Fluid Intake in Critically Ill Patients: The "Save Useless Fluids For Intensive Resuscitation" Multicenter Prospective Cohort Study.

OBJECTIVES: Patients at risk of adverse effects related to positive fluid balance could benefit from fluid intake optimization. Less attention is paid to nonresuscitation fluids. We aim to evaluate the heterogeneity of fluid intake at the initial phase of resuscitation. DESIGN: Prospective multicenter cohort study. SETTING: Thirty ICUs across France and one in Spain. PATIENTS: Patients requiring vasopressors and/or invasive mechanical ventilation. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: All fluids administered by vascular or enteral lines were recorded over 24 hours following admission and were classified in four main groups according to their predefined indication: fluids having a well-documented homeostasis goal (resuscitation fluids, rehydration, blood products, and nutrition), drug carriers, maintenance fluids, and fluids for technical needs. Models of regression were constructed to determine fluid intake predicted by patient characteristics. Centers were classified according to tertiles of fluid intake. The cohort included 296 patients. The median total volume of fluids was 3546 mL (interquartile range, 2441-4955 mL), with fluids indisputably required for body fluid homeostasis representing 36% of this total. Saline, glucose-containing high chloride crystalloids, and balanced crystalloids represented 43%, 27%, and 16% of total volume, respectively. Whatever the class of fluids, center of inclusion was the strongest factor associated with volumes. Compared with the first tertile, the difference between the volume predicted by patient characteristics and the volume given was +1.2 ± 2.0 L in tertile 2 and +3.0 ± 2.8 L in tertile 3. CONCLUSIONS: Fluids indisputably required for body fluid homeostasis represent the minority of fluid intake during the 24 hours after ICU admission. Center effect is the strongest factor associated with the volume of fluids. Heterogeneity in practices suggests that optimal strategies for volume and goals of common fluids administration need to be developed.

Complementary Mechanisms for Degradation of Inulin-Type Fructans and Arabinoxylan Oligosaccharides among Bifidobacterial Strains Suggest Bacterial Cooperation.

Inulin-type fructans (ITF) and arabinoxylan oligosaccharides (AXOS) are broken down to different extents by various bifidobacterial strains present in the human colon. To date, phenotypic heterogeneity in the consumption of these complex oligosaccharides at the strain level remains poorly studied. To examine mechanistic variations in ITF and AXOS constituent preferences present in one individual, ITF and AXOS consumption by bifidobacterial strains isolated from the simulator of the human intestinal microbial ecosystem (SHIME) after inoculation with feces from one healthy individual was investigated. Among the 18 strains identified, four species-independent clusters displaying different ITF and AXOS degradation mechanisms and preferences were found. Bifidobacterium bifidum B46 showed limited growth on all substrates, whereas B. longum B24 and B. longum B18 could grow better on short-chain-length fractions of fructooligosaccharides (FOS) than on fructose. B. longum B24 could cleave arabinose substituents of AXOS extracellularly, without using the AXOS-derived xylose backbones, whereas B. longum B18 was able to consume oligosaccharides (up to xylotetraose) preferentially and consumed AXOS to a limited extent. B. adolescentis B72 degraded all fractions of FOS simultaneously, partially degraded inulin, and could use xylose backbones longer than xylotetraose extracellularly. The strain-specific degradation mechanisms were suggested to be complementary and indicated resource partitioning. Specialization in the degradation of complex carbohydrates by bifidobacteria present on the individual level could have in vivo implications for the successful implementation of ITF and AXOS, aiming at bifidogenic and/or butyrogenic effects. Finally, this work shows the importance of taking microbial strain-level differences into account in gut microbiota research.IMPORTANCE It is well known that bifidobacteria degrade undigestible complex polysaccharides, such as ITF and AXOS, in the human colon. However, this process has never been studied for strains coexisting in the same individual. To examine strain-dependent mechanistic variations in ITF and AXOS constituent preferences present in one individual, ITF and AXOS consumption by bifidobacterial strains isolated from the SHIME after inoculation with feces from one healthy individual was investigated. Among the 18 bifidobacterial strains identified, four species-independent clusters displaying different ITF and AXOS degradation mechanisms and preferences were found, indicating that such strains can coexist in the human colon. Such specialization in the degradation of complex carbohydrates by bifidobacteria present on the individual level could have in vivo implications for the successful implementation of ITF and AXOS, aiming at bifidogenic and/or butyrogenic effects.

Bifidobacteria and Butyrate-Producing Colon Bacteria: Importance and Strategies for Their Stimulation in the Human Gut.

