Mimicking the host and its microenvironment in vitro for studying mucosal infections by Pseudomonas aeruginosa

Antibacterial peptide Reg4 ameliorates Pseudomonas aeruginosa-induced pulmonary inflammation and fibrosis

Pseudomonas aeruginosa (P. aeruginosa) is a Gram-negative facultative anaerobe that has become an important cause of severe infections in humans, particularly in patients with cystic fibrosis. The development of efficacious methods or mendicants against P. aeruginosa is still needed. We previously reported that regenerating islet-derived family member 4 (Reg4) has bactericidal activity against Salmonella Typhimurium, a Gram-negative flagellated bacterium. We herein explore whether Reg4 has bactericidal activity against P. aeruginosa. In the P. aeruginosa PAO1-chronic infection model, Reg4 significantly inhibits the colonization of PAO1 in the lung and subsequently ameliorates pulmonary inflammation and fibrosis. Reg4 recombinant protein suppresses the growth motility and biofilm formation capability of PAO1 in vitro. Mechanistically, Reg4 not only exerts bactericidal action via direct binding to the P. aeruginosa cell wall but also enhances the phagocytosis of alveolar macrophages in the host. Taken together, our study demonstrates that Reg4 may provide protection against P. aeruginosa-induced pulmonary inflammation and fibrosis via its antibacterial activity.IMPORTANCEChronic lung infection with Pseudomonas aeruginosa is a leading cause of morbidity and mortality in patients with cystic fibrosis. Due to the antibiotic resistance of Pseudomonas aeruginosa, antimicrobial peptides appear to be a potential alternative to combat its infection. In this study, we report an antimicrobial peptide, regenerating islet-derived 4 (Reg4), that showed killing activity against clinical strains of Pseudomonas aeruginosa PAO1 and ameliorated PAO1-induced pulmonary inflammation and fibrosis. Experimental data also showed Reg4 directly bound to the bacterial cell membrane and enhanced the phagocytosis of host alveolar macrophages. Our presented study will be a helpful resource in searching for novel antimicrobial peptides that could have the potential to replace conventional antibiotics.

Antibiofilm and antivirulence activities of laminarin-gold nanoparticles in standard and host-mimicking media

The rapidly rising antimicrobial resistance (AMR) in pathogenic bacteria has become one of the most serious public health challenges, with a high death rate. Most pathogenic bacteria have been recognized as a source of AMR and a primary barrier to antimicrobial treatment failure due to the development of biofilms and the production of virulence factors. In this work, nanotechnology was employed as a substitute method to control the formation of biofilms and attenuate virulence features in Pseudomonas aeruginosa and Staphylococcus aureus. We synthesized biocompatible gold nanoparticles from marine-derived laminarin as potential biofilm and virulence treatments. Laminarin-gold nanoparticles (Lam-AuNPs) have been identified as spherical, 49.84 ± 7.32 nm in size and - 26.49 ± 1.29 mV zeta potential. The MIC value of Lam-AuNPs against several drug-resistant microbial pathogens varied from 2 to 1024 μg/mL in both standard and host-mimicking media. Sub-MIC values of Lam-AuNPs were reported to effectively reduce the production of P. aeruginosa and S. aureus biofilms in both standard and host-mimicking growth media. Furthermore, the sub-MIC of Lam-AuNPs strongly reduced hemolysis, pyocyanin, pyoverdine, protease, and several forms of flagellar and pili-mediated motility in P. aeruginosa. Lam-AuNPs also inhibited S. aureus hemolysis and the production of amyloid fibrils. The Lam-AuNPs strongly dispersed the preformed mature biofilm of these pathogens in a dose-dependent manner. The Lam-AuNPs would be considered an alternative antibiofilm and antivirulence agent to control P. aeruginosa and S. aureus infections. KEY POINTS: • Lam-AuNPs were biosynthesized to control biofilm and virulence. • Lam-AuNPs show effective biofilm inhibition in standard and host-mimicking media. • Lam-AuNPs suppress various virulence factors of P. aeruginosa and S. aureus.

Genome-wide identification of genes critical for in vivo fitness of multi-drug resistant porcine extraintestinal pathogenic Escherichia coli by transposon-directed insertion site sequencing using a mouse infection model

Extraintestinal pathogenic Escherichia coli (ExPEC) is an important zoonotic pathogen. Recently, ExPEC has been reported to be an emerging problem in pig farming. However, the mechanism of pathogenicity of porcine ExPEC remains to be revealed. In this study, we constructed a transposon (Tn) mutagenesis library covering Tn insertion in over 72% of the chromosome-encoded genes of a virulent and multi-drug resistant porcine ExPEC strain PCN033. By using a mouse infection model, a transposon-directed insertion site sequencing (TraDIS) assay was performed to identify in vivo fitness factors. By comparing the Tn insertion frequencies between the input Tn library and the recovered library from different organs, 64 genes were identified to be involved in fitness during systemic infection. 15 genes were selected and individual gene deletion mutants were constructed. The in vivo fitness was evaluated by using a competitive infection assay. Among them, ΔfimG was significantly outcompeted by the WT strain in vivo and showed defective adhesion to host cells. rfa which was involved in lipopolysaccharide biosynthesis was shown to be critical for in vivo fitness which may have resulted from its role in the resistance to serum killing. In addition, several metabolic genes including fepB, sdhC, fepG, gltS, dcuA, ccmH, ddpD, narU, glpD, malM, and yabL and two regulatory genes metJ and baeS were shown as important determinants of in vivo fitness of porcine ExPEC. Collectively, this study performed a genome-wide screening for in vivo fitness factors which will be important for understanding the pathogenicity of porcine ExPEC.

Using model systems to unravel host-Pseudomonas aeruginosa interactions

Using model systems in infection biology has led to the discoveries of many pathogen-encoded virulence factors and critical host immune factors to fight pathogenic infections. Studies of the remarkable Pseudomonas aeruginosa bacterium that infects and causes disease in hosts as divergent as humans and plants afford unique opportunities to shed new light on virulence strategies and host defence mechanisms. One of the rationales for using model systems as a discovery tool to characterise bacterial factors driving human infection outcomes is that many P. aeruginosa virulence factors are required for pathogenesis in diverse different hosts. On the other side, many host signalling components, such as the evolutionarily conserved mitogen-activated protein kinases, are involved in immune signalling in a diverse range of hosts. Some model organisms that have less complex immune systems also allow dissection of the direct impacts of innate immunity on host defence without the interference of adaptive immunity. In this review, we start with discussing the occurrence of P. aeruginosa in the environment and the ability of this bacterium to cause disease in various hosts as a natural opportunistic pathogen. We then summarise the use of some model systems to study host defence and P. aeruginosa virulence.

