Distinct Responses of Cystic Fibrosis Epithelial Cells to SARS-CoV-2 and Influenza A Virus.

The COVID-19 pandemic has underscored the impact of viral infections on individuals with cystic fibrosis (CF). Initial observations suggested lower COVID-19 rates among CF populations; however, subsequent clinical data have presented a more complex scenario. This study aimed to investigate how bronchial epithelial cells from CF and non-CF individuals, including various CF transmembrane conductance regulator (CFTR) mutations, respond to in vitro infection with SARS-CoV-2 variants and SARS-CoV. Comparisons with the Influenza A virus (IAV) were included based on evidence that CF patients experience heightened morbidity from IAV infection. Our findings showed that CF epithelial cells exhibited reduced replication of SARS-CoV-2, regardless of the type of CFTR mutation or SARS-CoV-2 variant, as well as the original 2003 SARS-Cove. In contrast, these cells displayed more efficient IAV replication compared to non-CF cells. Interestingly, the reduced susceptibility to SARS-CoV-2 in CF was not linked to the expression of angiotensin converting enzyme 2 (ACE2) receptor nor to CFTR dysfunction, as pharmacological treatments to restore CFTR function did not normalize the viral response. Both SARS-CoV-2 infection and CFTR function influenced the levels of certain cytokines and chemokines, although these effects were not correlated. Overall, this study reveals a unique viral response in CF epithelial cells, characterized by reduced replication for some viruses like SARS-CoV-2, while showing increased susceptibility to others such as IAV. This research offers a new perspective on CF and viral interactions, emphasizing the need for further investigation into the mechanisms underlying these differences. This article is open access and distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives License 4.0 (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Pamoic acid is an inhibitor of HMGB1·CXCL12 elicited chemotaxis and reduces inflammation in murine models of Pseudomonas aeruginosa pneumonia.

BACKGROUND: High-mobility group box 1 protein (HMGB1) is an ubiquitous nuclear protein that once released in the extracellular space acts as a Damage Associated Molecular Pattern and promotes inflammation. HMGB1 is significantly elevated during Pseudomonas aeruginosa infections and has a clinical relevance in respiratory diseases such as Cystic Fibrosis (CF). Salicylates are HMGB1 inhibitors. To address pharmacological inhibition of HMGB1 with small molecules, we explored the therapeutic potential of pamoic acid (PAM), a salicylate with limited ability to cross epithelial barriers. METHODS: PAM binding to HMGB1 and CXCL12 was tested by Nuclear Magnetic Resonance Spectroscopy using chemical shift perturbation methods, and inhibition of HMGB1·CXCL12-dependent chemotaxis was investigated by cell migration experiments. Aerosol delivery of PAM, with single or repeated administrations, was tested in murine models of acute and chronic P. aeruginosa pulmonary infection in C57Bl/6NCrlBR mice. PAM efficacy was evaluated by read-outs including weight loss, bacterial load and inflammatory response in lung and bronco-alveolar lavage fluid. RESULTS: Our data and three-dimensional models show that PAM is a direct ligand of both HMGB1 and CXCL12. We also showed that PAM is able to interfere with heterocomplex formation and the related chemotaxis in vitro. Importantly, PAM treatment by aerosol was effective in reducing acute and chronic airway murine inflammation and damage induced by P. aeruginosa. The results indicated that PAM reduces leukocyte recruitment in the airways, in particular neutrophils, suggesting an impaired in vivo chemotaxis. This was associated with decreased myeloperoxidase and neutrophil elastase levels. Modestly increased bacterial burdens were recorded with single administration of PAM in acute infection; however, repeated administration in chronic infection did not affect bacterial burdens, indicating that the interference of PAM with the immune system has a limited risk of pulmonary exacerbation. CONCLUSIONS: This work established the efficacy of treating inflammation in chronic respiratory diseases, including bacterial infections, by topical delivery in the lung of PAM, an inhibitor of HMGB1.

