Quantitative strain-specific detection of Lactobacillus rhamnosus GG in human faecal samples by real-time PCR.

AIMS: To develop a strain-specific rapid assay for identification and quantification of Lactobacillus rhamnosus GG in human faecal samples. METHODS AND RESULTS: A unique random amplified polymorphic DNA (RAPD) band of the L. rhamnosus GG strain was isolated and sequenced. Strain-specific polymerase chain reaction (PCR) primers and probes were designed based on the sequence. Quantification was performed by the real-time PCR using a fluorescent resonance energy transfer (FRET) system. The specificity of the assay was tested with DNA isolated from a set of known strains and human faecal samples. The analytical sensitivity of the method for L. rhamnosus GG was about 10 CFU per assay, which corresponds to 10(5) CFU g(-1) of wet faeces. CONCLUSIONS: Quantitative real-time PCR is a suitable method for strain-specific identification of L. rhamnosus GG in human faecal samples. SIGNIFICANCE AND IMPACT OF THE STUDY: Lactobacillus rhamnosus GG is one of the most studied probiotic strains in clinical trials but still lacks a DNA-based identification method. This study describes a real-time PCR method for strain-specific identification and quantification of L. rhamnosus GG in human faecal samples.

Effects of anti-Helicobacter pylori treatment and probiotic supplementation on intestinal microbiota.

The aims of this study were (i) to evaluate the effect of recommended antimicrobial treatment of Helicobacter pylori infection, consisting of clarithromycin, amoxicillin and lansoprazole, on intestinal microbiota and (ii) to determine the ability of a probiotic combination containing Lactobacillus rhamnosus GG, L. rhamnosus LC705, Propionibacterium freudenreichii ssp. shermanii JS and Bifidobacterium breve Bb99 to prevent treatment-induced alterations in the intestinal microbiota. Faecal samples were obtained from 39 H. pylori-infected patients randomised into two treatment groups. In addition, 19 H. pylori-negative volunteers were included in the study as a control group. Samples were collected before, during and after treatment and microbiota were analysed by fluorescence in situ hybridisation and culture. The quantities of the predominant bacterial groups were altered significantly in both groups and disturbances were seen even 9 weeks after treatment was complete. Probiotics slightly counteracted the effects of anti-H. pylori treatment, seen as significantly less alterations in the total numbers of aerobes and lactobacilli/enterococci. At baseline, the composition of the microbiota between H. pylori-positive versus H. pylori-negative control individuals differed with regard to clostridia and the total number of anaerobes. The recommended treatment for H. pylori infection induces long-term disturbances in the intestinal microbiota. The probiotic combination appeared to result in only minor changes in the microbiota.

Lactobacillus bacteremia, species identification, and antimicrobial susceptibility of 85 blood isolates.

BACKGROUND: Data regarding antimicrobial susceptibility of clinical Lactobacillus isolates are scarce, and appropriate interpretation criteria for susceptibility tests are not available. METHODS: We examined 85 cases of Lactobacillus bacteremia, of which 47 cases have been included in our previous studies. Overall, 14 antimicrobial agents were evaluated by the E-test method, and these results were compared with disk diffusion test findings. The clinical outcomes of the patients and their antimicrobial treatments were registered. RESULTS: The antimicrobial susceptibility of Lactobacillus strains was species dependent. The considerable number of Lactobacillus rhamnosus (n=46), Lactobacillus fermentum (n=12), and Lactobacillus casei (n=12) strains available for testing made it possible to compare the susceptibilities within 1 species, as well. Of the 46 L. rhamnosus isolates, 22 were identified as L. rhamnosus GG type by pulsed-field gel electrophoresis. All Lactobacillus isolates demonstrated low minimum inhibitory concentrations (MICs) of imipenem, piperacillin-tazobactam, erythromycin, and clindamycin. MICs of vancomycin were high (>256 microg/mL) for all other species except Lactobacillus gasseri and Lactobacillus jensenii. Disk diffusion and E-test results were concordant. The MICs of cephalosporins varied; cefuroxime demonstrated a higher level of activity than did ceftriaxone. Benzylpenicillin and ampicillin MICs had variable ranges between different species. Combination therapy was given to 83% of the patients, but, in 54% of them, therapy included only 1 microbiologically active agent, according to results of the susceptibility tests. Mortality at 1 week was 12% among patients who presumably were receiving adequate treatment and 27% among patients who were receiving inadequate treatment (P=.131, by E-test). CONCLUSION: Most clinical Lactobacillus blood isolates demonstrated low MICs of imipenem, piperacillin-tazobactam, erythromycin, and clindamycin, but they had variable susceptibility to penicillin and cephalosporins.

