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Results for “Pathogen diversity”

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PubMedDate not supplied

Recombinant avirulent Salmonella vaccine strains with stable maintenance and high level expression of cloned genes in vivo.

Salmonella typhimurium strains with deletion (delta) of the adenylate cyclase (cya) and cyclic AMP receptor protein (crp) genes are avirulent for mice and induce a high level of protective immunity to oral challenge with up to 10,000 times what would be a lethal dose of wild-type virulent S. typhimurium cells. This immunity begins as early as seven days after immunization and lasts for at least four months. S. typhimurium delta cya delta crp mutants stably maintain plasmids and give high-level expression of cloned gene products; in this they appear superior to other avirulent S. typhimurium strains. S. typhimurium delta cya delta crp strains with a delta asd mutation (abolishing production of aspartate beta-semialdehyde dehydrogenase), have an obligate requirement for diaminopimelic acid (DAP). This strain can be used in conjunction with plasmid vectors lacking antibiotic resistance markers but having the wild-type asd+ gene from Streptococcus mutans to complement the delta asd chromosomal mutation. The Asd+ plasmid vector can be used to express a diversity of colonization and virulence antigens from other pathogens. In the delta cya delta crp delta asd S. typhimurium vaccine strain, the plasmid is completely stable in the absence of any exogenous selective pressure either in vitro or in vivo.

Adenylyl Cyclases↗

PubMed2005

TLR4, but not TLR2, signals autoregulatory apoptosis of cultured microglia: a critical role of IFN-beta as a decision maker.

TLRs mediate diverse signaling after recognition of evolutionary conserved pathogen-associated molecular patterns such as LPS and lipopeptides. Both TLR2 and TLR4 are known to trigger a protective immune response as well as cellular apoptosis. In this study, we present evidence that TLR4, but not TLR2, mediates an autoregulatory apoptosis of activated microglia. Brain microglia underwent apoptosis upon stimulation with TLR4 ligand (LPS), but not TLR2 ligands (Pam(3)Cys-Ser-Lys(4), peptidoglycan, and lipoteichoic acid). Based on studies using TLR2-deficient or TLR4 mutant mice and TLR dominant-negative mutants, we also demonstrated that TLR4, but not TLR2, is necessary for microglial apoptosis. The critical difference between TLR2 and TLR4 signalings in microglia was IFN regulatory factor-3 (IRF-3) activation, followed by IFN-beta expression: while TLR4 agonist induced the activation of IRF-3/IFN-beta pathway, TLR2 did not. Nevertheless, both TLR2 and TLR4 agonists strongly induced NF-kappaB activation and NO production in microglia. Neutralizing Ab against IFN-beta attenuated TLR4-mediated microglial apoptosis. IFN-beta alone, however, did not induce a significant cell death. Meanwhile, TLR2 activation induced microglial apoptosis with help of IFN-beta, indicating that IFN-beta production following IRF-3 activation determines the apoptogenic action of TLR signaling. TLR4-mediated microglial apoptosis was mediated by MyD88 and Toll/IL-1R domain-containing adaptor-inducing IFN-beta, and was associated with caspase-11 and -3 activation rather than Fas-associated death domain protein/caspase-8 pathway. Taken together, TLR4 appears to signal a microglial apoptosis via autocrine/paracrine IFN-beta production, which may act as an apoptotic sensitizer.

Adaptor Proteins, Signal Transducing↗

PubMed1988

Interferon-gamma, the activated macrophage, and host defense against microbial challenge.

Recent research on human macrophage activation has reemphasized the critical role of the lymphokine-secreting T cell in converting quiescent macrophages to efficient microbicidal phagocytes. Interferon-gamma, a key lymphokine secreted by antigen-triggered T4+ helper cells, is capable of inducing the macrophage to act against a diverse group of microbial targets, in particular, intracellular pathogens. In animal models, treatment with recombinant interferon-gamma is beneficial in systemic intracellular infections, and inhibition of endogenous interferon-gamma activity impairs host resistance. Trials in patients with cancer, leprosy, and the acquired immunodeficiency syndrome (AIDS) have shown that interferon-gamma can activate the mononuclear phagocyte in humans. This research and the identification of patients whose T cells fail to produce interferon-gamma properly has set the stage for evaluating the role of macrophage-activating immunotherapy using interferon-gamma in various human infectious diseases.

Animals↗

PubMed2001

[The connection between sports and spores. The foot, its mycoses and onychomycoses].

