瑞士乳杆菌对小鼠肠道微生物区系的影响

本实验探讨瑞士乳杆菌对小鼠肠道微生物区系的影响,分析小鼠灌喂益生菌后肠道内各种微生物变化规律。研究将小鼠分成4组,日食对照组、生理盐水对照组、瑞士乳杆菌灌喂组和大肠杆菌灌喂组,连续灌喂15d,采集小鼠粪便利用选择性培养基对不同组别的小鼠肠道菌群作平板计数分析。研究结果表明,瑞士乳杆菌灌喂组与日食组和生理盐水组相比其肠道中乳酸菌类、双歧杆菌类、肠杆菌类、大肠杆菌类差异极显著（p〈O．01）,肠球菌类含量具有显著性差异（p〈0．05）;大肠杆菌灌喂组其肠道中乳酸菌类、双歧杆菌类、肠杆菌类、大肠杆菌类含量与对照组相比具有显著性差异（p〈0．05）,而肠球菌类的分析结果显示变化差异不显著。研究证实了瑞士乳杆菌能够促进小鼠肠道内有益菌的显著增殖,而对肠道内过路菌和可疑致病菌均有一定的抑制作用,表明灌喂瑞士乳杆菌对小鼠肠道微生物区系具有一定的调节作用。     

鼠李糖乳杆菌Probio-M9的特异性荧光原位杂交探针设计及应用

宿主口服益生菌的定性和局部检测具有重要意义。本研究通过设计株水平特异性荧光原位杂交（FISH）探针来研究鼠李糖乳杆菌在宿主肠道中的定殖。根据鼠李糖乳杆菌Probio-M9和其它相关物种的基因组序列,分别设计了鼠李糖乳杆菌种水平特异性探针（Probe-16S）和鼠李糖杆菌Probio-M9菌株水平特异性探针（Probe-SP）。在使用15株鼠李糖乳杆菌菌株和15株其它益生菌验证这些特异性探针后,通过荧光原位杂交（FISH）验证鼠李糖乳杆菌Probio-M9菌株的特异性探针在体外和体内的适用性。结合荧光D-氨基酸（FDAA）探针,在大鼠的肠道中检测到鼠李糖乳杆菌Probio-M9的活细胞。本研究设计的FISH探针可从肠道菌群中特异性鉴定鼠李糖乳杆菌Probio-M9,该方法可与FDAA探针结合使用,以进一步探索该益生菌菌株在宿主肠道中的定位。     

益生菌制剂对抗生素诱导腹泻模型小鼠肠道菌群的调节作用

研究了益生菌制剂对腹泻模型（Antibiotic-Associated Diarrhea,AAD）小鼠肠道菌群的调节作用。BALB/c小鼠随机分为6组,每组8只,灌胃给予氨苄青霉素（22.4 g/kg）,建立小鼠腹泻模型,空白组给予等体积生理盐水。模型建立后,阳性组灌胃给予培菲康（8 g/kg）、益生菌制剂低、中、高剂量组（2.5×106、5×106、1×107 CFU）给予复合益生菌制剂,模型组和空白组给予等体积生理盐水,连续14 d。观察益生菌制剂对小鼠体质量、稀便率、稀便级和腹泻指数的影响,测定小鼠IgA、IgG水平,肠道屏障功能相关基因表达水平以及肠道菌群组成。结果表明,与模型组相比三个剂量组在给予益生菌第14天时小鼠稀便率、稀便级和腹泻指数显著降低,IgA水平分别提高13.30%、20.25%、25.83%,IgG水平分别提高6.84%、19.81%、29.64%,TLR4基因表达水平下调16.88%、20.78%、40.91%,NF-κB基因表达水平下调24.91%、37.19%、55.79%,肠道双歧杆菌、乳杆菌数量明显增加,产气荚膜梭菌、肠球菌、肠杆菌数量明显减少。综上所述,益生菌制剂通过调节肠道菌群,调节免疫球蛋白水平,发挥改善AAD作用。     