Probiotic supplementation improves tolerance to Helicobacter pylori eradication therapy--a placebo-controlled, double-blind randomized pilot study.

BACKGROUND: H. pylori is the major cause of chronic gastritis, and a risk factor for peptic ulcer and gastric cancer. AIM: To investigate the effect of probiotic supplementation on the tolerance and efficacy of H. pylori eradication treatment in a randomized, double-blind, placebo-controlled trial. METHODS: A total of 338 volunteers were screened for H. pylori infection. The eligibility criteria were met by 47 subjects whose H. pylori infection was verified at the outset and re-evaluated after the treatment by the 13C-urea breath test and by enzyme immunoassay serology. The subjects were randomized to receive probiotic therapy (Lactobacillus rhamnosus GG, L. rhamnosusLC705, Bifidobacterium breve Bb99 and Propionibacterium freudenreichii ssp. shermanii JS) or a placebo during H. pylori eradication and for 3 weeks following the treatment, and recorded their daily symptoms in a standardized diary. RESULTS: When the frequencies of new or aggravated symptoms were evaluated, no significant differences were found between the two groups for individual symptoms. However, the probiotic group showed less treatment-related symptoms as measured by the total symptom score change (P = 0.038) throughout the H. pylori eradication therapy in contrast to the placebo group. The H. pylori eradication rate was non-significantly higher in the group receiving probiotic therapy (91% vs. 79%, P = 0.42). In this group the recovery of probiotic bacteria in the faeces increased significantly (P < 0.001). CONCLUSIONS: In this pilot study, probiotic supplementation did not diminish significantly the frequency of new or aggravated symptoms during H. pylori eradication. However, our data suggest an improved tolerance to the eradication treatment when total symptom severity was taken into account. Furthermore, the results show that probiotic bacteria are able to survive in the gastrointestinal tract despite the intensive antimicrobial therapy.

Effect of live and inactivated Lactobacillus rhamnosus GG on experimentally induced rhinovirus colds: randomised, double blind, placebo-controlled pilot trial.

The aim of this work was to investigate the usability of an experimental rhinovirus model in probiotic trials aiming to assess effectiveness in viral infections, and to provide preliminary data of live and inactivated probiotic Lactobacillus rhamnosus GG for larger-scale trials utilising the model. 59 subjects were randomised to receive 100 ml of fruit juice supplemented with 10(9) cfu of live or heat-inactivated (by spray-drying) L. rhamnosus GG or control juice daily for six weeks. After three weeks subjects were intranasally inoculated with experimental rhinovirus. Infection rate (at least one positive culture for challenge virus on five days following inoculation or at least four-fold rise in antibody response to challenge virus) was 14/19 in the group receiving live probiotic strain and 18/20 both in the group receiving heat-inactivated probiotic strain and in the control group (P=0.36). The occurrence and severity of cold symptoms on the five days following the inoculation was lowest in the group receiving live probiotic strain (P=0.45). This trial was the first one dedicated to the investigation of the effect of probiotics using the experimental rhinovirus model. The model showed potential for demonstration of efficacy of probiotics in controlled respiratory viral infections. Occurrence and severity of cold symptoms and number of subjects with rhinovirus infection was lowest in the group receiving live L. rhamnosus GG, but differences were not statistically significant. Further large-scale studies are needed to demonstrate the efficacy of L. rhamnosus GG in respiratory infections.

Characterization of a cloned chromosomal fragment affecting the proteinase activity of Streptococcus lactis ssp. lactis.

Plasmid pVS8 (14.3 kbp) contains a 9.3 kbp fragment of Streptococcus lactis ssp. lactis SSL135 chromosomal DNA associated with the ability of this strain to grow in milk. In this study, it was found that pVS8 complements a defective plasmid-linked proteinase gene of SSL135. Using deletions and insertions, it was found that the size of the complementing region of pVS8 is approximately 6.0 kbp, and that its main part is located within a 5.7 kbp BglII fragment.

