Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Microbial interactions”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 721 records · Page 40Linked to original sources
PubMed2005

Conformational change in the catalytic site of the ribonuclease YoeB toxin by YefM antitoxin.

The eubacterial chromosome encodes various addiction modules that control global levels of translation through RNA degradation. Crystal structures of the Escherichia coli YefM2 (antitoxin)-YoeB (toxin) complex and the free YoeB toxin have been determined. The structure of the heterotrimeric complex reveals an asymmetric disorder-to-order recognition strategy, in which one C terminus of the YefM homodimer exclusively interacts with an atypical microbial ribonuclease (RNase) fold of YoeB. Comparison with the YefM-free YoeB structure indicates a conformational rearrangement of the RNase catalytic site of YoeB, induced by interaction with YefM. Complementary biochemical experiments demonstrate that the YoeB toxin has an in vitro RNase activity that preferentially cleaves at the 3' end of purine ribonucleotides.

Amino Acid Sequence↗
PubMed2004

Toll-like receptor ligands: hygiene, atopy and therapeutic implications.

PURPOSE OF REVIEW: Allergic and certain other inflammatory diseases have become more common in industrialized countries over the past few decades. One potential explanation for such trends is that with a decreased incidence of microbial exposures, as a result of modern public health practices, an important source of immune stimulation has been lost, with a consequent increase in inflammatory responses and their associated diseases. This review will focus on our current understanding of how microbial exposures impact on host immunity and the pathogenesis of allergic diseases. RECENT FINDINGS: In the past decade, it has become clear that a number of molecular interactions between immunocytes and microbial compounds are mediated by Toll-like receptors on host cells. Moreover, recent investigations have suggested that ligands for different Toll-like receptors have the potential both to inhibit and promote the development of allergic hypersensitivities and diseases. SUMMARY: On the basis of studies discussed herein, we speculate that physiological exposures to Toll-like receptor ligands have important yet complex effects on immune homeostasis and host susceptibility towards atopic diseases. Moreover, we anticipate that a fuller understanding of how physiological Toll-like receptor ligand exposures impact on immune development will lead to novel therapeutic interventions for the prevention and treatment of atopic diseases.

Animals↗
PubMed2005

In vitro activity and killing effect of citropin 1.1 against gram-positive pathogens causing skin and soft tissue infections.

The in vitro activity of citropin 1.1 against gram-positive cocci was measured by MIC, minimal bactericidal concentration, time-kill studies, and a checkerboard titration method. Streptococci and staphylococci were inhibited at concentrations between 1 and 16 mg/liter, respectively. Enterococci showed less susceptibility. Synergy was demonstrated when citropin 1.1 was combined with clarithromycin and doxycycline.

Amphibian Proteins↗
PubMed1975

Model system for studying colonization and growth of bacteria on a hydroxyapatite surface.

A model system for the study of bacterial colonization and growth on a hydroxyapatite (HT) surface is described. Hydroxyapatite was crystallized over the surface of porous glass beads. Chemical analysis of the product showed that the ratio of Ca2+/P042- was indistinguishable from that of commercial HT powder. X-ray diffraction analysis supported the conclusion that the product was HT. A system employing [14C]polyethylene glycol, which selectively adsorbs to the glass surface of the beads, was developed to determine the amount of glass surface covered by HT. Over 90% of the glass surface could be covered by our method. The product, HT beads, consisted of approximately 20% (dry weight) HT. The HT beads possess several properties which make them potentially useful for studying microbial adherence, growth, and interactions. These include: (i) chemical similarity to the tooth surface, (ii) large surface area, and (iii) high density. We also describe a method for direct measurement of the microbial mass of cells growing on beads. The method entails immobilizing a sample on a membrane filter (Millipore), staining it with amido black dye, and eluting the dye for spectrophotometric measurement. Streptococcus mutans served as the test organism. For free-growing bacteria the values measured with the filter assay were directly proportional to cell number, with a value of 1 mug of "protein" corresponding to about 1.5 X 10(6) colony-forming units, determined by viable count. For bacteria colonizing the beads, 1 mug of protein corresponded to about 2 X 10(7) colony-forming units on the beads during logarithmic growth. As the culture approached stationary phase, the efficiency of the assay decreased. These data indicate that multiple random samples, taken at a given time, are representative of the entire culture.