Protective role of CFTR during fungal infection of cystic fibrosis bronchial epithelial cells with Aspergillus fumigatus

Lung infection with the fungus Aspergillus fumigatus (Af) is a common complication in cystic fibrosis (CF) and is associated with loss of pulmonary function. We established a fungal epithelial co-culture model to examine the impact of Af infection on CF bronchial epithelial barrier function using Af strains 10AF and AF293-GFP, and the CFBE41o- cell line homozygous for the F508del mutation with (CF+CFTR) and without (CF) normal CFTR expression. Following exposure of the epithelial surface to Af conidia, formation of germlings (early stages of fungal growth) was detected after 9-12 hours and hyphae (mature fungal growth) after 12-24 hours. During fungal morphogenesis, bronchial epithelial cells showed signs of damage including rounding, and partial detachment after 24 hours. Fluorescently labeled conidia were internalized after 6 hours and more internalized conidia were observed in CF compared to CF+CFTR cells. Infection of the apical surface with 10AF conidia, germlings, or hyphae was performed to determine growth stage-specific effects on tight junction protein zona occludens protein 1 (ZO-1) expression and transepithelial electrical resistance (TER). In response to infection with conidia or germlings, epithelial barrier function degraded time-dependently (based on ZO-1 immunofluorescence and TER) with a delayed onset in CF+CFTR cell monolayers and required viable fungi and apical application. Infection with hyphae caused an earlier onset and faster rate of decline in TER compared to conidia and germlings. Gliotoxin, a major Af virulence factor, caused a rapid decline in TER and induced a transient chloride secretory response in CF+CFTR but not CF cells. Our findings suggest growth and internalization of Af result in deleterious effects on bronchial epithelial barrier function that occurred more rapidly in the absence of CFTR. Bronchial epithelial barrier breakdown was time-dependent and morphotype-specific and mimicked by acute administration of gliotoxin. Our study also suggests a protective role for CFTR by turning on CFTR-dependent chloride transport in response to gliotoxin, a mechanism that will support mucociliary clearance, and could delay the loss of epithelial integrity during fungal development in vivo.

Antimicrobial Resistance Profile of Pseudomonas aeruginosa from Different Clinical Samples in Debre Tabor Comprehensive Specialized Hospital, Northwest Ethiopia

Background

Pseudomonas aeruginosa is one of the leading causes of hospital-acquired infections and the most common antimicrobial-resistant pathogens. It is associated with a variety of infections. This study aimed to determine the prevalence of P. aeruginosa and its antimicrobial resistance profile from different clinical specimens at Debre Tabor Comprehensive Referral Hospital (DTCRH).

Methods

A cross-sectional study was conducted from May to July 2022 at DTCRH. Socio-demographic and clinical data were collected using a structured questionnaire. Clinical samples (blood, wound swab, urine, and sputum) were collected from 348 study participants and processed following the standard bacteriological techniques. Antibiotic susceptibility testing was done by the Kirby-Bauer disc diffusion method. Data were entered and analyzed using SPSS version 25 statistical software. Descriptive statistics was used to present the findings of the study.

Results

The prevalence of P.aeruginosa was 74(19.3%). The detection of the isolates was different based on the type of samples that ranged from 0% to 54.5% from sputum and wound swabs, respectively. P.aeruginosa showed resistance against gentamicin at 62.2%, ceftazidime 51.4%, cefepime 50%, amikacin 29.7%, imipenem 28.4% and ciprofloxacin 14.9%. The level of multi-drug resistance (MDR) was 45.9%, and the suspicious extreme-drug resistance (XDR) rate was 9.5%. Being inpatient and wound swab samples were factors associated with the detection of P.aeruginosa from clinical samples.

Conclusion

The antibiotic resistance profile of P. aeruginosa isolates in the present study area was found to be alarming. Actions to minimize the effect of antimicrobial resistance should be strengthened, and further large-scale study should be conducted to find out the main reasons behind antibiotic resistance of P.aeruginosa and other clinically relevant isolates.

Clinically relevant in vitro biofilm models: A need to mimic and recapitulate the host environment

Biofilm-associated infections are difficult to treat and eradicate because of their increased antimicrobial tolerance. In vitro biofilm models have enabled the high throughput testing of an array of differing novel antimicrobials and treatment strategies. However, biofilms formed in these oftentimes basic in vitro systems do not resemble biofilms seen in vivo. As a result, translatability from the lab to the clinic is poor or limited. To improve translatability, in vitro models must better recapitulate the host environment. This review describes and critically evaluates new and innovative in vitro models that better mimic the environments of a variety of clinically important, biofilm-associated infections of the skin, oropharynx, lungs, and infections related to indwelling implants and medical devices. This review highlights that many of these models represent considerable advances in the field of biofilm research and help to translate laboratory findings into the clinical practice.

Gene therapy for cystic fibrosis: new tools for precision medicine

The discovery of the Cystic fibrosis (CF) gene in 1989 has paved the way for incredible progress in treating the disease such that the mean survival age of individuals living with CF is now ~58 years in Canada. Recent developments in gene targeting tools and new cell and animal models have re-ignited the search for a permanent genetic cure for all CF. In this review, we highlight some of the more recent gene therapy approaches as well as new models that will provide insight into personalized therapies for CF.

Three-Dimensional Culture of Rhipicephalus (Boophilus) microplus BmVIII-SCC Cells on Multiple Synthetic Scaffold Systems and in Rotating Bioreactors

Tick cell culture facilitates research on the biology of ticks and their role as vectors of pathogens that affect humans, domestic animals, and wildlife. Because two-dimensional cell culture doesn't promote the development of multicellular tissue-like composites, we hypothesized that culturing tick cells in a three-dimensional (3-D) configuration would form spheroids or tissue-like organoids. In this study, the cell line BmVIII-SCC obtained from the cattle fever tick, Rhipicephalus (Boophilus) microplus (Canestrini, 1888), was cultured in different synthetic scaffold systems. Growth of the tick cells on macrogelatinous beads in rotating continuous culture system bioreactors enabled cellular attachment, organization, and development into spheroid-like aggregates, with evidence of tight cellular junctions between adjacent cells and secretion of an extracellular matrix. At least three cell morphologies were identified within the aggregates: fibroblast-like cells, small endothelial-like cells, and larger cells exhibiting multiple cytoplasmic endosomes and granular vesicles. These observations suggest that BmVIII-SCC cells adapted to 3-D culture retain pluripotency. Additional studies involving genomic analyses are needed to determine if BmVIII-SCC cells in 3-D culture mimic tick organs. Applications of 3-D culture to cattle fever tick research are discussed.