Vancomycin resistance factor of Lactobacillus rhamnosus GG in relation to enterococcal vancomycin resistance (van) genes.

Lactobacillus rhamnosus GG (ATCC 53103) is a probiotic strain used in fermented dairy products in many countries and is also used as a food supplement in the form of freeze-dried powder. The relationship of the vancomycin resistance factor in L. rhamnosus GG and the vancomycin resistance (van) genes of Enterococcus faecalis and E. faecium were studied using polymerase chain reaction (PCR), Southern hybridization and conjugation methods. Our results show that the vancomycin resistance determinant in L. rhamnosus GG is not closely related to enterococcal van genes, since no PCR product was amplified in L. rhamnosus GG with any of the three sets of vanA primers used, and enterococcal vanA, vanB, vnH, vanX, vanZ, vanY, vanS and vanR genes did not hybridize with DNA of L. rhamnosus GG. This strain does not contain plasmids and transfer of chromosomal vancomycin resistance determinant from L. rhamnosus GG to enterococcal species was not detected. Our results are in accordance with previous findings of intrinsically vancomycin-resistant lactic acid bacteria.

Improving the storage stability of Bifidobacterium breve in low pH fruit juice.

Bifidobacterial food applications are limited since bifidobacteria are sensitive to e.g. acidic conditions prevalent in many food matrices. The aim of the present study was to investigate whether a low pH selection step alone or combined to UV mutagenesis could improve the viability of an acid sensitive Bifidobacterium strain, B. breve 99, in low pH food matrices. Furthermore, the potential of carriers and an oat fibre preparation to further improve the stability was studied. The best performing low pH tolerant variants in the present study were generated by UV-mutagenesis with 70-700µJ/cm(2) followed by incubation in growth medium at pH 4.5. The most promising variants regarding the low pH tolerance showed, in repeated tests with cells grown without pH control, about one Log-value better survival in pH 3.8 fruit juice after one week storage at 4°C compared to wild-type B. breve 99. Cells grown with pH control, PDX formulated and then frozen showed poorer viability in low pH fruit juice than cells grown with no pH control. For frozen concentrates pH 3.8 was too stressful and no or small differences between the variants and the wild-type strain were seen. The differences detected at pH 3.8 with the cells grown without pH control were also seen with the frozen concentrates at pH 4.5. Some improvement in the stability could be achieved by using a combination of trehalose, vitamin C and PDX as a freezing carrier material, whereas a significant improvement in the stability was seen when oat fibre was added into the fruit juice together with the frozen cells. Due to the initial very poor fruit juice tolerance of B. breve 99 the obtained improvement in the stability was not enough for commercial applications. However, the same methods could be applied to initially better performing strains to further improve their stability in the fruit juice.

Expression of Bacillus subtilis phytase in Lactobacillus plantarum 755.

Phytase enzymes can increase the nutritional value of food and feed by liberating inorganic phosphate from phytate, the major storage form of phosphorus in plants. The phytase (phyC) from Bacillus subtilis VTT E-68013 was expressed in Lactobacillus plantarum strain 755 using Lact. amylovorus alpha-amylase secretion signals. In an overnight cultivation in MRS medium containing cellobiose for induction of the alpha-amylase promoter, catalytically active phytase was secreted as a predominant extracellular protein. However, Western blot analysis revealed unprocessed and processed phytase in the cell fraction. Pulse chase experiments showed that the recombinant phytase was secreted at a slower rate in comparison to the native proteins of Lact. plantarum 755.

Construction of Streptococcus lactis subsp. lactis Strains with a Single Plasmid Associated with Mucoid Phenotype.

Lactose-fermenting mucoid (Lac Muc) variants of plasmid-free Streptococcus lactis subsp. lactis MG1614 were obtained by protoplast transformation with total plasmid DNA from MucS. lactis subsp. cremoris ARH87. By using plasmid DNA from these variants for further transformations followed by novobiocininduced plasmid curing, Lac Muc MG1614 strains containing only a single 30-megadalton plasmid could be constructed. This plasmid, designated pVS5, appeared to be associated with the Muc phenotype.