With the increasing amount of evidence linking certain disorders of the human body to a disturbed gut microbiota, there is a growing interest for compounds that positively influence its composition and activity through diet. Besides the consumption of probiotics to stimulate favorable bacterial communities in the human gastrointestinal tract, prebiotics such as inulin-type fructans (ITF) and arabinoxylan-oligosaccharides (AXOS) can be consumed to increase the number of bifidobacteria in the colon. Several functions have been attributed to bifidobacteria, encompassing degradation of non-digestible carbohydrates, protection against pathogens, production of vitamin B, antioxidants, and conjugated linoleic acids, and stimulation of the immune system. During life, the numbers of bifidobacteria decrease from up to 90% of the total colon microbiota in vaginally delivered breast-fed infants to <5% in the colon of adults and they decrease even more in that of elderly as well as in patients with certain disorders such as antibiotic-associated diarrhea, inflammatory bowel disease, irritable bowel syndrome, obesity, allergies, and regressive autism. It has been suggested that the bifidogenic effects of ITF and AXOS are the result of strain-specific yet complementary carbohydrate degradation mechanisms within cooperating bifidobacterial consortia. Except for a bifidogenic effect, ITF and AXOS also have shown to cause a butyrogenic effect in the human colon, i.e., an enhancement of colon butyrate production. Butyrate is an essential metabolite in the human colon, as it is the preferred energy source for the colon epithelial cells, contributes to the maintenance of the gut barrier functions, and has immunomodulatory and anti-inflammatory properties. It has been shown that the butyrogenic effects of ITF and AXOS are the result of cross-feeding interactions between bifidobacteria and butyrate-producing colon bacteria, such as Faecalibacterium prausnitzii (clostridial cluster IV) and Anaerostipes, Eubacterium, and Roseburia species (clostridial cluster XIVa). These kinds of interactions possibly favor the co-existence of bifidobacterial strains with other bifidobacteria and with butyrate-producing colon bacteria in the human colon.

Inulin-type fructan fermentation by bifidobacteria depends on the strain rather than the species and region in the human intestine.

Inulin-type fructans (ITF) are known to cause a health-promoting bifidogenic effect, although the ITF degradation capacity of bifidobacteria in different intestinal regions remains unclear. The present study aims at offering new insights into this link, making use of a collection of 190 bifidobacterial strains, encompassing strains from gut biopsies (terminal ileum and proximal colon; mucosa-associated strains) and the simulator of the human intestinal microbial ecosystem (SHIME®; proximal and distal colon vessels; lumen-associated strains). A multivariate data analysis of all fermentation data revealed four clusters corresponding with different types of ITF degradation fingerprints, which were not correlated with the region in the intestine, suggesting that the degradation of ITF is uniform along the human intestine. Strains from cluster 1 consumed fructose, while strains from cluster 2 consumed more oligofructose than fructose. Higher fructose and oligofructose consumption was characteristic for clusters 3 and 4 strains, which degraded inulin too. In general, the mucosa-associated strains from biopsy origin seemed to be more specialized in the consumption of fructose and oligofructose, while the lumen-associated strains from SHIME origin displayed a higher degradation degree of inulin. Further, intra-species variability in ITF degradation was found, indicating strain-specific variations. The coexistence of different bifidobacterial strains with different ITF degradation fingerprints within the same intestinal region suggests cooperation for the degradation of ITF, with opportunities for cross-feeding on strain and/or species level.

Mutual Cross-Feeding Interactions between Bifidobacterium longum subsp. longum NCC2705 and Eubacterium rectale ATCC 33656 Explain the Bifidogenic and Butyrogenic Effects of Arabinoxylan Oligosaccharides.

Arabinoxylan oligosaccharides (AXOS) are a promising class of prebiotics that have the potential to stimulate the growth of bifidobacteria and the production of butyrate in the human colon, known as the bifidogenic and butyrogenic effects, respectively. Although these dual effects of AXOS are considered beneficial for human health, their underlying mechanisms are still far from being understood. Therefore, this study investigated the metabolic interactions between Bifidobacterium longum subsp. longum NCC2705 (B. longum NCC2705), an acetate producer and arabinose substituent degrader of AXOS, and Eubacterium rectale ATCC 33656, an acetate-converting butyrate producer. Both strains belong to prevalent species of the human colon microbiota. The strains were grown on AXOS during mono- and coculture fermentations, and their growth, AXOS consumption, metabolite production, and expression of key genes were monitored. The results showed that the growth of both strains and gene expression in both strains were affected by cocultivation and that these effects could be linked to changes in carbohydrate consumption and concomitant metabolite production. The consumption of the arabinose substituents of AXOS by B. longum NCC2705 with the concomitant production of acetate allowed E. rectale ATCC 33656 to produce butyrate (by means of a butyryl coenzyme A [CoA]:acetate CoA-transferase), explaining the butyrogenic effect of AXOS. Eubacterium rectale ATCC 33656 released xylose from the AXOS substrate, which favored the B. longum NCC2705 production of acetate, explaining the bifidogenic effect of AXOS. Hence, those interactions represent mutual cross-feeding mechanisms that favor the coexistence of bifidobacterial strains and butyrate producers in the same ecological niche. In conclusion, this study provides new insights into the bifidogenic and butyrogenic effects of AXOS.

Bioaccessible antioxidants in milk fermented by Bifidobacterium longum subsp. longum strains.

