Staphylococcal fibronectin binding protein interacts with heat shock protein 60 and integrins: role in internalization by epithelial cells

Airway epithelial CD47 plays a critical role in inducing influenza virus-mediated bacterial super-infection

Respiratory viral infection increases host susceptibility to secondary bacterial infections, yet the precise dynamics within airway epithelia remain elusive. Here, we elucidate the pivotal role of CD47 in the airway epithelium during bacterial super-infection. We demonstrated that upon influenza virus infection, CD47 expression was upregulated and localized on the apical surface of ciliated cells within primary human nasal or bronchial epithelial cells. This induced CD47 exposure provided attachment sites for Staphylococcus aureus, thereby compromising the epithelial barrier integrity. Through bacterial adhesion assays and in vitro pull-down assays, we identified fibronectin-binding proteins (FnBP) of S. aureus as a key component that binds to CD47. Furthermore, we found that ciliated cell-specific CD47 deficiency or neutralizing antibody-mediated CD47 inactivation enhanced in vivo survival rates. These findings suggest that interfering with the interaction between airway epithelial CD47 and pathogenic bacterial FnBP holds promise for alleviating the adverse effects of super-infection.

Differentiation of keratinocytes or exposure to type 2 cytokines diminishes S. aureus internalization

Staphylococcus aureus is a leading cause of skin and soft tissue infections. Colonization by this bacterium is increased in individuals with chronic cutaneous diseases such as atopic dermatitis, psoriasis, and bullous pemphigoid. The greater abundance of S. aureus on the skin of subjects with atopic dermatitis in particular has been linked to recurrent cutaneous infections. The primary cell type of the epidermal layer of the skin is the keratinocyte, and it is thought that S. aureus internalized in keratinocytes associates with an increased incidence of skin infections. This study addresses whether keratinocyte differentiation and/or inflammation, two important characteristics altered in cutaneous diseases, influence bacterial internalization. To do this, S. aureus internalization was measured in immortalized and primary keratinocytes that were differentiated using high Ca2+-containing media and/or exposed to cytokines characteristic of atopic dermatitis (IL-4 and IL-13) or psoriasis (IL-17A and IL-22) skin. Our results indicate that S. aureus internalization is uniquely decreased upon keratinocyte differentiation, since this was not observed with another skin-resident bacterium, S. epidermidis. Additionally, treatment with IL-4 + IL-13 diminished bacterial internalization. We interpret this decrease as a mechanism of keratinocyte-based bacterial killing since a similar number of bacterial genomes were detected in cytokine-treated cells, but less viable internalized S. aureus was recovered. Finally, of the receptors reported for S. aureus binding/internalizing into keratinocytes, expression of the α5 component of the α5β1 integrin was in greatest accordance with the number of internalized bacteria in the context of keratinocyte differentiation.IMPORTANCEIndividuals with chronic cutaneous diseases demonstrate heightened susceptibility for severe and recurrent infections from Staphylococcus aureus. What drives this altered susceptibility remains poorly understood. Previous publications have detected S. aureus as deep as the dermal layer of skin in subjects with atopic dermatitis, suggesting that the cutaneous environment of this disease enables deeper bacterial infiltration than occurs in healthy individuals. This observation indicates that S. aureus has greater opportunity to interact with multiple skin cell types in individuals with chronic inflammatory skin diseases. Identifying the characteristics of the skin that influence bacterial internalization, a common method to establish reservoirs and evade the immune response, is critical for our understanding of S. aureus pathogenesis. The significance of this research is the novel identification of epidermal characteristics that influence S. aureus internalization. With this knowledge, methods can be developed to identify patient populations at greater risk for cutaneous infections.

Heat Shock Response and Heat Shock Proteins: Current Understanding and Future Opportunities in Human Diseases

The heat shock response is an evolutionarily conserved mechanism that protects cells or organisms from the harmful effects of various stressors such as heat, chemicals toxins, UV radiation, and oxidizing agents. The heat shock response triggers the expression of a specific set of genes and proteins known as heat shock genes/proteins or molecular chaperones, including HSP100, HSP90, HSP70, HSP60, and small HSPs. Heat shock proteins (HSPs) play a crucial role in thermotolerance and aiding in protecting cells from harmful insults of stressors. HSPs are involved in essential cellular functions such as protein folding, eliminating misfolded proteins, apoptosis, and modulating cell signaling. The stress response to various environmental insults has been extensively studied in organisms from prokaryotes to higher organisms. The responses of organisms to various environmental stressors rely on the intensity and threshold of the stress stimuli, which vary among organisms and cellular contexts. Studies on heat shock proteins have primarily focused on HSP70, HSP90, HSP60, small HSPs, and ubiquitin, along with their applications in human biology. The current review highlighted a comprehensive mechanism of heat shock response and explores the function of heat shock proteins in stress management, as well as their potential as therapeutic agents and diagnostic markers for various diseases.

Chlorogenic acid enhances PPARγ-mediated lipogenesis through preventing Lipin 1 nuclear translocation in Staphylococcus aureus-exposed bovine mammary epithelial cells

Chlorogenic acid (CGA) as one of the most ubiquitously dietary polyphenolic compounds, has been reported to have various antimicrobial effects and exhibit strong anti-inflammatory ability. Staphylococcus aureus is a gram-positive bacterium that can induce mastitis. However, the mechanism through which S. aureus infection affects lipid synthesis and whether CGA have protective effect on S. aureus reduced lipid synthesis is not fully understood. In this study, the internalization of S. aureus reduced intracellular lipid droplet formation, decreased the levels of intracellular triacylglycerol, total cholesterol and 7 types of fatty acid and downregulated the expression of lipogenic genes FAS, ACC, and DGAT1 in bovine mammary epithelial cells (BMECs). In addition, we found that S. aureus intracellular infection attenuated mTORC1 activation resulting in Lipin 1 nuclear localization. Remarkablely, S. aureus infection-mediated repression of lipid synthesis related to the mTORC1 signaling and Lipin 1 nuclear localization can be alleviated by CGA. Thus, our findings provide a novel mechanism by which lipid synthesis is regulated under S. aureus infection and the protective effects of CGA on lipid synthesis in BMECs.

Examining the Prevalence and Antibiotic Susceptibility of S. aureus Strains in Hospitals: An Analysis of the pvl Gene and Its Co-Occurrence with Other Virulence Factors

S. aureus is a pathogenic bacterium that causesinfections. Its virulence is due to surface components, proteins, virulence genes, SCCmec, pvl, agr, and SEs, which are low molecular weight superantigens. SEs are usually encoded by mobile genetic elements, and horizontal gene transfer accounts for their widespread presence in S. aureus. This study analyzed the prevalence of MRSA and MSSA strains of S. aureus in two hospitals in Greece between 2020–2022 and their susceptibility to antibiotics. Specimens collected were tested using the VITEK 2 system and the PCR technique to detect SCCmec types, agr types, pvl genes, and sem and seg genes. Antibiotics from various classes were also tested. This study examined the prevalence and resistance of S. aureus strains in hospitals. It found a high prevalence of MRSA and that the MRSA strains were more resistant to antibiotics. The study also identified the genotypes of the S. aureus isolates and the associated antibiotic resistances. This highlights the need for continued surveillance and effective strategies to combat the spread of MRSA in hospitals. This study examined the prevalence of the pvl gene and its co-occurrence with other genes in S. aureus strains, as well as their antibiotic susceptibility. The results showed that 19.15% of the isolates were pvl-positive and 80.85% were pvl-negative. The pvl gene co-existed with other genes, such as the agr and enterotoxin genes. The results could inform treatment strategies for S. aureus infections.

