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PubMed1989

Transcription of infectious yellow fever RNA from full-length cDNA templates produced by in vitro ligation.

Yellow fever (YF) virus is the prototype member of the flavivirus family, a diverse group of human and animal pathogens. A live-attenuated strain of YF virus, called 17D, has been used successfully for human vaccination for more than 50 years. In this report we describe the construction of full-length YF 17D cDNA templates that can be transcribed in vitro to yield infectious YF virus RNA. Because of the instability of full-length YF cDNA clones and their toxic effects on Escherichia coli, we developed a strategy in which full-length templates for transcription were constructed by in vitro ligation of appropriate restriction fragments. The YF virus recovered from cDNA was indistinguishable from the parental virus by several criteria. This system should facilitate the molecular genetic analysis of flavivirus replication and attenuation and may allow YF 17D to be used as a carrier for immunologically important epitopes from other disease agents.

Base Sequence↗

PubMed1987

[In vitro study of the effects of oxolinic acid at sub-inhibitory concentrations on the activity of hemagglutinins and adhesion to uroepithelial cells by Escherichia coli isolated from urine].

The aim of the present study was to investigate the effects of sub-MIC doses of oxolinic acid (quinolone), widely used in the treatment of urinary tract infections, on both haemagglutinating activity and adhesion capacity of 13 Escherichia coli strains isolated from urine during acute cystitis or pyelonephritis. All these strains adhered to uroepithelial cells and showed mannose-sensitive and/or mannose-resistant haemagglutinating activity. Sub-MIC doses of oxolinic acid induced filaments in most of the bacterial cultures; however, inhibition of haemagglutination and adhesion was variable in vitro. When inhibition did take place in any one strain, both haemagglutination and adhesion were affected. These results confirm those of other authors and indicate that the effect of sub-MIC doses of a given antibiotic is strain-specific; they also indirectly show the heterogeneity of E. coli strains isolated from urine. It thus seems unlikely that, in clinical conditions, a single antibiotic is capable of reducing adhesion, given the diversity of the adhesins found in pathogenic E. coli strains.

Bacterial Adhesion↗

PubMed1994

Salivary gland extracts of partially fed Dermacentor reticulatus ticks decrease natural killer cell activity in vitro.

The salivary glands and saliva of ticks (Arachnida, Acari, Ixodida) play a vital role in blood feeding, including manipulation of the host's immune response to tick infestation. Furthermore, a diverse number of tick-borne pathogens are transmitted to vertebrate hosts via tick saliva. A factor synthesized in the salivary glands of feeding ticks potentiates the transmission of certain tick-borne viruses. We show that salivary gland extracts (SGE) derived from Dermacentor reticulatus female ticks fed for 6 days on laboratory mice (SGED6) induced a decrease in the natural killer (NK) activity of effector cells obtained from 16 healthy blood donors. The decreased activity ranged from 14 to 69% of NK activity observed with the respective untreated effector cells. Such a decrease was not observed after treatment of effector cells with SGE from unfed ticks. Ten-fold dilution of SGED6 significantly reduced the capacity to decrease NK activity and a further 10-fold dilution almost eliminated the effect. After addition of IFN-alpha 2, the SGED6-induced decrease in NK activity was restored to activity levels approaching those of untreated cells. The apparent reversibility of the inhibition indicates that the effect of SGED6 on NK activity was not due to cytotoxicity. The results demonstrate the presence of a factor(s) in the salivary gland products of feeding D. reticulatus female ticks that influences human NK activity in vitro. These data suggest a possible mechanism by which tick SGE potentiates the transmission of some tick-borne viruses through suppression of NK activity.

Animals↗

PubMed2000

Molecular and pathogenic characterization of Borrelia burgdorferi sensu lato isolates from Spain.

Fifteen Borrelia burgdorferi sensu lato isolates from questing ticks and skin biopsy specimens from erythema migrans patients in three different areas of Spain were characterized. Four different genospecies were found (nine Borrelia garinii, including the two human isolates, three B. burgdorferi sensu stricto, two B. valaisiana, and one B. lusitaniae), showing a diverse spectrum of B. burgdorferi sensu lato species. B. garinii isolates were highly variable in terms of pulsed-field gel electrophoresis pattern and OspA serotype, with four of the seven serotypes described. One of the human isolates was OspA serotype 5, the same found in four of seven tick isolates. The second human isolate was OspA serotype 3, which was not present in ticks from the same area. Seven B. garinii isolates were able to disseminate through the skin of C3H/HeN mice and to cause severe inflammation of joints. One of the two B. valaisiana isolates also caused disease in mice. Only one B. burgdorferi sensu stricto isolate was recovered from the urinary bladder. One isolate each of B. valaisiana and B. lusitaniae were not able to disseminate through the skin of mice or to infect internal organs. In summary, there is substantial diversity in the species and in the pathogenicity of B. burgdorferi sensu lato in areas in northern Spain where Lyme disease is endemic.

