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PubMed1997

The effects of females' susceptibility on the coexistence of multiple pathogen strains of sexually transmitted diseases.

We study the dynamics of sexually transmitted pathogens in a heterosexually active population, where females are divided into two different groups based on their susceptibility to two distinct pathogenic strains. It is assumed that a host cannot be invaded simultaneously by both disease agents and that when symptoms appear--a function of the pathogen, strain, virulence, and an individual's degree of susceptibility--then individuals are treated and/or recover. Heterogeneity in susceptibility to the acquisition of infection and/or in variability in the length of the infection period of the female subpopulations is incorporated. Pathogens' coexistence is highly unlikely on homogeneously mixing female and male populations with no heterogeneity among individuals of either gender. Variability in susceptibility in the female subpopulation makes coexistence possible albeit under a complex set of circumstances that must include differences in contact/mixing rates between the groups of females and the male population as well as differences in the lengths of their average periods of infectiousness for the three groups.

Animals↗
PubMed2003

Mating, conidiation and pathogenicity of Fusarium graminearum, the main causal agent of the head-blight disease of wheat, are regulated by the MAP kinase gpmk1.

To date, only very little is known about the molecular infection mechanisms of the head-blight pathogen of wheat, Fusarium graminearum (teleomorph Gibberella zeae). Here, we report on the isolation and characterization of the Fus3/Pmk1 mitogen-activated protein kinase homologue Gpmk1 from F. graminearum. Disruption of the gpmk1 gene in F. graminearum results in mutants that are reduced in conidial production, are sexually sterile and are fully apathogenic. This leads to the conclusion that gpmk1 is responsible for signal transduction processes taking place during the most important developmental stages in the life cycle of this fungal pathogen. Thus, Delta gpmk1 mutants are a useful tool to find other important genes involved in plant-infection mechanisms. Previously, only the trichothecene biosynthesis pathway was identified as a virulence factor in F. graminearum. Hence, Gpmk1 is now the second pathogenicity trait to be known in this important plant pathogen.

Amino Acid Sequence↗
PubMed1999

Molecular karyotypes for Alternaria plant pathogens known to produce host-specific toxins.

There are at least ten plant diseases caused by Alternaria species in which host-specific toxins (HSTs) are responsible for fungal pathogenicity. Of these HST-producers, seven are considered distinct pathotypes of the species Alternaria alternata, and the remaining three are among other species of pathogenic Alternaria. Inter- and intra-specific variation among Alternaria taxa, including HST-producers, was determined by electrophoretic karyotyping using pulsed-field gel electrophoresis. A. alternata including seven pathotypes of A. alternata and eight non-pathogenic strains had 9-11 chromosomal bands with estimated sizes ranging from 0.4 to 5.7 Mb. In contrast, Alternaria species that are morphologically distinct from A. alternata had 8-10 bands with sizes between 0.9 and 5.7 Mb. Estimated genome sizes of A. alternata and other Alternaria species ranged from 28.8 to 33.6 Mb and 25.1 to 30.7 Mb, respectively. Other species of pathogenic Alternaria were difficult to differentiate from A. alternata on the basis of chromosome-size polymorphisms alone, but Southern analysis using rDNA as a probe could, in some cases, differentiate between them. These results were cytologically confirmed by 4',6-diamidino-2-phenylindole (DAPI) staining and fluorescence in situ hybridization with a rDNA probe for mitotic metaphase chromosomes prepared by the germ-tube burst method.

Alternaria↗
PubMed2004

Powdery mildew pathogens can suppress the chitinase gene expression induced in detached inner epidermis of barley coleoptile.