R othia mucilaginosa is an anti-inflammatory bacterium in the respiratory tract of patients with chronic lung disease.

BACKGROUND: Chronic airway inflammation is the main driver of pathogenesis in respiratory diseases such as severe asthma, chronic obstructive pulmonary disease, cystic fibrosis (CF) and bronchiectasis. While the role of common pathogens in airway inflammation is widely recognised, the influence of other microbiota members is still poorly understood. METHODS: We hypothesised that the lung microbiota contains bacteria with immunomodulatory activity which modulate net levels of immune activation by key respiratory pathogens. Therefore, we assessed the immunomodulatory effect of several members of the lung microbiota frequently reported as present in CF lower respiratory tract samples. RESULTS: We show that Rothia mucilaginosa, a common resident of the oral cavity that is also often detectable in the lower airways in chronic disease, has an inhibitory effect on pathogen- or lipopolysaccharide-induced pro-inflammatory responses, in vitro (three-dimensional cell culture model) and in vivo (mouse model). Furthermore, in a cohort of adults with bronchiectasis, the abundance of Rothia species was negatively correlated with pro-inflammatory markers (interleukin (IL)-8 and IL-1ß) and matrix metalloproteinase (MMP)-1, MMP-8 and MMP-9 in sputum. Mechanistic studies revealed that R. mucilaginosa inhibits NF-κB pathway activation by reducing the phosphorylation of IκBα and consequently the expression of NF-κB target genes. CONCLUSIONS: These findings indicate that the presence of R. mucilaginosa in the lower airways potentially mitigates inflammation, which could in turn influence the severity and progression of chronic respiratory disorders.

New TMA (4,6,4'-Trimethyl angelicin) Analogues as Anti-Inflammatory Agents in the Treatment of Cystic Fibrosis Lung Disease.

A series of new-generation TMA (4,6,4'-trimethyl angelicin) analogues was projected and synthetized in order to ameliorate anti-inflammatory activity, with reduced or absent toxicity. Since the NF-κB transcription factor (TF) plays a critical role in the expression of IL-8 (Interluekin 8), a typical marker of lung inflammation in Cystic Fibrosis (CF), the use of agents able to interfere with the NF-κB pathway represents an interesting therapeutic strategy. Through preliminary EMSA experiments, we identified several new TMA derivatives able to inhibit the NF-κB/DNA complex. The selected active molecules were then analyzed to evaluate the anti-inflammatory effect using both Pseudomonas aeruginosa (PAO1) infection and TNF-alpha stimulus on the CF IB3-1 cell line. It was demonstrated that mainly two TMA analogues, GY971a mesylate salt (6-p-minophenyl-4,4'-dimethyl-angelicin) and GY964 (4-phenyl-6,4'-dimethyl-angelicin), were able to decrease the IL-8 gene expression. At the same time, these molecules were found to have no pro-apoptotic, mutagenic and phototoxic effects, facilitating our decision to test the efficacy in vivo by using a mouse model of acute P. aeruginosa lung infection. The anti-inflammatory effect of GY971a was confirmed in vivo; this derivative was able to deeply decrease the total number of inflammatory cells, the neutrophil count and the cytokine/chemokine profile in the P. aeruginosa acute infection model, without evident toxicity. Considering all the obtained and reported in vitro and in vivo pre-clinical results, GY971a seems to have interesting anti-inflammatory effects, modulating the NF-κB pathway, as well as the starting lead compound TMA, but without side effects.

Lung and Gut Microbiota Changes Associated with Pseudomonas aeruginosa Infection in Mouse Models of Cystic Fibrosis.