Deciphering the mechanism of action of antitubercular compounds with metabolomics

Tuberculosis (TB), one of the oldest and deadliest bacterial diseases, continues to cause serious global economic, health, and social problems. Current TB treatments are lengthy, expensive, and routinely ineffective against emerging drug resistant strains. Thus, there is an urgent need for the identification and development of novel TB drugs possessing comprehensive and specific mechanisms of action (MoAs). Metabolomics is a valuable approach to elucidating the MoA, toxicity, and potency of promising chemical leads, which is a critical step of the drug discovery process. Recent advances in metabolomics methodologies for deciphering MoAs include high-throughput screening techniques, the integration of multiple omics methods, mass spectrometry imaging, and software for automated analysis. This review describes recently introduced metabolomics methodologies and techniques for drug discovery, highlighting specific applications to the discovery of new antitubercular drugs and the elucidation of their MoAs.

Pseudomonas aeruginosa biofilms and their partners in crime

Pseudomonas aeruginosa biofilms and the capacity of the bacterium to coexist and interact with a broad range of microorganisms have a substantial clinical impact. This review focuses on the main traits of P. aeruginosa biofilms, such as the structural composition and regulatory networks involved, placing particular emphasis on the clinical challenges they represent in terms of antimicrobial susceptibility and biofilm infection clearance. Furthermore, the ability of P. aeruginosa to grow together with other microorganisms is a significant pathogenic attribute with clinical relevance; hence, the main microbial interactions of Pseudomonas are especially highlighted and detailed throughout this review. This article also explores the infections caused by single and polymicrobial biofilms of P. aeruginosa and the current models used to recreate them under laboratory conditions. Finally, the antimicrobial and antibiofilm strategies developed against P. aeruginosa mono and multispecies biofilms are detailed at the end of this review.

Metabolic Modeling to Interrogate Microbial Disease: A Tale for Experimentalists

The explosion of microbiome analyses has helped identify individual microorganisms and microbial communities driving human health and disease, but how these communities function is still an open question. For example, the role for the incredibly complex metabolic interactions among microbial species cannot easily be resolved by current experimental approaches such as 16S rRNA gene sequencing, metagenomics and/or metabolomics. Resolving such metabolic interactions is particularly challenging in the context of polymicrobial communities where metabolite exchange has been reported to impact key bacterial traits such as virulence and antibiotic treatment efficacy. As novel approaches are needed to pinpoint microbial determinants responsible for impacting community function in the context of human health and to facilitate the development of novel anti-infective and antimicrobial drugs, here we review, from the viewpoint of experimentalists, the latest advances in metabolic modeling, a computational method capable of predicting metabolic capabilities and interactions from individual microorganisms to complex ecological systems. We use selected examples from the literature to illustrate how metabolic modeling has been utilized, in combination with experiments, to better understand microbial community function. Finally, we propose how such combined, cross-disciplinary efforts can be utilized to drive laboratory work and drug discovery moving forward.

Pseudomonas aeruginosa Volatilome Characteristics and Adaptations in Chronic Cystic Fibrosis Lung Infections

Pseudomonas aeruginosa is a leading cause of chronic lung infections in cystic fibrosis (CF), which are correlated with lung function decline. Significant clinical efforts are therefore aimed at detecting infections and tracking them for phenotypic changes, such as mucoidy and antibiotic resistance. Both the detection and tracking of lung infections rely on sputum cultures, but due to improvements in CF therapies, sputum production is declining, although risks for lung infections persist. Therefore, we are working toward the development of breath-based diagnostics for CF lung infections. In this study, we characterized of the volatile metabolomes of 81 P. aeruginosa clinical isolates collected from 17 CF patients over a duration of at least 5 years of a chronic lung infection. We found that the volatilome of P. aeruginosa adapts over time and is correlated with infection phenotype changes, suggesting that it may be possible to track chronic CF lung infections with a breath test.

Pseudomonas aeruginosa chronic lung infections in individuals with cystic fibrosis (CF) significantly reduce quality of life and increase morbidity and mortality. Tracking these infections is critical for monitoring patient health and informing treatments. We are working toward the development of novel breath-based biomarkers to track chronic P. aeruginosa lung infections in situ. Using comprehensive two-dimensional gas chromatography coupled with time-of-flight mass spectrometry (GC×GC–TOF-MS), we characterized the in vitro volatile metabolomes (“volatilomes”) of 81 P. aeruginosa isolates collected from 17 CF patients over at least a 5-year period of their chronic lung infections. We detected 539 volatiles produced by the P. aeruginosa isolates, 69 of which were core volatiles that were highly conserved. We found that each early infection isolate has a unique volatilome, and as infection progresses, the volatilomes of isolates from the same patient become increasingly dissimilar, to the point that these intrapatient isolates are no more similar to one another than to isolates from other patients. We observed that the size and chemical diversity of P. aeruginosa volatilomes do not change over the course of chronic infections; however, the relative abundances of core hydrocarbons, alcohols, and aldehydes do change and are correlated with changes in phenotypes associated with chronic infections. This study indicates that it may be feasible to track P. aeruginosa chronic lung infections by measuring changes to the infection volatilome and lays the groundwork for exploring the translatability of this approach to direct measurement using patient breath.

IMPORTANCEPseudomonas aeruginosa is a leading cause of chronic lung infections in cystic fibrosis (CF), which are correlated with lung function decline. Significant clinical efforts are therefore aimed at detecting infections and tracking them for phenotypic changes, such as mucoidy and antibiotic resistance. Both the detection and tracking of lung infections rely on sputum cultures, but due to improvements in CF therapies, sputum production is declining, although risks for lung infections persist. Therefore, we are working toward the development of breath-based diagnostics for CF lung infections. In this study, we characterized of the volatile metabolomes of 81 P. aeruginosa clinical isolates collected from 17 CF patients over a duration of at least 5 years of a chronic lung infection. We found that the volatilome of P. aeruginosa adapts over time and is correlated with infection phenotype changes, suggesting that it may be possible to track chronic CF lung infections with a breath test.

Sex Steroids Induce Membrane Stress Responses and Virulence Properties in Pseudomonas aeruginosa

Molecular mechanisms by which sex steroids interact with P. aeruginosa to modulate its virulence have yet to be reported. Our work provides the first characterization of a steroid-induced membrane stress mechanism promoting P. aeruginosa virulence, which includes the release of proinflammatory outer membrane vesicles, resulting in inflammation, host tissue damage, and reduced bacterial clearance. We further demonstrate that at nanomolar (physiological) concentrations, male and female sex steroids promote virulence in clinical strains of P. aeruginosa based on their dynamic membrane fluidic properties. This work provides, for the first-time, mechanistic insight to better understand and predict the P. aeruginosa related response to sex steroids and explain the interindividual patient variability observed in respiratory diseases such as cystic fibrosis that are complicated by gender differences and chronic P. aeruginosa infection.