Two-step PCR (RT-PCR and nested PCR) was used to detect gene expression in powdery mildew pathogen-infected cells of detached inner epidermis of barley coleoptiles. Cellular contents of infected cells were microscopically suctioned with a micropipette and subjected to PCR. Triosephosphate isomerase and glyceraldehyde-3-phosphate dehydrogenase genes involved in the glycolytic pathway and a stimulus-induced endochitinase gene were targeted, and their expression was determined by detecting cDNAs derived from spliced transcripts. The two gycolysis-related genes were constantly expressed in the tissue irrespective of pathogen inoculation. In contrast, chitinase gene expression was induced in non-infected inner epidermis after detachment. After inoculation, this expression was selectively suppressed in pathogen-invaded cells, in spite of continuous expression in non-invaded cells of the same epidermis. Thus, the present method enabled us to directly analyze transcripts in individual cells at the infection site and assess the capability of the pathogen to regulate host gene expression.

Biological Assay↗
PubMed2002

Induction of protection against the necrotrophic pathogens Phytophthora citrophthora and Alternaria solani in Lycopersicon esculentum Mill. by a novel synthetic glycoside combined with amines.

1,2,3,4-tetra-O-acetyl-6-ethyladipate-beta- D-glucopyranose (TOGE), a glycoside derivative of adipic acid monoethyl ester and 1,2,3,4-tetra-O-acetyl-beta- D-glucopyranose, was synthesized and the resistance-inducing activity shown by TOGE-1 (TOGE plus furfurylamine) and TOGE-2 (TOGE plus 1,3-diaminepropane) was assayed. TOGE-1 and TOGE-2 protected tomato plants against two different fungal pathogens Phytophthora citrophthora and Alternaria solani. Foliar treatments at very low concentrations (2.5 mg l(-1) TOGE, 0.5 mg l(-1) amine) clearly reduced the disease incidence for both pathogens. TOGE-2 application was the most effective on intact plants as well as on detached leaves, reducing fungal growth by more than 46% with respect to control plants. On the other hand TOGE-1 treatment reduced fungal advance by 21%. These results demonstrate a high protective effect against fungal infections for both chemicals. A possible direct antimicrobial effect was discounted due to the weak activity observed in vitro against these pathogens at the low concentrations used in plants. TOGE-2 treatment clearly activates resistance against both pathogens and improves the protective effect previously shown by FGA mixture (adipic acid monoethyl ester, 1,2,3,4-tetra-O-acetyl-beta- D-glucopyranose and furfurylamine) [V. Flors et al. (2001) J Agric Food Chem 49:2569-2575]. The obtained results indicate that TOGE-1 and TOGE-2 act as resistance inducers. Although their mode of action is still unknown, pre-challenge studies have demonstrated the induction of the phenylpropanoid pathway and antioxidant activities. Both chemicals have demonstrated a beneficial effect on plant development, increasing chlorophyll and protein contents, photosynthetic rate and water-use efficiency. The improvement of plant growth and development produced by these treatments suggests crop tolerance to these chemicals, although effective formulations that are safe to humans must be developed before this technology can be used commercially.

Adipates↗
PubMed2004

Fusicoccin activates pathogen-responsive gene expression independently of common resistance signalling pathways, but increases disease symptoms in Pseudomonas syringae-infected tomato plants.

Fusicoccin (FC), an activator of the plant plasma membrane H+-ATPase, induces several components of plant pathogen resistance responses, including defence hormone biosynthesis and pathogenesis-related (PR) gene expression. The mechanism by which these responses occur, and the effect they have on plant-pathogen interactions is unknown. Here, we show that PR gene expression in response to FC in tomato (Lycopersicon esculentum Mill.) plants does not strictly require the common defence hormones, salicylic acid, jasmonic acid and ethylene. We also show that FC-induced PR gene expression requires neither Ca2+ nor reactive oxygen species, typical early pathogen-resistance response signals. The possibility that PR gene expression is related to FC-induced dehydration stress is also discounted. Finally, we show that the defence responses elicited by FC in tomato are not sufficient to confer resistance to the bacterial pathogen Pseudomonas syringae. Rather, FC increases the rate and severity of disease symptom formation in an ethylene-dependent manner.

Gene Expression↗
PubMed2006

Comparative anatomy of gall development on Gypsophila paniculata induced by bacteria with different mechanisms of pathogenicity.

