Tularaemia is an emerging anthropozoonosis transmitted by contact with infected animals and throu... more Tularaemia is an emerging anthropozoonosis transmitted by contact with infected animals and through arthropod bites, inhalation, or ingestion. We describe a pulmonary nodule suggesting cancer in a 70-year-old man. Histological analysis excluded neoplasia, and bacteriological culture excluded tuberculosis. Serological testing and PCR Francisella were positive for this hunter patient, then treated by ciprofloxacin with a favourable outcome.
Les infections virales respiratoires communautaires sont fréquentes et le plus souvent bénignes. ... more Les infections virales respiratoires communautaires sont fréquentes et le plus souvent bénignes. Beaucoup d'agents différents comme les virus influenza, ou para-influenza, le virus respiratoire syncitial, les rhinovirus, coronavirus, adénovirus et les herpès virus peuvent être isolés chez les patients immunocompétents. Parmi ces virus, le cytomégalovirus (CMV) peut être responsable de pneumonie nosocomiale en réanimation. Le diagnostic des infections virales est difficile car les signes cliniques sont non spécifiques et l'isolement du virus responsable difficile. Cependant, une symptomatologie clinique associant fièvre, myalgies, céphalées, pharyngite est fréquente dans les infections à Inflenza qui peuvent aboutir à des tableaux sévères. Enfin, le virus plus récent responsable d'infection respiratoire est un virus nouvellement découvert de la famille des coronavirus, le SRAS-CoV qui a été responsable d'une épidémie d'infections respiratoires sévères. Les pneumonies virales sont fréquentes mais probablement non diagnostiquées chez les patients immunocompétents. Cependant le diagnostic est nécessaire car pour la plupart des pathogènes il existe un traitement efficace. Le diagnostic repose sur l'histologie mais de nouvelles techniques comme la PCR doivent devenir d'utilisation courante pour améliorer le rendement diagnostique.Respiratory infections are frequently encountered in the community; these infections are usually associated with only minor consequences. Many different agents, such as influenza and parainfluenza virus, respiratory syncitial virus, rhinovirus, coronavirus, adenovirus and herpes virus can be found in immuno-competent patients. Among these pathogens, cytomegalovirus (CMV) has been found to be responsible for nosocomial pneumonia in ICU. The main problem for viral infections, is the diagnosis, isolation of the pathogen is often difficult and not always reliable and the symptoms not specific. However, influenza is characterised by fever, myalgia, headache and pharyngitis, this infection may be very mild, even asymptomatic, moderate or very severe. Finally, the most recent viral pathogen involved in respiratory disease is a newly discovered coronavirus, the SARS-CoV which was responsible for the worldwide outbreak of Severe Acute Respiratory Syndrome. Viral pneumonia is a common pathology which is probably underdiagnosed in immuno-competent patients; many reports show that even if the diagnosis is difficult to obtain, it is not useless as long as we have, for most of the pathogens, an effective treatment. The gold standard was histology, new techniques like PCR can probably make a difference and should be included in the guidelines to improve diagnostic efficiency.
Pneumonia with septicemia caused by Pasteurella multocida was diagnosed in an immunocompetent pat... more Pneumonia with septicemia caused by Pasteurella multocida was diagnosed in an immunocompetent patient exposed to a dog. This case is remarkable by two aspects: first the absence of visible cutaneous lesion, and second the localization and severity of the infection caused by P. multocida even though the patient was immunocompetent. P. multocida can cause respiratory and systemic infection, and it is a possible diagnosis in case of exposure to animals, even without history of bite or scratch. Furthermore, severe infections caused by this pathogen can occur in immunocompetent patients, so that the implication of specific host factors in the severity of the disease can be suspected. Genetic features could be one of these.
Background: While the functional consequences of acute pulmonary infections are widely documented... more Background: While the functional consequences of acute pulmonary infections are widely documented, few studies focused on chronic pneumonia. We evaluated the consequences of chronic Pseudomonas lung infection on alveolar function. Methods: P. aeruginosa, included in agar beads, was instilled intratracheally in Sprague Dawley rats. Analysis was performed from day 2 to 21, a control group received only sterile agar beads. Alveolar-capillary barrier permeability, lung liquid clearance (LLC) and distal alveolar fluid clearance (DAFC) were measured using a vascular ( 131 I-Albumin) and an alveolar tracer ( 125 I-Albumin).