Cystic fibrosis (CF) disease leads to altered lung and gut microbiomes compared to healthy subjects. The magnitude of this dysbiosis is influenced by organ-specific microenvironmental conditions at different stages of the disease. However, how this gut-lung dysbiosis is influenced by Pseudomonas aeruginosa chronic infection is unclear. To test the relationship between CFTR dysfunction and gut-lung microbiome under chronic infection, we established a model of P. aeruginosa infection in wild-type (WT) and gut-corrected CF mice. Using 16S ribosomal RNA gene, we compared lung, stool, and gut microbiota of C57Bl/6 Cftr tm1UNCTgN(FABPCFTR) or WT mice at the naïve state or infected with P. aeruginosa. P. aeruginosa infection influences murine health significantly changing body weight both in CF and WT mice. Both stool and gut microbiota revealed significantly higher values of alpha diversity in WT mice than in CF mice, while lung microbiota showed similar values. Infection with P. aeruginosa did not changed the diversity of the stool and gut microbiota, while a drop of diversity of the lung microbiota was observed compared to non-infected mice. However, the taxonomic composition of gut microbiota was shown to be influenced by P. aeruginosa infection in CF mice but not in WT mice. This finding indicates that P. aeruginosa chronic infection has a major impact on microbiota diversity and composition in the lung. In the gut, CFTR genotype and P. aeruginosa infection affected the overall diversity and taxonomic microbiota composition, respectively. Overall, our results suggest a cross-talk between lung and gut microbiota in relation to P. aeruginosa chronic infection and CFTR mutation.

Antibiotic efficacy varies based on the infection model and treatment regimen for Pseudomonas aeruginosa.

Antibiotic discovery and preclinical testing are needed to combat the Pseudomonas aeruginosa health threat. Most frequently, antibiotic efficacy is tested in models of acute respiratory infection, with chronic pneumonia remaining largely unexplored. This approach generates serious concerns about the evaluation of treatment for chronically infected patients, and highlights the need for animal models that mimic the course of human disease.In this study, the efficacy of the marketed antibacterial drugs tobramycin (TOB) and colistin (COL) was tested in murine models of acute and chronic P. aeruginosa pulmonary infection. Different administration routes (intranasal, aerosol or subcutaneous) and treatment schedules (soon or 7 days post-infection) were tested.In the acute infection model, aerosol and subcutaneous administration of TOB reduced the bacterial burden and inflammatory response, while intranasal treatment showed modest efficacy. COL reduced the bacterial burden less effectively but dampened inflammation. Mice treated soon after chronic infection for 7 days with daily aerosol or subcutaneous administration of TOB showed higher and more rapid body weight recovery and reduced bacterial burden and inflammation than vehicle-treated mice. COL-treated mice showed no improvement in body weight or change in inflammation. Modest bacterial burden reduction was recorded only with aerosol COL administration. When treatment for chronic infection was commenced 7 days after infection, both TOB and COL failed to reduce P. aeruginosa burden and inflammation, or aid in recovery of body weight.Our findings suggest that the animal model and treatment regimen should be carefully chosen based on the type of infection to assess antibiotic efficacy.

A New Model of Chronic Mycobacterium abscessus Lung Infection in Immunocompetent Mice.

Pulmonary infections caused by Mycobacterium abscessus (MA) have increased over recent decades, affecting individuals with underlying pathologies such as chronic obstructive pulmonary disease, bronchiectasis and, especially, cystic fibrosis. The lack of a representative and standardized model of chronic infection in mice has limited steps forward in the field of MA pulmonary infection. To overcome this challenge, we refined the method of agar beads to establish MA chronic infection in immunocompetent mice. We evaluated bacterial count, lung pathology and markers of inflammation and we performed longitudinal studies with magnetic resonance imaging (MRI) up to three months after MA infection. In this model, MA was able to establish a persistent lung infection for up to two months and with minimal systemic spread. Lung histopathological analysis revealed granulomatous inflammation around bronchi characterized by the presence of lymphocytes, aggregates of vacuolated histiocytes and a few neutrophils, mimicking the damage observed in humans. Furthermore, MA lung lesions were successfully monitored for the first time by MRI. The availability of this murine model and the introduction of the successfully longitudinal monitoring of the murine lung lesions with MRI pave the way for further investigations on the impact of MA pathogenesis and the efficacy of novel treatments.

