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At least 631 records · Page 35Linked to original sources

PubMed2005

Prediction of pathogen growth on iceberg lettuce under real temperature history during distribution from farm to table.

The growth of pathogenic bacteria Escherichia coli O157:H7, Salmonella spp., and Listeria monocytogenes on iceberg lettuce under constant and fluctuating temperatures was modelled in order to estimate the microbial safety of this vegetable during distribution from the farm to the table. Firstly, we examined pathogen growth on lettuce at constant temperatures, ranging from 5 to 25 degrees C, and then we obtained the growth kinetic parameters (lag time, maximum growth rate (micro(max)), and maximum population density (MPD)) using the Baranyi primary growth model. The parameters were similar to those predicted by the pathogen modelling program (PMP), with the exception of MPD. The MPD of each pathogen on lettuce was 2-4 log(10) CFU/g lower than that predicted by PMP. Furthermore, the MPD of pathogens decreased with decreasing temperature. The relationship between mu(max) and temperature was linear in accordance with Ratkowsky secondary model as was the relationship between the MPD and temperature. Predictions of pathogen growth under fluctuating temperature used the Baranyi primary microbial growth model along with the Ratkowsky secondary model and MPD equation. The fluctuating temperature profile used in this study was the real temperature history measured during distribution from the field at harvesting to the retail store. Overall predictions for each pathogen agreed well with observed viable counts in most cases. The bias and root mean square error (RMSE) of the prediction were small. The prediction in which mu(max) was based on PMP showed a trend of overestimation relative to prediction based on lettuce. However, the prediction concerning E. coli O157:H7 and Salmonella spp. on lettuce greatly overestimated growth in the case of a temperature history starting relatively high, such as 25 degrees C for 5 h. In contrast, the overall prediction of L. monocytogenes under the same circumstances agreed with the observed data.

Colony Count, Microbial↗

PubMed2006

From insects to human hosts: Identification of major genomic differences between entomopathogenic strains of Photorhabdus and the emerging human pathogen Photorhabdus asymbiotica.

Pathogenic bacteria of the genus Photorhabdus are naturally found in symbiotic association with soil entomopathogenic nematodes, and are of increasing economic interest in view of their potential for the development of novel biopesticides. This bipartite natural system is currently used for the biological control of crop pests in several countries. However, an increasing number of Photorhabdus strains have recently been isolated from human clinical specimens in both the United States and Australia, associated with locally invasive soft tissue infections and disseminated bacteraemia. In view of their growing use in biological control, which increases the potential rate of exposure of humans to these pathogens, we decided to undertake a comparative study of the genomic differences between insect and human pathogenic strains of Photorhabdus, in an attempt to understand the genetic mechanisms involved in the apparent change of host specificity, presumably responsible for their recently acquired capacity to infect humans. The data presented here demonstrates that major genomic differences exist between strains of Photorhabdus exhibiting virulence against insects or humans. Several individual genes, coding for virulence factors, were isolated and shown to be specific to the Photorhabdus asymbiotica human pathogens. One of these genes, sopB, encoding a host cell invasion factor translocated via the type III secretion system, has been cloned and the comparison of its genomic context in different pathogens strongly indicates that horizontal gene transfer is implicated in the acquisition of these virulence factors specific to the human pathogens. The precise role of this and other virulence factors identified here in the pathogenicity of P. asymbiotica towards humans is currently under investigation.

Animals↗

PubMed2005

Characteristics of pathogenic and mutualistic relationships of ascoviruses in field populations of parasitoid wasps.

