Resistance to Simulated Gastrointestinal Conditions and Adhesion to Mucus as Probiotic Criteria for Bifidobacterium longum Strains

Eight Bifidobacterium longum strains, including reported probiotic strains (commercial and noncommercial), collection strains, and laboratory isolates, were investigated for their ability to adhere to mucin as well as their ability to tolerate acid and bile. Strains could be discriminated based on their sensitivity at pH values of 2.0 to 2.5 and bile concentrations of 0.5% to 2.0%. B. longum NCC 2705, a strain known for its probiotic properties, showed the highest resistance to gastrointestinal conditions, whereas the commercial probiotic strains B. longum BB 536 and SP 07/3 were the least resistant. In parallel, the human isolate B. longum BIF 53 showed the highest adhesion to mucin, whereas the commercial probiotic strains B. longum W 11, BB 536, and SP 07/3 were the least adhesive. The bacterial adhesion to mucin of strains B. longum NCC 2705 and BIF 53 could be reduced by lysozyme, indicating that cell-wall components are involved in the adhesion process. These results showed that there is no obvious link between adhesion and resistance to gastrointestinal conditions and the probiotic status of the studied strains. This calls for a definition of conditions for in vitro tests that better predict the in vivo functionality of probiotic strains.     

Probiotic characteristics and in vitro compatibility of a combination of Bifidobacterium breve M-16 V,Bifidobacterium longum subsp. infantis M-63 and Bifidobacterium longum subsp. longum BB536

The consumption of probiotic-based products has risen greatly in recent decades. Due to their probiotic characteristics, microorganisms such as lactobacilli and bifidobacteria are in daily use in the production of food supplements. In the present study, three bifidobacterial strains (Bifidobacterium breve M-16 V, Bifidobacterium longum subsp. infantis M-63 and Bifidobacterium longum subsp. longum BB536) were tested for growth compatibility, resistance to antimicrobial agents, antibacterial activity against pathogens, resistance to gastric acidity, bile salt hydrolysis and adhesion to the human intestinal epithelial cell line HT29. All of these strains were resistant to gentamycin, but none showed in vitro growth incompatibility or the presence of known resistance determinants. B. breve M-16 V had the best probiotic characteristics and, indeed, was the only strain possessing antibacterial activity against Escherichia coli and Klebsiella pneumoniae. All strains were resistant to simulated gastric juice, while only B. longum subsp. longum BB536 and B. breve M-16 V showed a bile salt hydrolytic activity. Interestingly, a strong adhesion to HT29 cells was observed in all Bifidobacterium strains. In conclusion, B. breve M-16 V, B. longum subsp. longum BB536 and B. longum subsp. infantis M-63 showed several promising characteristics as probiotic strains.     

Cross-Feeding between Bifidobacterium longum BB536 and Acetate-Converting, Butyrate-Producing Colon Bacteria during Growth on Oligofructose

In vitro coculture fermentations of Bifidobacterium longum BB536 and two acetate-converting, butyrate-producing colon bacteria, Anaerostipes caccae DSM 14662 and Roseburia intestinalis DSM 14610, with oligofructose as the sole energy source, were performed to study interspecies interactions. Two clearly distinct types of cross-feeding were identified. A. caccae DSM 14662 was not able to degrade oligofructose but could grow on the fructose released by B. longum BB536 during oligofructose breakdown. R. intestinalis DSM 14610 could degrade oligofructose, but only after acetate was added to the medium. Detailed kinetic analyses of oligofructose breakdown by the last strain revealed simultaneous degradation of the different chain length fractions, in contrast with the preferential degradation of shorter fractions by B. longum BB536. In a coculture of both strains, initial oligofructose degradation and acetate production by B. longum BB536 took place, which in turn also allowed oligofructose breakdown by R. intestinalis DSM 14610. These and similar cross-feeding mechanisms could play a role in the colon ecosystem and contribute to the combined bifidogenic/butyrogenic effect observed after addition of inulin-type fructans to the diet.     

