Detection of Alpha-Toxin and Other Virulence Factors in Biofilms of Staphylococcus aureus on Polystyrene and a Human Epidermal Model

BACKGROUND & AIM

The ability of Staphylococcus aureus to successfully colonize (a)biotic surfaces may be explained by biofilm formation and the actions of virulence factors. The aim of the present study was to establish the presence of 52 proteins, including virulence factors such as alpha-toxin, during biofilm formation of five different (methicillin resistant) S. aureus strains on Leiden human epidermal models (LEMs) and polystyrene surfaces (PS) using a competitive Luminex-based assay.

RESULTS

All five S. aureus strains formed biofilms on PS, whereas only three out of five strains formed biofilms on LEMs. Out of the 52 tested proteins, six functionally diverse proteins (ClfB, glucosaminidase, IsdA, IsaA, SACOL0688 and nuclease) were detected in biofilms of all strains on both PS and LEMs. At the same time, four toxins (alpha-toxin, gamma-hemolysin B and leukocidins D and E), two immune modulators (formyl peptide receptor-like inhibitory protein and Staphylococcal superantigen-like protein 1), and two other proteins (lipase and LytM) were detectable in biofilms by all five S. aureus strains on LEMs, but not on PS. In contrast, fibronectin-binding protein B (FnbpB) was detectable in biofilms by all S. aureus biofilms on PS, but not on LEMs. These data were largely confirmed by the results from proteomic and transcriptomic analyses and in case of alpha-toxin additionally by GFP-reporter technology.

CONCLUSION

Functionally diverse virulence factors of (methicillin-resistant) S. aureus are present during biofilm formation on LEMs and PS. These results could aid in identifying novel targets for future treatment strategies against biofilm-associated infections.

Biocompatibility of a fish scale-derived artificial cornea: Cytotoxicity, cellular adhesion and phenotype, and in vivo immunogenicity

PURPOSE

To determine whether a fish scale-derived collagen matrix (FSCM) meets the basic criteria to serve as an artificial cornea, as determined with in vitro and in vivo tests.

METHODS

Primary corneal epithelial and stromal cells were obtained from human donor corneas and used to examine the (in)direct cytotoxicity effects of the scaffold. Cytotoxicity was assessed by an MTT assay, while cellular proliferation, corneal cell phenotype and adhesion markers were assessed using an EdU-assay and immunofluorescence. For in vivo-testing, FSCMs were implanted subcutaneously in rats. Ologen(®) Collagen Matrices were used as controls. A second implant was implanted as an immunological challenge. The FSCM was implanted in a corneal pocket of seven New Zealand White rabbits, and compared to sham surgery.

RESULTS

The FSCM was used as a scaffold to grow corneal epithelial and stromal cells, and displayed no cytotoxicity to these cells. Corneal epithelial cells displayed their normal phenotypical markers (CK3/12 and E-cadherin), as well as cell-matrix adhesion molecules: integrin-α6 and β4, laminin 332, and hemi-desmosomes. Corneal stromal cells similarly expressed adhesion molecules (integrin-α6 and β1). A subcutaneous implant of the FSCM in rats did not induce inflammation or sensitization; the response was comparable to the response against the Ologen(®) Collagen Matrix. Implantation of the FSCM in a corneal stromal pocket in rabbits led to a transparent cornea, healthy epithelium, and, on histology, hardly any infiltrating immune cells.

CONCLUSION

The FSCM allows excellent cell growth, is not immunogenic and is well-tolerated in the cornea, and thus meets the basic criteria to serve as a scaffold to reconstitute the cornea.

Reduced filaggrin expression is accompanied by increased Staphylococcus aureus colonization of epidermal skin models

BACKGROUND

Atopic dermatitis is an inflammatory skin disease that is characterized by a reduced skin barrier function, reduced filaggrin (FLG) expression as well as increased colonization by Staphylococcus aureus.

OBJECTIVE

This study focused on the possible involvement of FLG in epidermal colonization by S. aureus and/or whether it affects the epidermal defence mechanisms, including the expression of antimicrobial peptides (AMPs) and enzymes involved in stratum corneum barrier lipid synthesis. Furthermore, IL-31 has been shown to reduce FLG expression, but its effects on bacterial colonization and on the expression of AMPs and enzymes involved in the barrier lipid synthesis are not known.

MATERIAL AND METHODS

We established N/TERT-based epidermal models (NEMs), after FLG knockdown (FLG-KD) and/or cultured with IL-31, that were colonized with S. aureus for 24 h.

RESULTS

Both FLG-KD and IL-31 supplementation resulted in significantly increased epidermal S. aureus colonization, as well as in an up-regulation of S. aureus-induced IL-8 expression. IL-31, but not FLG-KD, prevented S. aureus-induced up-regulation of mRNA expression for the AMPs human β-defensin 2 and -3 and RNAse7, whereas psoriasin expression remained unchanged. Furthermore, the S. aureus colonization induced changes in mRNA expression of ELOVL4 was not affected by FLG-KD, but was blocked by IL-31. Expression of SCD-1 and Gcase mRNA was reduced by IL-31, but not by FLG-KD.

CONCLUSION

This study shows that NEMs, with FLG-KD and/or cultured in the presence of IL-31, mimic the skin of patients with atopic dermatitis in several aspects, including enhanced bacterial colonization, increased inflammatory and reduced protective responses.