Galls induced on Gypsophila paniculata by Pantoea agglomerans pv. gypsophilae (Pag) and Agrobacterium tumefaciens (At), bacteria with different mechanisms of pathogenicity, were compared morphologically and anatomically. The pathogenicity of Pag is dependent on the presence of an indigenous plasmid that harbors hrp gene cluster, genes encoding Hop virulence proteins and biosynthetic genes for auxin (IAA) and cytokinins (CKs), whereas that of At involves host transformation. The Pag-induced gall was rough, brittle and exhibited limited growth, in contrast to the smooth, firm appearance and continuous growth of the At-induced gall. Anatomical analysis revealed the presence of cells with enlarged nuclei and multiple nucleoli, giant cells and suberin deposition in Pag that were absent from At-induced galls. Although circular vessels were observed in both gall types, they were more numerous and the vascular system was more organized in At. An aerenchymal tissue was observed in the upper part of the galls. Ethylene emission from Pag galls, recorded 6 days after inoculation, was eight times as great as that from non-infected controls. In contrast, a significant decrease in ethylene production was observed in Gypsophila cuttings infected with Pag mutants deficient in IAA and CK production. The results presented are best accounted for by the two pathogens having distinct pathogenicity mechanisms that lead to their differential recognition by the host as non-self (Pag) and self (At).

Caryophyllaceae↗
PubMed2006

Gastrodia anti-fungal protein from the orchid Gastrodia elata confers disease resistance to root pathogens in transgenic tobacco.

Diseases of agricultural crops are caused by pathogens from several higher-order phylogenetic lineages including fungi, straminipila, eubacteria, and metazoa. These pathogens are commonly managed with pesticides due to the lack of broad-spectrum host resistance. Gastrodia anti-fungal protein (GAFP; gastrodianin) may provide a level of broad-spectrum resistance due to its documented anti-fungal activity in vitro and structural similarity to insecticidal lectins. We transformed tobacco (Nicotiana tabacum cv. Wisconsin 38) with GAFP-1 and challenged transformants with agriculturally important plant pathogens from several higher-order lineages including Rhizoctonia solani (fungus), Phytophthora nicotianae (straminipile), Ralstonia solanacearum (eubacterium), and Meloidogyne incognita (metazoan). Quantitative real-time PCR and western blotting analysis indicated that GAFP-1 was transcribed and translated in transgenic lines. When challenged by R. solani and P. nicotianae, GAFP-1 expressing lines had reduced symptom development and improved plant vigor compared to non-transformed and empty vector control lines. These lines also exhibited reduced root galling when challenged by M. incognita. Against R. solanacearum expression of GAFP-1 neither conferred resistance, nor exacerbated disease development. These results indicate that heterologous expression of GAFP-1 can confer enhanced resistance to a diverse set of plant pathogens and may be a good candidate gene for the development of transgenic, root-disease-resistant crops.

Base Sequence↗
PubMed2001

Anti-Acanthamoeba IgG, IgM, and IgA immunoreactivities in correlation to strain pathogenicity.

Several representatives of the genus Acanthamoeba are known as causative agents of Acanthamoeba keratitis and granulomatous amoebic encephalitis. These occur predominantly in the immunocompromised host, but it is still unclear what primes the amoebae for pathogenicity. The aim of this study was to assess possible immunological differences between a highly pathogenic and a nonpathogenic Acanthamoeba strain. A total of 20 sera, including two sera of Acanthamoeba keratitis patients, were tested for anti-Acanthamoeba IgG, IgM, and IgA immunoreactivities using immunoblotting. All sera were positive for Acanthamoeba, revealing two predominant bands at 29 kDa and at 47 kDa, respectively. Interestingly, IgG and particularly IgA immunoreactivity enabled a clear discrimination between the pathogenic and nonpathogenic strains. Moreover, compared to the control sera, the two sera of Acanthamoeba keratitis patients showed rather weak immunoreactivities and they lacked the 29 kDa and the 47 kDa band in the IgA immunoblot against the pathogenic strain. The results of our study support the assumption that immunological predisposition might also be of importance in Acanthamoeba keratitis.

Acanthamoeba↗
PubMed2006

Soil calcium and plant disease in serpentine ecosystems: a test of the pathogen refuge hypothesis.

