Biochemical analysis of sword beans (Canavalia gladiata) extract

Objective: Canavalia gladiata, usually called sword beans, is a domesticated plant species in the legume family and the main component of which is canavanine. The fruit has been long used in Chinese herbal medicine for discharge of pus, but the functional mechanism of which is little understood. The aim of this study was to examine the effects of sword beans on oral bacteria and oral epithelial cell line. Methods: The sword beans were extracted with 41.9% ethanol and lyophilized. The lyophilized sword beans extract (SBE) were stored at -20°C until use. The minimum inhibitory concentration (MIC), and minimum bactericidal concentration (MBC) of SBE, canavanine and 0.2% chlorhexidine gluconate solution (CHX) on bacterial growth were examined. Streptococcus mutans (S.m), Streptococcus salivarius (S.s), Lactobacillus casei (L.c), Actinomyces viscosus (A.v), Fusobacterium nucleatum (F.n), Aggregatibacter actinomycetemcomitans (A.a) and Porphyromonas gingivalis (P.g) were used as oral bacteria. The cytotoxicity of SBE, canavanine and CHX on oral epithelial cell line (KB cells) were determined by using a lactate dehydrogenase assay. Results: Growth of P.g and F.n were inhibited with MIC values of 29.5 µg/ml and 1875 µg/ml SBE, respectively. Canavanine also inhibited the growth of P.g and F.n with MIC values of 1458.5 µg/ml and 1875 µg/ml, respectively. The MBC of SBE for P.g and F.n was 29.5 µg/ml and 1875 µg/ml, respectively. The MBC of canavanine for P.g and F.n was 1458.5 µg/ml and 2083.5 µg/ml respectively. However, growth of S.m, S.s, L.c, A.v, and A.a were not affected by SBE and canavanine. CHX inhibited the growth of all the oral bacteria tested. The cytotoxicity of SBE and canavanine on KB cells were significantly lower than that of CHX (p<0.05). Conclusion: The present study suggests that SBE have an antibacterial activity against P.g and F.n with lower cytotoxicity to epithelial cells than CHX.