Estrogen, a major female sex steroid hormone, has been shown to promote the selection of mucoid Pseudomonas aeruginosa in the airways of patients with chronic respiratory diseases, including cystic fibrosis. This results in long-term persistence, poorer clinical outcomes, and limited therapeutic options. In this study, we demonstrate that at physiological concentrations, sex steroids, including testosterone and estriol, induce membrane stress responses in P. aeruginosa. This is characterized by increased virulence and consequent inflammation and release of proinflammatory outer membrane vesicles promoting in vivo persistence of the bacteria. The steroid-induced P. aeruginosa response correlates with the molecular polarity of the hormones and membrane fluidic properties of the bacteria. This novel mechanism of interaction between sex steroids and P. aeruginosa explicates the reported increased disease severity observed in females with cystic fibrosis and provides evidence for the therapeutic potential of the modulation of sex steroids to achieve better clinical outcomes in patients with hormone-responsive strains.

Contribution of Short Chain Fatty Acids to the Growth of Pseudomonas aeruginosa in Rhinosinusitis

Background: Chronic rhinosinusitis (CRS) is characterized by complex bacterial infections with persistent inflammation. Based on our rabbit model of sinusitis, blockage of sinus ostia generated a shift in microbiota to a predominance of mucin degrading microbes (MDM) with acute inflammation at 2 weeks. This was followed by conversion to chronic sinus inflammation at 3 months with a robust increase in pathogenic bacteria (e.g., Pseudomonas). MDMs are known to produce acid metabolites [short chain fatty acids (SCFA)] that have the potential to stimulate pathogen growth by offering a carbon source to non-fermenting sinus pathogens (e.g., Pseudomonas). The objective of this study is to evaluate the concentrations of SCFA within the mucus and its contribution to the growth of P. aeruginosa. Methods: Healthy and sinusitis mucus from the rabbit model were collected and co-cultured with the PAO1 strain of P. aeruginosa for 72 h and colony forming units (CFUs) were determined with the targeted quantification of three SCFAs (acetate, propionate, butyrate). Quantification of SCFAs in healthy and sinusitis mucus from patients with P. aeruginosa was also performed via high performance liquid chromatography. Results: To provide evidence of fermentative activity, SCFAs were quantified within the mucus samples from rabbits with and without sinusitis. Acetate concentrations were significantly greater in sinusitis mucus compared to controls (4.13 ± 0.53 vs. 1.94 ± 0.44 mM, p < 0.01). After 72 h of co-culturing mucus samples with PAO1 in the presence of mucin medium, the blue-green pigment characteristic of Pseudomonas was observed throughout tubes containing sinusitis mucus. CFUs were higher in cultures containing mucus samples from sinusitis (8.4 × 10⁹ ± 4.8 × 10⁷) compared to control (1.4 × 10⁹ ± 2.0 × 10⁷) or no mucus (1.5 × 10⁹ ± 2.1 × 10⁷) (p < 0.0001). To provide evidence of fermentative activity in human CRS with P. aeruginosa, the presence of SCFAs in human mucus was analyzed and all SCFAs were significantly higher in CRS with P. aeruginosa compared to controls (p < 0.05). Conclusion: Given that SCFAs are solely derived from bacterial fermentation, our evidence suggests a critical role for mucin-degrading bacteria in generating carbon-source nutrients for pathogens. MDM may contribute to the development of recalcitrant CRS by degrading mucins, thus providing nutrients for potential pathogens like P. aeruginosa.

A three-dimensional intestinal tissue model reveals factors and small regulatory RNAs important for colonization with Campylobacter jejuni

The Gram-negative Epsilonproteobacterium Campylobacter jejuni is currently the most prevalent bacterial foodborne pathogen. Like for many other human pathogens, infection studies with C. jejuni mainly employ artificial animal or cell culture models that can be limited in their ability to reflect the in-vivo environment within the human host. Here, we report the development and application of a human three-dimensional (3D) infection model based on tissue engineering to study host-pathogen interactions. Our intestinal 3D tissue model is built on a decellularized extracellular matrix scaffold, which is reseeded with human Caco-2 cells. Dynamic culture conditions enable the formation of a polarized mucosal epithelial barrier reminiscent of the 3D microarchitecture of the human small intestine. Infection with C. jejuni demonstrates that the 3D tissue model can reveal isolate-dependent colonization and barrier disruption phenotypes accompanied by perturbed localization of cell-cell junctions. Pathogenesis-related phenotypes of C. jejuni mutant strains in the 3D model deviated from those obtained with 2D-monolayers, but recapitulated phenotypes previously observed in animal models. Moreover, we demonstrate the involvement of a small regulatory RNA pair, CJnc180/190, during infections and observe different phenotypes of CJnc180/190 mutant strains in 2D vs. 3D infection models. Hereby, the CJnc190 sRNA exerts its pathogenic influence, at least in part, via repression of PtmG, which is involved in flagellin modification. Our results suggest that the Caco-2 cell-based 3D tissue model is a valuable and biologically relevant tool between in-vitro and in-vivo infection models to study virulence of C. jejuni and other gastrointestinal pathogens.

Enteric pathogens have evolved numerous strategies to successfully colonize and persist in the human gastrointestinal tract. However, especially for the research of virulence mechanisms of human pathogens, often only limited infection models are available. Here, we have applied and further advanced a tissue-engineered human intestinal tissue model based on an extracellular matrix scaffold reseeded with human cells that can faithfully mimic pathogenesis-determining processes of the zoonotic pathogen Campylobacter jejuni. Our three-dimensional (3D) intestinal infection model allows for the assessment of epithelial barrier function during infection as well as for the quantification of bacterial adherence, internalization, and transmigration. Investigation of C. jejuni mutant strains in our 3D tissue model revealed isolate-specific infection phenotypes, in-vivo relevant infection outcomes, and uncovered the involvement of a small RNA pair during C. jejuni pathogenesis. Overall, our results demonstrate the power of tissue-engineered models for studying host-pathogen interactions, and our model will also be helpful to investigate other gastrointestinal pathogens.

l-aspartic acid promotes fish survival against Vibrio alginolyticus infection through nitric oxide-induced phagocytosis

Bacterial infection severely impairs aquaculture development throughout the world. Despite the use of antibiotics to control bacterial infection, few other options are available especially in the area of complex ecosystem and various types of fish. In search for novel approaches in controlling bacterial infection, we adopt zebrafish, Danio reiro, as infection host and the bacteria, Vibrio alginolyticus, as pathogen to explore potential metabolites that boost host's capability to eliminate bacterial infection. By comparing the metabolome of dying fish, l-aspartic acid is a metabolite of differential abundance between the dying fish and surviving fish upon Vibrio alginolyticus infection. Exogenous l-aspartic acid increases fish survival rate from 46.67% to 76.67%. We further demonstrated that l-aspartic acid drives the production of nitrogen oxide that promotes phagocytosis. Whereas the inhibition of nitrogen oxide synthase would abolish l-aspartic acid-triggered phagocytosis as well as in vivo protective ability to V. alginolyticus. The importance of nitrogen oxide production in fish survival is also consistent with the observation in the dying fish that showed increased urea production but not nitrogen oxide. Thus, our results exemplify a novel approach in promoting fish survival in an eco-friendly way.