Pseudomonas aeruginosa is an opportunistic bacteria causing a wide variety of infections. The bac... more Pseudomonas aeruginosa is an opportunistic bacteria causing a wide variety of infections. The bacterial virulence depends on a large panel of cell-associated and extracellular factors. Quorum sensing (QS) allows cell-to-cell communication: sensing the environment, this system coordinates the expression of various genes within the bacterial population. QS is based on an interaction between a small diffusible molecule, an acylhomoserine lactone (AHL), and a transcriptionnal activator. Two QS systems, the las and rhl systems, have been identified in P. aeruginosa. The las system associates the transcriptionnal activator protein LasR and LasI responsible for the synthesis of a specific AHL: C12-HSL. This system was shown to activate the expression of a large number of virulence factors. Similarly, the rhl system associates the transcriptionnal activator protein RhlR with RhlI, which is responsible for the synthesis of another AHL: C4-HSL. Synthesis and secretion of a number of virulence factors are controlled by QS. Utilization of different animals models showed the crucial role of QS in the pathogenesis of P. aeruginosa infections. The discovery of QS has given a new opportunity to treat bacterial infection by another means than growth inhibition. New drugs inhibiting QS were recently discovered: furanone compounds can repress a large number of QS-regulated genes, including numerous P. aeruginosa virulence factor genes. Furanone administration to mice infected with P. aeruginosa significantly reduced lung bacterial load compared with the control group.
Pseudomonas aeruginosa lung infections are a major cause of death in cystic fibrosis and hospital... more Pseudomonas aeruginosa lung infections are a major cause of death in cystic fibrosis and hospitalized patients. Treating these infections is becoming difficult due to the emergence of conventional antimicrobial multiresistance. While monosaccharides have proved beneficial against such bacterial lung infection, the design of several multivalent glycosylated macromolecules has been shown to be also beneficial on biofilm dispersion. In this study, calix[4]arene-based glycoclusters functionalized with galactosides or fucosides have been synthesized. The characterization of their inhibitory properties on Pseudomonas aeruginosa aggregation, biofilm formation, adhesion on epithelial cells, and destruction of alveolar tissues were performed. The antiadhesive properties of the designed glycoclusters were demonstrated through several in vitro bioassays. An in vivo mouse model of lung infection provided an almost complete protection against Pseudomonas aeruginosa with the designed glycoclusters.
Pseudomonas aeruginosa and Candida albicans are two pathogens frequently encountered in the inten... more Pseudomonas aeruginosa and Candida albicans are two pathogens frequently encountered in the intensive care unit microbial community. We have demonstrated that C. albicans airway exposure protected against P. aeruginosa-induced lung injury. The goal of the present study was to characterize the cellular and molecular mechanisms associated with C. albicans-induced protection. Airway exposure by C. albicans led to the recruitment and activation of natural killer cells, innate lymphoid cells (ILCs), macrophages, and dendritic cells. This recruitment was associated with the secretion of interleukin-22 (IL-22), whose neutralization abolished C. albicansinduced protection. We identified, by flow cytometry, ILCs as the only cellular source of IL-22. Depletion of ILCs by anti-CD90.2 antibodies was associated with a decreased IL-22 secretion and impaired survival after P. aeruginosa challenge. Our results demonstrate that the production of IL-22, mainly by ILCs, is a major and inducible step in protection against P. aeruginosa-induced lung injury. This cytokine may represent a clinical target in Pseudomonas aeruginosa-induced lung injury.
