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At least 1,549 records · Page 86Linked to original sources
PubMed1994

Serious occurrences in the natural history of advanced climatic keratopathy.

BACKGROUND: Climatic or chronic actinic keratopathy is an important corneal degeneration occurring after prolonged climatic exposure. The advanced stages of disease are confined generally to tropical or arid localities (including the Arctic) with high levels of sunlight. After many years of disease evolution, the advent of stage 3 keratopathy often presages a rapid downhill course. The instability of advanced climatic keratopathy has received little attention. METHODS: Eighteen patients with advanced climatic keratopathy are described from the Transvaal region in South Africa and from Saudi Arabia. Patients with rapid disease progression, spontaneous sterile ulceration, and secondary microbial keratitis are described. RESULTS: The rapid progression characteristic of stage 3 climatic keratopathy is illustrated. Severe, focal, sterile ulceration of the devitalized corneal degeneration may be common. Secondary infection may occur, leading to rapid dissolution of the climatic keratopathy material. Corneal perforation may ensue. The occurrence of yellow or brown fragments of the climatic keratopathy within or adjacent to the corneal inflammatory infiltrate indicates the predisposing cause of the infection, as usually also with examination of the opposite eye. CONCLUSIONS: These observations emphasize the inherent instability of advanced climatic keratopathy, which frequently takes a relentless downhill course. In rural populations of the developing world, climatic keratopathy is an important cause of blindness. Disease pathogenesis, treatment, and prevention deserve greater study.

Adult↗
PubMed2000

A genetic analysis of crystal growth.

The regulation of crystal morphology by proteins is often observed in biology. It is a central feature in the formation of hard tissues such as bones, teeth and mollusc shells. We have developed a genetic system in the bacterium Escherichia coli to study the protein-mediated control of crystal growth. We have used the crystallization of gold as a model system and found polypeptides that control the morphology of the resulting gold crystals. Analysis of the crystallization process influenced by these polypeptides indicates they act catalytically by an acid mechanism. Our results suggest that the concepts and methods of microbial genetics are general and can be applied to substances not commonly found in biological systems.

Acids↗
PubMed1992

Cloning and sequencing of a plasmid-mediated erythromycin resistance determinant from Staphylococcus xylosus.

A 2.3-kb DNA fragment cloned from plasmid pCH200, the largest (52 kb) of four plasmids detected in Staphylococcus xylosus, was found to confer resistance to 14-membered ring macrolides in Bacillus subtilis and Staphylococcus aureus. DNA-sequence analysis of the fragment revealed the presence of an open-reading frame, the deduced product of which was identical to one of the two ATP-binding domains encoded by the macrolide/streptogramin-B-resistance gene msrA of Staphylococcus epidermidis. The observation that a polypeptide homologous to the C-terminus of MsrA is capable of mediating erythromycin resistance in the absence of the N-terminal region is of significance both to the evolution and functional activity of members of the ATP-binding transport super-gene family.

Amino Acid Sequence↗
PubMed1993

Responsible use of antimicrobials in veterinary medicine: perspectives in France.

In France a survey of the use of antimicrobials in veterinary medicine was set up in connection with the Committee for the Marketing Authorization of Veterinary Medicinal Products. This survey has emphasized the importance of antimicrobials in veterinary medicine and the reality of antibiotic resistance in both man and animals. Certain epidemiological data tend to demonstrate that the use of antibiotics in animals increases the risk of antibiotic resistance in man, through selection in animals of resistant pathogenic bacteria or of a non-pathogenic resistant bacteria carrying resistance plasmids. Four proposals are put forward for the control of these different risks: reserve certain antibiotics (life-saving antibiotics) for human medicine, conform to a code of good practices for antibiotic use in animals, strengthen and connect up existing networks for the epidemiosurveillance of antibiotic resistance, provide for studies on the ecological impact of antibiotics in the registration dossiers for veterinary medicinal products. These evolutive measures, based on scientific progress in microbiology, epidemiology and clinical studies should respond satisfactorily to the expectations of all concerned.

