Flavone-Rich Fractions and Extracts from <i>Oroxylum indicum</i> and Their Antibacterial Activities against Clinically Isolated Zoonotic Bacteria and Free Radical Scavenging Effects

• Main Authors: Patchima Sithisarn, Piyanuch Rojsanga, Pongtip Sithisarn
• Format: Article
• Language: English
• Published: MDPI AG 2021-03-01
• Series: Molecules
• Subjects: <i>Oroxylum indicum</i>; zoonotic infection; mechanism of action; flavone; HPLC; DPPH
• Online Access: https://www.mdpi.com/1420-3049/26/6/1773

<i>Oroxylum indicum</i> extracts from the seeds collected from Lampang and Pattani provinces in Thailand, and young fruits and flowers exhibited in vitro display antioxidant and antibacterial activities against clinically isolated zoonotic bacteria including <i>Staphylococcus intermedius</i>, <i>Streptococcus suis</i>, <i>Pseudomonas aeruginosa</i>, <i>β</i>-hemolytic <i>Escherichia coli</i> and <i>Staphylococcus aureus</i>. The orange crystals and yellow precipitates were obtained from the preparation processes of the seed extracts. The orange-red crystals from the seeds collected from Lampang province exhibited strong in vitro 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging effects (EC₅₀ value = 25.99 ± 3.30 μg/mL) and antibacterial effects on <i>S. intermedius</i> and <i>β</i>-hemolytic <i>E. coli</i> while the yellow precipitate from the same source exhibited only antioxidant activity. Quantitative analysis of phytochemicals in <i>O. indicum</i> samples by spectrophotometric and HPLC techniques showed that they contained different amounts of total phenolic, total flavonoid and three major flavones; baicalin, baicalein and chrysin contents. Young fruit extract, which contained low amounts of flavone contents, still promoted antibacterial effects against the tested bacteria with IC₅₀ values lower than 1 mg/mL and MIC values between 4 to 10 mg/mL in <i>S. intermedius, S. aureus</i> and <i>S suis</i> while higher IC₅₀ and MIC values against <i>P. aeruginosa</i> and <i>β</i>-hemolytic <i>E. coli</i> were found. From scanning electron microscopy, the extract of the young fruit of <i>O. indicum</i> promoted morphological changes in the bacterial cells by disrupting the bacterial cell walls, inducing leakage of the cellular content, and generating the abnormal accumulation of cells. The mechanism of action of the extract for this antibacterial effect may be the disruption of the cell membrane and abnormal cell aggregations. Regression analysis of the results suggests the correlation between total phenolic and total flavonoid contents and antioxidant and antibacterial effects. Baicalin was found to have a high correlation with an inhibitory effect against <i>β</i>-hemolytic <i>E. coli</i> while three unidentified peaks, which could be flavones, showed high correlations with an inhibitory effect against <i>S. intermedius</i>, <i>S. suis</i>, <i>P. aeruginosa</i> and <i>S. aureus</i>.