Localization of Staphylococcus aureus in infected airways of patients with cystic fibrosis and in a cell culture model of S. aureus adherence

Intracellular Pseudomonas aeruginosa within the Airway Epithelium of Cystic Fibrosis Lung Tissues

Rationale: Pseudomonas aeruginosa is the major bacterial pathogen colonizing the airways of adult patients with cystic fibrosis (CF) and causes chronic infections that persist despite antibiotic therapy. Intracellular bacteria may represent an unrecognized reservoir of bacteria that evade the immune system and antibiotic therapy. Although the ability of P. aeruginosa to invade and survive within epithelial cells has been described in vitro in different epithelial cell models, evidence of this intracellular lifestyle in human lung tissues is currently lacking. Objectives: To detect and characterize intracellular P. aeruginosa in CF airway epithelium from human lung explant tissues. Methods: We sampled lung explant tissues from patients with CF undergoing lung transplantation and non-CF lung donor control tissue. We analyzed lung tissue sections for the presence of intracellular P. aeruginosa using quantitative culture and microscopy, in parallel to histopathology and airway morphometry. Measurements and Main Results: P. aeruginosa was isolated from the lungs of seven patients with CF undergoing lung transplantation. Microscopic assessment revealed the presence of intracellular P. aeruginosa within airway epithelial cells in three of the seven patients analyzed at a varying but low frequency. We observed those events occurring in lung regions with high bacterial burden. Conclusions: This is the first study describing the presence of intracellular P. aeruginosa in CF lung tissues. Although intracellular P. aeruginosa in airway epithelial cells is likely relatively rare, our findings highlight the plausible occurrence of this intracellular bacterial reservoir in chronic CF infections.

Biofilm Formation by Staphylococcus aureus in the Specific Context of Cystic Fibrosis

Staphylococcus aureus is a major human pathogen whose characteristics support its success in various clinical settings including Cystic Fibrosis (CF). In CF, S. aureus is indeed the most commonly identified opportunistic pathogen in children and the overall population. S. aureus colonization/infection, either by methicillin-susceptible or methicillin-resistant strains, will become chronic in about one third of CF patients. The persistence of S. aureus in CF patients' lungs, despite various eradication strategies, is favored by several traits in both host and pathogen. Among the latter, living in biofilm is a highly protective way to survive despite deleterious environmental conditions, and is a common characteristic shared by the main pathogens identified in CF. This is why CF has earned the status of a biofilm-associated disease for several years now. Biofilm formation by S. aureus, and the molecular mechanisms governing and regulating it, have been extensively studied but have received less attention in the specific context of CF lungs. Here, we review the current knowledge on S. aureus biofilm in this very context, i.e., the importance, study methods, molecular data published on mono- and multi-species biofilm and anti-biofilm strategies. This focus on studies including clinical isolates from CF patients shows that they are still under-represented in the literature compared with studies based on reference strains, and underlines the need for such studies. Indeed, CF clinical strains display specific characteristics that may not be extrapolated from results obtained on laboratory strains.

The thematic role of extracellular loop of VraG in activation of the membrane sensor GraS in a cystic fibrosis MRSA strain differs in nuance from the CA-MRSA strain JE2

Patients with cystic fibrosis (CF) often suffer recurrent bronchial bacterial infections that lead to deterioration of lung function over time. The infections in CF patients are often due to S. aureus and P. aeruginosa that colonize the airways. Significantly, methicillin-resistant S. aureus (MRSA) makes it challenging for treatment in CF patients due to its feature of multiple antibiotic resistance. In bronchial airways, cationic antimicrobial peptides are often present in mucosa cells, neutrophils, and macrophages that interfere with bacterial proliferation. The major mechanism for resistance to the bactericidal activity of cationic peptides in S. aureus is mediated by the GraRS two-component system that activates expression of MprF and DltABCD to increase surface positive charge to repel interactions with cationic peptides. We recently found that VraG, a membrane permease component of the VraFG efflux pumps, harbors a long 200-residue extracellular loop (EL) that utilizes K380 to interact with the negatively charged 9-residue extracellular loop of the membrane sensor GraS to control mprF expression in a community-acquired MRSA strain JE2. In this study, we extended this observation to a CF MRSA strain CF32A1 where we affirmed that the EL loop of VraG controls GraS-mediated signal transduction; however, in contrast to community acquired MRSA strain JE2, the CF MRSA strain CF32A1 requires both K380 and K388 in the EL of VraG to properly modulate signal transduction mediated by GraS. This effect was not attributable to the several single nucleotide polymorphisms that exist between VraG and GraS in the two MRSA strains.

A simple method to generate human airway epithelial organoids with externally orientated apical membranes

Organoids, which are self-organizing three-dimensional cultures, provide models that replicate specific cellular components of native tissues or facets of organ complexity. We describe a simple method to generate organoid cultures using isolated human tracheobronchial epithelial cells grown in mixed matrix components and supplemented at day 14 with the Wnt pathway agonist R-spondin 2 (RSPO2) and the bone morphogenic protein antagonist Noggin. In contrast to previous reports, our method produces differentiated tracheobronchospheres with externally orientated apical membranes without pretreatments, providing an epithelial model to study cilia formation and function, disease pathogenesis, and interaction of pathogens with the respiratory mucosa. Starting from 3 × 10⁵ cells, organoid yield at day 28 was 1,720 ± 302. Immunocytochemistry confirmed the cellular localization of airway epithelial markers, including CFTR, Na⁺/K⁺ ATPase, acetylated-α-tubulin, E-cadherin, and ZO-1. Compared to native tissues, expression of genes related to bronchial differentiation and ion transport were similar in organoid and air-liquid interface (ALI) cultures. In matched primary cultures, mean organoid cilia length was 6.1 ± 0.2 µm, similar to that of 5.7 ± 0.1 µm in ALI cultures, and ciliary beating was vigorous and coordinated with frequencies of 7.7 ± 0.3 Hz in organoid cultures and 5.3 ± 0.8 Hz in ALI cultures. Functional measurement of osmotically induced volume changes in organoids showed low water permeability. The generation of numerous single testable units from minimal starting material complements prior techniques. This culture system may be useful for studying airway biology and pathophysiology, aiding diagnosis of ciliopathies, and potentially for high-throughput drug screening.

An ex vivo cystic fibrosis model recapitulates key clinical aspects of chronic Staphylococcus aureus infection

Staphylococcus aureus is the most prevalent organism isolated from the airways of people with cystic fibrosis (CF), predominantly early in life. Yet its role in the pathology of lung disease is poorly understood. In mice, and many experiments using cell lines, the bacterium invades cells or interstitium, and forms abscesses. This is at odds with the limited available clinical data: interstitial bacteria are rare in CF biopsies and abscesses are highly unusual. Bacteria instead appear to localize in mucus plugs in the lumens of bronchioles. We show that, in an established ex vivo model of CF infection comprising porcine bronchiolar tissue and synthetic mucus, S. aureus demonstrates clinically significant characteristics including colonization of the airway lumen, with preferential localization as multicellular aggregates in mucus, initiation of a small colony variant phenotype and increased antibiotic tolerance of tissue-associated aggregates. Tissue invasion and abscesses were not observed. Our results may inform ongoing debates relating to clinical responses to S. aureus in people with CF.