Animals↗
PubMed2001

Application of HIV-1 genotypic-resistance testing prevents the evolution of further resistance mutations in heavily pretreated patients.

BACKGROUND: Resistance-associated mutations in HIV-1 evolve even under highly active antiretroviral therapy. OBJECTIVE: To evaluate the clinical efficacy of genotypic-resistance testing (GRT), to estimate the potential of a given antiretroviral therapy for prevention of further resistance mutations. STUDY DESIGN: Ten patients were treated prospectively with drugs, according to the results of a GRT. Five patients were allocated to group I in which antiretroviral therapy could be switched to an effective regimen (consisting of at least three sensitive drugs, from at least two different classes of antiretroviral substances). Five patients (group II) had no option for effective therapy, and continued to be treated non-effectively (at least one applicated substance class only intermediately sensitive, or resistant). GRT and quantitative viral cultures were performed longitudinally for 8 months. Also, plasma HIV-1 RNA, total CD4+ cells, and rates of productively infected CD4+ cells were determined. RESULTS: All the patients in group I showed a significant decrease of HIV-RNA of >1 log/ml (mean, -1.35 log/ml, P=0.025). The mean increase of CD4+ cells was 46 (not significant). The rate of productively infected CD4+ cells decreased significantly (mean, -16 productively infected CD4+ cells per 10(6) total CD4+ cells, P=0.04). In this group no further resistance mutations were detected after 8 months. In group II, none of the patients showed a significant decrease of HIV-1 RNA (mean, +0.05 log/ml), total CD4+ cells decreased (mean, -35, not significant), the rate of productively infected CD4+ cells increased significantly (mean, +124 productively infected CD4+ cells per 10(6) total CD4+ cells, P=0.04), and 4 of 5 patients had additional mutations in the RT gene conferring multi-drug resistance within 8 months (P=0.048). CONCLUSIONS: GRT is predictive of the efficacy of a therapeutic regimen, in particular regarding evolution of further resistance mutations.

Adult↗
PubMed2001

The 2.0-A crystal structure of tachylectin 5A provides evidence for the common origin of the innate immunity and the blood coagulation systems.

Because invertebrates lack an adaptive immune system, they had to evolve effective intrinsic defense strategies against a variety of microbial pathogens. This ancient form of host defense, the innate immunity, is present in all multicellular organisms including humans. The innate immune system of the Japanese horseshoe crab Tachypleus tridentatus, serving as a model organism, includes a hemolymph coagulation system, which participates both in defense against microbes and in hemostasis. Early work on the evolution of vertebrate fibrinogen suggested a common origin of the arthropod hemolymph coagulation and the vertebrate blood coagulation systems. However, this conjecture could not be verified by comparing the structures of coagulogen, the clotting protein of the horseshoe crab, and of mammalian fibrinogen. Here we report the crystal structure of tachylectin 5A (TL5A), a nonself-recognizing lectin from the hemolymph plasma of T. tridentatus. TL5A shares not only a common fold but also related functional sites with the gamma fragment of mammalian fibrinogen. Our observations provide the first structural evidence of a common ancestor for the innate immunity and the blood coagulation systems.

Amino Acid Sequence↗
PubMed2002

Microbial beta-glucosidases: cloning, properties, and applications.

Beta-glucosidases constitute a major group among glycosylhydrolase enzymes. Out of the 82 families classified under glycosylhydrolase category, these belong to family 1 and family 3 and catalyze the selective cleavage of glucosidic bonds. This function is pivotal in many crucial biological pathways, such as degradation of structural and storage polysaccharides, cellular signaling, oncogenesis, host-pathogen interactions, as well as in a number of biotechnological applications. In recent years, interest in these enzymes has gained momentum owing to their biosynthetic abilities. The enzymes exhibit utility in syntheses of diverse oligosaccharides, glycoconjugates, alkyl- and aminoglucosides. Attempts are being made to understand the structure-function relationship of these versatile biocatalysts. Earlier reviews described the sources and properties of microbial beta-glucosidases, yeast beta-glucosidases, thermostable fungal beta-glucosidase, and the physiological functions, characteristics, and catalytic action of native beta-glucosidases from various plant, animal, and microbial sources. Recent efforts have been directed towards molecular cloning, sequencing, mutagenesis, and crystallography of the enzymes. The aim of the present article is to describe the sources and properties of recombinant beta-glucosidases, their classification schemes based on similarity at the structural and molecular levels, elucidation of structure-function relationships, directed evolution of existing enzymes toward enhanced thermostability, substrate range, biosynthetic properties, and applications.

