Uncaria gambier Roxb flavonoid extraction, antibacterial activity assessment against Escherichia coli, and flavonoid bio-nanoparticle preparation

Escherichia coli (E. coli) was reported to cause 1.7 billion diarrhea cases per year in Indonesia, with a population of 275 million projected for 2024. This study reports the successful use of natural flavonoids from the medicinal plant Uncaria gambier Roxb (UGR) against E. coli. The flavonoid extraction was performed using the decoction method on small pieces of very hard UGR stem to replicate the traditional method, which has been proven effective for generations. The flavonoid content was determined using the aluminum chloride colorimetric assay and visible spectrophotometry. The antibacterial assessment was carried out using the Kirby-Bauer method. Furthermore, bio-nanoparticles were created using filtration, centrifugation, and subsequent characterization using the dynamic light scattering technique. The results showed that the flavonoid content in UGR was (31.55 ± 0.29) mg QE/g. By using the prediction curve and employing the same concentration unit, namely %, the effectiveness of 5% chloramphenicol was found to be the same as that of 0.0225% flavonoids. E. coli showed resistance to 5% chloramphenicol after 39 hours, which continued to decrease slowly, as indicated by the reduction in clear zone diameter. However, it did not show resistance against the flavonoid at all concentrations up to the last measurement at 75 hours. These findings suggest that UGR can be a promising source of natural flavonoids that have been proven to be efficacious in combating E. coli.