In VitroStudy of Bile Salt Hydrolase (BSH) Activity of BSH IsogenicLactobacillus plantarum80 Strains and Estimation of Cholesterol Lowering through Enhanced BSH Activity

Live encapsulated Lactobacillus acidophilus cells in yogurt for therapeutic oral delivery: preparation and in vitro analysis of alginate–chitosan microcapsulesThis article is one of a selection of papers published in this special issue (part 1 of 2) on the Safety and Efficacy of Natural Health Products

Targeted delivery of live microencapsulated bacterial cells has strong potential for application in treating various diseases, including diarrhea, kidney failure, liver failure, and high cholesterol, among others. This study investigates the potential of microcapsules composed of two natural polymers, alginate and chitosan (AC), and the use of these artificial cells in yogurt for delivery of probiotic Lactobacillus acidophilus bacterial live cells. Results show that the integrity of AC microcapsules was preserved after 76 h of mechanical shaking in MRS broth and after 12 h and 24 h in simulated gastric and intestinal fluids. Using an in vitro computer-controlled simulated human gastrointestinal (GI) model, we found 8.37 log CFU/mL of viable bacterial cells were present after 120 min of gastric exposure and 7.96 log CFU/mL after 360 min of intestinal exposure. In addition, AC microcapsules composed of chitosan 10 and 100 at various concentrations were subjected to 4-week storage in 2% milk fat yogurt or 0.85% physiological solution. It was found that 9.37 log CFU/mL of cells encapsulated with chitosan 10 and 8.24 log CFU/mL of cells encapsulated with chitosan 100 were alive after 4 weeks. The AC capsule composed of 0.5% chitosan 10 provided the highest bacterial survival of 9.11 log CFU/mL after 4 weeks. Finally, an investigation of bacterial viability over 72 h in different pH buffers yielded highest survival of 6.34 log CFU/mL and 10.34 log CFU/mL at pH 8 for free and AC-encapsulated cells, respectively. We conclude from these findings that encapsulation allows delivery of a higher number of bacteria to desired targets in the GI tract and that microcapsules containing bacterial cells are good candidates for oral artificial cells for bacterial cell therapy.

In Vitro Assessment of the Gastrointestinal Transit Tolerance of Taxonomic Reference Strains from Human Origin and Probiotic Product Isolates of Bifidobacterium

Next to health promoting effects, the functional aspect of probiotic strains also involves their capacity to reach the colon as viable metabolically active cells. The present study aimed to assess the potential of 24 probiotic product isolates and 42 human reference strains of Bifidobacterium to survive gastrointestinal transit under in vitro conditions. The survival capacity of exponential and stationary phase cultures upon exposure to gastric and small intestinal juices was determined using a recently developed microplate-based assay in combination with the LIVE/DEAD BacLight Bacterial Viability kit. All 66 strains tested displayed a considerable loss in viability during exposure to an acidic pepsin containing solution (pH 2.0). Among the 10 taxa tested, cultures of B. animalis ssp. lactis appeared to be most capable to survive gastric transit. Although to a lesser extent, the presence of bile salts also affected the viability of most of the strains tested. Except for 3 strains, all 66 strains showed bile salt hydrolase activity using an agar-based assay. In contrast, the bifidobacterial strains used in this study appeared to possess a natural ability to survive the presence of pancreatin (pH 8.0). Although the effect was not significant, a slightly enhanced tolerance to gastrointestinal transit was observed when cells were in the stationary phase, especially when exposed to acid, compared with cells being in the exponential phase. Survival in the gastrointestinal tract appeared to be largely strain-dependent and hence implies that different strains will likely display a different behavior in functionality. The assay used in this study allows an initial assessment of strains for use as probiotic cultures prior to selecting potential candidate strains for further investigation in vivo.

