Characterization of Lactiplantibacillus plantarum IM3, a Salmonella-antagonistic strain isolated from garbage enzyme: genome analysis, mechanism of action, and mRNA transcription kinetics.

Contamination of raw vegetables by Salmonella spp. is an increasing food safety concern and a major cause of foodborne illness. This study aimed to isolate and characterize an antagonistic lactic acid bacterium from garbage enzyme (GE), investigate its inhibitory mechanisms against Salmonella enterica (S. enterica), and analyze its genomic features. Lactiplantibacillus plantarum IM3 (L. plantarum IM3) was isolated from GE and exhibited clear antagonistic activity against S. enterica serovar Typhimurium, producing an inhibition zone of 8.10 ± 0.25 mm in the agar well diffusion assay using cell-free supernatant (CFS). In a co-culture model, L. plantarum IM3 inhibited S. enterica with an inhibition rate of 99.44%. The inhibitory effect was associated with lactic acid production, secreted protein compounds in the CFS, and damage to pathogen cell integrity. Time-course mRNA transcription profiling indicated that plantaricin-related genes in L. plantarum IM3 were increasingly induced toward the late growth stage (16 h), consistent with stronger antibacterial activity of the corresponding CFS samples. Shotgun genome sequencing analysis confirmed the taxonomic identity of IM3 as L. plantarum with > 98% similarity and revealed bacteriocin-associated loci, including plantaricin and sactipeptide clusters, together with genes related to stress tolerance and adhesion. Finally, CFS from L. plantarum IM3 significantly reduced the number of recoverable S. enterica on inoculated Lactuca sativa var. Bastavia (10² CFU/mL) after 24 h, highlighting L. plantarum IM3 as a promising biocontrol candidate for improving the microbiological safety of fresh produce.