Background: The increase in the prevalence of multi-drug resistant bacteria has necessitated the search for new antimicrobials from alternative
sources such as traditional medicinal plants.
Materials and Methods: The agar well diffusion method was employed to determine the susceptibilities of four plant derived triterpenes namely,
3β-hydroxylanosta-9, 24-dien-21-oic acid (RA5), and methyl-3β-hydroxylanosta-9, 24-dien-21oate (RA3), a mixture of oleanolic acid and betulinic
acid (SF1) and a mixture of 3β-acetonyloleanolic acid and 3β-acetonylbetulinic acid (SF2), at a concentration of 10 mg/ml against seven
Escherichia coli
, one
Bacillus cereus
, five
Enterococcus
and nine
Vibrio
bacteria. The minimum inhibitory concentration (MIC) and minimum bactericidal
concentration (MBC) were determined through the micro-broth dilution assay. The checkerboard method was used to determine the antibiotictriterpene
interactions while the cytosolic lactate dehydrogenase test was used to determine the membrane damaging potentials of the triterpenes in
comparison to 3% Triton X-100.
Results: The triterpenes RA3, RA5, SF1 and SF2 had activities against 86.4%, 54.6%, 22.7% and 9.09% of the test bacteria respectively. SF1 had
the lowest MIC values ranging 0.625-10 mg/ml with lower MIC values being noted against Gram negative bacteria in comparison to Gram positive
bacteria; this trend was also noted among the activities of RA3 and RA5 although they had higher MIC value ranges of 1.25-10 mg/ml and 5- 10
mg/ml respectively. MBC studies proved the triterpenes to be mostly bacteriostatic. The interaction studies with ciprofloxacin were mainly ranging
between indifference and antagonism. RA3 alone showed minimal membrane damaging potential with the levels of cytosolic lactate dehydrogenase
released ranging from 1-36% in comparison to 3%Triton X-100 against
E.coli (DSM-8695) and
V. vulnificus
(AL 042).
Conclusion: The results hereby show the potential that the test triterpenes have as antibacterial agents, especially against the Gram negative bacteria
namely
E. coli and
Vibrio bacteria.
