Getting better with bifidobacteria

Characterization of the serpin-encoding gene of Bifidobacterium breve 210B

Members of the serpin (serine protease inhibitor) superfamily have been identified in higher multicellular eukaryotes, as well as in bacteria, although examination of available genome sequences has indicated that homologs of the bacterial serpin-encoding gene (ser) are not widely distributed. In members of the genus Bifidobacterium this gene appears to be present in at least 5, and perhaps up to 9, of the 30 species tested. Moreover, phylogenetic analysis using available bacterial and eukaryotic serpin sequences revealed that bifidobacteria produce serpins that form a separate clade. We characterized the ser(210B) locus of Bifidobacterium breve 210B, which encompasses a number of genes whose deduced protein products display significant similarity to proteins encoded by corresponding loci found in several other bifidobacteria. Northern hybridization, primer extension, microarray, reverse transcription-PCR (RT-PCR), and quantitative real-time PCR (qRT-PCR) analyses revealed that a 3.5-kb polycistronic mRNA encompassing the ser(210B) operon with a single transcriptional start site is strongly induced following treatment of B. breve 210B cultures with some proteases. Interestingly, transcription of other bifidobacterial ser homologs appears to be triggered by different proteases.

Sugar source modulates exopolysaccharide biosynthesis in Bifidobacterium longum subsp. longum CRC 002

The effect of four sugars (glucose, galactose, lactose and fructose) on exopolysaccharide (EPS) production by Bifidobacterium longum subsp. longum CRC 002 was evaluated. More EPS was produced when CRC 002 was grown on lactose in the absence of pH control, with a production of 1080±120 mg EPS l−1 (P<0.01) after 24 h of incubation. For fructose, galactose and glucose, EPS production was similar, at 512±63, 564±165 and 616±93 mg EPS l−1, respectively. The proposed repeating unit composition of the EPS is 2 galactose to 3 glucose. The effect of sugar and fermentation time on expression of genes involved in sugar nucleotide production (galK, galE1, galE2, galT1, galT2, galU, rmlA, rmlB1 and rmlCD) and the priming glycosyltransferase (wblE) was quantified using real-time reverse transcription PCR. A significantly higher transcription level of wblE (9.29-fold) and the genes involved in the Leloir pathway (galK, 4.10-fold; galT1, 2.78-fold; and galE2, 4.95-fold) during exponential growth was associated with enhanced EPS production on lactose compared to glucose. However, galU expression, linking glucose metabolism with the Leloir pathway, was not correlated with EPS production on different sugars. Genes coding for dTDP-rhamnose biosynthesis were also differentially expressed depending on sugar source and growth phase, although rhamnose was not present in the composition of the EPS. This precursor may be used in cell wall polysaccharide biosynthesis. These results contribute to understanding the changes in gene expression when different sugar substrates are catabolized by B. longum subsp. longum CRC 002.

Intertwinement of stress response regulons in Bifidobacterium breve UCC2003

Bifidobacteria constitute an important component of the microbiota of the gastrointestinal tract of humans and other mammals. Various bifidobacterial strains are commercially exploited because of their perceived beneficial role in the maintenance of gut homeostasis. We have determined the response of B. breve UCC2003, a Gram-positive bacterium originally isolated from the nursling stool of a breast-fed infant, to several stresses (heat, osmotic, solvent) using transcriptomics, classical techniques and in silico analysis, as well as the transcriptional response of B. breve UCC2003 to oxidative stresses caused by the exposure to diamide, peroxide and environmental oxygen. Integration of these results allowed the formulation of a model for an interacting regulatory network for stress response in B. breve UCC2003, where HspR controls SOS response and the ClgR regulon, which in turn regulates and is regulated by HrcA. This model of an interacting regulatory network is believed to represent the paradigm for stress adaptation in bifidobacteria.

The Bifidobacterium dentium Bd1 genome sequence reflects its genetic adaptation to the human oral cavity

