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.

SourceResearch connectionFrom yearThrough year

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

At least 901 records · Page 50Linked to original sources

PubMed2001

Bacterial interactions with contact lenses; effects of lens material, lens wear and microbial physiology.

Contact lens wear is a successful form of vision correction. However, adverse responses can occur during wear. Many of these adverse responses are produced as a consequence of bacterial colonization of the lens. The present study demonstrated that during asymptomatic contact lens wear lenses are colonized by low levels of bacteria with gram-positive bacteria, such as coagulase negative staphylococci, predominating. Gram-negative bacteria are frequently the causative agents of adverse responses during contact lens wear. Measuring the adhesion of different strains and/or species of bacteria to different contact lens materials demonstrated considerable differences. In particular. Pseudormonas aeruginosa strains Paerl and 6294 and Aeromonas hydrophilia strain Ahyd003 adhered in larger numbers to the highly oxygen permeable contact lenses Balafilcon A compared to hydrogel lenses manufactured from either Etafilcon A or HEMA. Furthermore, after Balafilcon A lenses had been worn for 6 h during the day bacteria were able to adhere in greater numbers to the worn lenses compared to the unworn lenses with increases in adhesion ranging from 243% to 1393%. However, wearing Etafilcon A lenses usually resulted in a decrease in adhesion (22-48%). Bacteria were able to grow after adhesion to lenses soaked in artificial tear fluid and formed biofilms, visualized by scanning confocal microscopy. Chemostat grown bacterial cultures were utilized to enable control of bacterial growth conditions and bacteria were shown to adhere in the greatest numbers if grown under low temperature (25 degrees C compared to 37 degrees C). The changes in growth temperature was shown. using 2D gel electrophoresis, to change the experssion of cell-surface proteins and, using ID gel electrophoresis, to change the expression of surface lipopolysaccharide of P. aeruginosa Paerl. Thus, these surface changes would have been likely to have mediated the increased adhesion to Etafilcon A contact lenses.

Aeromonas hydrophila↗

PubMed1998

Could synergistic interactions among reactive oxygen species, proteinases, membrane-perforating enzymes, hydrolases, microbial hemolysins and cytokines be the main cause of tissue damage in infectious and inflammatory conditions?

The mechanisms of cellular damage caused by infectious and inflammatory processes are complex and are still not fully understood. There is, however, a consensus that reactive oxygen species (ROS) generated by phagocytes migrating to injured tissues might be the main agents responsible for cellular damage in inflammatory processes. However, because both activated phagocytes and catalase-negative, peroxide-producing, toxigenic bacteria (Streptococci, Clostridiae) secrete a near-identical array of proinflammatory agonists, including reactive oxygen species (ROS), and because these microbial species might kill their targets by a synergism among several of their secreted enzymes (a multicomponent system), we postulated that activated phagocytes might also function in the same way. Using radiolabeled targets, in culture, we demonstrated that subtoxic amounts of a variety of oxidants (H2O2, radicals produced by xanthine-xanthine-oxidase, peroxyl radical, NO) acted synergistically with subtoxic amounts of a large series of membrane-perforating agents (microbial hemolysins, phospholipases, fatty acids, cationic proteins, proteinases, bile salts, the attack complex of complement, the xenobiotics, lindane, ethanol, methanol) to kill cells in culture and to release large amounts of arachidonic acid and metabolites. Membrane perforators might act primarily to overcome the potent antioxidant systems present in all mammalian cells and scavengers of ROS and inhibitors of the additional agonists might act to abolish the synergism among ROS and the membrane-damaging agents. It is also proposed that protection against tissue damage in vivo should also include 'cocktails' of appropriate antagonists. It is enigmatic that those publications which do describe both in-vitro and in-vivo models proposing that a synergism among a multiplicity of agonists might truly represent the mechanisms by which tissues are injured, in vivo, are hardly ever quoted in the current literature.

Animals↗

PubMed2005

Multifunctional roles of lactoferrin: a critical overview.

