Caracterização química, avaliação da atividade antioxidante e investigação do potencial antibacteriano de extratos etanólicos de folhas de Vernonia polyanthes Less. contra Escherichia coli uropatogênica

Abstract

Vernonia polyanthes Less., commonly known in Brazil as "assa-peixe", is traditionally used to treat various ailments, including those affecting the urinary system. Based on this, the hypothesis arose that extracts from this plant might act on uropathogenic Escherichia coli (UPEC), the primary cause of urinary tract infections (UTIs). In this context, the aim of this study was to evaluate the antibacterial activity of ethanolic extracts from V. polyanthes leaves against reference E. coli and clinical uropathogenic E. coli strains, as well as to chemically characterize these extracts and assess their antioxidant activity, providing scientific data to support the medicinal use of this plant in UTI treatment. Ethanolic extracts at concentrations of 50% (EE-50), 70% (EE-70), and 100% (EE-100) were obtained by ultrasonic bath extraction using ethanol at the respective concentrations. Chemical characterization was performed by high-performance liquid chromatography coupled with diode array detection (HPLC-DAD), while the total phenolic and flavonoid contents were determined by the Folin-Ciocalteu and aluminum chloride complexation methods, respectively. Antioxidant activity was assessed using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging method, and antibacterial potential was investigated using the broth microdilution method to determine the Minimal Inhibitory Concentration (MIC), followed by subculturing to determine the Minimal Bactericidal Concentration (MBC) and classify the antibacterial effect against a panel consisting of two reference strains and eight clinical E. coli strains, totaling ten strains. The results showed similar yields for all three extracts. HPLC-DAD characterization revealed that 5-caffeoylquinic acid is the major compound in EE-50, EE-70, and EE-100. The total phenolic determination indicated that EE-50 and EE-70 contained statistically similar and higher amounts of these compounds compared to EE-100. As for total flavonoids, EE-100 had the highest concentration of these phytoconstituents. The antioxidant activity showed that all extracts inhibited the DPPH free radical, with EE-50 standing out, showing the lowest 50% inhibitory concentration (IC50) of 3.81 ± 0.44 µg/mL. The evaluation of antibacterial potential demonstrated that the extracts inhibited the growth of eight out of the ten E. coli strains tested, with MIC values ranging from 625 to 5,000 µg/mL. EE-100 exhibited moderate to weak activity, with MIC values lower than those found in EE-50 and EE-70. These results suggest that ethanolic extracts from V. polyanthes leaves possess potential antioxidant and antibacterial activities, likely related to the presence of phenolic acids and flavonoids, respectively. The field remains open for the development of new extraction methodologies aimed at optimizing the extraction of more promising extracts, with the goal of developing plant-derived products for the treatment of inflammatory and infectious disorders caused by UPEC.