Nasal Epithelial Cell-Based Models for Individualized Study in Cystic Fibrosis

The emergence of highly effective CFTR modulator therapy has led to significant improvements in health care for most patients with cystic fibrosis (CF). For some, however, these therapies remain inaccessible due to the rarity of their individual CFTR variants, or due to a lack of biologic activity of the available therapies for certain variants. One proposed method of addressing this gap is the use of primary human cell-based models, which allow preclinical therapeutic testing and physiologic assessment of relevant tissue at the individual level. Nasal cells represent one such tissue source and have emerged as a powerful model for individual disease study. The ex vivo culture of nasal cells has evolved over time, and modern nasal cell models are beginning to be utilized to predict patient outcomes. This review will discuss both historical and current state-of-the art use of nasal cells for study in CF, with a particular focus on the use of such models to inform personalized patient care.

Major Determinants of Airway Epithelial Cell Sensitivity to S. aureus Alpha-Toxin: Disposal of Toxin Heptamers by Extracellular Vesicle Formation and Lysosomal Degradation

Alpha-toxin is a major virulence factor of Staphylococcus aureus. Monomer binding to host cell membranes results in the formation of heptameric transmembrane pores. Among human model airway epithelial cell lines, A549 cells were most sensitive toward the toxin followed by 16HBE14o^- and S9 cells. In this study we investigated the processes of internalization of pore-containing plasma membrane areas as well as potential pathways for heptamer degradation (lysosomal, proteasomal) or disposal (formation of exosomes/micro-vesicles). The abundance of toxin heptamers upon applying an alpha-toxin pulse to the cells declined both in extracts of whole cells and of cellular membranes of S9 cells, but not in those of 16HBE14o^- or A549 cells. Comparisons of heptamer degradation rates under inhibition of lysosomal or proteasomal degradation revealed that an important route of heptamer degradation, at least in S9 cells, seems to be the lysosomal pathway, while proteasomal degradation appears to be irrelevant. Exosomes prepared from culture supernatants of toxin-exposed S9 cells contained alpha-toxin as well as low amounts of exosome and micro-vesicle markers. These results indicate that lysosomal degradation of internalized toxin heptamers may be the most important determinant of toxin-resistance of some types of airway epithelial cells.

S. aureus alpha-toxin monomer binding and heptamer formation in host cell membranes - Do they determine sensitivity of airway epithelial cells toward the toxin?

Alpha-toxin (Hla) is a major virulence factor of Staphylococcus aureus (S. aureus) and plays an important role in S. aureus-induced pneumonia. It binds as a monomer to the cell surface of eukaryotic host cells and forms heptameric transmembrane pores. Sensitivities toward the toxin of various types of potential host cells have been shown to vary substantially, and the reasons for these differences are unclear. We used three human model airway epithelial cell lines (16HBE14o-, S9, A549) to correlate cell sensitivity (measured as rate of paracellular gap formation in the cell layers) with Hla monomer binding, presence of the potential Hla receptors ADAM10 or α5β1 integrin, presence of the toxin-stabilizing factor caveolin-1 as well as plasma membrane lipid composition (phosphatidylserine/choline, sphingomyelin). The abundance of ADAM10 correlated best with gap formation or cell sensitivities, respectively, when the three cell types were compared. Caveolin-1 or α5β1 integrin did not correlate with toxin sensitivity. The relative abundance of sphingomyelin in plasma membranes may also be used as a proxi for cellular sensitivity against alpha-toxin as sphingomyelin abundances correlated well with the intensities of alpha-toxin mediated gap formation in the cell layers.

Importance of superoxide dismutases A and M for protection of Staphylococcus aureus in the oxidative stressful environment of cystic fibrosis airways

Staphylococcus aureus is one of the earliest pathogens that persists the airways of cystic fibrosis (CF) patients and contributes to increased inflammation and decreased lung function. In contrast to other staphylococci, S. aureus possesses two superoxide dismutases (SODs), SodA and SodM, with SodM being unique to S. aureus. Both SODs arm S. aureus for its fight against oxidative stress, a by-product of inflammatory reactions. Despite complex investigations, it is still unclear if both enzymes are crucial for the special pathogenicity of S. aureus. To investigate the role of both SODs during staphylococcal persistence in CF airways, we analysed survival and gene expression of S. aureus CF isolates and laboratory strains in different CF-related in vitro and ex vivo settings. Bacteria located in inflammatory and oxidised CF sputum transcribed high levels of sodA and sodM. Especially expression values of sodM were remarkably higher in CF sputum than in bacterial in vitro cultures. Interestingly, also S. aureus located in airway epithelial cells expressed elevated transcript numbers of both SODs, indicating that S. aureus is exposed to oxidative stress at various sites within CF airways. Both enzymes promoted survival of S. aureus during polymorphonuclear leukocyte killing and seem to act compensatory, thereby giving evidence that the interwoven interaction of SodA and SodM contributes to S. aureus virulence and facilitates S. aureus persistence within CF airways.

Myxobacteria-Derived Outer Membrane Vesicles: Potential Applicability Against Intracellular Infections

In 2019, it was estimated that 2.5 million people die from lower tract respiratory infections annually. One of the main causes of these infections is Staphylococcus aureus, a bacterium that can invade and survive within mammalian cells. S. aureus intracellular infections are difficult to treat because several classes of antibiotics are unable to permeate through the cell wall and reach the pathogen. This condition increases the need for new therapeutic avenues, able to deliver antibiotics efficiently. In this work, we obtained outer membrane vesicles (OMVs) derived from the myxobacteria Cystobacter velatus strain Cbv34 and Cystobacter ferrugineus strain Cbfe23, that are naturally antimicrobial, to target intracellular infections, and investigated how they can affect the viability of epithelial and macrophage cell lines. We evaluated by cytometric bead array whether they induce the expression of proinflammatory cytokines in blood immune cells. Using confocal laser scanning microscopy and flow cytometry, we also investigated their interaction and uptake into mammalian cells. Finally, we studied the effect of OMVs on planktonic and intracellular S. aureus. We found that while Cbv34 OMVs were not cytotoxic to cells at any concentration tested, Cbfe23 OMVs affected the viability of macrophages, leading to a 50% decrease at a concentration of 125,000 OMVs/cell. We observed only little to moderate stimulation of release of TNF-alpha, IL-8, IL-6 and IL-1beta by both OMVs. Cbfe23 OMVs have better interaction with the cells than Cbv34 OMVs, being taken up faster by them, but both seem to remain mostly on the cell surface after 24 h of incubation. This, however, did not impair their bacteriostatic activity against intracellular S. aureus. In this study, we provide an important basis for implementing OMVs in the treatment of intracellular infections.

PLGA nanocapsules improve the delivery of clarithromycin to kill intracellular Staphylococcus aureus and Mycobacterium abscessus

Drug delivery systems are promising for targeting antibiotics directly to infected tissues. To reach intracellular Staphylococcus aureus and Mycobacterium abscessus, we encapsulated clarithromycin in PLGA nanocapsules, suitable for aerosol delivery by nebulization of an aqueous dispersion. Compared to the same dose of free clarithromycin, nanoencapsulation reduced 1000 times the number of intracellular S. aureus in vitro. In RAW cells, while untreated S. aureus was located in acidic compartments, the treated ones were mostly situated in non-acidic compartments. Clarithromycin-nanocapsules were also effective against M. abscessus (70-80% killing efficacy). The activity of clarithromycin-nanocapsules against S. aureus was also confirmed in vivo, using a murine wound model as well as in zebrafish. The permeability of clarithromycin-nanocapsules across Calu-3 monolayers increased in comparison to the free drug, suggesting an improved delivery to sub-epithelial tissues. Thus, clarithromycin-nanocapsules are a promising strategy to target intracellular S. aureus and M. abscessus.