Bifidobacteria, one of the relatively dominant components of the human intestinal microbiota, are considered one of the key groups of beneficial intestinal bacteria (probiotic bacteria). However, in addition to health-promoting taxa, the genus Bifidobacterium also includes Bifidobacterium dentium, an opportunistic cariogenic pathogen. The genetic basis for the ability of B. dentium to survive in the oral cavity and contribute to caries development is not understood. The genome of B. dentium Bd1, a strain isolated from dental caries, was sequenced to completion to uncover a single circular 2,636,368 base pair chromosome with 2,143 predicted open reading frames. Annotation of the genome sequence revealed multiple ways in which B. dentium has adapted to the oral environment through specialized nutrient acquisition, defences against antimicrobials, and gene products that increase fitness and competitiveness within the oral niche. B. dentium Bd1 was shown to metabolize a wide variety of carbohydrates, consistent with genome-based predictions, while colonization and persistence factors implicated in tissue adhesion, acid tolerance, and the metabolism of human saliva-derived compounds were also identified. Global transcriptome analysis demonstrated that many of the genes encoding these predicted traits are highly expressed under relevant physiological conditions. This is the first report to identify, through various genomic approaches, specific genetic adaptations of a Bifidobacterium taxon, Bifidobacterium dentium Bd1, to a lifestyle as a cariogenic microorganism in the oral cavity. In silico analysis and comparative genomic hybridization experiments clearly reveal a high level of genome conservation among various B. dentium strains. The data indicate that the genome of this opportunistic cariogen has evolved through a very limited number of horizontal gene acquisition events, highlighting the narrow boundaries that separate commensals from opportunistic pathogens.

Genetic analyses of the antibiotic resistance of Bifidobacterium bifidum strain Yakult YIT 4007

Bifidobacterium bifidum strain Yakult YIT 4007 (abbreviated as B. bifidum YIT 4007) is a commercial strain and resistant to erythromycin, neomycin, and streptomycin. Resistances to these antibiotics were endowed by sequential isolation of resistant mutants from its susceptible progenitor strain YIT 4001. Comparison of nucleotide sequences of various candidate genes of both strains led us to find that B. bifidum YIT 4007 had mutations on three copies of 23S ribosomal RNA genes, an 8 bp deletion of the rluD gene for pseudouridine synthase, and a mutation on the rpsL gene for ribosomal protein S12. The responsibility of these mutations to antibiotic resistances was supported by analyses of newly isolated mutants resistant to these antibiotics. The antibiotic resistances of B. bifidum YIT 4007 were evidently acquired by mutations of the structural genes on the chromosome and not associated with mobile genetic elements like insertion sequences, phages, and plasmids.

Ribose utilization by the human commensal Bifidobacterium breve UCC2003

Growth of Bifidobacterium breve UCC2003 on ribose leads to the transcriptional induction of the rbsACBDK gene cluster. Generation and phenotypic analysis of an rbsA insertion mutant established that the rbs gene cluster is essential for ribose utilization, and that its transcription is likely regulated by a LacI‐type regulator encoded by rbsR, located immediately upstream of rbsA. Gel mobility shift assays using purified RbsR_His indicate that the promoter upstream of rbsABCDK is negatively controlled by RbsR_His binding to an 18 bp inverted repeat and that RbsR_His binding activity is modulated by d‐ribose. The rbsK gene of the rbs operon of B. breve UCC2003 was shown to specify a ribokinase (EC 2.7.1.15), which specifically directs its phosphorylating activity towards d‐ribose, converting this pentose sugar to ribose‐5‐phosphate.

Growth promotion and cell binding ability of bovine lactoferrin to Bifidobacterium longum

Lactoferrin, a major whey protein of human milk, is considered as growth promoter for bifidobacteria, the predominant microorganisms of human intestine. In the present study, in vitro growth promotion and cell binding ability of bovine lactoferrin to several strains of Bifidobacterium longum have been demonstrated. A dose-dependent as well as strain-dependent growth promotion effect by lactoferrin was observed. Cell binding ability of lactoferrin was inspected under an inverted confocal laser scanning microscope by incubation bacterial cells with biotinylated bovine lactoferrin and FITC-conjugated avidin. Fluorescence staining showed bovine lactoferrin binding to all tested strains. A lactoferrin-binding protein with a molecular weight of approximately 67 kDa was also detected in the extracted membrane and cytosolic fraction of each B. longum strain by far-Western blot technique using biotinylated lactoferrin and horseradish peroxidase-conjugated streptavidin. Based on these results, we suggest that existence of lactoferrin-binding protein could be a common characteristic in bifidobacteria. It can also be hypothesized that lactoferrin-binding protein in bifidobacteria is not only involved in growth stimulation mechanism but also could play different roles.

