR) and downstream genes (RhlA and lasB) while synthase genes were less affected (lasI and rhlI) were most affected. HPLC-DAD analysis, allowed the identification and quantification some compounds such as gallic acid, vanillic acid, ellagic acid, sinapic acid and quercetin. Caffeic acid, rutin and kaempferol were detected in trace amounts. The presence of these phytochemicals could be responsible for the observed anti-quorum activity. The present study is probably the first attempt to investigate the anti-QS potential of A. conyzoides against P. aeruginosa. These data provide additional scientific evidence to justify the wide use of A conyzoides in traditional medicine in Burkina Faso.

Keywords: Ageratum conyzoides; Chromobacterium violaceum; Pseudomonas aeruginosa; Quorum sensing.