Cystic Fibrosis: Microbiology and Host Response

The earliest descriptions of lung disease in people with cystic fibrosis (CF) showed the involvement of 3 interacting pathophysiologic elements in CF airways: mucus obstruction, inflammation, and infection. Over the past 7 decades, our understanding of CF respiratory microbiology and inflammation has evolved with the introduction of new treatments, increased longevity, and increasingly sophisticated laboratory techniques. This article reviews the current understanding of infection and inflammation and their roles in CF lung disease. It also discusses how this constantly evolving information is used to inform current therapeutic strategies, measures and predictors of disease severity, and research priorities.

Host-microbe interactions in distal airways: relevance to chronic airway diseases

This article is the summary of a workshop, which took place in November 2013, on the roles of microorganisms in chronic respiratory diseases. Until recently, it was assumed that lower airways were sterile in healthy individuals. However, it has long been acknowledged that microorganisms could be identified in distal airway secretions from patients with various respiratory diseases, including cystic fibrosis (CF) and non-CF bronchiectasis, chronic obstructive pulmonary disease, asthma and other chronic airway diseases (e.g. post-transplantation bronchiolitis obliterans). These microorganisms were sometimes considered as infectious agents that triggered host immune responses and contributed to disease onset and/or progression; alternatively, microorganisms were often considered as colonisers, which were considered unlikely to play roles in disease pathophysiology. These concepts were developed at a time when the identification of microorganisms relied on culture-based methods. Importantly, the majority of microorganisms cannot be cultured using conventional methods, and the use of novel culture-independent methods that rely on the identification of microorganism genomes has revealed that healthy distal airways display a complex flora called the airway microbiota. The present article reviews some aspects of current literature on host–microbe (mostly bacteria and viruses) interactions in healthy and diseased airways, with a special focus on distal airways.

Understanding host–microbe interactions in distal airways may lead to novel therapies for chronic airway diseaseshttp://ow.ly/HfENz

Developing accurate models of the human airways

Objectives

Particle delivery to the airways is an attractive prospect for many potential therapeutics, including vaccines. Developing strategies for inhalation of particles provides a targeted, controlled and non-invasive delivery route but, as with all novel therapeutics, in vitro and in vivo testing are needed prior to clinical use. Whilst advanced vaccine testing demands the use of animal models to address safety issues, the production of robust in vitro cellular models would take account of the ethical framework known as the 3Rs (Replacement, Reduction and Refinement of animal use), by permitting initial screening of potential candidates prior to animal use. There is thus a need for relevant, realistic in vitro models of the human airways.

Key findings

Our laboratory has designed and characterised a multi-cellular model of human airways that takes account of the conditions in the airways and recapitulates many salient features, including the epithelial barrier and mucus secretion.

Summary

Our human pulmonary models recreate many of the obstacles to successful pulmonary delivery of particles and therefore represent a valid test platform for screening compounds and delivery systems.

mCLCA3 modulates IL-17 and CXCL-1 induction and leukocyte recruitment in murine Staphylococcus aureus pneumonia

The human hCLCA1 and its murine ortholog mCLCA3 (calcium-activated chloride channel regulators) are exclusively expressed in mucus cells and linked to inflammatory airway diseases with increased mucus production, such as asthma, cystic fibrosis and chronic obstructive pulmonary disease. Both proteins have a known impact on the mucus cell metaplasia trait in these diseases. However, growing evidence points towards an additional role in innate immune responses. In the current study, we analyzed Staphylococcus aureus pneumonia, an established model to study pulmonary innate immunity, in mCLCA3-deficient and wild-type mice, focusing on the cellular and cytokine-driven innate inflammatory response. We compared clinical signs, bacterial clearance, leukocyte immigration and cytokine responses in the bronchoalveolar compartment, as well as pulmonary vascular permeability, histopathology, mucus cell number and mRNA expression levels of selected genes (mClca1 to 7, Muc5ac, Muc5b, Muc2, Cxcl-1, Cxcl-2, Il-17). Deficiency of mCLCA3 resulted in decreased neutrophilic infiltration into the bronchoalveolar space during bacterial infection. Only the cytokines IL-17 and the murine CXCL-8 homolog CXCL-1 were decreased on mRNA and protein levels during bacterial infection in mCLCA3-deficient mice compared to wild-type controls. However, no differences in clinical outcome, histopathology or mucus cell metaplasia were observed. We did not find evidence for regulation of any other CLCA homolog that would putatively compensate for the lack of mCLCA3. In conclusion, mCLCA3 appears to modulate leukocyte response via IL-17 and murine CXCL-8 homologs in acute Staphylococcus aureus pneumonia which is well in line with the proposed function of hCLCA1 as a signaling molecule acting on alveolar macrophages.

Staphylococcus aureus in early cystic fibrosis lung disease

Staphylococcus aureus: is a common bacterial organism infecting children with cystic fibrosis (CF). Emerging evidence suggests early lower airway infection with this organism in young children with CF results in the deterioration of lung function, poorer nutrition parameters and heightens the airway inflammatory response. Despite contributing significantly to the burden of early lung disease among this group, there are ongoing controversies in the management of S. aureus infection, and gaps in our understanding of exactly how this organism causes lung disease. To reduce the morbidity and mortality of early infection ongoing research is needed to: (i) understand the early host immune response that enables this pathogen to reside within the CF lung; (ii) determine if there are organism specific factors that are associated with CF lung disease; and (iii) clarify the utility of anti-staphylococcal antibiotic prophylaxis and/or eradication in the treatment of this patient population.

Empyema in a woman with cystic fibrosis: a cautionary tale

Cystic fibrosis (CF) is a disease which predisposes individuals to recurrent infective exacerbations of suppurative lung disease; however, empyema is a rare complication in these patients. Empyemas secondary to Staphylococcus aureus and Burkholderia cepacia have been described in patients with CF. We report the case of pleural empyema with mixed S. aureus and Pseudomonas aeruginosa infection in a 34-year-old woman with CF, which was managed with ultrasound-guided pigtail catheter insertion, fibrinolysis, and antibiotic therapy. Physicians should be aware of this unusual complication in CF patients, especially those receiving an immunosuppressive therapy.