Bacteriological Techniques↗
PubMed2004

Microbially induced flotation and flocculation of pyrite and sphalerite.

Cells of Paenibacillus polymyxa and their metabolite products were successfully utilized to achieve selective separation of sphalerite from pyrite, through microbially induced flocculation and flotation. Adsorption studies and electrokinetic investigations were carried out to understand the changes in the surface chemistry of bacterial cells and the minerals after mutual interaction. Possible mechanisms in microbially induced flotation and flocculation are outlined.

Adsorption↗
PubMed2005

Microbial co-operation in the rhizosphere.

Soil microbial populations are immersed in a framework of interactions known to affect plant fitness and soil quality. They are involved in fundamental activities that ensure the stability and productivity of both agricultural systems and natural ecosystems. Strategic and applied research has demonstrated that certain co-operative microbial activities can be exploited, as a low-input biotechnology, to help sustainable, environmentally-friendly, agro-technological practices. Much research is addressed at improving understanding of the diversity, dynamics, and significance of rhizosphere microbial populations and their co-operative activities. An analysis of the co-operative microbial activities known to affect plant development is the general aim of this review. In particular, this article summarizes and discusses significant aspects of this general topic, including (i) the analysis of the key activities carried out by the diverse trophic and functional groups of micro-organisms involved in co-operative rhizosphere interactions; (ii) a critical discussion of the direct microbe-microbe interactions which results in processes benefiting sustainable agro-ecosystem development; and (iii) beneficial microbial interactions involving arbuscular mycorrhiza, the omnipresent fungus-plant beneficial symbiosis. The trends of this thematic area will be outlined, from molecular biology and ecophysiological issues to the biotechnological developments for integrated management, to indicate where research is needed in the future.

Bacteria↗
PubMed1997

Shared themes of antigenic variation and virulence in bacterial, protozoal, and fungal infections.

Pathogenic microbes have evolved highly sophisticated mechanisms for colonizing host tissues and evading or deflecting assault by the immune response. The ability of these microbes to avoid clearance prolongs infection, thereby promoting their long-term survival within individual hosts and, through transmission, between hosts. Many pathogens are capable of extensive antigenic changes in the face of the multiple constitutive and dynamic components of host immune defenses. As a result, highly diverse populations that have widely different virulence properties can arise from a single infecting organism (clone). In this review, we consider the molecular and genetic features of antigenic variation and corresponding host-parasite interactions of different pathogenic bacterial, fungal, and protozoan microorganisms. The host and microbial molecules involved in these interactions often determine the adhesive, invasive, and antigenic properties of the infecting organisms and can dramatically affect the virulence and pathobiology of individual infections. Pathogens capable of such antigenic variation exhibit mechanisms of rapid mutability in confined chromosomal regions containing specialized genes designated contingency genes. The mechanisms of hypermutability of contingency genes are common to a variety of bacterial and eukaryotic pathogens and include promoter alterations, reading-frame shifts, gene conversion events, genomic rearrangements, and point mutations.

Animals↗
PubMed2004

Recognition of commensal microflora by toll-like receptors is required for intestinal homeostasis.

Toll-like receptors (TLRs) play a crucial role in host defense against microbial infection. The microbial ligands recognized by TLRs are not unique to pathogens, however, and are produced by both pathogenic and commensal microorganisms. It is thought that an inflammatory response to commensal bacteria is avoided due to sequestration of microflora by surface epithelia. Here, we show that commensal bacteria are recognized by TLRs under normal steady-state conditions, and this interaction plays a crucial role in the maintenance of intestinal epithelial homeostasis. Furthermore, we find that activation of TLRs by commensal microflora is critical for the protection against gut injury and associated mortality. These findings reveal a novel function of TLRs-control of intestinal epithelial homeostasis and protection from injury-and provide a new perspective on the evolution of host-microbial interactions.