The epidemiological survey Achillus on over 76,000 subjects has highlighted the high prevalence of foot diseases. In particular, the risk of contracting skin and nail infections of the foot by fungi is quite important during some sport practices. The interhuman transmission is due to propagules commonly called spores. It often occurs by indirect contamination from the soil. Clinical presentations are diverse, largely depending upon the identity of the pathogen fungus. Prevention and treatment of these infections require both patience and perseverance. Boosting the transformation of spores into an active growing phase might paradoxically increase the clinical efficacy of antifungals.

Disease Transmission, Infectious↗

PubMedDate not supplied

Modeling and risk assessment for Salmonella in meat and poultry.

Microbial risk assessment is rapidly becoming a well-recognized concept in the management of food- and waterborne microbial hazards. The process of conducting a risk assessment is a structured, systematic approach to integrate and evaluate information from diverse sources concerning the origin and fate of pathogens along the food chain and to determine the magnitude of public health risks. Quantitative modeling of the sources, prevalence, numbers, and behavior of food chain pathogens, such as Salmonella, and of the host/pathogen interaction and consequences are providing scientific information and insights useful for decision makers in managing the safety of the food supply.

Animals↗

PubMed2006

DNA fingerprinting elicited evolutionary trend of oral Candida tropicalis isolates from diverse geographic locales.

PURPOSE: To study molecular profiles of oral Candida tropicalis isolates from five different geographic locales to determine the molecular diversity, clonality and evolutionary trends of this opportunistic pathogen. METHODS: A total of 36 strains from five countries (China, Canada, Scotland, Japan and Tanzania) were genotyped by PCR fingerprinting with 11 separate primers. Of these, primers RSG9, RSG8, T3B and RSD12 generated complex fingerprinting patterns. RESULTS: Three significantly dissimilar profiles were derived from the primer T3B and particularly focused on tDNA suggested the prevalence of genetic subtypes within the species. Comparison of tDNA and rDNA (RSD12) fingerprints of C. tropicalis suggested that rDNA is much more heterogeneous than the relatively distinct tDNA. Further analysis of similarity coefficient (SAB) of gel profiles derived from computer-generated dendrograms indicated some degree of similarity in isolates from five-disparate geographic locales as well as the presence of unique isotypes in each region. CONCLUSIONS: This study demonstrates the evolutionary divergence of distinct genetic subgroups within Candida tropicalis .

AIDS-Related Opportunistic Infections↗

PubMed1981

Alien-driven diversity and alien-selected escape: a rationale for allogeneic cancer immunotherapy.

We have presented two theories relating to the function of histocompatibility antigens and their presence as alien antigens on tumor cells. The theory of alien-driven diversity suggests that the ability to effectively recognize pathogens in the form of "altered-self" derives from prior exposure to antigens cross-reactive with "altered-self" during development. Furthermore, these cross-reactive antigens are alloantigens that are expressed on autologous cells during somatic development. These somatically generated alloantigens could be the result of the same genetic alterations that produced the polymorphism of these antigens within the species. Second, the theory of alien-selected escape suggests that a tumorigenic pathogen selects a cell bearing an alien H* antigen so that the alien-infected cell is recognized as self rather than altered-self by the tumor host. We than summarized data from mouse and man consistent with these theories and with the concept that clinically evident tumors have escaped the host's immune system. Finally, we have discussed potential directions for devising immunotherapy with allogeneic cells that might circumvent the apparent unresponsiveness of the patient's immune system to his own tumor.

Animals↗

PubMed1994

The Mallory body: theories on development and pathological significance (Part 2 of a literature survey).

