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At least 163 records · Page 9Linked to original sources
PubMed2003

Immunologic regulation of toll-like receptors in gut epithelium.

PURPOSE OF REVIEW: In response to the presence of pathogens in the environment, the innate immune system has evolved to provide a rapid defense against microbes. This response involves the recognition of molecular patterns present in diverse microbes by a series of receptors termed toll-like receptors. The focus of this article is the regulation of toll-like receptor signaling in the intestinal epithelium. The intestinal epithelium is continually exposed to a high concentration of diverse bacteria. In spite of the density of commensal bacteria, the normal intestine is not inflamed. Idiopathic inflammatory bowel disease in humans and animals is characterized by aberrant host-microbial interactions. RECENT FINDINGS: Several studies demonstrate that intestinal epithelial cells are poorly responsive to microbial products. The reason for this hyporesponsiveness is decreased or polarized expression of toll-like receptor molecules. Inflammatory cytokines upregulate expression of toll-like receptors. SUMMARY: The intestinal epithelium has evolved under the pressure of the microbiota to mute a response to commensal bacteria while maintaining the ability to respond to pathogens. In inflammatory bowel disease, the loss of tolerance to the normal flora may be due in part to inappropriate toll-like receptor signaling.

Journal Article↗
PubMed2003

A thermodynamic interpretation of cell hydrophobicity in aerobic granulation.

Aerobic granulation can be regarded as a microorganism-to-microorganism self-immobilization process, in which cell hydrophobicity could be a decisive parameter in determining the microorganism-to-microorganism interaction and structural compactness of aerobic granules. This study looked into the thermodynamic interpretation of cell hydrophobicity in aerobic granulation; and a model that correlates microbial interaction and relative cell hydrophobicity defined as the ratio of cell hydrophobicity over cell hydrophilicity was derived. This model describes how cell hydrophobic and hydrophilic interactions affect aerobic granulation and offers deep insights into the thermodynamic mechanisms of microbial aggregation. The model prediction was in good agreement with experimental data. Results showed that aerobic granulation was a function of cell hydrophobicity over cell hydrophilicity, i.e. a high cell hydrophobicity strongly favors microbial aggregation and results in a more compact structure.

Aerobiosis↗
PubMed2004

Host-bacterial interactions in inflammatory bowel disease.

Large numbers of different bacterial species are resident in the lumen of the distal gastrointestinal tract. The normal intestinal host-microbial interactions are not well understood, but the relationship is generally believed to be either mutually beneficial or beneficial to one without disadvantage to the other. Animal model and clinical studies suggest that IBD (inflammatory bowel disease) may develop in a susceptible individual when the normal host-bacterial relationship is dysregulated. In addition to rodent models, this article reviews studies that have investigated the cellular and molecular mechanisms of interactions between intestinal mucosal cells and the resident luminal bacteria in healthy individuals and patients with ulcerative colitis and Crohn's disease. Mechanisms by which the intestinal mucosa is able to avoid pro-inflammatory responses to commensal bacteria (and their products) but able to respond appropriately to luminal pathogens is currently an area of active investigation. Such studies are beginning to provide important clues regarding possible alterations in the mucosa that lead to the development of pro-inflammatory responses to resident bacteria in patients with IBD. Approaches to alter the intestinal microflora for therapeutic purposes and their potential mechanisms of action are also discussed.

Animals↗
PubMed2003

Microbial surface thermodynamics and interactions in aqueous media.

Microbial surface thermodynamics and interactions in aqueous media were investigated for seven typical rod-shaped bacterial strains of Enterobacteriaceae, Pseudomonadaceas, and Bacillaceae, which included Escherichia coli HB101, Escherichia coli JM109, Pseudomonas fluorescens, Pseudomonas putida, Pseudomonas aeruginosa, Pseudomonas sp., and Bacillus subtilis. All the microorganisms studied exhibited a monopolar and predominant hydrophilic surface and a negative Delta G132tot, total free energy of interactions between microbes (1) and silica gel or Canadian River Alluvium (CRA) (2) immersed in water (3) at the equilibrium distance, which accounted for their attachment on the medium surface. The microbial attachment was proportional to the corresponding Delta G132tot values. Among the microorganisms studied, B. subtilis had the most attachment on both silica gel and CRA because it had the smallest Delta G132tot values (-17.14kT for silica gel and -21.84kT for CRA). The origins of Lifshitz-van der Waals, Lewis acid/base, and electrostatic interactions were discussed and related to experimental observations.

