Safety evaluation of Lacticaseibacillus rhamnosus KF7 based on complete genome, phenotypic assays and alternative models: Caenorhabditis elegans

This study evaluated the safety of Lacticaseibacillus rhamnosus (L. rhamnosus) KF7, a probiotic strain originating from kefir, for potential use in infant and children's food products in China. The safety evaluation was conducted through a comprehensive approach involving whole-genome sequencing, in vitro and in vivo studies using alternative models: Caenorhabditis elegans (nematodes). Genomic analysis confirmed the absence of virulence factors and antibiotic resistance genes in KF7. Phenotypic characterization demonstrated that KF7 exhibits no antibiotic resistance, does not produce indole, is non-hemolytic, and lacks amino acid decarboxylase activity. Furthermore, KF7 was found to not produce histamine and generate only a minimal amount of tyramine when cultured in MRS medium supplemented with amino acids. The strain was also shown to produce both L- and D-lactic acid, with the concentration of D-lactic acid falling within a safe range. To further evaluate the safety of KF7 in vivo, nematode model was employed, with Pseudomonas aeruginosa serving as a pathogenic control and L. rhamnosus GG, known to be safe for infants and children, as a positive control. The results demonstrated that KF7 does not adversely affect nematode egg-laying, egg development, growth, locomotion, or lifespan. Instead, it appeared to have beneficial effects on gut microbiota and extending the nematodes' lifespan. In summary, this study established the method of using nematode as an in vivo evaluation to the safety of probiotics, and the safety data of the KF7 strain was supplemented by in vitro research, which proved that KF7 has a certain degree of safety.