Drawing on data from a previously published literature survey on the clinical and experimental epidemiology of the Mallory body, we discuss current theories on its development in a pro et contra manner. Conclusions have been largely left open to the interpretations of the reader because many are still speculative. The main results of this study characterize Mallory bodies as stereotypical histological byproducts to diverse hepatic injuries (mostly alcohol associated) of questionable pathogenic importance. The temporal characteristics of Mallory bodies cast doubt on their role in hepatic neoplasia both as a disease marker and a causative agent, and prognosis studies suggest that they may be considered preterminal markers in some nonalcoholic liver diseases but remain prognostically unimportant in most studies on alcoholic patients. By similar line of inquiry, no consistent relationships may be found with disease severity or duration in alcoholic liver diseases. The roles of vitamin A deficiency and protein-calorie malnutrition are circumstantial. Drugs known to have calcium-antagonist properties and the physiological characteristics of the stress-response protein ubiquitin support the concept of defective protein systems in Mallory body pathogenesis. Disproportionate hepatic copper accumulation seems both epidemiologically and topographically associated with Mallory bodies, but these connections are largely unsupported by exposure studies. Many arguments still downplay the importance of uncoordinated changes in hepatic oxygen delivery and consumption, but ischemia-reperfusion studies suggest a role of oxygen-derived free radicals in the liver injuries under scrutiny. Finally, the role of Mallory bodies in the control system of hepatocyte function is addressed, and indirect evidence lends credence to a cybernetic approach in future study designs. It is reasonable to assume that different elements of a multifactorial setting operate with varying intensity over time as this may account for some of the controversies that exist. In conclusion, the biological significance of Mallory bodies is still mystery. It is not known whether Mallory bodies represent an epiphenomenon or play a role themselves in the initiation and continuation of liver damage.

Animals↗

PubMed2006

A critical assessment of Agrobacterium tumefaciens-mediated transformation as a tool for pathogenicity gene discovery in the phytopathogenic fungus Leptosphaeria maculans.

We evaluated the usefulness and robustness of Agrobacterium tumefaciens-mediated transformation (ATMT) as a high-throughput transformation tool for pathogenicity gene discovery in the filamentous phytopathogen Leptosphaeria maculans. Thermal asymmetric interlaced polymerase chain reaction allowed us to amplify the left border (LB) flanking sequence in 135 of 400 transformants analysed, and indicated a high level of preservation of the T-DNA LB. In addition, T-DNA preferentially integrated as a single copy in gene-rich regions of the fungal genome, with a probable bias towards intergenic and/or regulatory regions. A total of 53 transformants out of 1388 (3.8%) showed reproducible pathogenicity defects when inoculated on cotyledons of Brassica napus, with diverse altered phenotypes. Co-segregation of the altered phenotype with the T-DNA integration was observed for 6 of 12 transformants crossed. If extrapolated to the whole collection, this indicates that 1.9% of the collection actually corresponds to tagged pathogenicity mutants. The preferential insertion into gene-rich regions along with the high ratio of tagged mutants renders ATMT a tool of choice for large-scale gene discovery in L. maculans.

Agrobacterium tumefaciens↗

PubMed2003

Peroxiredoxins in antioxidant defense and redox regulation.

Peroxiredoxins constitute a family of peroxidases that lack prosthetic groups or catalytically active heteroatoms. Instead, their peroxidatic activity is due to a strictly conserved cysteine that is activated within a novel catalytic triad in which the cysteine thiol is coordinated to an arginine and a threonine or serine residue. Donor substrates are thiol compounds which differ between subtypes of peroxiredoxins and species. In pathogenic trypanosomatids that lack heme- or seleno-peroxidases peroxiredoxins have been shown to represent the major devices to detoxify hydroperoxides and an equivalent role may be assumed for other protozoal parasites and many bacterial pathogens. In mammals equipped with more efficient peroxidases the peroxiredoxins appear to be responsible for the redox regulation of diverse metabolic processes. The substantial differences in the cosubstrate requirements of the peroxiredoxins of pathogenic microorganisms and their mammalian host may be exploited to selectively inhibit the antioxidant defense of pathogens. Thereby, the pathogen would be more readily eliminated by the innate immune response of the host's phagocytes.

Animals↗

PubMed2004

Lipoproteins of Mycobacterium tuberculosis: an abundant and functionally diverse class of cell envelope components.

Mycobacterium tuberculosis remains the predominant bacterial scourge of mankind. Understanding of its biology and pathogenicity has been greatly advanced by the determination of whole genome sequences for this organism. Bacterial lipoproteins are a functionally diverse class of membrane-anchored proteins. The signal peptides of these proteins direct their export and post-translational lipid modification. These signal peptides are amenable to bioinformatic analysis, allowing the lipoproteins encoded in whole genomes to be catalogued. This review applies bioinformatic methods to the identification and functional characterisation of the lipoproteins encoded in the M. tuberculosis genomes. Ninety nine putative lipoproteins were identified and so this family of proteins represents ca. 2.5% of the M. tuberculosis predicted proteome. Thus, lipoproteins represent an important class of cell envelope proteins that may contribute to the virulence of this major pathogen.

