Immunoprotective Effect of Probiotic Dahi Containing Lactobacillus acidophilus and Bifidobacterium bifidum on Dextran Sodium Sulfate-Induced Ulcerative Colitis in Mice

In the present study, probiotic Dahi (LaBb Dahi) containing Lactobacillus acidophilus LaVK2 and Bifidobacterium bifidum BbVK3 was selected as a probiotic therapy to investigate its protective effect on dextran sodium sulfate (DSS)-induced ulcerative colitis model in mice that mimics the picture in human. LaBb Dahi was prepared by co-culturing Dahi bacteria (Lactococcus lactis ssp. cremoris NCDC-86 and Lactococcus lactis ssp. lactis biovar diacetylactis NCDC-60) along with selected strain of L. acidophilus LaVK2 and B. bifidum BbVK3 in buffalo milk (3% fat). Four groups of swiss albino male mice (12 each) were fed buffalo milk (3% fat), buffalo milk (3% fat) plus DSS, Dahi plus DSS, and LaBb Dahi plus DSS, respectively, for 17?days with basal diet. The myeloperoxidase (MPO) activity, levels of tumor necrosis factor-?? (TNF-??), interleukin-6 (IL-6) and interferon (IFN-??) were assessed as inflammatory markers, and the histopathological picture of the colon of mice was studied. DSS-induced colitis appeared to induce significant increase in MPO activity, levels of TNF-??, IL-6 and IFN-??. Feeding with LaBb Dahi offered significant reduction in MPO activity, levels of TNF-??, IL-6 and IFN-?? when compared to either buffalo milk group or group III (Dahi). The present study suggests that LaBb probiotic Dahi can be used to combat DSS-induced biochemical and histological changes and to achieve more effective treatment for ulcerative colitis.     

Cholesterol-lowering probiotics: in vitro selection and in vivo testing of bifidobacteria

Thirty-four strains of bifidobacteria belonging to Bifidobacterium adolescentis, Bifidobacterium animalis, Bifidobacterium bifidum, Bifidobacterium breve, Bifidobacterium longum, and Bifidobacterium pseu-docatenulatum were assayed in vitro for the ability to assimilate cholesterol and for bile salt hydrolase (BSH) against glycocholic and taurodeoxycholic acids (GCA and TDCA). Cholesterol assimilation was peculiar characteristic of two strains belonging to the species B. bifidum (B. bifidum MB 107 and B. bifidum MB 109), which removed 81 and 50 mg of cholesterol per gram of biomass, being the median of specific cholesterol absorption by bifidobacteria 19 mg/g. Significant differences in BSH activities were not established among bifidobacterial species. However, the screening resulted in the selection of promising strains able to efficiently deconjugate GCA and TDCA. No relationship was recognized between BSH phenotype and the extent of cholesterol assimilation. On the basis of cholesterol assimilation or BSH_GCA and BSH_TDCA activities, B. bifidum MB 109 (DSMZ 23731), B. breve MB 113 (DSMZ 23732), and B. animalis subsp. lactis MB 2409 (DSMZ 23733) were combined in a probiotic mixture to be fed to hypercholesterolemic rats. The administration of this probiotic formulation resulted in a significant reduction of total cholesterol and low-density cholesterol (LDL-C), whereas it did not affect high-density cholesterol (HDL-C) and HDL-C/LDL-C ratio.     