Staphylococcus aureus Fibronectin-Binding Proteins Contribute to Colonization of the Female Reproductive Tract

Methicillin-resistant Staphylococcus aureus (MRSA) is an opportunistic pathogen and frequent colonizer of human skin and mucosal membranes, including the vagina, with vaginal colonization reaching nearly 25% in some pregnant populations. MRSA vaginal colonization can lead to aerobic vaginitis (AV), and during pregnancy, bacterial ascension into the upper reproductive tract can lead to adverse birth outcomes. USA300, the most prominent MRSA lineage to colonize pregnant individuals, is a robust biofilm former and causative agent of invasive infections; however, little is known about how it colonizes and ascends in the female reproductive tract (FRT). Our previous studies showed that a MRSA mutant of seven fibrinogen-binding adhesins was deficient in FRT epithelial attachment and colonization. Using both monolayer and multilayer air-liquid interface cell culture models, we determine that one class of these adhesins, the fibronectin binding proteins (FnBPA and FnBPB), are critical for association with human vaginal epithelial cells (hVECs) and hVEC invasion through interactions with α₅β₁ integrin. We observe that both FnBPs are important for biofilm formation as single and double fnbAB mutants exhibit reduced biofilm formation on hVECs. Using heterologous expression of fnbA and fnbB in Staphylococcus carnosus, FnBPs are also found to be sufficient for hVEC cellular association, invasion, and biofilm formation. In addition, we found that an ΔfnbAB mutant displays attenuated ascension in our murine vaginal colonization model. Better understanding of MRSA FRT colonization and ascension can ultimately inform treatment strategies to limit MRSA vaginal burden or prevent ascension, especially during pregnancy and in those prone to AV.

Strategies to prevent, curb and eliminate biofilm formation based on the characteristics of various periods in one biofilm life cycle

Biofilms are colonies of bacteria embedded inside a complicated self-generating intercellular. The formation and scatter of a biofilm is an extremely complex and progressive process in constant cycles. Once formed, it can protect the inside bacteria to exist and reproduce under hostile conditions by establishing tolerance and resistance to antibiotics as well as immunological responses. In this article, we reviewed a series of innovative studies focused on inhibiting the development of biofilm and summarized a range of corresponding therapeutic methods for biological evolving stages of biofilm. Traditionally, there are four stages in the biofilm formation, while we systematize the therapeutic strategies into three main periods precisely:(i) period of preventing biofilm formation: interfering the colony effect, mass transport, chemical bonds and signaling pathway of plankton in the initial adhesion stage; (ii) period of curbing biofilm formation:targeting several pivotal molecules, for instance, polysaccharides, proteins, and extracellular DNA (eDNA) via polysaccharide hydrolases, proteases, and DNases respectively in the second stage before developing into irreversible biofilm; (iii) period of eliminating biofilm formation: applying novel multifunctional composite drugs or nanoparticle materials cooperated with ultrasonic (US), photodynamic, photothermal and even immune therapy, such as adaptive immune activated by stimulated dendritic cells (DCs), neutrophils and even immunological memory aroused by plasmocytes. The multitargeted or combinational therapies aim to prevent it from developing to the stage of maturation and dispersion and eliminate biofilms and planktonic bacteria simultaneously.

Staphylococcus aureus cell wall maintenance - the multifaceted roles of peptidoglycan hydrolases in bacterial growth, fitness, and virulence

Staphylococcus aureus is an important human and livestock pathogen that is well-protected against environmental insults by a thick cell wall. Accordingly, the wall is a major target of present-day antimicrobial therapy. Unfortunately, S. aureus has mastered the art of antimicrobial resistance, as underscored by the global spread of methicillin-resistant S. aureus (MRSA). The major cell wall component is peptidoglycan. Importantly, the peptidoglycan network is not only vital for cell wall function, but it also represents a bacterial Achilles' heel. In particular, this network is continuously opened by no less than 18 different peptidoglycan hydrolases (PGHs) encoded by the S. aureus core genome, which facilitate bacterial growth and division. This focuses attention on the specific functions executed by these enzymes, their subcellular localization, their control at the transcriptional and post-transcriptional levels, their contributions to staphylococcal virulence and their overall importance in bacterial homeostasis. As highlighted in the present review, our understanding of the different aspects of PGH function in S. aureus has been substantially increased over recent years. This is important because it opens up new possibilities to exploit PGHs as innovative targets for next-generation antimicrobials, passive or active immunization strategies, or even to engineer them into effective antimicrobial agents.

Mechanisms and Implications of Bacterial Invasion across the Human Skin Barrier

Atopic dermatitis (AD) is associated with a deficiency of skin lipids, increased populations of Staphylococcus aureus in the microbiome, and structural defects in the stratum corneum (SC), the outermost layer of human skin. However, the pathogenesis of AD is ambiguous, as it is unclear whether observed changes are the result of AD or contribute to the pathogenesis of the disease. Previous studies have shown that S. aureus is capable of permeating across isolated human SC tissue when lipids are depleted to levels consistent with AD conditions. In this study, we expand upon this discovery to determine the mechanisms and implications of bacterial penetration into the SC barrier. Specifically, we establish if bacteria are permeating intercellularly or employing a combination of both inter- and intracellular travel. The mechanical implications of bacterial invasion, lipid depletion, and media immersion are also evaluated using a newly developed, physiologically relevant, temperature-controlled drip chamber. Results reveal for the first time that S. aureus can be internalized by corneocytes, indicating transcellular movement through the tissue during permeation, consistent with previous theoretical models. S. aureus also degrades the mechanical integrity of human SC, particularly when the tissue is partially depleted of lipids. These observed mechanical changes are likely the cause of broken or ruptured tissue seen as exudative lesions in AD flares. This work further highlights the necessity of lipids in skin microbial barrier function.

IMPORTANCE Millions of people suffer from the chronic inflammatory skin disease atopic dermatitis (AD), whose symptoms are associated with a deficiency of skin lipids that exhibit antimicrobial functions and increased populations of the opportunistic pathogen Staphylococcus aureus. However, the pathogenesis of AD is ambiguous, and it remains unclear if these observed changes are merely the result of AD or contribute to the pathogenesis of the disease. In this article, we demonstrate the necessity of skin lipids in preventing S. aureus from penetrating the outermost barrier of human skin, thereby causing a degradation in tissue integrity. This bacterial permeation into the viable epidermis could act as an inflammatory trigger of the disease. When coupled with delipidated AD tissue conditions, bacterial permeation can also explain increased tissue fragility, potentially causing lesion formation in AD patients that results in further enhancing bacterial permeability across the stratum corneum and the development of chronic conditions.

Comparative Study of Two-Dimensional (2D) vs. Three-Dimensional (3D) Organotypic Kertatinocyte-Fibroblast Skin Models for Staphylococcus aureus (MRSA) Infection

The invasion of skin tissue by Staphylococcus aureus is mediated by mechanisms that involve sequential breaching of the different stratified layers of the epidermis. Induction of cell death in keratinocytes is a measure of virulence and plays a crucial role in the infection progression. We established a 3D-organotypic keratinocyte-fibroblast co-culture model to evaluate whether a 3D-skin model is more effective in elucidating the differences in the induction of cell death by Methicillin-resistant Staphylococcus aureus (MRSA) than in comparison to 2D-HaCaT monolayers. We investigated the difference in adhesion, internalization, and the apoptotic index in HaCaT monolayers and our 3D-skin model using six strains of MRSA representing different clonal types, namely, ST8, ST30, ST59, ST22, ST45 and ST239. All the six strains exhibited internalization in HaCaT cells. Due to cell detachment, the invasion study was limited up to two and a half hours. TUNEL assay showed no significant difference in the cell death induced by the six MRSA strains in the HaCaT cells. Our 3D-skin model provided a better insight into the interactions between the MRSA strains and the human skin during the infection establishment as we could study the infection of MRSA in our skin model up to 48 h. Immunohistochemical staining together with TUNEL assay in the 3D-skin model showed co-localization of the bacteria with the apoptotic cells demonstrating the induction of apoptosis by the bacteria and revealed the variation in bacterial transmigration among the MRSA strains. The strain representing ST59 showed maximum internalization in HaCaT cells and the maximum cell death as measured by Apoptotic index in the 3D-skin model. Our results show that 3D-skin model might be more likely to imitate the physiological response of skin to MRSA infection than 2D-HaCaT monolayer keratinocyte cultures and will enhance our understanding of the difference in pathogenesis among different MRSA strains.

Overexpression and extra-mitochondrial localization of the chaperonin Hsp60 in ameloblastoma

OBJECTIVES

Ameloblastoma is an odontogenic neoplasm of the mandible and maxilla with various histological types and subtypes. It has been reported that some ameloblastomas could arise from dentigerous cyst walls; thus, the development of ameloblastoma from dentigerous cysts may be due to differential protein expression. Our aim was to identify a membrane protein that is differentially expressed in ameloblastomas with respect to dentigerous cysts.