An interactive regulatory network controls stress response in Bifidobacterium breve UCC2003

Members of the genus Bifidobacterium are gram-positive bacteria that commonly are found in the gastrointestinal tract (GIT) of mammals, including humans. Because of their perceived probiotic properties, they frequently are incorporated as functional ingredients in food products. From probiotic production to storage and GIT delivery, bifidobacteria encounter a plethora of stresses. To cope with these environmental challenges, they need to protect themselves through stress-induced adaptive responses. We have determined the response of B. breve UCC2003 to various stresses (heat, osmotic, and solvent) using transcriptome analysis, DNA-protein interactions, and GusA reporter fusions, and we combined these with results from an in silico analysis. The integration of these results allowed the formulation of a model for an interacting regulatory network for stress response in B. breve UCC2003 where HspR controls the SOS response and the ClgR regulon, which in turn regulates and is regulated by HrcA. This model of an interacting regulatory network is believed to represent the paradigm for stress adaptation in bifidobacteria.

Antimicrobial susceptibility of Bifidobacterium breve strains and genetic analysis of streptomycin resistance of probiotic B. breve strain Yakult

The minimum inhibitory concentrations (MICs) of 17 antimicrobials for 26 Bifidobacterium breve strains of various origins were determined by broth microdilution. MIC distributions for 17 antimicrobials except streptomycin and tetracycline were unimodal for all strains tested, whereas bimodal distributions were observed for streptomycin and tetracycline. The probiotic strain B. breve strain Yakult showed intrinsic susceptibility to all antimicrobials except streptomycin to which the strain showed an atypically higher MIC of >256 microg/ml. Because this strain is a commercial strain, which is often ingested by many consumers on a daily basis, it is very important to determine the genetic basis for streptomycin resistance of this strain. Molecular analysis revealed that a mutation of the rpsL gene for ribosomal protein S12 was responsible for this streptomycin resistance. The resistance of B. breve strain Yakult to streptomycin, therefore, is caused by a chromosomal mutation and very unlikely to be transferred to other microorganisms.

Expression of four beta-galactosidases from Bifidobacterium bifidum NCIMB41171 and their contribution on the hydrolysis and synthesis of galactooligosaccharides

This paper deals with two aspects tightly related to the enzymatic characteristics and expression of four beta-galactosidases (BbgI, BbgII, BbgIII and BbgIV) from Bifidobacterium bifidum NCIMB41171. The growth patterns of this strain indicated a preference towards complex (i.e. lactose, galactooligosaccharides (GOSs)) rather than simple carbohydrates (i.e. glucose and galactose) and a collaborative action and synergistic relation of more than one beta-galactosidase isoenzyme for either lactose or GOS hydrolysis and subsequent assimilation. Native polyacrylamide gel electrophoresis analysis of protein extracts from cells growing on different carbohydrates (i.e. glucose, lactose or GOS) indicated that two lactose hydrolysing enzymes (BbgI and BbgIII) and one GOS hydrolysing enzyme (BbgII) were constitutively expressed, whereas a fourth lactose hydrolysing enzyme (BbgIV) was induced in the presence of lactose or different GOS fractions. Furthermore, the beta-galactosidase expression profiles of B. bifidum cells and the transgalactosylating properties of each individual isoenzyme, with lactose as substrate, clearly indicated that mainly three isoenzymes (BbgI, BbgIII and BbgIV) are implicated in GOS synthesis when whole B. bifidum cells are utilised. Two of the isoenzymes (BbgI and BbgIV) proved to have better transgalactosylating properties giving yields ranging from 42% to 47% whereas the rest (BbgI and BbgIII) showed lower yields (15% and 29%, respectively).

Bile-inducible efflux transporter from Bifidobacterium longum NCC2705, conferring bile resistance

Bifidobacteria are normal inhabitants of the human gut. Some strains of this genus are considered health promoting or probiotic, being included in numerous food products. In order to exert their health benefits, these bacteria must overcome biological barriers, including bile salts, to colonize and survive in specific parts of the intestinal tract. The role of multidrug resistance (MDR) transporters in bile resistance of probiotic bacteria and the effect of bile on probiotic gene expression are not fully understood. In the present study, the effect of subinhibitory concentrations of bile on the expression levels of predicted MDR genes from three different bifidobacterial strains, belonging to Bifidobacterium longum subsp. longum, Bifidobacterium breve, and Bifidobacterium animalis subsp. lactis, was tested. In this way, two putative MDR genes whose expression was induced by bile, BL0920 from B. longum and its homolog, Bbr0838, from B. breve, were identified. The expression of the BL0920 gene in Escherichia coli was shown to confer resistance to bile, likely to be mediated by active efflux from the cells. To the best of our knowledge, this represents the first identified bifidobacterial bile efflux pump whose expression is induced by bile.

