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At least 613 records · Page 34Linked to original sources
PubMed1986

Enzyme-substrate interactions in the hydrolysis of peptide substrates by thermitase, subtilisin BPN', and proteinase K.

Peptide substrates of the general structure acetyl-Alan (n = 2-5), acetyl-Pro-Ala-Pro-Phe-Alan-NH2 (n = 0-3), and acetyl-Pro-Ala-Pro-Phe-AA-NH2 (AA = various amino acids) were synthesized and used to investigate the enzyme-substrate interactions of the microbial serine proteases thermitase, subtilisin BPN', and proteinase K on the C-terminal side of the scissile bond. The elongation of the substrate peptide chain up to the second amino acid on the C-terminal side (P'2) enhances the hydrolysis rate of thermitase and subtilisin BPN', whereas for proteinase K an additional interaction with the third amino acid (P'3) is possible. The enzyme subsite S'1 specificity of the proteases investigated is very similar. With respect to kcat/Km values small amino acid residues such as Ala and Gly are favored in this position. Bulky residues such as Phe and Leu were hydrolyzed to a lower extent. Proline in P'1 abolishes the hydrolysis of the substrates. Enzyme-substrate interactions on the C-terminal side of the scissile bond appear to affect kcat more than Km for all three enzymes.

Chymotrypsin↗
PubMed1999

Fungal resistance.

Fungal resistance is caused by an acquisition of intrinsically resistant species, by selection of resistant strains from a population or by mutation of an initially susceptible strain. According to different classes of antimycotics there are different resistance mechanisms: differences in the uptake mechanisms, drug target alterations, mostly the ergosterol-biosynthesis pathway, and the efflux or pumping mechanisms to the outside.

Animals↗
PubMed1990

Recent advances in rumen microbial ecology and metabolism: potential impact on nutrient output.

Feedstuffs consumed by ruminants are all initially exposed to fermentative activity in the rumen prior to gastric and intestinal digestion. The extent and type of transformation of feedstuffs thus determines the productive performance of the host. Research on rumen microbial ecology and metabolism is essentially a study of the interactions between the host, microorganisms present, substrates available, and end products of digestion. Furthermore, the interactions of the normal microbial flora with the host can be manipulated to improve the efficiency of nutrient utilization in ruminant animals. Three important areas of ruminal fermentation will be reviewed, N metabolism, fiber degradation, and biotransformation of toxic compounds. The extent of protein degradation and the rate of uptake of resultant peptides and ammonia are extremely important factors in determining the efficiency of N utilization by rumen bacteria and, therefore, the relative amounts of microbial or bypass protein available to the host. Strategies aimed at identifying and characterizing rate-limiting enzymes of cellulolytic bacteria are essential in elucidating mechanisms involved in ruminal fiber degradation. Results obtained with ruminococci will be described. The detoxification of phytotoxins by passage through the gastrointestinal tract of ruminants is a process deserving special attention and several examples will be presented. Opportunities for manipulation of rumen fermentation are good. However, successful manipulation and full exploitation depend on a through understanding of the mechanisms involved.

Animal Feed↗
PubMed2004

Nanoscale investigation of pathogenic microbial adhesion to a biomaterial.

Microbial infections of medical implants occur in more than 2 million surgical cases each year in the United States alone. These increase patient morbidity and mortality, as well as patient cost and recovery time. Many treatments are available, but none are guaranteed to remove the infection. In many cases, the device infections are caused by the adhesion of microbes to the implant, ensuing growth, pathogenesis, and dissemination. The purpose of this work is to examine the initial events in microbial adhesion by simulating the approach and contact between a planktonic cell, immobilized on an atomic force microscope (AFM) cantilever, and a biomaterial or biofilm substrate. The two model microbes used in this study, Candida parapsilosis (ATCC 90018) and Pseudomonas aeruginosa (ATCC 10145), were chosen for both their clinical relevance and their ease of acquisition and handling in the laboratory setting. Attractive interactions exist between C. parapsilosis and both unmodified silicone rubber and P. aeruginosa biofilms. Using C. parapsilosis cells immobilized on AFM cantilevers with a silicone substrate, we have measured attractive forces of 4.3 +/- 0.25 nN in the approach portion of the force cycle. On P. aeruginosa biofilms, the magnitude of the attractive force decreases to 2.0 +/- 0.40 nN and is preceded by a 2.0-nN repulsion at approximately 75 nm from the cell surface. These data suggest that C. parapsilosis may adhere to both silicone rubber and P. aeruginosa biofilms, possibly contributing to patient morbidity and mortality. Characterization of cell-biomaterial and cell-cell interactions allows for a quantitative link between the physicomechanical and physicochemical properties of implant materials and the nanoscale interactions leading to microbial colonization and infection.