METHODS

We analyzed the SDS-PAGE profiles of membrane proteins from ameloblastomas and dentigerous cysts. The protein in a band present in the ameloblastoma sample, but apparently absent in the dentigerous cyst sample was identified via mass spectrometry as the chaperonin Hsp60. We used western blotting and immunohistochemistry to analyze its overexpression and localization in ameloblastoma.

RESULTS

We found a differential band of 95 kDa in the membrane proteins of ameloblastoma. In this band, the chaperonin Hsp60 was identified, and its overexpression was corroborated using western blotting and immunohistochemistry. Hsp60 was localized in the plasma membrane of all ameloblastoma samples studied; in addition, it was found in the cell nucleus of the plexiform subtype of conventional ameloblastoma.

CONCLUSIONS

Our results suggest that Hsp60 may be involved in ameloblastoma development, and could therefore be a potential therapeutic target for ameloblastoma treatment.

Revisiting Bap Multidomain Protein: More Than Sticking Bacteria Together

One of the major components of the staphylococcal biofilm is surface proteins that assemble as scaffold components of the biofilm matrix. Among the different surface proteins able to contribute to biofilm formation, this review is dedicated to the Biofilm Associated Protein (Bap). Bap is part of the accessory genome of Staphylococcus aureus but orthologs of Bap in other staphylococcal species belong to the core genome. When present, Bap promotes adhesion to abiotic surfaces and induces strong intercellular adhesion by self-assembling into amyloid like aggregates in response to the levels of calcium and the pH in the environment. During infection, Bap enhances the adhesion to epithelial cells where it binds directly to the host receptor Gp96 and inhibits the entry of the bacteria into the cells. To perform such diverse range of functions, Bap comprises several domains, and some of them include several motifs associated to distinct functions. Based on the knowledge accumulated with the Bap protein of S. aureus, this review aims to summarize the current knowledge of the structure and properties of each domain of Bap and their contribution to Bap functionality.

Characterization of the Atl-mediated staphylococcal internalization mechanism

Staphylococcus aureus internalization by non-professional phagocytes is considered a main pathogenicity mechanism leading to chronic infections. The well-established mechanism of Staphylococcus aureus internalization is mediated by fibronectin (Fn)-binding proteins (FnBPs), Fn as a bridging molecule and the host cell α₅β₁ integrin. We previously identified a novel alternative internalization mechanism in Staphylococcus aureus, which involves the major autolysin Atl and the host cell heat shock cognate protein 70 (Hsc70). Atl-dependent internalization is also employed by the coagulase-negative Staphylococcus epidermidis, where it might represent the major or even sole internalization mechanism, because of the lack of FnBP-homologous proteins. In this study, we aimed to further characterize the Atl-dependent staphylococcal internalization mechanism. We performed biomolecular interaction analysis (BIA) to quantify the adhesive properties of Atl and found multivalent and high affinity interactions of Atl with Fn and Hsc70. Confocal laser scanning microscopy (CLSM) and a flow-cytometric internalization assay in combination with different pharmacological inhibitors suggested an involvement of the α₅β₁ integrin, Fn and Hsc70 and subsequent signaling events mediated by Src and phosphoinositide 3 (PI3) kinases in the Atl-dependent staphylococcal uptake by EA.hy 926 cells. Further characterization of the endocytic machinery implicated a role for clathrin-dependent receptor-mediated endocytosis involving actin cytoskeletal rearrangements and microtubules. In conclusion, Atl ubiquitous among staphylococcal species may substitute for the FnBPs ensuring low-level internalization via a mechanism that seems to share important features with the FnBP-mediated staphylococcal uptake potentially being the prerequisite for the development of therapy-resistant chronic infections by staphylococcal strains that lack FnBPs.

Hsp60 Post-translational Modifications: Functional and Pathological Consequences

Hsp60 is a chaperone belonging to the Chaperonins of Group I and typically functions inside mitochondria in which, together with the co-chaperonin Hsp10, maintains protein homeostasis. In addition to this canonical role, Hsp60 plays many others beyond the mitochondria, for instance in the cytosol, plasma-cell membrane, extracellular space, and body fluids. These non-canonical functions include participation in inflammation, autoimmunity, carcinogenesis, cell replication, and other cellular events in health and disease. Thus, Hsp60 is a multifaceted molecule with a wide range of cellular and tissue locations and functions, which is noteworthy because there is only one hsp60 gene. The question is by what mechanism this protein can become multifaceted. Likely, one factor contributing to this diversity is post-translational modification (PTM). The amino acid sequence of Hsp60 contains many potential phosphorylation sites, and other PTMs are possible such as O-GlcNAcylation, nitration, acetylation, S-nitrosylation, citrullination, oxidation, and ubiquitination. The effect of some of these PTMs on Hsp60 functions have been examined, for instance phosphorylation has been implicated in sperm capacitation, docking of H2B and microtubule-associated proteins, mitochondrial dysfunction, tumor invasiveness, and delay or facilitation of apoptosis. Nitration was found to affect the stability of the mitochondrial permeability transition pore, to inhibit folding ability, and to perturb insulin secretion. Hyperacetylation was associated with mitochondrial failure; S-nitrosylation has an impact on mitochondrial stability and endothelial integrity; citrullination can be pro-apoptotic; oxidation has a role in the response to cellular injury and in cell migration; and ubiquitination regulates interaction with the ubiquitin-proteasome system. Future research ought to determine which PTM causes which variations in the Hsp60 molecular properties and functions, and which of them are pathogenic, causing chaperonopathies. This is an important topic considering the number of acquired Hsp60 chaperonopathies already cataloged, many of which are serious diseases without efficacious treatment.

Evasion of host defenses by intracellular Staphylococcus aureus

Staphylococcus aureus is one of the leading causes of hospital and community-acquired infections worldwide. The increasing occurrence of antibiotic resistant strains and the high rates of recurrent staphylococcal infections have placed several treatment challenges on healthcare systems. In recent years, it has become evident that S. aureus is a facultative intracellular pathogen, able to invade and survive in a range of cell types. The ability to survive intracellularly provides this pathogen with yet another way to evade antibiotics and immune responses during infection. Intracellular S. aureus have been strongly linked to several recurrent infections, including severe bone infections and septicemias. S. aureus is armed with an array of virulence factors as well as an intricate network of regulators that enable it to survive, replicate and escape from a number of immune and nonimmune host cells. It is able to successfully manipulate host cell pathways and use it as a niche to multiply, disseminate, as well as persist during an infection. This bacterium is also known to adapt to the intracellular environment by forming small colony variants, which are metabolically inactive. In this review we will discuss the clinical evidence, the molecular pathways involved in S. aureus intracellular persistence, and new treatment strategies for targeting intracellular S. aureus.

Host-Targeted Therapeutics against Multidrug Resistant Intracellular Staphylococcus aureus

Staphylococcus aureus is a facultative intracellular pathogen that invades and replicates within many types of human cells. S. aureus has shown to rapidly overcome traditional antibiotherapy by developing multidrug resistance. Furthermore, intracellular S. aureus is protected from the last-resort antibiotics—vancomycin, daptomycin, and linezolid—as they are unable to achieve plasma concentrations sufficient for intracellular killing. Therefore, there is an urgent need to develop novel anti-infective therapies against S. aureus infections. Here, we review the current state of the field and highlight the exploitation of host-directed approaches as a promising strategy going forward.

Staphylococcus aureus Lpl protein triggers human host cell invasion via activation of Hsp90 receptor

Staphylococcus aureus is a facultative intracellular pathogen. Recently, it has been shown that the protein part of the lipoprotein-like lipoproteins (Lpls), encoded by the lpl cluster comprising of 10 lpls paralogue genes, increases pathogenicity, delays the G2/M phase transition, and also triggers host cell invasion. Here, we show that a recombinant Lpl1 protein without the lipid moiety binds directly to the isoforms of the human heat shock proteins Hsp90α and Hsp90ß. Synthetic peptides covering the Lpl1 sequence caused a twofold to fivefold increase of S. aureus invasion in HaCaT cells. Antibodies against Hsp90 decrease S. aureus invasion in HaCaT cells and in primary human keratinocytes. Additionally, inhibition of ATPase function of Hsp90 or silencing Hsp90α expression by siRNA also decreased the S. aureus invasion in HaCaT cells. Although the Hsp90ß is constitutively expressed, the Hsp90α isoform is heat-inducible and appears to play a major role in Lpl1 interaction. Pre-incubation of HaCaT cells at 39°C increased both the Hsp90α expression and S. aureus invasion. Lpl1-Hsp90 interaction induces F-actin formation, thus, triggering an endocytosis-like internalisation. Here, we uncovered a new host cell invasion principle on the basis of Lpl-Hsp90 interaction.