Probiotics modulate the Bifidobacterium microbiota of elderly nursing home residents

Gut Bifidobacterium microbiota of the elderly has been suggested to differ from that of adults, possibly promoting the risk of infections and gut barrier dysfunction. Specific probiotics may improve the gut barrier. In this randomized, placebo-controlled intervention study, 66 elders consumed a fermented oat drink containing probiotic Bifidobacterium longum 46 and B. longum 2C or a non-fermented placebo oat drink for 6 months. Faecal samples were collected before, during and after the intervention. Levels of faecal bifidobacteria were determined using species-specific quantitative PCR and plate counting. The Bifidobacterium levels in the elderly were high and the species composition diverse. Probiotic intervention increased the levels bifidobacteria significantly. Specifically, the levels of B. catenulatum, B. bifidum and B. breve were enhanced. Consumption of the fermented oat drink itself was also associated with certain changes in microbiota. In conclusion, Bifidobacterium microbiota of elderly subjects may be modulated by probiotic administration. In some healthy elderly populations, Bifidobacterium microbiota may be more abundant and diverse than previously suggested.

Culture-independent identification of gut bacteria correlated with the onset of diabetes in a rat model

Bacteria associated with the onset of type 1 diabetes in a rat model system were identified. In two experiments, stool samples were collected at three time points after birth from bio-breeding diabetes-prone (BB-DP) and bio-breeding diabetes-resistant (BB-DR) rats. DNA was isolated from these samples and the 16S rRNA gene was amplified using universal primer sets. In the first experiment, bands specific to BB-DP and BB-DR genotypes were identified by automated ribosomal intergenic spacer analysis at the time of diabetes onset in BB-DP. Lactobacillus and Bacteroides strains were identified in the BB-DR- and BB-DP-specific bands, respectively. Sanger sequencing showed that the BB-DP and BB-DR bacterial communities differed significantly but too few reads were available to identify significant differences at the genus or species levels. A second experiment confirmed these results using higher throughput pyrosequencing and quantitative PCR of 16S rRNA with more rats per genotype. An average of 4541 and 3381 16S rRNA bacterial reads were obtained from each of the 10 BB-DR and 10 BB-DP samples collected at time of diabetes onset. Nine genera were more abundant in BB-DP whereas another nine genera were more abundant in BB-DR. Thirteen and eleven species were more abundant in BB-DP and BB-DR, respectively. An average of 23% and 10% of all reads could be classified at the genus and species levels, respectively. Quantitative PCR verified the higher abundance of Lactobacillus and Bifidobacterium in the BB-DR samples. Whether these changes are caused by diabetes or are involved in the development of the disease is unknown.

Characterization of two novel alpha-glucosidases from Bifidobacterium breve UCC2003

Two alpha-glucosidase-encoding genes (agl1 and agl2) from Bifidobacterium breve UCC2003 were identified and characterized. Based on their similarity to characterized carbohydrate hydrolases, the Agl1 and Agl2 enzymes are both assigned to a subgroup of the glycosyl hydrolase family 13, the alpha-1,6-glucosidases (EC 3.2.1.10). Recombinant Agl1 and Agl2 into which a His(12) sequence was incorporated (Agl1(His) and Agl2(His), respectively) exhibited hydrolytic activity towards panose, isomaltose, isomaltotriose, and four sucrose isomers--palatinose, trehalulose, turanose, and maltulose--while also degrading trehalose and, to a lesser extent, nigerose. The preferred substrates for both enzymes were panose, isomaltose, and trehalulose. Furthermore, the pH and temperature optima for both enzymes were determined, showing that Agl1(His) exhibits higher thermo and pH optima than Agl2(His). The two purified alpha-1,6-glucosidases were also shown to have transglycosylation activity, synthesizing oligosaccharides from palatinose, trehalulose, trehalose, panose, and isomaltotriose.

Overcoming the restriction barrier to plasmid transformation and targeted mutagenesis in Bifidobacterium breve UCC2003

In silico analysis of the Bifidobacterium breve UCC2003 genome predicted two distinct loci, which encode three different restriction/modification systems, each comprising a modification methylase and a restriction endonuclease. Based on sequence homology and observed protection against restriction we conclude that the first restriction endonuclease, designated BbrI, is an isoschizomer of BbeI, the second, BbrII, is a neoschizomer of SalI, while the third, BbrIII, is an isoschizomer of PstI. Expression of each of the B. breve UCC2003 methylase‐encoding genes in B. breve JCM 7017 established that BbrII and BbrIII are active and restrict incoming DNA. By exploiting knowledge on restriction/modification in B. breve UCC2003 we successfully increased the transformation efficiency to a level that allows the reliable generation of mutants by homologous recombination using a non‐replicative plasmid.