Interplay between host-microbe and microbe-microbe interactions in cystic fibrosis

The respiratory tract of individuals with cystic fibrosis is host to polymicrobial infections that persist for decades and lead to significant morbidity and mortality. Improving our understanding of CF respiratory infections requires coordinated efforts from researchers in the fields of microbial physiology, genomics, and ecology, as well as epithelial biology and immunology. Here, we have highlighted examples from recent CF microbial pathogenesis literature of how the host nutritional environment, immune response, and microbe-microbe interactions can feedback onto each other, leading to diverse effects on lung disease pathogenesis in CF.

Pseudomonas aeruginosa Biofilms: Host Response and Clinical Implications in Lung Infections

Pseudomonas aeruginosa is a major health challenge that causes recalcitrant multidrug-resistant infections, especially in immunocompromised and hospitalized patients. P. aeruginosa is an important cause of nosocomial and ventilator-associated pneumonia characterized by high prevalence and fatality rates. P. aeruginosa also causes chronic lung infections in individuals with cystic fibrosis. Multidrug- and totally drug-resistant strains of P. aeruginosa are increasing threats that contribute to high mortality in these patients. The pathogenesis of many P. aeruginosa infections depends on its ability to form biofilms, structured bacterial communities that can coat mucosal surfaces or invasive devices. These biofilms make conditions more favorable for bacterial persistence, as embedded bacteria are inherently more difficult to eradicate than planktonic bacteria. The molecular mechanisms that underlie P. aeruginosa biofilm pathogenesis and the host response to P. aeruginosa biofilms remain to be fully defined. However, it is known that biofilms offer protection from the host immune response and are also extremely recalcitrant to antimicrobial therapy. Therefore, development of novel therapeutic strategies specifically aimed at biofilms is urgently needed. Here, we review the host response, key clinical implications of P. aeruginosa biofilms, and novel therapeutic approaches to treat biofilms relevant to lung infections. Greater understanding of P. aeruginosa biofilms will elucidate novel avenues to improve outcomes for P. aeruginosa pulmonary infections.

Influence of the lung microbiome on antibiotic susceptibility of cystic fibrosis pathogens

The lungs of patients with cystic fibrosis (CF) are colonised by a microbial community comprised of pathogenic species, such as Pseudomonas aeruginosa and Staphylococcus aureus, and microorganisms that are typically not associated with worse clinical outcomes (considered as commensals). Antibiotics directed at CF pathogens are often not effective and a discrepancy is observed between activity of these agents in vitro and in the patient. This review describes how interspecies interactions within the lung microbiome might influence the outcome of antibiotic treatment targeted at common CF pathogens. Protective mechanisms by members of the microbiome such as antibiotic degradation (indirect pathogenicity), alterations of the cell wall, production of matrix components decreasing antibiotic penetration, and changes in metabolism are discussed. Interspecies interactions that increase bacterial susceptibility are also addressed. Furthermore, we discuss how experimental conditions, such as culture media, oxygen levels, incorporation of host–pathogen interactions, and microbial community composition may influence the outcome of microbial interaction studies related to antibiotic activity. Hereby, the importance to create in vitro conditions reflective of the CF lung microenvironment is highlighted. Understanding the role of the CF lung microbiome in antibiotic efficacy may help find novel therapeutic and diagnostic approaches to better tackle chronic lung infections in this patient population.

Interspecies interactions in the lung microbiome may influence the outcome of antibiotic treatment targeted at cystic fibrosis pathogenshttp://bit.ly/2WQp0iQ

Host metabolites stimulate the bacterial proton motive force to enhance the activity of aminoglycoside antibiotics

Antibiotic susceptibility of bacterial pathogens is typically evaluated using in vitro assays that do not consider the complex host microenvironment. This may help explaining a significant discrepancy between antibiotic efficacy in vitro and in vivo, with some antibiotics being effective in vitro but not in vivo or vice versa. Nevertheless, it is well-known that antibiotic susceptibility of bacteria is driven by environmental factors. Lung epithelial cells enhance the activity of aminoglycoside antibiotics against the opportunistic pathogen Pseudomonas aeruginosa, yet the mechanism behind is unknown. The present study addresses this gap and provides mechanistic understanding on how lung epithelial cells stimulate aminoglycoside activity. To investigate the influence of the local host microenvironment on antibiotic activity, an in vivo-like three-dimensional (3-D) lung epithelial cell model was used. We report that conditioned medium of 3-D lung cells, containing secreted but not cellular components, potentiated the bactericidal activity of aminoglycosides against P. aeruginosa, including resistant clinical isolates, and several other pathogens. In contrast, conditioned medium obtained from the same cell type, but grown as conventional (2-D) monolayers did not influence antibiotic efficacy. We found that 3-D lung cells secreted endogenous metabolites (including succinate and glutamate) that enhanced aminoglycoside activity, and provide evidence that bacterial pyruvate metabolism is linked to the observed potentiation of antimicrobial activity. Biochemical and phenotypic assays indicated that 3-D cell conditioned medium stimulated the proton motive force (PMF), resulting in increased bacterial intracellular pH. The latter stimulated antibiotic uptake, as determined using fluorescently labelled tobramycin in combination with flow cytometry analysis. Our findings reveal a cross-talk between host and bacterial metabolic pathways, that influence downstream activity of antibiotics. Understanding the underlying basis of the discrepancy between the activity of antibiotics in vitro and in vivo may lead to improved diagnostic approaches and pave the way towards novel means to stimulate antibiotic activity.

There is a poor correlation between the activity of antibiotics in the laboratory and in patients, including in several infectious diseases of the respiratory tract. What may help explaining differences between antibiotic activity in vitro and in vivo is that current antibiotic susceptibility tests do not consider the in vivo lung environment. The lung environment contains many factors that may influence bacterial susceptibility to antibiotics. This includes lung epithelial cells, which have been shown to improve the activity of aminoglycoside antibiotics. Yet, how lung epithelial cells increase aminoglycoside activity is currently unknown. Here, we cultured lung epithelial cells in an in vivo-like model and found that they secrete metabolites that enhance the activity of aminoglycoside antibiotics. We found that host cell secretions increased antibiotic uptake through stimulation of bacterial metabolism, which in turn resulted in enhanced activity. Our findings highlight that cross-talk between host and bacterial metabolisms contributes to the efficacy of antibiotic treatment. Understanding how the host metabolism influences antibiotic activity may open up therapeutic avenues to exploit host metabolism for improving antibiotic activity and help explaining discrepancies between antibiotic efficacy in vitro and in vivo.

