Browsing by Author "Lopez-Velasco, Gabriela"
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- Helicobacter pylori Colonization Ameliorates Glucose Homeostasis in Mice through a PPAR γ-Dependent MechanismBassaganya-Riera, Josep; Dominguez-Bello, Maria Gloria; Kronsteiner, Barbara; Carbo, Adria; Pinyi, Lu; Viladomiu, Monica; Pedragosa, Mireia; Zhang, Xiaoying; Sobral, Bruno; Mane, Shrinivasrao P.; Mohapatra, Saroj K.; Horne, William T.; Guri, Amir J.; Groeschl, Michael; Lopez-Velasco, Gabriela; Hontecillas, Raquel (Public Library of Science, 2012-11-15)Background: There is an inverse secular trend between the incidence of obesity and gastric colonization with Helicobacter pylori, a bacterium that can affect the secretion of gastric hormones that relate to energy homeostasis. H. pylori strains that carry the cag pathogenicity island (PAI) interact more intimately with gastric epithelial cells and trigger more extensive host responses than cag− strains. We hypothesized that gastric colonization with H. pylori strains differing in cag PAI status exert distinct effects on metabolic and inflammatory phenotypes. Methodology/Principal Findings: To test this hypothesis, we examined metabolic and inflammatory markers in db/db mice and mice with diet-induced obesity experimentally infected with isogenic forms of H. pylori strain 26695: the cag PAI wild-type and its cag PAI mutant strain 99–305. H. pylori colonization decreased fasting blood glucose levels, increased levels of leptin, improved glucose tolerance, and suppressed weight gain. A response found in both wild-type and mutant H. pylori strain-infected mice included decreased white adipose tissue macrophages (ATM) and increased adipose tissue regulatory T cells (Treg) cells. Gene expression analyses demonstrated upregulation of gastric PPAR γ-responsive genes (i.e., CD36 and FABP4) in H. pylori-infected mice. The loss of PPAR γ in immune and epithelial cells in mice impaired the ability of H. pylori to favorably modulate glucose homeostasis and ATM infiltration during high fat feeding. Conclusions/Significance: Gastric infection with some commensal strains of H. pylori ameliorates glucose homeostasis in mice through a PPAR γ-dependent mechanism and modulates macrophage and Treg cell infiltration into the abdominal white adipose tissue.
- Molecular Characterization of Spinach (Spinacia Oleracea) Microbial Community Structure and its Interaction With Escherichia coli O157:H7 in Modified Atmosphere ConditionsLopez-Velasco, Gabriela (Virginia Tech, 2010-03-31)Leafy greens like lettuce and spinach are a common vehicle for foodborne illness in United States. It is unknown if native plant epiphytic bacteria may play a role in the establishment of enteric pathogens on leaf surfaces. The objective of this study was to characterize the bacterial communities of fresh and packaged spinach leaves and to explore interactions with E. coli O157:H7. We assessed the bacterial diversity present on the spinach leaf surfaces and how parameters such as spinach cultivar, field conditions, post-harvest operations and the presence of E. coli O157:H7 affected its diversity. Differences in bacterial population size and species richness were associated with differences in plant topography; flat leaves had smaller bacterial populations than savoy leaves, which correlated with larger number of stomata and trichomes in savoy leaves. During spinach growing season shifts in environmental conditions affected richness and population size of the spinach bacterial community. Decreases in the overall soil and ambient temperature and increased rainfall decreased richness and bacterial population size. Fresh spinach richness and composition assessed by parallel pyrosequencing of 16S rRNA elucidated 600 operational taxonomic units, with 11 different bacterial phyla. During postharvest operations diversity indexes and evenness tended to decrease, likely attributed to storage at low temperature and time of storage (4°C and 10°C), that promoted the dominance of g-Proteobacteria. Bacteria isolated from fresh spinach elicited growth inhibition of E. coli O157:H7 in vitro, which was associated with nutrient competition. In contrast growth enhancement produced by epiphytes was associated to low correlations in carbon source utilization and the ability of E. coli O157:H7 to rapidly utilize carbon resources. In packaged spinach, E. coli O157:H7 altered the composition of the bacterial community and its growth was promoted on packaged spinach when a disinfection and temperature abuse occurred, removal of the epiphytic bacteria resulted in significant increases in numbers of E. coli O157:H7 at 10°C and was associated with increased expression of E. coli O157:H7 virulence and stress response genes. The large diversity present on the surface of spinach leaves significantly impacted the ecology of enteric pathogens like E. coli O157:H7 on the phyllosphere.
- Phyllopshere Bacterial Community Structure of Spinach (Spinacia oleracea) as Affected by Cultivar and Environmental Conditions at Time of HarvestLopez-Velasco, Gabriela; Welbaum, Gregory E.; Falkinham, Joseph O. III; Ponder, Monica A. (MDPI, 2011-12-20)Modern molecular ecology techniques were used to demonstrate the effects of plant genotype and environmental conditions prior to harvest on the spinach epiphytic bacterial community. Three cultivars of spinach with different leaf topographies were collected at three different periods during the fall growing season. Leaf surface topography had an effect on diversity and number of culturable bacteria on the phylloepiphtyic community of spinach. Savoy cultivars, which had larger surface area and more stomata and glandular trichomes, where bacterial aggregates were observed, featured more diverse communities with increased richness and larger bacterial populations compared to flat-leaved cultivars. Bacterial community richness was compared using denaturant gradient gel electrophoresis (DGGE), while abundance was quantified using 16s rRNA primers for major phyla. The most diverse communities, both in richness and abundance, were observed during the first sampling period, immediately following a period of rapid spinach growth. Exposure to lower air and soil temperatures and decreased precipitation resulted in significantly reduced bacterial population size and bacterial community richness in November and December. This study describes the effect of the plant characteristics and environmental conditions that affect spinach microbiota population size and diversity, which might have implications in the survival of food and plant bacterial pathogens.