Green-synthesized metal oxide nanoparticles enhance the antibacterial activity of Portulaca oleracea through foliar nano-elicitation

Acne-associated and other skin-related bacterial infections are increasingly difficult to manage because of antimicrobial resistance and the need for safer therapeutic alternatives. Portulaca oleracea is a medicinal plant with recognized bioactive potential, yet its antibacterial activity can potentially be enhanced through nano-elicitation. Unlike studies that examine nanoparticles as direct antimicrobials, this work investigated green-synthesized metal oxide nanoparticles as foliar elicitors to improve the antibacterial potential of P. oleracea extracts. This approach links sustainable nanoparticle synthesis with medicinal-plant priming to generate extracts with greater activity against acne-associated pathogens. Zinc oxide, magnesium oxide, and alpha-iron oxide nanoparticles were synthesized using aqueous Psidium guajava leaf extract and verified by standard physicochemical characterization. P. oleracea plants received foliar applications of 100 ppm nanoparticle suspensions under greenhouse conditions, after which methanolic aerial-part extracts were evaluated against Staphylococcus aureus, Escherichia coli, and Cutibacterium acnes. Iron oxide treatment produced the strongest response without visible phytotoxicity. By day 25, FeNP-treated plants reached 10.7 ± 0.7 cm in height and 12 ± 1 leaves, compared with 9.1 ± 0.6 cm and 10 ± 1 leaves in untreated controls. Extracts from FeNP-treated plants also showed the highest antibacterial activity, with inhibition zones of 20.0 ± 1.7 mm against S. aureus, 15.7 ± 1.5 mm against E. coli, and 18.3 ± 1.5 mm against C. acnes. These findings show that foliar nano-elicitation, particularly with FeNPs, can enhance plant growth and strengthen the antibacterial potential of P. oleracea. Because phytochemical changes were inferred indirectly from FTIR patterns and antibacterial response rather than direct metabolite quantification, future studies should perform quantitative phytochemical profiling and confirm extract potency through MIC and MBC assays.