Cinnamon-Derived Iron Oxide Nanoparticles Show Potent Activity Against Carbapenem-Resistant Uropathogenic E. coli

Researchers in Iraq and Malaysia have reported that iron oxide nanoparticles synthesised using an aqueous bark extract of Ceylon cinnamon (Cinnamomum verum) exhibit powerful antibacterial, anti-biofilm and virulence-suppressing activity in vitro against clinically isolated carbapenem-resistant uropathogenic Escherichia coli (UPEC). The study, published in International Microbiology, addresses one of the most urgent problems in infectious disease medicine: urinary tract infections caused by Enterobacteriaceae that no longer respond to carbapenems, the last-line beta-lactam antibiotics. Carbapenem-resistant Enterobacteriaceae (CRE) are designated critical priority pathogens by the World Health Organization, and the isolates examined in this work were resistant to all three clinically used carbapenems, retaining susceptibility only to amikacin, gentamicin, fosfomycin and nitrofurantoin, all of which carry limitations in efficacy, toxicity or bioavailability.

The research team, led by Ahmed Abass Fadel and Khalid H. Alobaidi of Al-Nahrain University in Baghdad together with Jameel R. Al-Obaidi of Universiti Pendidikan Sultan Idris in Malaysia, screened 100 midstream urine samples from patients with symptomatic urinary tract infections at three Baghdad hospitals. Two E. coli isolates fulfilled the formal criteria for carbapenem resistance, showing minimum inhibitory concentrations of ertapenem of at least 8 mg/L, imipenem of at least 16 mg/L and meropenem of 8 mg/L, and they were additionally resistant to 15 of the 19 antimicrobial agents tested by the VITEK 2 automated system. The authors stress that the low recovery rate of only two CRE isolates reflects the actual prevalence of carbapenem resistance in their cohort rather than deliberate selection, and they frame their findings explicitly as proof-of-concept evidence.

The synthesis route was deliberately simple and environmentally benign. Dried cinnamon bark purchased from local markets in Baghdad was authenticated by the College of Agriculture at Al-Qasim Green University, ground into powder, and extracted in distilled water for 24 hours at room temperature. Anhydrous ferric chloride was then dissolved in the freshly prepared extract and stirred in darkness for 45 minutes, with the phytochemicals in the extract acting simultaneously as bioreductants, converting ferric iron into iron oxide, and as capping agents that adsorb onto the particle surface and stabilise the growing nanoparticles. The researchers recovered the precipitate by centrifugation, washed it with ethanol, and dried it at approximately 40 degrees Celsius before comprehensive physicochemical characterisation.

Characterisation data converged on the formation of an iron oxide nanoparticle preparation carrying a substantial organic corona. Ultraviolet-visible spectroscopy showed that the extract’s absorption maximum at 300 nanometres shifted to 290 nanometres in the nanoparticle preparation, a blue shift consistent with a change in the coordination environment of ferric iron during particle formation. Fourier-transform infrared spectroscopy revealed the diagnostic iron-oxygen stretching vibration at 621.08 per centimetre, alongside retained bands attributed to the phenolic hydroxyl, aliphatic carbon-hydrogen, carbonyl and carbon-carbon double bond functionalities of trans-cinnamaldehyde and related phytochemicals, confirming that the plant-derived molecules remained on the particle surface. Field-emission scanning electron microscopy showed dense, semi-spherical aggregates with an illustrative mean diameter of 65.63 nanometres, while atomic force microscopy, which the authors regard as the more statistically robust measurement because it sized 905 particles, yielded a mean diameter of 49.23 nanometres.

Energy-dispersive X-ray spectroscopy quantified the elemental composition as 61.01 percent carbon, 23.43 percent oxygen, 9.15 percent chlorine and 6.41 percent iron. The high carbon fraction reflects the abundance of the phytochemical capping layer, and the co-presence of iron and oxygen signals, together with the infrared evidence, supports iron oxide formation. However, X-ray powder diffraction showed a broad amorphous hump centred near 15 to 25 degrees two-theta with no discrete Bragg peaks, indicating that the room-temperature biogenic synthesis produced a predominantly amorphous or poorly crystalline material rather than a well-defined crystalline hematite phase. The authors accordingly use the designation iron oxide nanoparticles as a working label, note that the residual chlorine most plausibly represents trapped chloride within the organic corona, and identify calcination with confirmatory diffraction, together with X-ray photoelectron or Moessbauer spectroscopy, as priorities for unambiguous phase identification in future work.

The antibacterial results were striking. The crude cinnamon extract alone required a concentration of 25 milligrams per millilitre to inhibit the carbapenem-resistant UPEC culture, whereas the nanoparticle preparation achieved a minimum inhibitory concentration of 0.19 milligrams per millilitre, a 131.6-fold improvement in potency. The authors attribute this enhancement to three concurrent and synergistic mechanisms: Fenton-type hydroxyl radical generation by the iron oxide core, in which ferric iron is reduced to ferrous iron that reacts with hydrogen peroxide to produce highly reactive hydroxyl radicals capable of simultaneously attacking nucleic acids, membrane lipids and proteins; electrostatic interaction between the charged nanoparticle surface and the anionic lipopolysaccharide of the Gram-negative outer membrane, which promotes localisation of reactive oxygen generation at the cell surface; and the intrinsic antibacterial activity of the retained cinnamaldehyde- and eugenol-rich capping layer, which disrupts bacterial membranes and inhibits amino acid decarboxylases. Crucially, none of these mechanisms depends on the molecular machinery of carbapenem resistance, which typically involves carbapenemase enzymes that hydrolyse the beta-lactam ring, loss of porin channels such as OmpC, and active efflux via pumps such as AcrAB-TolC.