The Antimicrobial Peptide lin-SB056-1 and Its Dendrimeric Derivative Prevent Pseudomonas aeruginosa Biofilm Formation in Physiologically Relevant Models of Chronic Infections

Antimicrobial peptides (AMPs) are promising templates for the development of novel antibiofilm drugs. Despite the large number of studies on screening and optimization of AMPs, only a few of these evaluated the antibiofilm activity in physiologically relevant model systems. Potent in vitro activity of AMPs often does not translate into in vivo effectiveness due to the interference of the host microenvironment with peptide stability/availability. Hence, mimicking the complex environment found in biofilm-associated infections is essential to predict the clinical potential of novel AMP-based antimicrobials. In the present study, we examined the antibiofilm activity of the semi-synthetic peptide lin-SB056-1 and its dendrimeric derivative (lin-SB056-1)₂-K against Pseudomonas aeruginosa in an in vivo-like three-dimensional (3-D) lung epithelial cell model and an in vitro wound model (consisting of an artificial dermis and blood components at physiological levels). Although moderately active when tested alone, lin-SB056-1 was effective in reducing P. aeruginosa biofilm formation in association with 3-D lung epithelial cells in combination with the chelating agent EDTA. The dimeric derivative (lin-SB056-1)₂-K demonstrated an enhanced biofilm-inhibitory activity as compared to both lin-SB056-1 and the lin-SB056-1/EDTA combination, reducing the number of biofilm-associated bacteria up to 3-Log units at concentrations causing less than 20% cell death. Biofilm inhibition by (lin-SB056-1)₂-K was reported both for the reference strain PAO1 and cystic fibrosis lung isolates of P. aeruginosa. In addition, using fluorescence microscopy, a significant decrease in biofilm-like structures associated with 3-D cells was observed after peptide exposure. Interestingly, effectiveness of (lin-SB056-1)₂-K was also demonstrated in the wound model with a reduction of up to 1-Log unit in biofilm formation by P. aeruginosa PAO1 and wound isolates. Overall, combination treatment and peptide dendrimerization emerged as promising strategies to improve the efficacy of AMPs, especially under challenging host-mimicking conditions. Furthermore, the results of the present study underlined the importance of evaluating the biological properties of novel AMPs in in vivo-like model systems representative of specific infectious sites in order to make a more realistic prediction of their therapeutic success, and avoid the inclusion of unpromising peptides in animal studies and clinical trials.

Human Cellular Models for the Investigation of Lung Inflammation and Mucus Production in Cystic Fibrosis

Chronic inflammation, oxidative stress, mucus plugging, airway remodeling, and respiratory infections are the hallmarks of the cystic fibrosis (CF) lung disease. The airway epithelium is central in the innate immune responses to pathogens colonizing the airways, since it is involved in mucociliary clearance, senses the presence of pathogens, elicits an inflammatory response, orchestrates adaptive immunity, and activates mesenchymal cells. In this review, we focus on cellular models of the human CF airway epithelium that have been used for studying mucus production, inflammatory response, and airway remodeling, with particular reference to two- and three-dimensional cultures that better recapitulate the native airway epithelium. Cocultures of airway epithelial cells, macrophages, dendritic cells, and fibroblasts are instrumental in disease modeling, drug discovery, and identification of novel therapeutic targets. Nevertheless, they have to be implemented in the CF field yet. Finally, novel systems hijacking on tissue engineering, including three-dimensional cocultures, decellularized lungs, microfluidic devices, and lung organoids formed in bioreactors, will lead the generation of relevant human preclinical respiratory models a step forward.

Modeling Host-Pathogen Interactions in the Context of the Microenvironment: Three-Dimensional Cell Culture Comes of Age

Tissues and organs provide the structural and biochemical landscapes upon which microbial pathogens and commensals function to regulate health and disease. While flat two-dimensional (2-D) monolayers composed of a single cell type have provided important insight into understanding host-pathogen interactions and infectious disease mechanisms, these reductionist models lack many essential features present in the native host microenvironment that are known to regulate infection, including three-dimensional (3-D) architecture, multicellular complexity, commensal microbiota, gas exchange and nutrient gradients, and physiologically relevant biomechanical forces (e.g., fluid shear, stretch, compression). A major challenge in tissue engineering for infectious disease research is recreating this dynamic 3-D microenvironment (biological, chemical, and physical/mechanical) to more accurately model the initiation and progression of host-pathogen interactions in the laboratory. Here we review selected 3-D models of human intestinal mucosa, which represent a major portal of entry for infectious pathogens and an important niche for commensal microbiota. We highlight seminal studies that have used these models to interrogate host-pathogen interactions and infectious disease mechanisms, and we present this literature in the appropriate historical context. Models discussed include 3-D organotypic cultures engineered in the rotating wall vessel (RWV) bioreactor, extracellular matrix (ECM)-embedded/organoid models, and organ-on-a-chip (OAC) models. Collectively, these technologies provide a more physiologically relevant and predictive framework for investigating infectious disease mechanisms and antimicrobial therapies at the intersection of the host, microbe, and their local microenvironments.

Influence of three-dimensional lung epithelial cells and interspecies interactions on antibiotic efficacy against Mycobacterium abscessus and Pseudomonas aeruginosa

Mycobacterium abscessus lung infection is a major health problem for cystic fibrosis (CF) patients. Understanding the in vivo factors that influence the outcome of therapy may help addressing the poor correlation between in vitro and in vivo antibiotic efficacy. We evaluated the influence of interspecies interactions and lung epithelial cells on antibiotic efficacy. Therefore, single and dual-species biofilms of M. abscessus and a major CF pathogen (Pseudomonas aeruginosa) were cultured on a plastic surface or on in vivo-like three-dimensional (3-D) lung epithelial cells, and the activity of antibiotics (colistin, amikacin, clarithromycin, ceftazidime) in inhibiting biofilm formation was evaluated. Using the most physiologically relevant model (dual-species biofilms on 3-D cells), we observed that treatment with antibiotics during biofilm development inhibited P. aeruginosa but not M. abscessus biofilms, resulting in a competitive advantage for the latter. Clarithromycin efficacy against P. aeruginosa was inhibited by 3-D lung cells. In addition, biofilm induction of M. abscessus was observed by certain antibiotics on plastic but not on 3-D cells. Pseudomonas aeruginosa influenced the efficacy of certain antibiotics against M. abscessus, but not vice versa. In conclusion, these results suggest a role of host cells and interspecies interactions in bacterial responses to antimicrobials.

