A hypervirulent
(hvKp) pathotype is undergoing global dissemination. In contrast to the usual health care-associated epidemiology of classical
(cKp) infections, hvKp causes tissue-invasive infections ...in otherwise healthy individuals from the community, often involving multiple sites. An accurate test to identify hvKp strains is needed for improved patient care and epidemiologic studies. To fill this knowledge gap, clinical criteria or random blood isolates from North American and United Kingdom strain collections were used to assemble hvKp-rich (
= 85) and cKp-rich (
= 90) strain cohorts, respectively. The isolates were then assessed for multiple candidate biomarkers hypothesized to accurately differentiate the two cohorts. The genes
,
,
, plasmid-borne
gene (
), and
all demonstrated >0.95 diagnostic accuracy for identifying strains in the hvKp-rich cohort. Next, to validate this epidemiological analysis, all strains were assessed experimentally in a murine sepsis model.
,
,
,
, and
were all associated with a hazard ratio of >25 for severe illness or death, additionally supporting their utility for identifying hvKp strains. Quantitative siderophore production of ≥30 μg/ml also strongly predicted strains as members of the hvKp-rich cohort (accuracy, 0.96) and exhibited a hazard ratio of 31.7 for severe illness or death. The string test, a widely used marker for hvKp strains, performed less well, achieving an accuracy of only 0.90. Last, using the most accurate biomarkers to define hvKp, prevalence studies were performed on two Western strain collections. These data strongly support the utility of several laboratory markers for identifying hvKp strains with a high degree of accuracy.
Proinflammatory immune responses to Gram‐negative bacterial lipopolysaccharides (LPS) are crucial to innate host defenses but can also contribute to pathology. How host cells sensitively detect ...structural features of LPS was a mystery for years, especially given that a portion of the molecule essential for its potent proinflammatory properties—lipid A—is buried in the bacterial membrane. Studies of responses to extracellular and vacuolar LPS revealed a crucial role for accessory proteins that specifically bind LPS‐rich membranes and extract LPS monomers to generate a complex of LPS, MD‐2, and TLR4. These insights provided means to understand better both the remarkable host sensitivity to LPS and the means whereby specific LPS structural features are discerned. More recently, the noncanonical inflammasome, consisting of caspases‐4/5 in humans and caspase‐11 in mice, has been demonstrated to mediate responses to LPS that has reached the host cytosol. Precisely how LPS gains access to cytosolic caspases—and in what form—is not well characterized, and understanding this process will provide crucial insights into how the noncanonical inflammasome is regulated during infection. Herein, we briefly review what is known about LPS detection by cytosolic caspases‐4/5/11, focusing on lessons derived from studies of the better‐characterized TLR4 system that might direct future mechanistic questions.
Review on how LPS is detected by cytosolic caspases‐4/5/11 and how it might direct future mechanistic questions.
Increased temperatures and concomitant changes in vegetation patterns are expected to dramatically alter the functioning of northern ecosystems over the next few decades. Predicting the ecosystem ...response to such a shift in climate and vegetation is complicated by the lack of knowledge about the links between aboveground biota and belowground process rates. Current models suggest that increasing temperatures and rising concentrations of atmospheric CO
2 will be partly mitigated by elevated C sequestration in plant biomass and soil. However, empirical evidence does not always support this assumption, as elevated temperature and CO
2 concentrations also accelerate the belowground C flux, in many cases extending to increased decomposition of soil organic matter (SOM) and ultimately resulting in decreased soil C stocks. The mechanism behind the increase has remained largely unknown, but it has been suggested that priming might be the causative agent. Here, we provide quantitative evidence of a strong coupling between root exudation, SOM decomposition, and release of plant available N caused by rhizosphere priming effects. As plants tend to increase belowground C allocation with increased temperatures and CO
2 concentrations, priming effects need to be considered in our long‐term analysis of soil C budgets in a changing environment. The extent of priming seems to be intimately linked to resource availability, as shifts in the stoichiometric nutrient demands of plants and microorganisms will lead to either cooperation (resulting in priming) or competition (no priming will occur). The findings lead us on the way to resolve the varying response of primary production, SOM decomposition, and release of plant available N to elevated temperatures, CO
2 concentrations, and N availability.