The pathogenesis and the outcome of Pseudomonas aeruginosa ventilator-acquired pneumonia depend o... more The pathogenesis and the outcome of Pseudomonas aeruginosa ventilator-acquired pneumonia depend on the virulence factors displayed by the bacteria as well as the host response. Thus, quorum sensing, lipopolysaccharide, and type 3 secretion system have each individually been shown to be important virulence systems in laboratory reference strains. However, the relative contribution of these three factors to the in vivo pathogenicity of clinically relevant strains has never been studied. We analyzed the virulence of 56 nonclonal Pseudomonas aeruginosa strains isolated from critically ill patients with ventilator-acquired pneumonia. To avoid the variation of human immune response, we used a murine model of pneumonia. The aim was to determine which virulence factor was the most important. Research laboratory of a university. Male adult BALB/c mice. In vitro, the phenotype of each strain was established as to the expression of quorum sensing-regulated factors (elastase and pyocyanin), type 3 secretion system exotoxin secretion (Exotoxin U, S and/or T, or "nonsecreting"), and lipopolysaccharide O-antigen serotype. Strain pathogenicity was evaluated in vivo in a mouse model of acute pneumonia through lung injury assessment by measuring alveolar-capillary barrier permeability to proteins, lung wet/dry weight ratio, and bacterial dissemination. Associations were then sought between virulence system phenotypes and levels of lung injury. In univariate analysis, elastase production, O11 serotype, and type 3 secretion system exotoxin secretion were associated with increased lung injury and exotoxin U was linked to an increase risk of bacteremia. In multivariate analysis, we observed that type 3 secretion system exotoxin secretion and to a lesser degree elastase production were associated with increased lung injury. In a murine model of pneumonia, our data suggest that type 3 secretion system and elastase are the most important virulence factors in clinically relevant P. aeruginosa strains.
Respiratory isolates of Pseudomonas aeruginosa were collected from 58 critically-ill patients wit... more Respiratory isolates of Pseudomonas aeruginosa were collected from 58 critically-ill patients with ventilator-associated pneumonia. Expression of elastase and pyocyanin was assessed semi-quantitatively, while quorum-sensing activity was assessed by quantifying the levels of the autoinducers N-3-oxododecanoyl-L-homoserine lactone (C12-HSL) and N-butanoyl-L-homoserine lactone (C4-HSL). Correlations were sought between quorum-sensing activity and the expression of these two virulence factors, and all results were compared to those obtained with the laboratory reference strains PA103, a strain defective in quorum-sensing, and PAO1, a functional quorum-sensing strain. More than twothirds of clinically pathogenic isolates had increased levels of elastase and ⁄ or pyocyanin, and high quorum-sensing activity, as assessed by autoinducer levels. However, a strong correlation between quorum-sensing activity and virulence factor production was revealed only for elastase and not for pyocyanin (C12-HSL ⁄ elastase, r = 0.7, p 2 · 10 )9 ; C4-HSL ⁄ elastase, r = 0.7, p 2 · 10 )9 ). These data suggest that the pathogenicity of P. aeruginosa isolates from critically-ill patients with ventilatorassociated pneumonia is caused, at least in part, by an increase in elastase production regulated by quorum-sensing, while increased pyocyanin production in these isolates may be regulated predominantly by mechanisms other than quorum-sensing.
American Journal of Respiratory and Critical Care Medicine, 2014
Pseudomonas aeruginosa, a major problem pathogen responsible for severe infections in critically ... more Pseudomonas aeruginosa, a major problem pathogen responsible for severe infections in critically ill patients, triggers, through a functional type-3 secretion system (T3SS), the activation of an intracellular cytosolic sensor of innate immunity, NLRC4. Although the NLRC4-inflammasome-dependent response contributes to increased clearance of intracellular pathogens, it seems that NLRC4 inflammasome activation decreases the clearance of P. aeruginosa, a mainly extracellular pathogen. We sought to determine the underlying mechanisms of this effect of the activation of NLRC4 by P. aeruginosa. We established acute lung injury in wild-type and Nlrc4(-/-) mice using sublethal intranasal inocula of P. aeruginosa strain CHA expressing or not a functional T3SS. We studied 96-hour survival, lung injury, bacterial clearance from the lungs, cytokine secretion in bronchoalveolar lavage, lung antimicrobial peptide expression by quantitative polymerase chain reaction, and flow cytometry analysis of lung cells. Nlrc4(-/-) mice showed enhanced bacterial clearance and decreased lung injury contributing to increased survival against extracellular P. aeruginosa strain expressing a functional T3SS. The mechanism involved decreased NLRC4-inflammasome-driven IL-18 secretion attenuating lung injury caused by excessive neutrophil recruitment. Additionally, in the lungs of Nlrc4(-/-) mice secretion of IL-17 by innate immune cells was increased and responsible for increased expression of lung epithelial antimicrobial peptides. Furthermore, IL-18 secretion was found to repress IL-17 and IL-17-driven lung antimicrobial peptide expression. We report a new role of the T3SS apparatus itself, independently of exotoxin translocation. Through NLRC4 inflammasome activation, the T3SS promotes IL-18 secretion, which dampens a beneficial IL-17-mediated antimicrobial host response.
