Antibacterial Activity and Metabolite Content of Water and Methanolic Extracts of Purple and White Bougainvillea sp.

Bougainvillea sp. is a common ornamental plant grown all over Malaysia with several medicinal claims including the treatment for bacterial infection. This study investigated the extraction of the bracts and leaves of purple and white Bougainvillea sp. using methanol and water, tested the extracts' antibacterial activity against Escherichia coli and Bacillus cereus, and identified the metabolites using gas chromatography and mass spectrometry (GC/MS).  The extraction yields of the extracts ranged from 9.6% to 31.3% with the highest yield observed in purple Bougainvillea sp. methanolic leaf extract. No significant differences were observed between water and methanol extraction of the bract samples, while in leaf samples, significantly higher extraction yield can be achieved using 80% aqueous methanol. All the extracts exhibited mild antibacterial activities against E. coli and B. cereus and especially higher in the methanolic extracts of bracts of white and leaves of purple Bougainvillea sp. A total of 71 volatile compounds were identified using GC/MS, in which 55 and 60 compounds were identified in bract and leaf extracts, respectively. The two extracts with the highest antibacterial activities shared six similar metabolites which are pyridine, benzoic acid, 2-methoxy-4-vinylphenol, methyl hexadecanoic acid, n-hexadecanoic acid and phytol.  These compounds are known to possess antibacterial as well as other bioactivities. In conclusion, the metabolite identification and profile provide more insight into the antibacterial activity of the leaf and bract extracts of Bougainvillea sp., which might be further explored as a potential natural antibacterial agent source.