Biotechnology↗
PubMed1993

Testing of some assumptions about biodegradability in soil as measured by carbon dioxide evolution.

Conversion to CO2 upon incubation in aerobic soil is one of the standard test procedures to assess biodegradability. It may be measured with unlabeled test compounds in biometer flasks. In this case, the background CO2 evolution by unamended soil is subtracted from the CO2 evolution by the amended soil and the resulting net CO2 evolution becomes the measure of biodegradation. Alternately, 14CO2 release from radiocarbon substrates is measured to assess biodegradability. Both approaches measure ultimate (complete) biodegradation and bypass the theoretical and technical limitations of residue analysis. This report examines the underlying assumptions that, except for carbon content, conversion percentage to CO2 is relatively independent of chemical composition, that CO2 production is proportional to the amount of added test compound, and that the background CO2 evolution of the soil is not influenced by the test substance. Work with unlabeled and radiolabeled substrates proved the first two assumptions to be essentially correct. However, more than half of net CO2 production may represent the mineralization of biomass and soil organic matter, some of it unrelated to the test compound. The soil microbial community in its nongrowing steady state appears to convert a much lower percentage of a radiocarbon substrate to 14CO2 than a growing soil community that responds to a substantial substrate addition. These findings may help to improve test methods and may aid in the interpretation of test results.

Adipates↗
PubMed2000

Brucella abortus and its closest phylogenetic relative, Ochrobactrum spp., differ in outer membrane permeability and cationic peptide resistance.

The outer membrane (OM) of the intracellular parasite Brucella abortus is permeable to hydrophobic probes and resistant to destabilization by polycationic peptides and EDTA. The significance of these unusual properties was investigated in a comparative study with the opportunistic pathogens of the genus Ochrobactrum, the closest known Brucella relative. Ochrobactrum spp. OMs were impermeable to hydrophobic probes and sensitive to polymyxin B but resistant to EDTA. These properties were traced to lipopolysaccharide (LPS) because (i) insertion of B. abortus LPS, but not of Escherichia coli LPS, into Ochrobactrum OM increased its permeability; (ii) permeability and polymyxin B binding measured with LPS aggregates paralleled the results with live bacteria; and (iii) the predicted intermediate results were obtained with B. abortus-Ochrobactrum anthropi and E. coli-O. anthropi LPS hybrid aggregates. Although Ochrobactrum was sensitive to polymyxin, self-promoted uptake and bacterial lysis occurred without OM morphological changes, suggesting an unusual OM structural rigidity. Ochrobactrum and B. abortus LPSs showed no differences in phosphate, qualitative fatty acid composition, or acyl chain fluidity. However, Ochrobactrum LPS, but not B. abortus LPS, contained galacturonic acid. B. abortus and Ochrobactrum smooth LPS aggregates had similar size and zeta potential (-12 to -15 mV). Upon saturation with polymyxin, zeta potential became positive (1 mV) for Ochrobactrum smooth LPS while remaining negative (-5 mV) for B. abortus smooth LPS, suggesting hindered access to inner targets. These results show that although Ochrobactrum and Brucella share a basic OM pattern, subtle modifications in LPS core cause markedly different OM properties, possibly reflecting the adaptive evolution of B. abortus to pathogenicity.

Alphaproteobacteria↗
PubMed2006

The current and future applications of microorganism in the bioremediation of cyanide contamination.