Bacillus subtilis↗
PubMed1995

Cellulose degradation in anaerobic environments.

In anaerobic environments rich in decaying plant material, the decomposition of cellulose is brought about by complex communities of interacting microorganisms. Because the substrate, cellulose, is insoluble, bacterial and fungal degradation occurs exocellularly, either in association with the outer cell envelope layer or extracellularly. Products of cellulose hydrolysis are available as carbon and energy sources for other microbes that inhabit environments in which cellulose is biodegraded, and this availability forms the basis of many microbial interactions that occur in these environments. This review discusses interactions among members of cellulose-decomposing microbial communities in various environments. It considers cellulose decomposing communities in soils, sediments, and aquatic environments, as well as those that degrade cellulose in association with animals. These microbial communities contribute significantly to the cycling of carbon on a global scale.

Anaerobiosis↗
PubMed1999

Modelling the interactions between Lactobacillus curvatus and Enterobacter cloacae. I. Individual growth kinetics.

Mixed cultures of Lactobacillus curvatus and Enterobacter cloacae were chosen as a model system to quantitatively study microbial interactions involved in food spoilage and food preservation. In this paper models were developed to predict the individual behaviour of L. curvatus and E. cloacae in pure suspension cultures as a function of the glucose and lactate concentration and the pH. In a second paper these models will be used to predict the moment of interaction in mixed suspension cultures and the cell concentrations at this moment. The effect of pH on the maximum specific growth rate could be described by a parabolic equation for L. curvatus and E. cloacae. E. cloacae is clearly more sensitive to a pH decrease than L. curvatus, as may be concluded from the theoretical minimum pH for growth of 5.6 for E. cloacae and 4.3 for L. curvatus. For both organisms no effect of glucose on the maximum specific growth rate could be detected and Monod kinetics with a low Monod constant was assumed. For L. curvatus the effect of lactate on the maximum specific growth rate at different initial pH values could be described by a linear relationship. For E. cloacae a slight effect of lactate on the maximum specific growth rate could only be detected at pH 7. However, this effect was negligible compared to the effect of the pH. For both organisms the lag time was modelled by the inverse of the specific growth rate. It can be concluded that, with regard to interactions between L. curvatus and E. cloacae, the pH is likely to be the most important factor in the case where L. curvatus is the dominant organism. Substrate limitation is likely to become important in the case where E. cloacae is the dominant organism or for media with a high buffer capacity.

Animals↗
PubMed2005

Interaction of Klebsiella oxytoca and Burkholderia cepacia in dual-species batch cultures and biofilms as a function of growth rate and substrate concentration.

Dual-species microbial interactions have been extensively reported for batch and continuous culture environments. However, little research has been performed on dual-species interaction in a biofilm. This research examined the effects of growth rate and substrate concentration on dual-species population densities in batch and biofilm reactors. In addition, the feasibility of using batch reactor kinetics to describe dual-species biofilm interactions was explored. The scope of the research was directed toward creating a dual-species biofilm for the biodegradation of trichloroethylene, but the findings are a significant contribution to the study of dual-species interactions in general. The two bacterial species used were Burkholderia cepacia PR1-pTOM(31c), an aerobic organism capable of constitutively mineralizing trichloroethylene (TCE), and Klebsiella oxytoca, a highly mucoid, facultative anaerobic organism. The substrate concentrations used were different dilutions of a nutrient-rich medium resulting in dissolved organic carbon (DOC) concentrations on the order of 30, 70, and 700 mg/L. Presented herein are single- and dual-species population densities and growth rates for these two organisms grown in batch and continuous-flow biofilm reactors. In batch reactors, planktonic growth rates predicted dual-species planktonic species dominance, with the faster-growing organism (K. oxytoca) outcompeting the slower-growing organism (B. cepacia). In a dual-species biofilm, however, dual-species planktonic growth rates did not predict which organism would have the higher dual-species biofilm population density. The relative fraction of each organism in a dual-species biofilm did correlate with substrate concentration, with B. cepacia having a greater proportional density in the dual-species culture with K. oxytoca at low (30 and 70 mg/L DOC) substrate concentrations and K. oxytoca having a greater dual-species population density at a high (700 mg/L DOC) substrate concentration. Results from this research demonstrate the effectiveness of using substrate concentration to control population density in this dual-species biofilm.