Inhibitory effect of conjugated alpha-linolenic acid from bifidobacteria of intestinal origin on SW480 cancer cells

In this study, we assessed the ability of six strains of bifidobacteria (previously shown by us to possess the ability to convert linoleic acid to c9, t11-conjugated linoleic acid (CLA) to grow in the presence of alpha-linolenic acid and to generate conjugated isomers of the fatty acid substrate during fermentation for 42 h. The six strains of bifidobacteria were grown in modified MRS (mMRS) containing alpha-linolenic acid for 42 h at 37 degrees C, after which the fatty acid composition of the growth medium was assessed by gas liquid chromatography (GLC). Indeed, following fermentation of one of the strains, namely Bifidobacterium breve NCIMB 702258, in the presence of 0.41 mg/ml alpha-linolenic acid, 79.1% was converted to the conjugated isomer, C18:3 c9, t11, c15 conjugated alpha-linolenic acid (CALA). To examine the inhibitory effect of the fermented oils produced, SW480 colon cancer cells were cultured in the presence of the extracted fermented oil (10-50 microg/ml) for 5 days. The data indicate an inhibitory effect on cell growth (p <or= 0.001) of CALA, with cell numbers reduced by 85% at a concentration of 180 microM, compared with a reduction of only 50% with alpha-linolenic acid (p <or= 0.01).

Synbiotics growth optimization of Bifidobacterium pseudocatenulatum G4 with prebiotics using a statistical methodology

AIMS

This study demonstrated the optimum growth of Bifidobacterium pseudocatenulatum G4 with prebiotics via statistical model.

METHODS AND RESULTS

Commercial prebiotics [inulin and fructooligosaccharide (FOS)], together with sorbitol, arabinan and inoculum rate, were tested by fractional factorial design to determine their impact on growth of Bif. pseudocatenulatum G4 in skim milk. At 48 h incubation, bacterial growth was mainly influenced by FOS and inoculum rate. Growth reduction was observed in all samples incubated for 72 h. Central composite design (CCD) was adopted using FOS and inoculum rate at 48 h incubation to develop the statistical model for optimization. The model predicted that 2.461 log CFU ml(-1) produced the optimum growth increase of Bif. pseudocatenulatum G4. The combination that produced the optimum point was 2.86% FOS (g/v) and 0.67% inoculum rate (v/v).

CONCLUSION

At optimum combination of inoculum rate and FOS, validation experiments recorded 2.40 +/- 10.02 log CFU ml(-1). The application in 1-l bioreactor for 24 h showed higher growth increase of 2.95 log CFU ml(-1).

SIGNIFICANT AND IMPACT OF THE STUDY

Response surface methodology approach is useful to develop optimum synbiotics combination for strain G4 with FOS.

Human flora-associated rodents--does the data support the assumptions?

There is little direct literature detailing exhaustive bacteriological studies comparing human donor faecal flora, human flora‐associated (HFA) mouse models and conventional rodent faecal flora. While there is a premise that the implanted donor faecal flora from humans is established in the rodent model the evidence is incomplete and indeed for groups such as Bifidobacterium spp. it is lacking. The reviewed bacteriology studies are generally lacking in detail with the exception of one study from which the data have mostly been overlooked when cited by other workers. While there are studies that suggest that the HFA rodent model is more relevant to man than studies with conventional rodents, the hypothesis remains to be proven. This review concludes that the established microbial flora in the HFA rodent model is different to that of donor human faecal flora, and this clearly raises the question as to whether this matters, after all a model is a model and as such models can be useful even should they fail to be a true representation of, in this case, the gastrointestinal tract. What matters is that there is a proper understanding of the limitations of the model as we attempt to unravel the significance of the components of the gastrointestinal flora in health and disease; examples of why such an analysis is important are provided with regard to obesity and nutritional studies. The data do unsurprisingly suggest that diet is an extremely influential variable when interpreting HFA and conventional rodent data. The microbiology data from direct bacteriology and indirect enzyme studies show that the established microbial flora in the HFA rodent model is different to that of donor human faecal flora. The significance of this conclusion remains to be established.

