Isolation and Identification of Lactiplantibacillus plantarum ST3.5 and Its Inhibitory Effect on Mold

Lactic acid bacteria (LAB) has the potential to antagonize harmful microorganisms such as molds, which is expected to be safe and stable biological antimicrobial agents of the next generation. In present study, a strain ST3.5 with inhibiting mold activity was screened and obtained, which was identified as Lactiplantibacillus plantarum (L. plantarum) based on 16S rRNA sequencing. And its characteristics of acid resistance, bile salt resistance, inhibition of pathogenic bacteria, and drug resistance were analyzed. Furtherly, the cell-free supernatant (CFS) of L. plantarum ST3.5 was treated with acid, heat and enzyme, which the main antifungal substances were analyzed. The content of organic acids in supernatant was analyzed by high performance liquid chromatography (HPLC) and the destruction of mold mycelium was observed by scanning electron microscope (SEM). Meanwhile, the biological control experiment was carried out with corn kernels as an actual sample. The results showed that L. plantarum ST3.5 had good acid resistance and weak bile salt resistance. The strain was resistant to antibiotics (e.g., gentamicin and kanamycin) and sensitive to antibiotics (e.g., ampicillin and chloramphenicol), which could inhibit the growth of pathogenic bacteria. Analysis of organic acid found that the content of lactic acid in the CFS was the highest (22.02±0.23) g/L, followed by citric acid (4.99±0.04) g/L and acetic acid (3.67±0.06) g/L. The SEM results demonstrated the CFS could damage mold hyphae. Additionally, the biocontrol experiment confirmed that the CFS of L. plantarum ST3.5 could inhibit the mold residing growth of the corn surface. In conclusion, L. plantarum ST3.5 can inhibit the growth of mold, which can be used to develop biological control agents to minimize mold pollution and ensure food safety.