Kinetic Analysis of Bifidobacterial Metabolism Reveals a Minor Role for Succinic Acid in the Regeneration of NAD+ through Its Growth-Associated Production

Several strains belonging to the genus Bifidobacterium were tested to determine their abilities to produce succinic acid. Bifidobacterium longum strain BB536 and Bifidobacterium animalis subsp. lactis strain Bb 12 were kinetically analyzed in detail using in vitro fermentations to obtain more insight into the metabolism and production of succinic acid by bifidobacteria. Changes in end product formation in strains of Bifidobacterium could be related to the specific rate of sugar consumption. When the specific sugar consumption rate increased, relatively more lactic acid and less acetic acid, formic acid, and ethanol were produced, and vice versa. All Bifidobacterium strains tested produced small amounts of succinic acid; the concentrations were not more than a few millimolar. Succinic acid production was found to be associated with growth and stopped when the energy source was depleted. The production of succinic acid contributed to regeneration of a small part of the NAD⁺, in addition to the regeneration through the production of lactic acid and ethanol.     

A Phytase-Based Reporter System for Identification of Functional Secretion Signals in Bifidobacteria

Health-promoting effects have been attributed to a number of Bifidobacterium sp. strains. These effects as well as the ability to colonise the host depend on secreted proteins. Moreover, rational design of protein secretion systems bears the potential for the generation of novel probiotic bifidobacteria with improved health-promoting or therapeutic properties. To date, there is only very limited data on secretion signals of bifidobacteria available. Using in silico analysis, we demonstrate that all bifidobacteria encode the major components of Sec-dependent secretion machineries but only B. longum strains harbour Tat protein translocation systems. A reporter plasmid for secretion signals in bifidobacteria was established by fusing the coding sequence of the signal peptide of a sialidase of Bifidobacterium bifidum S17 to the phytase gene appA of E. coli. The recombinant strain showed increased phytase activity in spent culture supernatants and reduced phytase levels in crude extracts compared to the control indicating efficient phytase secretion. The reporter plasmid was used to screen seven predicted signal peptides in B. bifidum S17 and B. longum E18. The tested signal peptides differed substantially in their efficacy to mediate protein secretion in different host strains. An efficient signal peptide was used for expression and secretion of a therapeutically relevant protein in B. bifidum S17. Expression of a secreted cytosine deaminase led to a 100-fold reduced sensitivity of B. bifidum S17 to 5-fluorocytosine compared to the non-secreted cytosine deaminase suggesting efficient conversion of 5-fluorocytosine to the cytotoxic cancer drug 5-fluorouracil by cytosine deaminase occurred outside the bacterial cell. Selection of appropriate signal peptides for defined protein secretion might improve therapeutic efficacy as well as probiotic properties of bifidobacteria.     

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.     

In Vitro Kinetic Analysis of Oligofructose Consumption by Bacteroides and Bifidobacterium spp. Indicates Different Degradation Mechanisms

The growth of pure cultures of Bacteroides thetaiotaomicron LMG 11262 and Bacteroides fragilis LMG 10263 on fructose and oligofructose was examined and compared to that of Bifidobacterium longum BB536 through in vitro laboratory fermentations. Gas chromatography (GC) analysis was used to determine the different fractions of oligofructose and their degradation during the fermentation process. Both B. thetaiotaomicron LMG 11262 and B. fragilis LMG 10263 were able to grow on oligofructose as fast as on fructose, succinic acid being the major metabolite produced by both strains. B. longum BB536 grew slower on oligofructose than on fructose. Acetic acid and lactic acid were the main metabolites produced when fructose was used as the sole energy source. Increased amounts of formic acid and ethanol were produced when oligofructose was used as an energy source at the cost of lactic acid. Detailed kinetic analysis revealed a preferential metabolism of the short oligofructose fractions (e.g., F₂ and F₃) for B. longum BB536. After depletion of the short fractions, the larger oligofructose fractions (e.g., F₄, GF₄, F₅, GF₅, and F₆) were metabolized, too. Both Bacteroides strains did not display such a preferential metabolism and degraded all oligofructose fractions simultaneously, transiently increasing the fructose concentration in the medium. This suggests a different mechanism for oligofructose breakdown between the strain of Bifidobacterium and both strains of Bacteroides, which helps to explain the bifidogenic nature of inulin-type fructans.     