Ascoviruses are disseminated among larvae in lepidopteran populations by parasitic wasps during oviposition. Ascovirus relationships with these wasps vary from pathogenic to mutualistic, and experimentally can be shown possibly to be commensal non-pathogenic virus having little or no effect. Most ascoviruses are pathogens that female wasps vector mechanically. Other ascoviruses have a more intimate relationship with their wasp vectors in that their genome is stably maintained in all wasp nuclei through several generations by vertical transmission. In this relationship, these viruses are mutualistic, enhancing the successful development of the wasp larvae by suppressing lepidopteran defence mechanisms. The DpAV4 ascovirus is a mutualist in certain Diadromus wasps but is pathogenic or not when vectored by other species of this genus. These various biologies suggest that ascovirus/wasp relationships depend on wasp regulatory factors that control virus replication. Thus, certain ascoviruses can potentially have either a pathogenic, mutualistic, or non-pathogenic relationship with a specific wasp vector, the type of relationship being dependent upon the species system in which the relationship evolved. Finally, because ascoviruses appear to be related to ichnoviruses (Polydnaviridae), the DpAV4/Diadromus system constitutes a possible interesting intermediate between the pathogenic ascoviruses and symbiotic viruses that evolved to be ichnoviruses.

Animals↗

PubMed2006

Evolution of pathogens towards low R0 in heterogeneous populations.

Maximization of the basic reproduction ratio or R(0) is widely believed to drive the emergence of novel pathogens. The presence of exploitable heterogeneities in a population, such as high variance in the number of potentially infectious contacts, increases R(0) and thus pathogens that can exploit heterogeneities in the contact structure have an advantage over those that do not. However, exploitation of heterogeneities results in a more rapid depletion of the potentially susceptible neighbourhood for an infected host. Here a simple model of pathogen evolution in a heterogeneous environment is developed and placed in the context of HIV transmission. In this model, it is shown that pathogens may evolve towards lower R(0), even if this results in pathogen extinction. For sufficiently high transmissibility, two locally stable strategies exist for an evolving pathogen, one that exploits heterogeneities and results in higher R(0), and one that does not, and results in lower R(0). While the low R(0) strategy is never evolutionarily stable, invading strains with higher R(0) will also converge to the low R(0) strategy if not sufficiently different from the resident strain. Heterogenous transmission is increasingly recognized as fundamental to epidemiological dynamics and the evolution of pathogens; here, it is shown that the ability to exploit heterogeneity is a strategy that can itself evolve.

Disease Outbreaks↗

PubMed2006

Surprising niche for the plant pathogen Pseudomonas syringae.

The biology and ecology of plant pathogenic bacteria have been studied almost exclusively in agricultural contexts. In contrast, for numerous human pathogens their biological activity in niches outside of medical contexts is well-known. Whereas there is increasing evidence that traits fostering survival in 'environmental' niches can be the basis for virulence factors of human pathogens, niches for plant pathogenic bacteria outside of plants or of agricultural settings have not been elucidated. Most phytopathogenic bacteria are not obligate parasites, some of them can be transported to altitudes of several kilometres, they are scrubbed from the atmosphere by rainfall, and thus they are presumably transported to and might survive in a wide range of habitats. We isolated Pseudomonas syringae from river epilithon (rock-attached biofilms composed of algae, diatoms, rotifers, bacteria and nematodes) at densities up to 6000 cells g(-1) in France and the USA, some in pristine settings where waters flowed directly from snow melt and had not passed through agricultural zones. These strains induced hypersensitivity in indicator plants (tobacco) suggesting the presence of functional pathogenicity systems, and many induced disease in 1-7 of the plant species tested and produced a syringomycin-like toxin. Strains also were resistant to some antibiotics used to control plant diseases but not to copper sulphate. Sequencing of the 16S rDNA of epilithon strains and of reference strains of P. syringae revealed that a genetic lineage containing the strains with the broadest host range was distributed across several continents. Is it likely that wide spread dissemination of P. syringae occurs via aerosols and precipitation. This work highlights our limited understanding of non-agricultural niches in the ecology and evolution of plant pathogenic bacteria, of their role in the development of agricultural epidemics both as sources of inoculum and as sources of novel traits that may enhance bacterial pathogenicity and fitness.

Bacterial Physiological Phenomena↗

PubMed2006

Antimicrobial drugs that target human--not microbial--genotypes or phenotypes: a paradigm change in human evolutionary response to pathogen selection pressure.