Aerosolized Bovine Lactoferrin Counteracts Infection, Inflammation and Iron Dysbalance in A Cystic Fibrosis Mouse Model of Pseudomonas aeruginosa Chronic Lung Infection.

Cystic fibrosis (CF) is a genetic disorder affecting several organs including airways. Bacterial infection, inflammation and iron dysbalance play a major role in the chronicity and severity of the lung pathology. The aim of this study was to investigate the effect of lactoferrin (Lf), a multifunctional iron-chelating glycoprotein of innate immunity, in a CF murine model of Pseudomonas aeruginosa chronic lung infection. To induce chronic lung infection, C57BL/6 mice, either cystic fibrosis transmembrane conductance regulator (CFTR)-deficient (Cftrtm1UNCTgN(FABPCFTR)#Jaw) or wild-type (WT), were intra-tracheally inoculated with multidrug-resistant MDR-RP73 P. aeruginosa embedded in agar beads. Treatments with aerosolized bovine Lf (bLf) or saline were started five minutes after infection and repeated daily for six days. Our results demonstrated that aerosolized bLf was effective in significantly reducing both pulmonary bacterial load and infiltrated leukocytes in infected CF mice. Furthermore, for the first time, we showed that bLf reduced pulmonary iron overload, in both WT and CF mice. In particular, at molecular level, a significant decrease of both the iron exporter ferroportin and iron storage ferritin, as well as luminal iron content was observed. Overall, bLf acts as a potent multi-targeting agent able to break the vicious cycle induced by P. aeruginosa, inflammation and iron dysbalance, thus mitigating the severity of CF-related pathology and sequelae.

Staphylococcus aureus Impacts Pseudomonas aeruginosa Chronic Respiratory Disease in Murine Models.

Background: Staphylococcus aureus and Pseudomonas aeruginosa are key bacterial pathogens of the respiratory tract in patients with cystic fibrosis (CF). Although P. aeruginosa chronic bronchial infection is associated with a poorer prognosis, the consequences of S. aureus colonization on CF outcomes are controversial. Methods: In this paper, murine models of infection resembling traits of the CF human airways disease have been revisited using an infection schedule that mimics the sequence of events of pulmonary disease in CF patients. First, mice were infected with S. aureus, embedded in agar beads; this was followed by P. aeruginosa infection and analysis of bacterial load, leukocyte infiltration, and lung tissue damage. Results: We reveal that (1) S. aureus promotes severe lesions including abscess formation, (2) S. aureus increases the risk of subsequent chronic P. aeruginosa respiratory infection, and (3) once the chronic infection has been established, P. aeruginosa influences most of the inflammatory responses independent of S. aureus. Conclusions: Our findings established the significance of S. aureus colonization per se and the impact on the subsequent P. aeruginosa infection. This would point towards a thorough assessment for the need of treatment against S. aureus.

Platelet Depletion Impairs Host Defense to Pulmonary Infection with Pseudomonas aeruginosa in Mice.

Platelets have been implicated in pulmonary inflammatory cell recruitment after exposure to allergic and nonallergic stimuli, but little is known about the role of platelets in response to pulmonary infection with Pseudomonas aeruginosa. In this study, we have investigated the impact of the experimental depletion of circulating platelets on a range of inflammatory and bacterial parameters, and their subsequent impact on mortality in a murine model of pulmonary infection with P. aeruginosa. P. aeruginosa infection in mice induced a mild, but significant, state of peripheral thrombocytopenia in addition to pulmonary platelet accumulation. Increased platelet activation was detected in infected mice through increased levels of the platelet-derived mediators, platelet factor-4 and ß-thromboglobulin, in BAL fluid and blood plasma. In mice depleted of circulating platelets, pulmonary neutrophil recruitment was significantly reduced 24 hours after infection, whereas the incidence of systemic dissemination of bacteria was significantly increased compared with non-platelet-depleted control mice. Furthermore, mortality rates were increased in bacterial-infected mice depleted of circulating platelets. This work demonstrates a role for platelets in the host response toward a gram-negative bacterial respiratory infection.