In vitro Th1 cytokine-independent Th2 suppressive effects of bifidobacteria

A comparison between 17 strains of lactic acid bacteria and 15 strains of bifidobacteria indicated that bifidobacteria induced significantly lower levels of interleukin-12 (IL-12) in murine splenic cells. The present study aims to evaluate the effect and mechanism of Bifidobacterium longum BB536, a probiotic strain, in suppressing antigen-induced Th2 immune response in vitro. BB536 suppressed immunoglobulin (Ig) E and IL-4 production by ovalbumin-sensitized splenic cells, but induction of Th1-inducing cytokine production, such as IL-12 and gamma interferon (IFN-gamma) tended to be lower compared with lactic acid bacteria. Neutralization with antibodies to IL-12, IFN-gamma, IL-10 and transforming growth factor beta indicated negative involvement of Th1-inducing cytokines and regulatory cytokines in the suppression of Th2 immune response by BB536, especially when treated at higher doses of BB536 (>10 microg cells/ml). Furthermore, BB536 induced the maturation of immature bone marrow-derived dendritic cells (BM-DCs), and suppressed antigen-induced IL-4 production mediated by BM-DCs. These results suggested that BB536 suppressed Th2 immune responses, partially independent of Th1-inducing cytokines and independent of regulatory cytokines, mediated by antigen-presenting cells such as dendritic cells.     

Cloning and sequence analysis of bile salt hydrolase (bsh) gene from Bifidobacterium longum

A pair of PCR primers for the rapid detection of bile salt hydrolase (bsh) gene from Bifidobacterium longum BB536 has been synthesised and have revealed the bsh gene of approx 970 bp in Bifidobacterium longum BB 536 but not in other species of bacteria tested. The bsh gene was cloned and sequenced showing a high similarity to bsh gene previously published. The resulting nucleotide sequence encodes a predicted protein of 317 amino acids, Mw = 35 kDa.     

Survival of bifidobacteria administered to calves

Twenty-five bifidobacteria were isolated from feces of calves. Isolates were identified, and their functional properties and antimicrobial activity were determined. From 10 strains with suitable properties rifampicin-resistant mutants (RRBs) were prepared and mixture of RRBs was administered to 2-d-old calves. These strains were identified by sequencing as Bifidobacterium animalis ssp. animalis (6 strains), B. thermophilum (2 strains), B. choerinum (1 strain) and B. longum ssp. suis (1 strain). The control group was without probiotic treatment. Survival ability of administered bifidobacteria was monitored in fecal samples by cultivation on modified TPY agar supplemented with mupirocin, acetic acid, and rifampicin. Administered bifidobacteria survived in gastrointestinal tract of calves for at least 60 d. Other bacteria were also determined after cultivation using fluorescence in situ hybridization (FISH). Bifidobacteria and lactobacilli dominated in fecal microflora. Significantly lower amounts of E. coli and higher amounts of bifidobacteria and total anaerobes were found in the treated group relative to the control group.     

Immunoregulatory Effect of Bifidobacteria Strains in Porcine Intestinal Epithelial Cells through Modulation of Ubiquitin-Editing Enzyme A20 Expression

Background

We previously showed that evaluation of anti-inflammatory activities of lactic acid bacteria in porcine intestinal epithelial (PIE) cells is useful for selecting potentially immunobiotic strains.

Objective

The aims of the present study were: i) to select potentially immunomodulatory bifidobacteria that beneficially modulate the Toll-like receptor (TLR)-4-triggered inflammatory response in PIE cells and; ii) to gain insight into the molecular mechanisms involved in the anti-inflammatory effect of immunobiotics by evaluating the role of TLR2 and TLR negative regulators in the modulation of proinflammatory cytokine production and activation of mitogen-activated protein kinase (MAPK) and nuclear factor-κB (NF-κB) pathways in PIE cells.

Results

Bifidobacteria longum BB536 and B. breve M-16V strains significantly downregulated levels of interleukin (IL)-8, monocyte chemotactic protein (MCP)-1 and IL-6 in PIE cells challenged with heat-killed enterotoxigenic Escherichia coli. Moreover, BB536 and M-16V strains attenuated the proinflammatory response by modulating the NF-κB and MAPK pathways. In addition, our findings provide evidence for a key role for the ubiquitin-editing enzyme A20 in the anti-inflammatory effect of immunobiotic bifidobacteria in PIE cells.

