Bacterial translocation from the gastrointestinal tracts of thymectomized mice

The incidence of translocation of viable indigenous bacteria from the gastrointestinal tract to the mesenteric lymph node, spleen, liver, and kidney was compared in neonatally thymectomized mice and sham-thymectomized specific pathogen-free mice. The immunologic responses of the thymectomized mice to sheep erythrocytes were decreased compared to the responses of sham-thymectomized mice. Strictly anaerobic bacteria were isolated from only 1.8% of the organs from thymectomized mice and from none of the organs of shamthymectomized mice. Aerobic or facultatively anaerobic bacteria were cultured from 27.4% of the organs of thymectomized mice. Of the thymectomized mice, 70.7% contained viable aerobic or facultatively anaerobic bacteria in one or more of their organs tested, compared with only 10% of the sham-thymectomized mice.Escherichia coli was the predominant bacterial species isolated from these organs, althoughStaphylococcus aureus, Streptococcus, andCorynebacterium also were present.Bacteroides were the only strictly anaerobic bacteria cultured. Neonatal thymectomy promotes the translocation of certain indigenous bacteria from the gastrointestinal tract to the mesenteric lymph node, spleen, liver, and kidney.     

Assessment of mouse strain on bacterial translocation from the gastrointestinal tract

The translocation of indigenous bacteria from the gastrointestinal tract to the mesenteric lymphnodes was compared in ten strains of mice. Indigenous Escherichia coli were cultured from the mesenteric lymphnodes of only two of the six mouse strains examined. Thus, spontaneous translocation of indigenous enteric bacteria across the intestinal barrier did not occur to any significant extent in any of the mouse strains examined. Since bacterial overgrowth in the gastrointestinal tract promotes bacterial translocation, bacterial translocation was tested in ten mouse strains including B10 series after antibiotic-decontaminated and subsequent colonization with streptomycin-resistant E. coli C25. E. coli C25 populated the ceca of the mice at levels of 10(8) to 10(9) per gram and translocated to 90-100% of the mesenteric lymphnodes with mean of 10(1.13) to 10(1.86) per mesenteric lymphnode. However, there were no significant differences between mouse strains as to the translocation incidence or the numbers of viable E. coli C25 per mesenteric lymphnode. Thus, genetic differences between mouse strains did not influence bacterial translocation from the gastrointestinal tract to the mesenteric lymphnodes.     

Bacterial translocation from the gastrointestinal tracts of mice receiving immunosuppressive chemotherapeutic agents

Specific pathogen-free (SPF) mice were treated with certain classes of immunosuppressive chemotherapeutic agents to determine if they would promote bacterial translocation from the gastrointestinal tract to the mesenteric lymph node, spleen, or liver. The antimetabolites methotrexate, 5-fluorouracil, and cytosine arabinoside were injected once intraperitoneally into SPF mice, and the mice were tested for bacterial translocation from the gastrointestinal tract. When total organs from the treated mice were compared with the total organs from the control mice, the alkylating agent cyclophosphamide promoted bacterial translocation when injected once intraperitoneally at doses of 100–400 mg/kg. Increasing the number of injections of cyclophosphamide did not increase the incidence of bacterial translocation. The steroid prednisone also promoted bacterial translocation after one intraperitoneal injection of 10–150 mg/kg. Prednisone and cyclophosphamide at various doses appeared to be more effective in promoting bacterial translocation from the gastrointestinal tract than the antimetabolites. The aerobic and facultatively anaerobic bacteria translocating to the various organs were identified asLactobacillus acidophilus, Escherichia coli, Klebsiella pneumoniae, Streptococcus faecalis, Staphylococcus aureus, andProteus mirabilis. Groups of SPF mice also were injected once intraperitoneally with the minimal dose of each chemotherapeutic drug that induced bacterial translocation, and then tested for immune responsiveness toE. coli vaccination. Each of the chemotherapeutic agents at the minimal doses promoting bacterial translocation also suppressed the serum antibody responses to antigens of indigenousE. coli. However, other toxic manifestations of these chemotherapeutic agents also may be involved in promoting bacterial translocation. The promotion of bacterial translocation from the gastrointestinal tract by these chemotherapeutic agents has important implications for the pathogenesis of infectious disease in patients receiving these drugs.     

