PHYLOGENY AND CYTOTOXICITY SCREENING OF LACTIC ACID BACTERIA FROM CABBAGE KIMCHI SAMPLES

Abstract

Colon cancer is one of the most common and fatal cancers in the Philippines. Anticancer treatments are available but are known to produce serious side effects, showing the need for alternatives, such as those derived from natural sources. This study aimed to identify lactic acid bacteria (LAB) isolated from cabbage kimchi products sourced from the Philippines and investigate their cytotoxic activities on colorectal adenocarcinoma (HT-29), colorectal carcinoma (HCT-116), normal liver epithelial (THLE-3), and normal human neonatal dermal fibroblast (HDFn) cell lines. Phenotypic characterization and 16S rRNA gene sequencing identified the isolates as Lactiplantibacillus plantarum (six isolates), Limosilactobacillus fermentum (one isolate), and Levilactobacillus brevis (four isolates). Phylogenetic analysis using maximum likelihood (ML) and neighbor-joining (NJ) methods revealed close evolutionary associations among all L. plantarum isolates from Kimchi 1, and among all L. brevis isolates from Kimchi 2. At the same time, the different L. plantarum and L. brevis isolates were found to be of different strains based on the differences in their branch lengths. The L. plantarum isolates from K1 were shown to share a closer relationship with L. brevis from K2, while L. fermentum isolated from K1 was shown to be more distantly related to both L. plantarum and L. brevis. The secondary metabolites in the ethyl acetate extracts of the sterile culture supernatants of five  LAB isolates were assayed for cytotoxic activities using the resazurin-based PrestoBlue™ reagent. Results showed that all the extracts did not produce an IC₅₀, indicating that these were not cytotoxic to the cell lines tested, in contrast to the positive control, Zeocin, which showed cytotoxicity to the different cell lines. This study provides the first insight into the LAB diversity in cabbage kimchi sourced from the Philippines and suggests the potential for further investigation of other bioactivities of these LAB isolates, particularly given their non-toxicity to the normal human cell lines THLE-3 and HDFn.