Animals↗

PubMed2000

Antigenic and sequence diversity in gonococcal transferrin-binding protein A.

Neisseria gonorrhoeae is a gram-negative pathogen that is capable of satisfying its iron requirement with human iron-binding proteins such as transferrin and lactoferrin. Transferrin-iron utilization involves specific binding of human transferrin at the cell surface to what is believed to be a complex of two iron-regulated, transferrin-binding proteins, TbpA and TbpB. The genes encoding these proteins have been cloned and sequenced from a number of pathogenic, gram-negative bacteria. In the current study, we sequenced four additional tbpA genes from other N. gonorrhoeae strains to begin to assess the sequence diversity among gonococci. We compared these sequences to those from other pathogenic bacteria to identify conserved regions that might be important for the structure and function of these receptors. We generated polyclonal mouse sera against synthetic peptides deduced from the TbpA sequence from gonococcal strain FA19. Most of these synthetic peptides were predicted to correspond to surface-exposed regions of TbpA. We found that, while most reacted with denatured TbpA in Western blots, only one antipeptide serum reacted with native TbpA in the context of intact gonococci, consistent with surface exposure of the peptide to which this serum was raised. In addition, we evaluated a panel of gonococcal strains for antigenic diversity using these antipeptide sera.

Amino Acid Sequence↗

PubMed2025

Candida glabrata replicating within macrophages experiences amino acid deprivation, DNA damage, and chromosome instability.

Macrophages, the central players of innate immunity, control invading microbes by encapsulating them inside the phagosome, a nutrient-poor, reactive oxidant species-rich organelle. Nevertheless, some microbes, including the opportunistic yeast pathogen Candida glabrata, noted for its karyotype diversity, rapid evolution of antifungal drug resistance, and lack of meiosis, can survive and even replicate inside macrophages. However, it is not fully understood how C. glabrata responds to macrophage engulfment, and it is unknown how this presumably DNA-damaging environment influences the pathogen's genome stability. In this study, we used comparative transcriptomics to identify amino acid starvation and DNA damage as conditions eliciting C. glabrata responses most similar to macrophage engulfment. Consistent with this, we found that C. glabrata intra-macrophage survival and replication require master regulator of amino acid biosynthesis GCN4 and functional DNA double-strand break repair. Furthermore, comet assays provided the first direct evidence for increased DNA breaks in intra-macrophage yeast, and pulse-field gel electrophoresis showed that chromosomal alterations occur frequently in macrophage-passaged C. glabrata. Interestingly, these alterations could not be resolved by long read DNA sequencing, suggesting that they involved highly complex repetitive regions. Finally, we identified several point mutations emerging during macrophage passaging and showed that among them, a frameshift in RME1 (repressor of meiosis in Saccharomyces cerevisiae), increased C. glabrata intra-macrophage fitness. Together, these analyses point to amino acid deprivation, reveal elevated DNA breakage and chromosome instability, and raise intriguing questions about the role of meiotic gene orthologs in C. glabrata persisting and replicating within macrophages.

Journal Article↗

PubMed2006

[The role of integrins in the physiologic and pathogenic processes].

Cell adhesion molecules (CAM) are a numerous, diverse group of cell surface proteins, which are both receptors and ligands for receptors. Their functions include adhesion, recognition, cell-cell interaction, and communication between mediate cells and extracellular matrix. The following groups of CAM can be distinguished: seletins, integrins, cadherins and other isoforms, including CD 44. Integrins are heterodimers formed from the alpha and beta chains. The a subclass is responsible for a specific bond with ligands. It defines the specificity of integrins. The 8 chain participates in the integration with cytoskeleton ptoteins. It determines the functions of the integrin receptor. The best recognized integrins include: integrin beta1, beta2 and beta3. The expression and activity of integrins have been found to be affected by a variety of factors being either activators or inhibitors. Adhesion molecules (including integrins) play a significant role in both physiological processes (embryogenesis, organogenesis, the normal growth and tissue development) and pathogenic ones. In the latter case, they are particularly involved in inflammatory, allergic and neoplastic diseases. The role of integrins is also emphasized in organ response to trauma and in skin lesion redevelopment. The knowlegde of the integrin molecular basis and that of other adhesion molecules can contribute significantly to the creation of new diagnostic and therapeutic perspectives. An adequate modification of cellular adhesion constitutes a promising way of the pathogenic processes control.

