Brucella abortus Induces the Premature Death of Human Neutrophils through the Action of Its Lipopolysaccharide

Most bacterial infections induce the activation of polymorphonuclear neutrophils (PMNs), enhance their microbicidal function, and promote the survival of these leukocytes for protracted periods of time. Brucella abortus is a stealthy pathogen that evades innate immunity, barely activates PMNs, and resists the killing mechanisms of these phagocytes. Intriguing clinical signs observed during brucellosis are the low numbers of Brucella infected PMNs in the target organs and neutropenia in a proportion of the patients; features that deserve further attention. Here we demonstrate that B. abortus prematurely kills human PMNs in a dose-dependent and cell-specific manner. Death of PMNs is concomitant with the intracellular Brucella lipopolysaccharide (Br-LPS) release within vacuoles. This molecule and its lipid A reproduce the premature cell death of PMNs, a phenomenon associated to the low production of proinflammatory cytokines. Blocking of CD14 but not TLR4 prevents the Br-LPS-induced cell death. The PMNs cell death departs from necrosis, NETosis and classical apoptosis. The mechanism of PMN cell death is linked to the activation of NADPH-oxidase and a modest but steadily increase of ROS mediators. These effectors generate DNA damage, recruitments of check point kinase 1, caspases 5 and to minor extent of caspase 4, RIP1 and Ca++ release. The production of IL-1β by PMNs was barely stimulated by B. abortus infection or Br-LPS treatment. Likewise, inhibition of caspase 1 did not hamper the Br-LPS induced PMN cell death, suggesting that the inflammasome pathway was not involved. Although activation of caspases 8 and 9 was observed, they did not seem to participate in the initial triggering mechanisms, since inhibition of these caspases scarcely blocked PMN cell death. These findings suggest a mechanism for neutropenia in chronic brucellosis and reveal a novel Brucella-host cross-talk through which B. abortus is able to hinder the innate function of PMN.Fondo Especial de la Educación Superior/[0500-13]/FEES/Costa RicaFondo Especial de la Educación Superior/[0504-13]/FEES/Costa RicaFondo Especial de la Educación Superior/[0505-13]/FEES/Costa RicaFondo Especial de la Educación Superior/[0248-13]/FEES/Costa RicaUCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias de la Salud::Centro de Investigación en Enfermedades Tropicales (CIET)UCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias de la Salud::Instituto Clodomiro Picado (ICP)UCR::Vicerrectoría de Docencia::Salud::Facultad de Microbiologí

Amphibian abundance and diversity in Meru National Park, Kenya

The diversity and abundance of amphibians were investigated in Meru National Park, Kenya, using transect sampling, drift-fence and pitfall trapping and opportunistic collecting. A total of 430 individuals under seven genera (Amietophrynus, Hemisus, Hyperolius, Phrynobatrachus, Phrynomantis, Ptychadena, Xenopus) comprising eleven species were sampled in three different habitats (apart from this, two additional species are known from Meru National Park): Acacia wooded grassland; Combretum wooded grassland; Acacia-Commiphora bushland. The sex ratio for almost all species was balanced (Chi-Square, X2; P > 0.5) and was not affected by habitat type (ANOVA: F = 8.3026, P = 0.6914). Shannon-Weaver Index (2.227) and Simpson’s Index (8.244) were relatively high, and most of the eleven species sampled appeared to have a relatively even distribution (Shannon Evenness Index, E = 0.927). However, Hemisus marmoratus and Phrynomantis bifasciatus were exclusively recorded in Acacia wooded grassland and in low abundances. There was a positive linear relationship of body weight against snout-vent length for two randomly selected anurans (Hyperolius glandicolor, Phrynobatrachus natalensis) among all three vegetation communities. Keywords: Frogs, Savanna, Foraging Habitat, Community Ecology, Africa

Habitat association of amphibians in East African bush- and grassland: an example from Meru National Park, Kenya

The amphibian diversity in different vegetation communities was investigated in Meru National Park (Kenya), using transect sampling, drift-fences, pitfalls and opportunistic collection. Acacia wooded grassland had highest amphibian diversity (H' = 2.071, D = 6.74), Acacia-Commiphora bushland ranked second (H' = 1.858, D = 5.88) and Combretum wooded grassland ranked third (H' = 1.581, D = 5.08). Acacia wooded grassland had the highest amphibian abundance (n = 173 individuals) and species richness (10 species). Combretum wooded grassland had eight species with less abundance (n = 113 individuals), while the Acacia - Commiphora bushland had seven species only, with higher abundance (n = 144 individuals). Detrended Correspondence Analysis showed the plots, which occur close together with similar species composition. Correspondence Analysis was performed to investigate the association of amphibian species with plant assemblages. There was a positive linear correlation between amphibian species richness and plant species diversity in all vegetation communities. However, as the Spearman Rank Test could not establish any significant correlation between plant and amphibian diversities in the respective habitats, the amphibians recorded in the present study area cannot be used as surrogate organisms to evaluate environmental changes