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PubMed2005

Virulence and molecular diversity in Colletotrichum graminicola from Brazil.

Genetic diversity among 37 isolates of the sorghum anthracnose pathogen Colletotrichum graminicola, from four geographically distinct regions of Brazil, was evaluated by RAPD and RFLP-PCR markers and virulence characters on a set of 10 differential sorghum genotypes. Twenty-two races were identified and race 13B was the most frequent, but present in only two regions. RAPD analysis revealed 143 polymorphic bands that grouped the isolates according to their geographic origin, but not by their virulence phenotypes. RFLP with HaeIII, MspI, HinfI, HhaI, HpaII, EcoRI, HindIII, PstI, RsaI, Taq alphaI, and AluI enzymes over ITS domains and 5.8 rDNA genes of C. graminicola did not show differences among the isolates, indicating high conservation of these restriction sites. Molecular polymorphism was observed among isolates belonging to the same race. No association between virulence phenotypes and molecular profiles was observed.

Brazil↗

PubMed2006

Ecological and evolutionary forces shaping microbial diversity in the human intestine.

The human gut is populated with as many as 100 trillion cells, whose collective genome, the microbiome, is a reflection of evolutionary selection pressures acting at the level of the host and at the level of the microbial cell. The ecological rules that govern the shape of microbial diversity in the gut apply to mutualists and pathogens alike.

Animals↗

PubMed2006

Reshaping the past: Strategies for modulating T-cell memory immune responses.

Memory T cells are generated following an initial encounter with antigen, persist over the lifetime of an individual, and mediate rapid and robust functional responses upon antigenic recall. While immune memory is generally associated with protective immune response to pathogens, memory T cells can be generated to diverse types of antigens including autoantigens and alloantigens through homologous or crossreactive priming and comprise the majority of circulating T cells during adulthood. Memory T cells can therefore play critical roles in propagating and perpetuating autoimmune disease and in mediating allograft rejection, although the precise pathways for regulation of memory immune responses remain largely undefined. Moreover, evaluating and designing strategies to modulate memory T-cell responses are challenging given the remarkable heterogeneity of memory T cells, with different subsets predominating in lymphoid versus non-lymphoid tissue sites. In this review, we discuss what is presently known regarding the effect of current immunomodulation strategies on the memory T-cell compartment and potential strategies for controlling immunological recall.

Animals↗

PubMed2005

Endophytic and ectophytic potato-associated bacterial communities differ in structure and antagonistic function against plant pathogenic fungi.

Differences between endophytic and ectophytic bacterial communities with stress on antagonistic bacteria, were studied by comparing the composition of communities isolated from the rhizosphere, phyllosphere, endorhiza and endosphere of field-grown potato plants using a multiphasic approach. Terminal restriction fragment length polymorphism analysis of 16S rDNA of the bacterial communities revealed discrete microenvironment-specific patterns. To measure the antagonistic potential of potato-associated bacteria, a total of 2648 bacteria were screened by dual testing of antagonism to the soilborne pathogens Verticillium dahliae and Rhizoctonia solani. Composition and diversity of bacterial antagonists were mainly specific for each microenvironment. The rhizosphere and endorhiza were the main reservoirs for antagonistic bacteria and showed the highest similarity in their colonisation by antagonists. The most prominent species of all microenvironments was Pseudomonas putida, and rep-PCR with BOX primers showed that these isolates showed microenvironment-specific DNA fingerprints. P. putida isolates from the rhizosphere and endorhiza gave nearly identical fingerprints confirming the high similarity of bacterial populations. The phlD gene, involved in the production of the antibiotic 2,4-diacetyl-phloroglucinol, was found only among Pseudomonas isolates from the rhizosphere and endorhiza. Evaluation of the bacterial isolates for biocontrol potential based on fungal antagonism and physiological characteristics resulted in the selection of five promising isolates from each microenvironment. The most effective isolate was Serratia plymuthica 3Re4-18 isolated from the endorhiza.

Bacteria↗

PubMed2005

Biofilm formation and dispersal and the transmission of human pathogens.

Several pathogenic bacterial species that are found in the environment can form complex multicellular structures on surfaces known as biofilms. Pseudomonas aeruginosa, Vibrio cholerae and certain species of nontuberculous mycobacteria are examples of human pathogens that form biofilms in natural aquatic environments. We suggest that the dynamics of biofilm formation facilitates the transmission of pathogens by providing a stable protective environment and acting as a nidus for the dissemination of large numbers of microorganisms; both as detached biofilm clumps and by the fluid-driven dispersal of biofilm clusters along surfaces. We also suggest that emerging evidence indicates that biofilm formation conveys a selective advantage to certain pathogens by increasing their ability to persist under diverse environmental conditions.