唾液乳杆菌CCFM 1054通过改变肠道菌群缓解空肠弯曲杆菌在小鼠体内的感染

考察了唾液乳杆菌(Lactobacillus salivarius)CCFM 1054体外培养产酸及发酵上清液抑制空肠弯曲杆菌(Campylobacter jejuni)生长能力、对人工模拟胃肠液中的耐受、对共培养条件下的抑菌能力、对HT-29细胞的粘附以及自我形成生物膜的能力,并以鼠李糖乳杆菌LGG和植物乳杆菌N49作为对比菌株,分别干预空肠弯曲杆菌和弓形虫复合感染的小鼠。结果显示,CCFM 1054能显著改变小鼠肠道菌群的组成,降低空肠弯曲杆菌在小鼠体内的定植率并缓解其感染。肠道菌群变化和乳酸菌拮抗空肠弯曲杆菌相关的体内外特性的相关性分析表明,CCFM 1054对细胞的高粘附性及其较强的生物膜形成能力使得其能在小鼠体内显著改变肠道菌群丰度。     

表达鼠源β-防御素14的植物乳植杆菌减轻小鼠急性结肠炎

抗菌肽β-防御素除抗菌活性以外,还具有免疫调节功能,在维持肠道稳态中发挥重要作用。本研究旨在探讨鼠源β-防御素14（mouse β-defensin 14,mBD14）在炎症性肠病（inflammatory bowel disease,IBD）中的作用。本实验采用植物乳植杆菌为载体,利用基因工程技术实现mBD14在小鼠肠道中的靶向递送,同时评估其对葡聚糖硫酸钠盐（dextran sulfate sodium,DSS）诱发的小鼠结肠炎的调控作用。结果显示,表达mBD14的植物乳植杆菌能够缓解小鼠急性结肠炎症状。基于表观指标的明显变化,进一步探究表达mBD14的植物乳植杆菌在结肠炎中的作用机制,发现该菌株可调节肠道菌群,进而缓解上皮损伤,维持肠道屏障,同时抑制结肠内促炎因子的分泌,并阻断NOD样受体热蛋白结构域相关蛋白3炎症小体以及下游炎症通路的激活。综上所述,表达mBD14的植物乳植杆菌可通过维持肠道稳态来减轻DSS诱导的小鼠急性结肠炎,本研究可为通过益生菌和抗菌肽防治IBD提供新思路。     

不同剂量植物乳杆菌对小鼠肠道菌群的影响

植物乳杆菌是人体肠道中的益生菌,可自发酵乳肉制品中分离。本实验将处于正常生理状态下的小鼠分为4组,通过灌喂不同剂量的植物乳杆菌X3-2B来探讨其对小鼠肠道各类微生物菌群的影响。结果表明,灌喂植物乳杆菌X3-2B时,小鼠对饲料的利用率优于对照组,且小鼠粪便p H低于对照组(高剂量组最低)。灌喂乳酸菌的小鼠其肠道内乳酸菌与双歧杆菌数显著(p<0.05)高于对照组。高剂量组与中剂量组小鼠在灌喂14d时小鼠肠道内大肠杆菌数无显著差异,但总肠杆菌和肠球菌数显著低于灌喂第1d(p<0.05),即植物乳杆菌X3-2B对肠道内致病菌有一定的抑制作用,对肠道微生物区系有一定的调节作用。     

