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At least 91 records · Page 5Linked to original sources
PubMed2000

Potentiation of pathogen-specific defense mechanisms in Arabidopsis by beta -aminobutyric acid.

The nonprotein amino acids gamma-aminobutyric acid (GABA) and beta-aminobutyric acid (BABA) have known biological effects in animals and plants. Their mode of action has been the object of thorough research in animals but remains unclear in plants. Our objective was to study the mode of action of BABA in the protection of Arabidopis plants against virulent pathogens. BABA protected Arabidopsis against the oomycete pathogen Peronospora parasitica through activation of natural defense mechanisms of the plant such as callose deposition, the hypersensitive response, and the formation of trailing necroses. BABA was still fully protective against P. parasitica in transgenic plants or mutants impaired in the salicylic acid, jasmonic acid, and ethylene signaling pathways. Treatment with BABA did not induce the accumulation of mRNA of the systemic acquired resistance (SAR)-associated PR-1 and the ethylene- and jasmonic acid-dependent PDF1.2 genes. However, BABA potentiated the accumulation of PR-1 mRNA after attack by virulent pathogenic bacteria. As a result, BABA-treated Arabidopsis plants were less diseased compared with the untreated control. In the case of bacteria, BABA protected mutants insensitive to jasmonic acid and ethylene but was not active in plants impaired in the SAR transduction pathway. Thus, BABA protects Arabidopsis against different virulent pathogens by potentiating pathogen-specific plant resistance mechanisms. In addition, we provide evidence that BABA-mediated papilla formation after P. parasitica infection is independent of the SAR signaling pathway.

Aminobutyrates↗
PubMed1996

Relevance, pathogenicity and virulence of microorganisms in implant related infections.

It is impossible to imagine modern medicine today without indwelling devices of various kinds. The time that these implants or prostheses remain in the patient's body can vary from a few hours, e.g. intravenous catheter, to his entire life, e.g. hip prosthesis, heart valve. Besides the indisputable use and advantages of this type of medical intervention for the patient, e.g. saving his life or improving its quality, the associated complications should not be overlooked. One of the most frequent and significant complications of implant surgery is the manifestation of infection in the tissue around the implant. That infection occurs is not surprising since the indwelling devices predispose to bacterial and mycotic infection on the one hand and impede its eradication on the other. The consequences of infection for the patient may mean the loss of regained mobility and independence, hospitalization for sepsis, or even death. Microbes per se are not necessarily pathogenic, however, there are numerous virulence factors which affect the degree of pathogenicity of the microorganisms. These include, for example, various enzymes, (e.g. catalase, hyaluronidase, collagenase and other proteases), and specific surface structures, e.g. the polysaccharide capsules of pneumococci or the lipopolysaccharides of Gram negative bacteria, and the production of bacterial toxins, e.g. leucozidin, streptolysine. The strategies which the pathogenic bacteria employ in their efforts to occupy the host include adherence, penetration and multiplication, antiphagocytosis and serum resistance, the formation of siderophores, antiimmunity, and cell and tissue damage. An attempt will be made here to present an overview of this multifactorial event in which the host obviously plays an important role.

Animals↗
PubMedDate not supplied

Virulence of pathogenic and non-pathogenic zymodemes of Entamoeba histolytica (Indian strains) in guinea-pigs.

Guinea-pigs were inoculated with Entamoeba histolytica strains isolated from cases of amoebic liver abscess, amoebic dysentery and asymptomatic cyst passers and the strains were classified in zymodemes by isoenzyme electrophoresis. It was observed that certain non-pathogenic zymodemes were potentially pathogenic for the guinea-pigs. The relationship of zymodemes and virulence in laboratory animals is discussed.

Amebiasis↗
PubMed1993

Evaluation of the pathogenicity and virulence of Yersinia species isolated in Edo and Delta States of Nigeria.

Sixteen isolates of four species of Yersinia comprising five of Yersinia enterocolitica and Yersinia fredricksenii, four of Yersinia intermedia and two of Yersinia kristensenii isolated from domestic and wild animals in villages in Edo and Delta States, Nigeria, were evaluated for their pathogenicity using laboratory animal models and virulence characteristics tests which included autoagglutinability, calcium dependency for growth, heat-stable enterotoxin production and conjunctivities in guinea pig eye. Results obtained revealed that Yersinia enterocolitica isolates were enteropathogenic as demonstrated by the production of diarrhoea and eventual recovery from faeces, spleen and liver of the infected animals. Three (60%) (2 serotypes 0:3 and 1 serotype 0:8) of the five Yersinia enterocolitica isolates were lethal to the animals. Other Yersinia isolates (Yersinia kristensenii, Yersinia fredricksenii and Yersinia intermedia) were uniformly non pathogenic to the animals. However, a strain of Yersinia intermedia isolate produced diarrhoea in the inoculated animals and caused lethality in guinea pigs and mice, but was negative for autoagglutination test, calcium dependency, conjunctivities, and positive for heat-stable enterotoxin production. We are of the view that this strain may be another Yersinia intermedia--like bacterium, previously isolated in Nigeria. Results therefore, suggest an emergence of a pathogenic Yersinia intermedia species in this environment.