The type III secretion system (TTSS) is a specialized cytotoxin-translocating apparatus of gram-n... more The type III secretion system (TTSS) is a specialized cytotoxin-translocating apparatus of gram-negative bacteria which is involved in lung injury, septic shock, and a poor patient outcome. Recent studies have attributed these effects mainly to the ExoU effector protein. However, few studies have focused on the ExoUindependent pathogenicity of the TTSS. For the present study, we compared the pathogenicities of two strains of Pseudomonas aeruginosa in a murine model of acute lung injury. We compared the CHA strain, which has a functional TTSS producing ExoS and ExoT but not ExoU, to an isogenic mutant with an inactivated exsA gene, CHA-D1, which does not express the TTSS at all. Rats challenged with CHA had significantly increased lung injury, as assessed by the wet/dry weight ratio for the lungs and the protein level in bronchoalveolar lavage fluid (BALF) at 12 h, compared to those challenged with CHA-D1. Consistent with these findings, the CHA strain was associated with increased in vitro cytotoxicity on A549 cells, as assessed by the release of lactate dehydrogenase. CHA was also associated at 12 h with a major decrease in polymorphonuclear neutrophils in BALF, with a proinflammatory response, as assessed by the amounts of tumor necrosis factor alpha and interleukin-1, and with decreased bacterial clearance from the lungs, ultimately leading to an increased mortality rate. These results demonstrate that the TTSS has a major role in P. aeruginosa pathogenicity independent of the role of ExoU. This report underscores the crucial roles of ExoS and ExoT or other TTSSrelated virulence factors in addition to ExoU.
Tularaemia is an emerging anthropozoonosis transmitted by contact with infected animals and throu... more Tularaemia is an emerging anthropozoonosis transmitted by contact with infected animals and through arthropod bites, inhalation, or ingestion. We describe a pulmonary nodule suggesting cancer in a 70-year-old man. Histological analysis excluded neoplasia, and bacteriological culture excluded tuberculosis. Serological testing and PCR Francisella were positive for this hunter patient, then treated by ciprofloxacin with a favourable outcome.
Les infections virales respiratoires communautaires sont fréquentes et le plus souvent bénignes. ... more Les infections virales respiratoires communautaires sont fréquentes et le plus souvent bénignes. Beaucoup d'agents différents comme les virus influenza, ou para-influenza, le virus respiratoire syncitial, les rhinovirus, coronavirus, adénovirus et les herpès virus peuvent être isolés chez les patients immunocompétents. Parmi ces virus, le cytomégalovirus (CMV) peut être responsable de pneumonie nosocomiale en réanimation. Le diagnostic des infections virales est difficile car les signes cliniques sont non spécifiques et l'isolement du virus responsable difficile. Cependant, une symptomatologie clinique associant fièvre, myalgies, céphalées, pharyngite est fréquente dans les infections à Inflenza qui peuvent aboutir à des tableaux sévères. Enfin, le virus plus récent responsable d'infection respiratoire est un virus nouvellement découvert de la famille des coronavirus, le SRAS-CoV qui a été responsable d'une épidémie d'infections respiratoires sévères. Les pneumonies virales sont fréquentes mais probablement non diagnostiquées chez les patients immunocompétents. Cependant le diagnostic est nécessaire car pour la plupart des pathogènes il existe un traitement efficace. Le diagnostic repose sur l'histologie mais de nouvelles techniques comme la PCR doivent devenir d'utilisation courante pour améliorer le rendement diagnostique.Respiratory infections are frequently encountered in the community; these infections are usually associated with only minor consequences. Many different agents, such as influenza and parainfluenza virus, respiratory syncitial virus, rhinovirus, coronavirus, adenovirus and herpes virus can be found in immuno-competent patients. Among these pathogens, cytomegalovirus (CMV) has been found to be responsible for nosocomial pneumonia in ICU. The main problem for viral infections, is the diagnosis, isolation of the pathogen is often difficult and not always reliable and the symptoms not specific. However, influenza is characterised by fever, myalgia, headache and pharyngitis, this infection may be very mild, even asymptomatic, moderate or very severe. Finally, the most recent viral pathogen involved in respiratory disease is a newly discovered coronavirus, the SARS-CoV which was responsible for the worldwide outbreak of Severe Acute Respiratory Syndrome. Viral pneumonia is a common pathology which is probably underdiagnosed in immuno-competent patients; many reports show that even if the diagnosis is difficult to obtain, it is not useless as long as we have, for most of the pathogens, an effective treatment. The gold standard was histology, new techniques like PCR can probably make a difference and should be included in the guidelines to improve diagnostic efficiency.