益生菌复合制剂对头孢曲松钠作用小鼠的抗氧化指标、细胞因子及肠道菌群的影响

目的:探究长双歧杆菌BB536和乳双歧杆菌HN019组成的益生菌复合制剂对头孢曲松钠引起的肠道菌群失调的改善效果。方法:头孢曲松钠（2 mg/g）连续灌胃小鼠5 d,构建肠道菌群失调模型小鼠,然后随机分为模型组,益生菌复合制剂低剂量组（2×105 CFU/g）、中剂量组（4×105 CFU/g）、高剂量组（1.2×106 CFU/g）,另设正常鼠为对照组,第6 d起各剂量组灌胃相应剂量的益生菌复合制剂,对照组和模型组灌胃等体积的生理盐水,连续灌胃30 d。灌胃结束后无菌收集小鼠粪便对肠道菌群计数,并进行16S rDNA高通量测序分析菌群的多样性以及结构,测定血清中白细胞介素2（Interleukin-2,IL-2）、白细胞介素6（Interleukin-6,IL-6）、白细胞介素1β（Interleukin-1β,IL-1β）和肿瘤坏死因子-α（tumor necrosis factor,TNF-α）水平,测定空肠和肝脏中丙二醛（Malondialdehyde,MDA）、总超氧化物歧化酶（Total Superoxide Dismutase,T-SOD）、谷胱甘肽（glutathione,GSH）和谷胱甘肽过氧化物酶（Glutathione peroxidase,GSH-PX）水平。结果:给药头孢曲松钠后,血清中IL-2、IL-6、IL-1β和TNF-α水平有上升趋势,空肠中MDA水平显著上升（P<0.05）且T-SOD水平显著下降（P<0.05）,在高剂量的益生菌复合制剂的干预下,IL-6和IL-1β水平显著降低（P<0.05）,IL-2和TNF-α水平极显著降低（P<0.01）,此外空肠和肝脏中的MDA水平均明显下降、T-SOD水平显著提高（P<0.05）,GSH-PX水平极显著提高（P<0.01）,空肠中GSH水平极显著提高（P<0.01）。在肠道微生物方面,抗生素造损后再灌胃益生菌复合制剂,与灌胃益生菌复合制剂前相比小鼠粪便中肠球菌和肠杆菌数量降低,乳杆菌和双歧杆菌数量提高,微生物多样性分析结果表明各剂量组与模型组相比微生物丰富度有所恢复,且中、高剂量组预测的肠道功能与对照组相比更为接近。结论:益生菌复合制剂可以促进抗氧化物质产生,降低细胞因子水平,促进有益菌的繁殖,提高肠道菌群的丰富度,改善了由头孢曲松钠引起的肠道菌群失调状态。     

植物乳植杆菌CCFM8661对小鼠肠道菌群及肠道屏障的影响

为探讨植物乳植杆菌CCFM8661对小鼠肠道菌群的影响,将小鼠适应性培养一周后,分别用低（1.6×106CFU/只）、中（1.6×107CFU/只）、高（1.6×108CFU/只）剂量的植物乳植杆菌CCFM8661灌胃,干预14 d。分别检测干预前后小鼠粪便中双歧杆菌、乳杆菌、肠球菌、肠杆菌、产气荚膜梭菌的变化情况,并测定组织病理、肠道屏障、肠道通透性、短链脂肪酸相关指标,评价植物乳植杆菌CCFM8661对肠道微生物及肠道屏障的调节作用。结果表明,植物乳植杆菌CCFM8661可增加小鼠肠道双歧杆菌及乳杆菌含量并抑制产气荚膜梭菌的增殖;同时,喂食植物乳植杆菌CCFM8661可明显改变小鼠的肠道通透性、降低肠道中脂多糖（lipopolysaccharide,LPS）和D-乳酸的含量、增强肠道屏障、提高肠道中短链脂肪酸（乙酸、丙酸和丁酸）的含量。综上,植物乳植杆菌CCFM8661能够调节肠道菌群,对肠道屏障具有一定的保护作用。     

木糖调节小鼠肠道菌群作用的研究

本实验研究木糖对小鼠肠道菌群的影响。实验小鼠灌胃不同剂量的木糖,观察双歧杆菌、乳杆菌、肠杆菌和肠球菌等4 种肠道菌群的变化。结果表明,木糖具有调节小鼠肠道菌群及促进双歧杆菌增殖功能。     