Lactoferrin (LF) is a member of the transferrin family that is expressed and secreted by glandular epithelial cells and is found in the secondary granules of neutrophils. Originally viewed as an iron-binding protein in milk, with bacteriostatic properties, it is becoming increasingly evident that LF is a multifunctional protein to which several physiological roles have been attributed. These include regulation of iron homeostasis, host defense against a broad range of microbial infections, anti-inflammatory activity, regulation of cellular growth and differentiation and protection against cancer development and metastasis. While iron binding is likely central to some of the biological roles of LF, other activities, including specific interactions with mammalian receptors and microbial components, also contribute to the pleoitropic functional nature of this protein. In this article, recent advances in the understanding of these functions at the cellular and molecular level are discussed.

Animals↗

PubMed1998

Host-microbial symbiosis in the mammalian intestine: exploring an internal ecosystem.

The mammalian intestine contains a complex, dynamic, and spatially diversified society of nonpathogenic bacteria. Very little is known about the factors that help establish host-microbial symbiosis in this open ecosystem. By introducing single genetically manipulatable components of the microflora into germfree mice, simplified model systems have been created that will allow conversations between host and microbe to be heard and understood. Other paradigms of host-microbial symbiosis suggest that these interactions will involve an exchange of biochemical signals between host and symbionts as well as among the bacteria themselves. The integration of molecular microbiology, cell biology, and gnotobiology should provide new insights about how we adapt to a microbial world and reveal the roles played by our indigenous, 'nonpathogenic' flora.

Adaptation, Physiological↗

PubMed2004

The behaviour of microbes.

Viruses and bacteria have complex interactions with their hosts, beyond mere replication in them. They range from those that are detrimental, to others that may be non-pathogenic or even beneficial. Molecular techniques can help to unravel these interactions, sometimes revealing phenomena that benefit host as well as microbial populations.

Adaptation, Physiological↗

PubMed2005

Clarithromycin destroys biofilms and enhances bactericidal agents in the treatment of Pseudomonas aeruginosa osteomyelitis.

In this study, the effect of clarithromycin on the destruction of bacterial biofilm in Pseudomonas aeruginosa osteomyelitis was investigated. Foreign body-related osteomyelitis caused by ceftazidime-sensitive Pseudomonas aeruginosa was produced in the tibias of 26 rats. After osteomyelitis was verified on Day 14, 10 rats had ceftazidime (1500 mg/kg/day) given subcutaneously, and 10 rats had ceftazidime given subcutaneously and clarithromycin (100 mg/kg/day, two 50-mg/kg doses every 12 hours) given orally; three rats formed the control group. After a treatment period of 20 days, the tibias and the foreign bodies were removed, cultured, and examined by electron microscopy. The number of microorganisms growing on the bone tissue in the group receiving combined treatment was significantly lower than in the other groups. The number of microorganisms growing on the foreign body in the group receiving only ceftazidime was significantly higher than that of the group receiving combined treatment. Electron microscope examination revealed that the biofilm layer was eradicated in the group that had combined therapy; however, biofilm formation was evident on the foreign body in the group receiving only ceftazidime. Clarithromycin enhanced the activity of concomitantly used bactericidal agents by destroying biofilm on the surface of the materials.

Animals↗

PubMed1996

Co-adhesion of oral microbial pairs under flow in the presence of saliva and lactose.

