Phytochemical Constituents of Justicia carnea Leaves and their Antibacterial Activity

Abstract

The use of plant-based therapeutics in the treatment of bacterial infections is of utmost importance in ethnomedicine and the research into the bioactive constituents of ethnomedicinal plants is still ongoing. Hence, this research aimed to determine the phytochemical constituents of Justicia carnea extracts and their antibacterial activities against Streptococcus pneumoniae, Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae, and Salmonella typhi, which are responsible for infections such as urinary tract infection, sepsis, abscesses, pneumonia and diarrhea. The methanol (MCE), n-hexane (HCE), chloroform (CCE), and methanol/water (MWCE) crude extracts were prepared using the pulverized leaves of J. carnea. The crude extract was extracted using the column chromatographic technique while purification was achieved using Sephadex LH-20 over flash chromatography. The isolated compounds’ purity was assessed using TLC and melting point. 1D and 2D NMR spectra identified chlorogenic acid (1), quinaldic acid (2), and oleic acid (3) as compounds in n-hexane leaves extract. We report for the first time the isolation of quinaldic and chlorogenic acids from J. carnea. The antibacterial activities were assessed based on the average diameter of the zone of inhibition, MIC, and MBC. All bacterial assayed were susceptible to MCE (≥ 11.2 ± 0.12 mm), HCE (≥ 13.1 ± 0.09 mm), CCE (≥ 9.2 ± 0.12 mm), MWCE (≥ 10.10 ± 0.10 mm), chlorogenic acid (1) (≥ 11.1 ± 0.13 mm), quinaldic acid (2) (≥ 8.1 ± 0.07 mm) and not to oleic acid (3) (≤ 2.1 ± 0.07 mm). The results showed that J. carnea contained medicinal compounds that are viable antibacterial agents.