不同乳杆菌缓解慢性酒精性肝损伤的作用比较

该文探究不同乳杆菌对小鼠慢性酒精性肝损伤的缓解作用。利用C57BL/6小鼠,随机分为空白对照组、酒精模型组、阳性对照组和乳杆菌干预组。8周后,通过分析小鼠的血清转氨酶活性、肝脏氧化指标、血清内毒素含量、肝脏炎症因子表达、肠道紧密连接蛋白表达水平等,并进行肝组织病理学观察,从而比较不同乳杆菌对慢性酒精性肝损伤的缓解作用。结果表明,所选乳杆菌均能够一定程度地改善慢性酒精引起的小鼠肝损伤。其中,植物乳杆菌LP45(Lactobacillus plantarum 45,LP45)和鼠李糖乳杆菌L519(Lactobacillus rhamnosus 519,L519)效果最为显著。植物乳杆菌LP45和鼠李糖乳杆菌L519显著降低了慢性酒精引起的肝脏脂肪积累和氧化应激,抑制了血液中转氨酶和内毒素的增加,降低了肝脏中炎症因子的升高,并改善了肠道紧密连接蛋白表达的降低。因此,所选乳杆菌中,植物乳杆菌LP45和鼠李糖乳杆菌L519可以通过改善氧化应激和增强肠道屏障功能从而有效缓解小鼠慢性酒精性肝损伤。     

Assessment of adhesion properties of novel probiotic strains to human intestinal mucus

Potential new probiotic strains Lactobacillus brevis PELI, L. reuteri ING1, L. rhamnosus VTT E-800 and L. rhamnosus LC-705 were assessed for their adhesion properties using the human intestinal mucus model. The effect on the adhesion of exposure to acid and pepsin and to milk were tested to simulate gastric and food processing conditions, and the effect of different growth media on adhesion was tested. The properties of the four strains were compared to the well-investigated probiotic L. rhamnosus strain GG. Three of the tested strains showed significant adhesion properties in the mucus model, while L. brevis PELI had intermediate adhesion and L. rhamnosus LC-705 adhered poorly. Pretreatment with different milks decreased the adhesion and low pH and pepsin treatment reduced the adhesion of all tested strains except L. rhamnosus LC-705. No competitive exclusion of pathogenic Salmonella typhimurium or Escherichia coli SfaII was observed. The results indicate that major differences exist between tested proposed probiotic strains. The growth media and the food matrix significantly affect the adhesive ability of the tested strains. This has previously not been taken into account when selecting novel probiotic strains.     

The potential influence of fruit polyphenols on colonic microflora and human gut health

The effect of common dietary polyphenols on growth of human gut bacteria and their adhesion to enterocytes was investigated. The influence on the growth of a probiotic (Lactobacillus rhamnosus), a commensal (Escherichia coli) and two pathogenic bacteria (Staphylococcus aureus, Salmonella typhimurium) was determined, together with effects on adhesion of pathogenic and probiotic bacteria to cultured Caco-2 cells. All polyphenols, except rutin, were found to affect the viability of representative gut flora in vitro, at doses likely to be present in the gastrointestinal tract, but to differing degrees. Naringenin and quercetin were the most active with the lowest minimum inhibitory concentrations for all the four bacteria tested. The remaining polyphenols had the most marked effect on the Gram positive enteropathogen S. aureus. Naringenin and phloridzin were the most effective inhibitors of S. typhimurium adherence to Caco-2 enterocytes while phloridzin and rutin enhanced the adherence of the probiotic L. rhamnosus. Polyphenols appear to have potential to alter gut microecology and, by affecting the total number of beneficial microflora in the gut, may confer positive gut health benefits.     

