Background and Objective: In the field of healthcare, bacterial infections are a leading cause of global morbidity and mortality. With growing concerns about multidrug-resistant strains and zoonotic (human-aquatic) infections, there is an urgent need to develop novel antibacterial agents based on nanotechnology. Therefore, these studies aimed to biosynthesize and evaluate a biocompatible magnetite iron oxide/PEG/rosemary essential oil/alginate bio-nanocomposite film for targeting human and aquatic microbial pathogens.

Materials and Methods: The bio-nanocomposite films were synthesized via a high-temperature copolymerization process using a polymeric matrix of sodium alginate, glycerol, and polyethylene glycol (PEG). This matrix was incorporated with biosynthesized superparamagnetic magnetite iron oxide nanoparticles (Bio-Fe₃O₄ MNPs). These nanoparticles were phycosynthesized in a concentration range (0.375% - 6%) using an aqueous extract of the green marine alga Ulva prolifera. Additionally, rosemary (Rosmarinus officinalis) essential oil and honey were used. The successful synthesis of the iron-based bio-nanocomposite films was confirmed by qualitative analyses including TEM, FESEM, EDX, and FTIR. Subsequently, their antimicrobial potential was tested against human pathogens (four bacterial strains and one fungal strain) and four aquatic pathogenic strains using the disk diffusion method and minimum inhibitory concentration (MIC) assays.

Results: The results demonstrated that the inhibitory activity of the magnetite iron oxide/PEG/rosemary essential oil/alginate bio-nanocomposite films against Gram-positive and Gram-negative bacterial pathogens was significantly stronger compared to standard antibiotics (ampicillin, oxytetracycline, and florfenicol). The most sensitive human and aquatic bacterial pathogens to the antibacterial effects of the iron bio-nanocomposite were P. aeruginosa (ZI = 33 ± 0.2 mm) and A. hydrophila (ZI = 23 ± 0.7 mm), respectively. Regarding antifungal activity, the results indicated a relatively comparable effect to the standard antifungal agent, nystatin.

Conclusion: This study confirmed the presence of enhanced synergistic antimicrobial effects in the final biosynthesized iron bio-nanocomposite structure, resulting from the combined actions of biosynthesized magnetite nanoparticles, polyethylene glycol, sodium alginate, and the phytotherapeutic compounds of rosemary essential oil.