Characterization of Biofilm-Forming Lactic Acid Bacteria from Traditional Fermented Foods and Their Probiotic Potential

A biofilm is a self-protective material formed by microorganisms to resist adverse environments. As an important group of microorganisms in the food industry and the human intestine, lactic acid bacteria (LAB) demonstrate enhanced probiotic activity in their biofilm state. In this study, a total of 90 LAB isolates from various traditional fermented foods across China were evaluated for their biofilm-forming capacity using the crystal violet staining method. Of these, eight isolates showed strong biofilm-forming capacity. These eight isolates were further evaluated for environmental stress responses, including tolerance to high acid and high bile salt concentrations, resistance to simulated gastrointestinal conditions, and adherence to Caco-2 cells. Four isolates with strong resistance to these stresses and adhesion to Caco-2 cells were selected for comparison between their planktonic and biofilm forms. Among these, the two isolates demonstrating the highest biofilm production capacity were AQ-4 and SY1-3, which were isolated from fermented pear juice and apple juice, respectively. Isolate AQ-4 was then identified as <i>Lactiplantibacillus plantarum</i> based on 16S rDNA sequencing. By integrating biofilm-forming capacity with key biological properties, including stress tolerance and epithelial adhesion, this study focuses on <i>L. plantarum</i> AQ-4, which exhibits distinct microstructural differences between planktonic and biofilm states, as revealed by scanning electron microscopy. The findings suggest that <i>L. plantarum</i> AQ-4 could be used to investigate the differential mechanisms in the planktonic and biofilm states and to act as the theoretical basis for the application of LAB biofilms in the food industry.