Pneumonia with septicemia caused by Pasteurella multocida was diagnosed in an immunocompetent pat... more Pneumonia with septicemia caused by Pasteurella multocida was diagnosed in an immunocompetent patient exposed to a dog. This case is remarkable by two aspects: first the absence of visible cutaneous lesion, and second the localization and severity of the infection caused by P. multocida even though the patient was immunocompetent. P. multocida can cause respiratory and systemic infection, and it is a possible diagnosis in case of exposure to animals, even without history of bite or scratch. Furthermore, severe infections caused by this pathogen can occur in immunocompetent patients, so that the implication of specific host factors in the severity of the disease can be suspected. Genetic features could be one of these.
Background: While the functional consequences of acute pulmonary infections are widely documented... more Background: While the functional consequences of acute pulmonary infections are widely documented, few studies focused on chronic pneumonia. We evaluated the consequences of chronic Pseudomonas lung infection on alveolar function. Methods: P. aeruginosa, included in agar beads, was instilled intratracheally in Sprague Dawley rats. Analysis was performed from day 2 to 21, a control group received only sterile agar beads. Alveolar-capillary barrier permeability, lung liquid clearance (LLC) and distal alveolar fluid clearance (DAFC) were measured using a vascular ( 131 I-Albumin) and an alveolar tracer ( 125 I-Albumin).
Pseudomonas aeruginosa is an opportunistic bacteria causing a wide variety of infections. The bac... more Pseudomonas aeruginosa is an opportunistic bacteria causing a wide variety of infections. The bacterial virulence depends on a large panel of cell-associated and extracellular factors. Quorum sensing (QS) allows cell-to-cell communication: sensing the environment, this system coordinates the expression of various genes within the bacterial population. QS is based on an interaction between a small diffusible molecule, an acylhomoserine lactone (AHL), and a transcriptionnal activator. Two QS systems, the las and rhl systems, have been identified in P. aeruginosa. The las system associates the transcriptionnal activator protein LasR and LasI responsible for the synthesis of a specific AHL: C12-HSL. This system was shown to activate the expression of a large number of virulence factors. Similarly, the rhl system associates the transcriptionnal activator protein RhlR with RhlI, which is responsible for the synthesis of another AHL: C4-HSL. Synthesis and secretion of a number of virulence factors are controlled by QS. Utilization of different animals models showed the crucial role of QS in the pathogenesis of P. aeruginosa infections. The discovery of QS has given a new opportunity to treat bacterial infection by another means than growth inhibition. New drugs inhibiting QS were recently discovered: furanone compounds can repress a large number of QS-regulated genes, including numerous P. aeruginosa virulence factor genes. Furanone administration to mice infected with P. aeruginosa significantly reduced lung bacterial load compared with the control group.
Pseudomonas aeruginosa lung infections are a major cause of death in cystic fibrosis and hospital... more Pseudomonas aeruginosa lung infections are a major cause of death in cystic fibrosis and hospitalized patients. Treating these infections is becoming difficult due to the emergence of conventional antimicrobial multiresistance. While monosaccharides have proved beneficial against such bacterial lung infection, the design of several multivalent glycosylated macromolecules has been shown to be also beneficial on biofilm dispersion. In this study, calix[4]arene-based glycoclusters functionalized with galactosides or fucosides have been synthesized. The characterization of their inhibitory properties on Pseudomonas aeruginosa aggregation, biofilm formation, adhesion on epithelial cells, and destruction of alveolar tissues were performed. The antiadhesive properties of the designed glycoclusters were demonstrated through several in vitro bioassays. An in vivo mouse model of lung infection provided an almost complete protection against Pseudomonas aeruginosa with the designed glycoclusters.