Bacterial translocation can increase plasma corticosterone and brain catecholamine and indoleamine metabolism

The potential contribution of stress-induced bacterial translocation to the activation of the hypothalamo-pituitary-adrenocortical (HPA) axis and brain biogenic amines was assessed. Mice were restrained for various periods, and brain concentrations of tryptophan, catecholamines, serotonin, and their metabolites, plasma corticosterone, and the translocation of viable bacteria from the gastrointestinal tract to the mesenteric lymph nodes, spleen, and liver were measured. Restraint induced the translocation of indigenous gram-positive bacteria in only a small proportion of animals, but translocation of gram-negative bacteria did not occur. Restraint induced short-lived increases in plasma corticosterone and brain amine metabolism, whereas bacterial translocation was slower and persisted long after the HPA axis and neurochemical responses had dissipated. When mice were infected with Salmonella typhimurium, spontaneous translocation occurred and plasma corticosterone, interleukin-6 concentrations, and brain catecholamine and indoleamine metabolism were elevated. These findings indicate that the translocation of indigenous gastrointestinal bacteria did not contribute to the HPA axis and neurochemical changes induced by restraint. However, translocation of nonindigenous S. typhimurium with or without restraint did induce HPA and neurochemical responses.     

Endogenous infection in mice with streptozotocin-induced diabetes. A feature of bacterial translocation

Slc:ddY mice that received a single intraperitoneal injection of 200 mg/kg streptozotocin (STZ) were examined for persistency of diabetes (changes of indigenous bacterial floras, and bacterial translocation. Significant diabetes (increase in plasma glucose and decrease in insulin) was recognized 2 weeks after the injection, and persisted for 12 weeks. The numbers of aerobic gram-negative bacilli, staphylococci (including micrococci), and streptococci in caecal and oral floras were significantly increased, but the numbers of anaerobic bacteria in caecal flora were hardly changed. Bacterial translocation of indigenous bacteria to the mesenteric lymph node, lung, or kidney was detectable in some mice 2 weeks after the injection. The incidence of bacterial translocation in these STZ-treated mice then increased; infection caused by several organisms, e.g., Klebsiella pneumoniae, Staphylococcus epidermidis, streptococci, or Lactobacillus sp., occurred in lung, liver, spleen, kidneys, and mesenteric lymph node. No indigenous bacteria were cultured from these organs of control mice. This endogenous infection may have been due to the over population of several bacterial strains caused by disruption of indigenous floras along with depression of immunological function.     

Bacterial translocation from the intestines

Bacterial translocation is defined as the passage of viable bacteria from the gastrointestinal (GI) tract through the mucosal epithelium to other sites, such as the mesenteric lymph nodes, spleen, liver and blood. This paper reviews results from animal models utilized to obtain information concerning the defense mechanisms operating in the healthy host to confine bacteria to the GI tract. Gnotobiotic and antibiotic-decontaminated mice colonized with particular bacteria demonstrated that the indigenous GI flora maintains an ecologic equilibrium to prevent intestinal bacterial overgrowth and translocation from the GI tract. Studies with athymic (nu/nu) mice, thymus-grafted (nu/nu) mice, neonatally thymectomized mice, and mice injected with immunosuppressive agents demonstrated that the host immune system is another defense mechanism inhibiting bacterial translocation from the GI tract. Ricinoleic acid given orally to mice disrupted the intestinal epithelial barrier allowing indigenous bacteria to translocate from the GI tract. Thus, bacterial translocation from the GI tract of healthy adult mice is inhibited by: (a) an intact intestinal epithelial barrier, (b) the host immune defense system, and (c) an indigenous GI flora maintaining ecological equilibrium to prevent bacterial overgrowth. Deficiencies in host defense mechanisms act synergistically to promote bacterial translocation from the GI tract as demonstrated by animal models with multiple alterations in host defenses. Bacterial translocation occurred to a greater degree in mice with streptozotocin-induced diabetes, mice receiving nonlethal thermal injury, and mice receiving the combination of an immunosuppressive agent plus an oral antibiotic than in mice with only a primary alteration in host defenses. The study of bacterial translocation in these complex models suggests that opportunistic infections from the GI tract occur in discrete stages. In the healthy adult animal, bacterial translocation from the GI tract either does not occur or occurs at a very low level and the host immune defenses eliminate the translocating bacteria. Bacterial translocation does take place if one of the host defense mechanisms is compromised, such as a deficiency in the immune response, bacterial overgrowth in the intestines, or an increase in the permeability of the intestinal barrier. In this first stage, the bacteria usually translocate in low numbers to the mesenteric lymph node, and sometimes spleen or liver, but do not multiply and spread systemically.(ABSTRACT TRUNCATED AT 400 WORDS)     