Conclusions

We show new data regarding the mechanism involved in the anti-inflammatory effect of immunobiotics. Several strains with immunoregulatory capabilities used a common mechanism to induce tolerance in PIE cells. Immunoregulatory strains interacted with TLR2, upregulated the expression of A20 in PIE cells, and beneficially modulated the subsequent TLR4 activation by reducing the activation of MAPK and NF-κB pathways and the production of proinflammatory cytokines. We also show that the combination of TLR2 activation and A20 induction can be used as biomarkers to screen and select potential immunoregulatory bifidobacteria strains.     

Effect of Encapsulation on Viability of <Emphasis Type="Italic">Bifidobacterium longum</Emphasis> CFR815j and Physiochemical Properties of Ice Cream

The health beneficial attributes of bifidobacteria and its safe association with the host gut has increased its significance as a probiotic. However delivering probiotic bifidobacteria with Minimum Biological Value (MBV) through product has always been a challenge. In the present study, an attempt was made to maintain the viability of native isolate of Bifidobacterium longum CFR 815j and deliver through ice-cream. B. longum CFR815j was microencapsulated in alginate starch capsules by emulsification followed by evaluation of bead stability in simulated gastrointestinal conditions. After incorporation in ice-cream, the effect on chemical properties, sensory parameters and meltdown characteristics of the product were also evaluated. Survival studies of B. longum revealed higher counts than 10⁷ in the product which is essential for probiotic bacteria to exhibit beneficial effect. Further, all the properties of this ice-cream were comparable to the regular ice-cream. Our studies conclude that encapsulation was able to maintain the requisite MBV of bifidobacteria in ice-cream without affecting the sensory characteristics.     

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.     

Study of Adhesion and Survival of Lactobacilli and Bifidobacteria on Table Olives with the Aim of Formulating a New Probiotic Food

With the aim of developing new functional foods, a traditional product, the table olive, was used as a vehicle for incorporating probiotic bacterial species. Survival on table olives of Lactobacillus rhamnosus (three strains), Lactobacillus paracasei (two strains), Bifidobacterium bifidum (one strain), and Bifidobacterium longum (one strain) at room temperature was investigated. The results obtained using a selected olive sample demonstrated that bifidobacteria and one strain of L. rhamnosus (Lactobacillus GG) showed a good survival rate, with a recovery of about 10⁶ CFU g⁻¹ after 30 days. The Lactobacillus GG population remained unvaried until the end of the experiment, while a slight decline (to about 10⁵ CFU g⁻¹) was observed for bifidobacteria. High viability, with more than 10⁷ CFU g⁻¹, was observed throughout the 3-month experiment for L. paracasei IMPC2.1. This strain, selected for its potential probiotic characteristics and for its lengthy survival on olives, was used to validate table olives as a carrier for transporting bacterial cells into the human gastrointestinal tract. L. paracasei IMPC2.1 was recovered from fecal samples in four out of five volunteers fed 10 to 15 olives per day carrying about 10⁹ to 10¹⁰ viable cells for 10 days.     

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.     

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.     

Characterization of Bifidobacterium spp. strains for the treatment of enteric disorders in newborns

Several studies support the use of probiotics for the treatment of minor gastrointestinal problems in infants. Positive effects on newborn colics have been evidenced after administration of Lactobacillus strains, whereas no studies have been reported regarding the use of bifidobacteria for this purpose. This work was therefore aimed at the characterization of Bifidobacterium strains capable of inhibiting the growth of pathogens typical of the infant gastrointestinal tract and of coliforms isolated from colic newborns. Among the 46 Bifidobacterium strains considered, 16 showed high antimicrobial activity against potential pathogens; these strains were further characterized from a taxonomic point of view, for the presence and transferability of antibiotic resistances, for citotoxic effects and adhesion to nontumorigenic gut epithelium cell lines. Moreover, their ability to stimulate gut health by increasing the metabolic activity and the immune response of epithelial cells was also studied. The examination of all these features allowed to identify three Bifidobacterium breve strains and a Bifidobacterium longum subsp. longum strain as potential probiotics for the treatments of enteric disorders in newborns such as infantile colics. A validation clinical trial involving the selected strains is being planned.     