Characterization of Lactobacillus plantarum PH04, a potential probiotic bacterium with cholesterol-lowering effects

The bacterium Lactobacillus plantarum PH04 was isolated from infant feces and tested positive for bile/acid tolerance and bile salt hydrolase activity. It was evaluated as a potential probiotic with cholesterol-lowering effect. Bile salt hydrolase activity was nine times greater in stationary phase than in exponential phase cells and increased when the cells were exposed to conjugated bile salts. L. plantarum PH04 was resistant to seven of nine antibiotics tested and did not produce beta-glucuronidase. L. plantarum PH04 was fed to hypercholesterolemic mice at numbers of 10(7) CFU per mouse per day for 14 days. Compared with a control group, the serum cholesterol and triglycerides were respectively 7 and 10% lower in the group fed L. plantarum PH04, and fecal lactic acid bacteria increased while no any significant differences (P<0.05) in body weight, visceral weigh index or bacteria translocation between two groups were observed. The results indicated that L. plantarum PH04 might be effective as a probiotic with cholesterol-lowering activities.

Preparation and characterization of novel polymeric microcapsules for live cell encapsulation and therapy

This article describes the preparation and in vitro characterization of novel genipin cross-linked alginate-chitosan (GCAC) microcapsules that have potential for live cell therapy applications. This microcapsule system, consisting of an alginate core with a covalently cross-linked chitosan membrane, was formed via ionotropic gelation between calcium ions and alginate, followed by chitosan coating by polyelectrolyte complexation and covalent cross-linking of chitosan by naturally derived genipin. Results showed that, using this design concept and the three-step procedure, spherical GCAC microcapsules with improved membrane strength, suppressed capsular swelling, and suitable permeability can be prepared. The suitability of this novel membrane formulation for live cell encapsulation was evaluated, using bacterial Lactobacillus plantarum 80 (pCBH1) (LP80) and mammalian HepG2 as model cells. Results showed that capsular integrity and bacterial cell viability were sustained 6 mo postencapsulation, suggesting the feasibility of using this microcapsule formulation for live bacterial cell encapsulation. The metabolic activity of the encapsulated HepG2 was also investigated. Results suggested the potential capacity of this GCAC microcapsule in cell therapy and the control of cell signaling; however, further research is required.

Genes involved in obesity: Adipocytes, brain and microflora

The incidence of obesity and related metabolic disorders such as cardiovascular diseases and type 2 diabetes, are reaching worldwide epidemic proportions. It results from an imbalance between caloric intake and energy expenditure leading to excess energy storage, mostly due to genetic and environmental factors such as diet, food components and/or way of life. It is known since long that this balance is maintained to equilibrium by multiple mechanisms allowing the brain to sense the nutritional status of the body and adapt behavioral and metabolic responses to changes in fuel availability. In this review, we summarize selected aspects of the regulation of energy homeostasis, prevalently highlighting the complex relationships existing between the white adipose tissue, the central nervous system, the endogenous microbiota, and nutrition. We first describe how both the formation and functionality of adipose cells are strongly modulated by the diet before summarizing where and how the central nervous system integrates peripheral signals from the adipose tissue and/or the gastro-intestinal tract. Finally, after a short description of the intestinal commensal flora, rangingfrom its composition to its importance in immune surveillance, we enlarge the discussion on how nutrition modified this perfectly well-balanced ecosystem.

Influence of Daily Consumption of Probiotic and Conventional Yoghurt on the Plasma Lipid Profile in Young Healthy Women

BACKGROUND

A number of studies have found conflicting results concerning the modulation of plasma lipids induced by probiotics. Therefore, the aim of this study was to verify and compare the effects of probiotic and conventional yoghurt on the plasma lipid profile of normocholesterolemic women.

METHODS

In this study, female volunteers consumed 100 g/day of probiotic (n = 17) or conventional yoghurt (n = 16) for 2 weeks (T1-T2) and 200 g/day for further 2 weeks (T2-T3). A washout phase lasting 2 weeks followed (T4). Total and HDL cholesterol and triglycerides were determined by enzymatic methods; LDL cholesterol was calculated using the Friedewald formula.