Bacterial Proteins↗

PubMed2004

Comparative evolutionary histories of chitinase genes in the Genus zea and Family poaceae.

Patterns of DNA sequence diversity vary widely among genes encoding proteins that protect plants against pathogens and herbivores. Comparative studies may help determine whether these differences are due to the strength of selection acting on different types of defense, in different evolutionary lineages, or both. I analyzed sequence diversity at three chitinases, a well-studied component of defense, in two species of Zea and several Poaceae taxa. Although the Zea species are closely related and these genes code for proteins with similar biochemical function, patterns of diversity vary widely within and among species. Intraspecific diversity at chiB, chiI, and Z. mays ssp. parviglumis chiA are consistent with a neutral-equilibrium model whereas chiA had no segregating sites within Z. diploperennis--consistent with a recent and strong selective sweep. Codons identified as having diverged among Poaceae taxa in response to positive selection were significantly overrepresented among targets of selection in Arabis, suggesting common responses to selection in distantly related plant taxa. Divergence of the recent duplicates chiA and chiB is consistent with positive selection but relaxed constraint cannot be rejected. Weak evidence for adaptive divergence of these duplicated downstream components of defense contrasts with strong evidence for adaptive divergence of genes involved in pathogen recognition.

Amino Acid Sequence↗

PubMed2000

High-throughput sequencing in the population analysis of bacterial pathogens of humans.

High-throughput nucleotide sequence determination technologies present new opportunities for studies of bacterial pathogens by enabling the accumulation of large volumes of biodiversity information from isolate collections. Population studies, which combine these data with epidemiological, phylogenetic, and evolutionary concepts, provide insights into the behaviour of pathogens that are unavailable from other approaches as they address questions of relevance to pathogenesis from the perspective of the infectious organism rather from that of the host. Hypothesis-driven analyses applied to these data permit the determination of microbial population diversity and structure, the identification of the mechanisms of genetic change in bacterial populations, and the generation of models of pathogen evolution. The nucleotide sequence-based population studies performed to date demonstrate a spectrum of nucleotide sequence diversity, population structure, and evolutionary mechanisms among pathogenic bacteria. The rapid development of nucleotide sequence determination and analysis techniques provides the tools necessary for the prosecution of population studies on an increasing number of bacterial pathogens.

Bacteria↗

PubMed1993

Investigation of the structural heterogeneity of lipooligosaccharides from pathogenic Haemophilus and Neisseria species and of R-type lipopolysaccharides from Salmonella typhimurium by electrospray mass spectrometry.

Heterogeneity in the lipooligosaccharides (LOS) of pathogenic Haemophilus and Neisseria species is evident from the multiplicity of components observed with electrophoretic analyses. Knowledge of the precise structures that make up these diverse LOS molecules is clearly the key to reaching an understanding of pathogenic processes such as phase variation and molecular mimicry. Except for a few cases, little is known about the specific structural features of LOS that underlie phase variation and molecular mimicry, partly because of the inherent difficulties in the structural elucidation of these complex glycolipids. In the lipopolysaccharides (LPS) from Salmonella typhimurium and Escherichia coli, rough, or R-type, mutants have been isolated that have provided insight into the biosynthetic pathways and associated genetics that control LPS expression. Nonetheless, recent work has shown that these R-type LPS are more complex than originally thought, and significant heterogeneity is still observed, primarily in their phosphorylation states. In order to investigate the structures of LPS and LOS in a more rapid fashion, we have determined the precise molecular weights of LOS (and LPS) preparations from various Haemophilus, Neisseria, and Salmonella species by electrospray ionization-mass spectrometry. The LOS (or LPS) were first O-deacylated under mild hydrazine conditions to remove O-linked esters primarily from the lipid A portion. Under negative-ion conditions, the O-deacylated LOS yield abundant multiply deprotonated molecular ions, (M-nH)n-, where n refers to the number of protons removed and therefore determines the absolute charge state, n = z. Mass spectra from different LOS and LPS preparations have provided detailed information concerning the structural basis for LOS (and LPS) heterogeneity and corresponding saccharide compositions. The identification of sialic acid in the LOS of Haemophilus and Neisseria species and the variable phosphorylation of the core of S. typhimurium LPS have afforded insights into the biosynthetic pathways used by these organisms. Information of this type is important for understanding the underlying genetic and environmental factors controlling LOS and LPS expression.