Co-aggregation (interactions between two suspended micro-organisms) between oral microbial pairs has been studied extensively and is believed to be an important factor in dental plaque formation. However, co-adhesion (interactions between suspended and already-adhering micro-organisms) may well be equally important. The aim of this paper was to determine the influence of saliva and lactose on the co-adhesion of streptococci (S. oralis 34 and S. sanguis PK1889) to actinomyces (A. naeslundii T14V-J1 or 5951) adhering on glass under flow from buffer and saliva in the absence and presence of lactose. The kinetics of co-adhesion as well as co-adhesion in a stationary end-point of co-aggregating and non-co-aggregating pairs was studied in a parallel plate flow chamber by analysis of the spatial arrangement of co-adhering micro-organisms as a function of time. For co-aggregating pairs, initial deposition rates of streptococci in the immediate vicinity of adhering actinomyces (local initial deposition rates) were up to 5 to 10 times higher than the non-local initial deposition rates in buffer and in saliva, respectively. In a stationary end-point of co-adhesion, 5 to 6 times more streptococci co-adhered with the adhering actinomyces than averaged over the entire substratum surface. A non-co-aggregating pair showed only minor preferential (co-)adhesion near the adhering actinomyces. Co-adhesion in buffer was fully lost when lactose was added. However, addition of lactose to saliva did not inhibit co-adhesion, but co-adhesion became more reversible. Detachment of micro-organisms from the substratum due to the passage of an air-liquid interface, as occurs in the oral cavity during eating, drinking, and speaking, was minimal when deposition was carried out from buffer to bare glass. Major detachment of streptococci adhering to the substratum occurred when adhesion was mediated through a salivary conditioning film on the glass, while detachment of adhering actinomyces and streptococci co-adhering with them remained low. It is suggested that, in the development of dental plaque, adhering actinomyces may act as strongholds for other micro-organisms, like streptococci, to adhere.

Actinomyces↗

PubMed1985

Bioreactor for the study of defined interactions of toxic metals and biofilms.

A novel bioreactor system constructed for studies of the interactions of heavy metals and microbial cells at the solid-solution interface is described. The applicability of this experimental system to meet the severe constraints imposed on such an apparatus by the requirements for an unambiguous interpretation of data and for mathematical modeling of these interactions was explored with the trace metal lead and with the marine bacterium Pseudomonas atlantica. A chemically defined medium composed of the major components of seawater, simple salts required for growth, glucose, and the single amino acid glycine was derived. It supported a maximum growth rate several times less than that in a complex medium, but provided growth to high cell densities and the formation of biopolymer and supported the development of a monolayer biofilm. The use of such a medium in conjunction with our bioreactor system minimized trace metal contamination while allowing quantification of the partitioning of lead onto various reactor surfaces. Lead adsorption by reactor walls and model surfaces was linear with equilibrium led concentration up to 6 X 10(-6) mol/liter. Equilibrium lead adsorption due to P. atlantica biofilm surfaces ranged from 20 to 40% at a total lead concentration of 10(-6) mol/liter depending upon solution pH and ionic composition, indicating that biofilms can play an important role in controlling toxic metal concentrations in natural systems.

Bacteria↗

PubMed2002

Infectomics: genomics and proteomics of microbial infections.

The completion of genomic sequences is the greatest triumph of molecular reductionism since the discovery of the DNA double helix in 1953. However, the utility of reductionism is becoming limited and holistic approaches, including theories and techniques, are desperately needed in the postgenomic era. In the field of infectious diseases there is an urgent need for global approaches that can efficiently, precisely and integratively study structural and functional genomics and proteomics of microbial infections (infectomics). The combination of new (e.g. DNA and protein microarrays) and traditional approaches (e.g. cloning, PCR, gene knockout and knockin, and antisense) will help overcome the challenges we are facing today. We assume that the global phenotypic changes (infectomes) in microbes and their host during infections are encoded by the genomes of microbial pathogens and their hosts, expressed in certain environmental conditions devoted to specific microbe-host interactions. Global drug responses (pharmacomes) in microbes and their host can be detected by genomic and proteomic approaches. Genome-wide approaches to genotyping and phenotyping or expression profiling will eventually lead to global dissection of microbial pathogenesis, efficient and rapid diagnosis of infectious diseases, and the development of novel strategies to control infections. The key fundamental issue of infectious diseases is how to globally and integratively understand the interactions between microbial pathogens and their hosts by using infectomics. In this review, we focus on the events that are considered important in infectomics.