Influence of bovine lactoferrin on the growth of selected probiotic bacteria under aerobic conditions

Bovine lactoferrin (bLf) is a natural glycoprotein, and it shows broad-spectrum antimicrobial activity. However, reports on the influences of bLf on probiotic bacteria have been mixed. We examined the effects of apo-bLf (between 0.25 and 128 mg/mL) on both aerobic and anaerobic cultures of probiotics. We found that bLf had similar effects on the growth of probiotics under aerobic or anaerobic conditions, and that it actively and significantly (at concentrations of >0.25 mg/mL) retarded the growth rate of Bifidobacterium bifidum (ATCC 29521), B. longum (ATCC 15707), B. lactis (BCRC 17394), B. infantis (ATCC 15697), Lactobacillus reuteri (ATCC 23272), L. rhamnosus (ATCC 53103), and L. coryniformis (ATCC 25602) in a dose-dependent manner. Otherwise, minimal inhibitory concentrations (MICs) were 128 or >128 mg/mL against B. bifidum, B. longum, B. lactis, L. reuteri, and L. rhamnosus (ATCC 53103). With regard to MICs, bLf showed at least four-fold lower inhibitory effect on probiotics than on pathogens. Intriguingly, bLf (>0.25 mg/mL) significantly enhanced the growth of Rhamnosus (ATCC 7469) and L. acidophilus (BCRC 14065) by approximately 40–200 %, during their late periods of growth. Supernatants produced from aerobic but not anaerobic cultures of L. acidophilus reduced the growth of Escherichia coli by about 20 %. Thus, bLf displayed a dose-dependent inhibitory effect on the growth of most probiotic strains under either aerobic or anaerobic conditions. An antibacterial supernatant prepared from the aerobic cultures may have significant practical use.     

Lysed and disrupted Bifidobacterium bifidum BGN4 cells promote anti-inflammatory activities in lipopolysaccharide-stimulated RAW 264.7 cells

Bifidobacterium bifidum BGN4 has been shown to improve the immune system by regulating interleukin (IL)-6 in RAW 264.7 macrophage cells. In this study, the dead cells of B. bifidum BGN4 were produced by enzymatic and physical processing to enhance the inhibition properties of pro-inflammatory cytokines using lipopolysaccharide (LPS)-stimulated RAW 264.7 cells. Notably, the secretion levels of cytokines such as interleukin (IL)-1β, IL-6, IL-8, and tumor necrosis factor (TNF)-α were decreased by the cell-wall disrupted extracts compared to heat-killed cells. The result suggests that the exposed interior-surface of B. bifidum BGN4 has a potential ability to regulate the immune-responses in the gastrointestinal tract due to major substances in inside-cell wall such as peptidoglycan and teichoic acids. In conclusion, the lysed and disrupted cells from the inside out of B. bifidum BGN4 have anti-inflammatory properties as paraprobiotic agents to control chronic inflammatory related-diseases.     

Intestinal anti-inflammatory effect of the probiotic Saccharomyces boulardii in DSS-induced colitis in mice: Impact on microRNAs expression and gut microbiota composition

The beneficial effects exerted by probiotics in inflammatory bowel disease (IBD) are well known, although their exact mechanisms have not been fully elucidated, and only few studies have focused on their impact on selected miRNAs and the gut microbiota composition. Therefore, our aim was to correlate the intestinal anti-inflammatory activity of the probiotic Saccharomyces boulardii in the dextran sodium sulphate (DSS) model of mouse colitis and the changes induced in miRNA expression and gut microbiota populations. Probiotic was given orally (5×10⁹ CFU) to C57BL/6 mice for 26 days. After 2 weeks, the colitis was induced adding DSS to the drinking water. Mice were scored daily using a Disease Activity Index (DAI). After sacrifice, the colonic specimens were evaluated by determining the expression of inflammatory markers and micro-RNAs by qRT-PCR. Moreover, changes in microbiota populations were evaluated by pyrosequencing. Probiotic ameliorated the colonic damage induced by DSS, as evidenced by lower DAI values and colonic weight/length compared with untreated mice. The treatment modified the colonic expression of different inflammatory markers and the epithelial integrity proteins, and induced changes in micro-RNAs expression. Moreover, microbiota characterization showed that probiotic treatment increased bacterial diversity, thus ameliorating the dysbiosis produced by DSS-colitis. Saccharomyces boulardii exerted intestinal anti-inflammatory effects in DSS-mouse colitis, through the modulation in the immune response, involving modification of altered miRNA expression, being associated to the improvement of the inflammation-associated dysbiosis in the intestinal lumen, which could be of great interest to control the complex pathogenesis of IBD.     

