Analysis of the main bioactive compounds from Ocimum basilicum for their antimicrobial and antioxidant activity

The interest in bioactives especially from botanicals to treat vancomycin-resistant enterococcal (VRE) infections is increased. Many species of Ocimum have a long history in folk medicinal and food industries. Nevertheless, their bioactive compounds remain unexplored. This study is aimed to assess the antimicrobial and antioxidant activity of basil leaf extract prepared using ethanol, methanol, and water. The ethanol and methanol extract have all the phytochemicals (alkaloids, flavonoids, phenolic compounds, tannins, saponins, quinones, carbohydrates, and proteins) except steroids and terpenoids. In addition to steroids and terpenoids, tannin was also absent in the aqueous extract. Total phenolic and flavonoid content was high in ethanol and followed by methanol and aqueous extract. Similarly, ethanol and methanol extract showed strong antimicrobial activity against VRE and MTCC strains at a concentration of 20 mg/mL than aqueous extract. Among the 10 indicators, Staphylococcus aureus is highly susceptible to ethanol extract at a concentration of 8 mg/mL and followed by other MTCC strains. Vancomycin-resistant enterococci pathogens were inhibited at the minimum inhibitory concentration of 14, 16, and 20 mg/mL of ethanol, methanol, and aqueous extract. Further, on the basis of determining the absorbing material (nucleic acid and protein) at 260 nm and scanning electron microscopic, it was confirmed that the loss of cell membrane integrity and cell membrane damage were the effective mechanisms of plant extract antimicrobial activity. All three solvents have shown remarkable antioxidant activity. Gas chromatography-mass spectrometry analysis of basil leaves ethanol extract identified 19 compounds with various therapeutic and food applications.