Animals↗

PubMed2026

Functional analysis of Candida albicans protein kinases identifies Crk1 as a modulator of epithelial cell damage.

UNLABELLED: The commensal and pathogenic lifestyles of the opportunistic fungal pathogen Candida albicans require complex signaling networks regulated by protein kinases. To investigate the role of C. albicans protein kinases at the intestinal epithelial interface, we screened a comprehensive protein kinase deletion library for the capacity of the mutants to damage intestinal epithelial cells (IEC). Mutants showing altered IEC cytotoxicity relative to the wild type were further analyzed for their growth and morphology, focusing on hyper-damaging strains to identify kinases that rather prevent host cell damage. Deletion of CRK1 caused increased IEC-specific damage, despite slower growth, reduced hyphal length, and reduced adhesion as compared to wild-type cells. While tissue invasion levels and the formation of transcellular tunnels of the crk1Δ/Δ mutant were increased, the translocation capacity through the IEC barrier was reduced. Transcriptional and metabolic profiling suggested a role for Crk1 in metabolic adaptation to carbon and nitrogen sources, which was validated by showing that high glucose and amino acids are required for crk1Δ/Δ to cause increased IEC damage. Deletion of CRK1 rendered C. albicans more susceptible to cell wall and membrane stressors, but caused higher resistance to a catalase-specific and histidine biosynthesis inhibitor. This phenotypic pattern of medium- and epithelial cell type-specific cytotoxicity displayed by a C. albicans protein kinase mutant suggests that Crk1 regulates processes linked to carbon and amino acid metabolism that are relevant to interactions with intestinal epithelial cells. IMPORTANCE: Microbial signal transduction pathways regulate adaptation to changing environmental conditions and facilitate the success of many microbes during interactions with their hosts. The fungal pathobiont Candida albicans exists as a harmless commensal on mucosal surfaces of most humans but can also cause superficial and invasive infections under certain circumstances. Both lifestyles require complex signaling networks, predominantly regulated by protein kinases. The C. albicans genome was predicted to encode 108 protein kinases, yet nearly 50% remain uncharacterized. We aimed to dissect the role of C. albicans protein kinases during the transition from commensal to pathogen. We showed that multiple protein kinase genes are involved in epithelial cell damage. Particularly, the protein kinase gene Crk1 was of interest because deletion of CRK1 caused increased damage to intestinal epithelial cells under distinct conditions. Our study links Crk1 with regulation of metabolic processes relevant for commensalism and pathogenicity of C. albicans.

Candida albicans↗

PubMed2007

Genomics of host-pathogen interactions.

The complete sequences of hundreds of microbial genomes have provided drug discovery pipelines with thousands of new potential drug targets. Their availability has also stimulated the development of a variety of innovative approaches that allow functional studies to be performed on the entire genome of an organism. This chapter describes how these approaches have been applied to the analysis of host-pathogen interactions and discusses how such studies might facilitate the development of new antibiotics.

Anti-Bacterial Agents↗

PubMed1990

Formation and physiological role of biosurfactants produced by hydrocarbon-utilizing microorganisms. Biosurfactants in hydrocarbon utilization.

Microbial growth on water-insoluble carbon sources such as hydrocarbons is accompanied by metabolic and structural alterations of the cell. The appearance of surface-active compounds (biosurfactants) in the culture medium or attached to the cell boundaries is often regarded as a prerequisite for initial interactions of hydrocarbons with the microbial cell. Under this point of view, biosurfactants produced by hydrocarbon-utilizing microorganisms, their structures and physico-chemical properties are reviewed. The production of such compounds is mostly connected with growth limitation in the late logarithmic and the stationary growth phase, in which specific enzymes are induced or derepressed. Addition of purified biosurfactants to microbial cultures resulted in inhibitory as well as in stimulatory effects on growth. Therefore, a more differentiated view of microbial production of surface-active compounds is proposed. Biosurfactants should not only be regarded as prerequisites of hydrocarbon uptake, but also as secondary metabolic products.

