Antibacterial Activities and Chemical Compounds of Plantago lanceolata (Ribwort Plantain) and Plantago major (Broadleaf Plantain) Leaf Extracts

Background: Plantago lanceolata L. (ribwort plantain) and Plantago major L. (broadleaf plantain) are widely used in ethnobotanical studies and for treating various diseases. This study aims to investigate the antimicrobial activity and chemical compounds of these plants.  Methods: The leaf extracts of P. lanceolata and P. major were fractioned using different solvents. The phytochemical screening was carried out by the gas chromatography-mass spectrometry (GC-MS) method. The antibacterial activity of extracts was assessed using the disc diffusion method, and the minimum inhibitory concentration (MIC) and the minimum bactericidal concentrations (MBC) were measured by microtiter-broth dilution method.  Results: The dichloromethane leaf extract of P. lanceolata and P. major showed the highest antibacterial activity against Salmonella paratyphi (diameter of the inhibition zone: ۱۸.۸۳ and ۲۰.۰۰ mm, respectively) at ۱۰۰ mg/mL concentration. The lowest MIC was related to dichloromethane extracts of both plants against S. paratyphi (۵۰۰ µg/mL). The lowest MBC (۱۰۰۰ µg/mL) was related to the dichloromethane extract of P. major against S. paratyphi. The main compounds of P. lanceolata leaf extracts were bis(۲-ethylhexyl) phthalate (۴۱.۹۶%), ۱-methoxy-۳-(۲-hydroxyethyl)nonane (۳۲.۶۹%), bicyclo[۳.۱.۱]heptane, ۲,۶,۶-trimethyl- (۱.alpha.,۲.beta.,۵.alpha.)- (۱۰.۴۵%), and cycloheptasiloxane tetradecamethyl- (۲۷.۹۶% and ۳۱.۳۳%). The main compounds of P. major leaf extracts were eicosane (۲۳.۶۲%), cyclohexasiloxane dodecamethyl- (۱۸.۲۱%), ۱-methyl-۳-n-propyl-۲-pyrazolin-۵-one (۱۸.۰۸%), cycloheptasiloxane tetradecamethyl- (۳۳.۸۵%), and ۱,۲-benzisothiazole-۳-acetic acid, methyl ester (۳۴.۲۶%).  Conclusion: Fractionation of the methanolic leaf extract of P. lanceolata and P. major can help better isolate active components from these plants. The antibacterial properties of the extracts of two plants may be due to the presence of antibacterial compounds detected in GC-MS.

Keywords:

Disc diffusion method , Phytochemical analysis , Microtiter broth dilution , Plantago lanceolata , Plantago major