Staphylococcus aureus adherence to nasal epithelial cells in a physiological in vitro model

Cohort description: The Danish Blood Donor Staphylococcus aureus Carriage Study

Purpose

Staphylococcus aureus carriage poses an increased risk of S. aureus infection. The aim of this study was to investigate the colonization of S. aureus among healthy individuals and to establish a prospective cohort and biobank for research in the health consequences of colonization.

Population and methods

The Danish Blood Donor S. aureus Carriage Study (DBDSaCS) was established in 2014. So far, a total of 6082 healthy participants have been included with nasal swabs and repeated swabs are performed at subsequent donations. Samples from the first 2217 participants were cultured using a two-step method to evaluate the effect of using enrichment broth. Furthermore, 262 participants were sampled from both the nares and the throat. All participants completed a questionnaire with self-reported health, anthropometric measurements, current smoking status, and physical activity. Plasma samples, nasal swab transport media, and S. aureus isolates were stored.

Results

The prevalence of S. aureus nasal colonization was 41%. The prevalence of colonization was higher in men (46%) than women (34%), lower for smokers, and decreased with increasing age (<25 years: 44% vs >55 years: 35%). In participants swabbed from the nose and throat, the prevalence of S. aureus colonization after enrichment was 55% with significantly higher prevalence in the throat (45%) than in the nose (40%). The use of an enrichment broth increased the proportion of S. aureus colonization.

Conclusion

We describe a large and growing cohort of healthy individuals established to investigate predictors for S. aureus carriage and the health consequences of carriage. Multiple projects using data from DBDSaCS linked with Danish health registers, biomarkers, and genetic markers are ongoing. Results will be published in the coming years.

Characterization of Virulence Factors of Staphylococcus aureus: Novel Function of Known Virulence Factors That Are Implicated in Activation of Airway Epithelial Proinflammatory Response

Airway epithelial cells play a major role in initiating inflammation in response to bacterial pathogens. S. aureus is an important pathogen associated with activation of diverse types of infection characterized by inflammation dominated by polymorphonuclear leukocytes. This bacterium frequently causes lung infection, which is attributed to virulence factors. Many of virulence determinants associated with S. aureus-mediated lung infection have been known for several years. In this paper, we discuss recent advances in our understanding of known virulence factors implicated in pneumonia. We anticipate that better understanding of novel functions of known virulence factors could open the way to regulate inflammatory reactions of the epithelium and to develop effective strategies to treat S. aureus-induced airway diseases.

Staphylococcus aureus: An old pathogen with new weapons

Staphylococcus aureus has been recognized as an important human pathogen for more than 100 years. S aureus has been able to adapt and evolve in terms of its resistance traits and virulence factors; it is among the most important causes of human infections in the twenty-first century. Rapid molecular identification in the clinical microbiology laboratory of these resistance and virulence factors expressed by S aureus will play an important role in the future in decreasing the morbidity and mortality of infections. This article addresses the emerging aspects of infections caused by S aureus, including microbiology, epidemiology, clinical presentation, pathogenesis, diagnosis, treatment and prognosis, and immunity.

The use of human nasal in vitro cell systems during drug discovery and development

The nasal route is widely used for the administration of drugs for both topical and systemic action. At an early stage in drug discovery and during the development process, it is essential to gain a thorough insight of the nasal absorption potential, metabolism and toxicity of the active compound and the components of the drug formulation. Human nasal epithelial cell cultures may provide a reliable screening tool for pharmaco-toxicological assessment of potential nasal drug formulations. The aim of this review is to give an overview of the information relevant for the development of a human nasal epithelial cell culture model useful during drug discovery and development. A primary goal in the development of in vitro cell culture systems is to maintain differentiated morphology and biochemical features, resembling the original tissue as closely as possible. The potential and limitations of the existing in vitro human nasal models are summarized. The following topics related to cell culture methodology are discussed: (i) primary cultures versus cell lines; (ii) cell-support substrate; (iii) medium and medium supplements; and (iv) the air-liquid interface model versus liquid-liquid. Several considerations with respect to the use of in vitro systems for pharmaceutical applications (transport, metabolism, assessment of ciliary toxicity) are also discussed.

Stable ciliary activity in human nasal epithelial cells grown in a perfusion system

PURPOSE

Explore the usefulness of a perfusion system in order to establish human nasal epithelial cell cultures suitable for long-term in vitro ciliary beat frequency (CBF) and cilio-toxicity studies.

