Murine pulmonary infection with Listeria monocytogenes: differential susceptibility of BALB/c, C57BL/6 and DBA/2 mice

Type 2 immune predisposition results in accelerated neutrophil aging causing susceptibility to bacterial infection

Atopic individuals show enhanced type 2 immune cell responses and a susceptibility to infections with certain bacteria and viruses. Although patients with allergic diseases harbor normal counts of circulating neutrophils, these cells exert deficient effector functions. However, the underlying mechanism of this dysregulation of neutrophils remains ill defined. Here, we find that development, aging, and elimination of neutrophils are accelerated in mice with a predisposition to type 2 immunity, which, in turn, causes susceptibility to infection with several bacteria. Neutrophil-mediated immunity to bacterial infection was greatly decreased in mice with a genetic or induced bias to type 2 immunity. Abrogation of interleukin-4 (IL-4) receptor signaling in these animals fully restored their antibacterial defense, which largely depended on Ly6G⁺ neutrophils. IL-4 signals accelerated the maturation of neutrophils in the bone marrow and caused their rapid release to the circulation and periphery. IL-4-stimulated neutrophils aged more rapidly in the periphery, as evidenced by their phenotypic and functional changes, including their decreased phagocytosis of bacterial particles. Moreover, neutrophils from type 2 immune predisposed mice were eliminated at a higher rate by apoptosis and phagocytosis by macrophages and dendritic cells. Collectively, IL-4 signaling-mediated neutrophil aging constitutes an important adaptive deficiency in type 2 inflammation, contributing to recurrent bacterial infections.

Flagella hook protein FlgE is a novel vaccine candidate of Pseudomonas aeruginosa identified by a genomic approach

Infections due to Pseudomonas aeruginosa (PA) are becoming a serious threat to patients in intensive care units. A PA vaccine is a practical and economical solution to solve the problems caused by PA infection successfully. In recent years, several antigen candidates have been tested in animal and human clinical trials, but none of them has been approved to date. An alternative strategy for antigen screening and protective antigens is in urgent demand. In this study, we generated a genome-wide library of PA protein fragments tagged with maltose-binding protein (MBP). Using sera from patients who recovered after PA infection, we identified a novel protective antigen, FlgE, which is the structural component of the flagella hook. Vaccination with recombinant FlgE (reFlgE) induced a Th2-predominant immune response and reduced bacterial load and inflammation in PA-infected mice. Anti-reFlgE antibodies recognized native FlgE on the bacterial membrane in vitro and conferred protection in mice, which may be due to the mediation of opsonophagocytic killing and inhibition of bacterial motility. In addition, the combination of reFlgE with rePcrV_NH, an engineered antigen we reported previously, provided elevated protection against PA infection. Our data demonstrate that FlgE is a promising vaccine candidate for PA and provide a new strategy for the efficient screening of antigens of other pathogens.

Lung infection caused by Pseudomonas aeruginosa in a CD26/DPP4 deficient F344 rat model

Background

Pseudomonas aeruginosa (PA) is the most important opportunistic pathogen in causing nosocomial infections and, furthermore, poses a permanent threat for severe chronic infections in patients with cystic fibrosis or COPD. The transmembrane protein CD26 with dipeptidyl peptidase-4 (DPP4) activity shows an increased expression in inflamed tissue. We tested whether CD26/DPP4 deficiency leads to reduced inflammation and decreased structural damage when infected with PA.

Methods

CD26/DPP4⁺ and CD26/DPP4⁻ rats were instilled intratracheally with NaCl (controls) or with PA. Six hours later, bacterial distribution was detected with the in vivo imaging system 200 (IVIS). Lungs were then processed for molecular biology, light and electron microscopy and analyzed qualitatively, quantitatively and stereologically. Bacterial numbers were determined in homogenized lungs.

Results

Compared to saline treated controls, in both infected groups (1) the acinar airspace was significantly increased, (2) the volume density of the alveolar epithelium was significantly decreased, (3) the septal thickness was significantly reduced, (4) more than 40% of the alveolar epithelial surface was damaged, and up to 36% of the epithelial surface was covered with edema. In infected CD26⁻ rats, the increase in lung weight was significantly less pronounced, the portion of edematous alveolar airspace was significantly lower and the part of edema interspersed with PA was decreased significantly.

Conclusions

CD26/DPP4 deficiency resulted in reduced pulmonary edema under sublethal PA infection, implicating a role for CD26 in infection progression. The partly pronounced structural damage may mask further possible influences of CD26 on the inflammatory response.

The Pseudomonas aeruginosa ExoY phenotype of high-copy-number recombinants is not detectable in natural isolates

The nucleotidyl cyclase ExoY is an effector protein of the type III secretion system of Pseudomonas aeruginosa. We compared the cyclic nucleotide production and lung disease phenotypes caused by the ExoY-overexpressing strain PA103ΔexoUexoT::Tc pUCPexoY, its vector control strain PA103ΔexoUexoT::Tc pUCP18, its loss-of-function control PA103ΔexoUexoT::Tc pUCPexoY K81M and natural ExoY-positive and ExoY-negative isolates in a murine acute airway infection model. Only the P. aeruginosa carrier of the exoY-plasmid produced high levels of cUMP and caused the most severe course of infection. The pathology ascribed to ExoY from studies using the high-copy-number plasmid on mammalian cells in vitro and in vivo was not observed with natural P. aeruginosa isolates. This indicates that the role of ExoY during infection with real-life P. aeruginosa still needs to be resolved.