Needle-free injection into skin and soft matter with highly focused microjets

The development of needle-free drug injection systems is of great importance to global healthcare. However, in spite of its great potential and research history over many decades, these systems are not commonly used. One of the main problems is that existing methods use diffusive jets, which result in scattered penetration and severe deceleration of the jets, causing frequent pain and insufficient penetration. Another long-standing challenge is the development of accurate small volume injections. In this paper we employ a novel method of needle-free drug injection, using highly-focused high speed microjets, which aims to solve these challenges. We experimentally demonstrate that these unique jets are able to penetrate human skin: the focused nature of these microjets creates an injection spot smaller than a mosquito's proboscis and guarantees a high percentage of the liquid being injected. The liquid substances can be delivered to a much larger depth than conventional methods, and create a well-controlled dispersion pattern. Thanks to the excellent controllability of the microjet, small volume injections become feasible. Furthermore, the penetration dynamics is studied through experiments performed on gelatin mixtures (human soft tissue equivalent) and human skin, agreeing well with a viscous stress model which we develop. This model predicts the depth of the penetration into both human skin and soft tissue. The results presented here take needle-free injections a step closer to widespread use.

ECM1 interacts with fibulin-3 and the beta 3 chain of laminin 332 through its serum albumin subdomain-like 2 domain

The extracellular matrix protein 1 (ECM1) is an 85 kDa secreted glycoprotein, comprising four variants and playing a pivotal role in endochondral bone formation, angiogenesis, and tumour biology. A computational model for the three-dimensional structure of ECM1a was determined to identify the potential and/or concealed region(s) for binding with candidate partners in human skin. Multiple alignments for the secondary structure of ECM1a and b revealed similarity with serum albumin. The N-terminal domain of ECM1a consists mainly of alpha-helices (alphaD1), while the remaining three domains, namely serum albumin subdomain-like (SASDL) domains 2-4, were topologically comparable with the subdomain of the third serum albumin domain. Yeast-two-hybrid screening of a human foreskin cDNA library using both full-length ECM1a and the hot spot region for ECM1 gene mutations in lipoid proteinosis, an autosomal recessive genodermatosis (complete SASDL2 and the linker to SASDL3: aa177-aa361), as bait, isolated seven extracellular proteins. The site-specific interaction of ECM1a with two of these candidate binders, laminin 332 beta-3 chain and fibulin-3, was confirmed by in vitro and in vivo co-immunoprecipitation experiments. Immunohistologically both binders co-localized with ECM1 in human skin. Together, ECM1 is a multifunctional binding core and/or a scaffolding protein interacting with a variety of extracellular and structural proteins, contributing to the maintenance of skin integrity and homeostasis. Hence, disruption of the ECM1 function may cause the failure of multi-communication among the surrounding skin interstitial molecules, as seen in lipoid proteinosis pathology.

Leiden reconstructed human epidermal model as a tool for the evaluation of the skin corrosion and irritation potential according to the ECVAM guidelines

In the ECVAM validation studies two common skin protocols have been developed, the skin corrosion and skin irritation protocol. Both protocols include next to general and functional conditions that the skin model must meet, also the correct prediction of the activity of certain reference chemicals. For the skin corrosion protocol, the OECD TG 431 defined 12 reference chemicals that should be correctly predicted by the epidermal skin model. For skin irritation 20 test substances should meet the defined criteria. In this study we aimed to subject our Leiden human epidermal (LHE) model to both common protocols according to the ECVAM guidelines. The LHE model generated in this study has been fully characterized and shows very high similarities with the native skin. After minor technical changes in both protocols, corrosion classifications were obtained in concordance with those reported for the validated human skin models EpiSkin and EpiDerm. The results obtained with the common skin irritation protocol were very similar to that of earlier studies with the SkinEthic, EpiSkin and EpiDerm models. This means that the protocols and prediction models developed during the validation studies with a specific skin model can be used with other similar skin models. This study demonstrates that reconstructed human skin equivalents have been proven to be efficient and reliable alternatives to animal testing.

An in vitro model of allogeneic stimulation of cord blood: induction of Fas independent apoptosis

Cord blood is increasingly used in transplantation as it is a readily available source of progenitor cells and is reputed to generate less severe graft-versus-host disease (GVHD) than adult bone marrow. We have compared apoptosis of cord blood lymphocytes (CB) and adult lymphocytes (PBMC) after stimulation via HLA class I, HLA class II or CD3 in order to reproduce in vitro some of the stimuli occurring after allotransplantation. CB spontaneously apoptose more than PBMC ex vivo, stimulation via HLA class I dramatically increased CB apoptosis without altering viability of PBMC. Expression of Fas was markedly lower on CB than on PBMC and this difference was maintained even after activation. Fas ligand was expressed in CB and in PBMC. CB were activated via either HLA class I or class II molecules although proliferation was not observed. Only phorbol ester pre-activation allowed Fas to subsequently induce a death signal. Proliferation of PBMC via CD3 led to enhanced Fas signals. CB therefore differ from PBMC with regard to both spontaneous and activation induced apoptosis and either allo- or CD3 mediated stimulation. Finally, the apoptosis of CB via HLA-class I could have an important role in the moderation of graft-versus-host disease.

Characterisation of the roles of CD95 and CD95 ligand in cord blood

The increasing use of umbilical cord blood in transplantation has led to a renewed interest in the immunological characterisation of this material. This study addresses the question of whether the CD95 molecule and its ligand are expressed and are functional in mediating cell death in cord blood mononuclear cells. These molecules have a crucial role in the homeostasis of haematopoietic cell populations in the adult and also contribute to graft-versus-host disease. CD95 is the most well studied receptor mediating a signal for cell death by apoptosis and its inducible ligand has been demonstrated to mediate cell death of multiple types of CD95 expressing cells. The object of this study was to examine whether cord blood mononuclear cells could behave either as targets for CD95-mediated cell death or as mediators of cell death due to the expression of CD95L. The results of this study lead us to suggest that cord blood mononuclear cells enjoy some immunological privilege due to the relatively low level of expression of CD95 (in comparison with adult peripheral blood lymphocytes) and the expression of the CD95 ligand.