Bacterial Adhesion↗
PubMed2026

Friends or foes: Unraveling the tsetse fly-Spiroplasma symbiosis.

Tsetse flies (Glossina spp.) transmit African trypanosomes, the causative agents of human African and African animal trypanosomiases (HAT and AAT, respectively). These neglected tropical diseases impose significant public health and economic burdens across sub-Saharan Africa. Trypanosome transmission by tsetse flies is influenced by multiple factors, including host genetic background, ecological factors, and interactions with heritable microbial endosymbionts. Spiroplasma glossinidia has recently emerged as an important modulator of tsetse reproductive fitness and vector competence, making it a potential target for symbiont-based vector control strategies. In this review, we summarize the current knowledge of the tsetse-Spiroplasma symbiosis. We detail Spiroplasma's spatial and temporal infection dynamics in laboratory-reared and natural populations. Additionally, we highlight key aspects of the bacterium's genomics, phylogenetics, and physiological interactions with its tsetse host, including influences on host gene expression reproductive physiology, and vector competence. Finally, we discuss how the tsetse-Spiroplasma symbiosis could be harnessed to develop innovative, biological-based vector control and trypanosome transmission-blocking strategies, and we identify critical gaps that must be addressed to translate these findings into effective disease control interventions.

Animals↗
PubMed1977

Elastases from human and canine granulocytes, II. Interaction with protease inhibitors of animal, plant, and microbial origin.

Inhibitors of animal, plant, and microbial origin were tested against human and canine granulocytic elastases. The trypsin-chymotrypsin inhibitors from dog submandibular glands, from soybeans (Bowman-Birk) and from chickpeas show strong interaction with these proteases (Ki = 10(-8) - 10(-9)M). The trypsin-kallikrein inactivator of bovine organs (Trasylol) is not active against granulocytic elastases or against human granulocytic cathepsin G. Elastatinal, a specific inhibitor of elastases, isolated from actinomycetes (Streptomyces griseoruber), forms stable complexes with elastase from human (Ki = 6.2 X 10(-6)M) and canine granulocytes (Ki = 1.1 X 10(-6)M). A possible therapeutic application of these inhibitors for the inactivation of granulocytic proteases, which are able to degrade connective tissue in different pathological states, is discussed.

Animals↗
PubMed2005

Complete conversion of nitrate into dinitrogen gas in co-cultures of denitrifying bacteria.

In the past 10 years many molecular aspects of microbial nitrate reduction have been elucidated, but the ecophysiology of this process is hardly understood. In this contribution, our efforts to study the complex microbial communities and interactions involved in the reduction of nitrate to dinitrogen gas are summarized. The initial work concentrated on emission of the greenhouse gas nitrous oxide during incomplete denitrification by Alcaligenes faecalis. As more research methods became available, the fitness of A. faecalis could be tested in mixed cultures with other denitrifying bacteria, most notably with the nitrate-reducing bacterium Pseudomonas G9. Finally, the advancement of molecular diagnostic tools made it possible to survey complex microbial communities using specific primer sets for/and antibodies raised against the various NO(x) reductases. Given the enormous complexity of substrates and environmental conditions, it is evident that mixed cultures rather than single species are responsible for denitrification in man-made and natural ecosystems. However, it is surprising that even for the breakdown of a single compound, such as acetate, mixed cultures are responsible, and that the consecutive denitrification steps are commonly performed by mutualistic co-operating species. Our observations also indicate that we seldom know the identity of the major key players in the nitrogen cycle of these ecosystems.

Alcaligenes faecalis↗
PubMed2003

Natural killer cells: emerging concepts in immunity to infection and implications for assessment of immunodeficiency.

PURPOSE OF REVIEW: As the molecular networks that connect innate and adaptive immunity are untangled, the prominence of natural killer (NK) cells in host defense continues to emerge. Herein we highlight recent findings pertaining to NK cell development, trafficking, and interactions with other innate and adaptive immune cells in the context of predicting how NK cells may be involved in a wider range of clinical immunodeficiency. RECENT FINDINGS: NK cells contribute vital roles in innate and adaptive immunity, especially in collaboration with dendritic cells (DC). Fascinating new details have been reported about cell surface integrins and receptors that regulate NK functions, as well as the cytokine/chemokine networks that provide for NK-DC interactions. Moreover, NK cells appear to play an important role in the attenuation or resolution of an immune response through either action against CD8 T cells or indirect control of certain DC. These findings shed important insights as to how NK cells and DC cooperate to control primary infections and shape the subsequent adaptive immune responses. SUMMARY: Natural killer cells are heterogeneous lymphocytes that provide an essential function in host defense. NK cells respond early to microbial assault and interact with other cells of the innate immune system, but they recognize and intercept pathogenic infections through highly specific mechanisms that are similar to T cells. Thus, NK cells are positioned as a cellular bridge between innate and adaptive immunity. It is imperative, then, to include a careful assessment of NK cell populations and functions in most cases of suspected immunodeficiency.