Ecologists have long sought mechanistic explanations for the patterns of plant distribution and endemism associated with serpentine soils. We conducted the first empirical test of the serpentine pathogen refuge hypothesis, which posits that the low levels of calcium found in serpentine soils provide associated plants with a refuge from attack by pathogens. We measured the range of soil calcium concentrations experienced by 16 wild population of California dwarf flax (Hesperolinon californicum) and experimentally recreated part of this range in the greenhouse by soaking serpentine soils in calcium chloride solutions of varying molarity. When flax plants grown in these soils were inoculated with spores of the rust fungus Melampsora lini we found a significant negative relationship between infection rates and soil calcium concentrations. This result refutes the pathogen refuge hypothesis and suggests that serpentine plants, by virtue of their association with low calcium soils, may be highly vulnerable to attack by pathogens. This interaction between plant nutrition and disease may in part explain demographic patterns associated with serpentine plant populations and suggests scenarios for the evolution of life history traits and the distribution of genetic resistance to infection in serpentine plant communities.

Analysis of Variance↗
PubMed2003

Role of reactive oxygen species in the response of barley to necrotrophic pathogens.

The interactions between Hordeum vulgare(barley) and two fungal necrotrophs, Rhynchosporium secalis and Pyrenophora teres (causal agents of barley leaf scald and net blotch), were investigated in a detached-leaf system. An early oxidative burst specific to epidermal cells was observed in both the susceptible and resistant responses to R. secalis, and later on, a second susceptible-specific burst was observed. Time points of the first and the second burst correlated closely with pathogen contact to the plasma membrane and subsequent cell death, respectively. HO(2)(*)/O(2)(-) levels in resistant and susceptible responses to P. teres were limited in comparison. During later stages, HO(2)(*)/O(2)(-) was only detected in 2 to 3 epidermal cells immediately adjacent to phenolic browning and cell death observed during the susceptible response. However, H(2)O(2) was detected in the majority of mesophyll cells adjacent to the observed lesion caused by P. teres. In contrast to observations during challenge with R. secalis, no direct contact between P. teres and the plasma membrane at sites of reactive oxygen species production was evident. Preinfiltration of leaves with antioxidants prior to challenge with either pathogen had no effect on resistance responses but did limit the growth of the pathogens and inhibit the extent of cell death during susceptible responses. These results suggest a possible role for reactive oxygen species in the induction of cell death during the challenge of a susceptible plant cell with a necrotrophic fungal leaf pathogen.

Ascomycota↗
PubMed2004

Recognition of fungal pathogens by Toll-like receptors.

Toll-like receptors (TLRs) have been identified as a major class of pattern-recognition receptors. Recognition of pathogen-associated molecular patterns by TLRs, either alone or in heterodimerization with other TLR or non-TLR receptors, induces signals responsible for the activation of the innate immune response. Recent studies have demonstrated a crucial involvement of TLRs in the recognition of fungal pathogens such as Candida albicans, Aspergillus fumigatus, and Cryptococcus neoformans. Through the study of fungal infection in knock-out mice deficient in either TLRs or TLR-associated adaptor molecules, it became apparent that specific TLRs such as TLR2 and TLR4 play differential roles in the activation of the various arms of the innate immune response. Recent data also suggest that TLRs offer escape mechanisms to certain pathogenic microorganisms, especially through TLR2-driven induction of anti-inflammatory cytokines. These new data have substantially increased our knowledge of the recognition of fungal pathogens, and the study of TLRs remains one of the most active areas of research in the field of fungal infections.

Animals↗
PubMed2003

Rotavirus type A and other enteric pathogens in stool samples from children with acute diarrhea on the Colombian northern coast.