Bacteria↗

PubMed2004

Classification of papillomaviruses.

One hundred eighteen papillomavirus (PV) types have been completely described, and a yet higher number of presumed new types have been detected by preliminary data such as subgenomic amplicons. The classification of this diverse group of viruses, which include important human pathogens, has been debated for three decades. This article describes the higher-order PV taxonomy following the general criteria established by the International Committee on the Taxonomy of Viruses (ICTV), reviews the literature of the lower order taxa, lists all known "PV types", and interprets their phylogenetic relationship. PVs are a taxonomic family of their own, Papillomaviridae, unrelated to the polyomaviruses. Higher-order phylogenetic assemblages of PV types, such as the "genital human PVs", are considered a genus, the latter group, for example, the genus "Alpha-Papillomavirus". Lower-order assemblages of PV types within each genus are treated as species because they are phylogenetically closely related, but while they have distinct genomic sequences, they have identical or very similar biological or pathological properties. The taxonomic status of PV types, subtypes, and variants remains unchanged and is based on the traditional criteria that the sequence of their L1 genes should be at least 10%, 2-10%, and maximally 2% dissimilar from one another.

Papillomaviridae↗

PubMed2002

DNA vaccination against feline calicivirus infection using a plasmid encoding the mature capsid protein.

Feline calicivirus (FCV), a member of the diverse family Caliciviridae, is a respiratory and oral pathogen of cats. Although conventional FCV vaccines are available, there are some safety and efficacy problems associated with their use. The potential of DNA vaccination against FCV infection was therefore explored. Four cats were inoculated intramuscularly with three 100 microg doses, 2 weeks apart, with a plasmid (pF9VAC) containing the mature capsid protein gene of FCV strain F9. Four control cats received the same plasmid lacking the FCV gene insert. All eight cats showed clinical signs following heterologous challenge with FCV strain LS027. However, rectal temperatures and general clinical sign scores were significantly lower in vaccinates compared to controls, and there was a marked difference in ulcer distribution between the two groups. Although no serological responses were detected in either group prior to challenge, post-challenge titres in the vaccinated group were generally higher. The results indicate that partial protection against a calicivirus is possible by DNA vaccination but that other approaches to enhance efficacy such as the use of cytokine genes or prime-boost protocols may also be required.

Animals↗

PubMed2001

The structure and function of drug pumps.

Resistance to drugs has emerged in biological systems as diverse as cancer cells undergoing chemotherapy and microbial pathogens undergoing treatment with antimicrobials. This medical problem is escalating and there is an urgent need for the development of new classes of drugs. In the case of pathogenic bacteria, we are rapidly approaching a scenario where there will be no effective antibiotics in the armoury of drugs available for treating the infectious diseases that these bacteria cause, returning us to the pre-antibiotic era when infectious diseases were rife because they were untreatable. One of the most frequently employed resistance strategies in both prokaryotes and eukaryotes is the transmembrane-protein-catalysed extrusion of drugs from the cell, with these proteins acting like bilge pumps, reducing the intracellular drug concentration to subtoxic levels. There is currently much scientific interest in understanding how these pumps operate, so that we might design transport inhibitors that would block them, allowing a renaissance for drugs that are no longer effective owing to their efflux.

Bacteria↗

PubMed2004

The collagen binding alpha1beta1 integrin VLA-1 regulates CD8 T cell-mediated immune protection against heterologous influenza infection.

A common feature of many infections is that many pathogen-specific memory T cells become established in diverse nonlymphoid tissues. A mechanism that promotes the retention and survival of the memory T cells in diverse tissues has not been described. Our studies show that the collagen binding alpha1beta1 integrin, VLA-1, is expressed by the majority of influenza-specific CD8 T cells recovered from nonlymphoid tissues during both the acute and memory phases of the response. Antibody treatment or genetic deficiency of VLA-1 decreased virus-specific CTL in the lung and other nonlymphoid tissues, and increased them in the spleen. In spite of the increase in the spleen, secondary heterosubtypic immunity against flu was compromised. This suggests that VLA-1 is responsible for retaining protective memory CD8 T cells in the lung and other tissues via attachment to the extracellular matrix.

Animals↗

PubMed1998

DNA vaccines with single-chain Fv fused to fragment C of tetanus toxin induce protective immunity against lymphoma and myeloma.