Bioreactor-based mass production of human iPSC-derived macrophages enables immunotherapies against bacterial airway infections

The increasing number of severe infections with multi-drug-resistant pathogens worldwide highlights the need for alternative treatment options. Given the pivotal role of phagocytes and especially alveolar macrophages in pulmonary immunity, we introduce a new, cell-based treatment strategy to target bacterial airway infections. Here we show that the mass production of therapeutic phagocytes from induced pluripotent stem cells (iPSC) in industry-compatible, stirred-tank bioreactors is feasible. Bioreactor-derived iPSC-macrophages (iPSC-Mac) represent a highly pure population of CD45⁺CD11b⁺CD14⁺CD163⁺ cells, and share important phenotypic, functional and transcriptional hallmarks with professional phagocytes, however with a distinct transcriptome signature similar to primitive macrophages. Most importantly, bioreactor-derived iPSC-Mac rescue mice from Pseudomonas aeruginosa-mediated acute infections of the lower respiratory tract within 4-8 h post intra-pulmonary transplantation and reduce bacterial load. Generation of specific immune-cells from iPSC-sources in scalable stirred-tank bioreactors can extend the field of immunotherapy towards bacterial infections, and may allow for further innovative cell-based treatment strategies.

Pulmonary infections constitute a substantial health problem worldwide. Here the authors show that phagocytes similar to primitive macrophages can be generated from human induced pluripotent stem cells, by the use of industry-compatible, stirred-tank bioreactors, and applied as a cell-based therapy to treat acute bacterial infections in mice.

The Role of Pseudomonas aeruginosa ExoY in an Acute Mouse Lung Infection Model

The effector protein Exotoxin Y (ExoY) produced by Pseudomonas aeruginosa is injected via the type III secretion system (T3SS) into host cells. ExoY acts as nucleotidyl cyclase promoting the intracellular accumulation of cyclic nucleotides. To what extent nucleotidyl cyclase activity contributes to the pathogenicity of ExoY and which mechanisms participate in the manifestation of lung infection is still unclear. Here, we used an acute airway infection model in mice to address the role of ExoY in lung infection. In infected lungs, a dose-dependent phenotype of infection with bacteria-expressing ExoY was mirrored by haemorrhage, formation of interstitial oedema in alveolar septa, and infiltration of the perivascular space with erythrocytes and neutrophilic granulocytes. Analyses of the infection process on the cellular and organismal level comparing infections with Pseudomonas aeruginosa mutants expressing either nucleotidyl cyclase-active or -inactive ExoY revealed differential cytokine secretion, increased prevalence of apoptosis, and a break of lung barrier integrity in mice infected with cyclase-active ExoY. Notably, of all measured cyclic nucleotides, only the increase of cyclic UMP in infected mouse lungs coincides temporally with the observed early pathologic changes. In summary, our results suggest that the nucleotidyl cyclase activity of ExoY can contribute to P. aeruginosa acute pathogenicity.

Listeria monocytogenes-associated respiratory infections: a study of 38 consecutive cases

OBJECTIVES

Listeria monocytogenes (Lm) is a foodborne human pathogen responsible for severe infections, including septicaemia, neurolisteriosis, and maternal-foetal and focal infections. Little is known about Lm-associated respiratory tract or lung infections.

METHODS

We conducted a retrospective study of culture-proven cases of Lm pleural infections and pneumonia reported to the French National Reference Centre for Listeria from January 1993 to August 2016.

RESULTS

Thirty-eight consecutive patients with pleural infection (n = 32), pneumonia (n = 5), or both (n = 1) were studied; 71% of these were men. Median age was 72 (range 29-90). Two patients presented with concomitant neurolisteriosis. All patients but one reported at least one immunosuppressive condition (97%), with a median number of 2 (range 0-5), including 29% (8/28) with current exposure to immunosuppressive therapy and 50% (17/34) with ongoing neoplasia; 75% (21/28) reported previous pleural or pulmonary disease. Antibiotic therapy mostly consisted in amoxicillin (72%) associated with aminoglycoside in 32%. Chest-tube drainage was performed in 7/19 patients with empyema (37%); 25% of the patients (7/30) required intensive care management. In-hospital mortality reached 35% and occurred after a median time interval of 4 days (range 1-33 days). Three patients had recurrence of empyema (time interval of 1 week to 4 months after treatment completion). Altogether, only 13/31 patients (42%) diagnosed with Lm respiratory infection experienced an uneventful outcome at 2-year follow-up.

CONCLUSION

Lm is a rare but severe cause of pneumonia and pleural infection in older immunocompromised patients, requiring prompt diagnosis and adequate management and follow-up.

Insights into host-pathogen interactions from state-of-the-art animal models of respiratory Pseudomonas aeruginosa infections

Pseudomonas aeruginosa is an important opportunistic pathogen that can cause acute respiratory infections in immunocompetent patients or chronic infections in immunocompromised individuals and in patients with cystic fibrosis. When acquiring the chronic infection state, bacteria are encapsulated within biofilm structures enabling them to withstand diverse environmental assaults, including immune reactions and antimicrobial therapy. Understanding the molecular interactions within the bacteria, as well as with the host or other bacteria, is essential for developing innovative treatment strategies. Such knowledge might be accumulated in vitro. However, it is ultimately necessary to confirm these findings in vivo. In the present Review, we describe state-of-the-art in vivo models that allow studying P. aeruginosa infections in molecular detail. The portrayed mammalian models exclusively focus on respiratory infections. The data obtained by alternative animal models which lack lung tissue, often provide molecular insights that are easily transferable to mammals. Importantly, these surrogate in vivo systems reveal complex molecular interactions of P. aeruginosa with the host. Herein, we also provide a critical assessment of the advantages and disadvantages of such models.