Inorganic cyanide and nitrile compounds are distributed widely in the environment, chiefly as a result of anthropogenic activity but also through cyanide synthesis by a range of organisms including higher plants, fungi and bacteria. The major source of cyanide in soil and water is through the discharge of effluents containing a variety of inorganic cyanide and nitriles. Here the fate of cyanide compounds in soil and water is reviewed, identifying those factors that affect their persistence and which determine whether they are amenable to biological degradation. The exploitation of cyanides by a variety of taxa, as a mechanism to avoid predation or to inhibit competitors has led to the evolution in many organisms of enzymes that catalyse degradation of a range of cyanide compounds. Microorganisms expressing pathways involved in cyanide degradation are briefly reviewed and the current applications of bacteria and fungi in the biodegradation of cyanide contamination in the field are discussed. Finally, recent advances that offer an insight into the potential of microbial systems for the bioremediation of cyanide compounds under a range of environmental conditions are identified, and the future potential of these technologies for the treatment of cyanide pollution is discussed.

Bacteria↗
PubMed2002

Inventing probiotic functional foods for patients with allergic disease.

OBJECTIVE: The primary objective of this review is to discuss the rationale for and applicability of probiotics as part of the nutritional approach to the prevention and management of allergic disease. DATA SOURCES: This review represents a synthesis of recent literature published in the fields of probiotics, nutrition, and allergic disease. STUDY SELECTION: The expert opinions of the authors were used to select the relevant data for the review. RESULTS: The hygiene hypothesis suggests that allergic disease may arise from a lack of counterbalancing microbial exposure at an early age. Thus, the initial compositional development of gut microbiota is considered a key determinant in the development of both the immune responder phenotype and the normal gut barrier functions. A wide range of data documents the specific actions of selected probiotics. The regulatory role of probiotics in allergic disease has been demonstrated as improving the clinical course or preventing the development of atopic eczema in infants given a probiotic-supplemented diet. In addition, certain types of fatty acids and antioxidants have been proposed for protective effects against the development of allergy and to diminish the inflammatory response in allergic disease. CONCLUSIONS: The increase in the prevalence of allergic disease during the past decades is likely to be explained by changes in the environment, including reduced microbial exposure and altered food consumption. Scientifically composed functional foods containing probiotics and other functional components offer a nutritional strategy for both the prevention and the management of allergic disease. Further research is needed to characterize the gut microbiota and to clarify the mechanisms of action that control specific physiologic processes not only in the evolution of allergic disease in at-risk populations but also in the management of allergic diseases.

Complementary Therapies↗
PubMedDate not supplied

Fossilized embryos are widespread but the record is temporally and taxonomically biased.

We report new discoveries of embryos and egg capsules from the Lower Cambrian of Siberia, Middle Cambrian of Australia and Lower Ordovician of North America. Together with existing records, embryos have now been recorded from four of the seven continents. However, the new discoveries highlight secular and systematic biases in the fossil record of embryonic stages. The temporal window within which the embryos and egg capsules are found is of relatively short duration; it ends in the Early Ordovician and is roughly coincident with that of typical "Orsten"-type faunas. The reduced occurrence of such fossils has been attributed to reducing levels of phosphate in marine waters during the early Paleozoic, but may also be owing to the increasing depth of sediment mixing by infaunal metazoans. Furthermore, most records younger than the earliest Cambrian are of a single kind-large eggs and embryos of the priapulid-like scalidophoran Markuelia. We explore alternative explanations for the low taxonomic diversity of embryos recovered thus far, including sampling, size, anatomy, ecology, and environment, concluding that the preponderance of Markuelia embryos is due to its precocious development of cuticle at an embryonic stage, predisposing it to preservation through action as a substrate on which microbially mediated precipitation of authigenic calcium phosphate may occur. The fossil record of embryos may be limited to a late Neoproterozoic to early Ordovician snapshot that is subject to dramatic systematic bias. Together, these biases must be considered seriously in attempts to use the fossil record to arbitrate between hypotheses of developmental and life history evolution implicated in the origin of metazoan clades.