Cloning of a Streptococcus lactis subsp. lactis Chromosomal Fragment Associated with the Ability To Grow in Milk.

A chromosomal fragment of 6.7 megadaltons (MDa), apparently containing the genes for milk protein utilization by Streptococcus lactis subsp. lactis SSL135, was cloned in S. lactis subsp. lactis MG1614, a proteinase-negative strain. For the cloning, the chromosomal DNA of SSL135 was cleaved with restriction enzyme BamHI and the resulting fragments were ligated to the single BclI site of pVS2, a 3.3-MDa chloramphenicol-erythromycin double-resistance plasmid constructed in this laboratory. S. lactis subsp. lactis MG1614 was transformed by using this ligation mixture and selecting for chloramphenicol resistance and growth in citrated milk medium. One clone containing a 10.0-MDa plasmid, subsequently designated as pVS6, was chosen for further studies. Despite the lack of homology with previously characterized proteinase genes of lactic streptococci, the cloned insert consistently conveyed the ability to grow in milk to proteinase-negative recipients in repeated transformation experiments. The genetic evidence suggests that the main part of the gene(s) for the proposed proteinase activity is located within a 3.8-MDa BglII fragment of the clone.

Highly bioluminescent Streptococcus thermophilus strain for the detection of diary-relevant antibiotics in milk.

Inefficient translational initiation is often the cause of poor foreign gene expression in gram-positive organisms. The expression of bacterial luciferase (lux) genes in Streptococcus thermophilus (bioluminescence) was improved by addressing this problem in two ways; by ribosome-binding site (RBS) replacement, and by enhancing lux RBS access by polymerase chain reaction modification either alone or combined with translational coupling to a truncated upstream open- reading frame (orf') having its own RBS. Lactococcal expression signals were employed for plasmid-based lux expression. The same constructs were used to monitor bioluminescence in Lactococcus lactis, as well as two non-lactic bacterial strains, for comparison. High lux expression was achieved in all four organisms with a heterodimeric thermostable enzyme. Surprisingly, where ready access to the lux RBS was predicted, translational coupling to the lactococcal orf remained a prerequisite for detectable lux expression in L. lactis. In contrast, high bioluminescence in S. thermophilus was independent of coupling. Consistent with these observations, inspection of published gene sequences suggests that RBS "strength" may be a more important factor in translation in S. thermophilus than in L. lactis. Using reduced light production in highly bioluminescent S. thermophilus as an indicator of biocide presence in milk, test times could be significantly shortened compared with a commercial test utilizing the related non-bioluminescent strain. lux genes appear to be sensitive, exponential-phase reporters of gene activity in S. thermophilus, an organism with molecular biology and genetics that remain largely unstudied.

Cloning and characterization of a prolinase gene (pepR) from Lactobacillus rhamnosus.

A peptidase gene expressing L-proline-beta-naphthylamide-hydrolyzing activity was cloned from a gene library of Lactobacillus rhamnosus 1/6 isolated from cheese. Peptidase-expressing activity was localized in a 1.5-kb SacI fragment. A sequence analysis of the SacI fragment revealed the presence of one complete open reading frame (ORF1) that was 903 nucleotides long. The ORF1-encoded 34.2-kDa protein exhibited 68% identity with the PepR protein from Lactobacillus helveticus. Additional sequencing revealed the presence of another open reading frame (ORF2) following pepR; this open reading frame was 459 bp long. Northern (RNA) and primer extension analyses indicated that pepR is expressed both as a monocistronic transcriptional unit and as a dicistronic transcriptional unit with ORF2. Gene replacement was used to construct a PepR-negative strain of L. rhamnosus. PepR was shown to be the primary enzyme capable of hydrolyzing Pro-Leu in L. rhamnosus. However, the PepR-negative mutant did not differ from the wild type in its ability to grow and produce acid in milk. The cloned pepR expressed activity against dipeptides with N-terminal proline residues. Also, Met-Ala, Leu-Leu, and Leu-Gly-Gly and the chromogenic substrates L-leucine-beta-naphthylamide and L-phenylalanine-beta-naphthylamide were hydrolyzed by the PepR of L. rhamnosus.

Isolation of a replication region of a large lactococcal plasmid and use in cloning of a nisin resistance determinant.