Animals↗
PubMed2005

Biological and chemical interactions with U(VI) during anaerobic enrichment in the presence of iron oxide coated quartz.

Microcosm experiments were performed to understand chemical and biological interactions with hexavalent uranium (U(VI)) in the presence of iron oxide bearing minerals and trichloroethylene (TCE) as a co-contaminant. Interactions of U(VI) and hydrous iron oxide moieties on the mineral oxide surfaces were studied during enrichments for dissimilatory iron reducing (DIRB) and sulfate reducing bacteria (SRB). Microbes enriched from groundwater taken from the Test Area North (TAN) site at the Idaho National Laboratory (INL) were able to reduce the U(VI) in the adsorption medium as well as the iron on quartz surfaces. Early in the experiment disappearance of U(VI) from solution was a function of chemical interactions since no microbial activity was evident. Abiotic removal of U(VI) was enhanced in the presence of carbonate. As the experiment proceeded, further removal of U(VI) from solution was associated with the fermentation of lactate to propionate and acetate. During later phases of the experiment when lactate was depleted from the growth medium in the microcosm containing the DIRB enrichments, U(VI) concentrations in the solution phase increased until additional lactate was added. When additional lactate was added and fermentation proceeded, U(VI) concentrations in the liquid phase again returned to near zero. Similar results were shown for the SRB enrichment but lower uranium concentrations were seen in the liquid phase, while in the enrichment with carbonate a similar increase in uranium concentration was not seen. Chemical and biological interactions appear to be important on the mobilization/immobilization of U(VI) in an iron oxide system when TCE is present as a co-contaminant. Interestingly, TCE present in the microcosm experiments was not dechlorinated which was probably an effect of redox conditions that were unsuitable for reductive dechlorination by the microbial culture tested.

Adsorption↗
PubMed2006

Dendritic cells in pathogen recognition and induction of immune responses: a functional genomics approach.

At the 38th Annual Meeting of the Society for Leukocyte Biology held in Oxford this year, the biology of dendritic cells (DCs) and macrophages was discussed. In particular, functional genomics approaches were presented to investigate transcriptional changes during microbe and phagocytes interactions. Here, we report functional genomics studies likely to be of interest to the Journal of Leukocyte Biology readers with a particular emphasis on DC biology. DCs are professional antigen-presenting cells, which are essential for the initiation and regulation of natural killer, T, and T regulatory cell responses. Immature DCs, resident in peripheral sites, are specialized in antigen capture and continually sample soluble and particulate antigens in their local environment. DCs express receptors for cytokines, chemokines, endogenous danger signals, and microbial structures. The interactions between DCs and microorganism are complex, but progress in the past few years has shed light on several aspects of these processes. Infectious disease is the result of an intimate relationship between pathogens and hosts. Thus, understanding the cross-talk between host and pathogen is essential to improve our knowledge of infectious disease. Functional genomics and proteomics applied to DCs and macrophage biology are now providing powerful tools to dissect, at the molecular level, host-pathogen interactions.

Animals↗
PubMed1989

Activation of a murine T-cell hybridoma by cationized bacteria.

Cationic particles interact by electrostatic forces with membrane components of diverse cell types, including lymphocytes. Contact with cationized streptococci was shown to induce a murine T-cell hybridoma to transcribe lymphokine mRNA as well as secrete interleukin-2. This activation was accompanied by a rise in intracellular calcium. Cationized streptococci-induced activation of this T-cell hybridoma could be specifically inhibited by either chelating extracellular calcium or by treating with CD4 monoclonal antibody. These data indicate that the in vitro behaviour of T cells can be modulated by charged microbial particles; such interactions may have relevance for chronic inflammation associated with some bacterial infections.

Animals↗
PubMed2004

Dendritic cell-derived IL-2 production is regulated by IL-15 in humans and in mice.

