Hypoxia Reduces the Pathogenicity of Pseudomonas Aeruginosa by Decreasing the Expression of Multiple Virulence Factors

Our understanding of how the course of opportunistic bacterial infection is influenced by the microenvironment is limited. We demonstrate that the pathogenicity of Pseudomonas aeruginosa strains derived from acute clinical infections is higher than that of strains derived from chronic infections, where tissues are hypoxic. Exposure to hypoxia attenuated the pathogenicity of strains from acute (but not chronic) infections, implicating a role for hypoxia in regulating bacterial virulence. Mass spectrometric analysis of the secretome of P. aeruginosa derived from an acute infection revealed hypoxia-induced repression of multiple virulence factors independent of altered bacterial growth. Pseudomonas aeruginosa lacking the Pseudomonas prolyl-hydroxylase domain-containing protein, which has been implicated in bacterial oxygen sensing, displays reduced virulence factor expression. Furthermore, pharmacological hydroxylase inhibition reduces virulence factor expression and pathogenicity in a murine model of pneumonia. We hypothesize that hypoxia reduces P. aeruginosa virulence at least in part through the regulation of bacterial hydroxylases

Prolyl hydroxylase-1 regulates hepatocyte apoptosis in an NF-kB-dependent manner

Hepatocyte death is an important contributing factor in a number of diseases of the liver. PHD1 confers hypoxic sensitivity upon transcription factors including the hypoxia inducible factor (HIF) and nuclear factor-kappaB (NF-κB). Reduced PHD1 activity is linked to decreased apoptosis. Here, we investigated the underlying mechanism(s) in hepatocytes. Basal NF-κB activity was elevated in PHD1(-/-) hepatocytes compared to wild type controls. ChIP-seq analysis confirmed enhanced binding of NF-κB to chromatin in regions proximal to the promoters of genes involved in the regulation of apoptosis. Inhibition of NF-κB (but not knock-out of HIF-1 or HIF-2) reversed the anti-apoptotic effects of pharmacologic hydroxylase inhibition. We hypothesize that PHD1 inhibition leads to altered expression of NF-κB-dependent genes resulting in reduced apoptosis. This study provides new information relating to the possible mechanism of therapeutic action of hydroxylase inhibitors that has been reported in pre-clinical models of intestinal and hepatic disease.status: publishe

Severe Pneumonia in Neonates Associated with Legionella pneumophila: Case Report and Review of the Literature

The causative agent of legionellosis is the Gram-negative intracellular bacteria Legionella spp. Its clinical presentation varies from a mild febrile illness called Pontiac fever to the severe and possible fatal pneumonia, Legionnaires’ disease. Immunocompromised patients, in particular, are affected. Only a small number of infected neonates are described in the literature. Most of them have been associated with water birth or the use of air humidifiers. In the last five years, a growing number of cases have been reported in Germany by the national institute of disease surveillance and prevention (Robert-Koch Institute). Here, we describe a fatal case report of pulmonary legionellosis with acute respiratory distress syndrome (ARDS), sepsis, associated cutaneous manifestation, and extracorporeal membrane oxygenation in a full-term neonate. Moreover, we present a review of the literature discussing the epidemiology, risk factors, clinical features, diagnostics, treatment options, and prevention for this rare condition in neonates

Investigations into the Antibacterial Activity of the Silver-Based Antibiotic Drug Candidate SBC3

The synthesis of N-heterocyclic carbene (NHC) silver(I) acetate complexes with varying lipophilic benzyl-substituents at the 1 and 3 positions starting from 4,5-diphenylimidazole, opened a new class of antibiotic drug candidates. These NHC-silver(I) acetate derivatives exhibit interesting structural motifs in the solid state and proved to be soluble and stable in biological media. The leading candidate, SBC3, which was known to exhibit good antibacterial activity in preliminary Kirby-Bauer tests, was tested quantitatively using minimum inhibitory concentrations. NHC-silver(I) acetate complexes were found to have MIC values ranging from 20 to 3.13 μg/mL for a variety of Gram-positive, Gram-negative and mycobacteria tested. These values represent good antibiotic activities against potential pathogens when compared to clinically approved antibiotics. Most striking is the fact that SBC3 is active against methicillin-resistant Staphylococcus aureus with a MIC value of 12.5 μg/mL

Hypoxia Modulates Infection of Epithelial Cells by <em>Pseudomonas aeruginosa</em>

<div><p><em>Pseudomonas aeruginosa (P. aeruginosa)</em> is an opportunistic pathogen commonly associated with lung and wound infections. Hypoxia is a frequent feature of the microenvironment of infected tissues which induces the expression of genes associated with innate immunity and inflammation in host cells primarily through the activation of the hypoxia-inducible factor (HIF) and Nuclear factor kappaB (NF-κB) pathways which are regulated by oxygen-dependent prolyl-hydroxylases. Hypoxia also affects virulence and antibiotic resistance in bacterial pathogens. However, less is known about the impact of hypoxia on host-pathogen interactions such as bacterial adhesion and infection. In the current study, we demonstrate that hypoxia decreases the internalization of <em>P. aeruginosa</em> into cultured epithelial cells resulting in decreased host cell death. This response can also be elicited by the hydroxylase inhibitor Dimethyloxallyl Glycine (DMOG). Reducing HIF-2α expression or Rho kinase activity diminished the effects of hypoxia on <em>P. aeruginosa</em> infection. Furthermore, in an in vivo pneumonia infection model, application of DMOG 48 h before infection with <em>P. aeruginosa</em> significantly reduced mortality. Thus, hypoxia reduces <em>P. aeruginosa</em> internalization into epithelial cells and pharmacologic manipulation of the host pathways involved may represent new therapeutic targets in the treatment of <em>P. aeruginosa</em> infection.</p> </div

Hypoxia increases NF-κB activity in response to <i>P. aeruginosa</i> but silencing of NF-κB fails to normalize hypoxia induced decreased internalization.

<p>A: Protein levels of nuclear p65 and cytosolic Cox2 were investigated by immunoblot in A549 cells stimulated with heat inactivated <i>P. aeruginosa</i> in normoxia (N) and hypoxia (H) for the indicated times. B: NF-κB transcription factor activity was measured by a NF-κB luciferase reporter assay in normoxic and hypoxic A549 cells stimulated with TLR ligands for TLR2 (Pam3CK4, 2 µg/ml), TLR4 (LPS, 0.5 µg/ml) and TLR5 (flagellin, 0.5 µg/ml). Data represent mean ± SEM of 6 independent experiments (*** p<0.0001). C: Intracellular <i>P. aeruginosa</i> in A549 cells in normoxia or hypoxia in the presence or absence of the NF-κB inhibitor BAY 11-7082 (10 µM) or its solvent DMSO were determined in an antibiotic protection assay. Data represent mean ± SEM of 4 independent experiments (* p<0.05, *** p<0.0001). D: Antibiotic protection assay with <i>P. aeruginosa</i> in MEF wt and IKK−/−cells under normoxic and hypoxic conditions. Data represent mean ± SEM of 2 independent experiments (* p<0.05).</p