New microbicidal functions of tracheal glands: defective anti-infectious response to Pseudomonas aeruginosa in cystic fibrosis

Tracheal glands (TG) may play a specific role in the pathogenesis of cystic fibrosis (CF), a disease due to mutations in the cftr gene and characterized by airway inflammation and Pseudomonas aeruginosa infection. We compared the gene expression of wild-type TG cells and TG cells with the cftr DeltaF508 mutation (CF-TG cells) using microarrays covering the whole human genome. In the absence of infection, CF-TG cells constitutively exhibited an inflammatory signature, including genes that encode molecules such as IL-1alpha, IL-beta, IL-32, TNFSF14, LIF, CXCL1 and PLAU. In response to P. aeruginosa, genes associated with IFN-gamma response to infection (CXCL10, IL-24, IFNgammaR2) and other mediators of anti-infectious responses (CSF2, MMP1, MMP3, TLR2, S100 calcium-binding proteins A) were markedly up-regulated in wild-type TG cells. This microbicidal signature was silent in CF-TG cells. The deficiency of genes associated with IFN-gamma response was accompanied by the defective membrane expression of IFNgammaR2 and altered response of CF-TG cells to exogenous IFN-gamma. In addition, CF-TG cells were unable to secrete CXCL10, IL-24 and S100A8/S100A9 in response to P. aeruginosa. The differences between wild-type TG and CF-TG cells were due to the cftr mutation since gene expression was similar in wild-type TG cells and CF-TG cells transfected with a plasmid containing a functional cftr gene. Finally, we reported an altered sphingolipid metabolism in CF-TG cells, which may account for their inflammatory signature. This first comprehensive analysis of gene expression in TG cells proposes a protective role of wild-type TG against airborne pathogens and reveals an original program in which anti-infectious response was deficient in TG cells with a cftr mutation. This defective response may explain why host response does not contribute to protection against P. aeruginosa in CF.

In vitro activities of a novel nanoemulsion against Burkholderia and other multidrug-resistant cystic fibrosis-associated bacterial species

Respiratory tract infection, most often involving opportunistic bacterial species with broad-spectrum antibiotic resistance, is the primary cause of death in persons with cystic fibrosis (CF). Species within the Burkholderia cepacia complex are especially problematic in this patient population. We investigated a novel surfactant-stabilized oil-in-water nanoemulsion (NB-401) for activity against 150 bacterial isolates recovered primarily from CF respiratory tract specimens. These specimens included 75 Burkholderia isolates and 75 isolates belonging to other CF-relevant species including Pseudomonas, Achromobacter, Pandoraea, Ralstonia, Stenotrophomonas, and Acinetobacter. Nearly one-third of the isolates were multidrug resistant, and 20 (13%) were panresistant based on standard antibiotic testing. All isolates belonging to the same species were genotyped to ensure that each isolate was a distinct strain. The MIC(90) of NB-401 was 125 microg/ml. We found no decrease in activity against multidrug-resistant or panresistant strains. MBC testing showed no evidence of tolerance to NB-401. We investigated the activity of NB-401 against a subset of strains grown as a biofilm and against planktonic strains in the presence of CF sputum. Although the activity of NB-401 was decreased under both conditions, the nanoemulsion remained bactericidal for all strains tested. These results support NB-401's potential role as a novel antimicrobial agent for the treatment of infection due to CF-related opportunistic pathogens.

Effects of cystic fibrosis transmembrane conductance regulator and DeltaF508CFTR on inflammatory response, ER stress, and Ca2+ of airway epithelia

We tested whether cystic fibrosis (CF) airway epithelia have larger innate immune responses than non-CF or cystic fibrosis transmembrane conductance regulator (CFTR)-corrected cells, perhaps resulting from ER stress due to retention of DeltaF508CFTR in the endoplasmic reticulum (ER) and activation of cytosolic Ca(2+) (Ca(i)) and nuclear factor (NF)-kappaB signaling. Adenovirus infections of a human CF (DeltaF508/DeltaF508) nasal cell line (CF15) provided isogenic comparisons of wild-type (wt) CFTR and DeltaF508CFTR. In the absence of bacteria, there were no or only small differences among CF15, CF15-lacZ (beta-galactosidase-expressing), CF15-wtCFTR (wtCFTR-corrected), and CF15-DeltaF508CFTR (to test ER retention of DeltaF508CFTR) cells in NF-kappaB activity, interleukin (IL)-8 secretion, Ca(i) responses, and ER stress. Non-CF and CF primary cultures of human bronchial epithelial cells (HBE) secreted IL-8 equivalently. Upon infection with Pseudomonas aeruginosa (PA) or flagellin (key activator for airway epithelia), CF15, CF15-lacZ, CF15-wtCFTR, and CF15DeltaF508CFTR cells exhibited equal PA binding, NF-kappaB activity, and IL-8 secretion; cells also responded similarly to flagellin when both CFTR (forskolin) and Ca(i) signaling (ATP) were activated. CF and non-CF HBE responded similarly to flagellin + ATP. Thapsigargin (Tg, releases ER Ca(2+)) increased flagellin-stimulated NF-kappaB and ER stress similarly in all cells. We conclude that ER stress, Ca(i), and NF-kappaB signaling and IL-8 secretion were unaffected by wt- or DeltaF508CFTR in control and during exposure to PA, flagellin, flagellin + ATP, or flagellin + ATP + forskolin. Tg, but not wt- or DeltaF508CFTR, triggered ER stress. Previous measurements showing hyperinflammatory responses in CF airway epithelia may have resulted from cell-specific, rather than CFTR- or DeltaF508CFTR-specific effects.

Effect of laparotomy on clearance and cytokine induction in Staphylococcus aureus infected lungs

RATIONALE

Staphylococcus aureus is a major pathogen complicating postsurgical care.

OBJECTIVES

To test the effect of sterile laparotomy (LAP) on pulmonary clearance of S. aureus in a murine model.

METHODS

Control and LAP mice were infected intranasally with 10(8) cfu of S. aureus. Microbial clearance, pulmonary leukocyte recruitment, and cytokine profiles were compared between the groups. Antibody neutralization or cytokine gene knockout mice were used to evaluate the role of cytokines.

MEASUREMENTS AND MAIN RESULTS

Laparotomy resulted in a 10-fold increase in S. aureus lung colony-forming units on Days 2 and 3 postinfection. Both groups cleared the infection by Day 4. No defect in leukocyte recruitment into the lungs was observed in infected LAP animals; however, an increase in the number of Mac-3-positive cells and a significant decrease of cells with high surface expression of Fc-gammaR suggest suboptimal activation of leukocytes in the lungs of infected LAP animals. Infected LAP mice had decreased expression of interferon (IFN)-gamma and increased expression of mRNA for IL-13 in the lungs on Day 1 postinfection and decreased levels of IL-6, keratinocyte-derived chemokine (KC), and macrophage inflammatory protein-2 (MIP-2) in bronchoalveolar lavage at Day 2 postinfection. Neutralization of IFN-gamma mimicked the effect of LAP with impaired clearance on Day 2.

CONCLUSIONS

Sterile LAP induced temporary deactivation of innate immune responses to pulmonary S. aureus challenge. Impaired microbial clearance was accompanied by altered cytokine expression and suboptimal activation of pulmonary leukocytes. Lack of early IFN-gamma induction in the infected lungs of LAP animals is a likely mechanism contributing to the observed phenotype.

Innate immune response in CF airway epithelia: hyperinflammatory?