The present study, conducted from March 1998 to July 2000, determined the etiology of acute diarrhea in 253 young children and infants from Cartagena and Sincelejo, Colombia. In 253 stool samples, the following enteric pathogens were recovered: rotavirus type A (36.6%) as the major agent, Salmonella spp (9.0%), Shigella spp (8.0%), enteric pathogenic Escherichia coli (6.0%), enteric hemorragic Esc. coli (2.8%), Providencia alcalifaciens (2.8%), Aeromonas hydrophila (2.0%), Yersinia enterocolitica (0.8%), Entamoeba hystolitica (10%), Giardia lamblia (4%), Endolimax nana (3.2%), Ascaris lumbricoides (2.8%), Ent. coli (1.2%), Balantidium coli (0.8%), Blastocystis hominis (0.8%), Dypilidium caninum (0.4%) and hook worm sp. (0.4%). Infection with more than one pathogen occurred in 96 (37.9%) patients. Rotavirus and enteric pathogenic Esc. coli were frequent. Concurrent infection by more than one parasite occurred in 18.6% of the infants. Most rotavirus infections (76.7%) occurred in infants under 12 months. Vomiting, severe dehydration and fever were frequent in children with rotavirus infection. At least one fecal marker of inflammatory diarrhea was registered in patients with bacterial infection. To our knowledge, this is first report of P. alcalifaciens associated with infantile diarrhea in Colombia and the first description of Esc. coli O157:H7 and Y. enterocolitica in our region.

Acute Disease↗
PubMed2006

The comparison of susceptibility patterns of Gram-negative invasive and non-invasive pathogens in Estonian hospitals.

A total of 560 invasive and 1062 non-invasive isolates were collected. The antimicrobial susceptibility of invasive versus non-invasive Pseudomonas aeruginosa, Acinetobacter baumannii, and Klebsiella pneumoniae isolates were evaluated using the E-tests. The equal domination of Gram-negative among both invasive and non-invasive pathogens was estimated in our study if contaminants were excluded. The emergence trend of Gram-positive microbes especially of coagulase negative staphylococci may be proved only after application of exclusive algorithms. Due to similar susceptibility, the data of non-invasive Gram-negative pathogens can be useful to predict resistance of invasive ones. Also, the surveillance of invasive pathogens provides useful information about the general susceptibility of pathogens.

Acinetobacter baumannii↗
PubMed2006

Effect of asymptomatic natural infections due to common mouse pathogens on the metastatic progression of B16 murine melanoma in C57BL/6 mice.

To investigate whether the presence of infections in C57BL/6 mice influences the metastatic ability of B16 melanoma (B16M) cells, we compared the susceptibility to metastasis development of pathogen-free mice with that of mice from a colony endemically infected with several mouse pathogens. We found that, compared to seronegative controls, mice that were seropositive at least to Mouse Hepatitis Virus (MHV) and Mycoplasma pulmonis: (i) exhibited a higher interindividual variability in all the parameters quantifying metastatic progression; (ii) had elevated serum levels of proinflammatory cytokines both before and at the end of the experiment; (iii) were more susceptible to hepatic metastasis. Interestingly, final levels of tumor necrosis factor (TNF)-alpha and interleukin (IL)-18 correlated with the extent of hepatic colonization by the melanoma cells. To confirm the metastasis-enhancing effect of MHV and M. pulmonis we measured the ability of B16M cells to metastasize in pathogen-free animals housed for increasing time-intervals in the vicinity of MHV(+) animals. Notably, susceptibility to metastasis was lower in animals seronegative to MHV than in MHV(+) mice, whereas the latter were less susceptible to metastasis than MHV(+) M. pulmonis(+) mice. Seropositive animals had increased levels of TNF-alpha and IL-18 suggesting that MHV and M. pulmonis enhance the metastatic ability of melanoma cells by inducing the release of proinflammatory cytokines. While our results highlight the importance of using pathogen-free animals in metastasis studies, they emphasize the need for a comprehensive health monitoring of the mice used in such studies, particularly in case of using facilities lacking appropriate containment measures.

Animals↗
PubMed2006

Evolutionary genetics of Carpodacus mexicanus, a recently colonized host of a bacterial pathogen, Mycoplasma gallisepticum.

