Antibacterial and antimycobacterial activity of crude extracts, fractions, and isolated compounds from leaves of sneezewood, Ptaeroxylon obliquum (Rutaceae)

Abstract

Ptaeroxylon obliquum (Thunb.) Radlk. (Rutaceae) is traditionally used to treat human and animal diseases in South Africa. In this study, the activity of leaf extracts, fractions, and isolated compounds was determined against nonpathogenic mycobacterial species and nosocomial bacterial pathogens. An acetone leaf extract was partitioned by liquid-liquid fractionation, and obliquumol, a mixture of lupeol and β-amyrin, and eranthin were isolated. Antimicrobial activity was determined using a serial microdilution assay against Mycobacterium smegmatis (American Type Culture Collection [ATCC] 1441), M. bovis (BCG P1172), M. aurum (NCTC 10437), M. fortuitum (ATCC 6841), Staphylococcus aureus (ATCC 29213), Enterococcus faecalis (ATCC 29212), Pseudomonas aeruginosa (ATCC 25922), and Escherichia coli (ATCC 27853). The n-hexane fraction had minimal inhibitory concentration (MIC) values as low as 20 and 40 µg/mL against M. fortuitum and S. aureus, respectively. The chloroform fraction also had promising activity with an MIC value of 80 µg/mL against both P. aeruginosa and M. fortuitum. Obliquumol had excellent activity (MIC 8 µg/mL) against M. fortuitum. Fractionation of the crude extract potentiated the antimicrobial activity of the nonpolar fractions. The isolated compound, obliquumol, had good antimicrobial and excellent antimycobacterial activities. The antimicrobial activity provides some scientific rationale for the use of P. obliquum against infectious diseases and related symptoms. This is the first report on the antibacterial activity of obliquumol.