Staphylococcus aureus in atopic dermatitis: Strain-specific cell wall proteins and skin immunity

Atopic dermatitis (AD) is a common chronic skin disease. The presence of the bacterium Staphylococcus aureus (S. aureus) is frequently detected on skin affected with AD. In this review, we focused on the characteristics of S. aureus strains isolated from AD skin, particularly the proteins on the cell surface that modulates the interactions between Langerhans cell, keratinocyte, and S. aureus. The skin microbiome plays an important role in maintaining homeostasis of the skin, and colonization of S. aureus in AD is considered to be deeply involved in the clinical manifestation and pathogenesis of skin flares. Colonizing S. aureus strains in AD harbor different surface proteins at the strain level, which are indicated as clonal complexes. Moreover, the cell wall proteins of S. aureus affect skin adhesion and induce altered immune responses. S. aureus from AD skin (AD strain) exhibits internalization into keratinocytes and induces imbalanced Th1/Th2 adaptive immune responses via Langerhans cells. AD strain-derived cell wall proteins and secreted virulence factors are expected to represent therapeutic targets. In addition, the microbiome on the AD skin surface is associated with skin immunity; thus, microbiome-based immunotherapy, whose mechanism of action completely differs from that of typical steroid ointments, are expected to be developed in the future.

Tet38 of Staphylococcus aureus Binds to Host Cell Receptor Complex CD36-Toll-Like Receptor 2 and Protects from Teichoic Acid Synthesis Inhibitors Tunicamycin and Congo Red

Using an affinity column retention assay, we showed that the purified Tet38 membrane transporter of Staphylococcus aureus bound specifically to host cell CD36 and to the complex CD36-Toll-like receptor 2 (TLR-2), but not to TLR-2 alone or TLR-2 and S. aureus lipoteichoic acid (LTA). We tested the effect of LTA on the internalization of S. aureus tet38 mutant QT7 versus RN6390 by A549 epithelial cells. Addition of anti-LTA antibody to the bacteria prior to adding to A549 cells reduced internalization of QT7 2-fold compared to that with nonspecific antibody treatment. QT7 internalized 4- to 6-fold less than RN6390 with or without anti-LTA antibody. These data suggested that Tet38 and LTA were independently involved in the invasion process. The wall teichoic acid (WTA) inhibitor tunicamycin had an 8-fold decrease in activity with overexpression of tet38 and a 2-fold increase in activity in QT7 (tet38). Reserpine (an inhibitor of efflux pumps) reduced the effect of tet38 overexpression on tunicamycin resistance 4-fold. In addition, tet38 affected growth in the presence of LTA inhibitor Congo red, with overexpression increasing growth and deletion of tet38 reducing growth. In conclusion, Tet38 contributes to S. aureus invasion of A549 via direct binding to CD36 of the complex CD36-TLR-2, and LTA independently bound to TLR-2. The reduction of tunicamycin resistance in the presence of reserpine and the survival ability of the tet38 overexpressor in the presence of Congo red suggest that Tet38 can also protect the synthesis of LTA and WTA in S. aureus against their inhibitors, possibly functioning as an efflux pump.

A new host cell internalisation pathway for SadA-expressing staphylococci triggered by excreted neurochemicals

Staphylococcus aureus is a facultative intracellular pathogen that invades a wide range of professional and nonprofessional phagocytes by triggering internalisation by interaction of surface‐bound adhesins with corresponding host cell receptors. Here, we identified a new concept of host cell internalisation in animal‐pathogenic staphylococcal species. This new mechanism exemplified by Staphylococcus pseudintermedius ED99 is not based on surface‐bound adhesins but is due to excreted small neurochemical compounds, such as trace amines (TAs), dopamine (DOP), and serotonin (SER), that render host cells competent for bacterial internalisation. The neurochemicals are produced by only one enzyme, the staphylococcal aromatic amino acid decarboxylase (SadA). Here, we unravelled the mechanism of how neurochemicals trigger internalisation into the human colon cell line HT‐29. We found that TAs and DOP are agonists of the α2‐adrenergic receptor, which, when activated, induces a cascade of reactions involving a decrease in the cytoplasmic cAMP level and an increase in F‐actin formation. The signalling cascade of SER follows a different pathway. SER interacts with 5HT receptors that trigger F‐actin formation without decreasing the cytoplasmic cAMP level. The neurochemical‐induced internalisation in host cells is independent of the fibronectin‐binding protein pathway and has an additive effect. In a sadA deletion mutant, ED99ΔsadA, internalisation was decreased approximately threefold compared with that of the parent strain, and treating S. aureus USA300 with TAs increased internalisation by approximately threefold.

Alternative Enzyme Protection Assay To Overcome the Drawbacks of the Gentamicin Protection Assay for Measuring Entry and Intracellular Survival of Staphylococci

Precise enumeration of living intracellular bacteria is the key step to estimate the invasion potential of pathogens and host immune responses to understand the mechanism and kinetics of bacterial pathogenesis. Therefore, quantitative assessment of host-pathogen interactions is essential for development of novel antibacterial therapeutics for infectious disease. The gentamicin protection assay (GPA) is the most widely used method for these estimations by counting the CFU of intracellular living pathogens. Here, we assess the longstanding drawbacks of the GPA by employing an antistaphylococcal endopeptidase as a bactericidal agent to kill extracellular Staphylococcus aureus We found that the difference between the two methods for the recovery of intracellular CFU of S. aureus was about 5 times. We prove that the accurate number of intracellular CFU could not be precisely determined by the GPA due to the internalization of gentamicin into host cells during extracellular bacterial killing. We further demonstrate that lysostaphin-mediated extracellular bacterial clearance has advantages for measuring the kinetics of bacterial internalization on a minute time scale due to the fast and tunable activity and the inability of protein to permeate the host cell membrane. From these results, we propose that accurate quantification of intracellular bacteria and measurement of internalization kinetics can be achieved by employing enzyme-mediated killing of extracellular bacteria (enzyme protection assay [EPA]) rather than the host-permeative drug gentamicin, which is known to alter host physiology.

Microbial uptake by the respiratory epithelium: outcomes for host and pathogen

Intracellular occupancy of the respiratory epithelium is a useful pathogenic strategy facilitating microbial replication and evasion of professional phagocytes or circulating antimicrobial drugs. A less appreciated but growing body of evidence indicates that the airway epithelium also plays a crucial role in host defence against inhaled pathogens, by promoting ingestion and quelling of microorganisms, processes that become subverted to favour pathogen activities and promote respiratory disease. To achieve a deeper understanding of beneficial and deleterious activities of respiratory epithelia during antimicrobial defence, we have comprehensively surveyed all current knowledge on airway epithelial uptake of bacterial and fungal pathogens. We find that microbial uptake by airway epithelial cells (AECs) is a common feature of respiratory host-microbe interactions whose stepwise execution, and impacts upon the host, vary by pathogen. Amidst the diversity of underlying mechanisms and disease outcomes, we identify four key infection scenarios and use best-characterised host-pathogen interactions as prototypical examples of each. The emergent view is one in which effi-ciency of AEC-mediated pathogen clearance correlates directly with severity of disease outcome, therefore highlighting an important unmet need to broaden our understanding of the antimicrobial properties of respiratory epithelia and associated drivers of pathogen entry and intracellular fate.

Crossing the Intestinal Barrier via Listeria Adhesion Protein and Internalin A

The intestinal epithelial cell lining provides the first line of defense, yet foodborne pathogens such as Listeria monocytogenes can overcome this barrier; however, the underlying mechanism is not well understood. Though the host M cells in Peyer's patch and the bacterial invasion protein internalin A (InlA) are involved, L. monocytogenes can cross the gut barrier in their absence. The interaction of Listeria adhesion protein (LAP) with the host cell receptor (heat shock protein 60) disrupts the epithelial barrier, promoting bacterial translocation. InlA aids L. monocytogenes transcytosis via interaction with the E-cadherin receptor, which is facilitated by epithelial cell extrusion and goblet cell exocytosis; however, LAP-induced cell junction opening may be an alternative bacterial strategy for InlA access to E-cadherin and its translocation. Here, we summarize the strategies that L. monocytogenes employs to circumvent the intestinal epithelial barrier and compare and contrast these strategies with other enteric bacterial pathogens. Additionally, we provide implications of recent findings for food safety regulations.