The lack of functional cystic fibrosis (CF) transmembrane conductance regulator (CFTR) in the apical membranes of CF airway epithelial cells abolishes cAMP-stimulated anion transport, and bacteria, eventually including Pseudomonas aeruginosa, bind to and accumulate in the mucus. Flagellin released from P. aeruginosa triggers airway epithelial Toll-like receptor 5 and subsequent NF-kappaB signaling and production and release of proinflammatory cytokines that recruit neutrophils to the infected region. This response has been termed hyperinflammatory because so many neutrophils accumulate; a response that damages CF lung tissue. We first review the contradictory data both for and against the idea that epithelial cells exhibit larger-than-normal proinflammatory signaling in CF compared with non-CF cells and then review proposals that might explain how reduced CFTR function could activate such proinflammatory signaling. It is concluded that apparent exaggerated innate immune response of CF airway epithelial cells may have resulted not from direct effects of CFTR on cellular signaling or inflammatory mediator production but from indirect effects resulting from the absence of CFTRs apical membrane channel function. Thus, loss of Cl-, HCO3-, and glutathione secretion may lead to reduced volume and increased acidification and oxidation of the airway surface liquid. These changes concentrate proinflammatory mediators, reduce mucociliary clearance of bacteria and subsequently activate cellular signaling. Loss of apical CFTR will also hyperpolarize basolateral membrane potentials, potentially leading to increases in cytosolic [Ca2+], intracellular Ca2+, and NF-kappaB signaling. This hyperinflammatory effect of CF on intracellular Ca2+ and NF-kappaB signaling would be most prominently expressed during exposure to both P. aeruginosa and also endocrine, paracrine, or nervous agonists that activate Ca2+ signaling in the airway epithelia.

The role of airway epithelium and blood neutrophils in the inflammatory response in cystic fibrosis

Cystic fibrosis (CF) is caused by mutations in the CF transmembrane conductance regulator (CFTR) gene, which accounts for the cAMP-modulated chloride conductance of airway epithelial cells. CFTR also regulates other membrane proteins like the negative regulation of the amiloride-sensitive epithelial sodium channel (ENaC). Mutations in the CFTR gene lead to hyperabsorption of sodium chloride and a reduction in the periciliary salt and water content which leads to impaired mucociliary clearance. It seems that a lack of functional CFTR leads to abnormal function of the NF-kappaB pathway in submucosal gland cells, causing an increased production of pro-inflammatory cytokines and the chemokine IL-8, and a pro-inflammatory environment. CFTR is also expressed in neutrophils and several neutrophil functions like cytokine production, migration, phagocytosis and apoptosis seem altered in CF. In this review we describe the role of airway epithelium and blood neutrophils in the viscious circle of inflammation and infection seen in CF.

Species specificity in the adherence of staphylococci to canine and human corneocytes: a preliminary study

Staphylococcal pyoderma is rarely contagious between dogs and humans, or humans and dogs. This study investigated the hypothesis that there are species differences in adherence of Staphylococcus intermedius (the most common isolate from dogs) and Staphylococcus aureus (the most common isolate from humans) to canine and human corneocytes. Sheets of corneocytes were collected from the ventral abdomen of 10 dogs and the medial forearm of 10 humans (all healthy and without any history or physical signs of skin disease) using double-sided tape. Staphylococcus intermedius from a case of canine bacterial pyoderma and a human strain of S. aureus were prepared in phosphate buffered saline (PBS) and applied in duplicate, respectively, to the canine and human corneocyte-covered tapes using PBS as negative control. After incubation, rinsing, and staining with crystal violet, quantification of the adherent bacteria was carried out blindly by computerized image analysis. Staphylococcus intermedius was found to adhere significantly more to canine corneocytes than S. aureus (P = 0.0006), whereas S. aureus showed greater adherence to human corneocytes than S. intermedius (P < 0.0001). In addition, the pattern of adherence differed between the two organisms, with S. intermedius adhering to the entire surface and S. aureus adhering mainly to the periphery of both canine and human corneocytes. Preference for adherence to these two hosts may explain, in part, why S. intermedius and S. aureus are uncommonly isolated from human and canine skin infections, respectively.

Who's talking to whom? Epithelial-bacterial pathogen interactions

Our perception that host-bacterial interactions lead to disease comes from rare, unsuccessful interactions resulting in the development of detectable symptoms. In contrast, the majority of host-bacterial interactions go unnoticed as the host and bacteria perceive each other to be no threat. In July 2004, a focused international symposium on epithelial-bacterial pathogen interactions was held in Newcastle upon Tyne (UK). The symposium concentrated on recent advances in our understanding of bacterial interactions at respiratory and gastrointestinal mucosal epithelial layers. For the host these epithelial tissues represent a first line of defence against invading bacterial pathogens. Through the discovery that the innate immune system plays a pivotal role during host-bacterial interactions, it has become clear that epithelia are being utilized by the host to monitor or communicate with both pathogenic and commensal bacteria. Interest in understanding the bacterial perspective of these interactions has lead researchers to realize that the bacteria utilize the same factors associated with disease to establish successful long-term interactions. Here we discuss several common themes and concepts that emerged from recent studies that have allowed physiologists and microbiologists to interact at a common interface similar to their counterparts -- epithelia and bacterial pathogens. These studies highlight the need for further multidisciplinary studies into how the host differentiates between pathogenic and commensal bacteria.

Three-dimensional human airway epithelial cell cultures

An epithelial airway-derived 3-D cell culture model is described. The long lifetime of this model, compared to monolayer cultures of primary cells, allows many experiments with material from one single patient to be performed.

Airway epithelial cell-pathogen interactions

Cystic fibrosis (CF) airway becomes colonized with only a limited number of bacterial pathogens. It is of paramount importance to establish in vitro and in vivo models to better understand bacterial-host interactions under CF-like conditions. In this article, in vitro methods suitable to study Pseudomonas aeruginosa (Pa) and Staphylococcus aureus (Sa) adherence to and uptake by airway epithelial cells are described. Acute and chronic respiratory infection models, which have been used in CF transgenic mice and mimic human CF lung pathology, are also taken into consideration.

Cystic fibrosis airway epithelial cell polarity and bacterial flagellin determine host response toPseudomonas aeruginosa

The role of epithelial polarity and bacterial factors in the control of the innate immune response of airway epithelial cells to Pseudomonas aeruginosa PAK was investigated using a human, nasal cystic fibrosis (DeltaF508/DeltaF508) epithelial cell line CF15 grown as confluent layers on permeable supports. Addition of PAK to the basal surface of CF15 layers caused significant expression changes in 1525 different genes (out of 12 625 examined), including the cytokines IL-6, IL-8, IL-1beta and TNF-alpha, as well as genes associated with leucocyte adhesion, antibacterial factors, and NF-kappaB signalling. Confocal microscopy showed that nuclear migration of NF-kappaB in all CF15 cells was preceded by PAK binding to the basal and lateral surfaces of some cells. Addition of PAK to the apical surface of CF15 monolayers elicited changes in expression of only 602 genes, including 256 not affected during basolateral PAK exposure. Over time, cytokine expression during apical PAK was similar to that exhibited by basal PAK, but the magnitudes during apical treatment were much smaller with little/no nuclear migration of NF-kappaB in CF15 cells. Furthermore, these responses depended on the presence of flagellin, but not pili on the bacteria. Thus, P. aeruginosa triggered a strong innate immune response that depended on the apical versus basolateral polarity of CF15 cells and the presence of flagellin on the bacteria.