Biodegradation, Environmental↗
PubMed1989

Interaction between cortisol and microbial proteases.

Binding (or interaction) of cortisol with microbial molecule(s) was observed by employing Bio-Gel HTP affinity chromatography and subsequently by fluorescence spectrophotometry. Molecule(s) in the crude extract of baker's yeast and in other microbial proteases exhibited varied degrees of cortisol-binding. Bacterial protease (type IX) had highest, while the type XXVI enzyme had the lowest, binding capacity. In addition, these two proteases exhibited a distinct difference in the alterations of ultraviolet spectra due to interaction with cortisol. Using casein as a substrate, cortisol, CTP, trypsin inhibitor or leupeptin appreciably inhibited type IX protease at low concentrations of Ca2+. However, thyroxine had no effect on this protease.

Bacteria↗
PubMed1999

Modelling the interactions between Lactobacillus curvatus and Enterobacter cloacae. II. Mixed cultures and shelf life predictions.

The modelling approach presented in this study can be used to predict when interactions between microorganisms in homogenous systems occur. It was tested for the interaction between Lactobacillus curvatus and Enterobacter cloacae. In this binary system, L. curvatus produces lactic acid which decreases the pH in the system. The pH decrease was found to be the main limiting factor of growth of both E. cloacae and L. curvatus. This resulted in E. cloacae reaching its final concentration earlier when compared to its growth in pure culture. The models consisted of a set of first order ordinary differential equations describing the growth, consumption and production rates of both microorganisms. The parameters for these equations were obtained from pure culture studies and from literature. These equations were solved using a combination of analytical and numerical methods. The prediction of growth in mixed culture using parameters from pure culture experiments and literature were close to the experimental data. Both model predictions and experimental validation indicated that interaction occurs when the concentration of L. curvatus reaches 10(8) cfu/ml. At that moment in time, the pH had decreased to inhibiting levels. These concentrations of microorganisms (10(8) cfu/ml) do occur in fermented products where interactions obviously are important. In nonfermented foods however, this level of microorganisms indicate that spoilage has occurred or is about to start. Microbial interactions can therefore be neglected when predicting shelf life or safety of food products in most cases.

Colony Count, Microbial↗
PubMed1976

A rumen linear programming model for evaluation of concepts of rumen microbial function.

A linear programming model provides for analysis of general input-output relationships in the rumen, for evaluation of competitive relationships among rumen microbes, and for computation of optimal relationships in the rumen. Eight rumen microbial groups defined on the bases of substrate specificity, nutrient requirements for growth, fermentation products, and relative metabolic activities comprise the central core of the model. Relative metabolic rates of microbial groups calculated from their cell sized were used as coefficients in the objective function. The model was used to evaluate effects of different amounts of protein from feed and various carbohydrates upon microbial population and fermentation patterns as accommodated by current concepts. During the several solutions of the model, considerable simplification of the rumen microflora occurred. This implies that current data and concepts, and the hypothesis regarding relative metabolic rate, as represented in the model, do not accommodate adequately competitions among the several rumen microbial species and, thus, that additional data and concepts regarding rumen microbial interactions are required. Also evaluated were effects of ingestion of bacteria by protozoa upon over-all rumen function, absolute microbial cell yields, cell yields per mole of adenosine triphosphate, and factors affecting these.