Agglutination Tests↗
PubMed2005

Characterization of AvrBs3-like effectors from a Brassicaceae pathogen reveals virulence and avirulence activities and a protein with a novel repeat architecture.

Xanthomonas campestris pv. armoraciae strain 5 is a Brassicaceae pathogen that expresses three members of the highly related avrBs3 gene family of type III effectors. Here, we report on the isolation and characterization of these genes, designated hax2, hax3, and hax4 (homolog of avrBs3 in Xanthomonas). All three Hax proteins are translocated from Xanthomonas spp. into the plant cell via the type III secretion system. Hax3 and Hax4 show the typical structure of AvrBs3-like effectors and contain a repetitive region in their central part consisting of 34-amino-acid (aa) repeats. By contrast, the Hax2 repeat region is composed of 35-aa repeats that are characterized by an additional proline residue. Hax2, Hax3, and Hax4 contain 21.5, 11.5, and 14.5 repeats, respectively. Genetic studies revealed an additive effect of hax2, hax3, and hax4 on disease symptom formation of X. campestris pv. armoraciae strain 5 on radish. The contribution of individual genes to the aggressiveness of strain 5 is quantitatively different, with hax2 showing the strongest effect on the development of chlorosis and necrosis. In addition, hax3 and hax4, but not hax2, have a Bs4-dependent avirulence activity in tomato and in transgenic Nicotiana benthamiana expressing the Bs4 resistance gene.

Amino Acid Sequence↗
PubMedDate not supplied

[Factors affecting the virulence and pathogenicity of avian and human viral strains (influenza virus type A)].

Most studies performed in avian viral strains seem to indicate that virulence is a polygenic phenomenon. However, hemagglutinin and neuraminidase and the genes codifying these substances (genes 4 and 6) play an essential role in viral pathogenesis. Avian strains can be classified as avirulent or virulent according to the ability of hemagglutinin to be activated by endoproteases of the respiratory tract only or by proteases from other tissues. This ability is based on the progressive development of mutations that lead to the substitution of the normal amino acids at the point of hemagglutinin hydrolysis by the other basic amino acids that determine the amplification of the spectrum of hydrolysis and activation. Neuraminidase participates in the acquisition of virulence through its capacity to bind to plasminogen and by increasing the concentration of activating proteases. Adaptation to the host, through recognition of the cell receptor, is another factor determining the virulence and interspecies transmission of avian strains. From an epidemiological point of view, viral strains should be subtyped and the activating capacity of hemagglutinin should be determined to identify their degree of virulence.

Hemagglutinins↗
PubMed2002

Preexisting systemic acquired resistance suppresses hypersensitive response-associated cell death in Arabidopsis hrl1 mutant.

The hypersensitive response (HR) displayed by resistant plants against invading pathogens is a prominent feature of plant-pathogen interactions. The Arabidopsis hypersensitive response like lesions1 (hrl1) mutant is characterized by heightened defense responses that make it more resistant to virulent pathogens. However, hrl1 suppresses avirulent pathogen-induced HR cell death. Furthermore, the high PR-1 expression observed in hrl1 remains unaltered after avirulent and virulent pathogen infections. The suppressed HR phenotype in hrl1 is observed even when an elicitor is expressed endogenously from an inducible promoter, suggesting that an impaired transfer of avirulent factors is not the reason. Interestingly, the lack of HR phenotype in hrl1 is reversed if the constitutive defense responses are compromised either by a mutation in NON EXPRESSOR OF PR-1 (NPR1) or by depleting salicylic acid due to the expression of the nahG gene. The rescue of HR cell death in hrl1 npr1 and in hrl1 nahG depends on the extent to which the constitutive systemic acquired response (SAR) is compromised. Pretreating Arabidopsis wild-type plants with SAR-inducers, before pathogen infection resulted in a significant decrease in HR cell death. Together, these results demonstrate that the preexisting SAR may serve as one form of negative feedback loop to regulate HR-associated cell death in hrl1 mutant and in the wild-type plants.

Apoptosis↗
PubMed2004

Immunity promotes virulence evolution in a malaria model.

