Incorporating nanoparticles into plant cultivation has been shown to improve growth parameters and alter the bioactive component compositions of many plant species, including Curcumin longa. The aim of the current study was to investigate the effects of foliar application of zinc oxide nanoparticles on the content of bioactive compounds and their antibacterial activities against potential bacterial pathogens. To this end, C. longa leaves were treated with different doses of ZnO NPs to see how this affected their bioactive component composition. The effect of different doses of ZnO NPs on the accumulation of bisdemethoxycurcumin, demethoxycurcumin, and curcumin in ethanolic extracts of C. longa rhizomes was evaluated using high-performance liquid chromatography (HPLC). When compared to the control treatment, foliar spraying with (5 and 40 mgL-1) of ZnO NPs increased bisdemethoxycurcumin, demethoxycurcumin, and curcumin levels approximately (2.69 and 2.84)-, (2.61 and 3.22)-, and (2.90 and 3.45)-fold, respectively. We then checked whether the ethanolic extracts produced from the plantlets changed in terms of their phytochemical makeup and antibacterial properties. Furthermore, the results revealed that C. long-ZnO NPs displayed antibacterial activity against the tested S. aureus and P. aeruginosa bacterium strains, but had a few effect against E. coli. The MIC for P. aeruginosa was 100 g/mL. The time-kill studies also revealed that ZnO NPs at 4 MIC killed P. aeruginosa, Actinobacteria baumannii, and Bacillus sp. after 2 h, while S. aureus did not grow when treated with 4 × MIC of the extract for 6 h. The strongest antibacterial activity was seen in the extract from plantlets grown without nanoparticles for P. aeruginosa, whereas it was seen in the extract from plantlets grown in the presence of 5 mg/L ZnO NPs for E. coli, S. aureus, and P. aeruginosa. These findings show that ZnO NPs are powerful enhancers of bioactive compound production in C. longa, a trait that can be used to combat antibiotic resistance in pathogenic bacterial species.
Keywords: Curcumin longa; antibacterial; nanoparticles; zinc oxide.