Toll-Like Receptor 2 and Lipoprotein-Like Lipoproteins Enhance Staphylococcus aureus Invasion in Epithelial Cells

Staphylococcus aureus contains a certain subclass of lipoproteins, the so-called lipoprotein-like lipoproteins (Lpl's), that not only represent Toll-like receptor 2 (TLR2) ligands but are also involved in host cell invasion. Here we addressed the question of which factors contribute to Lpl-mediated invasion of epithelial cells and keratinocytes. For this purpose, we compared the invasiveness of USA300 and its Δlpl mutant under different conditions. In the presence of the matrix proteins IgG, fibrinogen (Fg), and fibronectin (Fn), and of fetal bovine serum (FBS), the invasion ratio was increased in both strains, and always more in USA300 than in its Δlpl mutant. Interestingly, when we compared the invasion of HEK-0 and HEK-TLR2 cells, the cells expressing TLR2 showed a 9-times-higher invasion frequency. When HEK-TLR2 cells were additionally stimulated with a synthetic lipopeptide, Pam₃CSK₄ (P3C), the invasion frequency was further increased. A potential reason for the positive effect of TLR2 on invasion could be that TLR2 activation by P3C also activates F-actin formation. Here we show that S. aureus invasion depends on a number of factors, on the host side as well as on the bacterial side.

Listeria Adhesion Protein Induces Intestinal Epithelial Barrier Dysfunction for Bacterial Translocation

Intestinal epithelial cells are the first line of defense against enteric pathogens, yet bacterial pathogens, such as Listeria monocytogenes, can breach this barrier. We show that Listeria adhesion protein (LAP) induces intestinal epithelial barrier dysfunction to promote bacterial translocation. These disruptions are attributed to the production of pro-inflammatory cytokines TNF-α and IL-6, which is observed in mice challenged with WT and isogenic strains lacking the surface invasion protein Internalin A (ΔinlA), but not a lap^- mutant. Additionally, upon engagement of its surface receptor Hsp60, LAP activates canonical NF-κB signaling, facilitating myosin light-chain kinase (MLCK)-mediated opening of the epithelial barrier via cellular redistribution of the epithelial junctional proteins claudin-1, occludin, and E-cadherin. Pharmacological inhibition of MLCK or NF-κB in cells or genetic ablation of MLCK in mice prevents mislocalization of junctional proteins and L. monocytogenes translocation. Thus, L. monocytogenes uses LAP to exploit epithelial defenses and cross the intestinal epithelial barrier.

Antibody-Based Agents in the Management of Antibiotic-Resistant Staphylococcus aureus Diseases

Staphylococcus aureus is a human pathogen that can cause a wide spectrum of diseases, including sepsis, pneumonia, arthritis, and endocarditis. Ineffective treatment of a number of staphylococcal infections with antibiotics is due to the development and spread of antibiotic-resistant strains following decades of antibiotic usage. This has generated renewed interest within the scientific community in alternative therapeutic agents, such as anti-S. aureus antibodies. Although the role of antibodies in the management of S. aureus diseases is controversial, the success of this pathogen in neutralizing humoral immunity clearly indicates that antibodies offer the host extensive protection. In this review, we report an update on efforts to develop antibody-based agents, particularly monoclonal antibodies, and their therapeutic potential in the passive immunization approach to the treatment and prevention of S. aureus infections.

Growth performance, duodenal morphology and the caecal microbial population in female broiler chickens fed glycine-fortified low protein diets under heat stress conditions

1. This study was undertaken to examine the effect of feeding glycine (Gly)-fortified low protein (LP) diets on the growth performance, duodenal morphology and caecal microbial populations of broiler chickens raised under unheated, cyclic or constant heat stress environmental conditions. 2. From d 1 to 21 (starter phase), an equivalent number of birds were fed either a normal protein (NP) diet or a LP diet fortified with Gly. From d 22 to 42 (grower phase), an equivalent number of birds from each starter diet were distributed to one of the following dietary groups: (i) an NP diet during the starter and grower phases (NPNP), (ii) an NP diet during the starter phase and a LP diet during the grower phase (NPLP), (iii) an LP diet during the starter phase and an NP diet during the grower phase (LPNP) or (iv) LP diets during both phases (LPLP). 3. Commencing from d 22, an equivalent number of birds from each dietary group were exposed to (i) 23 ± 1°C throughout (unheated), (ii) 34 ± 1°C for 7 h each day from 10:00 to 17:00 (cyclic heat) or (iii) 34 ± 1°C throughout (constant heat). 4. Feeding the LP diet during the starter phase resulted in feed intake (FI), weight gain (WG), feed conversion ratios (FCR) and energy efficiency ratios (EER) similar to those for the NP diet. The birds fed the LP diet had a significantly higher protein efficiency ratio (PER) compared with the birds fed the NP diet. 5. During the grower phase, there were significant diet × temperature interactions for F, WG, FCR, PER, EER, villus height, crypt depth and caecal Clostridia. The birds fed the NPLP and LPLP diets had lower FI, WG and EER, higher FCR, shorter villus height and crypt depth and higher caecal Clostridia compared with the birds fed LPNP and NPNP diets under constant heat stress. However, feeding birds the NPLP and LPLP diets resulted in FI, WG, EER, FCR, morphology parameters and caecal Clostridia equivalent to the birds fed LPNP and NPNP diets, as well as improved PER, under unheated and cyclic heat stress conditions. 6. In conclusion, our results indicate that Gly-fortified LP diets can be fed to broilers under normal and acute heat stress environmental conditions without any adverse effects on performance. However, the use of such LP diets can be detrimental to broilers under chronic heat stress conditions.

Immunohistochemistry of Human Hsp60 in Health and Disease: From Autoimmunity to Cancer

Hsp60 (also called Cpn60) is a chaperonin with essential functions for cell physiology and survival. Additionally, its involvement in the pathogenesis of a variety of diseases (e.g., some autoimmune disorders and cancer) is becoming evident with new research. For example, the distribution and levels of Hsp60 in cells and tissues have been found altered in many pathologic conditions, and the significance of these alterations is being investigated in a number of laboratories. The aim of this ongoing research is to determine the meaning of these Hsp60 alterations with regard to pathogenetic mechanisms, diagnosis, classification of lesions, and assessing prognosis and response to treatment.Hsp60 occurs in the mitochondria, i.e., its typical residence according to classic knowledge, and also in other locales, such as the cytosol, the cell membrane, the intercellular space, and biological fluids (e.g., blood and cerebrospinal fluid). Detection and quantitative determinations in all these locations are becoming essential components of laboratory pathology in clinics and research. Consequently, immunohistochemistry targeting Hsp60 is also becoming essential for pathologists and researchers interested in disorders involving this chaperonin.In this chapter, we summarize some recent discoveries on the participation of Hsp60 in the pathogenesis of human diseases, and describe in detail how to perform immunohistochemical reactions for detecting the chaperonin, determining its location, and measuring its quantitative levels.

Staphylococcal Adhesion and Host Cell Invasion: Fibronectin-Binding and Other Mechanisms

Opportunistic bacteria from the genus Staphylococcus can cause life-threatening infections such as pneumonia, endocarditis, bone and joint infections, and sepsis. This pathogenicity is closely related to their capacity to bind directly to the extracellular matrix or to host cells. Adhesion is indeed the first step in the formation of biofilm or the invasion of host cells, which protect the bacteria from the host immune system and facilitate chronic infection. Adhesion relies on the expression of a repertoire of surface proteins called adhesins, notably microbial surface components recognizing adhesive matrix molecules. In this short review, we discuss the main pathway (FnBP-Fn-α5β1 integrin), as well as alternatives, through which Staphylococcus aureus adheres to and then invades non-professional phagocytic cells. We then examine the corresponding mechanisms for coagulase negative staphylococci. There is currently a little understanding of the molecular mechanisms that lead to internalization. Filling this gap in the literature would therefore be an important step toward limiting the duration of staphylococci infections in clinical practice.