In vitro adherence properties of Lactobacillus rhamnosus DR20 and Bifidobacterium lactis DR10 strains and their antagonistic activity against an enterotoxigenic Escherichia coli

Adhesion and colonisation properties of three probiotic strains namely, Lactobacillus rhamnosus DR20, L. acidophilus HN017, and Bifidobacterium lactis DR10, were determined in vitro using the differentiated human intestinal cell-lines including HT-29, Caco-2, and HT29-MTX, and compared with properties of L. acidophilus LA-1 and L. rhamnosus GG (two commercial probiotic strains). Two independent methods were employed to quantitate the "adhesiveness" of each strain. In the first method, the bacteria adhered to human cells were detected by Gram staining and counted in different fields under a microscope. Bacteria were also radio-labelled and extent of adhesion determined by scintillation counting. All three strains showed strong adhesion with the human intestinal cell lines in vitro. Adhesion indices of the three strains to two cell lines, i.e. HT-29, and Caco-2 varied between 99 +/- 17 and 219 +/- 36. With mucus-secreting cell-line HT29-MTX, the adhesion indices of all the strains were 2-3 times higher. The adhesion indices of L. acidophilus LA-1 and L. rhamnosus GG were comparable to the other three probiotic strains. We also investigated the inhibitory effect of adhering strains against the intestinal cell monolayer colonization by a known enterotoxigenic strain of Escherichia coli (strain O157:H7). Pre-treatment of E. coli O157:H7 with 2.5-fold concentrated cell-free culture supernatants from L. acidophilus HN017, L. rhamnosus DR20 and B. lactis DR10 reduced the culturable E. coli numbers on TSB plates and also reduced the invasiveness and cell association characteristics of this toxic strain. The inhibitory molecules secreted into the spent media by these strains were partially affected by treatments with lactate dehydrogenase, trypsin and proteinase K suggesting that overall inhibition may be due to a synergistic action of lactic acid and proteinaceous substances.     

Effect of Bifidobacterium thermacidophilum probiotic feeding on enterohemorrhagic Escherichia coli O157:H7 infection in BALB/c mice

The effectiveness of Bifidobacterium thermacidophilum RBL 71 as a probiotic against enterohemorrhagic Escherichia coli O157:H7 infection was studied using a murine model. BALB/c mice were fed the probiotic for 7 days before or after single challenge with E. coli O157:H7. Fecal B. thermacidophilum RBL 71 and E. coli O157:H7 counts obtained by selective culturing methods were assessed for 1 week before and after infection while feed intake, body weight and composition were monitored during 1 week after infection. Histology of gut tissue (jejunum, ileum and colon) and production of fecal IgA antibodies and serum IgG+IgM antibodies to E. coli O157:H7 were analyzed until 1 and 2 weeks post-infection, respectively. The pathogenicity of E. coli O157:H7, marked by body weight loss and intestinal histopathological changes in the infected group, was significantly reduced in the B. thermacidophilum-treated group. Feeding B. thermacidophilum RBL 71 for 7 days before infection resulted in greater post-challenge feed intake and weight gain and lower fecal levels of E. coli O157:H7. Post-infection levels of anti-E. coli O157:H7-specific IgA in feces and IgG+IgM in serum were higher in mice fed bifidobacteria. Intestinal injuries were also attenuated and reaction of the lymphoid component in the mucosa of the ileum was greater in the bifidobacteria-fed group. A lesser degree of protection against E. coli O157:H7 infection was observed when bifidobacteria were given during the 7 days after E. coli O157:H7 infection. These results demonstrate that feeding the probiotic B. thermacidophilum RBL 71 to mice can reduce the severity of E. coli O157:H7 infection, and suggest that this strain represents a good candidate for the prevention of enteric infections in human.     