Dendritic cells (DCs) are involved in the initiation and regulation of innate and adaptive immune responses. Several molecular mechanisms regulate these diverse DC functions, and we have previously reported that mouse dendritic cells (mDCs) can produce interleukin-2 (IL-2) in vitro and in vivo, in response to microbial activation and T-cell-mediated stimuli. This property is shared by different DC subtypes, including Langerhans cells. Here we show that, on appropriate stimulation, human DCs, both plasmacytoid and myeloid subtypes, also express IL-2. Interestingly, the production of IL-2 by myeloid DCs is induced by T-cell-mediated stimuli and depends on the presence of IL-15. The key role of this cytokine in regulating IL-2 production was also confirmed in the mouse system. In particular, we could show that DCs from IL-15-deficient mice were strongly impaired in the ability to produce IL-2 after interactions with different microbial stimuli. Our results indicate that DC-produced IL-2 is tightly coregulated with the expression of IL-15.

Animals↗
PubMed1998

Effects of hydrocarbon enrichment on trichloroethylene biodegradation and microbial populations in finished compost.

This study focused on the capacity of finished compost, often used as packing material in biofiltration units, to support microbial biodegradation of trichloroethylene (TCE). Finished compost was enriched with methane or propane (10% head space) to stimulate cometabolic biodegradation of gaseous TCE. Successful hydrocarbon enrichment, as indicated by rapid depletion of hydrocarbon gas and measurable growth of hydrocarbon-utilizing micro-organisms, occurred within a week. Within batch reactor flasks, approximately 75% of head space TCE (1-40 ppmv) was rapidly sorbed onto compost material. Up to 99% of the remaining head space TCE was removed via biodegradation in compost enriched with either hydrocarbon. Hydrocarbon enrichment with methane or propane corresponded to 10-fold increases in methanotrophic or propanotrophic populations, respectively. Based on growth assessment under different nutritional regimes, there appeared to be complex metabolic interactions within the microbial community in enriched compost. Five separate bacterial cultures were derived from the hydrocarbon-enriched compost and assayed for the ability to degrade TCE.

Actinomyces↗
PubMed1993

A mouse model of implant-associated infection.

Infections of implanted devices are of increasing frequency and importance, representing a significant limitation of many therapeutic modalities. There are puzzling features of implant-associated infection including the changes in microbial flora, the tendency to chronicity and impaired responses to conservative modes of treatment. The concept of the bacterial biofilm as a shielding mechanism generated by bacteria adherent to artificial surfaces has recently been proposed as an explanation for these features. The biofilm is a term applied to a complex comprising the implant surface, adherent bacteria and a specialized matrix enclosing the bacteria. The matrix of the biofilm is an electrostatically charged glue-like extracellular polymer derived by bacterial enzymes acting on tissue carbohydrates, formed by bacteria when adherent to surfaces. This matrix binds the bacteria to the surface providing a sequestration affording selective protection against harmful elements of the environment, especially mechanisms of host defenses and antimicrobial agents. These biological systems are complex to study because of the dynamic interaction of the microbial variables, host defenses, properties of synthetic materials and the biofilm matrix itself. There is a need for a laboratory model in which the variables can be controlled permitting the researcher to examine the outcomes of modifying one variable at a time in a planned and orderly manner. The practical way to attain this end is the conduct of studies in a stable reproducible animal model of localized biofilm-implant infection. Staphylococcus epidermidis is a representative of the class of microorganisms predominant in implant-associated infection. This paper describes the development of a model utilizing an implant-S. epidermidis-biofilm infection localized to the peritoneal cavity of the mouse. The natural history of the infection has been well documented and is stable in all respects for periods exceeding 3 months. This chronicity is especially advantageous in analyzing the impact of long-term therapeutic modalities and necessary periods of recovery and assessment. A representative example of an experimental use of this model to determine the relative efficacy of antibiotic therapeutic regimes is described, demonstrating its scope and efficacy.

Animals↗
PubMed2003

Pathogen self-defense: mechanisms to counteract microbial antagonism,.

Natural and agricultural ecosystems harbor a wide variety of microorganisms that play an integral role in plant health, crop productivity, and preservation of multiple ecosystem functions. Interactions within and among microbial communities are numerous and range from synergistic and mutualistic to antagonistic and parasitic. Antagonistic and parasitic interactions have been exploited in the area of biological control of plant pathogenic microorganisms. To date, biocontrol is typically viewed from the perspective of how antagonists affect pathogens. This review examines the other face of this interaction: how plant pathogens respond to antagonists and how this can affect the efficacy of biocontrol. Just as microbial antagonists utilize a diverse arsenal of mechanisms to dominate interactions with pathogens, pathogens have surprisingly diverse responses to counteract antagonism. These responses include detoxification, repression of biosynthetic genes involved in biocontrol, active efflux of antibiotics, and antibiotic resistance. Understanding pathogen self-defense mechanisms for coping with antagonist assault provides a novel approach to improving the durability of biologically based disease control strategies and has implications for the deployment of transgenes (microorganisms or plants).

