Influence of 2'-fucosyllactose and galacto-oligosaccharides on the growth and adhesion of Streptococcus mutans.

Human milk oligosaccharides, such as 2'-fucosyllactose (2'-FL), and galacto-oligosaccharides (GOS), a prebiotic carbohydrate mixture, are being increasingly added to infant formulas, necessitating the understanding of their impact on the oral microbiota. Here, for the first time, the effects of 2'-FL and GOS on the planktonic growth and adhesion characteristics of the caries-associated oral pathogen Streptococcus mutans were assessed, and the results were compared against the effects of xylitol, lactose and glucose. There were differences in S. mutans growth between 2'-FL and GOS. None of the three S. mutans strains grew with 2'-FL, while they all grew with GOS as well as lactose and glucose. Xylitol inhibited S. mutans growth. The adhesion of S. mutans CI 2366 to saliva-coated hydroxyapatite was reduced by 2'-FL and GOS. Exopolysaccharide-mediated adhesion of S. mutans DSM 20523 to a glass surface was decreased with 2'-FL, GOS and lactose, and the adhesion of strain CI 2366 strain was reduced only by GOS. Unlike GOS, 2'-FL did not support the growth of any S. mutans strain. Neither 2'-FL nor GOS enhanced the adhesive properties of the S. mutans strains, but they inhibited some of the tested strains. Thus, the cariogenic tendency may vary between infant formulas containing different types of oligosaccharides.

The effect of a probiotic blend on gastrointestinal symptoms in constipated patients: a double blind, randomised, placebo controlled 2-week trial.

Selected strains of lactobacilli and bifidobacteria are known to ameliorate constipation-related symptoms and have previously shown efficacy on digestive health. In this clinical trial, the safety and effectiveness of a probiotic blend containing lactobacilli and bifidobacteria were evaluated in adults with self-reported bloating and functional constipation. Constipation was diagnosed by the Rome III criteria. A total of 156 adults were randomised into this double-blind and placebo-controlled trial. Participants consumed the combination of Lactobacillus acidophilus NCFM (1010 cfu), Lactobacillus paracasei Lpc-37 (2.5×109 cfu), Bifidobacterium animalis subsp. lactis strains Bl-04 (2.5×109 cfu), Bi-07 (2.5×109 cfu) and HN019 (1010 cfu) (n=78), or placebo (microcrystalline cellulose) (n=78) for two weeks. After treatment the following were measured: primary outcome of bloating and secondary outcomes of colonic transit time, bowel movement frequency, stool consistency, other gastrointestinal symptoms (flatulence, abdominal pain, and burbling), constipation-related questionnaires (PAC-SYM and PAC-QoL) and product satisfaction. Faecal recovery of consumed strains was determined. The enrolled population was defined as constipated, however, the initial bloating severity was lower than in previous similar studies. No clinically significant observations related to the safety of the product were reported. Product efficacy was not shown in the primary analysis for bloating nor for the secondary efficacy analyses. The placebo functioned similarly as the probiotic product. In post-hoc analysis, a statistically significant decrease in flatulence in favour of the probiotic group was observed; day 7 (intention-to-treat (ITT): P=0.0313; per-protocol (PP): 0.0253) and on day 14 (ITT: P=0.0116; PP: P=0.0102) as measured by area under the curve (AUC) analysis. The mean AUC of all symptoms decreased in favour of the probiotic group, indicating less digestive discomfort. The study was registered at the ISRCTN registry (ISRCTN41607808).

Simulating colonic survival of probiotics in single-strain products compared to multi-strain products.