RESULTS

The average concentration of total cholesterol was consistent throughout the whole study in the control group, but decreased significantly (p < 0.01) in the probiotic group consuming 200 g yoghurt/day (T2-T3). During the period of daily yoghurt intake (T1-T3) the mean HDL cholesterol level increased significantly (p < 0.05) in the probiotic group, resulting in a significant (p < 0.05) improvement of the total/HDL cholesterol ratio. The significant (p < 0.01) reduction of the average plasma LDL cholesterol values found in this period (T1-T3) in the probiotic and the control groups was associated with a significant (p < 0.05) improvement of the LDL/HDL cholesterol ratios in both tested groups.

CONCLUSION

Although several lipid parameters changed during the study in both the probiotic and the control group, no significant differences between the groups were observed. Therefore, it can be concluded that the regular consumption of both probiotic and conventional yoghurt for 4 weeks had a positive effect on the lipid profile in plasma of healthy women.

Effect of bile acid on the cell membrane functionality of lactic acid bacteria for oral administration

Lactic acid bacteria and other species dwelling in the gut must be tolerant to bile salts. This study sought to determine the effects of the bile salts taurodeoxycholate (TDCA) and deoxycholate (DCA) on Lactobacillus reuteri CRL 1098, a strain of likely probiotic value. When compared to other lactobacilli, L. reuteri showed the highest survival rate but remained sensitive to high (>3 mM) DCA concentrations. DCA produced complete permeabilization of cells, abolished glucose uptake and severely distorted the cell envelope, as shown by electron microscopy. Detailed analytical studies revealed a change in the phospholipid to glycolipid ratio, and also in lipid proportions. The C18:1 W9C form remarkably increased, possibly following a rapid adaptive response during DCA treatment. This study provides the first solid evidence of the mechanism of DCA toxicity in a lactic acid bacterium.

The interaction between bacteria and bile

Commensal and pathogenic microorganisms must resist the deleterious actions of bile in order to survive in the human gastrointestinal tract. Herein we review the current knowledge on the mechanisms by which Gram-positive and Gram-negative bacteria contend with bile stress. We describe the antimicrobial actions of bile, assess the variations in bile tolerance between bacterial genera and examine the interplay between bile stress and other stresses. The molecular mechanisms underlying bile tolerance are investigated and the relationship between bile and virulence is examined. Finally, the potential benefits of bile research are briefly discussed.

Genetic analysis of two bile salt hydrolase activities in Lactobacillus acidophilus NCFM

Two genes, bshA and bshB, encoding bile salt hydrolase enzymes (EC 3.5.1.24) were identified in the genome sequence of Lactobacillus acidophilus NCFM. Targeted inactivation of these genes via chromosomal insertion of an integration vector demonstrated different substrate specificities for these two enzymes.

Yeast mediates lactic acidosis suppression after antibiotic cocktail treatment in short small bowel?

During acidotic periods in a girl with a short small bowel, very high D-lactic acid concentrations were measured in blood and urine; the patient's characteristic faecal flora contained mainly lactobacilli, and during antibiotic cocktail treatment also many yeasts. In this case report we sought to understand the beneficial effect of the antibiotic cocktail. Microbiological analysis was performed in faecal samples. Total lactic acid in serum and urine was studied using capillary gas chromatography-mass spectrometry, and D- and L-lactic acid in serum and urine by enzymatic assay. The results were coupled to patient's condition. Antibiotic cocktail therapy reduced the acidosis-associated symptoms, faecal lactobacilli and D-lactic acid production, but simultaneously the antibiotic therapy strongly increased the percentage of yeast in the faecal flora. Four to six weeks after each course of treatment the percentage of yeast decreased, whereas the percentage of intestinal lactobacilli increased; D-lactic acid also simultaneously increased in blood and urine. The patient felt well and showed a high percentage of intestinal yeast, but she often suffered from acidosis owing to a high percentage of lactobacilli. The yeast was identified as the pathogenic Candida glabrata. From the mentioned data together with data from the literature it was concluded that during several weeks the selected pathogenic yeast, C. glabrata, acted as a microbiological and metabolic buffer. Shortly after the course of antibiotic treatment this intestinal yeast strongly competed with the intestinal lactobacilli and thus prevented renewed rapid growth, massive D-lactic acid production from glucose and consequently also D-lactic acid-associated acidosis. The emergence of this yeast led us to consider probiotic lactobacilli or yeast for therapeutic use. The lack of knowledge regarding bile acid-deconjugating activity in both lactobacilli and probiotic yeast means that a final recommendation is not yet possible.

