Lactobacilli kefiranofaciens M1 has shown novel immunomodulation and anti-allergy probiotic attributes in cell and animal models. An acute oral toxicity assessment of L. kefiranofaciens M1 was evaluated in Sprague-Dawley rats. The rats were randomly assigned to four groups (12 rats/sex/group): the low dose group was orally gavaged with L. kefiranofaciens M1 at 3.0×108cfu/kg bw while the medium dose and high dose groups received 9.0×109cfu/kg bw and 1.8×1010cfu/kg bw, respectively, for 28days. The control group received phosphate buffer saline. The body weights were measured weekly while blood samples were collected for haematology and serum biochemistry tests. Histopathology of the organs (heart, liver, kidney, adrenal glands, spleen, ovary, testis), and urinalysis were conducted on study termination. The body weight gain of the L. kefiranofaciens M1 and control groups were comparable during the administration period. Overall, L. kefiranofaciens M1 did not induce adverse effects on haematology, serum biochemistry, and urinalysis parameters. Gross and microscopic histopathology of the organs revealed no toxicity effect of L. kefiranofaciens M1. In conclusion, 1.8×1010cfu/kg bw of L. kefiranofaciens M1 was considered as the no-observed-adverse-effect-level (NOAEL), which was the highest dose tested in the present study.
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