Background: Probiotic formulations can be single- or multi-strain. Commercially, multi-strain preparations have been suggested to have improved functionality over single-strain cultures. Probiotics are often tested as single-strain preparations but may subsequently be commercially formulated as multi-strain products. Objective: The aim of this study was to determine what happens at the site of action, the intestine, with probiotics as single- compared to multi-strain preparations. The human gastrointestinal tract contains a broad mixture of different microbes which may affect the survival of different probiotics in different ways. Design: The current study was performed to evaluate, in an in vitro colon simulation, whether probiotics influence each other's survival when they are taken as a combination of several strains (HOWARU Restore; Lactobacillus acidophilus NCFM, Lactobacillus paracasei Lpc-37, Bifidobacterium lactis Bl-04 and B. lactis Bi-07) compared to the strains as single preparations. Results: All strains could be detected after the colon simulations and there were no substantial differences in levels of the same strain when comparing single- and multi-strain products. Conclusions: It can be concluded that probiotics do not have an antagonistic effect on each other's survival when used in a multi-strain product compared to a single-strain product, at least within a microbiota in a simulated colonic environment.

Effect of probiotic supplementation on total lactobacilli, bifidobacteria and short chain fatty acids in 2-5-year-old children.

​Background: Consumption of Lactobacillus paracasei Lpc-37 or Bifidobacterium lactis HN019 by 2-5-year-old children was found to reduce risk for diarrhoea and fever during the rainy season. Objective: Can changes in faecal short chain fatty acids (SCFAs) or branched chain fatty acids (BCFAs) explain the observed positive influence of probiotics and their role on nutritional status and diarrhoea risk? Design: Faecal samples were analysed for SCFAs and BCFAs and correlated to Bifidobacterium and Lactobacillus levels; both at the start and after nine months' consumption of either of the two probiotic strains, or placebo. Results: No differences in SCFAs, BCFAs, Lactobacillus or Bifidobacterium levels were found between boys and girls. Severely underweight children were observed to have the highest Lactobacillus levels. Probiotic intervention was found to be associated with higher levels of selected SCFAs and BCFAs in subjects who had experienced diarrhoea. Treatment with either of the probiotics led to changes in SCFAs and BCFAs. SCFAs, acetate, propionate and butyrate, were found to correlate with each other. Likewise, BCFAs isobutyrate, 2-methylbutyrate and isovalerate correlated with each other. After the intervention, L. paracasei Lpc-37 correlated positively with total Bifidobacterium counts and isovalerate levels. B. lactis HN019 counts were found to correlate positively with total bacterial counts and negatively with propionate levels. Conclusions: ​Nutritional status was associated with higher levels of faecal lactobacilli; the meaning of this requires further investigation. The intervention with the two probiotics was observed to influence the levels of faecal SCFAs and BCFAs and there is a differential response in those who developed diarrhoea and those who did not. It is, however, not clear to what extent this is a mechanism that explains the earlier observed effect the strains had on diarrhoea risk.

A review of dose-responses of probiotics in human studies.

The probiotic definition requires the administration of an 'adequate amount' in order to obtain a health benefit. What that amount should be is not indicated. Here, an overview is given of studies that investigated the dose-response relation of probiotics in human interventions. Studies were divided in; meta-analyses, meta-analyses on specific probiotic strains, and studies testing two or more doses of a probiotic (combination) in the same study. Meta-analyses on the effect of probiotics on antibiotic associated diarrhoea (AAD) suggest a dose-response effect; for Clostridium difficile-associated diarrhoea on the other hand no dose-response was observed. For other end-points; such as necrotising enterocolitis, prevention of atopic dermatitis and slow intestinal transit, no dose-response relation was identified in meta-analyses. For prophylaxis in colorectal cancer and relief of irritable bowel syndrome, no dose-response relation was determined. However, for blood pressure, a meta-analysis observed that higher doses (greater than 1011 cfu) were more effective than lower doses. Meta-analyses of specific strains suggest a break-point for effectiveness of Lactobacillus rhamnosus GG in the treatment of acute gastroenteritis in children; no dose-response was observed for two other probiotics assessed. Studies comparing two or more doses indicate that faecal recovery and risk reduction of AAD follow a positive dose-response relationship. Other end-points such as immune markers, general health, and bowel function did not exhibit clear dose-response relations. For AAD, the findings are very compelling; both meta-analyses and dedicated dose-response studies observe a positive correlation between dose and AAD risk. These findings do not allow for extrapolation, but suggest that studying higher doses for this end-point would be worthwhile. The lack of a clear dose-response for other end-points, does not mean it does not exist; present data does just not allow drawing any conclusions.