Adaptor Proteins, Signal Transducing↗
PubMed2000

A fluorescence microscopy based genetic screen to identify mutants altered for interactions with host cells.

The study of microbial intracellular pathogenesis has benefited from the application of immunofluorescence microscopy to characterize interactions of the pathogen with host cells. Unfortunately, immunofluorescence microscopy is impractical for screening the large number of bacterial mutants necessary to represent the entire genome of the pathogen. Screening has been limited due to the lack of materials suitable for high-throughput processing (e.g. 96-well plates) that also possess the optical features needed for high resolution fluorescence microscopy. Recently marketed 96-well Special Optics (SO) plates provide both the 96-well template ideal for high-throughput analysis and optical features suitable for fluorescence microscopy. Until this work, mutants needed for the study of a fluorescence-based virulence phenotype could not be obtained by direct screening approaches. In this study, SO plates were used to examine 11520 individual Salmonella typhimurium MudJ mutants for the loss of the ability to disrupt host cell endocytic compartments. The direct application of the fluorescence phenotype for screening allowed us to obtain a set of mutants to characterize the formation of lysosomal membrane glycoprotein (lgp) containing tubules upon Salmonella infection of HeLa epithelial cells. This approach will facilitate the characterization of a wide range of microbial phenotypes detectable by fluorescence microscopy.

Antigens, CD↗
PubMed1988

On the dissection of binding epitopes on carbohydrate receptors for microbes using molecular modelling.

The most common receptors for microbes on animal cells seem to be carbohydrates. One characteristic property of microbial protein-carbohydrate interaction is the recognition of sequences placed within an oligosaccharide chain. This leads to a series of isoreceptors defined as saccharides carrying the particular receptor sequence with different neighbouring groups. A microbial ligand may have different binding affinities for such isoreceptors depending upon steric hindrance from neighbouring groups upon access to the binding epitope. By a comparison of binding preferences to a series of isoreceptors with their calculated conformation, the binding epitope on a particular receptor sequence may be approximated by use of molecular modelling. This approach is illustrated for two bacteria recognising lactosylceramide. The potential importance of the procedure for further developments including drug design is briefly discussed.

Animals↗
PubMed1980

[Interest in gnotoxenic systems for the study of host-microbial flora of the digestive tract].

It is necessary to use experimental models in all studies of interactions between a host, its digestive tract microbial flora and the environment because these interactions are complex. The gnotoxenic animal, reared in an isolator as the axenic animal and harbouring a known microbial flora, constitutes either an analytic or mimetic experimental model. The gnotoxenic animal may be considered as an analytic model when used to determine which biotic or abiotic environmental factor of the host-animal plays a role in the intestinal ecosystem. The potential metabolic or immunologic role of a given bacterial strain in the intestinal ecosystem may be determined when the axenic animal is associated with this strain. The variation of the expression of the potential role of this strain in relation to the environment can be ascertained by diversifying the diet of the host or by introducing other bacterial strains into the intestinal ecosystem. The role of an association of strains in host physiology and host protection against potentially pathogenic target strains can also be studied using this analytic model. An analytic model is created by associating either isolated strains of the holoxenic or heated or diluted suspensions of holoxenic digestive tract flora. Axenic mice associated with these simplified flora are called meroxenic. The gnotoxenic animal is considered to be a mimetic model when it harbours a microbial flora isolated from an animal of a different species. The advantage of the mimetic model is that it provides an easy-to-use biological tool, i.e. gnotoxenic mice, to first determine the potential role of these microbial strains. The validity of the mimetic model is then tested by comparing gnotoxenic mice and gnotoxenic piglets or chickens. When all the gnotoxenic animals are given the same diet, this comparison permits an estimation of the animal-host role in the expression of the potential activities of microbial strains. The mimetic model, composed of gnotoxenic animals harbouring microbial strains of human origin, is the only experimental model which can be used to study the role of microorganisms in the intestinal ecosystem of man.