Xylooligosaccharides and fructooligosaccharides affect the intestinal microbiota and precancerous colonic lesion development in rats

Certain nondigestible oligosaccharides can be selectively utilized by probiotics and reduce the risk of colon cancer. However, the inhibitory effects of xylooligosaccharides (XOS) on colon cancer are not well documented. This study evaluated the effects of xylooligosaccharides and fructooligosaccharides (FOS) on the alteration of cecal microbiota, cecal pH, cecal weight, and serum lipid levels, and also their inhibitory effect on precancerous colon lesions in male Sprague-Dawley rats. The rats were randomly assigned to 4 groups: control, treatment with 1,2-dimethylhydrazine (DMH) [15 mg/(kg body wt.wk) for 2 wk], treatment with DMH + 60 g XOS/kg diet, and treatment with DMH + 60 g FOS/kg diet. Rats were fed the experimental diets for 35 d, beginning 1 wk after the second dose of DMH. Both XOS and FOS markedly decreased the cecal pH and serum triglyceride concentration, and increased the total cecal weight and bifidobacteria population. XOS had a greater effect on the bacterial population than did FOS. Moreover, both XOS and FOS markedly reduced the number of aberrant crypt foci in the colon of DMH-treated rats. These results suggest that XOS and FOS dietary supplementation may be beneficial to gastrointestinal health, and indicate that XOS is more effective than FOS.

Purification and characterization of three different types of bile salt hydrolases from Bifidobacterium strains

Bile salt hydrolases were purified to electrophoretic homogeneity from Bifidobacterium bifidum ATCC 11863, Bifidobacterium infantis KL412, Bifidobacterium longum ATCC 15708, Bifidobacterium longum KL507, and Bifidobacterium longum KL515. Three different types (A, B, and C) of bile salt hydrolase (BSH) were revealed during the purification study, exhibiting the type-specific characteristics in their electrophoretic migration and elution profiles from anion exchange and hydrophobic interaction chromatographic columns. The subunit molecular mass estimated by sodium dodecylsulfate (SDS)-polyacrylamide gel electrophoresis (PAGE) was around 35 kDa, and the native molecular mass in all five Bifidobacterium strains was estimated to be between 130 and 150 kDa by gel filtration chromatography, indicating that all BSH enzymes have tetrameric structure. From the isoelectric focusing, an isoelectric point value of 4.45 was obtained with BSH (type B) from B. bifidum ATCC 11863 and the other BSH (types A and C) showed the similar pI values around 4.65. N-Terminal amino acid sequencing for the proteins of types A and C revealed that 6 out of 20 amino acid residues were different, and highly conserved residues were identified in both N-terminal sequences of types A and C. All BSH enzymes from five strains hydrolyzed six major human bile salts, and they showed a better deconjugation rate on glycine-conjugated bile salts than on taurine-conjugated forms.

An in vitro study of the probiotic potential of a bile-salt-hydrolyzing Lactobacillus fermentum strain, and determination of its cholesterol-lowering properties