The impact of host genetic background in the Pseudomonas aeruginosa respiratory infections.

Understanding the significance of human genetic diversity in modulating host susceptibility to opportunistic infections is an emerging challenge in the field of respiratory illnesses. While it is recognized that diverse bacterial strains account for differential disease manifestations, emerging data indicate that host genetic diversity is an important determinant factor that influences the severity of opportunistic infections. With particular regard to respiratory illnesses mediated by the gram-negative bacterium Pseudomonas aeruginosa, diverse genetic background is also emerging as a key contributor. Human-genome-wide association studies are a common approach for determining the inter-individual genetic variation associated with variability of the pulmonary infections. Historically, diverse murine inbred mouse strains and ex-vivo cellular models were considered complementary to human studies for establishing the contribution of genetic background to P. aeruginosa respiratory infections. More recently, the development of a new mouse model of infection, mirroring human airway diseases, combined with innovative murine resource populations, modelling human genetic variation, provides additional insights into the mechanisms of genetic susceptibility. In this review, we cover the recent state of the art of human and animal studies and we discuss future potential challenges in the field of P. aeruginosa respiratory infections.

Synthesized Heparan Sulfate Competitors Attenuate Pseudomonas aeruginosa Lung Infection.

Several chronic respiratory diseases are characterized by recurrent and/or persistent infections, chronic inflammatory responses and tissue remodeling, including increased levels of glycosaminoglycans which are known structural components of the airways. Among glycosaminoglycans, heparan sulfate (HS) has been suggested to contribute to excessive inflammatory responses. Here, we aim at (i) investigating whether long-term infection by Pseudomonas aeruginosa, one of the most worrisome threat in chronic respiratory diseases, may impact HS levels, and (ii) exploring HS competitors as potential anti-inflammatory drugs during P. aeruginosa pneumonia. P. aeruginosa clinical strains and ad-hoc synthesized HS competitors were used in vitro and in murine models of lung infection. During long-term chronic P. aeruginosa colonization, infected mice showed higher heparin/HS levels, evaluated by high performance liquid chromatography-mass spectrometry after selective enzymatic digestion, compared to uninfected mice. Among HS competitors, an N-acetyl heparin and a glycol-split heparin dampened leukocyte recruitment and cytokine/chemokine production induced by acute and chronic P. aeruginosa pneumonia in mice. Furthermore, treatment with HS competitors reduced bacterial burden during chronic murine lung infection. In vitro, P. aeruginosa biofilm formation decreased upon treatment with HS competitors. Overall, these findings support further evaluation of HS competitors as a novel therapy to counteract inflammation and infection during P. aeruginosa pneumonia.

Targeting the Bacterial Cytoskeleton of the Burkholderia cepacia Complex for Antimicrobial Development: A Cautionary Tale.

Burkholderia cepacia complex (BCC) bacteria are a group of opportunistic pathogens that cause severe lung infections in cystic fibrosis (CF). Treatment of BCC infections is difficult, due to the inherent and acquired multidrug resistance of BCC. There is a pressing need to find new bacterial targets for antimicrobials. Here, we demonstrate that the novel compound Q22, which is related to the bacterial cytoskeleton destabilising compound A22, can reduce the growth rate and inhibit growth of BCC bacteria. We further analysed the phenotypic effects of Q22 treatment on BCC virulence traits, to assess its feasibility as an antimicrobial. BCC bacteria were grown in the presence of Q22 with a broad phenotypic analysis, including resistance to H2O2-induced oxidative stress, changes in the inflammatory potential of cell surface components, and in-vivo drug toxicity studies. The influence of the Q22 treatment on inflammatory potential was measured by monitoring the cytokine responses of BCC whole cell lysates, purified lipopolysaccharide, and purified peptidoglycan extracted from bacterial cultures grown in the presence or absence of Q22 in differentiated THP-1 cells. BCC bacteria grown in the presence of Q22 displayed varying levels of resistance to H2O2-induced oxidative stress, with some strains showing increased resistance after treatment. There was strain-to-strain variation in the pro-inflammatory ability of bacterial lysates to elicit TNFα and IL-1ß from human myeloid cells. Despite minimal toxicity previously shown in vitro with primary CF cell lines, in-vivo studies demonstrated Q22 toxicity in both zebrafish and mouse infection models. In summary, destabilisation of the bacterial cytoskeleton in BCC, using compounds such as Q22, led to increased virulence-related traits in vitro. These changes appear to vary depending on strain and BCC species. Future development of antimicrobials targeting the BCC bacterial cytoskeleton may be hampered if such effects translate into the in-vivo environment of the CF infection.

