Introduction: Today, it is claimed that probiotics (some strains of lactic acid bacteria and yeasts) have positive impacts on the health of their hosts. Moreover, the relatively long history of probiotic use is considered as an indication of probiotics safety. For this reasons, the use of probiotics in the food and pharmaceutical industry is growing .However, presentation of new strains of probiotics is not so easy because some candidate strains of lactobacilli have shown toxic effects. Therefore, the aim of this study was to investigate the subacute oral toxicity of a new strain of native Iranian Lactobacillus pentosus (IBRC=11143) in female Wistar rats Methods: The toxicity of the strain of Lactobacillus pentosus was evaluated in a 28-days sub-acute toxicity study. Three groups of rats (n=5) received saline, 1 × 100000000 or 1×1000000000CFU/rat of this stain through gavage (once a day for 28 consecutive days). On day 29, all mice were anesthetized with ketamine and xylazine. Samples of Blood (through direct cardiac puncture), liver and kidney were obtained. Evaluation of blood parameters, liver enzymes (ALT, AST, and ALP), kidney health parameters (serum urea and creatinine) and tissue parameters were carried out to find any toxic effects of the bacterial strain on blood, kidney, and the liver. Results: Subacute oral administration of Lactobacillus pentosus did not cause any significant changes in hematological variables including HCT, MCV, MCH, MCHC, RDW, ,WBC, However Some blood parameters (RBC, and Hb) showed significant elevations in the groups that received the bacteria . Hepatic toxicity was monitored by quantitative analysis of serum ALT, AST, and ALP activity .In this study, activities of serum enzymes (ALT, AST, and ALP) were not affected . However, there were significant increase in the urea and creatinine levels of the experimental group compared to the control group. Analysis of tissue sections showed no significant alteration in the tissue sections of