Vaccination with idiotypic protein protects against B-cell lymphoma, mainly through anti-idiotypic antibody. For use in patients, DNA vaccines containing single-chain Fv derived from tumor provide a convenient alternative vaccine delivery system. However, single-chain Fv sequence alone induces low anti-idiotypic response and poor protection against lymphoma. Fusion of the gene encoding fragment C of tetanus toxin to single-chain Fv substantially promotes the anti-idiotypic response and induces strong protection against B-cell lymphoma. The same fusion design also induces protective immunity against a surface Ig-negative myeloma. These findings indicate that fusion to a pathogen sequence allows a tumor antigen to engage diverse immune mechanisms that suppress growth. This fusion design has the added advantage of overcoming potential tolerance to tumor that may exist in patients.

Animals↗

PubMed2002

Ubiquitin ligase-associated protein SGT1 is required for host and nonhost disease resistance in plants.

Homologues of the yeast ubiquitin ligase-associated protein SGT1 are required for disease resistance in plants mediated by nucleotide-binding site/leucine-rich repeat (NBS-LRR) proteins. Here, by silencing SGT1 in Nicotiana benthamiana, we extend these findings and demonstrate that SGT1 has an unexpectedly general role in disease resistance. It is required for resistance responses mediated by NBS-LRR and other R proteins in which pathogen-derived elicitors are recognized either inside or outside the host plant cell. A requirement also exists for SGT1 in nonhost resistance in which all known members of a host species are resistant against every characterized isolate of a pathogen. Our findings show that silencing SGT1 affects diverse types of disease resistance in plants and support the idea that R protein-mediated and nonhost resistance may involve similar mechanisms.

Amino Acid Sequence↗

PubMed1998

PCR-based subtractive hybridization and differences in gene content among strains of Helicobacter pylori.

Genes that are characteristic of only certain strains of a bacterial species can be of great biologic interest. Here we describe a PCR-based subtractive hybridization method for efficiently detecting such DNAs and apply it to the gastric pathogen Helicobacter pylori. Eighteen DNAs specific to a monkey-colonizing strain (J166) were obtained by subtractive hybridization against an unrelated strain whose genome has been fully sequenced (26695). Seven J166-specific clones had no DNA sequence match to the 26695 genome, and 11 other clones were mixed, with adjacent patches that did and did not match any sequences in 26695. At the protein level, seven clones had homology to putative DNA restriction-modification enzymes, and two had homology to putative metabolic enzymes. Nine others had no database match with proteins of assigned function. PCR tests of 13 unrelated H. pylori strains by using primers specific for 12 subtracted clones and complementary Southern blot hybridizations indicated that these DNAs are highly polymorphic in the H. pylori population, with each strain yielding a different pattern of gene-specific PCR amplification. The search for polymorphic DNAs, as described here, should help identify previously unknown virulence genes in pathogens and provide new insights into microbial genetic diversity and evolution.

Animals↗

PubMed1991

Genetic dissection of T cell receptor V beta gene requirements for spontaneous murine diabetes.

It has been demonstrated, in certain autoimmune disease models, that pathogenic T cells express antigen receptors of limited diversity. It has been suggested that the T cells responsible for the pathogenesis of type I diabetes mellitus might similarly demonstrate restricted T cell receptor (TCR) usage. Recently, attempts have been made to identify the V beta subset(s) that initiates and/or perpetuates the antiislet response in a mouse model of spontaneous autoimmune diabetes (non-obese diabetic [NOD] mice). In studies reported here, we have bred NOD mice to a mouse strain that congenitally lacks approximately one-half of the conventional TCR V beta alleles. Included in this deletion are TCR V beta gene products previously implicated as being involved in the pathogenesis of NOD disease. By studying second backcross-intercross animals, we were able to demonstrate that this deletion of TCR V beta gene segments did not prevent the development of insulitis or diabetes.

Animals↗

PubMed2000

Bacterial monopolists: the bundling and dissemination of antimicrobial resistance genes in gram-positive bacteria.

Antibiotic resistance is the unavoidable result of our placing selective pressure on the microbial community. Advances in molecular biology techniques in the past 2 decades have allowed us to greatly improve our understanding of the mechanisms by which resistance emerges and disseminates among human pathogenic bacteria. Gram-positive bacteria employ a diverse array of elements, including plasmids, transposons, insertion sequences, and bacteriophages, to disseminate resistance. An understanding of these mechanisms and their prevalence can improve our ability to treat clinical infections in hospitalized patients, as well as to predict and control the spread of resistant bacteria in the nosocomial environment.