Inhibitory Impact of Bifidobacteria on the Transfer of β-Lactam Resistance among Enterobacteriaceae in the Gnotobiotic Mouse Digestive Tract

While looking for new means to limit the dissemination of antibiotic resistance, we evaluated the role of potentially probiotic bifidobacteria on the transfer of resistance genes between enterobacteria. Transfers of bla genes encoding extended-spectrum β-lactamases (SHV-5 and CTX-M-15) were studied in the absence or presence of bifidobacteria. In vitro, transfer frequencies of these bla genes decreased significantly in the presence of three of five tested strains, i.e., Bifidobacterium longum CUETM-89-215, Bifidobacterium bifidum CIP-56.7T, and Bifidobacterium pseudocatenulatum CIP-104168T. Four transfer experiments were conducted in the digestive tract of gnotobiotic mice, the first three observing the effect of B. longum CUETM-89-215, B. bifidum CIP-56.7T, and B. pseudocatenulatum CIP-104168T on bla_SHV-5 transfer and the fourth experiment studying the effect of B. bifidum CIP-56.7T on bla_CTX-M-15 transfer. These experiments revealed significant decreases in the transconjugant levels (up to 3 logs) in mice having received B. bifidum CIP-56.7T or B. pseudocatenulatum CIP-104168T compared to control mice. Bifidobacteria appear to have an inhibitory impact on the transfer of antibiotic resistance genes. The inhibitory effect is associated to specific bifidobacterial strains and may be related to the production of thermostable metabolites by these strains.     

Identification and characterization of the serine/threonine protein kinases in Bifidobacterium

Six genes encoding the bifidobacterial Hanks-type (eukaryote-like) serine/threonine protein kinases (STPK) were identified and classified. The genome of each bifidobacterial strain contains four conserved genes and one species-specific gene. Bifidobacterium longum and Bifidobacterium bifidum possess the unique gene found only in these species. The STPK genes of Russian industrial probiotic strain B. longum B379M were cloned and sequenced. The expression of these genes in Escherichia coli and bifidobacteria was observed. Autophosphorylation of the conserved STPK Pkb5 and species-specific STPK Pkb2 was demonstrated. This is the first report on Hanks-type STPK in bifidobacteria.     

Early-Life Gut Bacteria Associate with IL-4?, IL-10? and IFN-γ Production at Two Years of Age

Microbial exposure early in life influences immune maturation and potentially also the development of immune-mediated disease. Here we studied early-life gut colonization in relation to cytokine responses at two years of age. Fecal samples were collected from infants during the first two months of life. DNA was extracted from the fecal samples and Bifidobacterium (B.) adolescentis, B. breve, B. bifidum, a group of lactobacilli (L. casei, L. paracasei and L. rhamnosus) as well as Staphylococcus (S.) aureus were detected with real time PCR. Peripheral mononuclear cells were stimulated with phytohaemagglutinin (PHA) and numbers of IL-4−, IL-10− and IFN-γ secreting cells were evaluated using ELISpot. We further stimulated peripheral blood mononuclear cells with bacterial supernatants in vitro and assessed the IL-4−, IL-10− and IFN-γ inducing capacity by flow cytometry and ELISA. Early S. aureus colonization associated with higher numbers of IL-4− (p = 0.022) and IL-10 (p = 0.016) producing cells at two years of age. In contrast to colonization with S. aureus alone, co-colonization with lactobacilli associated with suppression of IL-4− (p = 0.004), IL-10− (p = 0.004) and IFN-γ (p = 0.034) secreting cells. In vitro stimulations of mononuclear cells with bacterial supernatants supported a suppressive role of L. rhamnosus GG on S. aureus-induced cytokine responses. We demonstrate that the early gut colonization pattern associates with the PHA-induced cytokine profile at two years of age and our in vitro findings support that specific bacterial species influence the T helper cell subsets. This suggests that dysbiosis in the early microbiota may modulate the risk of developing inflammatory conditions like allergy.     

