Introduction: Probiotics are microorganisms, including bacteria and yeasts that according to the world health organization may have beneficial effects on their consumers. Lactobacilli are among the important probiotic bacteria that their effects depend on the strain of the bacteria. Due to the beneficial effects of these bacteria, the introduction of new strains has always been considered by scientists. Among the conditions that new strains should have to be considered as probiotics is the safety of the new strains. Therefore, the objective of the present study was to evaluate the sub-acute toxicity of a new Iranian native Lactobacillus paracasei in male rats. Materials and methods: a sub-acute study (lasted for 28 consecutive days) was conducted on three groups of male rats (n=6). On the days of experiments, one group as control received saline and the other two groups received 108 cfu/rat and 109 cfu/rat by gavage, respectively (one dose per day). On day 29, under systemic anesthesia, blood, serum, and tissue samples of liver and kidney were obtained for analyzing different blood, serum, and tissue factors. Data analyzed with SPSS software. Results: Histopathological analysis of liver and kidney tissues in the rats that received the bacteria showed no changes and both of the tissues were completely normal. No adverse effects were observed in general behavioral status, body weight, and food and water intake. There was no significant difference in hematological parameters between the control and treatment groups. Liver enzymes remained unchanged except for ALT which increased in the bacterial-treated group. Conclusion: This study showed that the present strain of Lactobacillus paracasei (IBRC-M =11110) is almost safe in male rats. However, further studies are needed to be done before we can consider the lactobacillus strain as probiotic.