Animals↗

PubMed2004

Management of disease resistance diversity of cultivars of a species in single fields: controlling epidemics.

The use of a diversity of resistance genes limits the development of polycyclic epidemics caused by airborne pathogens and reduces the risk that resistance be overcome by virulent races. Diversity can be easily achieved by growing mixtures of cultivars with different resistance genes and homogeneous agronomic traits. The mechanisms by which disease is reduced in cultivar mixtures include the loss of inoculum due to the presence of resistant plants between susceptible ones and resistance induced by avirulent pathogens. The complementary effects of individual mixture components reacting to disease pressure and to abiotic stresses result in greater yield stability compared with pure stands. The quality of products from mixtures is at least equal to that obtained with pure stands. This type of resistance management is applicable to both annual and perennial crops.

Agriculture↗

PubMed2025

Foliar disease resistance phenomics of fungal pathogens: image-based approaches for mapping quantitative resistance in cereal germplasm.

Host plant resistance is the most effective and environmentally sustainable means of reducing yield losses caused by fungal foliar pathogens of cereal species. Cereal genebank collections hold diverse pools of potentially underutilized disease resistance alleles, and cereal genomic resources are well advanced due to large-scale sequencing and genotyping efforts. Genome-Wide Association Studies (GWAS) have emerged as the predominant association genetics technique to initially discover novel disease resistance loci or alleles in these diverse collections. Traditional disease resistance phenotyping methods are reliant on visual estimation of disease symptom severity and have successfully supported genetic mapping studies either via GWAS or QTL mapping in biparental populations facilitating both marker development and gene cloning efforts. Due to foliar pathogens having a high capacity to evolve, there is a need to pyramid disease resistance genes with diverse mechanisms for durable control. Resistance expressed as a quantitative trait, known as quantitative resistance (QR), is hypothesized to be more durable, unlike major R-gene resistance that is race-specific and can be vulnerable to breaking down without gene stewardship. However, assessing QR visually is challenging, particularly when complicated by complex genotype × environment (G × E) effects in the field. High-throughput image-based phenotyping provides accurate and unbiased data that can support foliar disease resistance screening efforts of genebank collections using GWAS. In this review, we discuss image-based disease phenotyping based on macroscopic (visible symptoms) and microscopic features during the host-pathogen interaction. Quantitative image analysis approaches using conventional and artificial intelligence (AI) algorithms are also discussed.

Disease Resistance↗

PubMed1993

The identification of uncultured microbial pathogens.

Clinicians have long been aware of human diseases that are associated with visible but uncultured microorganisms. Without the ability to cultivate these organisms, they have remained unidentified. Environmental microbiologists have also discovered on the basis of recent advances in the field of molecular phylogeny that culture-based methods for detecting microorganisms are biased and insensitive. A culture-independent experimental approach is described for the identification of microbial pathogens. This approach incorporates fundamental aspects of 16S rRNA-based molecular phylogeny as well as nucleic acid amplification technology. From its application to Whipple's disease, one can speculate as to the potential insights a highly sensitive, culture-independent method may provide into the diversity and natural ecology of human microbial pathogens.

Bacteria↗

PubMed2006

Expression profiling and mutant analysis reveals complex regulatory networks involved in Arabidopsis response to Botrytis infection.