The SaeRS Two-Component System Controls Survival of Staphylococcus aureus in Human Blood through Regulation of Coagulase

The SaeRS two-component system plays important roles in regulation of key virulence factors and pathogenicity. In this study, however, we found that the deletion mutation of saeRS enhanced bacterial survival in human blood, whereas complementation of the mutant with SaeRS returned survival to wild-type levels. Moreover, these phenomena were observed in different MRSA genetic background isolates, including HA-MRSA WCUH29, CA-MRSA 923, and MW2. To elucidate which gene(s) regulated by SaeRS contribute to the effect, we conducted a series of complementation studies with selected known SaeRS target genes in trans. We found coagulase complementation abolished the enhanced survival of the SaeRS mutant in human blood. The coa and saeRS deletion mutants exhibited a similar survival phenotype in blood. Intriguingly, heterologous expression of coagulase decreased survival of S. epidermidis in human blood. Further, the addition of recombinant coagulase to blood significantly decreased the survival of S. aureus. Further, analysis revealed staphylococcal resistance to killing by hydrogen peroxide was partially dependent on the presence or absence of coagulase. Furthermore, complementation with coagulase, but not SaeRS, returned saeRS/coa double mutant survival in blood to wild-type levels. These data indicate SaeRS modulates bacterial survival in blood in coagulase-dependent manner. Our results provide new insights into the role of staphylococcal SaeRS and coagulase on bacterial survival in human blood.

Growth and adherence of Staphylococcus aureus were enhanced through the PGE2 produced by the activated COX-2/PGE2 pathway of infected oral epithelial cells

Staphylococcus aureus is a major pathogen of varieties of oral mucous infection. Prostaglandin E2 (PGE₂) is a pro-inflammatory factor and Cyclooxygenase 2 (COX-2) is a critical enzyme of PGE₂ biosynthesis. The purpose of this study is to investigate whether Staphylococcus aureus can increase PGE₂ production of oral epithelial cells and how PGE₂ functions in the growth and adherence of Staphylococcus aureus. mRNA levels of COX-2, fnbpA and fnbpB were estimated by quantitative PCR. PGE₂ production was measured by Enzyme Linked Immunosorbent Assay (ELISA). The binding biomass of Staphylococcus aureus to human fibronectin was investigated by crystal violet staining and confocal laser scanning microscopy and the adherent force was measured by atomic force microscope (AFM). The COX-2 mRNA level and PGE₂ production were increased by Staphylococcus aureus. PGE₂ promoted the growth and biofilm formation of Staphylococcus aureus, enhanced the attachment of Staphylococcus aureus to the human fibronectin as well as to the HOK cells. The transcription of fnbpB was up-regulated by PGE₂ in both early and middle exponential phase but not fnbpA. These results suggest that the activation of COX-2/PGE₂ pathway in oral epithelial cell by Staphylococcus aureus can in turn facilitate the growth and the ability to adhere of the pathogen. These findings uncover a new function of PGE₂ and may lead to the potential of COX-2/PGE₂ targeting in the therapy of inflammation and cancer in both which the COX-2/PGE₂ pathway were observed activated.

Tet38 Efflux Pump Affects Staphylococcus aureus Internalization by Epithelial Cells through Interaction with CD36 and Contributes to Bacterial Escape from Acidic and Nonacidic Phagolysosomes

We previously reported that the Tet38 efflux pump is involved in internalization of Staphylococcus aureus by A549 lung epithelial cells. A lack of tet38 reduced bacterial uptake by A549 cells to 36% of that of the parental strain RN6390. Using invasion assays coupled with confocal microscopy imaging, we studied the host cell receptor(s) responsible for bacterial uptake via interaction with Tet38. We also assessed the ability of S. aureus to survive following alkalinization of the phagolysosomes by chloroquine. Antibody to the scavenger receptor CD36 reduced the internalization of S. aureus RN6390 by A549 cells, but the dependence on CD36 was reduced in QT7 tet38, suggesting that an interaction between Tet38 and CD36 contributed to S. aureus internalization. Following fusion of the S. aureus-associated endosomes with lysosomes, alkalinization of the acidic environment with chloroquine led to a rapid increase in the number of S. aureus RN6390 bacteria in the cytosol, followed by a decrease shortly thereafter. This effect of chloroquine was not seen in the absence of intact Tet38 in mutant QT7. These data taken together suggest that Tet38 plays a role both in bacterial internalization via interaction with CD36 and in bacterial escape from the phagolysosomes.

Non-classical effects of prolactin on the innate immune response of bovine mammary epithelial cells: Implications during Staphylococcus aureus internalization

Staphylococcus aureus has the ability to invade mammary epithelial cells (bMECs) causing mastitis. This event depends primarily on the α5β1 integrin in the host cell. In addition, bMECs are a target for the hormone prolactin (PRL), which can regulate β1 integrin-dependent actions related to differentiation and lactation. Previously, we demonstrated that bovine PRL (bPRL, 5 ng/ml) stimulates S. aureus internalization into bMECs. TLR2 is important during S. aureus infections, but its activation by PRL has not yet been established. The objective of this study was to determine the role of α5β1 integrin and TLR2 during S. aureus internalization into bMECs stimulated with bPRL. We demonstrated that the prolactin-stimulated internalization of S. aureus decreases in response to the blockage of α5β1 integrin (∼ 80%) and TLR2 (∼ 80%). bPRL increases the membrane abundance (MA) of α5β1 integrin (∼ 20%) and induces TLR2 MA (∼ 2-fold). S. aureus reduces the α5β1 integrin MA in bMECs treated with bPRL (∼ 75%) but induces TLR2 MA in bMECs (∼ 3-fold). Bacteria and bPRL did not modify TLR2 MA compared with the hormone alone. S. aureus induces the activation of the transcription factor AP-1, which was inhibited in bMECs treated with bPRL and infected. In general, bPRL induces both pro- and anti-inflammatory responses in bMECs, which are abated in response to bacterial challenge. Interestingly, the canonical Stat-5 transcription factor was not activated in the challenged bMECs and/or treated with bPRL. Taken together, these results support novel functions of prolactin as a modulator of the innate immune response that do not involve the classical prolactin pathway.

The νSaα Specific Lipoprotein Like Cluster (lpl) of S. aureus USA300 Contributes to Immune Stimulation and Invasion in Human Cells

All Staphylococcus aureus genomes contain a genomic island, which is termed νSaα and characterized by two clusters of tandem repeat sequences, i.e. the exotoxin (set) and 'lipoprotein-like' genes (lpl). Based on their structural similarities the νSaα islands have been classified as type I to IV. The genomes of highly pathogenic and particularly epidemic S. aureus strains (USA300, N315, Mu50, NCTC8325, Newman, COL, JH1 or JH9) belonging to the clonal complexes CC5 and CC8 bear a type I νSaα island. Since the contribution of the lpl gene cluster encoded in the νSaα island to virulence is unclear to date, we deleted the entire lpl gene cluster in S. aureus USA300. The results showed that the mutant was deficient in the stimulation of pro-inflammatory cytokines in human monocytes, macrophages and keratinocytes. Purified lipoprotein Lpl1 was further shown to elicit a TLR2-dependent response. Furthermore, heterologous expression of the USA300 lpl cluster in other S. aureus strains enhanced their immune stimulatory activity. Most importantly, the lpl cluster contributed to invasion of S. aureus into human keratinocytes and mouse skin and the non-invasive S. carnosus expressing the lpl gene cluster became invasive. Additionally, in a murine kidney abscess model the bacterial burden in the kidneys was higher in wild type than in mutant mice. In this infection model the lpl cluster, thus, contributes to virulence. The present report is one of the first studies addressing the role of the νSaα encoded lpl gene cluster in staphylococcal virulence. The finding that the lpl gene cluster contributes to internalization into non-professional antigen presenting cells such as keratinocytes highlights the lpl as a new cell surface component that triggers host cell invasion by S. aureus. Increased invasion in murine skin and an increased bacterial burden in a murine kidney abscess model suggest that the lpl gene cluster serves as an important virulence factor.

