Assessment of antimicrobial and antibiofilm activities using culture filtrate of lactic acid bacteria (Lactiplantibacillus plantarum) from dairy product in (Menoufia)

Background: The spread of multidrug-resistant bacterial strains presents a serious risk to world health, mostly as a result of antibiotic abuse and overuse. Lactic acid bacteria (LAB) in this situation and their postbiotic compounds have gained increasing interest as natural alternatives with antibacterial and antibiofilm properties.This study aimed to evaluate the antibacterial and antibiofilm capabilities of postbiotics derived from LAB against four clinically significant bacterial pathogens Escherichia coli ATCC25922, Staphylococcus aureus ATCC6538, Pseudomonas aeruginosa ATCC9027and Klebsiella pneumonia . Results: LAB were isolated from traditional dairy products in Menoufia, Egypt (Kareish cheese, Rayeb milk, and local yoghurt) using MRS agar medium. Twelve isolates demonstrated antibacterial and antibiofilm activity against the tested pathogens, with isolate EH1 showing the most significant inhibition zone. Identification through VITEK 2 and 16S rRNA gene sequencing confirmed EH1 as Lactiplantibacillus plantarum . Optimal growth conditions for LAB included 48-hour incubation at 37 °C, pH 7.0, with yeast extract as the optimal nitrogen source and sucrose as the preferred carbon source. The antibiofilm potential of LAB postbiotics was confirmed using Congo red agar, well diffusion, ELISA reader, Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) showed significant disruption of the pathogens' biofilm structure. Conclusions: Postbiotics from LAB, particularly from L. plantarum , demonstrated strong antibacterial and antibiofilm properties, highlighting their potential as promising natural agents to combat multidrug-resistant bacterial infections. These findings support the further development of LAB-derived compounds in medical and pharmaceutical applications.