Abstract:
BACKGROUND : Cassia alata or Senna alata, also known as “ringworm bush” because of its very effective fungicidal
properties, is commonly used in African traditional medicine to treat fungal infections. Despite extensive
phytochemical and pharmacological studies previously reported on C. alata, the antibiofilm activity against
pathogenic yeast as well as the related anti-quorum sensing mechanism of some active constituents has not yet
been elucidated. The aim of the study was to isolate the bioactive constituents from the methanol extract of the
leaves of C. alata (CAExt) using antibiofilm-guided fractionation against yeast fungal pathogens and then to
investigate the anti-quorum sensing activity of the active constituents by assessing their ability to inhibit violacein
production in Chromobacterium violaceum.
METHODS : Chromatographic methods were used to isolate the constituents of CAExt, and spectroscopic methods
were used to elucidate the chemical structures of the isolated compounds. The broth microdilution assay was
used to evaluate the antifungal activity against Candida albicans and C. parapsilosis, while crystal violet staining
was used for the inhibition of biofilm formation and the disruption of preformed biofilm. The biosensor strain
C. violaceum ATCC 12472 was used to investigate the anti-quorum sensing activity of the most active
constituents.
RESULTS : The crude extract exhibited biofilm inhibition and eradication activities against the tested pathogenic
yeast. The biofilm inhibition percentages ranged from 53.22 % to 75.38 %, while the biofilm eradication percentages
ranged from 23.21 % to 64.25 %. The ethyl acetate fraction demonstrated high biofilm inhibition and
eradication activities against the tested microorganisms. The biofilm inhibition percentages ranged from 58.19 %
to 79.30 %, while the biofilm eradication percentages ranged from 34.105 % to 69.54 %. The purification of
subfractions led to the identification of six compounds: stigmasterol (1), sitosterol (2), lupeol (3), emodin (4),
kaempferol (5) and stigmasterol glycoside (6), two of which (4 and 5) showed potent biofilm inhibition and
eradication activities. Both compounds demonstrated significantly lower MBIC50 values of 70.81 μg/mL and
65.65 μg/mL against Candida albicans and MBEC50 values of 63.65 μg/mL and 82.66, respectively, against
C. albicans and C. parapsilosis. The crude extract and compounds (4) and (5) also demonstrated quorum sensing
inhibitory activity, as indicated by the MQSIC value of 1024 μg/mL for the crude extract and 128 μg/mL for the
two compounds. Moreover, compounds (4) and (5) displayed significant inhibitory effects on violacein production,
as indicated by their low IC50 values of 28.08 μg/mL and 26.44 μg/mL, respectively.
CONCLUSIONS : Data obtained in this study not only support the traditional use of C. alata in the treatment of fungal
infections but also reveal C. alata extract, as well as the two isolated bioactive compounds emodin (4) and kaempferol (5), as a potential source for developing antibiofilm alternative agents against biofilm-associated yeast infections.
LIST OF COMPOUNDS STUDIED :
stigmasterol (1), sitosterol (2), lupeol (3), emodin (4), kaempferol (5), stigmasterol glycoside (6)
