Purification and characterization of an antimicrobial compound produced by Lactobacillus plantarum EM showing both antifungal and antibacterial activities

Lactobacillus plantation EM exhibited antimicrobial activities against different food-borne pathogenic bacteria and food spoilage fungi. The compounds showing antibacterial and antifungal activities were identified as organic acids, lactic and acetic acids, and unidentified antimicrobial compounds. Thus the unidentified antimicrobial compounds were purified using solid phase extraction and recycling preparative HPLC and its structure was elucidated using NMR and LC/MS. The purified active compound of L. plantarum EM was identified as 3-hydroxy-5-dodecenoic acid (MW 214). Furthermore, the antimicrobial effects of the active compounds, 3-hydroxy-5-dodecenoic acid, lactic and acetic acids were greater with combined usage. 3-Hydroxy-5-dodecenoic acid caused severe damage to the surface of vegetative cells of B. cereus and led to shrunken B. cereus endospores and A. fumigatus conidium cells along with aggregation of damaged cells, resulting in bactericidal and fungicidal effects against B. cereus and A. fumigatus. The MICs of 3-hydroxy-5-dodecenoic acid against A. fumigatus and B. cereus were 0.21 g/L and 0.25 g/L, respectively, which were lower than those of the commonly used chemical preservative, sodium benzoate. Overall, these results suggest that the antimicrobial activity of L. plantarum EM may lead to the development of promising biopreservatives that prevent fungal spoilage and food-borne pathogens.