Conventional antimicrobial drugs that target microbial life processes impose a selection pressure on pathogens and attenuate pathogen imposed selection pressure on human hosts. The simultaneous increase and decrease that result in pathogen and human host evolvability/adaptability, respectively, distorts the natural Darwinian evolutionary process. Such drugs may create an aberrant Darwinian genotype in human hosts that is ill prepared to resist emerging virulent pathogenic strains in the event of a decrease in host ontogenic potential. In contrast, antimicrobial drugs that target host human genes exert a selective pressure both on the human genome (without population decimation) as well as on pathogenic microbes. Such drugs maintain the evolvability/adaptability of the host in tandem with that of the pathogens in the context of Darwinian evolution. Such drugs retain the capacity of the human host to evolve genotypes that may confer resistance to future pathogenic microbial strains, to assimilate prokaryotic endosymbionts and to increase the probability of survival in the event of a decrease in host ontogenic potential.

Anti-Infective Agents↗

PubMed2006

The evolutionary consequences of plasticity in host-pathogen interactions.

Interactions between individuals such as hosts and pathogens are often characterized by substantial phenotypic plasticity. Pathogens sometimes alter their exploitation strategies in response to defensive strategies adopted by their host and vice versa. Nevertheless, most game-theoretic models developed to explain the evolution of pathogen and host characteristics assume that no such plasticity occurs. Allowing for phenotypic plasticity in these models is difficult because one must focus on the evolution of pathogen and host reaction norms, and then allow for the potentially indefinite reciprocal changes in pathogen and host behaviour that occur during an infection as a result of their interacting reaction norms. Here, we begin to address these issues for a simple host-pathogen system in which the pathogen exhibits a level of virulence and the host exhibits a level of immune clearance. We find, quite generally, that plasticity promotes the evolution of higher levels of cooperation, in this case leading to reduced levels of both virulence and clearance.

Biological Evolution↗

PubMed2003

Description and analysis of two internet-based databases of insect pathogens: EDWIP and VIDIL.

In 1996, two searchable databases covering insect pathogens were posted on the World Wide Web: the Ecological Database of the World's Insect Pathogens (EDWIP) and the Viral Diseases of Insects in the Literature database (VIDIL). In this paper, we describe the format and contents of EDWIP and VIDIL on the World Wide Web. EDWIP contains over 9,400 pathogen-host association records, 677 negative test result or "no association" records, 4,454 host species, 2,285 pathogen species records, and 2,057 bibliographical references. Species of Coleoptera and Lepidoptera are the best represented groups in EDWIP. Lepidopteran species account for the most associations of any host order in EDWIP, over 2,500, or 27%. Of the pathogen groups, Protozoa (including microsporidia) accounted for nearly 66% of the pathogen species records and over 40% of the association records in EDWIP. Fungi account for only 18% of the pathogen species, but nearly 33% of the association records. Habitats dominated by human activities (e.g., crop, stored product, and human dwelling) account for most of the host habitats recorded in EDWIP. The United States and Japan are the most common locations and the Nearctic and Palearctic are the most common biogeographic regions reported in EDWIP. There are 4,801 annotated bibliographic records in VIDIL.

Animals↗

PubMed1992

Models of interactions between HIV and other pathogens.

We investigate possible interactions between HIV and other pathogens that would arise if HIV replication were enhanced by the activation of T helper cells specific to other pathogens. Using mathematical models of the population dynamics of T helper cells, HIV and other pathogens we address three facets of the interactions between HIV and other pathogens: enhanced HIV replication due to immune stimulation by other pathogens; modified immune control of other pathogens due to immunosuppression by HIV; and the vicious circle formed by positive feedback between these two effects. The models predict that there is a correlation between higher levels of activated TH cells and disease progression and that there is a threshold number of activated TH cells above which the HIV infected immune system is unable to control pre-established pathogens. This threshold marks the boundary between a suppressed but still functioning immune system and the vicious circle of CD4 cell depletion that marks the final stages of AIDS.

Acquired Immunodeficiency Syndrome↗

PubMed1999

Atypical pathogens in community-acquired pneumonia.