The replication region of a 28-kilobase-pair (kbp) cryptic plasmid from Lactococcus lactis subsp. lactis biovar diacetylactis SSD207 was cloned in L. lactis subsp. lactis MG1614 by using the chloramphenicol resistance gene from the streptococcal plasmid pGB301 as a selectable marker. The resulting 8.1-kbp plasmid, designated pVS34, was characterized further with respect to host range, potential cloning sites, and location of replication gene(s). In addition to lactococci, pVS34 transformed Lactobacillus plantarum and, at a very low frequency, Staphylococcus aureus but not Escherichia coli or Bacillus subtilis. The 4.1-kbp ClaI fragment representing lactococcal DNA in pVS34 contained unique restriction sites for HindIII, EcoRI, XhoII, and HpaII, of which the last three could be used for molecular cloning. A region necessary for replication was located within a 2.5-kbp fragment flanked by the EcoRI and ClaI restriction sites. A 3.8-kbp EcoRI fragment derived from a nisin resistance plasmid, pSF01, was cloned into the EcoRI site of pVS34 to obtain a nisin-chloramphenicol double-resistance plasmid, pVS39. From this plasmid, the streptococcal chloramphenicol resistance region was subsequently eliminated. The resulting plasmid, pVS40, contains only lactococcal DNA. Potential uses for this type of a nisin resistance plasmid are discussed.

Peptide Utilization Encoded by Lactococcus lactis subsp. lactis SSL135 Chromosomal DNA.

A cloned chromosomal fragment of Lactococcus lactis subsp. lactis SSL135 on plasmid p VS8 in an L. lactis subsp. lactis MG1614 background enabled proteinase-negative strain MG1614 to grow in autoclaved milk. The strain (VS230) did not, however, degrade milk proteins and did not grow in pasteurized milk. In contrast, a strain (VS150) carrying p VS9, the proteinase plasmid of SSL135, in an MG1614 background degraded beta-casein but did not grow in milk. VS230 was shown to utilize peptides produced by VS150 in growth experiments in pasteurized milk preincubated with the latter strain. The peptide utilization phenotype linked with p VS8 was further confirmed by growth of VS230 on tryptic peptide fractions, on which the plasmid-free but otherwise isogenic strain MG1614 failed to grow. Plasmid p VS8 produced 69-, 42-, 38-, and 36-kilodalton proteins, as determined by in vitro transcription-translation. At least three of these proteins affected the peptide utilization phenotype. We suggest that there could be a coupled peptidase-peptide transport system encoded by the chromosomal fragment.

Food-grade host/vector expression system for Lactobacillus casei based on complementation of plasmid-associated phospho-beta-galactosidase gene lacG.

A new food-grade host/vector system for Lactobacillus casei based on lactose selection was constructed. The wild-type non-starter host Lb. casei strain E utilizes lactose via a plasmid-encoded phosphotransferase system. For food-grade cloning, a stable lactose-deficient mutant was constructed by deleting a 141-bp fragment from the phospho-beta-galactosidase gene lacG via gene replacement. The deletion resulted in an inactive phospho-beta-galactosidase enzyme with an internal in-frame deletion of 47 amino acids. A complementation plasmid was constructed containing a replicon from Lactococcus lactis, the lacG gene from Lb. casei, and the constitutive promoter of pepR for lacG expression from Lb. rhamnosus. The expression of the lacG gene from the resulting food-grade plasmid pLEB600 restored the ability of the lactose-negative mutant strain to grow on lactose to the wild-type level. The vector pLEB600 was used for expression of the proline iminopeptidase gene pepI from Lb. helveticus in Lb. casei. The results show that the food-grade expression system reported in this paper can be used for expression of foreign genes in Lb. casei.

Genetic and biochemical characterization of the oligopeptide transport system of Lactococcus lactis.