Anti-biofilm activity, measured with a crystal violet microplate assay over 24 hours, was potent and concentration-dependent. For the first isolate, blank-corrected biofilm inhibition reached 93.4 percent at 50 milligrams per millilitre and 73.7 percent at 12.5 milligrams per millilitre, with statistical significance confirmed by one-way analysis of variance with Tukey’s post-hoc test across three biological replicates. Near-complete suppression was observed for the second isolate at the highest concentration, although the researchers interpret that particular result cautiously because the blank absorbance was elevated at that dose. Biofilm formation is central to the clinical persistence of UPEC, particularly in catheter-associated infections, because the curli and cellulose matrix shields bacteria from antibiotics and immune clearance and creates conditions favourable for the horizontal transfer of resistance plasmids, including those carrying carbapenemase genes.

Perhaps the most novel dimension of the study is the transcriptional analysis. When the isolates were exposed to a sub-lethal concentration of the nanoparticles, half of the minimum inhibitory concentration, quantitative reverse-transcription PCR with the 16S rRNA gene as the reference showed strong suppression of two key virulence genes. Expression of csgD, the master regulator of curli and cellulose biosynthesis, fell by 93.8 percent in the first isolate and 89.1 percent in the second, a mean reduction of 91.5 percent. Expression of fimH, which encodes the adhesin at the tip of type 1 fimbriae that binds mannosylated uroplakin receptors on bladder cells and initiates the invasion-persistence cycle underlying recurrent infection, was reduced by 98.3 percent in the first isolate, roughly a 59-fold suppression, and by 80.7 percent in the second, a mean of 89.5 percent. The transcriptional suppression of csgD is mechanistically coherent with the observed anti-biofilm phenotype, since silencing this regulator dismantles the genetic programme for extracellular matrix assembly. The authors propose three non-exclusive explanations: sub-lethal reactive oxygen species may activate global stress regulators such as OxyR and SoxRS that divert transcriptional resources away from virulence; nanoparticle perturbation of intracellular iron homeostasis could dysregulate the ferric uptake regulator, which controls roughly 90 genes in E. coli including virulence loci; or direct nanoparticle-DNA interaction may impede transcription factor binding at the target promoters. None of these hypotheses was directly tested, and the team identifies RNA sequencing, regulator activity assays and intracellular iron quantification as needed follow-up experiments.

The authors are notably candid about the limitations of their work. The virulence gene data derive from only two treated biological replicates, below the conventional threshold of three for inferential statistics, so the fold-change values are presented as strong preliminary evidence requiring independent confirmation. Only two clinical isolates were available for testing, and species identification relied solely on the VITEK 2 system at a 92 percent identification probability without orthogonal molecular confirmation. No reference antibiotic comparator was included in the minimum inhibitory concentration assays, no reactive oxygen species detection or scavenger-rescue experiment was performed, and no dynamic light scattering, zeta potential, cytotoxicity, biocompatibility or in vivo efficacy data were generated. The researchers emphasise that therapeutic potential remains prospective rather than demonstrated, and that validation across a larger, phylogenetically diverse panel of CRE UPEC isolates, formal toxicity assessment and bladder colonisation models constitute essential next steps. Nevertheless, the combination of a 131.6-fold potency gain over the crude extract, 93.4 percent anti-biofilm activity and profound transcriptional silencing of the two pivotal UPEC virulence genes, in pathogens resistant to every carbapenem tested, marks this cinnamon-derived nanoparticle platform as a compelling in vitro candidate in the search for alternatives to conventional antibiotics against critical-priority resistance threats.

Subject of Research: Green-synthesised iron oxide nanoparticles as antibacterial and anti-virulence agents against carbapenem-resistant uropathogenic Escherichia coli

Article Title: In Vitro antibacterial, anti-biofilm, and virulence-modulating activity of Cinnamomum verum–mediated iron oxide nanoparticles against carbapenem-resistant uropathogenic Escherichia coli

Article References: Fadel, A. A., Alobaidi, K. H., & Al-Obaidi, J. R. (2026). In Vitro antibacterial, anti-biofilm, and virulence-modulating activity of Cinnamomum verum–mediated iron oxide nanoparticles against carbapenem-resistant uropathogenic Escherichia coli. International Microbiology. https://doi.org/10.1007/s10123-026-00876-3

Image Credits: AI Generated

DOI: 10.1007/s10123-026-00876-3

Keywords: iron oxide nanoparticles, green synthesis, Cinnamomum verum, carbapenem-resistant Enterobacteriaceae, uropathogenic Escherichia coli, biofilm, csgD, fimH, anti-virulence, urinary tract infection, reactive oxygen species, nanomedicine