This study evaluated the use of a bile-salt-hydrolyzing Lactobacillus fermentum strain as a probiotic with potential hypocholesterolemic properties. The effect of L. fermentum on representative microbial populations and overall metabolic activity of the human intestinal microbiota was investigated using a three-stage continuous culture system. Also, the use of galactooligosaccharides as a prebiotic to enhance growth and/or activity of the Lactobacillus strain was evaluated. Administration of L. fermentum resulted in a decrease in the overall bifidobacterial population (ca. 1 log unit). In the in vitro system, no significant changes were observed in the total bacterial, Lactobacillus, Bacteroides, and clostridial populations through L. fermentum supplementation. Acetate production decreased by 9 to 27%, while the propionate and butyrate concentrations increased considerably (50 to 90% and 52 to 157%, respectively). A general, although lesser, increase in the production of lactate was observed with the administration of the L. fermentum strain. Supplementation of the prebiotic to the culture medium did not cause statistically significant changes in either the numbers or the activity of the microbiota, although an increase in the butyrate production was seen (29 to 39%). Results from this in vitro study suggest that L. fermentum KC5b is a candidate probiotic which may affect cholesterol metabolism. The short-chain fatty acid concentrations, specifically the molar proportion of propionate and/or bile salt deconjugation, are probably the major mechanism involved in the purported cholesterol-lowering properties of this strain.

Genes encoding bile salt hydrolases and conjugated bile salt transporters in Lactobacillus johnsonii 100-100 and other Lactobacillus species

Lactobacillus johnsonii strain 100-100 expresses two antigenically distinct conjugated bile salt hydrolases (BSH), alpha and beta, that combine to form native homo- and heterotrimers. This paper reports characterization of loci within the genome that encode this capacity. A locus that encodes BSH beta (cbsH beta), a partial (cbsT1) and a complete conjugated bile salt transporter (cbsT2) was identified previously. DNA sequence analysis at this locus was extended and revealed a complete ORF for cbsT1 and no other ORFs in tandem. The three genes, cbsT1, cbsT2 and cbsH beta, probably constitute an operon; a putative promoter was identified upstream of cbsT1. A second locus that expresses BSH activity in strain 100-100 was identified. Sequence analysis of the clone predicted a 978 nt ORF that did not share tandem organization with other ORFs, was similar in sequence to other BSH genes, and matched, in predicted protein sequence, the first 25 amino acids of BSH alpha. A phenotypic screen for BSH activity and a genetic screen for the cbsH beta locus were performed on 50 Lactobacillus isolates from humans or dairy products. Nearly all of the isolates that were positive for cbsH beta were from human sources. Variability in the BSH phenotype and cbsH beta genotype was identified in isolates of the same species. DNA sequence was obtained and analysed from the cbsH beta locus of one human isolate, L. acidophilus strain KS-13. This organism has cbsT1, cbsT2 and cbs beta genes that are 84, 87 and 85% identical in DNA sequence to those of strain 100-100. DNA sequence identity to strain 100-100 ends in regions flanking this locus. The findings of this study suggest that BSH genes have been acquired horizontally and that BSH activity is important at some level for lactobacilli to colonize the lower gastrointestinal tract.

Considerations for use of probiotic bacteria to modulate human health

Oral consumption of probiotic bacteria has the potential to support the health of American consumers. This paper will discuss the rationale of the probiotic theory, several health targets for probiotic bacteria, probiotic products in the U.S. and, finally, issues pertaining to communication about probiotic products to the consumer.

Screening of lactic acid bacteria for bile salt hydrolase activity

Bile salt hydrolysis is an important metabolic reaction in the bile salt metabolism of mammals. This reaction has a facilitating effect for bile salt excretion but can also be involved in various illnesses. In recent years interest has increased to use bile salt hydrolysis to influence the cholesterol metabolism of humans and farm animals. To understand the distribution and range of bile salt hydrolase activity in lactic acid bacteria, we screened more than 300 strains of the genera Bifidobacterium and Lactobacillus and the species Lactococcus lactis, Leuconostoc mesenteroides, and Streptococcus thermophilus. Results obtained for 273 strains showed that bile salt hydrolase activity is common in Bifidobacterium and Lactobacillus but absent in L. lactis, Leu. mesenteroides, and S. thermophilus. Nearly all bifidobacteria species and strains have bile salt hydrolase activity, whereas this activity can only be found in selected species of lactobacilli. A strong correlation can be observed between the habitat of a genus or species and the presence of bile salt hydrolase activity. Most often bile salt hydrolase activity is found in strains that have been isolated from the intestines or from feces from mammals--an environment rich in conjugated and unconjugated bile acids. Strains and species from other habitats like milk or vegetables--environments from which bile salts are absent--do normally not have bile salt hydrolase activity. In two independent assays, we established that bile salt hydrolase activity in bifidobacteria is, in general, much higher than in lactobacilli.