BopA Does Not Have a Major Role in the Adhesion of Bifidobacterium bifidum to Intestinal Epithelial Cells,Extracellular Matrix Proteins,and Mucus

The ability of bifidobacteria to adhere to the intestine of the human host is considered to be important for efficient colonization and achieving probiotic effects. Bifidobacterium bifidum strains DSM20456 and MIMBb75 adhere well to the human intestinal cell lines Caco-2 and HT-29. The surface lipoprotein BopA was previously described to be involved in mediating adherence of B. bifidum to epithelial cells, but thioacylated, purified BopA inhibited the adhesion of B. bifidum to epithelial cells in competitive adhesion assays only at very high concentrations, indicating an unspecific effect. In this study, the role of BopA in the adhesion of B. bifidum was readdressed. The gene encoding BopA was cloned and expressed without its lipobox and hydrophobic signal peptide in Escherichia coli, and an antiserum against the recombinant BopA was produced. The antiserum was used to demonstrate the abundant localization of BopA on the cell surface of B. bifidum. However, blocking of B. bifidum BopA with specific antiserum did not reduce adhesion of bacteria to epithelial cell lines, arguing that BopA is not an adhesin. Also, adhesion of B. bifidum to human colonic mucin and fibronectin was found to be BopA independent. The recombinant BopA bound only moderately to human epithelial cells and colonic mucus, and it failed to bind to fibronectin. Thus, our results contrast the earlier findings on the major role of BopA in adhesion, indicating that the strong adhesion of B. bifidum to epithelial cell lines is BopA independent.     

Gnotobiotic Mouse Immune Response Induced by Bifidobacterium sp. Strains Isolated from Infants

Bifidobacterium, which is a dominant genus in infants’ fecal flora and can be used as a probiotic, has shown beneficial effects in various pathologies, including allergic diseases, but its role in immunity has so far been little known. Numerous studies have shown the crucial role of the initial intestinal colonization in the development of the intestinal immune system, and bifidobacteria could play a major role in this process. For a better understanding of the effect of Bifidobacterium on the immune system, we aimed at determining the impact of Bifidobacterium on the T-helper 1 (T_H1)/T_H2 balance by using gnotobiotic mice. Germfree mice were inoculated with Bifidobacterium longum NCC2705, whose genome is sequenced, and with nine Bifidobacterium strains isolated from infants’ fecal flora. Five days after inoculation, mice were killed. Transforming growth factor β1 (TGF-β1), interleukin-4 (IL-4), IL-10, and gamma interferon (IFN-γ) gene expressions in the ileum and IFN-γ, tumor necrosis factor alpha (TNF-α), IL-10, IL-4, and IL-5 secretions by splenocytes cultivated for 48 h with concanavalin A were quantified. Two Bifidobacterium species had no effect (B. adolescentis) or little effect (B. breve) on the immune system. Bifidobacterium bifidum, Bifidobacterium dentium, and one B. longum strain induced T_H1 and T_H2 cytokines at the systemic and intestinal levels. One B. longum strain induced a T_H2 orientation with high levels of IL-4 and IL-10, both secreted by splenocytes, and of TGF-β gene expression in the ileum. The other two strains induced T_H1 orientations with high levels of IFN-γ and TNF-α splenocyte secretions. Bifidobacterium's capacity to stimulate immunity is species specific, but its influence on the orientation of the immune system is strain specific.     