Aerosolized bovine lactoferrin reduces neutrophils and pro-inflammatory cytokines in mouse models of Pseudomonas aeruginosa lung infections.

Lactoferrin (Lf), an iron-chelating glycoprotein of innate immunity, produced by exocrine glands and neutrophils in infection/inflammation sites, is one of the most abundant defence molecules in airway secretions. Lf, a pleiotropic molecule, exhibits antibacterial and anti-inflammatory functions. These properties may play a relevant role in airway infections characterized by exaggerated inflammatory response, as in Pseudomonas aeruginosa lung infection in cystic fibrosis (CF) subjects. To verify the Lf role in Pseudomonas aeruginosa lung infection, we evaluated the efficacy of aerosolized bovine Lf (bLf) in mouse models of P. aeruginosa acute and chronic lung infections. C57BL/6NCrl mice were challenged with 106 CFUs of P. aeruginosa PAO1 (acute infection) or MDR-RP73 strain (chronic infection) by intra-tracheal administration. In both acute and chronic infections, aerosolized bLf resulted in nonsignificant reduction of bacterial load but significant decrease of the neutrophil recruitment and pro-inflammatory cytokine levels. Moreover, in chronic infection the bLf-treated mice recovered body weight faster and to a higher extent than the control mice. These findings add new insights into the benefits of bLf as a mediator of general health and its potential therapeutic applications.

The shedding-derived soluble receptor for advanced glycation endproducts sustains inflammation during acute Pseudomonas aeruginosa lung infection.

BACKGROUND: The membrane-bound isoform of the receptor for advanced glycation end products (FL-RAGE) is primarily expressed by alveolar epithelial cells and undergoes shedding by the protease ADAM10, giving rise to soluble cleaved RAGE (cRAGE). RAGE has been associated with the pathogenesis of several acute and chronic lung disorders. Whether the proteolysis of FL-RAGE is altered by a given inflammatory stimulus is unknown. Pseudomonas aeruginosa causes nosocomial infections in hospitalized patients and is the major pathogen associated with chronic lung diseases. METHODS: P. aeruginosa was injected in Rage-/- and wild-type mice and the impact on RAGE expression and shedding, levels of inflammation and bacterial growth was determined. RESULTS: Acute P. aeruginosa lung infection in mice induces a reduction of the active form of ADAM10, which determines an increase of FL-RAGE expression on alveolar cells and a concomitant decrease of pulmonary cRAGE levels. This was associated with massive recruitment of leukocytes and release of pro-inflammatory factors, tissue damage and relocation of cRAGE in the alveolar and bronchial cavities. The administration of sRAGE worsened bacterial burden and neutrophils infiltration. RAGE genetic deficiency reduced the susceptibility to P. aeruginosa infection, mitigating leukocyte recruitment, inflammatory molecules production, and bacterial growth. CONCLUSIONS: These data are the first to suggest that inhibition of FL-RAGE shedding, by affecting the FL-RAGE/cRAGE levels, is a novel mechanism for controlling inflammation to acute P. aeruginosa pneumonia. sRAGE in the alveolar space sustains inflammation in this setting. GENERAL SIGNIFICANCE: RAGE shedding may determine the progression of inflammatory lung diseases.