Influence of sucrose and xylitol on an early Streptococcus mutans biofilm in a dental simulator.

OBJECTIVES: In vitro methods to study dental biofilms are useful in finding ways to support a healthy microbial balance in the oral cavity. The effects of sucrose, xylitol, and their combination on three strains of Streptococcus mutans and one strain of Streptococcus sobrinus were studied using a dental simulator. METHODS: A simulator was used to mimic the oral cavity environment. It provided a continuous-flow system using artificial saliva (AS), constant temperature, mixing, and hydroxyapatite (HA) surface in which the influence of xylitol was studied. The quantities of planktonic and adhered bacteria were measured by real-time qPCR. RESULTS: Compared against the untreated AS, adding 1% sucrose increased the bacterial colonization of HA (p<0.0001) whereas 2% xylitol decreased it (p<0.05), with the exception of clinical S. mutans isolate 117. The combination of xylitol and sucrose decreased the bacterial quantities within the AS and the colonization on the HA by clinical S. mutans isolate 2366 was reduced (p<0.05). Increasing the concentration (2%-5%) of xylitol caused a reduction in bacterial counts even in the presence of sucrose. CONCLUSIONS: The continuous-culture biofilm model showed that within a young biofilm, sucrose significantly promotes whereas xylitol reduces bacterial colonization and proliferation. The results indicate that xylitol affects the ability of certain S. mutans strains to adhere to the HA. Clinical studies have also shown that xylitol consumption decreases caries incidence and reduces the amount of plaque. This study contributes to the understanding of the mechanism behind these clinical observations.

Modulation of the host response by probiotic Lactobacillus brevis CD2 in experimental gingivitis.

OBJECTIVE: Probiotic Lactobacillus brevisCD2 (CD2) exerts anti-inflammatory properties by preventing nitric oxide synthesis. It is hypothesized that oral application of CD2 can inhibit naturally occurring gingival inflammation. MATERIALS AND METHODS: Thirty-four healthy adults were randomized to receive L. brevisCD2 lozenges or placebo, three times daily for 14 days. The subjects refrained from oral hygiene, the extent of which was determined at various time points. RESULTS: In both groups, bleeding on probing scores increased continuously throughout the study except on day 3. In the placebo group, scores increased significantly from 9.50 at baseline to 14.75 and 14.81 on days 10 and 14, respectively (P < 0.05). No significant change from baseline was observed in the CD2 group. However, scores were consistently higher with placebo, and significant intergroup differences were observed on day 10. Plaque and gingival indices increased from baseline in both treatment groups, but no intergroup differences were observed. Measurements of immune markers in gingival crevicular fluid revealed increased production of nitric oxide in the placebo group (P < 0.05). Prostaglandin E2 production decreased over time in both groups. CONCLUSION: Lactobacillus brevisCD2 may delay gingivitis development in this model by downregulating an inflammatory cascade.

The fermentation of polydextrose in the large intestine and its beneficial effects.

Polydextrose is a randomly bonded glucose polymer with a highly branched and complex structure. It resists digestion in the upper gastrointestinal tract and is partially fermented in the large intestine by the colonic microbes. Due to its complex structure, a plethora of microbes is required for the catabolism of polydextrose and this process occurs slowly. This gradual fermentation of polydextrose gives rise to moderate amounts of fermentation products, such as short chain fatty acids and gas. The production of these metabolites continues in the distal part of the colon, which is usually considered to be depleted of saccharolytic fermentation substrates. The fermentation of polydextrose modifies the composition of the microbiota in the colon, and has been shown to impact appetite and satiety in humans and improve the gastrointestinal function. The purpose of this short review is to summarise the in vitro, in vivo and human studies investigating the fermentation properties of polydextrose in the large intestine.

Lactobacillus acidophilus supplementation in human subjects and their resistance to enterotoxigenic Escherichia coli infection.

