Genome-based assessment of safety characteristics of Lacticaseibacillus paracasei NY1301 and genomic differences in closely related strains marketed as probiotics.

The probiotic attributes of Lacticaseibacillus paracasei NY1301 were comprehensively characterized, and a comparison between the closely related LcA (Actimel) and LcY (Yakult) probiotic strains was conducted using genomic tools. All strains exhibited high genetic similarity and likely shared a common ancestor; differences were primarily expressed as minor chromosomal re-arrangements, substitutions, insertions, and deletions. Compared with LcY, NY1301 exhibited 125 single-nucleotide polymorphisms. NY1301 lacked virulence factors, antibiotic resistance genes, and mutations associated with antibiotic resistance and had a 46-kbp prophage. This prophage is spontaneously induced at low levels and remains in a non-lytic state under standard culture conditions. The observed causal adaptive mutations were likely related to niche adaptation within the respective laboratory or manufacturing processes that occurred during the maintenance of the strains. However, the phenotypic effects of these genomic differences remain unclear. To validate the safety of NY1301, we conducted an open-label trial with healthy participants who consumed excessive amounts of NY1301 (3.0 × 10¹¹ cfu) daily for 28 days. The results of this trial and those of other in vivo studies, coupled with the long history of human consumption without established risks to humans, provide strong evidence confirming the safety of NY1301.