Lentiviral Vector Gene Therapy Protects XCGD Mice From Acute Staphylococcus aureus Pneumonia and Inflammatory Response.

Chronic granulomatous disease (CGD) is a primary immunodeficiency due to a deficiency in one of the subunits of the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase complex. CGD patients are characterized by an increased susceptibility to bacterial and fungal infections, and to granuloma formation due to the excessive inflammatory responses. Several gene therapy approaches with lentiviral vectors have been proposed but there is a lack of in vivo data on the ability to control infections and inflammation. We set up a mouse model of acute infection that closely mimic the airway infection in CGD patients. It involved an intratracheal injection of a methicillin-sensitive reference strain of S. aureus. Gene therapy, with hematopoietic stem cells transduced with regulated lentiviral vectors, restored the functional activity of NADPH oxidase complex (with 20-98% of dihydrorhodamine positive granulocytes and monocytes) and saved mice from death caused by S. aureus, significantly reducing the bacterial load and lung damage, similarly to WT mice even at low vector copy number. When challenged, gene therapy-treated XCGD mice showed correction of proinflammatory cytokines and chemokine imbalance at levels that were comparable to WT. Examined together, our results support the clinical development of gene therapy protocols using lentiviral vectors for the protection against infections and inflammation.

Environmental Burkholderia cenocepacia Strain Enhances Fitness by Serial Passages during Long-Term Chronic Airways Infection in Mice.

Burkholderia cenocepacia is an important opportunistic pathogen in cystic fibrosis (CF) patients, and has also been isolated from natural environments. In previous work, we explored the virulence and pathogenic potential of environmental B. cenocepacia strains and demonstrated that they do not differ from clinical strains in some pathogenic traits. Here, we investigated the ability of the environmental B. cenocepacia Mex1 strain, isolated from the maize rhizosphere, to persist and increase its virulence after serial passages in a mouse model of chronic infection. B. cenocepacia Mex1 strain, belonging to the recA lineage IIIA, was embedded in agar beads and challenged into the lung of C57Bl/6 mice. The mice were sacrificed after 28 days from infection and their lungs were tested for bacterial loads. Agar beads containing the pool of B. cenocepacia colonies from the four sequential passages were used to infect the mice. The environmental B. cenocepacia strain showed a low incidence of chronic infection after the first passage; after the second, third and fourth passages in mice, its ability to establish chronic infection increased significantly and progressively up to 100%. Colonial morphology analysis and genetic profiling of the Mex1-derived clones recovered after the fourth passage from infected mice revealed that they were indistinguishable from the challenged strain both at phenotypic and genetic level. By testing the virulence of single clones in the Galleria mellonella infection model, we found that two Mex1-derived clones significantly increased their pathogenicity compared to the parental Mex1 strain and behaved similarly to the clinical and epidemic B. cenocepacia LMG16656T. Our findings suggest that serial passages of the environmental B. cenocepacia Mex1 strain in mice resulted in an increased ability to determine chronic lung infection and the appearance of clonal variants with increased virulence in non-vertebrate hosts.

Activation of Human Toll-like Receptor 4 (TLR4)·Myeloid Differentiation Factor 2 (MD-2) by Hypoacylated Lipopolysaccharide from a Clinical Isolate of Burkholderia cenocepacia.