Conjugation, Genetic↗

PubMed1999

Susceptibility to infectious diseases: Leishmania as a paradigm.

The diverse response of individuals within populations to infectious pathogens remains poorly understood, although genetic determinants undoubtedly contribute in substantial ways to the outcome of infection. In a mouse model of infection with the intramacrophage protozoan Leishmania major, susceptibility correlates both with aberrant helper T cell differentiation biased towards the production of interleukin 4 and with the presence of an endogenous CD4 T cell repertoire that recognizes an immunodominant parasite antigen with high frequency. In the setting of the particular ecological niche occupied by Leishmania, this combination of otherwise unrelated factors synergizes to result in exquisite susceptibility to this single pathogen, without seemingly compromising host defenses against other agents. Similar paradigms could underlie susceptibility to other pathogenic organisms.

Amino Acid Sequence↗

PubMed1997

Helicobacter pylori populations in Peruvian patients.

Helicobacter pylori is an extremely diverse species. The characterization of strains isolated from individual patients should give insights into colonization and disease mechanisms and bacterial evolution. We studied H. pylori isolates from patients in the Japanese-Peruvian Polyclinic in Lima, Peru, by determining metronidazole susceptibility or resistance and by random amplified polymorphic DNA (RAPD) fingerprinting (a measure of overall genotype). Strains isolated from several biopsy specimens from each of 24 patients were studied. Both metronidazole-susceptible and -resistant strains were isolated from 13 patients, whereas strains of more than one RAPD type were isolated from only seven patients. We propose that the homogeneity in RAPD fingerprints for strains isolated from most persons reflects selection for particular H. pylori genotypes during chronic infection in individual hosts and the human diversity in traits that are important to this pathogen. Carriage of related metronidazole-resistant and -susceptible strains could reflect frequent metronidazole use in Peru and alternating selection for resistant and susceptible phenotypes during and after metronidazole therapy.

Adult↗

PubMed1979

Pseudogonococcal ophthalmia neonatorum. Branhamella (Neisseria) catarrhalis conjunctivitis.

A culture from conjunctivitis occurring in a neonate in association with a recurrent fever yielded a nearly pure growth of Branhamella (Neisseria) catarrhalis. The conjunctivitis was not appreciated and effectively treated until a second hospitalization in the fourth week of life. Partial suppression of symptoms had followed short-term parenteral antibiotic therapy during the first admission. Resolution quickly occurred in response to instillation of sodium sulfacetamide ophthalmic solution. Although B. catarrhalis is considered a non-pathogen, the literature reviewed included a number of diverse infections, but no previous instance of conjunctivitis. The organism's close similarities to Neisseria gonorrhoeae necessitate isolation and correct biochemical differentiation. Misdiagnosis of gonococcal conjunctivitis carries obvious social, psychological and medical impact.

Conjunctivitis↗

PubMed1999

Population structure and dynamics of Magnaporthe grisea in the Indian Himalayas.

The population genetics of Magnaporthe grisea, the rice blast pathogen, were analyzed in a center of rice diversity (the Uttar Pradesh hills of the Indian Himalayas) using multilocus and single-, or low-copy, DNA markers. Based on DNA fingerprinting with the multilocus probe MGR586 and single-locus probes, 157 haplotypes clustered into 56 lineages (at >/=70% MGR586 band similarity, each with unique single-locus profiles) and high diversity indices were detected among 458 isolates collected from 29 sites during 1992-1995. Most valleys sampled had distinct populations (73% of the lineages were site specific) with some containing one or a few lineages, confirming the importance of clonal propagation, and others were very diverse. Widely distributed lineages suggested that migration occurs across the region and into the Indo-Gangetic plains. Repeated sampling at one site, Matli, (170 isolates, 1992-1995) yielded 19 lineages and diversity significantly greater than that reported from similar samples from Colombia and the Philippines. Analysis of allelic associations using pairwise comparisons and multilocus variance analysis failed to reject the hypothesis of gametic phase equilibrium. The Matli population shifted from highly diverse in 1992 to almost complete dominance by one lineage in 1995. Such population dynamics are consistent with recombination followed by differential survival of clonal descendants of recombinant progeny. At another site, Ranichauri, population (n = 84) composition changed from 2 to 11 lineages over 2 yr and yielded additional evidence for equilibrium. Sexually fertile and hermaphrodite isolates of both mating types were recovered from rice in both Matli and Ranichauri. We demonstrate that Himalayan M. grisea populations are diverse and dynamic and conclude that the structure of some populations may be affected to some extent by sexual recombination.

Crosses, Genetic↗