The objective of this experiment was to identify links between plant C exudation and belowground C and N turnover caused by rhizosphere priming effects. Our findings suggest that increased belowground allocation of plant C results in a massive stimulation of soil organic matter decomposition, with concurrent release of plant available N. The increase could be assigned to rhizosphere priming effects, and the extent of priming seems to be intimately linked to C and N availability.
The post-partum period is a risk factor for tuberculosis (TB), possibly including the period after miscarriage as illustrated here. This case demonstrates how non-specific symptoms can hide widely ...disseminated TB. Disseminated and extrapulmonary TB can present with non-specific symptoms. Recognition of risk factors for TB is critical for prompt diagnostic evaluation and treatment of this deadly disease. A paradoxical reaction needs to be taken into consideration when any new neurological symptoms occur during TB treatment.
Wildfire severity in forests is projected to increase with warming and drying conditions associated with climate change. Our objective was to determine the impact of wildfire and clearcutting ...severity on the ectomycorrhizal fungal (EMF) community of Douglas-fir seedlings in the dry forests of interior British Columbia, Canada. We located our study within and surrounding the area of the McLure fire (August 2003). We hypothesized that disturbance would affect EMF community assembly due to reductions in fungal inoculum. Five treatments representing a range of disturbance severities were compared: high severity burn, low severity burn, screefed clearcut (manual removal of forest floor), clearcut, and undisturbed forest. EMF communities in the undisturbed forest were more complex than those in all disturbance treatments. However, aspects of community assembly varied with disturbance type, where the burn treatments had the simplest communities. After 4 months, regenerating seedlings in the burn treatments had the lowest colonization, but seedlings in all treatments were fully colonized within 1 year. EMF communities were similar among the four disturbance types, largely due to dominance of Wilcoxina throughout the study period. However, forest floor retention influenced community assembly as the EMF in the clearcut treatment, where forest floor was retained, had levels of diversity and richness comparable to the undisturbed forest. Overall, the results suggest that increasing forest floor disturbance can alter EMF community assembly in the first year of regeneration. A correlation between poorly colonized seedlings and seedling productivity also suggests a role for productivity in influencing community assembly.
Francisella tularensis, the Gram-negative bacterium that causes tularemia, produces a high molecular weight capsule that is immunologically distinct from Francisella lipopolysaccharide but contains ...the same O-antigen tetrasaccharide. To pursue the possibility that the capsule of Francisella live vaccine strain (LVS) has a structurally unique lipid anchor, we have metabolically labeled Francisella with 14Cacetate to facilitate highly sensitive compositional analysis of capsule-associated lipids. Capsule was purified by two independent methods and yielded similar results. Autoradiographic and immunologic analysis confirmed that this purified material was largely devoid of low molecular weight LPS and of the copious amounts of free lipid A that the Francisellae accumulate. Chemical hydrolysis yielded 14C-labeled free fatty acids characteristic of Francisella lipid A but with a different molar ratio of 3-OH C18:0 to 3-OH C16:0 and different composition of non-hydroxylated fatty acids (mainly C14:0 rather than C16:0) than that of free Francisella lipid A. Mild acid hydrolysis to induce selective cleavage of KDO-lipid A linkage yielded a 14C-labeled product that partitioned during Bligh/Dyer extraction and migrated during thin-layer chromatography like lipid A. These findings suggest that the O-antigen capsule of Francisella contains a covalently linked and structurally distinct lipid A species. The presence of a discrete lipid A-like molecule associated with capsule raises the possibility that Francisella selectively exploits lipid A structural heterogeneity to regulate synthesis, transport, and stable bacterial surface association of the O-antigen capsular layer.
In humans and other mammals, recognition of endotoxins-abundant surface lipopolysaccharides (LPS) of Gram-negative bacteria-provides a potent stimulus for induction of inflammation and mobilization ...of host defenses. The structurally unique lipid A region of LPS is the principal determinant of this pro-inflammatory activity. This region of LPS is normally buried within the bacterial outer membrane and aggregates of purified LPS, making even more remarkable its picomolar potency and the ability of discrete variations in lipid A structure to markedly alter the pro-inflammatory activity of LPS. Two recognition systems-MD-2/TLR4 and "LPS-sensing" cytosolic caspases-together confer LPS responsiveness at the host cell surface, within endosomes, and at sites physically accessible to the cytosol. Understanding how the lipid A of LPS is delivered and recognized at these diverse sites is crucial to understanding how the magnitude and character of the inflammatory responses are regulated.
