Probiotic potential and antimicrobial efficacy of exopolysaccharide-producing lactic acid bacteria isolated from yoghurt

Aim: The study investigates the probiotic potential of exopolysaccharide (EPS)-producing lactic acid bacteria (LAB) isolated from yoghurt samples. It assesses their antimicrobial efficacy against foodborne pathogens, particularly Escherichia coli and Staphylococcus aureus. The objective is to identify LAB strains that can be used as natural preservatives and health-promoting probiotics in functional foods. Methods: Yoghurt samples were collected from household local markets in Rawalpindi, Pakistan. LAB was isolated and identified using selective media, Gram staining, and biochemical tests. EPS production was quantified using the phenol-sulfuric acid method. Probiotic properties, including antimicrobial activity against E. coli and S. aureus, were evaluated using the disc diffusion method. Strains producing the highest EPS were biochemically characterised using the API Strep system. Results: Of 29 LAB isolates, 12 were identified as significant EPS producers, with Streptococcus thermophilus, Lactococcus lactis, and Limosilactobacillus fermentum demonstrating the highest EPS production (up to 62 µg/mL). These strains exhibited strong antimicrobial activity against E. coli and S. aureus, with inhibition zones ranging from 2 mm to 32.1 mm. The results confirmed the dual functionality of these strains as both texture enhancers and natural preservatives in food products. Conclusions: The EPS-producing LAB strains, particularly S. thermophilus, L. lactis, and L. fermentum, showed significant potential as probiotics and natural preservatives. Their antimicrobial activity and ability to enhance food texture suggest their applicability in the food industry to promote health and improve food safety. Further research should explore their stability in different food matrices for commercial use.