Effects on selected fecal bacterial populations and safety assessment of Lacticaseibacillus rhamnosus LRa05

Abstract This study aimed to investigate the effects of Lacticaseibacillus rhamnosus LRa05 on fecal bacterial populations and evaluate its safety profile. First, the effects of LRa05 on selected fecal bacterial populations were evaluated in a rodent model. Second, safety assessments were conducted through genetic stability testing, acute oral toxicity test in male and female mice and rats, and teratogenicity study. Healthy mice were administered LRa05 at specified doses for 14 consecutive days. LRa05 significantly increased fecal Lactobacillus counts at all dose levels, while Bifidobacterium increased only in the medium-dose group and other measured bacterial populations were not significantly changed. Genetic stability analysis revealed no significant differences between the parental (P0) and twentieth-passage (P20) strains in morphological characteristics, physiological-biochemical properties, 16 S rDNA gene sequences, or pheS gene sequences. The acute oral LD 50 was determined to be greater than 10.0 g/kg BW in rats and greater than 20.0 g/kg BW in mice. In the teratogenicity study, maternal rats showed no toxic signs, and no statistically significant differences were observed in body weight gain, pregnancy rate, number of corpora lutea, or implantation rate compared with the negative control group ( P > 0.05). Fetal body weight, body length, sex ratio, and incidences of sternal absence and enlarged fontanelles in treated groups showed no statistically significant differences from the negative control ( P > 0.05), and no external or visceral malformations were detected in the fetuses. In conclusion, oral administration in rodents supported an effect of LRa05 on fecal Lactobacillus counts under the conditions tested, while genetic stability, acute oral toxicity and teratogenicity tests demonstrated its favorable safety profile.