Magnesium oxide nanoparticles made using turnip leaf extract, magnesium nitrate, sodium hydroxide and heat have shown striking antibacterial and antibiofilm power against some of the most troublesome drug-resistant Gram-negative bacteria, according to a new laboratory study published in International Microbiology. All four isolates were multidrug-resistant strains obtained from clinical settings, which makes the result particularly relevant at a time when infections that no longer respond to conventional antibiotics are a growing global threat.
The synthesis itself is deliberately simple. The researchers collected fresh turnip leaves from a local market in Faisalabad, dried and powdered them, and steeped the powder in distilled water to create a leaf extract rich in plant secondary metabolites. They then added magnesium nitrate to the extract, raised the temperature to 80 degrees Celsius, and stirred in sodium hydroxide for two hours. The reaction mixture shifted from green to pale brown, signalling the formation of magnesium hydroxide nanoparticles, which were dried in a muffle furnace and then calcinated at 600 degrees Celsius to yield the final white magnesium oxide powder. The plant compounds in the extract act as natural reducing and capping agents, steering the formation of the nanoparticles without the harsh solvents and reagents that conventional chemical synthesis typically requires.
Characterisation confirmed that the nanoparticles were genuine, well-formed magnesium oxide. Ultraviolet-visible spectroscopy showed a sharp absorption peak at 295 nanometres, with no significant absorption beyond 400 nanometres, consistent with the wide band gap expected of magnesium oxide. Infrared spectroscopy revealed a strong magnesium-oxygen vibration band between 500 and 600 inverse centimetres, along with surface hydroxyl groups and a small carbonate signal from adsorbed carbon dioxide. Elemental analysis by energy-dispersive X-ray detection found magnesium at 27.6 percent by weight and oxygen at 54.9 percent, with only minor traces of carbon, sulfur, potassium, iron and cobalt. Scanning electron microscopy showed mostly spherical to quasi-spherical particles with clear boundaries and an average size of 62.78 nanometres, distributed fairly uniformly, though some aggregation was visible, a common behaviour for metal oxide nanoparticles owing to their high surface energy.
When the nanoparticles were tested against the four bacterial isolates using an agar well diffusion assay, they produced inhibition zones ranging from 14 to 29 millimetres in a dose-dependent manner. The largest zone, 29 millimetres, appeared against K. pneumoniae, followed by 27 millimetres against P. aeruginosa. At the lowest concentration tested, 62.5 micrograms per millilitre, no inhibition zone was observed against any of the isolates. The minimum inhibitory concentrations ranged from 125 to 250 micrograms per millilitre, with the lowest values recorded against E. coli and K. pneumoniae. Minimum bactericidal concentrations reached 500 micrograms per millilitre against P. aeruginosa and E. coli, and 1000 micrograms per millilitre against K. pneumoniae and A. baumannii.
The antibiofilm results were the most dramatic part of the study. In tests of planktonic growth, meaning free-floating bacteria rather than those attached to surfaces, the nanoparticles suppressed growth by more than 90 percent at 50 micrograms per millilitre after 48 hours, and by 99 percent at 100 micrograms per millilitre after 72 hours. When the researchers examined whether the nanoparticles could prevent biofilms from forming in the first place, they found that biofilm development was blocked by 60 to 90 percent at 50 micrograms per millilitre, with the effect strengthening as both concentration and exposure time increased. E. coli proved the most susceptible, with biofilm formation inhibited by roughly 97 percent, followed by A. baumannii at about 94 percent and P. aeruginosa at about 93 percent, while K. pneumoniae reached a maximum of around 90 percent inhibition at the highest concentration tested.
Even more striking was what happened to biofilms that had already been established. The researchers allowed biofilms to mature for 24, 48 or 72 hours before adding the nanoparticles, mimicking the stubborn, entrenched communities that form on medical devices and hospital surfaces. At half the minimum inhibitory concentration, biofilm disruption exceeded 50 percent for all isolates within 24 hours, rose above 87 percent at 48 hours, and approached complete removal, exceeding 97 percent, after 72 hours for E. coli, A. baumannii and K. pneumoniae. At the full minimum inhibitory concentration, inhibition reached 95 to 99 percent in most strains by 48 to 72 hours, with E. coli and K. pneumoniae showing near-total eradication of mature biofilms at 99 and 99.1 percent respectively, and P. aeruginosa and A. baumannii showing reductions of 99.5 and 97 percent.