Pathophysiology and management of pulmonary infections in cystic fibrosis

This comprehensive State of the Art review summarizes the current published knowledge base regarding the pathophysiology and microbiology of pulmonary disease in cystic fibrosis (CF). The molecular basis of CF lung disease including the impact of defective cystic fibrosis transmembrane regulator (CFTR) protein function on airway physiology, mucociliary clearance, and establishment of Pseudomonas aeruginosa infection is described. An extensive review of the microbiology of CF lung disease with particular reference to infection with P. aeruginosa is provided. Other pathogens commonly associated with CF lung disease including Staphylococcal aureus, Burkholderia cepacia, Stenotrophomonas maltophilia, Achromobacter xylosoxidans and atypical mycobacteria are also described. Clinical presentation and assessment of CF lung disease including diagnostic microbiology and other measures of pulmonary health are reviewed. Current recommendations for management of CF lung disease are provided. An extensive review of antipseudomonal therapies in the settings of treatment for early P. aeruginosa infection, maintenance for patients with chronic P. aeruginosa infection, and treatment of exacerbation in pulmonary symptoms, as well as antibiotic therapies for other CF respiratory pathogens, are included. In addition, the article discusses infection control policies, therapies to optimize airway clearance and reduce inflammation, and potential future therapies.

State of the art: why do the lungs of patients with cystic fibrosis become infected and why can't they clear the infection?

Cystic Fibrosis (CF) lung disease, which is characterized by airway obstruction, chronic bacterial infection, and an excessive inflammatory response, is responsible for most of the morbidity and mortality. Early in life, CF patients become infected with a limited spectrum of bacteria, especially P. aeruginosa. New data now indicate that decreased depth of periciliary fluid and abnormal hydration of mucus, which impede mucociliary clearance, contribute to initial infection. Diminished production of the antibacterial molecule nitric oxide, increased bacterial binding sites (e.g., asialo GM-1) on CF airway epithelial cells, and adaptations made by the bacteria to the airway microenvironment, including the production of virulence factors and the ability to organize into a biofilm, contribute to susceptibility to initial bacterial infection. Once the patient is infected, an overzealous inflammatory response in the CF lung likely contributes to the host's inability to eradicate infection. In response to increased IL-8 and leukotriene B₄ production, neutrophils infiltrate the lung where they release mediators, such as elastase, that further inhibit host defenses, cripple opsonophagocytosis, impair mucociliary clearance, and damage airway wall architecture. The combination of these events favors the persistence of bacteria in the airway. Until a cure is discovered, further investigations into therapies that relieve obstruction, control infection, and attenuate inflammation offer the best hope of limiting damage to host tissues and prolonging survival.

Infection control recommendations for patients with cystic fibrosis: microbiology, important pathogens, and infection control practices to prevent patient-to-patient transmission

Infection Control Recommendations for Patients With Cystic Fibrosis: Microbiology, Important Pathogens, and Infection Control Practices to Prevent Patient-to-Patient Transmissionupdates, expands, and replaces the consensus statement,Microbiology and Infectious Disease in Cystic Fibrosispublished in 1994. This consensus document presents background data and evidence-based recommendations for practices that are intended to decrease the risk of transmission of respiratory pathogens among CF patients from contaminated respiratory therapy equipment or the contaminated environment and thereby reduce the burden of respiratory illness. Included are recommendations applicable in the acute care hospital, ambulatory, home care, and selected non-healthcare settings. The target audience includes all healthcare workers who provide care to CF patients. Antimicrobial management is beyond the scope of this document.

Absent secretion to vasoactive intestinal peptide in cystic fibrosis airway glands

We are testing the hypothesis that the malfunctioning of airway gland serous cells is a component of cystic fibrosis (CF) airway disease. CF is caused by mutations that disrupt CF transmembrane conductance regulator, an anion channel essential for proper fluid secretion in some epithelia. Submucosal glands supply most of the mucus in upper airways, and gland serous cells are the primary site of CF transmembrane conductance regulator expression in airways. We have discovered a major defect in CF glands by in situ optical monitoring of secretions from single human airway glands. CF glands did not secrete to agents that elevated [cAMP](i) (0 responses/450 glands, 8 subjects), whereas glands were responsive in all donor tracheas (605/827 glands, 15 subjects) and in bronchi from subjects who were transplanted because of other lung diseases (148/166 glands, n = 10). CF glands secreted to cholinergic stimulation, and serous cells were abundant in glands from all CF subjects. The complete absence of secretion to agents that elevate [cAMP](i) suggests that altered secretion of gland mucus could contribute to CF lung disease.

Polarized expression of cystic fibrosis transmembrane conductance regulator and associated epithelial proteins during the regeneration of human airway surface epithelium in three-dimensional culture

We have previously shown that, in normal human airway tissue, localization of the cystic fibrosis transmembrane conductance regulator (CFTR) can be affected by epithelial maturation, polarity, and differentiation and that CFTR trafficking and apical localization depend on the integrity of the airway epithelium. In this study, we addressed the question of whether the three-dimensional (3-D) organization of adult human airway epithelial cells in suspension culture under rotation, leading to spheroid-like structures, could mimic the in vivo phenomenon of differentiation and polarization. The kinetics of the differentiation, polarity, and formation of the CFTR-ZO-1-ezrin complex was analyzed by transmission, scanning, and immunofluorescence microscopy. Functional activity of the airway surface epithelium was assessed by monitoring the degree of cAMP-stimulated chloride efflux from cultured cells. Our results show that after the initial step of dedifferentiation, characterized by a loss of ciliated cells and disappearance of epithelial subapical CFTR-ezrin-ZO-1 complex, the isolated cells formed 3-D spheroid structures within 24 hours. After 15 days, progressive ciliogenesis was observed and secretory cells could be identified. After 35 days of 3-D culture, ZO-1, CFTR, ezrin, and CD59 were apically or subapically located, and well-differentiated secretory and ciliated cells were identified. CFTR functionality was assessed by analyzing the Cl(-) secretion after amiloride and forskolin perfusion. After 35 days of culture of spheroids in suspension, a significant increase in Cl(-) efflux was observed in well-differentiated ciliated cells.

Susceptibilities of Mycoplasma fermentans and Mycoplasma hyorhinis to membrane-active peptides and enrofloxacin in human tissue cell cultures

Mycoplasmas, which are bacteria that are devoid of a cell wall and which belong to the class Mollicutes, are pathogenic for humans and animals and are frequent contaminants of tissue cell cultures. Although contamination of cultures with mycoplasma can easily be monitored with fluorescent dyes that stain DNA and/or with molecular probes, protection and decontamination of cultures remain serious challenges. In the present work, we investigated the susceptibilities of Mycoplasma fermentans and Mycoplasma hyorhinis to the membrane-active peptides alamethicin, dermaseptin B2, gramicidin S, and surfactin by growth inhibition and lethality assays. In the absence of serum, the four peptides killed mycoplasmas at minimal bactericidal concentrations that ranged from 12.5 to 100 microM, but in all cases the activities were decreased by the presence of serum. As a result, under standard culture conditions (10% serum) only alamethicin and gramicidin S were able to inhibit mycoplasma growth (MICs, 50 microM), while dermaseptin B2 and surfactin were ineffective. Furthermore, 8 days of treatment of HeLa cell cultures experimentally contaminated with either mycoplasma species with 70 microM enrofloxacin cured the cultures of infection, whereas treatment with alamethicin and gramicidin S alone was not reliable because the concentrations and treatment times required were toxic to the cells. However, combination of alamethicin or gramicidin S with 70 microM enrofloxacin allowed mycoplasma eradication after 30 min or 24 h of treatment, depending on the mycoplasma and peptide considered. HeLa cell cultures experimentally infected with mycoplasmas should prove to be a useful model for study of the antimycoplasma activities of antibiotics and membrane-active peptides under conditions close to those found in vivo.

