Antimicrobial and antibiofilm activities of culture filtrates from Lactiplantibacillus plantarum isolated from traditional dairy products in Menoufia, Egypt

BACKGROUND: The global rise in multidrug-resistant (MDR) bacterial infections poses a serious threat to public health, largely driven by the overuse and misuse of antibiotics. In this context, lactic acid bacteria (LAB) and their postbiotic metabolites have attracted attention for their natural antimicrobial and antibiofilm activities. This study aimed to evaluate the effects of LAB-derived postbiotics against four clinically relevant pathogens: Escherichia coli ATCC 25,922, Staphylococcus aureus ATCC 6538, Pseudomonas aeruginosa ATCC 9027, and a clinical isolate of Klebsiella pneumoniae. RESULTS: LAB strains were isolated from traditional fermented dairy products in Menoufia, Egypt, including Kareish cheese, Rayeb milk, and local yoghurt, using MRS agar medium. Among twelve active isolates, strain EH1 demonstrated the highest inhibitory activity. Identification via VITEK 2 and 16 S rRNA sequencing confirmed the isolate as Lactiplantibacillus plantarum. Optimal culture conditions for EH1 included 48 h incubation at 37 °C, pH 7.0, with yeast extract and sucrose as the preferred nitrogen and carbon sources, respectively. Antibiofilm activity was confirmed through Congo red agar assay, agar well diffusion, ELISA-based quantification, and visualization by SEM and TEM, all indicating substantial disruption of biofilm structure and cell morphology. CONCLUSIONS: Postbiotics produced by L. plantarum exhibited strong antibacterial and antibiofilm activity against resistant bacterial strains. These results highlight the promising potential of LAB-derived metabolites as natural, safe, and effective alternatives for inhibiting biofilm formation and mitigating the growing threat of antibiotic resistance.