Isolation and Characterization of Bacteriocin-Producing Lactic Acid Bacteria from Mbithi: A Kenyan Traditional Fermented Porridge

Abstract

Introduction: Mbithi is a non-alcoholic, spontaneously fermented product that remains a traditional food cuisine in Kenya, valued for its nutritional properties. Lactic acid bacteria (LAB) are utilized in the food business as a starting culture, with their preservation properties linked to their ability to produce bacteriocins. Due to their eco-friendly properties, LAB's bacteriocins offer a viable solution to the health risks associated with chemical preservatives in the food industry. Objectives: This study presents results on isolating and characterizing bacteriocin-producing lactic acid bacteria from Mbithi. Methods: Lactic acid bacteria (LAB) were isolated using MRS and M17 agar. These isolates were then phenotypically characterized, including biochemical and physical tests. The isolates were screened for antimicrobial activity by agar well-diffusion assay, while genotypic characterization was performed based on the 16S rRNA gene sequence. Results: A total of 50 LAB strains were extracted. Of the fifty (50) isolates, 47 (94%) were selected due to their demonstration of gram-positive characteristics and catalase activity. Furthermore, 12 isolates were heterofermentative for they fermented glucose, whereas (35) isolates did not metabolize glucose (homofermentative). The results on salinity, acidity, and temperature demonstrated that most of the isolates tolerated the salinity with 6.5% of NaCl, acidic at pH 2.0 and pH 2.5 and temperature of 45°C. Nonetheless, none of the isolates withstood a temperature of 10℃. From the inhibition tests, we identified 10 candidate isolates, including three isolates—FP2 24, FP2 28, and FP22—that exhibited antagonism against all evaluated indicator pathogenic microorganisms. The three isolates exhibited inhibitory activity against E. coli, Bacillus subtilis, and Staphylococcus aureus, with inhibition zones of 21±1.41, 26±1.41, and 21±1.41, respectively, and a P-value of less than (P<0.05, P=0.000). The phylogenetic and Blast analyses indicated that the isolates were categorized into five clusters: Lactiplantibacillus, Levilactobacillus, Pediococcus, Weisella, and Leuconostoc, with the majority clustering within the Lactiplantibacillus genus, with similarities ranging from (95.1%-100%). Conclusions: The findings revealed potential isolates showing antagonistic activity against pathogenic indicators, suggesting their possible production of secondary metabolites. Despite this research presenting promising outcomes, further characterization is requested to get insights on probiotics properties for the usage of the isolates in preservatives in the food industry domains.