婴儿肠道源格氏乳杆菌的安全性评价及益生特性

以广州1?月龄婴儿肠道中分离出的乳酸杆菌为实验菌株，经分子生物学鉴定，确认为格氏乳杆菌（Lactobacillus gasseri）LGZ 1029。对格氏乳杆菌LGZ 1029进行体内外安全性评价和益生特性研究，结果表明：格氏乳杆菌LGZ?1029不产溶血毒素，对多类抗生素表现出敏感性，小鼠经口急性无毒；该菌具有较好的胃肠液耐受力及自凝聚能力，疏水性（79.75%）强于商业标准菌株鼠李糖乳杆菌ATCC?7469（43.01%）；菌株对大肠杆菌ATCC?25922抑菌圈直径为17.31～20.70?mm，对金黄色葡萄球菌ATCC?12598的抑菌圈直径为21.71～31.08?mm，抑菌效果强于鼠李糖乳杆菌ATCC?7469；活菌数为1×107?CFU/mL发酵液的1,1-苯基-2-三硝基苯肼自由基清除率可达87.07%。本实验为格氏乳杆菌LGZ?1029在膳食补充剂、乳品制造和防腐剂替代品领域的应用提供理论依据。     

益生菌补充改善吡嗪酰胺致大鼠肝损伤及肠道菌群紊乱的效果

目的：吡嗪酰胺作为抗结核药物治疗结核病可引起患者肝损伤及肠道菌群紊乱,本研究拟探讨益生菌 （干酪乳杆菌（Lactobacillus casei,LcS））补充对吡嗪酰胺致大鼠肝损伤及肠道菌群紊乱的影响。方法：将40 只 成年雄性SD大鼠随机分为4 组,即正常对照组（NC组）、吡嗪酰胺组（L0组）、低剂量LcS组（L1组）、高剂 量LcS组（L2组）。L0组、L1组和L2组均给予吡嗪酰胺处理,以建立肝损伤模型;L0为阳性（药物肝损伤）组; L1组和L2组大鼠每天分别给予10、20 mL/（kg·d）LcS（108 CFU/mL）灌胃,持续10 周。苏木精-伊红染色观察 各组大鼠肝脏组织病理学变化;速率法检测各组大鼠血清丙氨酸氨基转移酶（alanine aminotransferase,ALT）和 天冬氨酸氨基转移酶（aspartate aminotransferase,AST）水平;实时荧光定量聚合酶链式反应技术对大鼠粪便中 的双歧杆菌、乳酸杆菌及大肠杆菌16S rDNA V3可变区进行定量分析。结果：经吡嗪酰胺处理10 周后,L0组大鼠 苏木精-伊红染色切片显示肝细胞中度水肿,出现明显的气球样变,肝索结构消失并伴有炎性细胞浸润,病理学 评分达到3.20 分,血清ALT及AST水平分别升高到95.90 U/L和188.60 U/L,显著高于正常对照组的73.90 U/L和 139.20 U/L,说明肝损伤造模成功。经过不同剂量的LcS干预10 周后,大鼠肝小叶结构均较L0组得到明显改善,病 理学评分、血清ALT和AST水平均降低到正常对照组水平。实验菌株定量分析结果显示,大鼠经过不同分组及干预 时间的延长,3 种代表菌株在组间及组内均具有统计学差异。从分组来看,高剂量LcS组大鼠在干预第6周末及干预 第10周末,双歧杆菌和乳酸杆菌的量均较L0组明显升高,大肠杆菌的量明显降低（P＜0.05）;从干预时间来看, 高剂量LcS组大鼠在干预第10周末,双歧杆菌和乳酸杆菌的量均较干预前显著增加,分别达到干预前的1.18 倍和 1.03 倍。结论：LcS对吡嗪酰胺诱导的肝损伤及肠道菌群紊乱具有一定的改善作用,且随着时间的延长及剂量的增 加,效果更明显。其作用机制可能与LcS维持肠道内环境稳态、调节肠道菌群有关。     

Screening of potential lactobacilli antigenotoxicity by microbial and mammalian cell-based tests