Adenosine Triphosphate↗
PubMed1985

Diffusion through a Double-Sided Plate: Development of a Method to Study Alga-Bacterium Interactions.

Bacteria and algae isolated from a wastewater oxidation pond were inoculated onto opposing surfaces of double-layer agar plates (Lutri plates) to determine the usefulness of such plates for studying microbial interactions. The altered growth characteristics of various algae depending on the species of bacteria on the adjacent medium surface indicated that there was diffusion of extracellular products through the agar, suggesting that this simple assay can be used for screening potential interactions of actively growing organisms.

Journal Article↗
PubMed2006

Probiotics modulate inflammatory cytokine secretion from inflamed mucosa in active ulcerative colitis.

Enteric microflora of ulcerative colitis patients becomes aberrant. The abnormal interaction between microflora and intestinal mucosal immune system leads the mucosal inflammation. Probiotic administration may recover the commensal microflora and normalise the host-microbial interaction. In this experiment, we cocultured colonic biopsies from active ulcerative colitis patients with bifidobacterium to investigate the modulation effect of probiotics on inflamed colonic tissues and its possible mechanism. Colonic biopsies from active ulcerative colitis were cocultured for 24 h with Bifidobacterium longum. Tumour necrosis factor (TNF)-alpha and interleukin (IL)-8 in supernatants were measured using enzyme-linked immunosorbent assays, the biopsies were fixed using paraffin and the expression of NF-kappaB P65 of tissues was studied using immunohistochemical staining. The concentrations of TNF-alpha and IL-8 in supernatants of tissues cocultured with probiotics were lower than those cultured alone. The number of lamina propria mononuclear cells (LPMC) with nuclear factor-kappa B (NF-kappaB) P65 positive in cocultured tissues was also decreased. When cocultured with inflamed tissues of active ulcerative colitis, probiotics could inhibit NF-kappaB activation in LPMC and down-regulate inflammatory cytokine secretion from inflamed tissues of active ulcerative colitis.

Adolescent↗
PubMed1995

Inhibition of ruminal staphylococci and enterococci by nisin in vitro.

A collection of 59 ureolytic and lactic acid-producing ruminal staphylococci and enterococci, isolates from domestic and wild ruminants, were tested for sensitivity or resistance to lantibiotic nisin. All strains tested were sensitive with zones of inhibition, around wells containing 250 micrograms nisin, from 6 to 26 mm. 74.6% of isolates had zones of inhibition more than 10 mm and 11.1% more than 20 mm. Nisin was more effective against enterococci than staphylococci. Sensitivity of ruminal isolates to nisin may be used to control bacterial growth during the colonization of the rumen or to study the role of antibacterial activity in microbial interactions. Results obtained can be also used in experiments on gnotobiotic animals.

Animals↗
PubMed1991

Effect of nutrients on defined bacterial plaques and Streptococcus mutans C67-1 implantation in a model mouth.

Actinomyces viscosus WVU 627, Streptococcus oralis LPA-1 and Veillonella dispar OMZ 193 were cocultured on teeth in a model mouth for 66 h. Synthetic saliva containing bovine salivary glycoprotein supported bacterial growth, although the delivery of an intermittent nutrient supplement, containing 1% (w/v) glucose or sucrose, gave greater bacterial cell and viable counts. When Streptococcus mutans C67-1 was super-inoculated onto 24-hour mixed plaques, it became established under all regimens, but there was pronounced colonization resistance. With saliva only, the proportion of S. mutans at 66 h was less than 0.5% of the total cultivable microflora. When a glucose supplement was delivered for 1 h every 6 h, S. mutans attained a final proportion of 2.4%. With sucrose, both S. mutans C67-1 and its non-cariogenic glucan-deficient mutant, C67-25, attained similar proportions of 15-20%. These experiments indicate how this model can be used to study the factors influencing colonizing ability and microbial interactions in biofilms under controlled conditions.