To assess the effect of Lactobacillus acidophilus (American Type Culture Collection (ATCC) 700396) on enterotoxigenic Escherichia coli (ETEC) infection, in the present study, a parallel, double-blind, placebo-controlled 4-week intervention was performed in healthy males. The subjects largely consumed their habitual diet, but had to abstain from consuming dairy foods generally high in Ca. The subjects were randomised into the L. acidophilus (dose 109 colony-forming units twice daily; n 20) or the placebo (n 19) group. After an adaptation period of 2 weeks, the subjects were orally infected with a live, but attenuated, ETEC vaccine, able to induce mild, short-lived symptoms. Before and after the challenge, the subjects recorded stool consistency, bowel habits, and frequency and severity of gastrointestinal complaints. The ETEC challenge led to a significant increase in faecal output on the 2nd day and a concomitant increase in Bristol stool scale scores. Likewise, abdominal pain, bloating, flatulence, fever, headache and nausea peaked 1 d after the oral challenge. The concentrations of faecal calprotectin and IgA peaked 2 d after and that of serum IgM peaked 9 and 15 d after the oral challenge. The concentrations of serum IgA and IgG were unaffected. The ETEC challenge led to a reduction in the number of Bacteroides-Prevotella, Bifidobacterium, Clostridium cluster XIVab and total faecal bacteria. Probiotic treatment was associated with a larger increase in Bristol stool scale scores and more fever, headache and nausea after the ETEC challenge compared with the placebo treatment. These differences were, however, small and with substantial variation within the groups. Oral application of an attenuated live ETEC vaccine provides a useful model for food-borne infections. Supplementation with L. acidophilus ATCC 700396, however, was ineffective in reducing ETEC infection symptoms in healthy men.

Lactobacillus species causing obesity in humans: where is the evidence?

By definition, probiotics are to provide health benefits and are expected not to cause any adverse effects in the general population. Recently, it has been suggested that probiotics and in particular lactobacilli are contributing to human obesity. Here, we critically review the data available on this topic. The main misconception in this hypothesis is that growth in livestock and children equals with obesity in adults. The former two are expected to grow and probiotics may, by reducing disease risk, contribute to an improved growth. It is not correct to extrapolate this growth (of all tissues) to body weight gain (growth of adipose tissue) in adults. Furthermore, when looking at animal models of obesity, it even appears the lactobacilli may potentially contribute to a reduction in body weight. Epidemiological studies lend strength to this. We therefore conclude that there is no evidence that consumption of lactobacilli or probiotics in general would contribute to obesity in humans.

The effect of probiotics on faecal microbiota and genotoxic activity of faecal water in patients with atopic dermatitis: a randomized, placebo-controlled study.

BACKGROUND: Colonic microbiota is involved in the etiology of colon cancer according to several reports. Studies also indicate that the microbiota differs between atopic patients and healthy subjects. OBJECTIVE: To evaluate whether a probiotic mix containing Lactobacillus paracasei Lpc-37, Lactobacillus acidophilus 74-2, and Bifidobacterium animalis subsp. lactis DGCC 420 can affect the microbiota and its genotoxic activity in healthy subjects and patients with atopic dermatitis (AD). METHODS: A placebo-controlled cross-over study was conducted. Fifteen healthy adults and 15 adult AD patients consumed 2×100 ml/d of either a probiotic or a placebo drink for 8 weeks followed by a wash out period of 2 weeks before crossing the intervention. Faecal water was isolated from stool samples collected at the end of each period. HT29c19a cells incubated with faecal water were measured for DNA damage using single-cell gel electrophoresis ("comet assay"). Bacterial species were determined by qPCR and concentrations of short-chain fatty acids were measured by means of gas chromatography. RESULTS: Probiotic supplementation resulted in a significant increase in lactobacilli, whereas numbers of Bifidobacteria and Bacteroidetes remained unchanged. Clostridium perfringens cluster I-II was significantly reduced in healthy subjects. Genotoxic potential (expressed as tail intensity) of faecal water, was not affected. However, tail intensity decreased significantly in the probiotic period compared to placebo (23.5 vs. 16.7%) in AD patients. Although faecal concentrations of short-chain fatty acids were not affected, faecal pH was significantly reduced (7.0 vs. 6.6) in AD patients after probiotics. CONCLUSION: The results indicate that probiotics lower the genotoxic potential of faecal water in AD patients. The faecal C. perfringens cluster I-II levels remained unaffected suggesting either a change in their activity, or the fact that other bacterial species are responsible for the reduced genotoxic activity of faecal water.