Bacteria↗

PubMed1995

Bacterial pyrogenic exotoxins as superantigens.

The recent discovery of the mode of interaction between a group of microbial proteins known as superantigens and the immune system has opened a wide area of investigation into the possible role of these molecules in human diseases. Superantigens produced by certain viruses and bacteria, including Mycoplasma species, are either secreted or membrane-bound proteins. A unique feature of these proteins is that they can interact simultaneously with distinct receptors on different types of cells, resulting in enhanced cell-cell interaction and triggering a series of biochemical reactions that can lead to excessive cell proliferation and the release of inflammatory cytokines. However, although superantigens share many features, they can have very different biological effects that are potentiated by host genetic and environmental factors. This review focuses on a group of secreted pyrogenic toxins that belong to the superantigen family and highlights some of their structural-functional features and their roles in diseases such as toxic shock and autoimmunity. Deciphering the biological activities of the various superantigens and understanding their role in the pathogenesis of microbial infections and their sequelae will enable us to devise means by which we can intervene with their activity and/or manipulate them to our advantage.

Autoimmune Diseases↗

PubMed2003

Antagonism between bacteria and fungi on decomposing aquatic plant litter.

Bacterial and fungal decomposers of aquatic plant litter may exhibit either synergistic or antagonistic interactions, which are likely to influence microbial growth as well as the decomposition of litter and, eventually, the carbon metabolism of aquatic systems. To elucidate such interactions, we inoculated decomposing Phragmites culms in microcosms with fungal isolates and with natural communities of bacteria and fungi in different combinations. The development of fungal and bacterial biomass and the carbon dynamics were studied during several months of degradation. The results show a bilateral antagonistic relationship between bacteria and fungi. After 3 months, fungal biomass accumulation was approximately 12 times higher in the absence than in the presence of bacteria. Bacterial biomass accumulation was about double in the absence of fungi compared to when fungi were present. Similar interactions developed between a natural assemblage of bacteria and five different fungal strains isolated from Phragmites litter (three identified hyphomycetes and two unidentified strains). Despite the great difference in biomass development between the treatments, the carbon metabolism was similar regardless of whether fungi and/or bacteria were present alone or in coexistence. We suggest that the antagonism between bacteria and fungi is an important controlling factor for microbial colonization and growth on aquatic plant litter.

Bacteria↗

PubMed2005

Assessment of potential interactions between phytase and glycosidase enzyme supplementation on nutrient digestibility in broilers.

The effects of microbial 3-phytase and glycosidase enzymes, and their interactions, on energy values and nutrient digestibility in diets rich in nonstarch polysaccharides (NSP) were studied in diets based on corn, wheat, or barley. Four diets were prepared with each cereal grain. One had no enzymes, a second had 500 units of phytase, a third had glycosidase enzyme, and a fourth had phytase and glycosidase. The glycosidases used were alpha-galactosidase (corn diet), xylanase (wheat), and beta-glucanase (barley). Glycosidase decreased intestinal viscosity, whereas phytase increased this parameter in corn diets. Phytase increased AME in corn diets, whereas beta-glucanase in barley diets improved AME and AMEn, and digestibility of dry matter, starch, beta-glucans, and lipid. Xylanase in wheat diets improved dry matter and starch digestibility. Phytase increased total phosphorus retention in all diets, and significant interactions between glycosidase enzymes and phytase were detected in wheat and barley diets. Phytase decreased phosphorus excretion in corn and barley diets, whereas alpha-galactosidase increased phosphorus excretion in corn diets. Phytase in corn diets and beta-glucanase in barley diets increased calcium retention, whereas inclusion of xylanase decreased calcium retention in wheat diets. Phytase and beta-glucanase decreased calcium excretion in corn- and barley-based diets, respectively. An interaction was detected between phytase and beta-glucanase in barley diets, in which calcium excretion was reduced. In general, no negative interactions between phytase and glycosidase enzymes were found, indicating that both types of enzymes may be used together in feeds based on corn, wheat, or barley.