In vivo Testing of Functional Properties of Three Selected Probiotic Strains

Summary Lactobacillus acidophilus M92, Lactobacillus plantarum L4 and Enterococcus faecium L3 were previously selected as probiotic strains on the base of in vitro selection criteria. To investigate functional properties of these three probiotic strains in vivo, Swiss albino mice were used as animal model. Survival, competition, adhesion and colonization were monitored in the gastrointestinal tract, as well as the immunomodulating capability of L. acidophilus M92, L. plantarum L4 and E. faecium L3. During the feeding of mice with probiotic strains with daily dose of 2 × 10¹⁰ rifampicin-resistant cells, the number of lactic acid bacteria in the faeces increased and reduction of enterobacteria and sulphite-reducing clostridia was observed. Rifampicin-resistant colonies of probiotic strains could be reisolated from the faeces of mice fed with the rifampicin-resistant cells. The similar results were obtained in homogenates of small and large intestine of mice on the first and fourteenth days after feeding with L. acidophilus M92, L. plantarum L4 and E. faecium L3. The adherence of the probiotic strains obtained in vitro correlated with their capability to adhere to mouse ileal epithelial cells in vivo. After oral immunization of mice with viable cells of L. acidophilus M92, L. plantarum L4 and E. faecium L3 with a daily dose of 2 × 10¹⁰ cells, the concentrations of serum IgA, IgG and IgM antibodies from all groups of mice were significantly higher in comparison to the control.     

Inhibition of Bacterial Translocation from the Gastrointestinal Tract of Mice Injected with Cyclophosphamide

Effects of intraperitoneal injection of cyclophosphamide, an immunosuppressant, on the degree of bacterial translocation and morphological changes of Peyer's patches (PP) in the intestine were investigated with antibiotic-decontaminated SPF mice and germfree mice monoassociated with Escherichia coli C25. It has been reported that treatment with cyclophosphamide induces bacterial translocation. Cyclophosphamide treatment in this study, however, significantly decreased E. coli C25 translocation from the gastrointestinal tract to the mesenteric lymph nodes (MLN), although the numbers of lymphoid cells, especially B cells, in the PP, MLN, and spleen were remarkably reduced. Four injections of cyclophosphamide at a dose of 100 mg/kg inhibited bacterial translocation more than one injection at a dose of 200 mg/kg in SPF mice. Germfree mice, however, treated with one dose of 200 mg/kg showed the same inhibition of bacterial translocation as those given 100 mg/kg four times. In cyclophosphamide-treated mice, lymph follicles in the PP were obviously smaller than those in control mice, M-cells were similar in appearance to absorption epithelial cells except for short microvilli, and immune cells among the M-cells had disappeared. These data suggested that inhibition of bacterial translocation in mice treated with cyclophosphamide may be the result of morphological and physiological changes of epithelial cells in the gastrointestinal tract, especially M-cells, as a point of entry of invading bacteria, independent of the changes in immunological function. Received: 16 November 1995 / Accepted: 12 December 1995     

Membrane filter method to study the effects of Lactobacillus acidophilus and Bifidobacterium longum on fecal microbiota

A large number of commensal bacteria inhabit the intestinal tract, and interbacterial communication among gut microbiota is thought to occur. In order to analyze symbiotic relationships between probiotic strains and the gut microbiota, a ring with a membrane filter fitted to the bottom was used for in vitro investigations. Test strains comprising probiotic nitto strains (Lactobacillus acidophilus NT and Bifidobacterium longum NT) and type strains (L. acidophilus JCM1132^T and B. longum JCM1217^T) were obtained from diluted fecal samples using the membrane filter to simulate interbacterial communication. Bifidobacterium spp., Streptococcus pasteurianus, Collinsella aerofaciens, and Clostridium spp. were the most abundant gut bacteria detected before coculture with the test strains. Results of the coculture experiments indicated that the test strains significantly promote the growth of Ruminococcus gnavus, Ruminococcus torques, and Veillonella spp. and inhibit the growth of Sutterella wadsworthensis. Differences in the relative abundances of gut bacterial strains were furthermore observed after coculture of the fecal samples with each test strain. Bifidobacterium spp., which was detected as the dominant strain in the fecal samples, was found to be unaffected by coculture with the test strains. In the present study, interbacterial communication using bacterial metabolites between the test strains and the gut microbiota was demonstrated by the coculture technique. The detailed mechanisms and effects of the complex interbacterial communications that occur among the gut microbiota are, however, still unclear. Further investigation of these relationships by coculture of several fecal samples with probiotic strains is urgently required.     