Highly pathogenic and epidemic Staphylococcus aureus strains carry a pathogenicity island in their genome that contains a cluster of lipoprotein-encoding genes termed lpl. As the role lpl in virulence is still unclear, we deleted the entire lpl cluster in the community-acquired methicillin-resistant S. aureus (CA-MRSA) USA300 and found that the mutant was defective in stimulation of pro-inflammatory cytokines in human immune cells. Moreover, the major finding highlighted in this study is that the lpl cluster contributes to invasion into non-professional phagocytes such as epithelial cells and keratinocytes. Furthermore, the lpl-dependent increase in invasive activity, most likely, accounts for the enhanced bacterial burden observed in a murine kidney abscess model. In general, internalization of a pathogen into host epithelial cells shields the pathogen from immune defense and antibiotic treatment. However, further investigation is needed to clarify whether the increased ability to invade host cells is responsible for the potent disseminative activity and hypervirulent phenotype characterizing the νSaα type I island expressing S. aureus strains, including the USA300 CA-MRSA strain.

Super-infection with Staphylococcus aureus inhibits influenza virus-induced type I IFN signalling through impaired STAT1-STAT2 dimerization

Bacterial super-infections are a major complication in influenza virus-infected patients. In response to infection with influenza viruses and bacteria, a complex interplay of cellular signalling mechanisms is initiated, regulating the anti-pathogen response but also pathogen-supportive functions. Here, we show that influenza viruses replicate to a higher efficiency in cells co-infected with Staphylococcus aureus (S. aureus). While cells initially respond with increased induction of interferon beta upon super-infection, subsequent interferon signalling and interferon-stimulated gene expression are rather impaired due to a block of STAT1-STAT2 dimerization. Thus, S. aureus interrupts the first line of defence against influenza viruses, resulting in a boost of viral replication, which may lead to enhanced viral pathogenicity.

Fibronectin-degrading activity of Trypanosoma cruzi cysteine proteinase plays a role in host cell invasion

Trypanosoma cruzi, the agent of Chagas disease, binds to diverse extracellular matrix proteins. Such an ability prevails in the parasite forms that circulate in the bloodstream and contributes to host cell invasion. Whether this also applies to the insect-stage metacyclic trypomastigotes, the developmental forms that initiate infection in the mammalian host, is not clear. Using T. cruzi CL strain metacyclic forms, we investigated whether fibronectin bound to the parasites and affected target cell invasion. Fibronectin present in cell culture medium bound to metacyclic forms and was digested by cruzipain, the major T. cruzi cysteine proteinase. G strain, with negligible cruzipain activity, displayed a minimal fibronectin-degrading effect. Binding to fibronectin was mediated by gp82, the metacyclic stage-specific surface molecule implicated in parasite internalization. When exogenous fibronectin was present at concentrations higher than cruzipain can properly digest, or fibronectin expression was stimulated by treatment of epithelial HeLa cells with transforming growth factor beta, the parasite invasion was reduced. Treatment of HeLa cells with purified recombinant cruzipain increased parasite internalization, whereas the treatment of parasites with cysteine proteinase inhibitor had the opposite effect. Metacyclic trypomastigote entry into HeLa cells was not affected by anti-β1 integrin antibody but was inhibited by anti-fibronectin antibody. Overall, our results have indicated that the cysteine proteinase of T. cruzi metacyclic forms, through its fibronectin-degrading activity, is implicated in host cell invasion.

Surface adhesins and exopolymers of selected foodborne pathogens

The ability of bacteria to bind different compounds and to adhere to biotic and abiotic surfaces provides them with a range of advantages, such as colonization of various tissues, internalization, avoidance of an immune response, and survival and persistence in the environment. A variety of bacterial surface structures are involved in this process and these promote bacterial adhesion in a more or less specific manner. In this review, we will focus on those surface adhesins and exopolymers in selected foodborne pathogens that are involved mainly in primary adhesion. Their role in biofilm development will also be considered when appropriate. Both the clinical impact and the implications for food safety of such adhesion will be discussed.

Bacteriophage as effective decolonising agent for elimination of MRSA from anterior nares of BALB/c mice

BACKGROUND

Nasal carriers not only pose serious threat to themselves but also to the community by playing an active role in the dissemination of serious and life threatening S. aureus especially MRSA strains. The present study focuses on the use of broad spectrum lytic phage as decolonising agent. In addition, the combined use of lytic phage with mupirocin has also been investigated as an effective decolonising regimen. The effect of phage on the adherence, invasion and cytotoxic effect of MRSA strains on nasal epithelial cells was studied in an ex-vivo model of cultured murine nasal epithelial cells. This was followed by demonstration of therapeutic potential of phage along with mupirocin in decolonising the nares of BALB/c mice using a nasal model of MRSA colonisation.

RESULTS

Phage was able to significantly reduce the in vitro adherence, invasion and cytotoxicity of MRSA 43300 as well as other clinical MRSA strains on murine nasal epithelial cells as compared to untreated control. Also, the frequency of emergence of spontaneous mutants decreased to negligible levels when both the agents (phage and mupirocin) were used together.

CONCLUSION

Phage MR-10, given along with mupirocin showed an additive effect and the combination was able to effectively eradicate the colonising MRSA population from the nares of mice by day 5.

Nonprofessional phagocytic cell receptors involved in Staphylococcus aureus internalization

Staphylococcus aureus is a successful human and animal pathogen. The majority of infections caused by this pathogen are life threatening, primarily because S. aureus has developed multiple evasion strategies, possesses intracellular persistence for long periods, and targets the skin and soft tissues. Therefore, it is very important to understand the mechanisms employed by S. aureus to colonize and proliferate in these cells. The aim of this review is to describe the recent discoveries concerning the host receptors of nonprofessional phagocytes involved in S. aureus internalization. Most of the knowledge related to the interaction of S. aureus with its host cells has been described in professional phagocytic cells such as macrophages. Here, we showed that in nonprofessional phagocytes the α 5 β 1 integrin host receptor, chaperons, and the scavenger receptor CD36 are the main receptors employed during S. aureus internalization. The characterization and identification of new bacterial effectors and the host cell receptors involved will undoubtedly lead to new discoveries with beneficial purposes.

BsaB, a novel adherence factor of group B Streptococcus

Streptococcus agalactiae (group B Streptococcus [GBS]) is a leading cause of neonatal sepsis and meningitis, peripartum infections in women, and invasive infections in chronically ill or elderly individuals. GBS can be isolated from the gastrointestinal or genital tracts of up to 30% of healthy adults, and infection is thought to arise from invasion from a colonized mucosal site. Accordingly, bacterial surface components that mediate attachment of GBS to host cells or the extracellular matrix represent key factors in the colonization and infection of the human host. We identified a conserved GBS gene of unknown function that was predicted to encode a cell wall-anchored surface protein. Deletion of the gene and a cotranscribed upstream open reading frame (ORF) in GBS strain 515 reduced bacterial adherence to VK2 vaginal epithelial cells in vitro and reduced GBS binding to fibronectin-coated microtiter wells. Expression of the gene product in Lactococcus lactis conferred the ability to adhere to VK2 cells, to fibronectin and laminin, and to fibronectin-coated ME-180 cervical epithelial cells. Expression of the recombinant protein in L. lactis also markedly increased biofilm formation. The adherence function of the protein, named bacterial surface adhesin of GBS (BsaB), depended both on a central BID1 domain found in bacterial intimin-like proteins and on the C-terminal portion of the BsaB protein. Expression of BsaB in GBS, like that of several other adhesins, was regulated by the CsrRS two-component system. We conclude that BsaB represents a newly identified adhesin that participates in GBS attachment to epithelial cells and the extracellular matrix.

The Staphylococcus aureus extracellular adherence protein promotes bacterial internalization by keratinocytes independent of fibronectin-binding proteins

Staphylococcus aureus, the leading causal pathogen of skin infections, is strongly associated with skin atopy, and a number of bacterial adhesins allow the microbe to adhere to and invade eukaryotic cells. One of these adhesive molecules is the multifunctional extracellular adherence protein (Eap), which is overexpressed in situ in authentic human wounds and was shown to delay wound healing in experimental models. Yet, its role during invasion of keratinocytes is not clearly defined. By using a gentamicin/lysostaphin protection assay we demonstrate here that preincubation of HaCaT cells or primary keratinocytes with Eap results in a concentration-dependent significant increase in staphylococcal adhesion, followed by an even more pronounced internalization of bacteria by eukaryotic cells. Flow cytometric analysis revealed that Eap increased both the number of infected eukaryotic cells and the bacterial load per infected cell. Moreover, treatment of keratinocytes with Eap strongly enhanced the internalization of coagulase-negative staphylococci, as well as of E. coli, and markedly promoted staphylococcal invasion into extended-culture keratinocytes, displaying expression of keratin 10 and involucrin as differentiation markers. Thus, wound-related staphylococcal Eap may provide a major cellular invasin function, thereby enhancing the pathogen's ability to hide from the host immune system during acute and chronic skin infection.