Temporal differentiation of bovine airway epithelial cells grown at an air-liquid interface

There is an urgent need to develop improved, physiologically-relevant in vitro models of airway epithelia with which to better understand the pathological processes associated with infection, allergies and toxicological insults of the respiratory tract of both humans and domesticated animals. In the present study, we have characterised the proliferation and differentiation of primary bovine bronchial epithelial cells (BBECs) grown at an air-liquid interface (ALI) at three-day intervals over a period of 42 days from the introduction of the ALI. The differentiated BBEC model was highly representative of the ex vivo epithelium from which the epithelial cells were derived; a columnar, pseudostratified epithelium that was highly reflective of native airway epithelium was formed which comprised ciliated, goblet and basal cells. The hallmark defences of the respiratory tract, namely barrier function and mucociliary clearance, were present, thus demonstrating that the model is an excellent mimic of bovine respiratory epithelium. The epithelium was fully differentiated by day 21 post-ALI and, crucially, remained healthy and stable for a further 21 days. Thus, the differentiated BBEC model has a three-week window which will allow wide-ranging and long-term experiments to be performed in the fields of infection, toxicology or general airway physiology.

Modelling upper respiratory tract diseases: getting grips on host-microbe interactions in chronic rhinosinusitis using in vitro technologies

Chronic rhinosinusitis (CRS) is a chronic inflammation of the mucosa of the nose and paranasal sinuses affecting approximately 11% of the adult population in Europe. Inadequate immune responses, as well as a dysbiosis of the sinonasal microbiota, have been put forward as aetiological factors of the disease. However, despite the prevalence of this disease, there is no consensus on the aetiology and mechanisms of pathogenesis of CRS. Further research requires in vitro models mimicking the healthy and diseased host environment along with the sinonasal microbiota. This review aims to provide an overview of CRS model systems and proposes in vitro modelling strategies to conduct mechanistic research in an ecological framework on the sinonasal microbiota and its interactions with the host in health and CRS.

Recent perspectives on the molecular basis of biofilm formation by Pseudomonas aeruginosa and approaches for treatment and biofilm dispersal

Pseudomonas aeruginosa, a Gram-negative, rod-shaped bacterium causes widespread diseases in humans. This bacterium is frequently related to nosocomial infections such as pneumonia, urinary tract infections (UTIs) and bacteriaemia especially in immunocompromised patients. The current review focuses on the recent perspectives on biofilms formation by these bacteria. Biofilms are communities of microorganisms in which cells stick to each other and often adhere to a surface. These adherent cells are usually embedded within a self-produced matrix of extracellular polymeric substance (EPS). Pel, psl and alg operons present in P. aeruginosa are responsible for the biosynthesis of extracellular polysaccharide which plays an important role in cell surface interactions during biofilm formation. Recent studies suggested that cAMP signalling pathway, quorum-sensing pathway, Gac/Rsm pathway and c-di-GMP signalling pathway are the main mechanism that leads to the biofilm formation. Understanding the bacterial virulence depends on a number of cell-associated and extracellular factors and is very essential for the development of potential drug targets. Thus, the review focuses on the major genes involved in the biofilm formation, the state of art update on the biofilm treatment and the dispersal approaches such as targeting adhesion and maturation, targeting virulence factors and other strategies such as small molecule-based inhibitors, phytochemicals, bacteriophage therapy, photodynamic therapy, antimicrobial peptides and natural therapies and vaccines to curtail the biofilm formation by P. aeruginosa.

Bacteria in the respiratory tract-how to treat? Or do not treat?

BACKGROUND

Acute and chronic respiratory tract infections are a common cause of inappropriate antimicrobial prescription. Antimicrobial therapy leads to the development of resistance and the emergence of opportunistic pathogens that substitute the indigenous microbiota.

METHODS

This review explores the major challenges and lines of research to adequately establish the clinical role of bacteria and the indications for antimicrobial treatment, and reviews novel therapeutic approaches.

RESULTS

In patients with chronic pulmonary diseases and structural disturbances of the bronchial tree or the lung parenchyma, clinical and radiographic signs and symptoms are almost constantly present, including a basal inflammatory response. Bacterial adaptative changes and differential phenotypes are described, depending on the clinical role and niche occupied. The respiratory tract has areas that are potentially inaccessible to antimicrobials. Novel therapeutic approaches include new ways of administering antimicrobials that may allow intracellular delivery or delivery across biofilms, targeting the functions essential for infection, such as regulatory systems, or the virulence factors required to cause host damage and disease. Alternatives to antibiotics and antimicrobial adjuvants are under development.

CONCLUSIONS

Prudent treatment, novel targets, and improved drug delivery systems will contribute to reduce the emergence of antimicrobial resistance in lower respiratory tract infections.

Antimicrobial efficacy against Pseudomonas aeruginosa biofilm formation in a three-dimensional lung epithelial model and the influence of fetal bovine serum

In vitro models that mimic in vivo host-pathogen interactions are needed to evaluate candidate drugs that inhibit bacterial virulence traits. We established a new approach to study Pseudomonas aeruginosa biofilm susceptibility on biotic surfaces, using a three-dimensional (3-D) lung epithelial cell model. P. aeruginosa formed antibiotic resistant biofilms on 3-D cells without affecting cell viability. The biofilm-inhibitory activity of antibiotics and/or the anti-biofilm peptide DJK-5 were evaluated on 3-D cells compared to a plastic surface, in medium with and without fetal bovine serum (FBS). In both media, aminoglycosides were more efficacious in the 3-D cell model. In serum-free medium, most antibiotics (except polymyxins) showed enhanced efficacy when 3-D cells were present. In medium with FBS, colistin was less efficacious in the 3-D cell model. DJK-5 exerted potent inhibition of P. aeruginosa association with both substrates, only in serum-free medium. DJK-5 showed stronger inhibitory activity against P. aeruginosa associated with plastic compared to 3-D cells. The combined addition of tobramycin and DJK-5 exhibited more potent ability to inhibit P. aeruginosa association with both substrates. In conclusion, lung epithelial cells influence the efficacy of most antimicrobials against P. aeruginosa biofilm formation, which in turn depends on the presence or absence of FBS.

