Green biosynthesis of selenium nanoparticles by <i>Ralstonia insidiosa</i> which demonstrate effectiveness against human cancer cells, <i>Candida</i> species and multidrug-resistant <i>Acinetobacter baumannii</i>

isolates. SeNP treatment resulted in strain-dependent modulation of MexB expression, indicating variable bacterial responses rather than consistent efflux inhibition. In addition, cytotoxicity assays demonstrated dose-dependent antiproliferative effects of SeNPs against PC3 prostate cancer cells, with lower toxicity toward normal WRL68 liver cells.