Unraveling the Leloir Pathway of Bifidobacterium bifidum: Significance of the Uridylyltransferases

The GNB/LNB (galacto-N-biose/lacto-N-biose) pathway plays a crucial role in bifidobacteria during growth on human milk or mucin from epithelial cells. It is thought to be the major route for galactose utilization in Bifidobacterium longum as it is an energy-saving variant of the Leloir pathway. Both pathways are present in B. bifidum, and galactose 1-phosphate (gal1P) is considered to play a key role. Due to its toxic nature, gal1P is further converted into its activated UDP-sugar through the action of poorly characterized uridylyltransferases. In this study, three uridylyltransferases (galT1, galT2, and ugpA) from Bifidobacterium bifidum were cloned in an Escherichia coli mutant and screened for activity on the key intermediate gal1P. GalT1 and GalT2 showed UDP-glucose-hexose-1-phosphate uridylyltransferase activity (EC 2.7.7.12), whereas UgpA showed promiscuous UTP-hexose-1-phosphate uridylyltransferase activity (EC 2.7.7.10). The activity of UgpA toward glucose 1-phosphate was about 33-fold higher than that toward gal1P. GalT1, as part of the bifidobacterial Leloir pathway, was about 357-fold more active than GalT2, the functional analog in the GNB/LNB pathway. These results suggest that GalT1 plays a more significant role than previously thought and predominates when B. bifidum grows on lactose and human milk oligosaccharides. GalT2 activity is required only during growth on substrates with a GNB core such as mucin glycans.     

Exploring the genome sequence of Bifidobacterium bifidum S17 for potential players in host-microbe interactions

Bifidobacterium bifidum S17 is a promising probiotic candidate, which displays potent anti-inflammatory activity both in vitro and in vivo. Furthermore, tight adhesion to intestinal epithelial cells (IECs) has been shown for this strain and is considered to be an important prerequisite for host colonization and consequently the anti-inflammatory properties. By analyzing the recently sequenced genome at least 9 surface proteins and various gene clusters encoding for putative pili were identified. Most of these proteins are expressed in vitro, with higher expression during exponential growth phase. Increased expression of the putative adhesins in exponential growth phase was associated with higher adhesion of B. bifidum S17 to Caco-2 cells.     

TgaA,a VirB1-Like Component Belonging to a Putative Type IV Secretion System of Bifidobacterium bifidum MIMBb75

Bifidobacterium bifidum MIMBb75 is a human intestinal isolate demonstrated to be interactive with the host and efficacious as a probiotic. However, the molecular biology of this microorganism is yet largely unknown. For this reason, we undertook whole-genome sequencing of B. bifidum MIMBb75 to identify potential genetic factors that would explain the metabolic and probiotic attributes of this bacterium. Comparative genomic analysis revealed a 45-kb chromosomal region that comprises 19 putative genes coding for a potential type IV secretion system (T4SS). Thus, we undertook the initial characterization of this genetic region by studying the putative virB1-like gene, named tgaA. Gene tgaA encodes a peptidoglycan lytic enzyme containing two active domains: lytic murein transglycosylase (LT, cd00254.3) and cysteine- and histidine-dependent amidohydrolase/peptidase (CHAP, pfam05257.4). By means of several in vitro assays, we experimentally confirmed that protein TgaA, consistent with its computationally assigned role, has peptidoglycan lytic activity, which is principally associated to the LT domain. Furthermore, immunofluorescence and immunogold labeling showed that the protein TgaA is abundantly expressed on the cell surface of B. bifidum MIMBb75. According to the literature, the T4SSs, which have not been characterized before in bifidobacteria, can have important implications for bacterial cell-to-cell communication as well as cross talk with host cells, justifying the interest for further studies aimed at the investigation of this genetic region.     