Regulation of autophagy by E3 ubiquitin ligase RNF216 through BECN1 ubiquitination

Autophagy is an evolutionarily conserved biological process involved in an array of physiological and pathological events. Without proper control, autophagy contributes to various disorders, including cancer and autoimmune and inflammatory diseases. It is therefore of vital importance that autophagy is under careful balance. Thus, additional regulators undoubtedly deepen our understanding of the working network, and provide potential therapeutic targets for disorders. In this study, we found that RNF216 (ring finger protein 216), an E3 ubiquitin ligase, strongly inhibits autophagy in macrophages. Further exploration demonstrates that RNF216 interacts with BECN1, a key regulator in autophagy, and leads to ubiquitination of BECN1, thereby contributing to BECN1 degradation. RNF216 was involved in the ubiquitination of lysine 48 of BECN1 through direct interaction with the triad (2 RING fingers and a DRIL [double RING finger linked]) domain. We further showed that inhibition of autophagy through overexpression of RNF216 in alveolar macrophages promotes Listeria monocytogenes growth and distribution, while knockdown of RNF216 significantly inhibited these outcomes. These effects were confirmed in a mouse model of L. monocytogenes infection, suggesting that manipulating RNF216 expression could be a therapeutic approach. Thus, our study identifies a novel negative regulator of autophagy and suggests that RNF216 may be a target for treatment of inflammatory diseases.

Rho GTPases in the regulation of pulmonary vascular barrier function

Pulmonary endothelial permeability is an important determinant of vascular adaptation to changes in oxygen tension, blood pressure, levels of growth factors or inflammatory cytokines. The Ras homologous (Rho) family of guanosine triphosphate phosphatases (Rho GTPases), key regulators of the actin cytoskeleton, regulate endothelial barrier function in response to a variety of environmental factors and signalling agents via the reorganization of the actin cytoskeleton, changes in receptor trafficking or the phosphorylation of junctional proteins. This review provides a brief summary of recent knowledge on Rho-GTPase-mediated effects on pulmonary endothelial barrier function and focuses in particular on their role in pulmonary vascular disorders, including pulmonary hypertension, chronic obstructive pulmonary disease, acute lung injury and acute respiratory distress syndrome.

Assessing Pseudomonas virulence using mammalian models: acute infection model

The acute murine lung infection model monitors Pseudomonas aeruginosa airway infections by multiple continuous and endpoint parameters. After intratracheal or intranasal infection it characterizes the course of infection via head-out spirometry, rectal temperature, weight loss, a body condition score based on nine physiological parameters, lung bacterial numbers, organ dissemination of bacteria, and a semiquantitative assessment of lung inflammation and further analysis. The generated data allows a robust classification of virulence of mutant or wild-type P. aeruginosa strains and/or of the susceptibility of wild-type or engineered mouse strains to infection. If standardized, the model is applicable to the preclinical assessment of antipseudomonal prevention and intervention strategies.

Severity of allergic airway disease due to house dust mite allergen is not increased after clinical recovery of lung infection with Chlamydia pneumoniae in mice

Chlamydia pneumoniae is associated with chronic inflammatory lung diseases like bronchial asthma and chronic obstructive pulmonary disease. The existence of a causal link between allergic airway disease and C. pneumoniae is controversial. A mouse model was used to address the question of whether preceding C. pneumoniae lung infection and recovery modifies the outcome of experimental allergic asthma after subsequent sensitization with house dust mite (HDM) allergen. After intranasal infection, BALB/c mice suffered from pneumonia characterized by an increased clinical score, reduction of body weight, histopathology, and a bacterial load in the lungs. After 4 weeks, when infection had almost resolved clinically, HDM allergen sensitization was performed for another 4 weeks. Subsequently, mice were subjected to a methacholine hyperresponsiveness test and sacrificed for further analyses. As expected, after 8 weeks, C. pneumoniae-specific antibodies were detectable only in infected mice and the titer was significantly higher in the C. pneumoniae/HDM allergen-treated group than in the C. pneumoniae/NaCl group. Intriguingly, airway hyperresponsiveness and eosinophilia in bronchoalveolar lavage fluid were significantly lower in the C. pneumoniae/HDM allergen-treated group than in the mock/HDM allergen-treated group. We did observe a relationship between experimental asthma and chlamydial infection. Our results demonstrate an influence of sensitization to HDM allergen on the development of a humoral antibacterial response. However, our model demonstrates no increase in the severity of experimental asthma to HDM allergen as a physiological allergen after clinically resolved severe chlamydial lung infection. Our results rather suggest that allergic airway disease and concomitant cellular changes in mice are decreased following C. pneumoniae lung infection in this setting.