The nucleotide sequence of a chromosomal DNA fragment of Lactococcus lactis subsp. lactis SSL135, previously implicated in peptide utilization, has been determined. The genes oppDFBCA, encoding the oligopeptide transport system (Opp), and that encoding the endopeptidase PepO were located on this 8.9-kb DNA fragment. The oppDFBCA and pepO genes are probably organized in an operon. Analysis of the deduced amino acid sequences of the genes indicated that the oligopeptide transport system consists of two ATP-binding proteins OppD and OppF, two integral membrane proteins OppB and OppC, and a substrate-binding protein OppA. On the basis of the homology of OppF and OppD of L. lactis with other ABC (ATP-binding cassette) transporter proteins, the L. lactis Opp system can be classified as a member of this group. Two integration mutants, one defective in OppA and the other defective in PepO, were constructed. Growth of these mutants in a chemically defined medium with oligopeptides showed that the transport system, but not the endopeptidase, is essential for the utilization of peptides longer than three residues. Uptake of the pentapeptide Leu-enkephalin in glycolyzing lactococcal cells was followed by rapid hydrolysis of the peptide intracellularly. Importantly, extracellular hydrolysis of Leu-enkephalin is not observed. The OppA-deficient mutant was unable to transport Leu-enkephalin. Growth experiments with pasteurized milk revealed that transport of oligopeptides forms an essential part of the proteolytic system in lactococci.

X-prolyl dipeptidyl aminopeptidase gene (pepX) is part of the glnRA operon in Lactobacillus rhamnosus.

A peptidase gene expressing X-prolyl dipeptidyl aminopeptidase (PepX) activity was cloned from Lactobacillus rhamnosus 1/6 by using the chromogenic substrate L-glycyl-L-prolyl-beta-naphthylamide for screening of a genomic library in Escherichia coli. The nucleotide sequence of a 3.5-kb HindIII fragment expressing the peptidase activity revealed one complete open reading frame (ORF) of 2,391 nucleotides. The 797-amino-acid protein encoded by this ORF was shown to be 40, 39, and 36% identical with PepXs from Lactobacillus helveticus, Lactobacillus delbrueckii, and Lactococcus lactis, respectively. By Northern analysis with a pepX-specific probe, transcripts of 4.5 and 7.0 kb were detected, indicating that pepX is part of a polycistronic operon in L. rhamnosus. Cloning and sequencing of the upstream region of pepX revealed the presence of two ORFs of 360 and 1,338 bp that were shown to be able to encode proteins with high homology to GlnR and GlnA proteins, respectively. By multiple primer extension analyses, the only functional promoter in the pepX region was located 25 nucleotides upstream of glnR. Northern analysis with glnA- and pepX-specific probes indicated that transcription from glnR promoter results in a 2.0-kb dicistronic glnR-glnA transcript and also in a longer read-through polycistronic transcript of 7.0 kb that was detected with both probes in samples from cells in exponential growth phase. The glnA gene was disrupted by a single-crossover recombinant event using a nonreplicative plasmid carrying an internal part of glnA. In the disruption mutant, glnRA-specific transcription was derepressed 10-fold compared to the wild type, but the 7.0-kb transcript was no longer detectable with either the glnA- or pepX-specific probe, demonstrating that pepX is indeed part of glnRA operon in L. rhamnosus. Reverse transcription-PCR analysis further supported this operon structure. An extended stem-loop structure was identified immediately upstream of pepX in the glnA-pepX intergenic region, a sequence that showed homology to a 23S-5S intergenic spacer and to several other L. rhamnosus-related entries in data banks.

Comparison of ribotyping, randomly amplified polymorphic DNA analysis, and pulsed-field gel electrophoresis in typing of Lactobacillus rhamnosus and L. casei strains.

A total of 24 strains, biochemically identified as members of the Lactobacillus casei group, were identified by PCR with species-specific primers. The same set of strains was typed by randomly amplified polymorphic DNA (RAPD) analysis, ribotyping, and pulsed-field gel electrophoresis (PFGE) in order to compare the discriminatory power of the methods. Species-specific primers for L. rhamnosus and L. casei identified the type strain L. rhamnosus ATCC 7469 and the neotype strain L. casei ATCC 334, respectively, but did not give any signal with the recently revived species L. zeae, which contains the type strain ATCC 15820 and the strain ATCC 393, which was previously classified as L. casei. Our results are in accordance with the suggested new classification of the L. casei group. Altogether, 21 of the 24 strains studied were identified with the species-specific primers. In strain typing, PFGE was the most discriminatory method, revealing 17 genotypes for the 24 strains studied. Ribotyping and RAPD analysis yielded 15 and 12 genotypes, respectively.