More Protection of Lactobacillus acidophilus Than Bifidobacterium bifidum Probiotics on Azoxymethane-Induced Mouse Colon Cancer

Based on the ability of the probiotics in the gut microflora modification, they can have the beneficial effects on diseases in the short and/or the long term. In previous study, we revealed that unlike Bifidobacterium bifidum, the amount of Lactobacillus acidophilus remained almost unchanged in mice gut microflora in the long term, indicating more stability of L. acidophilus than B. bifidum which can be used to prevent some incurable diseases such as cancer. Thirty-eight male BALB/c mice were divided into four groups, control, azoxymethane (AOM), L. acidophilus, and B. bifidum probiotics, to evaluate the protective effects of the probiotics on AOM-induced mouse colon cancer. Except for the control group, the rest of the animals were weekly given AOM (15 mg/kg, s.c) in three consecutive weeks. Colon lesion incidence was 74% in the AOM group in comparison with the control (0%) (P < 0.05). The lesions were varied from mild to severe dysplasia and colonic adenocarcinoma. Administration of the probiotics inhibited the incidence of colonic lesions by about 57% in L. acidophilus (P < 0.05) and 27% in B. bifidum (P > 0.05) compared to the AOM group. The serum levels of CEA and CA19-9 tumor markers were significantly decreased in L. acidophilus in comparison with the AOM group (P < 0.05). Moreover, the serum levels of IFN-γ and IL-10 and the number of CD4⁺ and CD8⁺ cells were significantly increased in L. acidophilus compared to AOM (P < 0.05). Our study highlighted the more potential effects of L. acidophilus probiotic than B. bifidum on mouse colon cancer.

     

Murein Lytic Enzyme TgaA of Bifidobacterium bifidum MIMBb75 Modulates Dendritic Cell Maturation through Its Cysteine- and Histidine-Dependent Amidohydrolase/Peptidase (CHAP) Amidase Domain

Bifidobacteria are Gram-positive inhabitants of the human gastrointestinal tract that have evolved close interaction with their host and especially with the host''s immune system. The molecular mechanisms underlying such interactions, however, are largely unidentified. In this study, we investigated the immunomodulatory potential of Bifidobacterium bifidum MIMBb75, a bacterium of human intestinal origin commercially used as a probiotic. Particularly, we focused our attention on TgaA, a protein expressed on the outer surface of MIMBb75''s cells and homologous to other known bacterial immunoactive proteins. TgaA is a peptidoglycan lytic enzyme containing two active domains: lytic murein transglycosylase (LT) and cysteine- and histidine-dependent amidohydrolase/peptidase (CHAP). We ran immunological experiments stimulating dendritic cells (DCs) with the B. bifidum MIMBb75 and TgaA, with the result that both the bacterium and the protein activated DCs and triggered interleukin-2 (IL-2) production. In addition, we observed that the heterologous expression of TgaA in Bifidobacterium longum transferred to the bacterium the ability to induce IL-2. Subsequently, immunological experiments performed using two purified recombinant proteins corresponding to the single domains LT and CHAP demonstrated that the CHAP domain is the immune-reactive region of TgaA. Finally, we also showed that TgaA-dependent activation of DCs requires the protein CD14, marginally involves TRIF, and is independent of Toll-like receptor 4 (TLR4) and MyD88. In conclusion, our study suggests that the bacterial CHAP domain is a novel microbe-associated molecular pattern actively participating in the cross talk mechanisms between bifidobacteria and the host''s immune system.     

Isolation of a Bifidogenic Peptide from the Pepsin Hydrolysate of Bovine Lactoferrin