Francisella tularensis is a facultative intracellular bacterium that infects many cell types, including neutrophils. We demonstrated previously that F. tularensis inhibits NADPH oxidase assembly and ...activity and then escapes the phagosome to the cytosol, but effects on other aspects of neutrophil function are unknown. Neutrophils are short-lived cells that undergo constitutive apoptosis, and phagocytosis typically accelerates this process. We now demonstrate that F. tularensis significantly inhibited neutrophil apoptosis as indicated by morphologic analysis as well as annexin V and TUNEL staining. Thus, ∼80% of infected neutrophils remained viable at 48 h compared with ∼50% of control cells, and ∼40% of neutrophils that ingested opsonized zymosan. In keeping with this finding, processing and activation of procaspases-8, -9, and -3 were markedly diminished and delayed. F. tularensis also significantly impaired apoptosis triggered by Fas crosslinking. Of note, these effects were dose dependent and could be conferred by either intracellular or extracellular live bacteria, but not by formalin-killed organisms or isolated LPS and capsule, and were not affected by disruption of wbtA2 or FTT1236/FTL0708-genes required for LPS O-antigen and capsule biosynthesis. In summary, we demonstrate that F. tularensis profoundly impairs constitutive neutrophil apoptosis via effects on the intrinsic and extrinsic pathways, and thereby define a new aspect of innate immune evasion by this organism. As defects in neutrophil turnover prevent resolution of inflammation, our findings also suggest a mechanism that may in part account for the neutrophil accumulation, granuloma formation, and severe tissue damage that characterizes lethal pneumonic tularemia.
Fine root litter is the principal source of carbon stored in forest soils and a dominant source of carbon for fungal decomposers. Differences in decomposer capacity between fungal species may be ...important determinants of fine-root decomposition rates. Variable-retention harvesting (VRH) provides refuge for ectomycorrhizal fungi, but its influence on fine-root decomposers is unknown, as are the effects of functional shifts in these fungal communities on carbon cycling. We compared fungal communities decomposing fine roots (in litter bags) under VRH, clear-cut, and uncut stands at two sites (6 and 13 years postharvest) and two decay stages (43 days and 1 year after burial) in Douglas fir forests in coastal British Columbia, Canada. Fungal species and guilds were identified from decomposed fine roots using high-throughput sequencing. Variable retention had short-term effects on β-diversity; harvest treatment modified the fungal community composition at the 6-year-postharvest site, but not at the 13-year-postharvest site. Ericoid and ectomycorrhizal guilds were not more abundant under VRH, but stand age significantly structured species composition. Guild composition varied by decay stage, with ruderal species later replaced by saprotrophs and ectomycorrhizae. Ectomycorrhizal abundance on decomposing fine roots may partially explain why fine roots typically decompose more slowly than surface litter. Our results indicate that stand age structures fine-root decomposers but that decay stage is more important in structuring the fungal community than shifts caused by harvesting. The rapid postharvest recovery of fungal communities decomposing fine roots suggests resiliency within this community, at least in these young regenerating stands in coastal British Columbia.
Globally, fine roots are a dominant source of carbon in forest soils, yet the fungi that decompose this material and that drive the sequestration or respiration of this carbon remain largely uncharacterized. Fungi vary in their capacity to decompose plant litter, suggesting that fungal community composition is an important determinant of decomposition rates. Variable-retention harvesting is a forestry practice that modifies fungal communities by providing refuge for ectomycorrhizal fungi. We evaluated the effects of variable retention and clear-cut harvesting on fungal communities decomposing fine roots at two sites (6 and 13 years postharvest), at two decay stages (43 days and 1 year), and in uncut stands in temperate rainforests. Harvesting impacts on fungal community composition were detected only after 6 years after harvest. We suggest that fungal community composition may be an important factor that reduces fine-root decomposition rates relative to those of above-ground plant litter, which has important consequences for forest carbon cycling.
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