Lung infections associated with cystic fibrosis

While originally characterized as a collection of related syndromes, cystic fibrosis (CF) is now recognized as a single disease whose diverse symptoms stem from the wide tissue distribution of the gene product that is defective in CF, the ion channel and regulator, cystic fibrosis transmembrane conductance regulator (CFTR). Defective CFTR protein impacts the function of the pancreas and alters the consistency of mucosal secretions. The latter of these effects probably plays an important role in the defective resistance of CF patients to many pathogens. As the modalities of CF research have changed over the decades from empirical histological studies to include biophysical measurements of CFTR function, the clinical management of this disease has similarly evolved to effectively address the ever-changing spectrum of CF-related infectious diseases. These factors have led to the successful management of many CF-related infections with the notable exception of chronic lung infection with the gram-negative bacterium Pseudomonas aeruginosa. The virulence of P. aeruginosa stems from multiple bacterial attributes, including antibiotic resistance, the ability to utilize quorum-sensing signals to form biofilms, the destructive potential of a multitude of its microbial toxins, and the ability to acquire a mucoid phenotype, which renders this microbe resistant to both the innate and acquired immunologic defenses of the host.

Characteristics of Staphylococcus aureus, isolated from airways of cystic fibrosis patients, and their small colony variants

The colonization of respiratory tract by Staphylococcus aureus is a frequent feature of cystic fibrosis (CF), especially in pediatric patients. The formation of small colony variants (SCVs), which produce reduced amounts of alpha-toxin, is one of the proposed ways of staphylococcal accommodation in an intracellular niche. The aim of the present study was to compare some properties of S. aureus SCVs and their parent strains. A site-directed S. aureus hemB mutant and parent strain 8325-4 were included in the study (control pair). Normal and SCV strain pairs from CF patients as well as control strains were tested for the susceptibility to defensins, killing activity of professional phagocytes and adhesion to A549 cell line. Because S. aureus are exposed to many cationic proteins in the host, we challenged a clinical isolate with minimal subinhibitory concentration (subMIC) of protamine and found that hemin and menadione auxotrophic SCVs emerged. SCVs were more resistant than normal strains to protamine but not to dermaseptin. The susceptibility to the bactericidal activity of magainin was the same for normal and SCV strains. The protamine resistance of normal as well as SCVs was strongly enhanced by high salt concentration. The adhesion of some SCVs to A549 cells was higher than adhesion of parental strains. However, the number of adherent bacteria (SCVs) was diminished in the presence of hemin for hemin auxotrophs. The uptake of SCVs by granulocytes was lower than ingestion of normal strains, but SCVs were killed with equal or greater potency. SCVs are adapted to intracellular survival and persistence in the host under certain circumstances. The ability to form a variant subpopulation affords S. aureus additional survival options.

Fibronectin-binding proteins of Staphylococcus aureus are involved in adherence to human airway epithelium

This study was designed to investigate the molecular mechanisms of Staphylococcus aureus adherence to human airway epithelium. Using a humanized bronchial xenograft model in the nude mouse and primary cultures of human airway epithelial cells (HAEC), we showed that S. aureus adhered mainly to undifferentiated HAEC whereas weak adherence (11- to 20-fold lower) to differentiated HAEC was observed (P < 0.01). A fibronectin (FN)-binding protein (FnBP)-deficient strain of S. aureus had a fivefold-lower adherence level to undifferentiated HAEC than did the parental strain (P < 0.005), suggesting that S. aureus FN-binding capacity is involved in the adherence to HAEC. We also showed that 97% of 32 S. aureus clinical strains, isolated from the airway secretions of cystic fibrosis patients (n = 18) and patients with nosocomial pneumonia (n = 14), possessed the two fnb genes. The strains from pneumonia patients had a significantly (P < 0.05) higher FN-binding capacity than did the strains from CF patients. This result was confirmed by the expression of FnBPs, investigated by Western ligand affinity blotting. Our results suggest a major role of FnBPs in the colonization of the airways by S. aureus and point to the importance of the adhesin regulatory pathways in the staphylococcal infectious process.

Effects of reduced mucus oxygen concentration in airway Pseudomonas infections of cystic fibrosis patients

Current theories of CF pathogenesis predict different predisposing "local environmental" conditions and sites of bacterial infection within CF airways. Here we show that, in CF patients with established lung disease, Pseudomonas aeruginosa was located within hypoxic mucopurulent masses in airway lumens. In vitro studies revealed that CF-specific increases in epithelial O(2) consumption, linked to increased airway surface liquid (ASL) volume absorption and mucus stasis, generated steep hypoxic gradients within thickened mucus on CF epithelial surfaces prior to infection. Motile P. aeruginosa deposited on CF airway surfaces penetrated into hypoxic mucus zones and responded to this environment with increased alginate production. With P. aeruginosa growth in oxygen restricted environments, local hypoxia was exacerbated and frank anaerobiosis, as detected in vivo, resulted. These studies indicate that novel therapies for CF include removal of hypoxic mucus plaques and antibiotics effective against P. aeruginosa adapted to anaerobic environments.

Staphylococcus aureus agr and sarA functions are required for invasive infection but not inflammatory responses in the lung

Staphylococcus aureus strains lacking agr- and sarA-dependent gene products or specific MSCRAMM (microbial surface components recognizing adhesive matrix molecules) adhesins were compared for the ability to activate inflammatory responses in the lung. The mutants were evaluated for virulence in a mouse model of pneumonia and by quantifying their ability to stimulate interleukin-8 (IL-8) and granulocyte-macrophage colony-stimulating factor (GM-CSF) expression in respiratory epithelial cells. In a neonatal mouse, only strains with intact agr and sarA loci were consistently associated with invasive, fatal pulmonary infection (P < 0.001) and sarA was specifically required to cause bacteremia (P < 0.001). The agr and/or sarA mutants were, nonetheless, fully capable of producing pneumonia and were as proficient as the wild-type strain in stimulating epithelial IL-8 expression, a polymorphonuclear leukocyte chemokine, in airway cells. In contrast, agr and especially sarA mutants induced less epithelial GM-CSF expression, and MSCRAMM mutants lacking fibronectin binding proteins or clumping factor A, a ligand for fibrinogen, were unable to stimulate epithelial GM-CSF production. The ability to induce IL-8 expression was independent of the adherence properties of intact bacteria, indicating that shed and/or secreted bacterial components activate epithelial responses. While conserved staphylococcal components such as peptidoglycan are sufficient to evoke inflammation and cause pneumonia, the agr and sarA loci of S. aureus are critical for the coordination of invasive infection of the lungs.

Attachment of Staphylococcus aureus to eukaryotic cells and experimental pitfalls in staphylococcal adherence assays: a critical appraisal

Staphylococcus aureus is a bacterial species with pathogenic potential to both humans and animals. The primary natural niche is said to be the human vestibulum nasi from where bacterial cells may spread to the environment or additional anatomical sites such as the perineum or the hands, where residence is usually transient. Apparently, S. aureus is capable of a precise and balanced interaction with specific types of eukaryotic nasal cells. Although a wide variety of important bacterial ligands and possible eukaryote receptors have been described, the precise mechanisms leading to persistent bacterial colonization and, even more importantly, associated infection have not yet been elucidated in detail. This may be a consequence of the fact that most of the adherence factors have been studied individually in simplified in vitro systems, not taking the complexity of multi-factorial in vivo cell-cell interactions into account. An overall scheme of the initial and sequential interactions leading to S. aureus colonization of eukaryotic cell surfaces has not yet emerged. This review concisely describes the current state of affairs in the multi-disciplinary field of staphylococcal adherence research. Specific emphasis is placed upon the pros and cons of the various artificial, mostly in vitro models employed to study the interaction between bacterial and human or animal cells.