Antigens, Bacterial↗

PubMed2006

Characterization and regulation of the trehalose synthesis pathway and its importance in the pathogenicity of Cryptococcus neoformans.

The disaccharide trehalose has been found to play diverse roles, from energy source to stress protectant, and this sugar is found in organisms as diverse as bacteria, fungi, plants, and invertebrates but not in mammals. Recent studies in the pathobiology of Cryptococcus neoformans identified the presence of a functioning trehalose pathway during infection and suggested its importance for C. neoformans survival in the host. Therefore, in C. neoformans we created null mutants of the trehalose-6-phosphate (T6P) synthase (TPS1), trehalose-6-phophate phosphatase (TPS2), and neutral trehalase (NTH1) genes. We found that both TPS1 and TPS2 are required for high-temperature (37 degrees C) growth and glycolysis but that the block at TPS2 results in the apparent toxic accumulation of T6P, which makes this enzyme a fungicidal target. Sorbitol suppresses the growth defect in the tps1 and tps2 mutants at 37 degrees C, which supports the hypothesis that these sugars (trehalose and sorbitol) act primarily as stress protectants for proteins and membranes during exposure to high temperatures in C. neoformans. The essential nature of this pathway for disease was confirmed when a tps1 mutant strain was found to be avirulent in both rabbits and mice. Furthermore, in the system of the invertebrate C. elegans, in which high in vivo temperature is no longer an environmental factor, attenuation in virulence was still noted with the tps1 mutant, and this supports the hypothesis that the trehalose pathway in C. neoformans is involved in more host survival mechanisms than simply high-temperature stresses and glycolysis. These studies in C. neoformans and previous studies in other pathogenic fungi support the view of the trehalose pathway as a selective fungicidal target for use in antifungal development.

Animals↗

PubMed2001

[Organization of the Helicobacter pylori genome].

Helicobacter pylori is a Gram-negative, spiral-shaped pathogenic bacterium that was firstly isolated and cultured from biopsy specimens by Marshall and Warren in 1983. This organism is a human gastric pathogen associated with peptic ulcer disease as well as chronic gastritis. Recent epidemiological studies have demonstrated that H. pylori is a primary risk factor for the development of intestinal type gastric adenocarcinoma. H. pylori is the first bacterium for which the genomes of two unrelated strains (26695 and J99) have been sequenced. The genome of H. pylori is relatively low in size (1.6-1.73 Mb). In this review, we compare the organization of two sequenced H. pylori genomes. A special emphasis on genetic diversity of H. pylori including plasticity zone and cag pathogenicity island has been placed.

Antigens, Bacterial↗

PubMed2000

Do infectious diseases drive MHC diversity?

The primary function of the major histocompatibility complex (MHC) is to allow the immune system to identify infectious pathogens and eliminate them. Infectious diseases are now thought to be the main selection force that drives and maintains the extraordinary diversity of the MHC.

Alleles↗

PubMed2004

Calcium signalling during cell interactions with bacterial pathogens.

The ability of a pathogenic microorganism to cause a disease is conditioned by its ability to colonise a given niche and implicates the expression of specific determinants, i.e. virulence factors, that allow the pathogen to adhere to or to invade epithelial cells. Diseases may be induced by bacteria that replicate extracellularly and alter the epithelial mucosa by producing toxins. Ca2+ signalling has been implicated in various steps of bacterial infection. Bacterial toxins can induce an increase in free cytosolic Ca2+ in host cells, itself required for the toxin-mediated effects. Such toxins, by diffusing in the extracellular media, can act at a distance from the site of infection and have a global effect on the integrity of the epithelium by promoting the expression of pro-inflammatory cytokines. Independent on toxins, bacteria can induce Ca2+ responses that play a role in cytoskeletal rearrangements required for cell binding or internalisation of the microorganism. In some instances, invasion of the epithelium may be followed by bacterial access to deeper tissue, dissemination to other organs, and sometimes persistence in host cells in a parasitic-like mode. Such strategies underline the pathogen abilities to control innate defence cells such as professional phagocytes, and may implicate the diversion of Ca(2+)-dependent cellular processes that normally result in killing of the ingested bacteria. Finally, bacterial pathogens can also induce the cell release of ATP, a Ca2+ agonist, that may expand bacterial cell signalling by a paracrine or autocrine route, leading to enhanced colonisation or enhanced host cell responses to the invading microorganism.

Animals↗