The effect of feeding essential oils on broiler performance and gut microbiota.

1. In this study the effect of a blend of essential oils (EO) comprising 15 g/tonne thymol and 5 g/tonne cinnamaldehyde on the performance and intestinal microbiota of broilers was investigated. 2. A total of 720 male Ross broilers were divided into two dietary treatments with 12 replicate pens per treatment. Broilers were given a control soybean-wheat-based diet with or without added EO in two diet phases (0-21 d and 22-42 d). 3. The blend of EO increased body weight gain of broilers from 0 to 42 d by 45%. 4. Caecal microbiota were affected by the EO blend; in particular increases in the proportions of Lactobacillus and Escherichia coli at 41 d was observed. 5. The EO blend had major effects on caecal metabolites. The proportion of caecal butyrate at 20 and 41 d of age increased, whereas the proportion of caecal acetic acid at 20 d, and propionic acid and isovaleric acid at 41 d, decreased with the EO blend. In addition, the caecal proportion of spermine increased and tyramine decreased at 41 d of age with the EO treatment. 6. The present study shows that EO supplementation exerts a positive effect on intestinal microbiota with a concomitant enhancement in growth performance. The study suggests that modulation of broiler gut microbiota composition and activity through the administration of EO offers an effective means for improving broiler performance.

Xylo-oligosaccharides enhance the growth of bifidobacteria and Bifidobacterium lactis in a simulated colon model.

A semi-continuous, anaerobic colon simulator, with four vessels mimicking the conditions of the human large intestine, was used to study the fermentation of xylo-oligosaccharides (XOS). Three XOS compounds and a xylan preparation were fermented for 48 hours by human colonic microbes. Fructo-oligosaccharides (FOS) were used as a prebiotic reference. As a result of the fermentation, the numbers of Bifidobacterium increased in all XOS and xylan simulations when compared to the growth observed in the baseline simulations, and increased levels of Bifidobacterium lactis were measured with the two XOS compounds that had larger distribution of the degree of polymerisation. Fermentation of XOS and xylan increased the microbial production of short chain fatty acids in the simulator vessels; especially the amounts of butyrate and acetate were increased. XOS was more efficient than FOS in increasing the numbers of B. lactis in the colonic model, whereas FOS increased the Bifidobacterium longum numbers more. The selective fermentation of XOS by B. lactis has been demonstrated in pure culture studies, and these results further indicate that the combination of B. lactis and XOS would form a successful, selective synbiotic combination.

Analysis of the human intestinal epithelial cell transcriptional response to Lactobacillus acidophilus, Lactobacillus salivarius, Bifidobacterium lactis and Escherichia coli.

The complex microbial population residing in the human gastrointestinal tract consists of commensal, potential pathogenic and beneficial species, which are probably perceived differently by the host and consequently could be expected to trigger specific transcriptional responses. Here, we provide a comparative analysis of the global in vitro transcriptional response of human intestinal epithelial cells to Lactobacillus acidophilus NCFM™, Lactobacillus salivarius Ls-33, Bifidobacterium animalis subsp. lactis 420, and enterohaemorrhagic Escherichia coli O157:H7 (EHEC). Interestingly, L. salivarius Ls-33 DCE-induced changes were overall more similar to those of B. lactis 420 than to L. acidophilus NCFM™, which is consistent with previously observed in vivo immunomodulation properties. In the gene ontology and pathway analyses both specific and unspecific changes were observed. Common to all was the regulation of apoptosis and adipogenesis, and lipid-metabolism related regulation by the probiotics. Specific changes such as regulation of cell-cell adhesion by B. lactis 420, superoxide metabolism by L. salivarius Ls-33, and regulation of MAPK pathway by L. acidophilus NCFM™ were noted. Furthermore, fundamental differences were observed between the pathogenic and probiotic treatments in the Toll-like receptor pathway, especially for adapter molecules with a lowered level of transcriptional activation of MyD88, TRIF, IRAK1 and TRAF6 by probiotics compared to EHEC. The results in this study provide insights into the relationship between probiotics and human intestinal epithelial cells, notably with regard to strain-specific responses, and highlight the differences between transcriptional responses to pathogenic and probiotic bacteria.