Evolutionary models predict that host immunity will shape the evolution of parasite virulence. While some assumptions of these models have been tested, the actual evolutionary outcome of immune selection on virulence has not. Using the mouse malaria model, Plasmodium chabaudi, we experimentally tested whether immune pressure promotes the evolution of more virulent pathogens by evolving parasite lines in immunized and nonimmunized ("naïve") mice using serial passage. We found that parasite lines evolved in immunized mice became more virulent to both naïve and immune mice than lines evolved in naïve mice. When these evolved lines were transmitted through mosquitoes, there was a general reduction in virulence across all lines. However, the immune-selected lines remained more virulent to naïve mice than the naïve-selected lines, though not to immunized mice. Thus, immune selection accelerated the rate of virulence evolution, rendering parasites more dangerous to naïve hosts. These results argue for further consideration of the evolutionary consequences for pathogen virulence of vaccination.

Animals↗
PubMed1996

Fusobacterium necrophorum infections: virulence factors, pathogenic mechanism and control measures.

Fusobacterium necrophorum, a Gram-negative, non-spore-forming anaerobe, is a normal inhabitant of the alimentary tract of animals and humans. Two types of F. necrophorum, subspecies necrophorum (biotype A) and funduliforme (biotype B), have been recognized, which differ morphologically, biochemically, and biologically. The organism is an opportunistic pathogen that causes numerous necrotic conditions (necrobacillosis) such as bovine hepatic abscesses, ruminant foot abscesses and human oral infections. The pathogenic mechanism of F. necrophorum is complex and not well defined. Several toxins, such as leukotoxin, endotoxin, haemolysin, haemagglutinin and adhesin, have been implicated as virulence factors. Among these, leukotoxin and endotoxin are believed to be more important than other toxins in overcoming the host's defence mechanisms to establish the infection. F. necrophorum is encountered frequently in mixed infections and, therefore, synergisms between F. necrophorum and other pathogens may play an important role in infection. Several investigators have attempted to induce protective immunity against F. necrophorum using bacterins, toxoids, and other cytoplasmic components. Generally, none of the immunogens has afforded satisfactory protection against Fusobacterium infections. Because of the unavailability of suitable immunoprophylaxis, the control of F. necrophorum infection has depended mainly on the use of antimicrobial compounds.

Animals↗
PubMed2005

Assessment of laboratory methods for evaluating cassava genotypes for resistance to root rot disease.

Field evaluation of six cassava genotypes for resistance to root rot disease was compared with three rapid laboratory methods (whole root inoculation, root slice inoculation, and stem inoculation) for resistance screening. Both the field evaluation and the three laboratory methods separated the varieties into resistant and susceptible groups. Genotypes 30572 and 91/02324 were resistant while 92/0247, 92/0057 and TME-1 were susceptible. One genotype (30001) was not consistent in its reaction between field evaluation and laboratory assays. In the laboratory assays with three fungal pathogens, different pathogens varied in their levels of virulence on host genotypes. With the most virulent pathogen (Botryodiplodia theobromae), the majority of the genotypes reacted in the same way across trials with the root slice and whole root assays. Due to the good correlation between the whole root assay and the field results, we recommend this for the routine assessment of cassava resistance to root rot disease and for the analysis of virulence of pathogen isolates. However, because of the advantages in terms of economy of labour, space, time, quantity of root and inoculum required, the root slice assay could be used for the preliminary screening of large cassava accessions. The selected genotypes can then be further screened with the whole root inoculation method.

Agriculture↗
PubMed2006

Different consequences of ACE2 and SWI5 gene disruptions for virulence of pathogenic and nonpathogenic yeasts.

Mutants of Candida albicans, Candida glabrata, and Saccharomyces cerevisiae with disruptions in the ACE2 gene and C. glabrata and S. cerevisiae swi5 disruption mutants were tested for virulence in a murine challenge model of disseminated yeast infection. All mutants showed a clumping phenotype, but clumping was minimized in challenge inocula by inclusion of chitinase in the growth medium. In animals rendered temporarily neutropenic by cyclophosphamide treatment, the C. glabrata ace2 null mutant was confirmed as hypervirulent: it led to early terminal illness and kidney, brain, and lung fungal burdens substantially and significantly larger than those in controls. The C. glabrata swi5 null mutant did not lead to terminal illness but generated significantly larger brain and lung burdens than those in controls. The C. albicans ace2 null mutant was very slightly attenuated and the S. cerevisiae ace2 and swi5 null mutants were substantially attenuated relative to their parental control strains. The phenotype of aggressive hypervirulence, unique to disruption of the C. glabrata ACE2 gene among the strains tested, was not seen when the C. glabrata ace2 strain was tested in immunologically intact mice. The different effects seen with these mutants rule out the clumping phenotype as the explanation for hypervirulence in the C. glabrata ace2 mutant. The absence of C. glabrata ace2 hypervirulence in healthy mice may be a tool for definitive future study of host-parasite cross talk in microbial opportunism.

Animals↗