Evaluation of the Antibiofilm and Antimicrobial Effects of Selenium Nanoparticles on Multidrug-Resistant Salmonella Isolates

<ns3:p> Background and Aim Globally, <ns3:italic>Salmonella</ns3:italic> is a leading cause of bloodstream infections and foodborne diseases. Treatment and public health are seriously threatened by the rise of multidrug-resistant (MDR) strains and biofilm formation. As a result, novel approaches are required to manage illnesses linked to biofilms. With a focus on the expression of biofilm-related genes, this work attempts to assess the antibiofilm and antibacterial activity of selenium nanoparticles (SeNPs) against MDR <ns3:italic>Salmonella</ns3:italic> isolates. Methods Thirty-two isolates were recovered from 167 blood samples collected from Baghdad, Iraq. All isolates were screened for biofilm formation using congo red and microtiter plate assays. Antimicrobial susceptibility was tested against a range of antibiotics. Selenium nanoparticles were biosynthesized and characterized (UV-Vis, DLS, TEM) and applied at sub-MIC concentrations. RT-qPCR was then done to quantify the expression levels of biofilm-associated genes <ns3:italic>csgD</ns3:italic> and <ns3:italic>ssrB.</ns3:italic> Results All isolates form biofilms, while 75% of them are classified as strong formers. High resistance was observed to beta-lactams; moderate resistance accompanied fluoroquinolones. RT-qPCR results indicated a dose-dependent downregulation of <ns3:italic>csgD</ns3:italic> and <ns3:italic>ssrB</ns3:italic> with the SeNP treatment with stronger suppressive effects at higher concentrations. Conclusions SeNPs effectively inhibit biofilm formation and hold strong antimicrobial activity against MDR <ns3:italic>Salmonella</ns3:italic> , presenting an opportunity for application as adjunctive therapeutic agents in food safety and clinical medicine. </ns3:p>