Oral administration of Bifidobacterium longum prevents gut-derived Pseudomonas aeruginosa sepsis in mice

Aims: The aim of the study was to evaluate the efficacy of probiotics on gut‐derived sepsis caused by Pseudomonas aeruginosa in immunocompromised mice. Methods and Results: After oral inoculation of P. aeruginosa, mice were treated with cyclophosphamide to induce leucopenia and translocation of the intestinal P. aeruginosa into blood, thereby producing gut‐derived sepsis. In this model, administration of 1 × 10⁹ CFU of Bifidobacterium longum strain BB536 for 10 days significantly (P < 0·01) increased the survival rate compared with groups of mice administered either with Bifidobacterium breve strain ATCC 15700 or excipients contained in the probiotic bacterial powder. Administration of B. longum significantly decreased viable counts of P. aeruginosa in the liver and blood compared with other groups. Culture of intestinal contents revealed a significantly lower viable count of P. aeruginosa in the jejunum of B. longum‐treated mice compared with other groups of mice. Furthermore, in vitro data demonstrated that B. longum possessed apparently higher adherent activity to Caco‐2 cell monolayers and significantly suppressed the adherence of P. aeruginosa to the monolayers of cells compared with other groups. Conclusion: Oral administration of B. longum protects mice against gut‐derived sepsis caused by P. aeruginosa, and the effect may be due to interference of P. aeruginosa adherence to intestinal epithelial cells. Significance and Impact of this Study: This study demonstrated that oral administration of B. longum BB536 is effective to protect against opportunistic infection with drug‐resistant bacteria such as P. aeruginosa. The results suggest that probiotics may play an important role even in the immunocompromised patients.     

Interactions between Bifidobacterium and Bacteroides Species in Cofermentations Are Affected by Carbon Sources,Including Exopolysaccharides Produced by Bifidobacteria

Cocultures of strains from two Bifidobacterium and two Bacteroides species were performed with exopolysaccharides (EPS) previously purified from bifidobacteria, with inulin, or with glucose as the carbon source. Bifidobacterium longum NB667 and Bifidobacterium breve IPLA20004 grew in glucose but showed poor or no growth in complex carbohydrates (inulin, EPS E44, and EPS R1), whereas Bacteroides grew well in the four carbon sources tested. In the presence of glucose, the growth of Bacteroides thetaiotaomicron DSM-2079 was inhibited by B. breve, whereas it remained unaffected in the presence of B. longum. Ba. fragilis DSM-2151 contributed to a greater survival of B. longum, promoting changes in the synthesis of short-chain fatty acids (SCFA) and organic acids in coculture with respect to monocultures. In complex carbohydrates, cocultures of bifidobacterium strains with Ba. thetaiotaomicron did not modify the behavior of Bacteroides nor improve the poor growth of bifidobacteria. The metabolic activity of Ba. fragilis in coculture with bifidobacteria was not affected by EPS, but greater survival of bifidobacteria at late stages of incubation occurred in cocultures than in monocultures, leading to a higher production of acetic acid than in monocultures. Therefore, cocultures of Bifidobacterium and Bacteroides can behave differently against fermentable carbohydrates as a function of the specific characteristics of the strains from each species. These results stress the importance of considering specific species and strain interactions and not simply higher taxonomic divisions in the relationship among intestinal microbial populations and their different responses to probiotics and prebiotics.     

Effect of bifidobacteria on nitrites and nitrosamines

The effects of six different bifidobacteria strains were studied on two procarcinogens: nitrite and nitrosamines. Growth of bifidobacteria was not affected by nitrite concentrations below 50 μmol 1^-1. At nitrite concentrations greater than 2000 μmol 1^-1, total growth inhibition was observed. Nitrite elimination by a non-enzymic mechanism was noted for six strains of bifidobacteria. Acids produced by the bacteria seem to be involved in nitrite elimination. Nitrosamines tested had no effect on growth of bifidobacteria. Only one strain ( Bifidobacterium longum BB 536) was able to metabolize nitrosamines by an intracellular mechanism.