METHODS

The cells were obtained by protease digestion of nasal biopsy material. The cells were plated at a density of 0.8-1 x 10(6)/cm2 on Vitrogen-coated polyethylene terephthalate membranes, and cultured under submerged conditions in a CO2 incubator or in a perfusion system (initiated on days 8-9 after plating). The CBF was determined at 24.1 +/- 0.8 degrees C by a computerized microscope photometry system. The morphology of the cultured cells was characterized by transmission electron microscopy (TEM).

RESULTS

Under CO2 incubator culture conditions, stable ciliary activity was expressed and maintained from day 2 to day 24. Under perfusion system culture conditions, the CBF (mean+/-S.D., n = 4) amounted to 8.4 +/- 0.9 and 8.8 +/- 0.4 Hz on days 7 and 14, respectively. These values were lower as compared to the corresponding CBF obtained in the CO2 incubator cultures (9.5 +/- 0.6 and 9.9 +/- 1.0 Hz, respectively). Reference cilio-stimulatory (glycocholate) and cilio-inhibitory (chlorocresol) compounds were used to assess CBF reactivity. In the CO2 incubator and 7- and 14-days perfusion system cultures, glycocholate (0.5%) showed a reversible cilio-stimulatory effect of 23, 26 and 21%, respectively, while chlorocresol (0.005%) exerted a reversible cilio-inhibitory effect of 36, 40 and 36%, respectively. TEM revealed polarized cuboidal to columnar epithelial morphology, with well-differentiated ciliated cells under CO2 and perfusion system conditions (up to day 23).

CONCLUSION

Culturing human nasal epithelial cells on Vitrogen-coated polyethylene terephthalate membranes in submerged conditions in a CO2 incubator and in a perfusion system offers the possibility for long-term preservation (up to 22-24 days) of stable and reactive CBF in vitro.

Dynamic interaction between airway epithelial cells andStaphylococcus aureus

Staphylococcus aureus is a major cause of pulmonary infection, particularly in cystic fibrosis (CF) patients. However, few aspects of the interplay between S. aureus and host airway epithelial cells have been investigated thus far. We investigated by videomicroscopy the time- and bacterial concentration-dependent (104, 106, and 108CFU/ml) effect of S. aureus on adherence, internalization, and the associated damage of the airway epithelial cells. The balance between the secretion by S. aureus of the α-toxin virulence factor and by the airway cells of the antibacterial secretory leukoproteinase inhibitor (SLPI) was also analyzed. After 1 h of interaction, whatever the initial bacterial concentration, a low percentage of S. aureus (<8%) adhered to airway cells, and no airway epithelial cell damage was observed. In contrast, after 24 h of incubation, more bacteria adhered to airway epithelial cells, internalized bacteria were observed, and a bacterial concentration-dependent effect on airway cell damage was observed. At 24 h, most airway cells incubated with bacteria at 108CFU/ml exhibited a necrotic phenotype. The necrosis was preceded by a transient apoptotic process. In parallel, we observed a time- and bacterial concentration-dependent decrease in SLPI and increase in α-toxin expression. These results suggest that airway cells can defend against S. aureus in the early stages of infection. However, in later phases, there is a marked imbalance between the bactericidal capacity of host cells and bacterial virulence. These findings reinforce the potential importance of S. aureus in the pathogenicity of airway infections, including those observed early in CF patients.

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.

Development and evaluation of detection systems for staphylococcal exfoliative toxin A responsible for scalded-skin syndrome

Staphylococcal scalded-skin syndrome is usually diagnosed clinically by its characteristic exfoliating rash. Isolation of Staphylococcus aureus from the patient further supports the diagnosis. Several detection systems have been developed to determine whether the isolated strain produces exfoliative toxin, but none are routinely available in hospital laboratories. In a novel approach, we used computer models to predict the structure of the exfoliative toxins based on other serine proteases and to identify surface epitopes for the production of antibodies that specifically bound the exfoliative toxin A (ETA) serotype. Several rapid immunologically based diagnostic tests for ETA were developed with these antibodies and compared with existing systems. Our results showed that Western blot analysis using these antibodies was in complete correlation with PCR, which has been validated against the "gold standard" mouse model. On the other hand, the double-antibody enzyme-linked immunosorbent assay (ELISA) and Ouchterlony immunodiffusion assay gave unacceptably high false-positive results due to interference by staphylococcal protein A. This problem was successfully overcome by the development of a F(ab')(2) fragment ELISA, which was rapid and reproducible and was as sensitive and specific as PCR and Western blot analysis. The F(ab')(2) fragment ELISA is superior to existing diagnostic systems because it is quantitative, which may be related to the severity of the condition, and can detect amounts of exfoliative toxin in the picogram range directly from serum. This is the first detection system with the potential to confirm the diagnosis of staphylococcal scalded-skin syndrome from a routine blood test within 3 h of presentation.