Selecting Lactic Acid Bacteria for Their Safety and Functionality by Use of a Mouse Colitis Model

Studies showed that specific probiotics might provide therapeutic benefits in inflammatory bowel disease. However, a rigorous screening of new probiotics is needed to study possible adverse interactions with the host, particularly when intended for administration to individuals with certain health risks. In this context, the objective of this study was to investigate the role of three lactobacilli (LAB) on intestinal inflammation and bacterial translocation using variations of the mouse model of 2,4,6-trinitrobenzene sulfonic acid (TNBS)-induced acute colitis. We first compared the in vitro ability of LAB to survive gastrointestinal tract (GIT) conditions and their ability to persist in the GIT of mice following daily oral administration. As a control, we included a nonprobiotic Lactobacillus paracasei strain, previously isolated from an endocarditis patient. Feeding high doses of LAB strains to healthy and to TNBS-treated mice did not induce any detrimental effect or abnormal translocation of the bacteria. Oral administration of Lactobacillus salivarius Ls-33 had a significant preventive effect on colitis in mice, while Lactobacillus plantarum Lp-115 and Lactobacillus acidophilus NCFM did not. None of the three selected LAB strains translocated to extraintestinal organs of TNBS-treated mice. In contrast, L. paracasei exacerbated colitis under severe inflammatory conditions and translocated to extraintestinal organs. This study showed that evaluations of the safety and functionality of new probiotics are recommended. We conclude that not all lactobacilli have similar effects on intestinal inflammation and that selected probiotics such as L. salivarius Ls-33 may be considered in the prevention or treatment of intestinal inflammation.     

Survival of silage lactic acid bacteria in the goat gastrointestinal tract as determined by denaturing gradient gel electrophoresis

Aims: To determine the survival rate of silage lactic acid bacteria (LAB) in the ruminant gastrointestinal tract. Methods and Results: Wilted Italian ryegrass (Lolium multiflorum Lam.) silage (containing 1·9 × 10⁶ CFU LAB g^?1) was fed ad libitum to three goats equipped with rumen cannulae. Silage was given alone or with concentrates at a 1 : 1 ratio on a dry matter basis. Rumen fluid was then obtained 2, 4 and 8 h after the morning feeding. Denaturing gradient gel electrophoresis was performed to compare LAB communities in silage, rumen fluid and faeces. The LAB detected in the wilted silage included Lactobacillus plantarum, Lactobacillus brevis, Lactobacillus murinus and Lactobacillus sakei. Bands indicative of Lact. murinus were detected in either the rumen fluid or faeces, whereas the bands indicative of Lact. plantarum, Lact. brevis and Lact. sakei were not. Although the rumen fluid LAB counts and volatile fatty acid concentrations were higher in goats fed silage plus concentrates compared with those fed silage alone, the LAB communities themselves remained unaffected. Sampling times and goat‐to‐goat variations did not affect the LAB communities found in the rumen fluid. Conclusion: LAB communities found in the gut are not remarkably affected by the consumption of silage LAB, even when the silage is accompanied by concentrates that facilitate gut fermentation. Significance and Impact of the Study: Although silage can improve probiotic function, it may be difficult for silage LAB to survive the digestive process in the ruminant gastrointestinal tract.     

Biochemical screening of Lactobacilli in midgut of wild Aedes aegypti mosquitoes. A step toward paratransgenesis candidate

This study was conducted to isolate and identify lactobacilli from larval and adult midgut of wild Aedes aegypti (Ae. aegypti) to find candidate bacteria for paratransgenic control. Characterization of the bacterial symbionts was done using Gram staining, motility test, catalase test, and biochemical tests, among others, and the morphological features were confirmed using a standard scheme that simplifies the identification of lactic acid bacteria. A total of 174 strains were isolated and identified, 135 strains from larval midgut and 39 strains from adult midgut (mean ± SE, 4.00 ± 0.72; P = 0.00). The isolated species were confirmed to be Lactobacillus fermentum, L. casei, L. acidophilus, L. viridescens, L. brevis and L. gasseri. It can be concluded that Ae. aegypti has the potential of harboring the cultivable bacterial symbionts. In conclusion, the isolated species were nominated for paratransgenic control, particularly L. fermentum, being found in large numbers from both larval and adulxt midgut.     