Genome-scale analyses of health-promoting bacteria: probiogenomics

The human body is colonized by an enormous population of bacteria (microbiota) that provides the host with coding capacity and metabolic activities. Among the human gut microbiota are health-promoting indigenous species (probiotic bacteria) that are commonly consumed as live dietary supplements. Recent genomics-based studies (probiogenomics) are starting to provide insights into how probiotic bacteria sense and adapt to the gastrointestinal tract environment. In this Review, we discuss the application of probiogenomics in the elucidation of the molecular basis of probiosis using the well-recognized model probiotic bacteria genera Bifidobacterium and Lactobacillus as examples.

Genome sequence of the probiotic bacterium Bifidobacterium animalis subsp. lactis AD011

Bifidobacterium animalis subsp. lactis is a probiotic bacterium that naturally inhabits the guts of most mammals, including humans. Here we report the complete genome sequence of B. animalis subsp. lactis AD011 that was isolated from an infant fecal sample. Biological functions encoded in a single circular chromosome of 1,933,695 bp, smallest among the completely sequenced bifidobacterial genomes, are suggestive of their probiotic functions, such as utilization of bifidogenic factors and a variety of glycosidic enzymes and biosynthesis of polysaccharides.

Clinical research on probiotics: the interface between science and regulation

Although there exists some evidence of the safety and efficacy of probiotics for treatment of disease, many of the clinical trials have lacked methodological quality, particularly with regard to protocol design, selection of population, and product characterization. Depending on the regulatory route, data need to be collected carefully to satisfy regulatory requirements in the United States and elsewhere. This article discusses how the regulations for probiotics affect clinical research. It also describes clinical trial design and issues that affect the design of trials for probiotics conducted to improve the scientific evidence for these products.

Characterization of plasmids from human infant Bifidobacterium strains: sequence analysis and construction of E. coli-Bifidobacterium shuttle vectors

A survey of infant fecal Bifidobacterium isolates for plasmid DNA revealed that a significant portion of the strains, 17.6%, carry small plasmids. The majority of plasmid-harboring strains belonged to the Bifidobacterium longum/infantis group. Most of the plasmids could be assigned into two groups based on their sizes and the restriction profiles. Three plasmids, pB44 (3.6 kb) from B. longum, pB80 (4.9 kb) from Bifidobacterium bifidum, and pB21a (5.2kb) from Bifidobacterium breve were sequenced. While the former two plasmids were found to be highly similar to previously characterized rolling-circle replicating pKJ36 and pKJ56, respectively, the third plasmid, pB21a, does not share significant nucleotide homology with known plasmids. However, it might be placed into the pCIBb1-like group of bifidobacterial rolling-plasmids based on the homology of its Rep protein and the overall molecular organization. Two sets of Escherichia coli-Bifidobacterium shuttle vectors constructed based on pB44 and pB80 replicons were capable of transforming B. bifidum and B. breve strains with efficiency up to 3x10(4)cfu/microg DNA. Additionally, an attempt was made to employ a broad host range conjugation element, RP4, in developing of E. coli-Bifidobacterium gene transfer system.

Proposal to reclassify the three biotypes of Bifidobacterium longum as three subspecies: Bifidobacterium longum subsp. longum subsp. nov., Bifidobacterium longum subsp. infantis comb. nov. and Bifidobacterium longum subsp. suis comb. nov

In the year 2002, Bifidobacterium longum, Bifidobacterium infantis and Bifidobacterium suis were unified into a single species, Bifidobacterium longum, preserving the former species names through the creation of the three biotypes 'longum', 'infantis' and 'suis'. Consequently, the use of the species names B. infantis and B. suis was to be discontinued. The above taxonomic rearrangement of B. longum was based on DNA-DNA hybridizations and 16S rRNA and HSP60 gene sequence analysis. However, a variety of other genotypic techniques including ribotyping, amplified rDNA restriction analysis (ARDRA), randomly amplified polymorphic DNA (RAPD)-PCR, BOX-PCR, PCR-denaturing gradient gel electrophoresis (DGGE), comparison of the recA, tuf and ldh gene sequences, plasmid profiling and considerable variation in carbohydrate fermentation patterns as well as results of starch and PAGE electrophoresis experiments clearly discriminate former B. longum, B. infantis and B. suis strains. In the present paper we compile this published information and propose the description of Bifidobacterium longum subsp. longum subsp. nov., Bifidobacterium longum subsp. infantis comb. nov. and Bifidobacterium longum subsp. suis comb. nov. The International Committee on Systematics of Prokaryotes Subcommittee on the taxonomy of Bifidobacterium, Lactobacillus and related organisms is in favour of this proposal. The type strains of Bifidobacterium longum subsp. longum subsp. nov., subsp. infantis comb. nov. and subsp. suis comb. nov. are E194b (variant a)T (ATCC 15707T=DSM 20219T), S12T (=ATCC 15697T=DSM 20088T) and Su859T (ATCC 27533T=DSM 20211T), respectively.

