Isolation, Characterization, Probiotic Potential and Safety Evaluation of Lactic Acid Bacteria from Curd

Abstract

Lactic Acid Bacteria (LAB) are widely recognized as beneficial microorganisms that play a crucial role in the production of various fermented foods. They contribute to improving food flavor and inhibiting the growth of pathogenic and spoilage microorganisms in these products. This study focused on isolating, characterizing, and identifying LAB from curd samples collected in Chennai, followed by evaluating their in vitro antimicrobial activity against pathogenic bacteria. Five Lactobacillus strains were isolated from curd and identified through biochemical and physiological tests. Preliminary classification suggested these isolates belonged to the Lactobacillus genus, which was further confirmed by genus-specific PCR and 16S rDNA sequencing. The identified strains included Lactiplantibacillus plantarum, Lactobacillus acidophilus, Limosilactobacillus fermentum, Lacticaseibacillus rhamnosus and Lactobacillus acidophilus. The isolates’ survival was tested under simulated gastrointestinal conditions, including low pH and bile salt exposure. All strains demonstrated growth at pH 3 and in the presence of bile salts. Hemolytic activity assays on sheep blood agar revealed γ-hemolysis in all isolates, indicating non-hemolytic behavior. The antimicrobial activity of the strains was evaluated against Escherichia coli (ATCC 25922) and Staphylococcus aureus (ATCC 25923) using the agar well diffusion method, where all isolates showed clear zones of inhibition. In conclusion, these findings indicate that the isolated LAB strains possess probiotic potential, demonstrated by their acid and bile tolerance, non-hemolytic activity and antimicrobial properties.