In vitro and in vivo characterization of DNA delivery using recombinant Lactococcus lactis expressing a mutated form of L. monocytogenes Internalin A

Background

The use of food-grade Lactic Acid Bacteria (LAB) as DNA delivery vehicles represents an attractive strategy to deliver DNA vaccines at the mucosal surfaces as they are generally regarded as safe (GRAS). We previously showed that either native Lactococcus lactis (LL) or recombinant invasive LL expressing Fibronectin Binding Protein A of Staphylococcus aureus (LL-FnBPA+) or Internalin A of Listeria monocytogenes (LL-InlA+), were able to deliver and trigger DNA expression by epithelial cells, either in vitro or in vivo. InlA does not bind to its receptor, the murine E-cadherin, thus limiting the use of LL-InlA+ in in vivo murine models. Moreover, FnBPA binds to its receptors, integrins, via fibronectin introducing another limiting factor. In order to avoid the limitations of LL-InlA+ and LL-FnBPA+, a new L. lactis strain was engineered to produce a previously described mutated form of InlA (LL-mInlA+) allowing the binding of mInlA on murine E-cadherin.

Results

After showing the expression of mInLA at the surface of LL-mInlA+ strain, in vitro gentamycin survival assay in Caco-2 cells showed that LL-mInlA+ is 1000 times more invasive than LL. LL-mInlA+ invasivity was also validated by fluorescence microscopy. LL and LL-mInlA+ were transformed with pValacBLG, a plasmid containing the cDNA of bovine β-Lactoglobulin (BLG), resulting in strains LL-BLG and LL-mInlA+BLG. The plasmid transfer in vitro using LL-mInlA+BLG was increased 10 times compared to LL-BLG. Moreover, the number of mice producing BLG in isolated enterocytes after oral administration of LL-mInlA+BLG in vivo was slightly higher than after oral administration of LL-BLG.

Conclusions

We confirmed in this study that the production of mInlA at the surface of L. lactis is a promising strategy for plasmid transfer in vitro and in vivo.

Interactions of Staphylococci with Osteoblasts and Phagocytes in the Pathogenesis of Implant-Associated Osteomyelitis

In spite of great advancements in the field of biomaterials and in surgical techniques, the implant of medical devices is still associated with a high risk of bacterial infection. Implant-associated osteomyelitis is a deep infection of bone around the implant. The continuous inflammatory destruction of bone tissues characterizes this serious bone infectious disease. Staphylococcus aureus and Staphylococcus epidermidis are the most prevalent etiologic agents of implant-associated infections, together with the emerging pathogen Staphylococcus lugdunensis. Various interactions between staphylococci, osteoblasts, and phagocytes occurring in the peri-prosthesis environment play a crucial role in the pathogenesis of implant-associated osteomyelitis. Here we focus on two main events: internalization of staphylococci into osteoblasts, and bacterial interactions with phagocytic cells.

Production of Fibronectin Binding Protein A at the surface of Lactococcus lactis increases plasmid transfer in vitro and in vivo

Lactococci are noninvasive lactic acid bacteria frequently used as protein delivery vectors and, more recently, as DNA delivery vehicles. We previously showed that Lactococcus lactis (LL) expressing the Fibronectin-Binding Protein A of Staphylococcus aureus (LL-FnBPA+) showed higher internalization rates in vitro in Caco-2 cells than the native (wt) lactococci and were able to deliver a eukaryotic Green Fluorescent Protein (GFP) expression plasmid in 1% of human Caco-2 cells. Here, using the bovine beta-lactoglobulin (BLG), one of the major cow's milk allergen, and GFP we characterized the potential of LL-FnBPA+ as an in vivo DNA vaccine delivery vehicle. We first showed that the invasive strain LL-FnBPA+ carrying the plasmid pValac:BLG (LL-FnBPA+ BLG) was more invasive than LL-BLG and showed the same invasivity as LL-FnBPA+. Then we demonstrated that the Caco-2 cells, co-incubated with LL-FnBPA+ BLG produced up to 30 times more BLG than the Caco-2 cells co-incubated with the non invasive LL-BLG. Using two different gene reporters, BLG and GFP, and two different methods of detection, EIA and fluorescence microscopy, we showed in vivo that: i) in order to be effective, LL-FnBPA+ required a pre-coating with Fetal Calf Serum before oral administration; ii) plasmid transfer occurred in enterocytes without regard to the strains used (invasive or not); iii) the use of LL-FnBPA+ increased the number of mice producing BLG, but not the level of BLG produced. We thus confirmed the good potential of invasive recombinant lactic acid bacteria as DNA delivery vector in vivo.

Differential adhesion and invasion by Staphylococcus aureus of epithelial cells derived from different anatomical sites

Staphylococcus aureus can invade epithelial cells, and the host-cell receptor α(5)β(1) integrin is thought to mediate this process. The aim of this study was to investigate S. aureus invasion of epithelial cell lines derived from oral (H357), skin (UP) and nasopharyngeal (Detroit 562) sites and to determine whether any differences were due to the levels of α(5)β(1) integrin expressed. While the adhesion and invasion of two S. aureus strains were similar in both oral and skin-derived keratinocytes, this was markedly reduced in the nasopharyngeal cell line, despite it expressing similar levels of α(5)β(1). While this might be explainable on the basis of availability of cell receptor, adhesion to and invasion of H357 and UP cells by S. aureus were enhanced when the epithelial cells were in suspension rather than on a surface, and levels of α(5) integrin subunit mRNA were also increased. Detroit 562 cells exhibited a similar α(5) gene upregulation, but this did not result in enhanced adhesion and invasion of S. aureus. The Detroit 562 cells also showed reduced adhesion to fibronectin compared with the other cell types. This, and the low S. aureus invasion, may result from reduced α(5)β(1) integrin activity or from variation in an as-yet-unidentified additional receptor or accessory molecule. These studies shed further light on the mechanisms of S. aureus invasion of human cells.

Staphylococcus aureus protein A plays a critical role in mediating bone destruction and bone loss in osteomyelitis

Staphylococcus aureus is the most frequent causative organism of osteomyelitis. It is characterised by widespread bone loss and bone destruction. Previously we demonstrated that S. aureus protein A (SpA) is capable of binding to tumour necrosis factor receptor-1 expressed on pre-osteoblastic cells, which results in signal generation that leads to cell apoptosis resulting in bone loss. In the current report we demonstrate that upon S. aureus binding to osteoblasts it also inhibits de novo bone formation by preventing expression of key markers of osteoblast growth and division such as alkaline phosphatase, collagen type I, osteocalcin, osteopontin and osteocalcin. In addition, S. aureus induces secretion of soluble RANKL from osteoblasts which in turn recruits and activates the bone resorbing cells, osteoclasts. A strain of S. aureus defective in SpA failed to affect osteoblast growth or proliferation and most importantly failed to recruit or activate osteoclasts. These results suggest that S. aureus SpA binding to osteoblasts provides multiple coordinated signals that accounts for bone loss and bone destruction seen in osteomyelitis cases. A better understanding of the mechanisms through which S. aureus leads to bone infection may improve treatment or lead to the development of better therapeutic agents to treat this notoriously difficult disease.

Intracellular Staphylococcus aureus: live-in and let die

Staphylococcus aureus uses a plethora of virulence factors to accommodate a diversity of niches in its human host. Aside from the classical manifestations of S. aureus-induced diseases, the pathogen also invades and survives within mammalian host cells.The survival strategies of the pathogen are as diverse as strains or host cell types used. S. aureus is able to replicate in the phagosome or freely in the cytoplasm of its host cells. It escapes the phagosome of professional and non-professional phagocytes, subverts autophagy, induces cell death mechanisms such as apoptosis and pyronecrosis, and even can induce anti-apoptotic programs in phagocytes. The focus of this review is to present a guide to recent research outlining the variety of intracellular fates of S. aureus.