The expression profiles of Botrytis-inoculated Arabidopsis plants were studied to determine the nature of the defense transcriptome and to identify genes involved in host responses to the pathogen. Normally resistant Arabidopsis wild-type plants were compared with coi1, ein2, and nahG plants that are defective in various defense responses and/or show increased susceptibility to Botrytis. In wild-type plants, the expression of 621 genes representing approximately 0.48% of the Arabidopsis transcriptome was induced greater than or equal to twofold after infection. Of these 621 Botrytis-induced genes (BIGs), 462 were induced at or before 36 h post-inoculation, and may be involved in resistance to the pathogen. The expression of 181 BIGs was dependent on a functional COI1 gene required for jasmonate signaling, whereas the expression of 63 and 80 BIGs were dependent on ethylene (ET) signaling or salicylic acid accumulation, respectively, based on results from ein2 and nahG plants. BIGs encode diverse regulatory and structural proteins implicated in pathogen defense and abiotic and oxidative-stress responses. Thirty BIGs encode putative DNA-binding proteins that belong to ET response, zinc-finger, MYB, WRKY, and HD-ZIP family transcription-factor proteins. Fourteen BIGs were studied in detail to determine their role in resistance to Botrytis. T-DNA insertion alleles of ZFAR1 (At2G40140), the gene encoding a putative zinc-finger protein with ankyrin-repeat domains, showed increased local susceptibility to Botrytis and sensitivity to germination in the presence of abscisic acid (ABA), supporting the role of ABA in mediating responses to Botrytis infection. In addition, two independent T-DNA insertion alleles in the WRKY70 gene showed increased susceptibility to Botrytis. The transcriptional activation of genes involved in plant hormone signaling and synthesis, removal of reactive oxygen species, and defense and abiotic-stress responses, coupled with the susceptibility of the wrky70 and zfar1 mutants, highlights the complex genetic network underlying defense responses to Botrytis in Arabidopsis.

Ankyrin Repeat↗

PubMed2002

Assessment of genetic management at three specific-pathogen-free rhesus macaque (Macaca mulatta) colonies.

Genetic management is required to maintain genetic diversity by minimizing inbreeding and genetic subdivision in colonies of animals bred for biomedical research. Polymorphic short tandem repeat (STR) loci are useful for genetic management because they facilitate parentage assignments, genetic characterization of individuals, and estimates of baseline population genetic parameters. Using highly informative STR loci, we estimated gene diversity and F-statistics to determine the level of genetic heterogeneity and genetic structure of three specific-pathogen-free (SPF) rhesus macaque (Macaca mulatta) colonies. Effective population sizes, variance in male reproductive success, and rate of decrease in genetic variability also were estimated for two of the three colonies. We documented the overall success of genetic management in maintaining genetic diversity in captive colonies. We report that even genetically managed SPF colonies, despite maintaining high and stable levels of gene diversity (over 0.75), are prone to genetic subdivision due to different management strategies, founder effects, genetic isolation, and drift. These processes are accelerated by the high variances in male reproductive success and low adult sex ratios that are typical of captive rhesus macaque breeding groups, both of which reduce the effective population sizes of these groups.

Animal Husbandry↗

PubMed2025

Mapping genetic and phenotypic diversity of Pseudomonas aeruginosa across clinical and environmental isolation sites.

Pseudomonas aeruginosa is a clinically significant opportunistic pathogen adept at thriving in both host-associated and environmental settings. To define the extent to which P. aeruginosa isolates specialize across niches and identify genotype-phenotype correlates, we performed whole genome sequencing and comprehensive phenotypic characterization of 125 P. aeruginosa isolates from diverse clinical and environmental sites, evaluating virulence-associated traits, including motility, cytotoxicity, biofilm formation, pyocyanin production, and antimicrobial susceptibility. We identify that genomic diversity does not correlate with isolation source or most virulence phenotypes. Instead, we find that the two major P. aeruginosa clades (Groups A and B) delineate phylogeny and cytotoxicity, with Group B strains showing significantly higher cytotoxicity than Group A. Sequence analysis revealed previously uncharacterized alleles of genes encoding type III secretion effector proteins. We observed high variability amongst strains and isolation sources in all four assayed virulence phenotypes. Antimicrobial resistance (AMR) is exclusively observed in clinical isolates, not environmental, reflecting antibiotic exposure-driven selection. Bacterial GWAS revealed a statistically significant association between cytotoxicity and exoU presence, and we identified a novel exoU allelic variant with decreased cytotoxicity, demonstrating that functional diversity within well-characterized virulence factors may still influence pathogenic outcomes. In summary, our analyses of 125 diverse isolates suggest that the ability of P. aeruginosa to thrive across diverse niches is driven by broadly conserved genetic repertoire rather than niche-specific accessory genes.

Journal Article↗

PubMed1989

Genetic variability for pathogenicity, isozyme, ribosomal DNA and colony color variants in populations of Rhynchosporium secalis.