The atypical pathogens are an important and significant cause of CAP. The clinical and radiologic manifestations of CAP caused by these pathogens are modulated by the immunologic and physiologic status of the host, and therefore are not pathogen-specific. The range of frequencies found in various studies for the atypical pathogens among the causes of CAP is broad. These frequencies are affected by very important factors that should be recognized. In a significant percentage of patients, an atypical pathogen can be identified together with an additional cause. The significance of multiple causes has not been clarified sufficiently. The principal diagnostic techniques in use today for the causative diagnosis of CAP are serologic tests. Different serologic methods have been used in various studies and diagnostic criteria are not standardized. In the future it is likely that diagnostic testing will be based on the PCR technique on serum samples. The effectiveness and importance of antimicrobial therapy in some patients with atypical pathogen CAP are unclear. The accepted therapy today for atypical pathogen CAP, which is based on erythromycin, will probably be changed in the near future in favor of the new generations of fluoroquinolone or the new macrolide preparations.

Adult↗

PubMed2001

[Plants and pathogenic agents, a refined and dangerous relationship: the example of fungi].

Plant-fungus interactions are highly diverse, either being beneficial to the host plant such as those leading to mycorhizal symbiosis, or very detrimental when leading to severe diseases. Since the beginning of agriculture, improvement of plant resistance to pathogens has remained a major challenge. Breeding for resistance, first conducted empirically in the past centuries, was then performed on a more theoretical basis after the statement of heredity laws by Mendel at the end of the XIXth century. As a result, most cultivated species contain various cultivars whose resistance or susceptibility to a given pathogen species depend on their interaction with various races of that pathogen. Such highly specific race-cultivar systems are particularly suited for understanding the molecular dialogue which underlies compatible (host susceptible/pathogen virulent) or incompatible (host resistant/pathogen avirulent) interactions. During the twentieth century, one of the major events that paved the way for future research was the statement by Flor [1946, 1947] of the gene-for-gene concept. Studying inheritance of the disease phenotype in the interaction between flax and Melampsora lini he showed that resistance in the host and avirulence in the pathogen are dictated by single dominant genes which correspond one to one, i.e. one resistance gene for one avirulence gene. The fact that incompatibility may depend on the presence of only one resistance (R) gene in the host and one avirulence (Avr) gene in the pathogen was fully confirmed about 40 years later. Molecular genetics and complementation experiments have allowed to isolate numerous R and Avr genes from various plant-pathogen systems, and to verify the gene-for-gene concept. These studies have enlightened the elicitor/receptor concept, formerly introduced to account for the specificity of the compatible and incompatible interactions. The present knowledge of R and Avr genes also allows to predict how such genes have evolved and how they could be used to improve disease resistance. At the beginning of the twenty first century, this remains a major challenge in view of the severe losses caused by pests and pathogens to most crops on the earth.

Fungal Proteins↗

PubMed1994

Pathogenicity of neutralization escape mutants of mouse hepatitis virus: correlation with T- and B-cell depletions.

Viral pathogenicity is a result of an imbalance between viral replication and the host's immune defences. When the virus is lymphotropic, understanding the pathogenic process of the viral disease becomes complicated because virus/lymphocyte interactions can alter the cell's integrity and subsequently induce immunodeficiency. The immune system plays an important role in the outcome of acute disease induced by the mouse hepatitis virus type 3 (MHV3). The use of attenuated escape mutants provides a tool to study the role of viral properties involved in its pathogenicity. We selected MHV3 mutants by virtue of their resistance to neutralization by monoclonal antibodies (mAb), in order to study their pathogenic properties. We reported that two MHV3 escape mutants were attenuated in their pathogenic properties according to inoculation site and with regard to survival time and ability to deplete T- and B-cell subpopulations in the spleen, thymus and bone marrow of susceptible Balb/c mice. The highly attenuated CL12 mutant could not induce depletion in T or B cells following intraperitoneal (i.p.) or intranasal (i.n.) inoculations, at three days postinfection. The less attenuated 51.6 mutant, however, maintained the ability to deplete T and B cells following i.p. inoculation, as described with the pathogenic MHV3. In contrast, no depletion of T cells following i.n. inoculation was induced with this mutant, although B lineage cells decreased. The use of such mutants enabled us to examine the role of each compartment of the immune system, since the highly attenuated CL12 mutant induced no immunodeficiency, as defined by immune cell depletion, whereas the less attenuated 51.6 mutant maintained its ability to decrease only the B-cell compartment after i.n. inoculation. Results are discussed with regard to the virus/lymphocyte interactions during the pathogenic process.