Pseudomonas aeruginosa and Candida albicans are two pathogens frequently encountered in the inten... more Pseudomonas aeruginosa and Candida albicans are two pathogens frequently encountered in the intensive care unit microbial community. We have demonstrated that C. albicans airway exposure protected against P. aeruginosa-induced lung injury. The goal of the present study was to characterize the cellular and molecular mechanisms associated with C. albicans-induced protection. Airway exposure by C. albicans led to the recruitment and activation of natural killer cells, innate lymphoid cells (ILCs), macrophages, and dendritic cells. This recruitment was associated with the secretion of interleukin-22 (IL-22), whose neutralization abolished C. albicansinduced protection. We identified, by flow cytometry, ILCs as the only cellular source of IL-22. Depletion of ILCs by anti-CD90.2 antibodies was associated with a decreased IL-22 secretion and impaired survival after P. aeruginosa challenge. Our results demonstrate that the production of IL-22, mainly by ILCs, is a major and inducible step in protection against P. aeruginosa-induced lung injury. This cytokine may represent a clinical target in Pseudomonas aeruginosa-induced lung injury.
The pathogenesis and the outcome of Pseudomonas aeruginosa ventilator-acquired pneumonia depend o... more The pathogenesis and the outcome of Pseudomonas aeruginosa ventilator-acquired pneumonia depend on the virulence factors displayed by the bacteria as well as the host response. Thus, quorum sensing, lipopolysaccharide, and type 3 secretion system have each individually been shown to be important virulence systems in laboratory reference strains. However, the relative contribution of these three factors to the in vivo pathogenicity of clinically relevant strains has never been studied. We analyzed the virulence of 56 nonclonal Pseudomonas aeruginosa strains isolated from critically ill patients with ventilator-acquired pneumonia. To avoid the variation of human immune response, we used a murine model of pneumonia. The aim was to determine which virulence factor was the most important. Research laboratory of a university. Male adult BALB/c mice. In vitro, the phenotype of each strain was established as to the expression of quorum sensing-regulated factors (elastase and pyocyanin), type 3 secretion system exotoxin secretion (Exotoxin U, S and/or T, or "nonsecreting"), and lipopolysaccharide O-antigen serotype. Strain pathogenicity was evaluated in vivo in a mouse model of acute pneumonia through lung injury assessment by measuring alveolar-capillary barrier permeability to proteins, lung wet/dry weight ratio, and bacterial dissemination. Associations were then sought between virulence system phenotypes and levels of lung injury. In univariate analysis, elastase production, O11 serotype, and type 3 secretion system exotoxin secretion were associated with increased lung injury and exotoxin U was linked to an increase risk of bacteremia. In multivariate analysis, we observed that type 3 secretion system exotoxin secretion and to a lesser degree elastase production were associated with increased lung injury. In a murine model of pneumonia, our data suggest that type 3 secretion system and elastase are the most important virulence factors in clinically relevant P. aeruginosa strains.
Respiratory isolates of Pseudomonas aeruginosa were collected from 58 critically-ill patients wit... more Respiratory isolates of Pseudomonas aeruginosa were collected from 58 critically-ill patients with ventilator-associated pneumonia. Expression of elastase and pyocyanin was assessed semi-quantitatively, while quorum-sensing activity was assessed by quantifying the levels of the autoinducers N-3-oxododecanoyl-L-homoserine lactone (C12-HSL) and N-butanoyl-L-homoserine lactone (C4-HSL). Correlations were sought between quorum-sensing activity and the expression of these two virulence factors, and all results were compared to those obtained with the laboratory reference strains PA103, a strain defective in quorum-sensing, and PAO1, a functional quorum-sensing strain. More than twothirds of clinically pathogenic isolates had increased levels of elastase and ⁄ or pyocyanin, and high quorum-sensing activity, as assessed by autoinducer levels. However, a strong correlation between quorum-sensing activity and virulence factor production was revealed only for elastase and not for pyocyanin (C12-HSL ⁄ elastase, r = 0.7, p 2 · 10 )9 ; C4-HSL ⁄ elastase, r = 0.7, p 2 · 10 )9 ). These data suggest that the pathogenicity of P. aeruginosa isolates from critically-ill patients with ventilatorassociated pneumonia is caused, at least in part, by an increase in elastase production regulated by quorum-sensing, while increased pyocyanin production in these isolates may be regulated predominantly by mechanisms other than quorum-sensing.