Improved cloning vectors for bifidobacteria, based on the Bifidobacterium catenulatum pBC1 replicon

This study reports the development of several cloning vectors for bifidobacteria based on the replicon of pBC1, a cryptic plasmid from Bifidobacterium catenulatum L48 thought to replicate via the theta mode. These vectors, in which antibiotic resistance genes encoding either erythromycin or tetracycline resistance acted as selection markers, were able to replicate in a series of eight Bifidobacterium species at frequencies ranging from 4.0 x 10(1) to 1.0 x 10(5) transformants microg(-1) but not in Lactococcus lactis or Lactobacillus casei. They showed a relative copy number of around 30 molecules per chromosome equivalent and a good segregational stability, with more than 95% of the cells retaining the vectors after 80 to 100 generations in the absence of selection. Vectors contain multiple cloning sites of different lengths, and the lacZalpha peptide gene was introduced into one of the molecules, thus allowing the easy selection of colonies harboring recombinant plasmids in Escherichia coli. The functionality of the vectors for engineering Bifidobacterium strains was assessed by cloning and examining the expression of an alpha-l-arabinofuranosidase gene belonging to Bifidobacterium longum. E. coli and Bifidobacterium pseudocatenulatum recombinant clones were stable and showed an increase in alpha-arabinofuranosidase activity of over 100-fold compared to that of the untransformed hosts.

The effect of probiotics and organic acids on Shiga-toxin 2 gene expression in enterohemorrhagic Escherichia coli O157:H7

Probiotics are known to have an inhibitory effect against the growth of various foodborne pathogens, however, the specific role of probiotics in Shiga-toxin-producing Escherichia coli (STEC) virulence gene expression has not been well defined. Shiga toxins are members of a family of highly potent bacterial toxins and are the main virulence marker for STEC. Shiga toxins inhibit protein synthesis in eukaryotic cells and play a role in hemorrhagic colitis and hemolytic uremic syndrome. STEC possesses Shiga toxin 1 (Stx1) and Shiga toxin 2 (Stx2), both of which have A and B subunits. Although STEC containing both Stx1 and Stx2 has been isolated from patients with hemorrhagic colitis, Stx2 is more frequently associated with human disease complications. Thus, the effect of Lactobacillus, Pediococcus, and Bifidobacterium strains on stx2A expression levels in STEC was investigated. Lactic acid bacteria and bifidobacteria were isolated from farm animals, dairy, and human sources and included L. rhamnosus GG, L. curvatus, L. plantarum, L. jensenii, L. acidophilus, L. casei, L. reuteri, P. acidilactici, P. cerevisiae, P. pentosaceus, B. thermophilum, B. boum, B. suis and B. animalis. E. coli O157:H7 (EDL 933) was coincubated with sub-lethal concentrations of each probiotic strain. Following RNA extraction and cDNA synthesis, relative stx2A mRNA levels were determined according to a comparative critical threshold (Ct) real-time PCR. Data were normalized to the endogenous control glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and the level of stx2A expression between treated and untreated STEC was compared. Observed for all probiotic strains tested, stx2A was down-regulated, when compared to the control culture. Probiotic production of organic acids, as demonstrated by a decrease in pH, influenced stx2A gene expression.

In vitro effects of bovine lactoferrin on autoaggregation ability and surface hydrophobicity of bifidobacteria

Changes in autoaggregation ability and surface hydrophobicity of bifidobacteria with addition of bovine lactoferrin in liquid media were investigated. Lactoferrin addition caused loss of autoaggregation ability, disappearance of microscopic clusters and produced consistent turbidity in the cultured medium compared with control. Similar outcomes with addition of bovine lactoferrin hydrolysates (pepsin), bovine transferrin or ovotransferrin suggested that the effect is not lactoferrin-specific. On the other hand, addition of proteins, except bovine transferrin, did not alter surface hydrophobicity. These results indicate that one or more surface components involved in autoaggregation of bifidobacteria are proteins.