Impact of the regulatory loci agr, sarA and sae of Staphylococcus aureus on the induction of alpha-toxin during device-related infection resolved by direct quantitative transcript analysis

The cytotoxic alpha-toxin (encoded by hla) of Staphylococcus aureus is regulated by three loci, agr, sarA and sae, in vitro. Here, we assess the regulation of hla in a guinea pig model of device-related infection by quantifying RNAIII (the effector molecule of agr) and hla directly in exudates accumulating in infected devices without subculturing of the bacteria. LightCycler reverse transcription-polymerase chain reaction (RT-PCR) was used to quantify the transcripts. Strains RN6390 and Newman expressed considerably smaller amounts of RNAIII in the guinea pig than during in vitro growth. The residual RNAIII expression decreased during the course of infection and was negatively correlated with bacterial densities. As with RNAIII, the highest hla expression was detected in both strains early in infection. Even in strain Newman, a weak hla producer in vitro, a pronounced expression of hla was observed during infection. Likewise, four S. aureus isolates from cystic fibrosis (CF) patients expressed Q1hla despite an inactive agr during device-related infection as in the CF lung. Mutation of agr and sarA in strain Newman and RN6390 had no consequence for hla expression in vivo. In contrast, the mutation in sae resulted in severe downregulation of hla in vitro as well as in vivo. In conclusion, S. aureus seems to be provided with regulatory circuits different from those characterized in vitro to ensure alpha-toxin synthesis during infections.

Human neutrophil elastase releases two pools of mucinlike glycoconjugate from tracheal submucosal gland cells

Neutrophil elastase can contribute to the pathogenesis of increased airway reactivity and excess mucus secretion in many pulmonary diseases. Ten nanomolar human neutrophil elastase (HNE) effectively empties airway serous cells, raising the question of why HNE is not equally effective at emptying mucous cells of their stored mucin because total release of mucin granules is not seen in postmortem examination of even the most severe disease. To better resolve the mucus secretagogue action of HNE, we measured secretion of mucinlike glycoconjugates (MGCs) released from freshly isolated swine tracheal submucosal gland cells in fractions of the superfusate acquired every 2 min. Six to fifty nanomolar HNE released a fixed quantity of MGCs at an increasing rate with increasing concentrations of enzyme, an action consistent with the release of cell surface mucinlike molecules. The polycation poly-L-lysine (1 microg/ml) released a similar transient of MGCs. A steady-state doubling of MGC rate of release was seen as long as 100 nM HNE was present, but this stimulus represented less than a 1% release of stored MGCs/min and was consistent with release of mucin vesicles from cell stores. Both actions of HNE were inhibited by the specific inhibitors L-680833 and DMP-777 but not by 30 microM erythromycin. Therefore, HNE release of MGCs from tracheal submucosal glands is limited by both the fixed quantity of the MGCs in the transient pool and by the small steady-state response to the higher concentrations of enzyme.

Cell wall-associated protein A as a tool for immunolocalization of Staphylococcus aureus in infected human airway epithelium

Staphylococcus aureus is a common human pathogen involved in non-bronchial diseases and in genetic and acquired bronchial diseases. In this study, we applied an immunolabeling approach for in vivo and in vitro detection of S. aureus, based on the affinity of staphylococcal protein A (SpA) for the Fc region of immunoglobulins, especially IgG. Most strains of S. aureus, including clinical strains, can be detected with this labeling technique. The approach can be used for detection and localization with transmission electron microscopy or light-fluorescence microscopy of S. aureus in infected tissues such as human bronchial tissue from cystic fibrosis (CF) patients. The methodology can also be applied to cell culture models with the aim of characterizing bacterial adherence to epithelial cells in backscattered electron imaging with scanning electron microscopy. Application to the study of S. aureus adherence to airway epithelium showed that the bacteria did not adhere in vivo to intact airway epithelium. In contrast, bacteria adhered to the basolateral plasma membrane of columnar cells, to basal cells, to the basement membrane and were identified beneath the lamina propria when the epithelium was injured and remodeled, or in vitro when the epithelial cells were dedifferentiated.

Direct quantitative transcript analysis of the agr regulon of Staphylococcus aureus during human infection in comparison to the expression profile in vitro

Bacteria possess a repertoire of distinct regulatory systems promoting survival in disparate environments. Under in vitro conditions it was demonstrated for the human pathogen Staphylococcus aureus that the expression of most virulence factors is coordinated by the global regulator agr. To monitor bacterial gene regulation in the host, we developed a method for direct transcript analysis from clinical specimens. Quantification of specific transcripts was performed by competitive reverse transcription-PCR, and results were normalized against the constitutively expressed gene for gyrase (gyr). Using sputum from cystic fibrosis (CF) patients infected with S. aureus we examined the transcription of the effector molecule RNAIII of agr, of spa (protein A), generally repressed by agr, and of hla (alpha-toxin), generally activated by agr. In the CF lung RNAIII was expressed poorly, indicating an inactive agr in vivo. Despite the low level of RNAIII expression, spa was detectable only in minute amounts and an irregular transcription of hla was observed in all sputum samples. After subculturing of patient strains agr-deficient isolates and isolates with unusual expression profiles, i.e., not consistent with those obtained from prototypic strains, were observed. In conclusion, the agr activity seems to be nonessential in CF, and from the described expression pattern of spa and hla, other regulatory circuits aside from agr are postulated in vivo.

Trefoil factor family domain peptides in the human respiratory tract

Trefoil factor family domain peptides (TFF) are thought to be involved in mucosal epithelial restitution and wound healing of the gastrointestinal tract and are up-regulated in ulceration and in a variety of solid tumours. It was hypothesized that TFFs are also expressed on mucosal surfaces of the human respiratory tract. Lung tissue, nasal polyps, and sputum samples from seven patients with cystic fibrosis (CF), two with chronic and acute bronchitis, and non-dysplastic material from two cases of bronchial adenocarcinoma were analysed for TFF expression by immunohistochemistry, immunofluorescence, western blot and RT-PCR. Expression of TFF1 and TFF3 was observed in material from all patients. TFFs were localized in goblet and ciliated cells, as well as in some submucosal cells of tracheobronchial tissues and nasal polyps from normal and CF individuals. In sputa of patients with CF and with chronic or acute bronchitis, TFF1 and TFF3 were detected by western blotting. Freshly cultivated nasal epithelial cells transcribed and secreted TFFs and mucins, whereas nasal cells cultivated for 6 weeks still expressed mucins, but not TFFs. Secreted TFFs and mucins also bound to the surface of Staphylococcus aureus in infected CF airways. In conclusion, TFF1 and TFF3 are expressed and secreted in normal and inflamed airways. The association of TFFs with bacteria may contribute to the anti-microbial mucociliary defence system.