Three-dimensional organotypic co-culture model of intestinal epithelial cells and macrophages to study Salmonella enterica colonization patterns

Three-dimensional models of human intestinal epithelium mimic the differentiated form and function of parental tissues often not exhibited by two-dimensional monolayers and respond to Salmonella in key ways that reflect in vivo infections. To further enhance the physiological relevance of three-dimensional models to more closely approximate in vivo intestinal microenvironments encountered by Salmonella, we developed and validated a novel three-dimensional co-culture infection model of colonic epithelial cells and macrophages using the NASA Rotating Wall Vessel bioreactor. First, U937 cells were activated upon collagen-coated scaffolds. HT-29 epithelial cells were then added and the three-dimensional model was cultured in the bioreactor until optimal differentiation was reached, as assessed by immunohistochemical profiling and bead uptake assays. The new co-culture model exhibited in vivo-like structural and phenotypic characteristics, including three-dimensional architecture, apical-basolateral polarity, well-formed tight/adherens junctions, mucin, multiple epithelial cell types, and functional macrophages. Phagocytic activity of macrophages was confirmed by uptake of inert, bacteria-sized beads. Contribution of macrophages to infection was assessed by colonization studies of Salmonella pathovars with different host adaptations and disease phenotypes (Typhimurium ST19 strain SL1344 and ST313 strain D23580; Typhi Ty2). In addition, Salmonella were cultured aerobically or microaerobically, recapitulating environments encountered prior to and during intestinal infection, respectively. All Salmonella strains exhibited decreased colonization in co-culture (HT-29-U937) relative to epithelial (HT-29) models, indicating antimicrobial function of macrophages. Interestingly, D23580 exhibited enhanced replication/survival in both models following invasion. Pathovar-specific differences in colonization and intracellular co-localization patterns were observed. These findings emphasize the power of incorporating a series of related three-dimensional models within a study to identify microenvironmental factors important for regulating infection.

Using spaceflight analog bioreactor technology, Cheryl Nickerson at Arizona State University and collaborators developed and validated a new three-dimensional (3-D) intestinal co-culture model containing multiple differentiated epithelial cell types and phagocytic macrophages with antibacterial function to study infection by multiple pathovars of Salmonella. This study is the first to show that these pathovars (known to possess different host adaptations, antibiotic resistance profiles and disease phenotypes), display markedly different colonization and intracellular co-localization patterns using this physiologically relevant new 3-D intestinal co-culture model. This advanced model, that integrates a key immune cell type important for Salmonella infection, offers a powerful new tool in understanding enteric pathogenesis and may lead to unexpected pathogenesis mechanisms and therapeutic targets that have been previously unobserved or unappreciated using other intestinal cell culture models.

Is There a Space-Based Technology Solution to Problems with Preclinical Drug Toxicity Testing?

Even the finest state-of-the art preclinical drug testing, usually in primary hepatocytes, remains an imperfect science. Drugs continue to be withdrawn from the market due to unforeseen toxicity, side effects, and drug interactions. The space program may be able to provide a lifeline. Best known for rockets, space shuttles, astronauts and engineering, the space program has also delivered some serious medical science. Optimized suspension culture in NASA’s specialized suspension culture devices, known as rotating wall vessels, uniquely maintains Phase I and Phase II drug metabolizing pathways in hepatocytes for weeks in cell culture. Previously prohibitively expensive, new materials and 3D printing techniques have the potential to make the NASA rotating wall vessel available inexpensively on an industrial scale. Here we address the tradeoffs inherent in the rotating wall vessel, limitations of alternative approaches for drug metabolism studies, and the market to be addressed. Better pre-clinical drug testing has the potential to significantly reduce the morbidity and mortality of one of the most common problems in modern medicine: adverse events related to pharmaceuticals.

Impact of the CFTR-potentiator ivacaftor on airway microbiota in cystic fibrosis patients carrying a G551D mutation

Background

Airway microbiota composition has been clearly correlated with many pulmonary diseases, and notably with cystic fibrosis (CF), an autosomal genetic disorder caused by mutation in the CF transmembrane conductance regulator (CFTR). Recently, a new molecule, ivacaftor, has been shown to re-establish the functionality of the G551D-mutated CFTR, allowing significant improvement in lung function.

Objective and Methods

The purpose of this study was to follow the evolution of the airway microbiota in CF patients treated with ivacaftor, using quantitative PCR and pyrosequencing of 16S rRNA amplicons, in order to identify quantitative and qualitative changes in bacterial communities. Three G551D children were followed up longitudinally over a mean period of more than one year covering several months before and after initiation of ivacaftor treatment.

Results

129 operational taxonomy units (OTUs), representing 64 genera, were identified. There was no significant difference in total bacterial load before and after treatment. Comparison of global community composition found no significant changes in microbiota. Two OTUs, however, showed contrasting dynamics: after initiation of ivacaftor, the relative abundance of the anaerobe Porphyromonas 1 increased (p<0.01) and that of Streptococcus 1 (S. mitis group) decreased (p<0.05), possibly in relation to the anti-Gram-positive properties of ivacaftor. The anaerobe Prevotella 2 correlated positively with the pulmonary function test FEV-1 (r=0.73, p<0.05). The study confirmed the presumed positive role of anaerobes in lung function.

Conclusion

Several airway microbiota components, notably anaerobes (obligate or facultative anaerobes), could be valuable biomarkers of lung function improvement under ivacaftor, and could shed light on the pathophysiology of lung disease in CF patients.

Vaccination against respiratory Pseudomonas aeruginosa infection

Respiratory infections caused by Pseudomonas aeruginosa are a major clinical problem globally, particularly for patients with chronic pulmonary disorders, such as those with cystic fibrosis (CF), non-CF bronchiectasis (nCFB) and severe chronic obstructive pulmonary disease (COPD). In addition, critically ill and immunocompromised patients are also at significant risk of P. aeruginosa infection. For almost half a century, research efforts have focused toward development of a vaccine against infections caused by P. aeruginosa, but a licensed vaccine is not yet available. Significant advances in identifying potential vaccine antigens have been made. Immunisations via both the mucosal and systemic routes have been trialled in animal models and their effectiveness in clearing acute infections demonstrated. The challenge for translation of this research to human applications remains, since P. aeruginosa infections in the human respiratory tract can present both as an acute or chronic infection. In addition, immunisation prior to infection may not be possible for many patients with CF, nCFB or COPD. Therefore, development of a therapeutic vaccine provides an alternative approach for treatment of chronic infection. Preliminary animal and human studies suggest that mucosal immunisation may be effective as a therapeutic vaccine against P. aeruginosa respiratory infections. Nevertheless, more research is needed to improve our understanding of the basic biology of P. aeruginosa and the mechanisms needed to upregulate the induction of host immune pathways to prevent infection. Recognition of variability in the host immune responses for a range of patient health conditions at risk from P. aeruginosa infection is also required to support development of a successful vaccine delivery strategy and vaccine. Activation of mucosal immune responses may provide improved efficacy of vaccination for P. aeruginosa during both acute exacerbations and chronic infection.