1,721,115 research outputs found
2-hydroxylation of Acinetobacter baumannii lipid A contributes to virulence
Full text linkcauses a wide range of nosocomial infections. This pathogen is considered a threat to human health due to the increasing isolation of multidrug resistant strains. There is a major gap in knowledge on the infection biology of , and only few virulence factors have been characterized including the lipopolysaccharide. The lipid A expressed by is hepta-acylated and contains 2-hydroxylaurate. The late acyltransferases controlling the acylation of the lipid A have been already characterized. Here we report the characterization of LpxO, which encodes the enzyme responsible for the 2-hydroxylation of the lipid A. By genetic methods and mass spectrometry, we demonstrate that LpxO catalyses the 2-hydroxylation of the laurate transferred by LpxL. LpxO-dependent lipid A 2-hydroxylation protects A. from polymyxin B, colistin, and human β-defensin 3. LpxO contributes to survival of in human whole blood, and is required for pathogen survival in the waxmoth LpxO also protects from antimicrobial peptides and limits the expression of them. Further demonstrating the importance of LpxO-dependent modification in immune evasion, 2-hydroxylation of the lipid A limits the activation of MAPK JNK to attenuate inflammatory responses. In addition, LpxO-controlled lipid A modification mediates the production of the anti-inflammatory cytokine IL-10 via the activation of the transcriptional factor CREB. IL-10, in turn, limits the production of inflammatory cytokines following infection. Altogether, our studies suggest that LpxO is a candidate to develop anti drugs
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IL-22-dependent responses and their role during Citrobacter rodentium infection
Full text linkThe mouse pathogen Citrobacter rodentium is utilized as a model organism for studying infections caused by the human pathogens enteropathogenic Escherichia coli (EPEC) and enterohemorrhagic E. coli (EHEC) and to elucidate mechanisms of mucosal immunity. In response to C. rodentium infection, innate lymphoid cells and T cells secrete interleukin (IL)-22, a cytokine that promotes mucosal barrier function. IL-22 plays a pivotal role in enabling mice to survive and recover from C. rodentium infection, although the exact mechanisms involved remain incompletely understood. Here, we investigated whether particular components of the host response downstream of IL-22 contribute to the cytokine's protective effects during C. rodentium infection. In line with previous research, mice lacking the IL-22 gene (Il22-/- mice) were highly susceptible to C. rodentium infection. To elucidate the role of specific antimicrobial proteins modulated by IL-22, we infected the following knockout mice: S100A9-/- (calprotectin), Lcn2-/- (lipocalin-2), Reg3b-/- (Reg3β), Reg3g-/- (Reg3γ), and C3-/- (C3). All knockout mice tested displayed a considerable level of resistance to C. rodentium infection, and none phenocopied the lethality observed in Il22-/- mice. By investigating another arm of the IL-22 response, we observed that C. rodentium-infected Il22-/- mice exhibited an overall decrease in gene expression related to intestinal barrier integrity as well as significantly elevated colonic inflammation, gut permeability, and pathogen levels in the spleen. Taken together, these results indicate that host resistance to lethal C. rodentium infection may depend on multiple antimicrobial responses acting in concert, or that other IL-22-regulated processes, such as tissue repair and maintenance of epithelial integrity, play crucial roles in host defense to attaching and effacing pathogens
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Listeria monocytogenes utilizes glutathione and limited inorganic sulfur compounds as sources of essential cysteine
Full text linkListeria monocytogenes (Lm) is a Gram-positive facultative intracellular pathogen that leads a biphasic lifecycle, transitioning its metabolism and selectively inducing virulence genes when it encounters mammalian hosts. Virulence gene expression is controlled by the master virulence regulator PrfA, which is allosterically activated by the host- and bacterially derived glutathione (GSH). The amino acid cysteine is the rate-limiting substrate for GSH synthesis in bacteria and is essential for bacterial growth. Unlike many bacteria, Lm is auxotrophic for cysteine and must import exogenous cysteine for growth and virulence. GSH is enriched in the host cytoplasm, and previous work suggests that Lm utilizes exogenous GSH for PrfA activation. Despite these observations, the import mechanism(s) for GSH remains elusive. Analysis of known GSH importers predicted a homologous importer in Lm comprised of the Ctp ABC transporter and the OppDF ATPases of the Opp oligopeptide importer. Here, we demonstrated that the Ctp complex is a high-affinity GSH/GSSG importer that is required for Lm growth at physiologically relevant concentrations. Furthermore, we demonstrated that OppDF is required for GSH/GSSG import in an Opp-independent manner. These data support a model where Ctp and OppDF form a unique complex for GSH/GSSG import that supports growth and pathogenesis. In addition, we show that Lm utilizes the inorganic sulfur sources thiosulfate and H2S for growth in a CysK-dependent manner in the absence of other cysteine sources. These findings suggest a pathoadaptive role for partial cysteine auxotrophy in Lm, where locally high GSH/GSSG or inorganic sulfur concentrations may signal arrival to distinct host niches