Actinomyces↗
PubMed1996

Enteric bacteria: friend or foe?

The normal gastrointestinal tract contains an enormous number of aerobic and anaerobic bacteria which normally enjoy a symbiotic relationship with the host but can have adverse effects with local and systemic consequences. The small intestine constitutes a zone of transition between the sparsely populated stomach and the luxuriant bacterial flora of the colon. Regulation of the intestinal flora depends on complex interactions between many factors including secretion of gastric acid, intestinal motility, biliary and pancreatic secretions, local immunity, the surface glycocalyx and mucus layer, and diet. Microbial interactions are also important, and can involve alterations in redox potential, substrate depletion and production of substances such as bacteriocins that inhibit bacterial growth. The beneficial effect of the normal enteric flora include the competitive exclusion of potentially pathogenic organisms, and the production of nutrients such as short-chain fatty acids (which represent an important energy source for the colonic mucosa) and vitamins. Detrimental effects of the enteric flora include competition for calories and essential nutrients, particularly by bacteria located in the small intestine, and a capacity to damage the mucosa, in some circumstances causing or contributing to inflammatory bowel disease. These problems can be accentuated by interference with the physiological regulation of intraluminal bacteria allowing overgrowth by a normal resident, or colonisation by transient pathogens. The pathophysiological consequences may involve direct damage to the intestinal mucosa, and bacterial metabolism of intraluminal constituents, for example forming deconjugated bile acids and hydroxylated fatty acids which stimulate fluid secretion. Additional problems arise if there is interference with the mucosal barrier since this can result in increased passage of bacteria and bacterial products stimulating mucosal inflammation, while bacterial translocation can result in bacteraemia and septicaemia. Problems associated with bacterial pathogens are illustrated by the properties of the spectrum of pathogenic Escherichia coli, some of which facilitate long-term colonisation by adherence to the surface or invasion of enterocytes.

Animals↗
PubMed2002

Bacteriocins: evolution, ecology, and application.

Microbes produce an extraordinary array of microbial defense systems. These include classical antibiotics, metabolic by-products, lytic agents, numerous types of protein exotoxins, and bacteriocins. The abundance and diversity of this potent arsenal of weapons are clear. Less clear are their evolutionary origins and the role they play in mediating microbial interactions. The goal of this review is to explore what we know about the evolution and ecology of the most abundant and diverse family of microbial defense systems: the bacteriocins. We summarize current knowledge of how such extraordinary protein diversity arose and is maintained in microbial populations and what role these toxins play in mediating microbial population-level and community-level dynamics. In the latter half of this review we focus on the potential role bacteriocins may play in addressing human health concerns and the current role they serve in food preservation.

Archaea↗
PubMed2002

Helicobacter pylori and gastrointestinal tract adenocarcinomas.

Although gastric adenocarcinoma is associated with the presence of Helicobacter pylori in the stomach, only a small fraction of colonized individuals develop this common malignancy. H. pylori strain and host genotypes probably influence the risk of carcinogenesis by differentially affecting host inflammatory responses and epithelial-cell physiology. Understanding the host-microbial interactions that lead to neoplasia will improve cancer-targeted therapeutics and diagnostics, and provide mechanistic insights into other malignancies that arise within the context of microbially initiated inflammatory states.

Adenocarcinoma↗
PubMed1994

Living biosensors for the management and manipulation of microbial consortia.

The increasing interest in microbial ecology has resulted in the creation of new tools for the study of complex microbial interactions. Bioreporter genes are particularly useful because they provide a means of determining gene activity. Most bioreporter genes utilize a biochemical assay requiring destructive sampling of the microbial consortium, but lux bioreporter genes produce visible light when active. The measurement of light is rapid, sensitive, and quantifiable, and background signal is usually absent. The usefulness of lux bioreporters is shown in several examples that demonstrate the unique attributes of this bioreporter. Despite some limitations, bioluminescence has proved to be a useful bioreporter under both laboratory and field conditions. Technological developments are discussed that have the potential to increase the number of bioreporter genes.

Bacteria↗