A new role of the complement system: C3 provides protection in a mouse model of lung infection with intracellular Chlamydia psittaci

The complement system modulates the intensity of innate and specific immunity. While it protects against infections by extracellular bacteria its role in infection with obligate intracellular bacteria, such as the avian and human pathogen Chlamydia (C.) psittaci, is still unknown. In the present study, knockout mice lacking C3 and thus all main complement effector functions were intranasally infected with C. psittaci strain DC15. Clinical parameters, lung histology, and cytokine levels were determined. A subset of infections was additionally performed with mice lacking C5 or C5a receptors. Complement activation occurred before symptoms of pneumonia appeared. Mice lacking C3 were ∼100 times more susceptible to the intracellular bacteria compared to wild-type mice, with all C3^−/− mice succumbing to infection after day 9. At a low infective dose, C3^−/− mice became severely ill after an even longer delay, the kinetics suggesting a so far unknown link of complement to the adaptive, protective immune response against chlamydiae. The lethal phenotype of C3^−/− mice is not based on differences in the anti-chlamydial IgG response (which is slightly delayed) as demonstrated by serum transfer experiments. In addition, during the first week of infection, the absence of C3 was associated with partial protection characterized by reduced weight loss, better clinical score and lower bacterial burden, which might be explained by a different mechanism. Lack of complement functions downstream of C5 had little effect. This study demonstrates for the first time a strong and complex influence of complement effector functions, downstream of C3 and upstream of C5, on the outcome of an infection with intracellular bacteria, such as C. psittaci.

Friend or foe: genetic and functional characterization of plant endophytic Pseudomonas aeruginosa

Endophytic Pseudomonas aeruginosa strain BP35 was originally isolated from black pepper grown in the rain forest in Kerala, India. Strain PaBP35 was shown to provide significant protection to black pepper against infections by Phytophthora capsici and Radopholus similis. For registration and implementation in disease management programmes, several traits of PaBP35 were investigated including its endophytic behaviour, biocontrol activity, phylogeny and toxicity to mammals. The results showed that PaBP35 efficiently colonized black pepper shoots and displayed a typical spatiotemporal pattern in its endophytic movement with concomitant suppression of Phytophthora rot. Confocal laser scanning microscopy revealed high populations of PaBP35::gfp2 inside tomato plantlets, supporting its endophytic behaviour in other plant species. Polyphasic approaches to genotype PaBP35, including BOX-PCR, recN sequence analysis, multilocus sequence typing and comparative genome hybridization analysis, revealed its uniqueness among P. aeruginosa strains representing clinical habitats. However, like other P. aeruginosa strains, PaBP35 exhibited resistance to antibiotics, grew at 25-41°C and produced rhamnolipids and phenazines. PaBP35 displayed strong type II secretion effectors-mediated cytotoxicity on mammalian A549 cells. Coupled with pathogenicity in a murine airway infection model, we conclude that this plant endophytic strain is as virulent as clinical P. aeruginosa strains. Safety issues related to the selection of plant endophytic bacteria for crop protection are discussed.

Animal models of listeriosis: a comparative review of the current state of the art and lessons learned

Listeriosis is a leading cause of hospitalization and death due to foodborne illness in the industrialized world. Animal models have played fundamental roles in elucidating the pathophysiology and immunology of listeriosis, and will almost certainly continue to be integral components of the research on listeriosis. Data derived from animal studies helped for example characterize the importance of cell-mediated immunity in controlling infection, allowed evaluation of chemotherapeutic treatments for listeriosis, and contributed to quantitative assessments of the public health risk associated with L. monocytogenes contaminated food commodities. Nonetheless, a number of pivotal questions remain unresolved, including dose-response relationships, which represent essential components of risk assessments. Newly emerging data about species-specific differences have recently raised concern about the validity of most traditional animal models of listeriosis. However, considerable uncertainty about the best choice of animal model remains. Here we review the available data on traditional and potential new animal models to summarize currently recognized strengths and limitations of each model. This knowledge is instrumental for devising future studies and for interpreting current data. We deliberately chose a historical, comparative and cross-disciplinary approach, striving to reveal clues that may help predict the ultimate value of each animal model in spite of incomplete data.

Acute intratracheal Pseudomonas aeruginosa infection in cystic fibrosis mice is age-independent

Background

Since the discovery of the human CFTR gene in 1989 various mouse models for cystic fibrosis (CF) have been generated and used as a very suitable and popular tool to approach research on this life-threatening disease. Age related changes regarding the course of disease and susceptibility towards pulmonary infections have been discussed in numerous studies.

Methods

Here, we investigated Cftr^{TgH(neoim)Hgu} and Cftr^tm1Unc-Tg(FABPCFTR)1Jaw/J CF mice and their non-CF littermates during an acute lung infection with Pseudomonas aeruginosa for age dependent effects of their lung function and immune response.

Mice younger than three or older than six months were intratracheally infected with P. aeruginosa TBCF10839. The infection was monitored by lung function of the animals using non-invasive head-out spirometry and the time course of physiological parameters over 192 hours. Quantitative bacteriology and lung histopathology of a subgroup of animals were used as endpoint parameters.

Results

Age-dependent changes in lung function and characteristic features for CF like a shallower, faster breathing pattern were observed in both CF mouse models in uninfected state. In contrast infected CF mice did not significantly differ from their non-CF littermates in susceptibility and severity of lung infection in both mouse models and age groups. The transgenic Cftr^tm1Unc-Tg(FABPCFTR)1Jaw/J and their non-CF littermates showed a milder course of infection than the Cftr^{TgH(neoim)Hgu} CF and their congenic C57Bl/6J non-CF mice suggesting that the genetic background was more important for outcome than Cftr dysfunction.

Conclusions

Previous investigations of the same mouse lines have shown a higher airway susceptibility of older CF mice to intranasally applied P. aeruginosa. The different outcome of intranasal and intratracheal instillation of bacteria implies that infected CF epithelium is impaired during the initial colonization of upper airways, but not in the subsequent response of host defense.

Lung function and inflammation during murine Pseudomonas aeruginosa airway infection

BACKGROUND

Following any acute irritation lung function declines rapidly. Reasons for pulmonary deterioration in humans had been attributed to the action of either interleukin-6 or interleukin-8 in the lungs.