Administration, Intranasal↗

PubMed1995

Genetics of Brassica rapa (syn. campestris). 2. Multiple disease resistance to three fungal pathogens: Peronospora parasitica, Albugo candida and Leptosphaeria maculans.

Although the genetic basis of multiple disease resistance (MDR) is poorly understood, it is of great value for understanding the evolution of disease resistance in natural plant populations and for increasing crop yields in agriculture. In Brassica rapa, we studied genetic correlations among levels of disease resistance to three fungal pathogens: Peronospora parasitica, Albugo candida and Leptosphaeria maculans. A large, replicated quantitative genetics experiment used artificial selection on resistance to individual pathogens, and examined correlated responses to selection for resistance to other, unselected pathogens. Data from 9518 plants, each measured simultaneously for resistance to three fungal pathogens, showed heritable genetic variation for resistance to each pathogen and a positive genetic correlation between resistance to P. parasitica and L. maculans. This indicates that some resistance genes provide defence against fundamental characteristics common to two taxonomic orders of fungal pathogens. Conceivably, such MDR could contribute to a durable defence that might not be easily circumvented by rapidly evolving fungal pathogens.

Brassica↗

PubMed2006

Insights from the genome of the biotrophic fungal plant pathogen Ustilago maydis.

Ustilago maydis is a ubiquitous pathogen of maize and a well-established model organism for the study of plant-microbe interactions. This basidiomycete fungus does not use aggressive virulence strategies to kill its host. U. maydis belongs to the group of biotrophic parasites (the smuts) that depend on living tissue for proliferation and development. Here we report the genome sequence for a member of this economically important group of biotrophic fungi. The 20.5-million-base U. maydis genome assembly contains 6,902 predicted protein-encoding genes and lacks pathogenicity signatures found in the genomes of aggressive pathogenic fungi, for example a battery of cell-wall-degrading enzymes. However, we detected unexpected genomic features responsible for the pathogenicity of this organism. Specifically, we found 12 clusters of genes encoding small secreted proteins with unknown function. A significant fraction of these genes exists in small gene families. Expression analysis showed that most of the genes contained in these clusters are regulated together and induced in infected tissue. Deletion of individual clusters altered the virulence of U. maydis in five cases, ranging from a complete lack of symptoms to hypervirulence. Despite years of research into the mechanism of pathogenicity in U. maydis, no 'true' virulence factors had been previously identified. Thus, the discovery of the secreted protein gene clusters and the functional demonstration of their decisive role in the infection process illuminate previously unknown mechanisms of pathogenicity operating in biotrophic fungi. Genomic analysis is, similarly, likely to open up new avenues for the discovery of virulence determinants in other pathogens.

Fungal Proteins↗

PubMed2006

Plant NBS-LRR proteins in pathogen sensing and host defense.

Plant proteins belonging to the nucleotide-binding site-leucine-rich repeat (NBS-LRR) family are used for pathogen detection. Like the mammalian Nod-LRR protein 'sensors' that detect intracellular conserved pathogen-associated molecular patterns, plant NBS-LRR proteins detect pathogen-associated proteins, most often the effector molecules of pathogens responsible for virulence. Many virulence proteins are detected indirectly by plant NBS-LRR proteins from modifications the virulence proteins inflict on host target proteins. However, some NBS-LRR proteins directly bind pathogen proteins. Association with either a modified host protein or a pathogen protein leads to conformational changes in the amino-terminal and LRR domains of plant NBS-LRR proteins. Such conformational alterations are thought to promote the exchange of ADP for ATP by the NBS domain, which activates 'downstream' signaling, by an unknown mechanism, leading to pathogen resistance.

Amino Acid Sequence↗

PubMed2003

DC-SIGN: escape mechanism for pathogens.