Bacterial colonization of the oral cavity of the BALB/c mouse

The acquisition of the human oral bacterial flora follows a relatively well known sequence of succession that can be influenced by various host factors. These factors have not been studied in the mouse. In the present work, we followed the bacterial colonization of the oral cavity of mice from birth, and tested our mouse model for its suitability in studying the influence of weaning and puberty on the indigenous oral bacterial flora. We observed that the first colonizers were staphylococci, followed by lactobacilli. The proportions of these two predominant bacteria fluctuated for a period of 30–50 days, but evolved towards the proportions previously observed among the indigenous bacterial species of 6–8 week-old BALB/c male mice (predominantly Lactobacillus murinus and Staphylococcus aureus). The weaning period significantly altered the equilibrium among the oral bacterial flora. This equilibrium was not significantly modified during puberty. Offprint requests to: M.C. Lavoie     

Alteration of the Canine Small-Intestinal Lactic Acid Bacterium Microbiota by Feeding of Potential Probiotics

Five potentially probiotic canine fecal lactic acid bacterium (LAB) strains, Lactobacillus fermentum LAB8, Lactobacillus salivarius LAB9, Weissella confusa LAB10, Lactobacillus rhamnosus LAB11, and Lactobacillus mucosae LAB12, were fed to five permanently fistulated beagles for 7 days. The survival of the strains and their potential effects on the indigenous intestinal LAB microbiota were monitored for 17 days. Denaturing gradient gel electrophoresis (DGGE) demonstrated that the five fed LAB strains survived in the upper gastrointestinal tract and modified the dominant preexisting indigenous jejunal LAB microbiota of the dogs. When the LAB supplementation was ceased, DGGE analysis of jejunal chyme showed that all the fed LAB strains were undetectable after 7 days. However, the diversity of the intestinal indigenous microbiota of the dogs, as characterized from jejunal chyme plated on Lactobacillus selective medium without acetic acid, was reduced and did not return to the original level during the study period. In all but one dog, an indigenous Lactobacillus acidophilus strain emerged as the dominant LAB strain. In conclusion, strains LAB8 to LAB12 have potential as probiotic strains for dogs as they survive in and dominate the jejunal LAB microbiota during feeding and have the ability to modify the intestinal microbiota.     

Characterization of the three selected probiotic strains for the application in food industry

Previously selected bacterial probiotic strains Enterococcus faecium L3, Lactobacillus plantarum L4 and Lactobacillus acidophilus M92 have shown their potential as functional starter cultures in silage, white cabbage and milk fermentation. Therefore, the phenotypic and genotypic characteristics important for their application in food industry were investigated. Pulsed-field gel electrophoresis (PFGE) of NotI digested genomic DNA, in combination with physiological traits determined by API tests, made a useful tool for identification of these probiotic strains and differentiation among them. Lyophilized probiotic cells remained viable during 75 days of storage at −20, +4 and +15°C, while fresh concentrated cells remained viable only at −20°C with addition of glycerol as cryoprotectant. After the lyophilization with addition of skim milk as lyoprotectant, the viability of L. acidophilus M92, L. plantarum L4 and E. faecium L3 was reduced by only 0.37, 0.44 and 0.50 log, respectively. Furthermore, probiotic strains L. acidophilus M92, L. plantarum L4, and E. faecium L3, demonstrated anti-Salmonella activity, and L. acidophilus M92 having also antilisterial activity demonstrated by in vitro competition test. Overnight cultures and cell-free supernatants of the three probiotic strains exerted also an antagonistic effect against the Gram-positive and Gram-negative test microorganisms examined, demonstrated by the agar-well diffusion test. The inhibition of Listeria monocytogenes, Salmonella typhimurium, Yersinia enterocolitica, and Acinetobacter calcoaceticus obtained, achieved by the neutralized, 5-fold concentrated supernatant of L. plantarum L4, may be the result of its bacteriocinogenic activity. On the basis of these results, the application of the three examined probiotic strains may become a point of great importance in respect of food safety.     