OBJECTIVES

The present study investigates the association between immune response and decline in lung function in a murine bacterial lung infection model.

METHODS

Upon intratracheal inoculation of C57BL/6J mice with a sublethal dose of Pseudomonas aeruginosa lung function, cytokine, chemokine and cytometry in bronchoalveolar lavage fluid, bacterial counts and lung histology was assessed at 2, 4, 6, 8, 10, 12, 18, 24, 48, 72, 96 and 120 h post inoculation.

RESULTS

Lung function measured by non-invasive head-out spirometry decreased most strongly between 6 and 10 h post inoculation and required up to 72 h to recover for selected parameters. CFU counts in the lungs peaked at 4h post inoculation with subsequent decline until at 24-48 h post inoculation background levels were reached. Cytokine and chemokine responses could be separated into an early pro-inflammatory phase (2-8h post inoculation; mainly tumor-necrosis factor α (TNFα) and interleukin-1α driven) and a late anti-inflammatory resolution phase (starting at 24h post inoculation; mainly interleukin-10 and interleukin-4 driven). Interleukin-6 levels correlated with the deterioration of lung function. Lung histology showed maximal changes in terms of inflammation and edema between 24 and 48 h post inoculation.

CONCLUSIONS

In summary, elevated interleukin-6, high local neutrophil counts and lung edema were found to be the most characteristic signs of the transient period of deterioration of lung function.

Community dynamics in the mouse gut microbiota: a possible role for IRF9-regulated genes in community homeostasis

Background

Gut microbial communities of mammals are thought to show stable differences between individuals. This means that the properties imparted by the gut microbiota become a unique and constant characteristic of the host. Manipulation of the microbiota has been proposed as a useful tool in health care, but a greater understanding of mechanisms which lead to community stability is required. Here we have examined the impact of host immunoregulatory phenotype on community dynamics.

Methods and Findings

Denaturing gradient gel electrophoresis was used to analyse the faecal bacterial community of BALB/c and C57BL/6 mice and C57BL/6 mice deficient for either type I interferon (IFN) signalling (IRF9 KO mice) or type I and type II IFN signalling (STAT1 KO mice). Temporal variation was found in all mouse strains. A measure of the ability for a community structure characteristic of the host to be maintained over time, the individuality index, varied between mouse strains and available data from pigs and human models. IRF9 KO mice had significantly higher temporal variation, and lower individuality, than other mouse strains. Examination of the intestinal mucosa of the IRF9 KO mice revealed an increased presence of T-cells and neutrophils in the absence of inflammation.

Significance

The high temporal variation observed in the gut microbiota of inbred laboratory mice has implications for their use as experimental models for the human gut microbiota. The distinct IRF9 and STAT1 phenotypes suggest a role for IRF9 in immune regulation within the gut mucosa and that further study of interferon responsive genes is necessary to understand host-gut microbe relationships.

The lectin-like domain of TNF protects from listeriolysin-induced hyperpermeability in human pulmonary microvascular endothelial cells - a crucial role for protein kinase C-alpha inhibition

Listeriosis can lead to potentially lethal pulmonary complications in newborns and immune compromised patients, characterized by extensive permeability edema. Listeriolysin (LLO), the main virulence factor of Listeria monocytogenes, induces a dose-dependent hyperpermeability in monolayers of human lung microvascular endothelial cells in vitro. The permeability increasing activity of LLO, which is accompanied by an increased reactive oxygen species (ROS) generation, RhoA activation and myosin light chain (MLC) phosphorylation, can be completely inhibited by the protein kinase C (PKC) alpha/beta inhibitor GO6976, indicating a crucial role for PKC in the induction of barrier dysfunction. The TNF-derived TIP peptide, which mimics the lectin-like domain of the cytokine, blunts LLO-induced hyperpermeability in vitro, upon inhibiting LLO-induced protein kinase C-alpha activation, ROS generation and MLC phosphorylation and upon restoring the RhoA/Rac 1 balance. These results indicate that the lectin-like domain of TNF has a potential therapeutic value in protecting from LLO-induced pulmonary endothelial hyperpermeability.

Genome diversity of Pseudomonas aeruginosa PAO1 laboratory strains

Pseudomonas aeruginosa PAO1 is the most commonly used strain for research on this ubiquitous and metabolically versatile opportunistic pathogen. Strain PAO1, a derivative of the original Australian PAO isolate, has been distributed worldwide to laboratories and strain collections. Over decades discordant phenotypes of PAO1 sublines have emerged. Taking the existing PAO1-UW genome sequence (named after the University of Washington, which led the sequencing project) as a blueprint, the genome sequences of reference strains MPAO1 and PAO1-DSM (stored at the German Collection for Microorganisms and Cell Cultures [DSMZ]) were resolved by physical mapping and deep short read sequencing-by-synthesis. MPAO1 has been the source of near-saturation libraries of transposon insertion mutants, and PAO1-DSM is identical in its SpeI-DpnI restriction map with the original isolate. The major genomic differences of MPAO1 and PAO1-DSM in comparison to PAO1-UW are the lack of a large inversion, a duplication of a mobile 12-kb prophage region carrying a distinct integrase and protein phosphatases or kinases, deletions of 3 to 1,006 bp in size, and at least 39 single-nucleotide substitutions, 17 of which affect protein sequences. The PAO1 sublines differed in their ability to cope with nutrient limitation and their virulence in an acute murine airway infection model. Subline PAO1-DSM outnumbered the two other sublines in late stationary growth phase. In conclusion, P. aeruginosa PAO1 shows an ongoing microevolution of genotype and phenotype that jeopardizes the reproducibility of research. High-throughput genome resequencing will resolve more cases and could become a proper quality control for strain collections.