American Journal of Respiratory and Critical Care Medicine, 2014
Pseudomonas aeruginosa, a major problem pathogen responsible for severe infections in critically ... more Pseudomonas aeruginosa, a major problem pathogen responsible for severe infections in critically ill patients, triggers, through a functional type-3 secretion system (T3SS), the activation of an intracellular cytosolic sensor of innate immunity, NLRC4. Although the NLRC4-inflammasome-dependent response contributes to increased clearance of intracellular pathogens, it seems that NLRC4 inflammasome activation decreases the clearance of P. aeruginosa, a mainly extracellular pathogen. We sought to determine the underlying mechanisms of this effect of the activation of NLRC4 by P. aeruginosa. We established acute lung injury in wild-type and Nlrc4(-/-) mice using sublethal intranasal inocula of P. aeruginosa strain CHA expressing or not a functional T3SS. We studied 96-hour survival, lung injury, bacterial clearance from the lungs, cytokine secretion in bronchoalveolar lavage, lung antimicrobial peptide expression by quantitative polymerase chain reaction, and flow cytometry analysis of lung cells. Nlrc4(-/-) mice showed enhanced bacterial clearance and decreased lung injury contributing to increased survival against extracellular P. aeruginosa strain expressing a functional T3SS. The mechanism involved decreased NLRC4-inflammasome-driven IL-18 secretion attenuating lung injury caused by excessive neutrophil recruitment. Additionally, in the lungs of Nlrc4(-/-) mice secretion of IL-17 by innate immune cells was increased and responsible for increased expression of lung epithelial antimicrobial peptides. Furthermore, IL-18 secretion was found to repress IL-17 and IL-17-driven lung antimicrobial peptide expression. We report a new role of the T3SS apparatus itself, independently of exotoxin translocation. Through NLRC4 inflammasome activation, the T3SS promotes IL-18 secretion, which dampens a beneficial IL-17-mediated antimicrobial host response.
The type III secretion system (TTSS) is a specialized cytotoxin-translocating apparatus of gram-n... more The type III secretion system (TTSS) is a specialized cytotoxin-translocating apparatus of gram-negative bacteria which is involved in lung injury, septic shock, and a poor patient outcome. Recent studies have attributed these effects mainly to the ExoU effector protein. However, few studies have focused on the ExoUindependent pathogenicity of the TTSS. For the present study, we compared the pathogenicities of two strains of Pseudomonas aeruginosa in a murine model of acute lung injury. We compared the CHA strain, which has a functional TTSS producing ExoS and ExoT but not ExoU, to an isogenic mutant with an inactivated exsA gene, CHA-D1, which does not express the TTSS at all. Rats challenged with CHA had significantly increased lung injury, as assessed by the wet/dry weight ratio for the lungs and the protein level in bronchoalveolar lavage fluid (BALF) at 12 h, compared to those challenged with CHA-D1. Consistent with these findings, the CHA strain was associated with increased in vitro cytotoxicity on A549 cells, as assessed by the release of lactate dehydrogenase. CHA was also associated at 12 h with a major decrease in polymorphonuclear neutrophils in BALF, with a proinflammatory response, as assessed by the amounts of tumor necrosis factor alpha and interleukin-1, and with decreased bacterial clearance from the lungs, ultimately leading to an increased mortality rate. These results demonstrate that the TTSS has a major role in P. aeruginosa pathogenicity independent of the role of ExoU. This report underscores the crucial roles of ExoS and ExoT or other TTSSrelated virulence factors in addition to ExoU.
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Papers by Karine Faure