Animals↗
PubMed1995

[Methanol from ethanol? On cleavage of the ethanol carbon bond and methanol formation within the scope of microbial metabolic processes].

While making investigations into microbiological literature, the following question was looked into: Are microorganisms able to generate methanol from the basic carbon frame of ethanol? Due to carbon monoxide dehydrogenase complexes some methanogens and acetate oxidisers are able to cleave the carbon bond of acetyl-CoA. Coenzyme bonded methyl groups (methyl-H4MPT, methyl-CoM, methyl-THF) are generated both by means of reduction (methano-genesis) and by means of oxidation (CO2 evolution) of the C2-unit. Usually these are looked at as precursors of methanol. Methanotrophs and certain methylotrophs are able to oxidise methane to methanol by means of oxigenase complexes. The C1-unit supplies coenzyme bonded CO; carbon monoxide can be reduced to methanol very effectively by several Clostridia. Both in vivo analysis of intestinal gases of alcoholised individuals and incubation experiments with certain intestinal groups with marked alcohol, might contribute in judging the real importance of the intestinal micro flora with regard to the problems of ethanol congeners.

Alcoholic Intoxication↗
PubMed1980

Studies of ribosomal proteins of yeast species and their hybrids: gel electrophoresis and immunochemical cross-reactions.

The cytoplasmic ribosomal proteins (r-proteins) of seventeen yeast species of the genera Saccharomyces and Kluyveromyces were analyzed by one-dimensional gradient polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulphate. The electrophoretic patterns of cytoplasmic r-proteins from different species display extensive differences in both the 40S and the 60S subunit. Relatedness of species suggested by r-protein patterns correlates well with that based on DNA/DNA homology (Bicknell and Douglas 1970). Immunochemical cross-reactions and antibiotic susceptibility tests were also used to compare different species. Analyses of r-proteins from two different interspecific hybrids showed that their ribosomes were hybrid, containing r-proteins from both parents. These findings are discussed in relation to the evolution of yeast species and the regulation of expression of r-proteins in eucaryotes.

Anti-Bacterial Agents↗
PubMed2006

Computational prediction of genomic functional cores specific to different microbes.

Computational and experimental attempts tried to characterize a universal core of genes representing the minimal set of functional needs for an organism. Based on the increasing number of available complete genomes, comparative genomics has concluded that the universal core contains < 50 genes. In contrast, experiments suggest a much larger set of essential genes (certainly more than several hundreds, even under the most restrictive hypotheses) that is dependent on the biological complexity and environmental specificity of the organism. Highly biased genes, which are generally also the most expressed in translationally biased organisms, tend to be over represented in the class of genes deemed to be essential for any given bacterial species. This association is far from perfect; nevertheless, it allows us to propose a new computational method to detect, to a certain extent, ubiquitous genes, nonorthologous genes, environment-specific genes, genes involved in the stress response, and genes with no identified function but highly likely to be essential for the cell. Most of these groups of genes cannot be identified with previously attempted computational and experimental approaches. The large variety of life-styles and the unusually detectable functional signals characterizing translationally biased organisms suggest using them as reference organisms to infer essentiality in other microbial species. The case of small parasitic genomes is discussed. Data issued by the analysis are compared with previous computational and experimental studies. Results are discussed both on methodological and biological grounds.

Bacillus subtilis↗
PubMed1994

Multidrug resistance pumps in bacteria: variations on a theme.

Multidrug resistance pumps (MDRs) arise from three different gene families and are widespread in bacteria. For example, in Escherichia coli alone, there seem to be seven distinct MDRs. The most common belong to the major facilitator family of membrane translocases; this type of MDR is closely related to specific antibiotic extrusion pumps such as the tetracycline/H+ antiporter. This similarity in design, and the high incidence of apparently independent evolution of MDRs, suggests that the property of multidrug resistance might have resulted from a loss of specificity in a specific hydrophobic-drug efflux pump.

Bacteria↗