Caenorhabditis elegans semi-automated liquid screen reveals a specialized role for the chemotaxis gene cheB2 in Pseudomonas aeruginosa virulence

Pseudomonas aeruginosa is an opportunistic human pathogen that causes infections in a variety of animal and plant hosts. Caenorhabditis elegans is a simple model with which one can identify bacterial virulence genes. Previous studies with C. elegans have shown that depending on the growth medium, P. aeruginosa provokes different pathologies: slow or fast killing, lethal paralysis and red death. In this study, we developed a high-throughput semi-automated liquid-based assay such that an entire genome can readily be scanned for virulence genes in a short time period. We screened a 2,200-member STM mutant library generated in a cystic fibrosis airway P. aeruginosa isolate, TBCF10839. Twelve mutants were isolated each showing at least 70% attenuation in C. elegans killing. The selected mutants had insertions in regulatory genes, such as a histidine kinase sensor of two-component systems and a member of the AraC family, or in genes involved in adherence or chemotaxis. One mutant had an insertion in a cheB gene homologue, encoding a methylesterase involved in chemotaxis (CheB2). The cheB2 mutant was tested in a murine lung infection model and found to have a highly attenuated virulence. The cheB2 gene is part of the chemotactic gene cluster II, which was shown to be required for an optimal mobility in vitro. In P. aeruginosa, the main player in chemotaxis and mobility is the chemotactic gene cluster I, including cheB1. We show that, in contrast to the cheB2 mutant, a cheB1 mutant is not attenuated for virulence in C. elegans whereas in vitro motility and chemotaxis are severely impaired. We conclude that the virulence defect of the cheB2 mutant is not linked with a global motility defect but that instead the cheB2 gene is involved in a specific chemotactic response, which takes place during infection and is required for P. aeruginosa pathogenicity.

The increase in hospital acquired and multi-drug resistant bacterial infections calls for an urgent development of new antimicrobials. As such, the identification and characterization of novel molecular targets involved in bacterial virulence has become a common goal for researchers. The use of non-mammalian hosts, such as the nematode Caenorhabditis elegans, is useful to accelerate this process. In our study, we developed a high-throughput screening method, which further facilitates the use of C. elegans, and allows the rapid screening of a large collection of bacterial mutants at the genomic scale. We have used Pseudomonas aeruginosa, a potent opportunistic pathogen, to perform this study. The screening of more than 2,000 mutant strains allowed the characterization of a mutant affected in the cheB2 gene. Importantly, this mutant was shown to be impaired in a mouse model of infection, supporting that our new screen is a good model to identify virulence genes relevant for infection in mammals. The cheB2 gene encodes a component of a chemotaxis pathway, which is likely involved in the perception of stimuli during the infection process, and allows an appropriate adaptive response for a successful infection. Our method could be applied to other bacterial pathogens and will help researchers discover candidate genes leading to the design of novel antimicrobials.

Identification of high- and low-virulent strains of Chlamydia pneumoniae by their characterization in a mouse pneumonia model

Contradicting reports exist about the pathogenicity of Chlamydia pneumoniae and the severity of the respiratory disease they cause. This study aimed to clarify, in mice, our hypothesis that marked differences in virulence of well-defined C. pneumoniae strains might exist for lung infections. C57BL/6J mice were intranasally infected with equal amounts of five different, identically prepared laboratory strains of C. pneumoniae. Based on the clinical score, weight, histopathological score, the granulocyte marker-enzyme myeloperoxidase, and the amount of Chlamydiae in the lung tissue, the C. pneumoniae isolates exhibited clear differences in overall growth characteristics or clearance, and pathological potential. Thus, we could identify chlamydial strains (Kajaani-K6 and CWL-029), where mice became seriously ill, as well as a relatively low-virulent isolate (TWAR-183). Cytokine profiles also varied drastically between the five strains in extent and kinetic. Our results indicate that C. pneumoniae isolates differ markedly with regard to their interaction with the host and their pathological potential. This might also be true for the infection in humans. Because the genomic diversity of C. pneumoniae is rather small, more subtle genomic deviations account most likely for the apparent functional differences. Our results will be useful to identify additional virulence factors in the future.

Multiple roles of Pseudomonas aeruginosa TBCF10839 PilY1 in motility, transport and infection

Polymorphonuclear neutrophils are the most important mammalian host defence cells against infections with Pseudomonas aeruginosa. Screening of a signature tagged mutagenesis library of the non-piliated P. aeruginosa strain TBCF10839 uncovered that transposon inactivation of its pilY1 gene rendered the bacterium more resistant against killing by neutrophils than the wild type and any other of the more than 3000 tested mutants. Inactivation of pilY1 led to the loss of twitching motility in twitching-proficient wild-type PA14 and PAO1 strains, predisposed to autolysis and impaired the secretion of quinolones and pyocyanin, but on the other hand promoted growth in stationary phase and bacterial survival in murine airway infection models. The PilY1 population consisted of a major full-length and a minor shorter PilY1* isoform. PilY1* was detectable in small extracellular quinolone-positive aggregates, but not in the pilus. P. aeruginosa PilY1 is not an adhesin on the pilus tip, but assists in pilus biogenesis, twitching motility, secretion of secondary metabolites and in the control of cell density in the bacterial population.