To understand how the nanoparticles were dismantling these biofilms, the team analysed the extracellular polymeric substances, the glue-like matrix of proteins, carbohydrates and extracellular DNA that holds a biofilm together and shields its residents from antibiotics and immune attack. The results showed substantial destruction of this matrix. Proteins decreased by 68 percent, carbohydrates by 55 percent, and extracellular DNA by 33 percent. The pattern varied by species: K. pneumoniae showed the strongest DNA-targeting effect, with inhibition reaching 32.7 percent after 72 hours, while protein inhibition exceeded 60 percent in K. pneumoniae and peaked at 67.8 percent at 24 hours. A Congo red agar assay reinforced these findings, as colonies grown on plates containing sub-inhibitory concentrations of the nanoparticles lost their characteristic black coloration and turned pinkish, indicating that slime production had been visibly curtailed.
The mechanistic picture that emerged centres on reactive oxygen species. When the bacteria were treated with sub-inhibitory concentrations of 50 micrograms per millilitre of the nanoparticles, intracellular ROS levels rose two to three times above those of untreated controls, with the largest increase observed in E. coli, followed by P. aeruginosa. The researchers propose that magnesium oxide nanoparticles release magnesium ions that dysregulate the formation of oxygen-derived free radicals, overwhelming the bacterial antioxidant defences and causing oxidative damage to cell membranes, DNA and proteins. The nanoparticles may also adhere to the cell wall, disrupt membrane integrity, interfere with the electron transport chain and denature proteins, a combination of effects that together compromise bacterial metabolism, structural stability and viability. Because this oxidative assault targets fundamental cellular components rather than a single enzyme or pathway, the researchers suggest it may be harder for bacteria to develop resistance against it than against conventional antibiotics.
The choice of turnip as the synthesis medium is not arbitrary. Brassica rapa contains phenolics, sulfur-based compounds, distinctive flavonoids and potent isoprenoids with antimicrobial and antioxidant properties, and its principal antimicrobial phytochemical, isothiocyanate, is derived from the breakdown of glucosinolates. These phytochemicals can disrupt microbial cell membranes and induce reactive oxygen species themselves, so the plant extract may complement the intrinsic antibacterial qualities of the magnesium oxide. The authors note that this is the first study to report an eco-friendly method for producing magnesium oxide nanoparticles using turnip extracts, and that the fluctuation of secondary metabolites in the plant could encourage nanoparticle development under mild conditions while potentially enhancing antimicrobial activity.
The findings come with important caveats. This was an in vitro study using a small number of clinical isolates, and the assays were performed in microtiter plates rather than in living organisms. The authors themselves state that developing these nanoparticles for clinical use requires further research to determine their compatibility with human cells, to test their effectiveness in vivo, and to work out suitable delivery methods. The comparison with other studies also shows variability: magnesium oxide nanoparticles made from other plants have shown minimum inhibitory concentrations ranging from 50 to 500 micrograms per millilitre against various pathogens, suggesting that synthesis protocols, particle size and strain-specific resistance mechanisms all influence potency. Nevertheless, the study adds to a growing body of evidence that plant-based nanomaterials can attack biofilms through multiple mechanisms at once, degrading the structural matrix, generating lethal oxidative stress and suppressing slime production simultaneously.
Subject of Research: Green synthesis of Brassica rapa-mediated magnesium oxide nanoparticles with antibacterial and antibiofilm activity against multidrug-resistant Gram-negative bacteria
Article Title: Green synthesis of Brassica rapa–mediated magnesium oxide nanoparticles MgO NPs with ROS-driven antibacterial and antibiofilm activities against multidrug-resistant gram-negative bacteria
Article References: Muzammil, S., Khalid, M. H., Siddique, M. H., Ijaz, M. U., Taj, Z., Nisar, M. A., Hayat, S., Hashem, A., Alarjani, K. M., Alharbi, M. G., & Abd＿Allah, E. F. (2026). Green synthesis of Brassica rapa–mediated magnesium oxide nanoparticles MgO NPs with ROS-driven antibacterial and antibiofilm activities against multidrug-resistant gram-negative bacteria. International Microbiology. https://doi.org/10.1007/s10123-026-00907-z
Image Credits: AI Generated
DOI: 10.1007/s10123-026-00907-z
Keywords: magnesium oxide nanoparticles, Brassica rapa, green synthesis, antibiofilm, multidrug-resistant bacteria, Gram-negative bacteria, reactive oxygen species, extracellular polymeric substances, Acinetobacter baumannii, Pseudomonas aeruginosa, Klebsiella pneumoniae, antimicrobial resistance
News Source: Drew Townsend. (October 28, 2026). Turnip-made magnesium nanoparticles dismantle drug-resistant bacterial biofilms in lab tests. Scienmag.