We present molecular data documenting how introduction to the eastern United States and an epizootic involving a bacterial pathogen has affected the genetic diversity of house finches, a cardueline songbird. Population bottlenecks during introduction can cause loss of genetic variation and may negatively affect a population's ability to adapt to novel stressors such as disease. Although a genome-wide survey using Amplified Fragment Length Polymorphism (AFLP) markers suggests little loss of genetic diversity in introduced populations, an epizootic of bacterial Mycoplasma has nonetheless caused dramatic declines in the eastern US population. Sequence analysis of a candidate gene for pathogen resistance in the Major Histocompatibity Complex (MHC) in pre- and post-epizootic population samples reveals allele frequency shifts since introduction of the pathogen, but similar shifts are also observed in control populations not exposed to the bacteria, and in a neutral non-coding locus. Expression studies using a novel subtractive hybridization approach indicate decreased expression of the class II MHC locus upon exposure to Mycoplasma, a pattern also seen in MHC class I loci in mice infected with cytomegalovirus and consistent with manipulation of the finch immune system by Mycoplasma. These results will be further expanded using experimental studies as well as examination of evolution of the pathogen genome itself.

Adaptation, Physiological↗
PubMed2006

Expression and functional roles of the pepper pathogen-induced transcription factor RAV1 in bacterial disease resistance, and drought and salt stress tolerance.

A novel pathogen-induced gene encoding the RAV (Related to ABI3/VP1) transcription factor, CARAV1, was isolated from pepper leaves infected with Xanthomonas campestris pv. vesicatoria. CARAV1 contains two distinct DNA-binding domains AP2 and B3 uniquely found in higher plants. Transient expression analysis of the smGFP:CARAV1 fusion construct in Arabidopsis protoplasts and pepper epidermal cells revealed the CARAV1 protein to be localized in the nucleus. The N-terminal region of CARAV1 fused to the GAL4 DNA-binding domain was required to activate transcription of reporter genes in yeast. In yeast one-hybrid, the recognition of CAACA and CACCTG motifs also were essential for the CARAV1 protein to bind to a specific target gene and activate the reporter gene. The expression of the CARAV1 gene was strongly induced early in pepper leaves during the pathogen infection, abiotic elicitors and environmental stresses. CARAV1 transcripts were localized in the phloem cells of leaf tissues during pathogen infection and ethylene treatment. Ectopic expression of the CARAV1 gene in transgenic Arabidopsis plants induced some PR genes and enhanced resistance against infection by Pseudomonas syringae pv. tomato DC3000 and osmotic stresses by high salinity and dehydration. The CARAV1 promoter activation was induced by P. syringae pv. tabaci, salicylic acid and abscisic acid. These data suggest that pathogen- and abiotic stress-inducible CARAV1 functions as a transcriptional activator triggering resistance to bacterial infection and tolerance to osmotic stresses.

Abscisic Acid↗
PubMed1985

Gram-negative bacillary infections. Pathogenic and pathophysiologic correlates.

Gram-negative bacillary infections continue to be extremely important. Escherichia coli is the single most frequently encountered pathogen, followed by organisms belonging to the tribe Klebsiella-Enterobacter-Serratia and Proteus-Providencia. Pseudomonas aeruginosa, although it receives considerable (perhaps excessive) attention, is found relatively less frequently, occurring principally in the hospitalized patient who is immunocompromised. Many factors, both host and microbial, are responsible for invasiveness, virulence, and pathogenicity of gram-negative bacilli, but their relative roles, importance, and the pathophysiologic reactions they trigger are yet to be precisely defined. Certain aspects of many (but certainly not all) of the pathogenic correlates considered important in gram-negative bacillary infections, such as microbial flora, local barriers, surface and serum antibodies, complement, cell-mediated immunity, slime production, capsules, pili, endotoxin, cell wall components, extracellular products, and inoculum size are discussed herein. Points at which preventive or therapeutic strategies might be developed are offered. The benefits of antibiotics in managing susceptible gram-negative bacillary infections appear to be plateauing. If further advances are to be made in the therapy of these infections, new approaches to rapidly identifying the responsible etiologic agent and a better understanding of the factors responsible for invasiveness, virulence, and pathogenicity are needed.

Antibodies, Bacterial↗