In vitro assessment of antibacterial activity of selected plant ethanolic extracts against streptococcus pneumoniae

Abstract

Emergence of drug resistant isolates of Streptococcus pneumoniae threatens the usefulness of common antibiotics in treatment of acute otitis media and has partly contributed to the popularity of herbal medicine use. It is estimated that 80% of the global population utilizes herbal medicine for some aspect of primary health care. However, there is limited scientific evidence to verify the efficacy of most herbal products; and thus many herbal preparations are being used without scientific data. This study determined the antimicrobial activity of ethanolic extracts of Markhamia lutea flowers, the bark of Acacia hockii, the leaves of Siegesbekia orientalis and the whole plant of Caralluma dummeri against penicillin susceptible and penicillin resistant S. pneumoniae. Isolates of S. pneumoniae were isolated from nasopharyngeal specimens of children under five years in the Iganga/Mayuge Demographic Surveillance Site (DSS). The isolates were also screened for the presence of β-lactam and macrolide resistance genes, PBP2B(b), mef(A) and erm(B), to test for any relationship between susceptibility to plant extracts and presence of these genes. Phytochemical analysis of M. lutea and S. orientalis was carried out to determine the presence of tannins, reducing compounds, alkaloid salts, anthracenosides, coumarin derivatives, steroid glycosides, flavonosides and anthocyanosides. Siegesbekia orientalis extract exhibited the highest antibacterial activity against S. pneumoniae isolates, with inhibition zone diameters of ≥15mm in 91 isolates. All isolates found to possess the β-lactam resistance gene (PBP2B(b) were highly susceptible to S. orientalis extract. This study has demonstrated that crude ethanolic extract of all four plant extracts have antibacterial activity against S. pneumoniae although this varied from extract to extract. However, S. orientalis extract had higher antibacterial activity against both penicillin susceptible and penicillin resistant S. pneumoniae; which activity could be due to the presence of tannins, alkaloid salts and flavonoids. Similar plants from other regions should be studied for antibacterial activity. Toxicity studies of these plants should also be done to establish their safety.