Improving gastric transit, gastrointestinal persistence and therapeutic efficacy of the probiotic strain Bifidobacterium breve UCC2003

Given the increasing commercial and clinical relevance of probiotic cultures, improving their stress tolerance profile and ability to overcome the physiological defences of the host is an important biological goal. In order to reach the gastrointestinal tract in sufficient numbers to exert a therapeutic effect, probiotic bacteria must resist the deleterious actions of low pH, elevated osmolarity and bile salts. Cloning the listerial betaine uptake system, BetL, into the probiotic strain Bifidobacterium breve UCC2003 significantly improved probiotic tolerance to gastric juice and conditions of elevated osmolarity mimicking the gut environment. Furthermore, whilst stable colonization of the murine intestine was achieved by oral administration of B. breve UCC2003, strains harbouring BetL were recovered at significantly higher levels in the faeces, intestines and caecum of inoculated animals. Finally, in addition to improved gastric transit and intestinal persistence, this approach improved the clinical efficacy of the probiotic culture: mice fed B. breve UCC2003-BetL(+) exhibited significantly lower levels of systemic infection compared to the control strain following oral inoculation with Listeria monocytogenes.

Antibiotic susceptibility testing of Bifidobacterium thermophilum and Bifidobacterium pseudolongum strains: Broth microdilution vs. agar disc diffusion assay

There is urgent need for having available suitable methods and data regarding the susceptibility levels of antibiotic resistant and sensitive strains of bifidobacteria. Based on a defined standard operation procedure, agar disc diffusion and broth microdilution were compared in order to evaluate the antimicrobial susceptibility profiles of 82 B. pseudolongum and 80 B. thermophilum strains mainly originating from the meat production chain. The methods that were assessed showed interpretable agreement within this study. The disc diffusion zone diameters are highly reproducible making the method a useful alternative to broth microdilution for antimicrobial susceptibility screening of bifidobacteria.

Effects of yogurt and bifidobacteria supplementation on the colonic microbiota in lactose-intolerant subjects

AIMS

Colonic metabolism of lactose may play a role in lactose intolerance. We investigated whether a 2-week supplementation of Bifidobacterium longum (in capsules) and a yogurt enriched with Bifidobacterium animalis could modify the composition and metabolic activities of the colonic microbiota in 11 Chinese lactose-intolerant subjects.

METHODS AND RESULTS

The numbers of total cells, total bacteria and the Eubacterium rectale/Clostridium coccoides group in faeces as measured with fluorescent in situ hybridization and the faecal beta-galactosidase activity increased significantly during supplementation. The number of Bifidobacterium showed a tendency to increase during and after supplementation. With PCR-denaturing gradient gel electrophoresis, in subjects in which B. animalis and B. longum were not detected before supplementation, both strains were present in faeces during supplementation, but disappeared after supplementation. The degree of lactose digestion in the small intestine and the oro-caecal transit time were not different before and after supplementation, whereas symptom scores after lactose challenge decreased after supplementation.

CONCLUSIONS

The results suggest that supplementation modifies the amount and metabolic activities of the colonic microbiota and alleviates symptoms in lactose-intolerant subjects. The changes in the colonic microbiota might be among the factors modified by the supplementation which lead to the alleviation of lactose intolerance.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study provides evidence for the possibility of managing lactose intolerance with dietary lactose (yogurt) and probiotics via modulating the colonic microbiota.

Efeito bifidogênico do frutooligossacarídeo na microbiota intestinal de pacientes com neoplasia hematológica

OBJETIVO: Verificar o efeito bifidogênico do frutooligossacarídeo nos pacientes com neoplasias hematológicas submetidos a quimioterapia. MÉTODOS: Trata-se de um estudo clínico randomizado duplo cego, desenvolvido na Unidade de Transplante de Medula Óssea do Centro de Pesquisas Oncológicas de Florianópolis, o qual envolve 25 pacientes divididos em 2 grupos que receberam, por 15 dias, 12g de frutooligossacarídeo (n=14) ou placebo (maltodextrina) (n=11). Foram avaliados a quantidade de bifidobactérias e os valores de pH fecal antes e após a suplementação. RESULTADOS: Observou-se na população estudada o predomínio do sexo masculino (72%) e a idade média de 34 anos. O grupo suplementado apresentou um aumento significante na quantidade de bifidobactérias (p<0,05) e o pH fecal não foi alterado em nenhum dos grupos. CONCLUSÃO: Verificou-se que a suplementação aumentou a quantidade de bifidobactérias, interferindo na composição da microbiota intestinal, e que não houve alteração do pH fecal.