Probing pathogen proliferation
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ABSTRACT White mold, caused by the fungus Sclerotinia sclerotiorum (Lib.) de Bary, can be a serious disease in pea ( Pisum sativum L.). Currently there are no pea genotypes with complete resistance to this pathogen. The objective of this research was to identify pea germplasm with partial resistance to S. sclerotiorum , focusing on initial infection and severity as influenced by environment. Selected pea genotypes from the USDA‐ARS Pisum core collection and two cultivars were assessed for the time required by S. sclerotiorum to severely infect these genotypes at all combinations of five temperatures (15.6, 18.3, 21.1, 23.9, and 29.4°C) and four periods of high relative humidity (PHRH) (12, 24, 48, and 72 h) under controlled environmental conditions. Severe infection is defined as the death of all plant tissue above a stem inoculation point, preventing reproduction. The commercial genotypes ‘Bolero’ and ‘1204‐3’ did not prevent severe infection at any temperature × PHRH combination. However, pea genotypes PI 164972, PI 169603, PI 197044, PI 240515, PI 270536, and PI 280611 prevented severe infection at 15.6, 18.3, 29.4, and either 21.1 or 23.9°C following a 12 h PHRH in repeated trials. Plant Introduction 164972, PI 169603, and PI 280611 also prevented severe infection following a 24 h PHRH but only at 29.4°C. Severe infection occurred for all genotypes after a 48 or 72 h PHRH at all temperatures tested. Plant Introduction 169603 and PI 240515 are recommended to pea breeders as the best germplasm to extend the time required for serious infection by S. sclerotiorum .
Sclerotinia Sclerotiorum
Germ plasm
Sclerotinia
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Stenotrophomonas maltophilia is an antibiotic resistant Gram-negative pathogen, which is associated with hospital-acquired infection. The genome encodes a protein highly related to the Ax21 protein of Xanthomonas oryzae pv. oryzae that is implicated in interactions of this plant pathogen with rice. Here we show that loss by mutation of Ax21 influences a variety of functions in Stenotrophomonas maltophilia , to include virulence, antibiotic resistance and biofilm formation in this nosocomial pathogen.
Stenotrophomonas maltophilia
Stenotrophomonas
Xanthomonas
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Abstract Repetitive genomic clones were used to differentiate between varieties within the species Pseudocercosporella herpotrichoides . From 21 clones tested 13 revealed restriction fragment length polymorphisms among isolates. Cluster analysis was performed based on these data. Differentiation of isolates according to growth speed corresponds better to genetic information than differentiation on the basis of spore morphology. Pathogen‐specific probes can be used in early diagnosis of the pathogen in infected plant material. Furthermore polymorphic pathogen‐specific probes allow varieties to be differentiated directly in infected plant material without isolation and culture of the fungus.
genomic DNA
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Sickness-induced anorexia is a conserved behavior induced during infections. Here, we report that an intestinal pathogen, Salmonella Typhimurium, inhibits anorexia by manipulating the gut-brain axis. Inhibition of inflammasome activation by the S. Typhimurium effector, SlrP, prevented anorexia caused by IL-1β-mediated signaling to the hypothalamus via the vagus nerve. Rather than compromising host defenses, pathogen-mediated inhibition of anorexia increased host survival. SlrP-mediated inhibition of anorexia prevented invasion and systemic infection by wild-type S. Typhimurium, reducing virulence while increasing transmission to new hosts, suggesting that there are trade-offs between transmission and virulence. These results clarify the complex and contextual role of anorexia in host-pathogen interactions and suggest that microbes have evolved mechanisms to modulate sickness-induced behaviors to promote health of their host and their transmission at the expense of virulence.
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Vibrio parahaemolyticus (V. parahaemolyticus) is a Gram-negative, halophilic bacterium recognized as one of the most important foodborne pathogen. When ingested, V. parahaemolyticus causes a self-limiting illness (Vibriosis), characterized mainly by watery diarrhoea. Treatment is usually oral rehydration and/or antibiotics in complicated cases. Since 1996, the pathogenic and pandemic V. parahaemolyticus O3:K6 serotype has spread worldwide, increasing the reported number of vibriosis cases. Thus, the design of new strategies for pathogen control and illness prevention is necessary. Lactobacillus sp. grouped Gram positive innocuous bacteria, part of normal intestinal microbiota and usually used as oral vaccines for several diarrheic diseases. Recombinants strains of Lactobacillus (RL) expressing pathogen antigens can be used as part of an anti-adhesion strategy where RL block the pathogen union sites in host cells. Thus, we aimed to express MAM-7 V. parahaemolyticus adhesion protein in Lactobacillus sp. to generate an RL that prevents pathogen colonization.We cloned the MAM-7 gene from V. parahaemolyticus RIMD 2210633 in Lactobacillus expression vectors. Recombinant strains (Lactobacillus rhamnosus pSEC-MAM7 and L. rhamnosus pCWA-MAM7) adhered to CaCo-2 cells and competed with the pathogen. However, the L. rhamnosus wild type strain showed the best capacity to inhibit pathogen colonization in vitro. In addition, LDH-assay showed that recombinant strains were cytotoxic compared with the wild type isogenic strain.MAM-7 expression in lactobacilli reduces the intrinsic inhibitory capacity of L. rhamnosus against V. parahaemolyticus.
Lactobacillus rhamnosus
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Four clonal lineages of Cephalosporium maydis, a soilborne vascular wilt pathogen that causes late wilt of maize, were differentiated previously with molecular markers. In Egypt, this fungus can cause significant losses in infected susceptible plants. In greenhouse tests of individual isolates we found that these lineages differ in their virulence toward a series of maize accessions commonly used in Egyptian maize breeding programs. We also determined the relative competitiveness of representatives of the four lineages when incorporated into the soil as a mixed inoculum. The lineage (IV) with greatest mean disease incidence (virulence), when tested alone, was the least competitive on susceptible maize accessions when coinoculated as a component of mixed inocula of all four lineages. In these coinoculation experiments, one of the less-virulent lineages (II) dominated (70% of infections) and appeared to be the most competitive. These results suggest that virulence and competitive ability are not the same in this host-pathogen system. These results also suggest that standard protocols that rely on mixed inocula for resistance screening need to be altered, and that the relative proportion of the different lineages of the pathogen recovered in a field may be influenced by the maize variety/hybrid planted.
Lineage (genetic)
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SUMMARY A laboratory method to inoculate seedlings uniformly with Gaeumannomyces graminis var. tritici is described. Resistance is defined via the rate of hyphal entry into the vascular tissue of host seedlings, and is measured by direct observation and by early stelar lesion development in seminal roots. The two scores for resistance are compared and evaluated, for infection with an isolate of low virulence. Evidence was obtained for resistance in the roots of wheat seedlings to G. graminis .
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