Probiotics, in particular Lactobacillus (lactic acid bacteria, LAB) strains, are widely used in clinical practice. Despite that these probiotics have GRAS (generally regarded as safe) and qualified presumption of safety (QPS) statuses, the safety of particular strains still needs to be thoroughly studied. The aim of the study was to evaluate the safety of Lact. casei IMV B-7280 strain by investigating toxicity and the effects on gut microbiota in experimental animal model. Male BALB/c mice (7–8 weeks, weight 20–24 g) were treated with amounts of Lact. casei IMV B-7280 strain: 5 × 10⁶, 5 × 10⁸, or 5 × 10⁹ CFU/animal once per day during 7 days, or in the amount of 1 × 10¹⁰ CFU/animal once per day during 3 days (most of the proposed probiotic doses for humans—from 10⁸ to 10⁹ CFU) and monitored during 14 days. Blood tests and serum biochemistry were conducted; the cecal content from mice of the experimental and control groups were freshly collected and analyzed. At the end of the experiments (15th day), the presence of LAB in the heart, liver, kidney, and mesenteric lymph nodes and peripheral blood was determined; histology of the brain, liver, heart, fragments of the small and large intestine, and mesenteric lymph nodes was conducted. Survival rate of BALB/c mice treated with Lact. casei IMV B-7280 strain in different concentrations in toxicity experiments during 14 days was 100%. We observed no signs of toxicity as changes in gait, lethargy, sleep, somatomotor activity as well as changes in fur, eyes, skin and mucous membranes, tremors, behavior pattern, convulsions, salivation, diarrhea, and local injuries in mice from all experimental groups. After administration of probiotic strain, the number of opportunistic bacteria in cecal contents, such as Staphylococcus spp., Candida spp., Pseudomonas spp., and total aerobic and optionally anaerobic bacteria decreased compared to controls; the population of beneficial bacteria such as lactobacilli increased in cecal contents of these mice. LAB were not detected in the peripheral blood, heart, liver, kidneys, and mesenteric lymph nodes after administration of this strain to intact mice. Lact. casei IMV B-7280 strain is safe at dose up to 10¹⁰ CFU/animal during 3- and 7-day oral administration to mice and has a positive effect on the gut microbiota composition; it could be potentially considered as safe probiotic for humans.

益生菌，特别是乳酸杆菌（乳酸菌，LAB）菌株，广泛用于临床实践。尽管这些益生菌具有 GRAS（通常被认为是安全的）和合格的安全假定 (QPS) 状态，但特定菌株的安全性仍需要深入研究。该研究的目的是评估Lact 的安全性。casei IMV B-7280 菌株在实验动物模型中研究毒性和对肠道微生物群的影响。雄性 BALB/c 小鼠（7-8 周，体重 20-24 g）用一定量的Lact 治疗。干酪IMV B-7280 菌株：5 × 10 ⁶、5 × 10 ⁸或 5 × 10 ⁹  CFU/动物，每天一次，持续 7 天，或量为 1 × 10 在 3 天内每天一次^{10 CFU/动物（大多数建议的人类益生菌剂量 - 从 10 8}到 10 ⁹  CFU）并在 14 天内监测。进行了血液检查和血清生化检查；新鲜采集实验组和对照组小鼠的盲肠内容物并进行分析。实验结束时（第 15 天），测定心脏、肝脏、肾脏和肠系膜淋巴结和外周血中 LAB 的存在；进行了脑、肝、心脏、小肠和大肠碎片以及肠系膜淋巴结的组织学检查。用Lact治疗的 BALB/c 小鼠的存活率。干酪不同浓度的IMV B-7280毒株在14天的毒性实验中为100%。我们没有观察到任何毒性迹象，因为所有实验小鼠的步态、嗜睡、睡眠、躯体运动活动以及皮毛、眼睛、皮肤和粘膜的变化、震颤、行为模式、抽搐、流涎、腹泻和局部损伤团体。施用益生菌菌株后，盲肠内容物中机会性细菌的数量，如葡萄球菌属、念珠菌属、假单胞菌属spp. 和总需氧菌和任选的厌氧菌与对照相比减少；在这些小鼠的盲肠内容物中，有益细菌（如乳酸杆菌）的数量增加了。将该菌株施用于完整小鼠后，在外周血、心脏、肝脏、肾脏和肠系膜淋巴结中未检测到 LAB。乳酸。casei IMV B-7280 菌株在 对小鼠口服给药 3 天和 7 天期间，剂量高达 10 ^{10 CFU/动物是安全的，并且对肠道微生物群组成有积极影响；}它可能被认为是对人类安全的益生菌。