Placental malaria in nineteenth-century Scotland
Full text linkIn the early 19th century, the Scottish obstetrician James Young Simpson (1811-1870), using an archived placental sample, very probably described for the first time, a case of malaria pigmentation. The sample, taken at 4 months gestation, would have resulted from an abortive pregnancy or maternal death. Black pigmentation of tissues had been previously described, but not in the placenta, although a possible association of morbidity with malaria infection in pregnant women had been considered, even by Hippocrates. This paper outlines the observations he made in what was the first academic review of placental pathology, which were presented in 1835 at his inaugural lecture as President of the Royal Edinburgh Medical Society. The background context of malaria in Scotland in the early 19th century is reviewed, as is the historic importance of Simpson's paper in first pioneering an understanding of placental inflammation and infection. Unknowingly, he was observing the consequences of one of the most important pregnancy infections to affect maternal and child health
Neisseria meningitidis induces pathology-associated cellular and molecular changes in trigeminal Schwann cells
No full textNeisseria meningitidis, a common cause of sepsis and bacterial meningitis, infects the meninges and central nervous system (CNS), primarily via paracellular traversal across the blood-brain barrier (BBB) or blood-cerebrospinal fluid barrier. N. meningitidis is often present asymptomatically in the nasopharynx, and the nerves extending between the nasal cavity and the brain constitute an alternative route by which the meningococci may reach the CNS. To date, the cellular mechanisms involved in nerve infection are not fully understood. Peripheral nerve glial cells are phagocytic and are capable of eliminating microorganisms, but some pathogens may be able to overcome this protection mechanism and instead infect the glia, causing cell death or pathology. Here, we show that N. meningitidis readily infects trigeminal Schwann cells (the glial cells of the trigeminal nerve) in vitro in both two-dimensional and three-dimensional cell cultures. Infection of trigeminal Schwann cells may be one mechanism by which N. meningitidis is able to invade the CNS. Infection of the cells led to multinucleation and the appearance of atypical nuclei, with the presence of horseshoe nuclei and the budding of nuclei increasing over time. Using sequential window acquisition of all theoretical mass spectra (SWATH-MS) proteomics followed by bioinformatics pathway analysis, we showed that N. meningitidis induced protein alterations in the glia that were associated with altered intercellular signaling, cell-cell interactions, and cellular movement. The analysis also suggested that the alterations in protein levels were consistent with changes occurring in cancer. Thus, infection of the trigeminal nerve by N. meningitidis may have ongoing adverse effects on the biology of Schwann cells, which may lead to pathology
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Discovering Functions of Host-Associated Microbiomes using Metabolic Footprinting
Full text linkAdvances in DNA sequencing technologies have galvanized research efforts into understanding the effects of host-associated microbiomes on host health. While a staggering amount of data has been generated to describe taxonomic differences between “healthy” and “dysbiotic” microbiomes, the functions performed by microbiomes during homeostasis remain incompletely understood. This in turn makes understanding dysbiosis in the context of different etiologies difficult. Thus, it is paramount to develop new frameworks to expand our knowledge on the beneficial functions of host-associated microbiomes. To accomplish that goal, we created metabolic footprinting, a methodological framework which utilizes gnotobiotics, comparative-untargeted metabolomics, and growth assays to determine what microbes consume in vivo. Using metabolic footprinting, we determined that commensal Clostridia perform an important digestive function for the mammalian host by consuming sugar alcohols in the large bowel. Sugar alcohol intolerance is commonly reported by patients with irritable bowel syndrome or inflammatory bowel disease, suggesting the loss of Clostridia may be an important factor in these etiologies. Additionally, we used metabolic footprinting to discover that the human fungal pathogen Candida albicans consumes small sugars in the gut. Interestingly, C. albicans required oxygen to utilize these sugars in vitro, and we found that the gut microbiota prevented the expansion of C. albicans in the gut by restricting access to oxygen in vivo. The finding that oxygen is a critical resource for C. albicans in the large bowel could improve prophylaxis aimed at preventing invasive candidiasis in susceptible patients. Collectively, the results in this thesis demonstrate that metabolic footprinting is a useful tool for elucidating the functions performed by host-associated microbiomes
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Interleukin-8 Receptor 2 (IL-8R2)-Deficient Mice Are More Resistant to Pulmonary Coccidioidomycosis than Control Mice.