Bile salt hydrolase activity of three strains of Lactobacillus acidophilus

Three strains of Lactobacillus acidophilus, two from human intestinal origin (016 and L1) and one from porcine intestinal origin (ATCC 43121), were tested for their bile salt deconjugation activity. The L. acidophilus ATCC 43121 had more deconjugating activity of both sodium glycocholate and sodium taurocholate at pH 6.5 than did either L. acidophilus 016 or L1. The activity of intracellular bile salt hydrolase found in strain ATCC 43121 was 14-fold higher than that in either of the other two strains. The optimum pH for deconjugation of sodium glycocholate was between 4 and 5.5 for all three strains. For deconjugation of sodium taurocholate, the optimum pH was between 3.5 and 4.5 for strains L1 and ATCC 43121 and was between pH 5 and 6 for strain O16. The molecular mass of the enzyme in all three strains of L. acidophilus was estimated to be 126 kDa by Sephadex G-200 gel filtration. All three strains exhibited more bile salt hydrolase activity towards sodium glycocholate than towards sodium taurocholate.

Measurement of bile salt hydrolase activity from Lactobacillus acidophilus based on disappearance of conjugated bile salts

Bile salt hydrolase activity of Lactobacillus acidophilus was measured based on the disappearance of sodium glycocholate and sodium taurocholate from the reaction mixture using HPLC. The amount of sodium glycocholate and sodium taurocholate that disappeared was proportional to the amount of sodium cholate that appeared in the mixture as detected by HPLC. Sodium glycocholate did not precipitate at the enzyme reaction conditions (37 degrees C and pH 5.4) for determining bile salt hydrolase activity. The bile salt hydrolase assay was insensitive to low oxidation-reduction potential when measuring bile salt hydrolase from L. acidophilus, an intestinal microorganism. However, EDTA and freezing temperatures were necessary to maintain stability of the partially purified enzyme during storage.

Effect of fermented milk (yogurt) containing Lactobacillus acidophilus L1 on serum cholesterol in hypercholesterolemic humans

OBJECTIVE

Two controlled clinical studies were performed to examine effects of consumption of one daily serving of fermented milk (FM) (yogurt) on serum lipids.

METHODS

In the first study, subjects were randomly allocated to FM containing Lactobacillus acidophilus L1 of human origin or to FM containing L. acidophilus ATCC 43211 of swine origin. In this single-blind study, subjects consumed one 200 ml serving of FM daily for 3 weeks. The second study was a double-blind, placebo-controlled, cross-over study. Subjects completed a 4-week first treatment, had a 2-week washout, and completed a second 4-week treatment. In the second study subjects consumed FM containing L. acidophilus L1 or placebo FM over 4 weeks.

RESULTS

In the first study, FM containing L. acidophilus L1 was accompanied by a 2.4% (p<0.05) reduction of serum cholesterol concentration. In the second study, strain L1 reduced serum cholesterol concentration by 3.2% (p<0.05) in the first treatment period. In the second treatment period there were no significant changes in serum cholesterol concentration. Combined analysis of the two L1 treatment studies demonstrated a 2.9% (p<0.01) reduction in serum cholesterol concentration.

CONCLUSION

Since every 1% reduction in serum cholesterol concentration is associated with an estimated 2% to 3% reduction in risk for coronary heart disease, regular intake of FM containing an appropriate strain of L. acidophilus has the potential of reducing risk for coronary heart disease by 6 to 10%.

