The study was conducted to investigate the efficacy of a probiotic Bacillus subtilis strain on growth performance, diarrhea, systemic immunity, and intestinal health of weaned pigs experimentally infected with an enterotoxigenic Escherichia coli (E. coli), and to compare the efficacy of Bacillus subtilis with that of carbadox. Weaned pigs (n = 48, 6.17 ± 0.36 kg BW) were individually housed in disease containment rooms and randomly allotted to one of four dietary treatments: negative control (NC, control diet without E. coli challenge), positive control (PC, control diet with E. coli challenge), and supplementation of 50 mg/kg of carbadox (AGP) or 2.56 × 10 ⁹ CFU/kg of Bacillus subtilis probiotics (PRO). The experiment lasted for 28 days with 7 days before and 21 days after the first E. coli inoculation. Fecal and blood samples were collected on d 0, 3, 7, 14, and 21 post inoculation (PI) to analyze β-hemolytic coliforms and complete blood cell count, respectively. Diarrhea score was recorded daily for each pig to calculate the frequency of diarrhea. All pigs were euthanized at d 21 PI to collect jejunal and ileal mucosa for gene expression analysis. Pigs in AGP had greater (P < 0.05) body weight on d 7, 14, and 21 PI than pigs in PC and PRO groups. Supplementation of PRO enhanced pigs’ body weight on d 21 PI, compared with the PC. E. coli F18 challenge reduced (P < 0.05) ADG and feed efficiency from d 0 to 21 PI, while supplementation of carbadox or PRO enhanced ADG and feed efficiency in E. coli F18 challenged pigs from d 0 to 21 PI. Pigs in AGP and PRO groups had reduced (P < 0.05) frequency of diarrhea throughout the experiment and fecal β-hemolytic coliforms on d 7 PI than pigs in the PC. Pigs in PRO had greater (P < 0.05) gene expression of CLDN1 in jejunal mucosa than pigs in the PC. Supplementation of carbadox or PRO reduced (P < 0.05) the gene expression of IL6 and PTGS2 in ileal mucosa of E. coli infected pigs compared with pigs in the PC. Pigs in PRO group had lower (P < 0.05) white blood cell number and neutrophil count, and serum haptoglobin concentration on d 7 PI, and less (P < 0.05) monocyte count on d 14 PI, compared with PC. In conclusion, supplementation of probiotic Bacillus subtilis sp. could enhance disease resistance and promote growth performance of weaned pigs under disease challenge condition. The potential mechanisms include but not limited to enhanced gut barrier integrity and local and systemic immune responses of weaned pigs.

中文翻译：

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枯草芽孢杆菌：与卡巴多糖相比，断奶猪的潜在生长促进剂。

本研究旨在研究益生菌枯草芽孢杆菌菌株对实验感染产肠毒素大肠杆菌( E.coli )的断奶猪的生长性能、腹泻、全身免疫和肠道健康的功效，并比较枯草芽孢杆菌的功效与卡巴多。断奶猪 (n = 48, 6.17 ± 0.36 kg BW) 单独饲养在疾病控制室，并随机分配到四种饮食处理之一：阴性对照（NC，没有大肠杆菌攻击的对照饮食），阳性对照（PC，对照）大肠杆菌挑战饮食），并补充 50 mg/kg 卡巴多 (AGP) 或 2.56 × 10 ⁹枯草芽孢杆菌益生菌 (PRO) 的CFU/kg 。实验持续了 28 天，包括第一次大肠杆菌接种前 7 天和后 21 天。在接种后 (PI) 的第 0、3、7、14 和 21 天收集粪便和血液样本，以分别分析 β-溶血性大肠菌群和全血细胞计数。每天记录每头猪的腹泻评分以计算腹泻频率。在感染后第 21 天对所有猪实施安乐死以收集空肠和回肠黏膜用于基因表达分析。AGP 组的猪在第7、14 和 21 天的体重高于 PC 和 PRO 组的猪（P < 0.05）。与 PC 相比，补充 PRO 提高了第 21 天猪的体重。大肠杆菌F18 攻击减少（P< 0.05) 感染后第 0 天至第 21 天的 ADG 和饲料效率，而在感染后第 0 天至第 21 天，添加卡巴多或 PRO 可提高大肠杆菌F18 攻击猪的ADG 和饲料效率。AGP 和 PRO 组的猪在整个实验过程中的腹泻频率和第 7 天的粪便 β-溶血性大肠菌群比 PC组的猪降低（P < 0.05）。PRO中的猪在空肠粘膜中的CLDN1基因表达高于PC中的猪（P <0.05）。与 PC 中的猪相比，添加卡巴多或 PRO 降低了（P < 0.05）大肠杆菌感染猪回肠粘膜中IL6和PTGS2的基因表达。PRO组的猪有较低的（P < 0.05）白细胞数量和中性粒细胞计数，以及第 7 天的血清结合珠蛋白浓度，与 PC 相比，第 14 天的单核细胞计数更少（P < 0.05）。总之，益生菌枯草芽孢杆菌的补充。可以增强疾病抵抗力，促进断奶仔猪在疾病挑战条件下的生长性能。潜在的机制包括但不限于增强断奶猪的肠道屏障完整性和局部和全身免疫反应。