Full text linkThe pathology of human coccidioidomycosis is granulomatous inflammation with many neutrophils surrounding ruptured spherules, but the chemotactic pathways that draw neutrophils into the infected tissues are not known. We previously showed that formalin-killed spherules (FKS) stimulate mouse macrophages to secret macrophage inflammatory protein 2 (MIP-2), which suggested that CXC ELR+ chemokines might be involved in neutrophil recruitment in vivo To test that hypothesis, we intranasally infected interleukin-8R2 (IL-8R2) (Cxcr2)-deficient mice on a BALB/c background with Coccidioides immitis RS. IL-8R2-deficient mice had fewer neutrophils in infected lungs than controls, but unexpectedly the IL-8R2-deficient mice had fewer organisms in their lungs than the control mice. Infected IL-8R2-deficient mouse lungs had higher expression of genes associated with lymphocyte activation, including the Th1 and Th17-related cytokines Ifnγ and Il17a and the transcription factors Stat1 and Rorc Additionally, bronchial alveolar lavage fluid from infected IL-8R2-deficient mice contained more IL-17A and interferon-γ (IFN-γ). We postulate that neutrophils in the lung directly or indirectly interfere with the development of a protective Th1/Th17 immune response to C. immitis at the site of infection
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Mechanisms of Ecosystem Invasion by Salmonella in the Large Intestine
Full text linkMicrobial invaders of the gastrointestinal ecosystem must overcome a myriad of oppositional forces in order to engraft themselves into the gut environment. While commensal gut microbes have evolved dispersal strategies that lack negative consequences for the host, these strategies only rarely allow for successful invasion into a microbiota that has matured past the initial stages of community assembly. In contrast, gastrointestinal pathogens have evolved virulence strategies that facilitate their dispersal into mature gut microbiotas. The mechanisms governing this antagonism and attempted exclusion of microbial newcomers, which we term colonization resistance, are not fully understood. Here, we utilize a model invader of the large intestinal ecosystem, the pathogen Salmonella enterica subsp. enterica serovar (S.) Typhimurium, to gain mechanistic insight into the determinants of gastrointestinal colonization resistance.In Chapter 1, we review the current understanding of colonization resistance to S. Typhimurium in the large intestine. Beginning with the principles microbiota assembly and the properties of the gut ecosystem during both homeostasis and dysbiosis, we provide a framework for understanding gut microbiome as a product of host-derived habitat filters. Evidence of colonization resistance being a phenomenon derived of both host and microbial activities is discussed, as is the fact that newcomer engraftment can occur if either part of this chimera is disturbed. Finally, we highlight the genus Salmonella’s contribution to our understanding of the large intestinal microbiota’s role in health and disease.
Chapter 2 presents our use of an oral S. Typhimurium infection in an antibiotic-naïve mouse model of to study ecosystem invasion by the pathogen in the presence of an intact microbiota. We find that S. Typhimurium overcomes colonization resistance on day 3 after infection, as evidenced by its increased population size in both the feces and the cecum. Metabolomics, microbial community profiling by 16S rRNA amplicon sequencing, and literature-informed reverse genetics approaches allowed us to elucidate mechanisms by which S. Typhimurium overcomes microbiota-mediated colonization resistance. We establish that S. Typhimurium targets the host to abolish epithelial hypoxia, inhibit short-chain fatty acid production by the microbiota, and gain access to simple carbohydrates. The resulting bloom of S. Typhimurium occurs in the presence of a compositionally intact microbiota and is driven by mixed acid fermentation and aerobic respiration via the nitric oxide-resistant cytochrome bd oxidase CydAB.
An extended discussion and contextualization of the findings presented in Chapter 2 is provided in Chapter 3. We discuss infection kinetics as a simple yet effective tool for gaining insight into colonization resistance, microbiota composition vs. microbiota function, the roles of Clostridia in colonization resistance, and the importance of host epithelial metabolism as the foundation of the gut ecosystem. Finally, potential future directions for the study of the gut environment using S. Typhimurium are discussed.
In conclusion, we provide new insights into the strategies that S. Typhimurium uses to successfully overcome microbiota-mediated colonization resistance in the gastrointestinal tract
Contribution of Asparagine Catabolism to Salmonella Virulence
Full text linkSalmonellae are pathogenic bacteria that cause significant morbidity and mortality in humans worldwide. Salmonellae establish infection and avoid clearance by the immune system by mechanisms that are not well understood. We previously showed that l-asparaginase II produced by Salmonella enterica serovar Typhimurium (S Typhimurium) inhibits T cell responses and mediates virulence. In addition, we previously showed that asparagine deprivation such as that mediated by l-asparaginase II of S Typhimurium causes suppression of activation-induced T cell metabolic reprogramming. Here, we report that STM3997, which encodes a homolog of disulfide bond protein A (dsbA) of Escherichia coli, is required for l-asparaginase II stability and function. Furthermore, we report that l-asparaginase II localizes primarily to the periplasm and acts together with l-asparaginase I to provide S Typhimurium the ability to catabolize asparagine and assimilate nitrogen. Importantly, we determined that, in a murine model of infection, S Typhimurium lacking both l-asparaginase I and II genes competes poorly with wild-type S Typhimurium for colonization of target tissues. Collectively, these results indicate that asparagine catabolism contributes to S Typhimurium virulence, providing new insights into the competition for nutrients at the host-pathogen interface
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