Bifidobacterium longum subsp. longum is among the dominant species of the human gastrointestinal microbiota and could thus have potential as probiotics. New targets such as antioxidant properties have interest for beneficial effects on health. The objective of this study was to evaluate the bioaccessibility of antioxidants in milk fermented by selected B. longum subsp. longum strains during in vitro dynamic digestion. The antioxidant capacity of cell extracts from 38 strains, of which 32 belong to B. longum subsp. longum, was evaluated with the ORAC (oxygen radical absorbance capacity) method. On the basis of screening and gene sequence typing by multilocus locus sequence analysis (MLSA), five strains were chosen for fermenting reconstituted skim milk. Antioxidant capacity varied among the strains tested (P = 0.0009). Two strains of B. longum subsp. longum (CUETM 172 and 171) showed significantly higher ORAC values than the other bifidobacteria strains. However, there does not appear to be a relationship between gene sequence types and antioxidant capacity. The milk fermented by each of the five strains selected (CUETM 268, 172, 245, 247, or PRO 16-10) did not have higher initial ORAC values compared to the nonfermented milk samples. However, higher bioaccessibility of antioxidants in fermented milk (175-358%) was observed during digestion.

The ability of bifidobacteria to degrade arabinoxylan oligosaccharide constituents and derived oligosaccharides is strain dependent.

Arabinoxylan oligosaccharides (AXOS) are prebiotic carbohydrates with promising health-promoting properties that stimulate the activity of specific colon bacteria, in particular bifidobacteria. However, the mechanisms by which bifidobacterial strains break down these compounds in the colon is still unknown. This study investigates AXOS consumption of a large number of bifidobacterial strains (36), belonging to 11 different species, systematically. To determine their degradation mechanisms, all strains were grown on a mixture of arabinose and xylose, xylo-oligosaccharides, and complex AXOS molecules as the sole added energy sources. Based on principal component and cluster analyses of their different arabinose substituent and/or xylose backbone consumption patterns, five clusters that were species independent could be distinguished among the bifidobacterial strains tested. In parallel, the strains were screened for the presence of genes encoding several putative AXOS-degrading enzymes, but no clear-cut correlation could be made with the different degradation mechanisms. The intra- and interspecies differences in the consumption patterns of AXOS indicate that bifidobacterial strains could avoid competition among each other or even could cooperate jointly to degrade these complex prebiotics. The knowledge gained on the AXOS degradation mechanisms in bifidobacteria can be of importance in the rational design of prebiotics with tailor-made composition and thus increased specificity in the colon.

Development of an ion-exchange chromatography method for monitoring the degradation of prebiotic arabinoxylan-oligosaccharides in a complex fermentation medium.

Arabinoxylan-oligosaccharides (AXOS) are a new class of prebiotics with promising health-promoting characteristics. However, the mechanism by which bacteria break down these compounds in the colon is still uncharacterized, due to their structural complexity. A new analytical method that offers structural information was developed to characterize AXOS degradation during fermentation. The method was based on the simultaneous determination of arabinose, xylose, xylo-oligosaccharides (XOS), and AXOS by applying high-performance anion-exchange chromatography with pulsed amperometric detection. To study the structural features of AXOS in solution without the use of spectroscopic techniques or standards, enzymatic-based reference degradation chromatograms were generated based on enzymes with known specificity. The new method for fingerprinting showed to be a powerful and fast tool to study AXOS degradation with high repeatability with respect to peak area, peak width at half height, and retention time (respective relative standard deviations of ≤3.1%, 2.8%, and 0.8%). This method was successfully applied to study the degradation kinetics of AXOS in a complex fermentation medium by Bifidobacterium longum LMG 11047. The results showed that this strain could use both the arabinose side chains and xylose backbones up to xylotetraose. The characterization of the degradation abilities of AXOS by colon bacteria will allow a better understanding of the beneficial effects of these prebiotics. Furthermore, if the appropriate enzymes are available to design the reference degradation chromatograms, this new method for the qualitative fingerprinting of AXOS breakdown can also be applied for the breakdown of other complex oligosaccharides and polysaccharides.

A putative transport protein is involved in citrulline excretion and re-uptake during arginine deiminase pathway activity by Lactobacillus sakei.

Arginine conversion through the arginine deiminase (ADI) pathway is a common metabolic trait of Lactobacillus sakei which is ascribed to an arc operon and which inquisitively involves citrulline excretion and re-uptake. The aim of this study was to verify whether a putative transport protein (encoded by the PTP gene) plays a role in citrulline-into-ornithine conversion by L. sakei strains. This was achieved through a combination of fermentation experiments, gene expression analysis via quantitative real-time reverse transcription PCR (RT-qPCR) and construction of a PTP knock-out mutant. Expression of the PTP gene was modulated by environmental pH and was highest in the end-exponential or mid-exponential growth phase for L. sakei strains CTC 494 and 23K, respectively. In contrast to known genes of the arc operon, the PTP gene showed low expression at pH 7.0, in agreement with the finding that citrulline-into-ornithine conversion is inhibited at this pH. The presence of additional energy sources also influenced ADI pathway activity, in particular by decreasing citrulline-into-ornithine conversion. Further insight into the functionality of the PTP gene was obtained with a knock-out mutant of L. sakei CTC 494 impaired in the PTP gene, which displayed inhibition in its ability to convert extracellular citrulline into ornithine. In conclusion, results indicated that the PTP gene may putatively encode a citrulline/ornithine antiporter.