Characterization of Sesquiterpenes and Antibacterial Activities of Extracts from Piliostigma reticulatum (DL.) Hochst and Cleistopholis patens (Benth.) Engl & Diels against Shigella dysenteriae and Streptococcus pyogenes

Abstract

Aim: The study characterized sesquiterpenes from the bark extracts of Piliostigma reticulatum and Cleistopholis patens and subsequently tested the extracts for their antibacterial activities. Methodology: Ground stem barks of P. reticulatum and C. patens were obtained and extracted with ethyl acetate. The extract from both plants were screened for antibacterial activities against Shigella dysenteriae and Streptococcus pyogenes using the agar well diffusion method. Furthermore, fractions obtained from the crude extracts were also assayed for antibacterial efficacy using the disc diffusion method. The phyto-constituents of the extracts were identified using Gas chromatography and mass spectra (GC-MS) and subsequent characterization was achieved via Nuclear Magnetic Resonance Spectroscopy (NMR). Results: The results showed that P. reticulatum extract had more antibacterial activities on S. dysenteriae with zones of inhibition ranging from 6 mm – 14 mm while it had lesser inhibitory effect against S. pyogenes with zones of inhibition of 10 mm and 8 mm at concentrations of 100 mg/mL and 80 mg/mL respectively. However, C. patens was effective against S. pyogenes with zones of inhibition of 18 mm, 16 mm, 14 mm, 13 mm, and 8 mm at concentrations  of 100, 60, 40, 20 and 10 mg/mL respectively. Crude extracts from both plants exhibited higher antibacterial activity compared to purified fractions against test organisms. A number of five (5) Sesquiterpenes (azulenes, alpha and beta pinene, Germacrene D, Limonene, and Farnesol) were identified from the extracts of both plants. Conclusion: The presence of sesquiterpenes in P. reticulatum and C. patens could be responsible for the antibacterial activities on the test organisms (S. dysenteriae and S. pyogenes) evaluated in this study and subsequently justify their use in folkloric medicine. Hence, the extracts obtained from P. reticulatum and C. patens could be considered as a potential and rich source of antibacterial agent to control infections posed by the test organisms (S. dysenteriae and S. pyogenes).