Animal models of Listeria infection

Listeria monocytogenes is an intracellular foodborne pathogen that causes listeriosis, an infection characterized by gastroenteritis, meningitis, encephalitis, and maternofetal infections in humans. L. monocytogenes enters the host via contaminated foods, invades the small intestine, translocates to mesenteric lymph nodes, and spreads to the liver, spleen, brain and, in pregnant women, the fetoplacental unit. Many pathogenicity tests for studying L. monocytogenes have been developed, including tests using laboratory animals. A number of small animal species can be experimentally infected with Listeria. Mice and guinea pigs can be infected either intragastrically or intravenously, and virulence evaluated either by enumerating bacteria within infected target organs or by evaluating the 50% lethal dose (LD50). Although mice and guinea pigs can be infected with Listeria by a variety of routes, the intragastric route is the most relevant to the human foodborne listeriosis.

Fitness of isogenic colony morphology variants of Pseudomonas aeruginosa in murine airway infection

Chronic lung infections with Pseudomonas aeruginosa are associated with the diversification of the persisting clone into niche specialists and morphotypes, a phenomenon called 'dissociative behaviour'. To explore the potential of P. aeruginosa to change its morphotype by single step loss-of-function mutagenesis, a signature-tagged mini-Tn5 plasposon library of the cystic fibrosis airway isolate TBCF10839 was screened for colony morphology variants under nine different conditions in vitro. Transposon insertion into 1% of the genome changed colony morphology into eight discernable morphotypes. Half of the 55 targets encode features of primary or secondary metabolism whereby quinolone production was frequently affected. In the other half the transposon had inserted into genes of the functional categories transport, regulation or motility/chemotaxis. To mimic dissociative behaviour of isogenic strains in lungs, pools of 25 colony morphology variants were tested for competitive fitness in an acute murine airway infection model. Six of the 55 mutants either grew better or worse in vivo than in vitro, respectively. Metabolic proficiency of the colony morphology variant was a key determinant for survival in murine airways. The most common morphotype of self-destructive autolysis did unexpectedly not impair fitness. Transposon insertions into homologous genes of strain PAO1 did not reproduce the TBCF10839 mutant morphotypes for 16 of 19 examined loci pointing to an important role of the genetic background on colony morphology. Depending on the chosen P. aeruginosa strain, functional genome scans will explore other areas of the evolutionary landscape. Based on our discordant findings of mutant phenotypes in P. aeruginosa strains PAO1, PA14 and TBCF10839, we conclude that the current focus on few reference strains may miss modes of niche adaptation and dissociative behaviour that are relevant for the microevolution of complex traits in the wild.

Functional genomics of Pseudomonas aeruginosa to identify habitat-specific determinants of pathogenicity

Half of all genes in the Pseudomonas aeruginosa genome have either no homology to any previously reported sequence or are homologues of previously reported genes of unknown function. The signature-tagged mutagenesis (STM) screening method allows to explore the role of these hypothetical and unknown proteins for the colonization and persistence of P. aeruginosa in eukaryotic hosts. A plasposon STM library was constructed in the virulent clinical P. aeruginosa isolate TBCF10839 that can persist in polymorphonuclear leukocytes (PMNs). The STM library was screened for plasposon mutants that were attenuated in the killing of the nematode Caenorhabditis elegans, deficient in quorum sensing and production of type II secretion effector proteins or had become more susceptible to killing by PMNs in phagocytosis assays. The three screens revealed in total 69 attenuated mutants. Fifteen mutants that carried the transposon in potential novel virulence determinants of yet unknown function were selected for further analysis. The mutants were characterized in their transcriptome and proteome and their cytotoxicity in vitro and their virulence in worm and mouse infection models in vivo. Previous studies had revealed a remarkable degree of conservation in the virulence mechanisms used by P. aeruginosa to infect hosts of divergent evolutionary origins. Testing of our novel targets did not reveal such a strict conservation. The functional characterization revealed that the fifteen proteins play highly diverse roles in the cell and become habitat-specific virulence factors upon exposure to specific hosts and/or upon exposure to specific stress conditions or host defense mechanisms.

Global expression profiles from C57BL/6J and DBA/2J mouse lungs to determine aging-related genes

This study identified gene expression profiles that provided evidence for genomic mechanisms underlying the pathophysiology of aging lung. Aging lungs from C57BL/6 (B6) and DBA/2 (D2) mouse strains differ in physiology and morphometry. Lungs were harvested from B6 mice at 2, 18, and 26 mo and from D2 mice at 2 and 18 mo of age. Purified RNA was subjected to oligonucleotide microarray analyses, and differential expression analyses were performed for comparison of various data sets. A significant majority of differentially expressed genes were upregulated with aging in both strains. Aging D2 lungs uniquely exhibited upregulation in stress-response genes including xenobiotic detoxification cascades. In contrast, aging B6 lungs showed downregulation of heat shock-response genes. Age-dependent downregulation of genes common to both B6 and D2 strains included several collagen genes (e.g., Col1a1 and Col3a1). There was a greater elastin gene (Eln) expression in D2 mice at 2 mo, and Eln was uniquely downregulated with age in this strain. The matrix metalloproteinase 14 gene (Mmp14), critical to alveolar structural integrity, was also downregulated with aging in D2 mice only. Several polymorphisms in the regulatory and untranslated regions of Mmp14 were identified between strains, suggesting that variation in Mmp14 gene regulation contributes to accelerated aging of lungs in D2 mice. In summary, lungs of B6 and D2 mice age with variable rates at the gene expression level, and these quantifiable genomic differences provide a template for understanding the variability in age-dependent changes in lung structure and function.