Dendritic cells (DCs) are crucial in the defence against pathogens. Invading pathogens are recognized by Toll-like receptors (TLRs) and receptors such as C-type lectins expressed on the surface of DCs. However, it is becoming evident that some pathogens, including viruses, such as HIV-1, and non-viral pathogens, such as Mycobacterium tuberculosis, subvert DC functions to escape immune surveillance by targeting the C-type lectin DC-SIGN (DC-specific intercellular adhesion molecule-grabbing nonintegrin). Notably, these pathogens misuse DC-SIGN by distinct mechanisms that either circumvent antigen processing or alter TLR-mediated signalling, skewing T-cell responses. This implies that adaptation of pathogens to target DC-SIGN might support pathogen survival.

Animals↗

PubMed2001

Microarray analysis of pathogens and their interaction with hosts.

Microarrays are a promising technique for elucidating and interpreting the mechanistic roles of genes in the pathogenesis of infectious disease. Microarrays have been used to analyse the genetic polymorphisms of specific loci associated with resistance to antimicrobial agents, to explore the distribution of genes among isolates from the same and similar species, to understand the evolutionary relationship between closely related species and to integrate the clinical and genomic data. This technique has also been used to study host-pathogen interactions, mainly by identifying genes from pathogens that may be involved in pathogenicity and by surveying the scope of the host response to infection. The RNA expression profile of pathogens has been used to identify regulatory mechanisms that ensure gene expression in the appropriate environment, to hypothesize functions of hundreds of uncharacterized genes and to identify virulence genes that promote colonization or tissue damage. This information also has the potential to identify targets for drug design. Furthermore, microarrays have been used to investigate the mechanism of drug action and to delineate and predict adverse effects of new drugs. In this paper, we review the use of spotted and high-density oligonucleotide arrays to study the genetic polymorphisms of pathogens, host-pathogen interactions and whole-genome expression profiles of pathogens, as well as their use for drug discovery.

Bacteria↗

PubMed2003

A UK multicentre study of the antimicrobial susceptibility of bacterial pathogens causing urinary tract infection.

OBJECTIVES: To determine the prevalence of resistance amongst urinary tract pathogens against antimicrobials used to treat urinary tract infections (UTIs) in the UK to provide data to help direct empirical therapy. METHOD: During 1999-2000, a total of 1291 bacterial isolates causing UTI were collected from 8 centres in the UK. Isolates were cultured from patients with (1). community-acquired UTI in those less than 65 years old (397), (2). hospital-acquired UTI other than those admitted with pyelonephritis (394), (3). pyelonephritis (108) and (4). community-acquired UTI in those greater than 65 years old (392). After re-identification, MICs for a range of antimicrobials were determined and interpreted using NCCLS procedures and interpretive guidelines. RESULTS: Escherichia coli was the predominant pathogen in all categories but the total percentage for each category varied (56.3-77.3%). The next three pathogens of importance were Enterococcus faecalis, Klebsiella pneumoniae and Proteus mirabilis which varied in prevalence slightly from category to category. The activity of amoxycillin against E. coli (51.3% susceptible) was greatly reduced as a result of beta-lactamase production and only partially restored by the addition of clavulanic acid (78.8% susceptible). Cefuroxime was very active against E. coli using parenteral form breakpoints (97.1% susceptible) but less so using oral form breakpoints (68.6% susceptible). Cefuroxime was inactive against Enterococcus spp. and Pseudomonas spp. Nitrofurantoin was very active against isolates of E. coli (96.3% susceptible) and E. faecalis but not against K. pneumoniae, P. mirabilis or Pseudomonas aeruginosa. Overall susceptibility to trimethoprim ranged from 58.1% to 84.5% for the most prevalent pathogens. Ciprofloxacin was highly active against the UTI pathogens examined in this study with susceptibilities of between 88.6% and 97.7% for the most prevalent pathogens (E. coli, n=864, 97.7% susceptible) and was the only oral agent tested with activity against Pseudomonas spp. CONCLUSION: These data provide much needed information on the prevalence of antimicrobial resistance amongst pathogens currently causing UTI in the UK.

Adolescent↗