Animals↗
PubMed2006

Effects of polymicrobial communities on host immunity and response.

Microorganisms grow as members of microbial communities in unique niches, such as the mucosal surfaces of the human body. These microbial communities, containing both commensals and opportunistic pathogens, serve to keep individual pathogens 'in check' through a variety of mechanisms and complex interactions, both between the microorganisms themselves and the microorganisms and the host. Recent studies shed new light on the diversity of microorganisms that form the human microbial communities and the interactions these microbial communities have with the host to stimulate immune responses. This occurs through their recognition by dendritic cells or their ability to induce differential cytokine and defensin profiles. The differential induction of defensins by commensals and pathogens and the ability of the induced defensins to interact with the antigens from these microorganisms may attenuate proinflammatory signaling and trigger adaptive immune responses to microbial antigens in a multistep process. Such an activity may be a mechanism that the host uses to sense what is on its mucosal surfaces, as well as to differentiate among commensals and pathogens.

Bacterial Infections↗
PubMed2002

Multiple archaeal groups mediate methane oxidation in anoxic cold seep sediments.

No microorganism capable of anaerobic growth on methane as the sole carbon source has yet been cultivated. Consequently, information about these microbes has been inferred from geochemical and microbiological observations of field samples. Stable isotope analysis of lipid biomarkers and rRNA gene surveys have implicated specific microbes in the anaerobic oxidation of methane (AOM). Here we use combined fluorescent in situ hybridization and secondary ion mass spectrometry analyses, to identify anaerobic methanotrophs in marine methane-seep sediments. The results provide direct evidence for the involvement of at least two distinct archaeal groups (ANME-1 and ANME-2) in AOM at methane seeps. Although both archaeal groups often occurred in direct physical association with bacteria, they also were observed as monospecific aggregations and as single cells. The ANME-1 archaeal group more frequently existed in monospecific aggregations or as single filaments, apparently without a bacterial partner. Bacteria associated with both archaeal groups included, but were not limited to, close relatives of Desulfosarcina species. Isotopic analyses suggest that monospecific archaeal cells and cell aggregates were active in anaerobic methanotrophy, as were multispecies consortia. In total, the data indicate that the microbial species and biotic interactions mediating anaerobic methanotrophy are diverse and complex. The data also clearly show that highly structured ANME-2/Desulfosarcina consortia are not the sole entities responsible for AOM at marine methane seeps. Other microbial groups, including ANME-1 archaea, are capable of anaerobic methane consumption either as single cells, in monospecific aggregates, or in multispecies consortia.

Archaea↗
PubMed2006

Medicinal plant extracts as anti-Escherichia coli O157:H7 agents and their effects on bacterial cell aggregation.

Ethanolic extracts of eight Thai medicinal plants (representing five families) that are used as traditional remedies for treating diarrhea were examined with a salt aggregation test for their ability to modulate cell surface hydrophobicity of enterohemorrhagic Escherichia coli strains, including E. coli O157:H7. Four of these medicinal plants, Acacia catechu, Peltophorum pterocarpum, Punica granatum, and Quercus infectoria, have high bacteriostatic and bactericidal activities. The ethanolic extract of Q. infectoria was the most effective against all strains of E. coli, with MICs of 0.12 to 0.98 mg/ml and MBCs of 0.98 to 3.91 mg/ml. The ethanolic extract of P. granatum had MICs of 0.49 to 1.95 mg/ml and MBCs of 1.95 to 3.91 mg/ml. Ethanolic extracts of Q. infectoria, P. pterocarpum, and P. granatum were among the most effective extracts against the two strains of E. coli O157:H7. The other four plants, Andrographis paniculata, Pluchia indica, Tamarindus indica, and Walsura robusta, did not have high bacteriostatic and bactericidal activities but were able to affect hydrophobicity characteristics on their outermost surface. All plants except Q. infectoria had some ability to increase cell surface hydrophobicity. There appears to be no correlation between antibacterial activity and cell aggregative properties.