Evaluation of the pathogenicity of Listeria spp. in Caenorhabditis elegans

Caenorhabditis has proven to be a useful model for studying host-pathogen interactions as well as the ability of nematodes to serve as vectors for the dispersal of foodborne pathogens. In this study, we evaluated whether C. elegans can serve as a host for Listeria spp. While there was an effect of growth media on C. elegans killing, C. elegans exposed to L. monocytogenes and L. innocua pregrown in Luria-Bertani medium showed reduced survival when compared to nonpathogenic E. coli OP50, while L. seeligeri showed survival similar to E. coli OP50. In a preference assay, C. elegans preferred E. coli over L. monocytogenes and L. innocua, but showed no preference between L. monocytogenes and L. innocua. A gentamicin assay indicated that L. monocytogenes did not persist within the C. elegans intestinal tract. Our findings that L. monocytogenes and L. innocua strains tested have equally deleterious effects on C. elegans and that L. monocytogenes did not establish intestinal infection conflict with other recently published results, which found intestinal infection and killing of C. elegans by L. monocytogenes. Further studies are thus needed to clarify the interactions between L. monocytogenes and C. elegans, including effects of environmental conditions and strain differences on killing and intestinal infection.

Radiation-induced apoptosis along with local and systemic cytokine elaboration is associated with DC plus radiotherapy-mediated renal cell tumor regression

Utilizing melanoma and sarcoma tumor models syngeneic to C57BL/6 mice, we previously reported the antitumor effects of intratumoral (i.t.) administration of dendritic cells (DC) combined with localized radiotherapy (RT). However, the mechanisms underlying the augmented therapeutic effects have yet to be fully defined. Using the BALB/c host, we explored in this study the capacity of RT to augment the therapeutic efficacy of DC in the syngeneic renal cell cancer, Renca. I.t. DC administration combined with RT inhibited tumor growth in a synergistic manner. This extends our previous findings using a different host strain and two histologically distinct tumor models. More importantly, we provide evidence in this report that RT induced significant apoptosis and necrosis in Renca tumor cells, which involved down-regulated expression of Bcl-2 and a concurrent up-regulated expression of Bax. We also found significantly elevated expression of TNFalpha in RT plus DC-treated Renca tumors. Furthermore, splenocytes isolated from DC plus RT-treated mice elaborated higher levels of IL-2, IL-4, IFNgamma and IgG, IgM in response to tumor cells compared with splenocytes from monotherapy-treated hosts. These data support the conclusion that radiotherapy enhanced DC vaccination by inducing tumor cell apoptosis in BABL/c host, and the significantly augmented therapeutic efficacy by RT+DC treatment was associated with an increased local production of TNFalpha as well as an amplified systemic antitumor responses conferred by the combined therapy. I.t. DC administration in concert with localized RT may represent a promising novel regimen for human cancer therapy.

Bacterial host resistance models in the evaluation of immunotoxicity

To assess potential immunomodulatory effects of a drug, pollutant, or natural product, an analysis of an exposed host's ability to resist challenge with a viable bacteria is one of the best gauges. Many factors govern whether a host exposed to a test agent and then infected becomes ill or dies at rates greater than infected control counterparts. Beyond the status of the host's immunocompetence, a bacterium's route of entry into the host and its inherent virulence are important variables determining how (and rate at which) an infection resolves. A pre-determination of endpoint(s) to be defined is critical during planning of resistance assays. If a study is to determine overall changes in immunocompetence due to exposure (regardless of regimen or dosage of test agent), then assessing shifts in morbidity/mortality at a defined lethal dose [LD(x)] value for the chosen route of infection would suffice. However, if a study is to define extent of immunomodulation in a particular body organ/cavity--or specific alterations in particular aspects of the humoral or cell-mediated immune responses--then careful selection of the pathogen, dose of the inoculum, means of infection of target site, and extent of the post-infection period to be examined, need to be made prior to host exposure to the test toxicant. This review will provide the Reader with background information about bacterial infections and how endpoint selection could be approached when designing resistance assays. An overview of protocols involved in the assays (e.g., bacterial preparation, host infection, post-infection endpoint analyses) and information about three bacteria that are among the most commonly employed in resistance assays is provided as well.

Elemental analysis of the Mycobacterium avium phagosome in Balb/c mouse macrophages

Using a hard X-ray microprobe, we showed recently that in unstimulated peritoneal macrophages from C57BL/6 mice, the phagosome of pathogenic mycobacteria (Mycobacterium tuberculosis and Mycobacterium avium) can accumulate iron. We expanded our studies to the M. avium infection of peritoneal macrophages of Balb/c mice that show a similar degree of M. tuberculosis and M. avium-related chronic disease, but a higher susceptibility towards other intracellular pathogens such as Listeria monocytogenes, Leishmania major, or Brucella abortus as compared to C57BL/6 mice. Similar to C57BL/6 macrophages, the iron concentration in Balb/c macrophages increased significantly after 24 h of infection. A significant increase of the chlorine and potassium concentrations was observed in the Balb/c phagosomes between 1 and 24 h, in contrast with macrophages from C57BL/6 mice. The absolute elemental concentrations of calcium and zinc were higher in the mycobacterial phagosomes of Balb/c mice. We hypothesize that a potassium channel is abundant in the phagosome in macrophages that may be related to microbiocidal killing, similar to the requirement of potassium channels for microbiocidal function in neutrophils.