Samples of Rhynchosporium secalis were collected from two experimental barley populations known to carry a diverse array of alleles for resistance to this fungal pathogen. Classification of 163 isolates for four putative isozyme systems, a colony color dimorphism and 20 ribosomal DNA restriction fragment length variants revealed 49 different multilocus phenotypes (haplotypes). The six most common haplotypes differed significantly in pathogenicity. Genetic analyses of the data indicated that effective population sizes of the fungus were very large, that the effects of genetic drift were small, and that negligible recombination occurred in the populations studied. Frequency dependent selection was suggested as an explanation for the maintenance of variation in pathogenicity in the fungus.

DNA, Fungal↗

PubMed2003

Making inroads into plant receptor kinase signalling pathways.

Cell-membrane-located receptor kinases play important roles in many plant signal-transduction pathways. Exciting progress has been made in recent years with the characterization of four ligand-receptor systems involved in physiological processes as diverse as self-pollen rejection, stem-cell maintenance and differentiation at the shoot meristem, the response to the brassinosteroid hormones and the innate response to bacterial pathogens. These new findings emphasize the remarkably high diversity of these signalling pathways, although some downstream components are shared. This observation supports the idea that the wide diversification of plant receptors is associated with a high degree of specialization, one receptor potentially regulating a single developmental process. However, the possibility that one receptor might have a dual recognition function cannot be ruled out.

Ligands↗

PubMed2001

Lipopolysaccharide endotoxins.

Bacterial lipopolysaccharides (LPS) typically consist of a hydrophobic domain known as lipid A (or endotoxin), a nonrepeating "core" oligosaccharide, and a distal polysaccharide (or O-antigen). Recent genomic data have facilitated study of LPS assembly in diverse Gram-negative bacteria, many of which are human or plant pathogens, and have established the importance of lateral gene transfer in generating structural diversity of O-antigens. Many enzymes of lipid A biosynthesis like LpxC have been validated as targets for development of new antibiotics. Key genes for lipid A biosynthesis have unexpectedly also been found in higher plants, indicating that eukaryotic lipid A-like molecules may exist. Most significant has been the identification of the plasma membrane protein TLR4 as the lipid A signaling receptor of animal cells. TLR4 belongs to a family of innate immunity receptors that possess a large extracellular domain of leucine-rich repeats, a single trans-membrane segment, and a smaller cytoplasmic signaling region that engages the adaptor protein MyD88. The expanding knowledge of TLR4 specificity and its downstream signaling pathways should provide new opportunities for blocking inflammation associated with infection.

ATP-Binding Cassette Transporters↗

PubMed2001

Pneumocystis carinii: genetic diversity and cell biology.

As an important opportunistic pulmonary pathogen, Pneumocystis carinii has been the focus of extensive research over the decades. The use of laboratory animal models has permitted a detailed understanding of the host-parasite interaction but an understanding of the basic biology of P. carinii has lagged due in large part to the inability of the organism to grow well in culture and to the lack of a tractable genetic system. Molecular techniques have demonstrated extensive heterogeneity among P. carinii organisms isolated from different host species. Characterization of the genes and genomes of the Pneumocystis family has supported the notion that the family comprises different species rather than strains within the genus Pneumocystis and contributed to the understanding of the pathophysiology of infection. Many of the technical obstacles in the study of the organisms have been overcome in the past decade and the pace of research into the basic biology of the organism has accelerated. Biochemical pathways have been inferred from the presence of key enzyme activities or gene sequences, and attempts to dissect cellular pathways have been initiated. The Pneumocystis genome project promises to be a rich source of information with regard to the functional activity of the organism and the presence of specific biochemical pathways. These advances in our understanding of the biology of this organism should provide for future studies leading to the control of this opportunistic pathogen.

Animals↗

PubMed1989

Active sensitization does not increase the responsivity of rat peritoneal mast cells to diverse chemical stimuli.

Peritoneal mast cells from specific pathogen-free rats that had been sensitized to the nematode Nippostrongylus brasiliensis released histamine in a dose-dependent fashion on challenge with antigen, anti-rat IgE, anti-rat IgG and concanavalin A. Cells from non-sensitized animals showed weak or insignificant responses to these agents. However, the two preparations did not obviously differ in their reactivity to a range of pharmacological agents including ATP, dextran, polyamines and calcium ionophores. Both populations were refractory to cholinergic stimulation. These results show that active sensitization does not per se lead to a global increase in mast cell reactivity or releasability.

Adenosine Triphosphate↗