Quorum Quenching Potential of the Indigenous Kalimantan Fern Stenochlaena palustris Against Pseudomonas aeruginosa.

&lt;b&gt;Background and Objective:&lt;/b&gt; Plant-derived compounds that disrupt bacterial quorum sensing (QS) provide alternatives to combat antibiotic resistance. This quorum quenching (QQ) strategy reduces virulence without inhibiting growth, thus minimizing resistance. Kelakai (&lt;i&gt;Stenochlaena palustris&lt;/i&gt; (Burm.) Bedd.), an endemic Kalimantan plant traditionally used by the Dayak people, was evaluated for QQ activity against &lt;i&gt;Pseudomonas aeruginosa&lt;/i&gt;. &lt;b&gt;Materials and Methods:&lt;/b&gt; Ethanolic extract of &lt;i&gt;S. palustris&lt;/i&gt; leaves was prepared by maceration with 96% ethanol. The extract was tested for inhibition of &lt;i&gt;P. aeruginosa &lt;/i&gt;motility, pyocyanin production and LasA activity. Antibiofilm effects were assessed using the microtiter plate method, EPS quantified, chemical profiling performed by Liquid Chromatography-High-Resolution Mass Spectrometry (LC-HRMS) and acute toxicity evaluated in &lt;i&gt;Rasbora lateristriata&lt;/i&gt; embryos. The results from three independent trials were analyzed in SPSS using one-way ANOVA followed by Dunn's test, with significance set at p<0.05. &lt;b&gt;Results:&lt;/b&gt; At 0.25 mg/mL, the extract inhibited swarming and twitching by 58.04±0.46% and 64.98±0.25%, reduced LasA activity to 58.27±0.70% and reduced pyocyanin to 49.96±1.15%. Although antibacterial activity was weak, at a concentration of 0.25 mg/mL the extract caused 52.47±0.58% inhibition of &lt;i&gt;P. aeruginosa&lt;/i&gt; biofilm formation and &lt;i&gt;P. aeruginosa&lt;/i&gt; EPS was reduced to 67.40±0.54% of the untreated control. At a concentration of 1 mg/mL, pre-formed biofilm was eradicated as much as 58.52±0.23%. The LC-HRMS identified (-)-Strychnine, D-(+)-Pipecolinic acid and Ethyl oleate as major constituents. Toxicity testing revealed developmental toxicity in embryos at 0.06 mg/mL. &lt;b&gt;Conclusion:&lt;/b&gt; &lt;i&gt;Stenochlaena palustris&lt;/i&gt; ethanol extract showed strong QQ activity against &lt;i&gt;P. aeruginosa&lt;/i&gt;, underscoring its potential as a natural anti-infective. Further isolation of active compounds with reduced toxicity is required for therapeutic development.