Lung infection by Burkholderia species, in particular Burkholderia cenocepacia, accelerates tissue damage and increases post-lung transplant mortality in cystic fibrosis patients. Host-microbe interplay largely depends on interactions between pathogen-specific molecules and innate immune receptors such as Toll-like receptor 4 (TLR4), which recognizes the lipid A moiety of the bacterial lipopolysaccharide (LPS). The human TLR4·myeloid differentiation factor 2 (MD-2) LPS receptor complex is strongly activated by hexa-acylated lipid A and poorly activated by underacylated lipid A. Here, we report that B. cenocepacia LPS strongly activates human TLR4·MD-2 despite its lipid A having only five acyl chains. Furthermore, we show that aminoarabinose residues in lipid A contribute to TLR4-lipid A interactions, and experiments in a mouse model of LPS-induced endotoxic shock confirmed the proinflammatory potential of B. cenocepacia penta-acylated lipid A. Molecular modeling combined with mutagenesis of TLR4-MD-2 interactive surfaces suggests that longer acyl chains and the aminoarabinose residues in the B. cenocepacia lipid A allow exposure of the fifth acyl chain on the surface of MD-2 enabling interactions with TLR4 and its dimerization. Our results provide a molecular model for activation of the human TLR4·MD-2 complex by penta-acylated lipid A explaining the ability of hypoacylated B. cenocepacia LPS to promote proinflammatory responses associated with the severe pathogenicity of this opportunistic bacterium.

Role of Iron Uptake Systems in Pseudomonas aeruginosa Virulence and Airway Infection.

Pseudomonas aeruginosa is a leading cause of hospital-acquired pneumonia and chronic lung infections in cystic fibrosis patients. Iron is essential for bacterial growth, and P. aeruginosa expresses multiple iron uptake systems, whose role in lung infection deserves further investigation. P. aeruginosa Fe(3+) uptake systems include the pyoverdine and pyochelin siderophores and two systems for heme uptake, all of which are dependent on the TonB energy transducer. P. aeruginosa also has the FeoB transporter for Fe(2+) acquisition. To assess the roles of individual iron uptake systems in P. aeruginosa lung infection, single and double deletion mutants were generated in P. aeruginosa PAO1 and characterized in vitro, using iron-poor media and human serum, and in vivo, using a mouse model of lung infection. The iron uptake-null mutant (tonB1 feoB) and the Fe(3+) transport mutant (tonB1) did not grow aerobically under low-iron conditions and were avirulent in the mouse model. Conversely, the wild type and the feoB, hasR phuR (heme uptake), and pchD (pyochelin) mutants grew in vitro and caused 60 to 90% mortality in mice. The pyoverdine mutant (pvdA) and the siderophore-null mutant (pvdA pchD) grew aerobically in iron-poor media but not in human serum, and they caused low mortality in mice (10 to 20%). To differentiate the roles of pyoverdine in iron uptake and virulence regulation, a pvdA fpvR double mutant defective in pyoverdine production but expressing wild-type levels of pyoverdine-regulated virulence factors was generated. Deletion of fpvR in the pvdA background partially restored the lethal phenotype, indicating that pyoverdine contributes to the pathogenesis of P. aeruginosa lung infection by combining iron transport and virulence-inducing capabilities.

Mapping genetic determinants of host susceptibility to Pseudomonas aeruginosa lung infection in mice.

BACKGROUND: P. aeruginosa is one of the top three causes of opportunistic human bacterial infections. The remarkable variability in the clinical outcomes of this infection is thought to be associated with genetic predisposition. However, the genes underlying host susceptibility to P. aeruginosa infection are still largely unknown. RESULTS: As a step towards mapping these genes, we applied a genome wide linkage analysis approach to a mouse model. A large F2 intercross population, obtained by mating P. aeruginosa-resistant C3H/HeOuJ, and susceptible A/J mice, was used for quantitative trait locus (QTL) mapping. The F2 progenies were challenged with a P. aeruginosa clinical strain and monitored for the survival time up to 7 days post-infection, as a disease phenotype associated trait. Selected phenotypic extremes of the F2 distribution were genotyped with high-density single nucleotide polymorphic (SNP) markers, and subsequently QTL analysis was performed. A significant locus was mapped on chromosome 6 and was named P . aeruginosa infection resistance locus 1 (Pairl1). The most promising candidate genes, including Dok1, Tacr1, Cd207, Clec4f, Gp9, Gata2, Foxp1, are related to pathogen sensing, neutrophils and macrophages recruitment and inflammatory processes. CONCLUSIONS: We propose a set of genes involved in the pathogenesis of P. aeruginosa infection that may be explored to complement human studies.