Antagonistic activity of Lactobacillus bacteria strains against anaerobic gastrointestinal tract pathogens (Helicobacter pylori, Campylobacter coli, Campylobacter jejuni, Clostridium difficile)]

Antagonistic activity of Lactobacillus strains has been known for some time. This property is connected with production of many active substances by lactobacilli e.g., organic acids and bacteriocin-like substances which interfere with other indigenous microorganisms inhabiting the same ecological niche, including also anaerobic gastrointestinal tract pathogens. Growing interest of clinical medicine in finding new approaches to treatment and prevention of common inflammatory infections of the digestive tract resulted in studies on a possible usage of lactic acid bacteria. Last years, several in vitro and in vivo experiments on antagonism of different Lactobacillus strains against Helicobacter pylori and Clostridium difficile were performed. These observations had been done on already established, well known probiotic Lactobacillus strains. We tested antibacterial activities of Lactobacillus strains isolated from human digestive tract. As indicator bacteria, four species known as anaerobic bacterial etiologic agents of gastroenteric infections: Helicobacter pylori, Campylobacter jejuni, C. coli and Clostridium difficile were used. Some of them were obtained from international collections, others were clinical isolates from specimens taken from patients with different defined gastrointestinal infections. We used a slab method of testing inhibitory activity described in details previously. Following conclusions were drawn from our study: All tested human Lactobacillus strains were able to inhibit the growth of all strains of anaerobic human gastrointestinal pathogens used in this study. Inhibitory activities of tested Lactobacillus strains against Helicobacter pylori, Campylobacter spp., and Clostridium difficile as measured by comparing mean diameters of the inhibition zones were similar. Differences in susceptibility of individual indicator strains of Campylobacter spp. and Clostridium difficile to inhibitory activity of Lactobacillus strains were small. A similar mechanism of inhibition of anaerobic bacteria by lactobacilli is postulated.     

The probiotic properties and potential of vaginal Lactobacillus spp. isolated from healthy women against some vaginal pathogens

During the last decade, probiotic research has progressed considerably and significant advances have been made in the selection and characterization of specific probiotic strains. The most studied probiotics belong to the genus Lactobacillus. In this study, 80 Lactobacillus spp. isolated from healthy women tolerated low pH and were able to grow in the presence of bile salts. RAPD PCR technique resulted in the identification of 38 different types. These isolates were then evaluated based on adhesion capacity, antibiotic susceptibility and tolerance in simulated gastrointestinal tract. Species-specific PCR and detection of bacteriocin-related genes were also surveyed. Among the isolates, five strains—Lacticaseibacillus rhamnosus NO21, Lacticaseibacillus casei NO1, Lactiplantibacillus plantarum NO4, Lactobacillus acidophilus NO7 and Lactobacillus gasseri NO38—presented acceptable antibiotic susceptibility pattern. Further analysis showed antimicrobial activity of Lacticaseibacillus culture against various bacterial pathogens and real-time PCR showed all five strains were able to prevent the colonization of bacterial pathogens. All five selected strains produced organic acids, hydrogen peroxide and were resistant to the spermicide. In addition, they lacked haemolytic activity with the ability of hydrophobicity, auto-aggregation and co-aggregation with pathogens. These results suggest that the vaginal microbiome could be a good source for the isolation of probiotics and the strains of this study may be considered as good probiotic candidates.     

Rapid Identification of <Emphasis Type="Italic">Lactobacillus</Emphasis><Emphasis Type="Italic">acidophilus</Emphasis> by Restriction Analysis of the 16S–23S rRNA Intergenic Spacer Region and Flanking 23S rRNA Gene

A rapid molecular approach was developed for the initial identification of Lactobacillus acidophilus strains which are difficult to identify using a single biochemical test. The 16S–23S rRNA intergenic spacer regions and flanking 23S rRNA genes of 19 strains of lactobacilli were amplified and the nucleotide sequences and restriction site polymorphisms were analyzed. AluI was the most useful of the restriction enzymes analyzed and produced reproducible digestion profiles in the L. helveticus, L. plantarum, and L. casei groups, as well as in L. acidophilus. This restriction fragment length polymorphism method may be useful for the identification of L. acidophilus strains in dairy products.     

Extensive horizontal transfer of core genome genes between two <Emphasis Type="Italic">Lactobacillus</Emphasis> species found in the gastrointestinal tract

Background  

While genes that are conserved between related bacterial species are usually thought to have evolved along with the species, phylogenetic trees reconstructed for individual genes may contradict this picture and indicate horizontal gene transfer. Individual trees are often not resolved with high confidence, however, and in that case alternative trees are generally not considered as contradicting the species tree, although not confirming it either. Here we conduct an in-depth analysis of 401 protein phylogenetic trees inferred with varying levels of confidence for three lactobacilli from the acidophilus complex. At present the relationship between these bacteria, isolated from environments as diverse as the gastrointestinal tract (Lactobacillus acidophilus and Lactobacillus johnsonii) and yogurt (Lactobacillus delbrueckii ssp. bulgaricus), is ambiguous due to contradictory phenotypical and 16S rRNA based classifications.