Characterisation and selection of probiotic lactobacilli for a preliminary minipig feeding trial and their effect on serum cholesterol levels, faeces pH and faeces moisture content

Three out of 297 Lactobacillus strains isolated from pig faeces were selected for a feeding trial on account of their high bile-salt hydrolase (BSH) activity, bile-salt resistance, low pH tolerance and the production of antimicrobial substances. Two strains were identified as Lactobacillus johnsonii and one as Lactobacillus reuteri by DNA-DNA hybridisation. L. johnsoniii BFE 1061 produced a bacteriocin active against a range of lactic acid bacteria (LAB) and nonrelated bacteria including Clostridium perfringens. Six minipigs were maintained on a high-fat, high-cholesterol ('Western Style') diet for 17 weeks after which the diet was supplemented with the 'probiotic mixture' containing the above mentioned three Lactobacillus strains at 2 x 10(12) CFU per pig per day for five weeks. The mixture was given as a resuspended lyophilisate. During a two week follow-up period the minipigs received only the 'Western-style' diet without probiotic supplementation. A lowering effect on serum cholesterol levels was indicated after three weeks probiotic feeding, concomitant with an increase in the moisture content of the faeces and Lactobacillus cell numbers. Triglycerides, pH and number of lactic acid bacteria in faeces were not significantly influenced by probiotic supplementation.

Cholesterol lowering in pigs through enhanced bacterial bile salt hydrolase activity

The effect of feeding live Lactobacillus reuteri cells containing active bile salt hydrolase (BSH) on plasma cholesterol levels was studied in pigs. During an experiment lasting 13 weeks, twenty pigs were fed on a high-fat, high-cholesterol, low-fibre for the first 10 weeks, and a regular pig diet for the last 3 weeks. One group of animals received, twice daily, 11.25 (SD 0.16) log10 colony forming units of the potential probiotic bacteria for 4 weeks (from week 3 until week 7). From week 8 onwards, the treated group was again fed on the same diet as the control group without additions. The total faecal Lactobacillus counts were only significantly higher in the treated pigs during the first 2 weeks of L reuteri feeding. Based on limited data, it was suggested that the administered Lactobacillus species had caused a temporary shift within the indigenous Lactobacillus population rather than permanently colonizing the intestinal tract. The probiotic feeding brought about significant lowering (P < or = 0.05) of total and LDL-cholesterol concentrations in the treated pigs compared with the control pigs, while no change in HDL-cholesterol concentration was observed. The data for faecal output of neutral sterols and bile salts were highly variable between the animals of each group, yet they indicated an increased output in the treated pigs. Although the blood cholesterol levels went up in both groups during the 3 weeks following the Lactobacillus administration period, significantly lower serum total and LDL-cholesterol levels were observed in the treated pigs. During the final 3 weeks of normalization to the regular diet, cholesterol concentrations significantly decreased in both animal groups and the differences in total and LDL-cholesterol concentrations between the groups largely disappeared.

Significance of bile salt hydrolytic activities of lactobacilli

Bile salt hydrolase (BSH) activity was shown to be constitutive and substrate-specific: the BSH isogenic Lactobacillus plantarum wild type (LP80 WT) and BSH overproducing LP80 (pCBH1) strains preferentially hydrolysed glycodeoxycholic acid (GDCA), whereas the hamster Lact. animalis isolates H362 and H364 showed a higher affinity for taurodeoxycholic acid (TDCA). In viability studies in the presence of nutrients, it was demonstrated that GDCA exerted a higher toxicity than TDCA in a pH-dependent manner. This toxicity was inversely proportionate to the BSH activity level of the strains tested, indicating that BSH activity contributed towards bile salt resistance when appropriate nutrients were available. The high toxicity of GDCA relative to TDCA was suggested to be caused by their weak and strong acid properties respectively. It was therefore hypothesized that the protonated form of bile salts exhibited toxicity as it imported protons in the cell. This puts an energy-burden on BSH- lactobacilli which undergo intracellular acidification. BSH+ cells primarily protect themselves through the formation of the weaker DCA compound, which can help negate the pH-drop by recapturing and exporting the co-transported proton. However, since DCA is more toxic than its conjugated counterparts, an additional energy-dependent detoxification of DCA is suggested.