Intestinal microbiota and overweight.

The microbes in our gut can influence our weight by providing us with energy through the degradation of nondigestable carbohydrates and by affecting the cellular energy status of liver and muscle cells and the accumulation of lipids in adipose tissue. Thus, it is not surprising that in several studies the gastrointestinal microbiota of overweight and obese subjects has been found to differ from that of lean subjects. The initial findings linked obesity with proportionally decreased levels of the phylum Bacteroidetes and increased levels of the phylum Firmicutes. Later, several studies have assessed the association between overweight or obesity and the gastrointestinal microbiota, applying an array of molecular methods targeting the microbiota as a whole or specific bacterial groups or species within. However, at present it is difficult to draw conclusions on which of the observed microbiota alterations are relevant; essentially all of the bacterial groups that have been studied in more than one trial have given contradictory results in regard to their association with weight. Some of these discrepancies can result from methodological issues and some from the nature of the gastrointestinal microbiota, which is an extremely complex and dynamic microbial ecosystem with high subject specificity. In addition, selecting subjects purely based on weight may result in a largely heterogeneous group with several potentially confounding factors. While it may be premature to conclude which specific groups of bacteria are prominent in the intestinal tract of overweight and obese subjects, it appears clear that microbes contribute to weight gain and related health issues, such as the metabolic syndrome and type II diabetes. Therefore, it is important to continue to search for common microbial markers and predictors of obesity, and to study how these may be modulated with probiotics and prebiotics to promote health.

Xylo-oligosaccharides and lactitol promote the growth of Bifidobacterium lactis and Lactobacillus species in pure cultures.

The current screening study aimed at identifying promising prebiotic and synbiotic candidates. The fermentation of xylo-oligosaccharides, xylan, galacto-oligosaccharide, fructo-oligosaccharide, polydextrose, lactitol, gentiobiose and pullulan was investigated in vitro. The ability of these established and potential prebiotic candidates to function as a sole carbon source for probiotic (Bifidobacterium and Lactobacillus), intestinal and potential pathogenic microbes (Eubacterium, Bacteroides, Clostridium, Escherichia coli, Salmonella, and Staphylococcus) was assessed in pure cultures. Xylo-oligosaccharides were fermented with high specificity by the tested Bifidobacterium lactis strains and lactitol by lactobacilli, whereas galacto-oligosaccharides, fructo-oligosaccharides and gentiobiose were utilised by a larger group of microbes. Xylan, polydextrose and pullulan were utilised to a limited extent by only a few of the tested microbes. The results of this screening study indicate that xylo-oligosaccharides and lactitol support the growth of a limited number of beneficial microbes in pure cultures. Such a high degree of specificity has not been previously reported for established prebiotics. Based on these results, the most promising prebiotics and synbiotic combinations can be selected for further testing.

Panose, a new prebiotic candidate.

AIMS: To investigate the prebiotic potential of two novel candidates, sophorose and panose, with in vitro methods. METHODS AND RESULTS: The growth of single microbial strains was first assessed for both substrates in pure cultures, and panose was further analysed in the simulated colon model with mixed human faecal culture. Quantitative PCR and flow cytometry were used to determine the microbial group and strain densities after the simulated colonic fermentation of panose, and chromatographic methods were utilized to analyse metabolite concentrations. In pure cultures, sophorose and panose were both fermented only by few beneficial strains, and in the colon simulator, panose gave a significant increase in the numbers of Bifidobacterium and Bifidobacterium lactis, concomitantly decreasing Bacteroides group. Butyrate and acetate production was significantly increased together with decreased markers of protein fermentation as a result of panose fermentation. CONCLUSIONS: Panose had bifidogenic activities in vitro, and these potential beneficial effects should be further assessed in vitro and in vivo. SIGNIFICANCE AND IMPACT OF THE STUDY: The current study has provided the first data on pure panose fermentation by the endogenous microbiota and extends our knowledge of the selective fermentation of oligosaccharides by the intestinal microbes.

