“Salvia officinalis extract–conjugated magnetite and selenium nanocomposites showed enhanced antibacterial and anti-biofilm activity against multidrug-resistant pathogens”

The increased prevalence of multidrug-resistant (MDR) pathogens and biofilm-associated infections underscores the urgent need for alternative antimicrobial strategies. In this study, MDR testing revealed lower resistance in Gram-positive bacteria (Staphylococcus pasteuri, Listeria monocytogenes, and Bacillus cereus; 69–77%) than in Gram-negative strains (Proteus mirabilis, Pseudomonas aeruginosa, and Escherichia coli; 83–92%). Magnetite nanoparticles (Fe3O4NPs) and selenium nanoparticles (SeNPs) were synthesized via a green chemical reduction using L-ascorbic acid, followed by their conjugation with Salvia officinalis (SaO) aqueous extract to enhance stability and biological activities. TEM, DLS, XRD, and FT-IR analyses confirmed the nanoscale crystalline structure of the synthesized metal nanoparticles (MNPs) and the successful integration of SaO phytoconstituents into the nanocomposites. Phytochemical characterization further revealed variable adhesion and retention of SaO bioactive compounds within the two nanocomposites. The MIC values of SaO-Fe3O4NPs (0.03–1) and SaO-SeNPs (0.03–0.5 µg/mL) were not only dramatically lower than the SaO extract (125–500 µg/mL) and MNPs (0.5–25 µg/mL), but also comparable to or even exceeded meropenem (0.25–2 µg/mL). Vigorous antibacterial activity validated by TEM, revealing extracellular and intracellular deformations, in accordance with the growth curve inhibition patterns. The nanocomposites also demonstrated potent antibiofilm activity, achieving 32.5–59.5% inhibition with SaO-Fe₃O₄NPs and 30.2–56.7% with SaO-SeNPs, surpassing meropenem, which exhibited maximum inhibition values of 32.5–47.6%.