Antigenotoxicity is considered an important property for probiotic lactobacilli. The ability of non probiotic lactobacilli from dairy products and starters to inhibit two reference genotoxins: 4-nitroquinoline-1-oxide and N-methyl-N'-nitro-N-nitrosoguanidine was evaluated. The study was carried out using short-term assays with different targets, such as procaryotic cells (SOS-Chromotest for genotoxicity in Escherichia coli and Ames test for mutagenicity in Salmonella typhimurium) and eucaryotic cells (Comet assay for genotoxicity in Caco-2 enterocytes). A high proportion of strains inhibiting 4-nitroquinoline-1-oxide activity was found in Lactobacillus casei, Lactobacillus acidophilus, Lactobacillus rhamnosus, Lactobacillus delbrueckii subsp. bulgaricus and Lactobacillus plantarum. Inhibition of N-methyl-N'-nitro-N-nitrosoguanidine activity occurred in only one L. acidophilus strain. All the strains with antigenotoxic properties also demonstrated antimutagenic activity and produced modifications in genotoxin spectroscopic profiles. Strain viability during and after genotoxin exposure was confirmed. Concordance of the results obtained with microbial and mammalian cell-based tests is underlined.     

乳源乳杆菌的益生特性及抗氧化活性研究

以5株乳源乳杆菌为研究对象,鼠李糖乳杆菌（Lactobacillus rhamnosus）LGG为阳性对照菌株,通过pH和胆盐耐受性试验、胃肠液耐受性试验、抗生素敏感性试验、抑菌活性试验、黏附Caco-2细胞试验、抗氧化活性试验考察5株菌的益生特性。结果表明,5株乳杆菌对环境胁迫均具有一定的抗逆性;对大肠杆菌、金黄色葡萄球菌和单增李斯特菌具有一定的抑制能力,抑菌圈直径均分别＞10 mm、＞20 mm、＞13 mm;其中鼠李糖乳杆菌260益生特性较优,黏附能力较强,黏附率为4.16%,DPPH自由基清除能力56.36%、羟自由基的清除能力23.09%、总抗氧化能力（T-AOC）为5.26 μmol/mL,具有潜在的应用价值。     

Effect of pepsin-treated bovine and goat caseinomacropeptide on Escherichia coli and Lactobacillus rhamnosus in acidic conditions

Caseinomacropeptide (CMP) is a 7-kDa phosphoglycopolypeptide released from κ-casein during milk digestion and in the cheesemaking process. The objective of the study was to analyze the effect of pepsin-treated CMP from cow and goat milk on the resistance of Escherichia coli and Lactobacillus rhamnosus during acid stress. Bacterial cells in the exponential growth phase were suspended in acidified phosphate buffered saline with or without pepsin-treated CMP. Viability was determined during a 90-min incubation period. Pepsin-treated CMP exhibited bactericidal activity at pH 3.5 when added in a dose-dependent manner to E. coli, decreasing survival by more than 90% within 15 min at 0.25 mg/mL. At pH >4.5, the bactericidal activity disappeared, indicating that pepsin-treated CMP was efficient at low pH only. The effectiveness of pepsin-treated CMP at pH 3.5 was not affected by the presence of glycoconjugates linked to CMP or by the bovine or caprine origin of milk. In contrast, L. rhamnosus, a probiotic, was more resistant to acid stress when pepsin-treated bovine or caprine CMP was added to the media. Viability reached 50% after 60 min of incubation at pH 3 compared with 5% survival in the media without added pepsin-treated CMP. Neither glycosylation extent nor sequence variations between CMP from bovine milk and caprine milk affected the protective activity of hydrolyzed CMP toward L. rhamnosus. This suggests that encrypted bioactive peptides released by the pepsin treatment of CMP had an antibacterial effect on E. coli in acidic media, but improved the resistance of L. rhamnosus to acid stress. The peptide fragment accountable for bactericidal activity is the N-terminal region κ-casein f(106-124).