Bacteria↗
PubMed1996

Analysis of the biotin-binding protein actinavidin using affinity capillary electrophoresis.

Affinity capillary electrophoresis (ACE) was applied to study the bioaffinity of ligand-receptor interaction between the microbial biotin-binding protein actinavidin and biotin. The ACE method is based on short time incubation of a mixture of actinavidin and increasing concentrations of biotinylated oligonucleotide (bio-ON), which was found to be an effective affinity ligand. Separation of intermediate loading forms of actinavidin from unbound ligand in the presence of micellar phase and by capillary zone electrophoresis enabled the quantitation of free bio-ON, permitting the evaluation of the biotin-binding capacity of actinavidin in absence and presence of sodium dodecyl sulfate (SDS). Although in the latter case actinavidin lost a part of its binding capacity (not more than 12%), it was still possible to develop an indirect, noncompetitive assay for the determination of actinavidin in culture liquid, utilizing the combination of micellar electrokinetic capillary chromatography (MEKC) and ACE. Due to the affinity interaction, actinavidin in the sample decreases the amount of bio-ON added, enabling quantitation of the protein. SDS, which is required in this assay to prevent protein adsorption to the capillary wall, greatly enhances the reproducibility and peak shape. Actinavidin levels determined are in agreement with those obtained by commonly used solid-phase analysis. The limit of detection was about 500 ng/mL. Thus the proposed method was found to be well suited for the evaluation of actinavidin affinity and monitoring of its levels in cultivation process.

Biotin↗
PubMed2002

[The influence of bioceramics on phagocytosis of human leukocytes].

BACKGROUND: After implantation of biomaterials in the regions of head and neck with resident microbial contamination the interaction between the implant and microbes play an important role for the success of the implantation. The host immune defence is important for the outcome after implantation, too. Phagocytosis plays an important role in the human immune response on infections. MATERIAL AND METHODS: The method described by Suess was used to investigate and measure the influence of the bioceramics Bioverit((R)) and Al(2)O(3)-ceramic on phagocytosis of yeast by human leukocytes. RESULTS: The bioceramics showed no statistically significant influence on phagocytosis function by human leukocytes. There was a tendency towards lower phagocytosis rates in all samples with bioceramics. CONCLUSIONS: The bioceramics Bioverit((R)) and Al(2)O(3) ceramic have no influence on phagocytosis of human leukocytes. In conclusion these biomaterials did not cause any inhibition of this important part of the human immune response on microbial infections after alloplastic implantation in head and neck regions.

Adult↗
PubMed1993

[Development, equilibrium and role of microbial flora in the newborn].

Development of the digestive tract intestinal flora is the result of a specific selection process to which the multiple maternal or environmental bacteria that penetrate into the neonatal gut are subjected. In breast-fed infants, Escherichia coli and streptococci are the first bacteria to appear in the gut. They are usually, but not always, followed by a population of Bifidobacterium which quickly becomes predominant. In bottle-fed infants, the intestinal flora is more variable and often includes, in addition to the organisms mentioned above, other enterobacteria and a wider range of obligate anaerobes. Studies of experimental models have shown that the nature of milk fed to the offspring and even the lactating mother's diet have substantial effects on the sequence of development of the neonatal intestinal flora. A large number of factors capable of inhibiting or permitting in vitro growth of various bacterial species have been identified in milk. However, no in vitro activity of these factors added to milk has ever been demonstrated. These factors include "bifidus factors", which promotes the growth of Bifidobacterium, and lactoferrin and immunoglobulins, which prevent colonisation of the gut by pathogenic enterobacteria. Immune factors in milk play a key role in interactions between the microbial flora and gut mucosa. However, they seem to have no effect on the growth of bacterial populations in the gut lumen. A number of pioneer bacteria, which are the first to arrive in the gut, are capable of effectively blocking growth of other bacteria introduced later in the ecosystem. In some instances, these pioneer bacteria also inhibit production of toxins by pathogenic species. Consequently, it is important to adhere to the recommended gradual changes in diet which allow these species to sequentially colonize the gut.

Bottle Feeding↗