Antibacterial-guided isolation of constituents from Senna alata leaves with a particular reference against Multi-Drug-Resistant Vibrio cholerae and Shigella flexneri

Abstract

Senna alata is widely used in Cameroon for the treatment of several infections which include gonorrhoea, gastro-intestinal and skin diseases. Therefore, its leaves were investigated for antibacterial principles. Extraction of plant material was done with methanol, follow by partition with hexane. Separation and purification of compounds was done using a combination of chromatographic techniques. Isolated compounds were identified by means of spectroscopic methods and comparison with literature data. The antibacterial activity of extracts, fractions and compounds was assessed by evaluating the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) against Multi-Drug-Resistant (MDR) Vibrio cholerae and Shigella flexneri. Three secondary metabolites namely kaempferol, luteolin and  aloeemodin were isolated from methanol residue active extract. The antibacterial results showed that the MeOH residue extract, fractions A and C, as well as compounds 1-3 exhibited variable MIC values, depending on the bacterial strains. Aloe-emodin (MIC = 4 to 128 μg/mL) exhibited the highest antibacterial activity against MDR Vibrio cholerae and Shigella flexneri. From these results obtained, S. alata leaf could be considered as a natural antibacterial source due to the presence of flavonoid and anthraquinone compounds.

Keywords: Senna alata, Fabaceae, kaempferol, luteolin, aloe-emodin, MDR strains.