Probiotic potential of enterococci isolated from canine feed.

Enterococci isolated from 28 different commercially available feeds (10-1000 CFU/mL) were identified and their probiotic potential was determined. Species identification of 22 selected strains was performed by intergenic length-polymorphism analysis (tRNA-PCR); PCR products were analyzed using capillary electrophoresis. Six strains were allotted to the species Enterococcus faecium, four to E. faecalis, one to E. hirae; the remaining strains were not classed. The strains were sensitive to vancomycin, ampicillin, tetracycline and rifampicin. They were able to adhere to human as well as canine intestinal mucus. They produced lactic acid (0.99-1.04 mmol/L) and most of them were urease-positive with sufficient survival in 5 % Oxgall-bile. They did not show any inhibitory activity due to antimicrobial substances. Plasmid DNA was detected in 8 strains, the bands responding to small molecular size (10 kbp). Considering all probiotically important properties, E. faecium strain EE3 was suggested as potential feed additive.

Degradation of 16S rRNA and attributes of viability of viable but nonculturable probiotic bacteria.

AIMS: To assess the stability of 16S rRNA of viable but nonculturable (VBNC) probiotics during storage when compared with different attributes of viability. METHODS AND RESULTS: Levels of RNA of the probiotic strains Bifidobacterium longum 46, B. longum 2C and B. animalis subsp. lactis Bb-12 were monitored during storage in fermented and nonfermented foods. Cells which gradually lost their culturability in fermented products retained high level of rRNA, whereas rRNA of acid-killed control cells decreased at faster rate. Furthermore, the viability of B. longum 2C was monitored during storage by measuring changes in reductase activity, cytoplasmic membrane integrity and esterase activity using a flow cytometer. All of the culture-independent viability assays suggested that the cells remained viable during storage. In nonfermented media, the observed losses in culturability were smaller, and the changes in cell counts were comparable with the changes in rRNA levels. CONCLUSIONS: Viable but nonculturable probiotics maintain high levels of rRNA and retain properties of viable bacteria including reductase activity. Quantification of 16S rRNA complements culture-independent viability assays. SIGNIFICANCE AND IMPACT OF THE STUDY: Culture-independent viability assays allow the detection of VBNC probiotics, and can be used parallel to conventional culture-dependent methods to obtain accurate information on probiotic viability.

The effects of polydextrose and xylitol on microbial community and activity in a 4-stage colon simulator.

This study focused on the effects of candidate prebiotics polydextrose (PDX) and xylitol on the microbial community and its metabolic activity in a colon simulator. A semicontinuous, anaerobic culture system was used with 4 vessels mimicking the conditions in the human large intestine from proximal to distal colon. Bacterial inocula for the independent simulations were obtained from fecal samples of different donors. Synthetic medium, mimicking the contents of the small intestine, containing either 2% of the prebiotic candidate or no added carbohydrates as a control, was fed to the system. After 48 h of simulation samples were collected and analyzed. A sustained degradation of polydextrose throughout the colon model and a more rapid degradation of xylitol were observed. The fermentation of both compounds was characterized by a significantly increased production of short-chain fatty acids (SCFA). Polydextrose increased the concentrations of all SCFA, especially acetate and propionate, and xylitol especially the concentration of butyrate. Branched-chain fatty acids (BCFA) levels decreased significantly as a result of polydextrose and xylitol supplementation, whereas biogenic amine levels remained mostly unchanged. Thus, a beneficial shift in the metabolic patterns of the colon microbes was measured with both of the tested products. These in vitro studies provide evidence to the prebiotic characteristics of polydextrose; also, further beneficial properties of xylitol were demonstrated in the colon model.