Microbial Identification of Kefir Grains and its Antimicrobial Effect against Gastrointestinal Pathogens

Background: The rising occurrence of gastrointestinal (GIT) cases and the escalation of antibiotic resistance underscore the critical need for effective alternative therapies. Kefir, a fermented dairy product derived from Kefir Grains (KGs), demonstrates varying antimicrobial spectra based on its geographical origins. This study aims to identify the predominant microbial isolates within USA-based KGs and assess their antimicrobial potential against pathogens responsible for GIT infections. Methodology: The phenotypic screening tests for lactic acid bacteria (LAB) included assessments of cell morphology, CO ₂ production from glucose, sugar fermentation tests (specifically starch and lactose), and growth evaluations in 6.5% salt conditions. Genomic identification was conducted through PCR amplification of the 16S rRNA gene, followed by Sanger sequencing, Nucleotide BLAST (BLASTn) analysis, and phylogenetic tree construction. The antimicrobial activity was evaluated using antimicrobial suspensions with varying concentrations of kefir milk supernatant (KMS) and suspensions of individual lactic acid bacteria (SILB). Results: The presence of gram-positive coccobacillary rods, identified as homo-fermenters and capable of growing in a 6.5% NaCl solution, confirmed the presence of LAB. Genotypic identification revealed the presence of Lactococcus spp. strain SJ1, Lactococcus lactis , and Bacillus cereus . The antimicrobial analysis demonstrated that KMS concentrations of 50%, 60%, and 70% completely prevented the growth of Pseudomonas aeruginosa, Staphylococcus aureus, and Salmonella typhi . In contrast, Escherichia coli, Vibrio cholera, Helicobacter pylori , and Bacillus subtilis exhibited resistance, with no inhibition observed when using SILB. Conclusion: This analysis provided valuable insights into the microbial composition of USA-based KGs and highlighted their synergistic antimicrobial effects, underscoring kefir as a potent alternative to antibiotics. Future studies are warranted to fully elucidate the metagenomic profile of USA-based kefir and to optimize dosing for the effective treatment of gastrointestinal illnesses.