6-Phytase↗

PubMed2006

Soluble adamantyl glycosphingolipid analogs as probes of glycosphingolipid function.

Despite the extensive structural characterization of glycosphingolipids (GSLs), their functions in cell physiology and pathobiology remain elusive. This is largely owing to the fact that they are difficult to handle, being insoluble in aqueous media, and that no one gene alone determines their synthesis. The heterogeneity of the lipid moiety provides a further confounding factor. GSLs are central components within lipid rafts, which are major foci for transmembrane signaling and interactions between eukaryotic cells and microbial pathogens. GSL receptor function often requires the lipid moiety, and lipid-free sugar analogs are ineffective inhibitors. In order to overcome some of these problems, we have synthesized adamantyl GSL analogs which, in part, mimic GSL membrane receptor function in solution. These compounds are made by replacing the endogenous fatty acid with an adamantan frame. This rigid hydrophobic structure surprisingly increases the water solubility of the conjugate and retains receptor function. These GSL mimics provide probes to study GSL receptor function within cells. They compete with native GSLs for ligand binding and are taken up by cells to potentially alter GSL-mediated interaction. We are focused on two derivatives, adamantyl globotriaosyl ceramide and adamantyl sulfogalactosyl ceramide, and have used these analogs to probe GSL function in microbial pathology and hsp70 function. This chapter describes the syntheses and uses of these mimics.

Adamantane↗

PubMed2003

Microbial globins.

Globins are an ancient and diverse superfamily of proteins. The globins of microorganisms were relatively ignored for many decades after their discovery by Warburg in the 1930s and rediscovery by Keilin in the 1950s. The relatively recent focus on them has been fuelled by recognition of their structural diversity and fine-tuning to fulfill (probably) discrete functions but particularly by the finding that a major role of certain globins is in protection from the stresses caused by exposure to nitric oxide (NO)--itself a molecule that has attracted intense curiosity recently. At least three classes of microbial globin are recognised, all having features of the classical globin protein fold. The first class is typified by the myoglobin-like haemprotein Vgb from the bacterium Vitreoscilla, which has attracted considerable attention because of its ability to improve growth and metabolism for biotechnological gain in a variety of host cells, even though its physiological function is not fully understood. The truncated globins are widely distributed in bacteria, microbial eukaryotes as well as plants and are characterised by being 20-40 residues shorter than Vgb. The polypeptide is folded into a two-over-two helical structure while retaining the essential features of the globin superfamily. Roles in oxygen and NO metabolism have been proposed. The third and best understood class comprises the flavohaemoglobins, which were first discovered and partly characterised in yeast. These are distinguished by the presence of an additional domain with binding sites for FAD and NAD(P)H. Widely distributed in bacteria, these proteins undoubtedly confer protection from NO and nitrosative stresses, probably by direct consumption of NO. However, a bewildering array of enzymatic capabilities and the presence of an active site in the haem pocket reminiscent of peroxidases hint at other functions. A full understanding of microbial globins promises advances in controlling the interactions of pathogenic bacteria with their animal and plant hosts, and manipulations of microbial oxygen transfer with biotechnological applications.

Amino Acid Sequence↗

PubMed2003

Recent progress in the application of atomic force microscopy imaging and force spectroscopy to microbiology.

Atomic force microscopy imaging and force spectroscopy have recently opened a range of novel applications in microbiology. During the past two years, rapid advances have been made using atomic force microscopy to visualize the surface structure of two-dimensional bacterial protein crystals, biofilms and individual cells in physiological conditions. There has also been remarkable progress in using force spectroscopy to measure biomolecular interactions and physical properties of microbial surfaces. Specific highlights include the imaging and manipulation of membrane proteins at the subnanometer level, the observation of the surface of living cells at high resolution, the mapping of local properties such as surface charges, the measurement of elastic properties of cell-surface constituents and the probing of cellular interactions using functionalized probes.

Bacteria↗