Antibacterial activity and metabolite profile of water and methanolic extracts of bougainvillea spectabilis

Abstract

Bougainvillea spectabilis is believed to possess several medicinal benefits that includes the use of the extract for the treatment of diseases related to bacterial infection. This study aimed at the extraction of water and methanol extracts of different colours of Bougainvillea spectabilis flowers and leaves, evaluation of antibacterial activity of the extracts against Escherichia coli and Bacillus cereus, and identification of the active metabolites via gas chromatography and mass spectrometry (GC/MS). Extraction of the plant extract was carried out using two different solvents, methanol and water. The B. spectabilis plant parts were extracted with two solvents (water and 80% methanol). The yield percentage of B. spectabilis extracts ranged from 9.63% to 31.3% with purple B. spectabilis leaves methanolic extracts (MLP) have the highest yield (28.85%). All the extracts exhibited mild antibacterial activities against the bacteria tested especially in the liquid culture test. The susceptibility of the bacteria was higher in the methanolic extract than in the water extract especially in white flower and leaves extracts (MWF and MLP) which were able to reduce the growth rate of Escherichia coli and Bacillus cereus during the lag phase and log phase. For the identification of metabolites via GC/MS, this analysis was able to identify a total of 71 volatile compounds, in which 32 compounds were identified in water extracts and 50 compounds in methanolic extracts. Both white flower and leaves methanolic extracts (MWF and MLP) shared 6 similar compounds which are pyridine, benzoic acid, 2- methoxy-4-vinylphenol, hexadecanoic acid, methyl ester, n-hexadecanoic acid and phytol. All of these 6 compounds were known to possess antibacterial activity. In conclusion, the identification and profiling of the metabolites using GC/MS offers more understanding of the antibacterial activity of B. spectabilis and this plant can be used as a potential source for natural antibacterial agent.