Acacia↗
PubMed1994

Microbial adaptation to a changeable environment: cell-cell interactions mediate physiological and genetic differentiation.

Recent work by Magnuson, Solomon and Grossman(1) adds to a growing body of evidence indicating that microorganisms possess sophisticated signaling systems that enable them to sense and respond to environmental challenges. Typically, this response results in morphological, physiological and even genetic differentiation, paralleling that observed among higher organisms. These signaling systems may be interpreted as adaptations that maximize the reproductive potential of a population.

Acclimatization↗
PubMed2002

Interactions between a polycyclic aromatic hydrocarbon mixture and the microbial communities in a natural freshwater sediment.

The toxicity of a polycyclic aromatic hydrocarbon (PAH) mixture was assessed on the indigenous microbial communities of a natural freshwater sediment. The fate and effects of the PAH mixture (phenanthrene, fluoranthene and benzo(k)fluoranthene) were studied over 28 days. Bacterial communities were described by bacterial counts (total bacteria and viable bacteria), and by some hydrolytic enzyme activities (beta-glucosidase and leucine-aminopeptidase), PAH concentrations were measured in the overlying waters and in the sediments. No effect of PAH was detected at 30 mg/kg for all bacterial parameters. At 300 mg/kg, the quantity of total bacteria and the proportion of viable bacteria markedly decreased, compared to the control (0 mg PAH/kg). At 300 mg/kg, an increase of the beta-glucosidase activity and a decrease of the leucine-aminopeptidase activity were observed. For all treatments, the benzo(k)fluoranthene concentration in the sediment was stable over 28 days whereas, in the same time, only 3-6% of the initial concentrations of phenanthrene and fluoranthene remained. This study shows that (1) PAH induce perturbations of sediment microbial communities in terms of density and metabolism (but not always as an inhibition), (2) indigenous bacteria of sediments might be used for toxicity assessment of specific organic pollutants, (3) native microorganisms of sediment seem to have a high capacity for PAH degradation, depending on the physico-chemical properties and the bioavailability of the substance encountered.

Bacteria↗
PubMed2004

Gnotobiotic zebrafish reveal evolutionarily conserved responses to the gut microbiota.

Animals have developed the means for supporting complex and dynamic consortia of microorganisms during their life cycle. A transcendent view of vertebrate biology therefore requires an understanding of the contributions of these indigenous microbial communities to host development and adult physiology. These contributions are most obvious in the gut, where studies of gnotobiotic mice have disclosed that the microbiota affects a wide range of biological processes, including nutrient processing and absorption, development of the mucosal immune system, angiogenesis, and epithelial renewal. The zebrafish (Danio rerio) provides an opportunity to investigate the molecular mechanisms underlying these interactions through genetic and chemical screens that take advantage of its transparency during larval and juvenile stages. Therefore, we developed methods for producing and rearing germ-free zebrafish through late juvenile stages. DNA microarray comparisons of gene expression in the digestive tracts of 6 days post fertilization germ-free, conventionalized, and conventionally raised zebrafish revealed 212 genes regulated by the microbiota, and 59 responses that are conserved in the mouse intestine, including those involved in stimulation of epithelial proliferation, promotion of nutrient metabolism, and innate immune responses. The microbial ecology of the digestive tracts of conventionally raised and conventionalized zebrafish was characterized by sequencing libraries of bacterial 16S rDNA amplicons. Colonization of germ-free zebrafish with individual members of its microbiota revealed the bacterial species specificity of selected host responses. Together, these studies establish gnotobiotic zebrafish as a useful model for dissecting the molecular foundations of host-microbial interactions in the vertebrate digestive tract.

Air Sacs↗