Lactoferrin is an iron-binding glycoprotein found in the milk of most mammals for which various biological functions have been reported, such as antimicrobial activity and bifidogenic activity. In this study, we compared the bifidogenic activity of bovine lactoferrin (bLF) and pepsin hydrolysate of bLF (bLFH), isolated bifidogenic peptide from bLFH, and investigated the bifidogenic spectra of bLF, bLFH, and its active peptide against 42 bifidobacterial strains comprising nine species. Against Bifidobacterium breve ATCC 15700^T, minimal effective concentrations of bLF and bLFH were 300 and 10 μg/ml. Against Bifidobacterium longum subsp. infantis ATCC 15697^T, the minimal effective concentration of bLFH was 30 μg/ml, and bLF did not show bifidogenic activity within 300 μg/ml. As an active peptide, a heterodimer of A¹-W¹⁶ and L⁴³-A⁴⁸ linked by a disulfide bond was isolated. Previously, this peptide was identified as having antibacterial activity. An amino acid mixture with the same composition as this peptide showed no bifidogenic activity. The strains of each species whose growth was highly promoted (>150%) by this peptide at 3.75 μM were as follows: B. breve (7 out of 7 strains [7/7]), B. longum subsp. infantis (5/5), Bifidobacterium bifidum (2/5), B. longum subsp. longum (1/3), Bifidobacterium adolescentis (3/6), Bifidobacterium catenulatum (1/4), Bifidobacterium pseudocatenulatum (0/4), Bifidobacterium dentium (0/5), and Bifidobacterium angulatum (0/3). Growth of none of the strains was highly promoted by bLF at 3.75 μM. We demonstrated that bLFH showed stronger bifidogenic activity than natural bLF, especially against infant-representative species, B. breve and B. longum subsp. infantis; furthermore, we isolated its active peptide. This is the first report about a bifidogenic peptide derived from bLF.     

Evaluation of in vitro antagonism and of in vivo immune modulation and protection against pathogenic experimental challenge of two probiotic strains of Bifidobacterium animalis var. lactis

The aim of the present study was to compare the effect of intragastric administration with two strains of Bifidobacterium animalis subsp. lactis (Bifido A and Bifido B), in gnotobiotic and conventional mice, challenged with Salmonella Typhimurium. In vitro antagonism test showed that the two strains were able to produce antagonistic substances against various pathogenic microorganisms. In an ex vivo antagonism test the production of antagonistic substances was observed only against three out ten pathogens tested. Both Bifidobacterium strains were able to colonize and to maintain high population levels in the digestive tract of gnotobiotic mice. In addition, the two strains had low and limited translocation ability and did not cause any histological lesion in any of the organs analyzed. Both strains were able to reduce the fecal number of Salmonella in gnotobiotic mice challenged with the pathogen, but only Bifido B was able to confer a protection as demonstrated by a lower mortality. Higher levels of sIgA and IL-10 were observed only in Bifido B mono-associated mice when compared to germ free group. We could conclude that, among the parameters analyzed, the strain Bifido B exhibited the more desirable characteristics to be used as a probiotic.     

Isolation of Bifidobacteria from Breast Milk and Assessment of the Bifidobacterial Population by PCR-Denaturing Gradient Gel Electrophoresis and Quantitative Real-Time PCR

The objective of this work was to elucidate if breast milk contains bifidobacteria and whether they can be transmitted to the infant gut through breastfeeding. Twenty-three women and their respective infants provided samples of breast milk and feces, respectively, at days 4 to 7 after birth. Gram-positive and catalase-negative isolates from specific media with typical bifidobacterial shapes were identified to the genus level by F6PPK (fructose-6-phosphate phosphoketolase) assays and to the species level by 16S rRNA gene sequencing. Bifidobacterial communities in breast milk were assessed by PCR-denaturing gradient gel electrophoresis (PCR-DGGE), and their levels were estimated by quantitative real-time PCR (qRTi-PCR). Bifidobacteria were present in 8 milk samples and 21 fecal samples. Bifidobacterium breve, B. adolescentis, and B. bifidum were isolated from milk samples, while infant feces also contained B. longum and B. pseudocatenulatum. PCR-DGGE revealed the presence of one to four dominant bifidobacterial bands in 22 milk samples. Sequences with similarities above 98% were identified as Bifidobacterium breve, B. adolescentis, B. longum, B. bifidum, and B. dentium. Bifidobacterial DNA was detected by qRTi-PCR in the same 22 milk samples at a range between 40 and 10,000 16S rRNA gene copies per ml. In conclusion, human milk seems to be a source of living bifidobacteria for the infant gut.