Isolation and Characterization of Probiotic Bacteria from Rice, Idli, and Dosa Batter and Their Antimicrobial Activity

Abstract

This study focuses on the isolation and characterization of probiotic bacteria from traditional fermented foods rice, idli, and dosa batter and evaluates their antimicrobial activity. Probiotic bacteria are known for their health benefits, particularly in improving gut health and preventing gastrointestinal infections. The research aims to identify diverse probiotic strains in these fermented foods and assess their potential applications in food safety and human health.Samples of rice, idli batter, and dosa batter were collected from various local sources. The samples were homogenized and subjected to serial dilution, followed by plating on selective de Man, Rogosa, and Sharpe (MRS) agar. The plates were incubated anaerobically at 37°C for 24-48 hours. Colonies exhibiting characteristic morphology of lactic acid bacteria (LAB) were selected for further analysis. Gram staining, biochemical tests, and molecular identification using 16S rRNA gene sequencing were employed to characterize the isolates. A total of 120 bacterial isolates were obtained, predominantly identified as Gram-positive, rod-shaped LAB. Detailed morphological examination revealed a diverse range of colony morphologies. Biochemical tests indicated varied metabolic activities, with isolates displaying different carbohydrate fermentation profiles. Molecular characterization confirmed the presence of several probiotic species, including Lactobacillus plantarum, Pediococcus pentosaceus, Leuconostoc mesenteroides, and Weissella spp.The antimicrobial activity of the isolated probiotic strains was evaluated using the agar well diffusion method against pathogenic bacteria such as Escherichia coli, Staphylococcus aureus, Salmonella spp., and Listeria monocytogenes. The probiotic isolates showed significant inhibitory effects, with inhibition zones ranging from 10 to 25 mm. Minimum inhibitory concentration (MIC) assays further quantified the antimicrobial potency, with some isolates displaying MIC values as low as 0.5 mg/mL. Time-kill kinetics assays demonstrated that the probiotics effectively reduced the viable counts of pathogens over time, indicating bactericidal properties.The probiotic potential of the isolates was also assessed by testing their survival in simulated gastric juice and bile salt conditions. The results showed high survival rates, exceeding 80%, suggesting that these probiotics could withstand gastrointestinal transit and exert beneficial effects in the human gut.