408 Chin J Nat Med Nov. 2012 Vol. 10 No. 6 2012 年 11 月 第 10 卷 第 6 期 Chinese Journal of Natural Medicines 2012, 10(5): 0408−0414 doi: 10.3724/SP.J.1009.2012.00408 Chinese Journal of Natural Medicines Antibacterial and antifungal properties of ent -kaurenoic acid from Smallanthus sonchifolius Eleanor P. Padla 1 , Ludivina T. Solis 1 , Consolacion Y. Ragasa 2* 1 Department of Microbiology & Parasitology, College of Medicine De La Salle Health Sciences Institute, Dasmariñas, Cavite, Philippines; 2 Chemistry Department, De La Salle University, 2401 Taft Avenue, Manila, 1004 Philippines Available online 20 Nov. 2012 [ABSTRACT] AIM: To screen for the antibacterial activity of ent-kaurenoic acid (1) from the dichloromethane extract of Smallanthus sonchifolius leaves against Staphylococcus aureus, Staphylococcus epidermidis, Bacillus subtilis, Escherichia coli, Enterobacter aero- genes, Klebsiella pneumoniae, and Pseudomonas aeruginosa, and for its antifungal activity against Candida albicans, Trichophyton rubrum, and Epidermophyton floccosum. METHODS: Compound 1 was isolated by silica gel chromatography and its structure was elucidated by NMR spectroscopy. For assaying the antibacterial and antifungal activities of 1, the disk diffusion method was used, while the minimum inhibitory concentrations (MICs) were determined by the broth dilution method. RESULTS: With the disk diffu- sion method, 1 was found to be active against all the Gram-positive organisms tested (S. aureus, S. epidermidis, B. subtilis) at the low- est concentration of 1 000 μg·mL −1 , while it was active against the fungus T. rubrum at 10 000 μg·mL −1 . No inhibitory activity was observed against C. albicans, E. floccosum and all the Gram-negative test strains. The activity indices (AI) of 1 were noted to be high- est against S. aureus and lowest against T. rubrum. Statistically significant differences were found between the mean inhibition zones (IZ) of 1 and the standard drugs (ofloxacin and clotrimazole). The results of the broth dilution MIC determination revealed that 1 ex- hibited moderate activity against S. aureus and S. epidermidis with MIC values of 125 μg·mL −1 and 250 μg·mL −1 , respectively; and weak activity against B. subtilis with a MIC of 1 000 μg·mL −1 . The growth of T. rubrum in the MIC assay was not inhibited at the highest tested concentration of 1 (10 000 μg·mL −1 ). CONCLUSION: The minimum bactericidal concentration (MBC) indicated that the bactericidal activities of 1 occurred at concentrations higher than its growth inhibitory concentrations. Furthermore, the MBC: MIC ratio of 2 : 1 clearly demonstrated the in vitro bactericidal effect of 1 against S. aureus and S. epidermidis. [KEY WORDS] Smallanthus sonchifolius; Yacon; ent-Kaurenoic acid; Antibacterial; Antifungal [CLC Number] R284.1; R965 [Document code] A [Article ID] 1672-3651(2012)06-0408-07 1 Introduction Smallanthus sonchifolius (Poepp. & Endl.) H.Rob. (As- teraceae), also known as yacon, was introduced in the Philip- pines in early 2000, and has since become commonly avail- able in local markets. The growing popularity of yacon can be attributed to its nutritive, as well as medicinal, value. It has long been valued as an edible root crop. More impor- tantly, studies have demonstrated that yacon has hypoglyce- mic [1-4] , antioxidant [5-6] , probiotic [7-9] , and antimicrobial properties [10-12] . The leaves and tubers contain phenolic compounds (chlorogenic, caffeic and ferulic acids) which [Received on] 14-Nov.-2011 [*Corresponding author] Consolacion Y. Ragasa: Tel/Fax: 0632- 5360230, E-mail: consolacion.ragasa@dlsu.edu.ph These authors have no any conflict of interest to declare. exhibit antioxidant, probiotic, and hypoglycemic effects [13-15] . Moreover, the tubers are rich in non-assimilable low-calorie oligofructan and inulin, hence their use as dietary sugar and dietary fiber [5] . Although yacon has not been customarily used as an anti-infective herbal medicine, a number of ses- quiterpene lactones have been identified in yacon leaves, which were shown to possess antimicrobial properties [12] . A previous study reported that ent-kaurenoic acid (1) from yacon exhibited significant anti-inflammatory and analgesic activities. Compound 1 dissolved in dimethyl sulfoxide (DMSO) also displayed potential anti-toxicity and hypogly- cemic activity. It also showed low antimicrobial activities against E. coli, P. aeruginosa, S. aureus, C. albicans and T. mentagrophytes, but was found to be inactive against A. niger at 30 μg·mL −1 concentration [16] . A recent study reported the hypoglycemic potential of the aqueous extract of yacon tea and 1 [17] , and an earlier study also reported 1 as a constituent of S. sonchifolius [18] .