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

Alpha-hemolysin promotes internalization of Staphylococcus aureus into human lung epithelial cells via caveolin-1- and cholesterol-rich lipid rafts

Staphylococcus aureus is a pathogen associated with severe respiratory infections. The ability of S. aureus to internalize into lung epithelial cells complicates the treatment of respiratory infections caused by this bacterium. In the intracellular environment, S. aureus can avoid elimination by the immune system and the action of circulating antibiotics. Consequently, interfering with S. aureus internalization may represent a promising adjunctive therapeutic strategy to enhance the efficacy of conventional treatments. Here, we investigated the host-pathogen molecular interactions involved in S. aureus internalization into human lung epithelial cells. Lipid raft-mediated endocytosis was identified as the main entry mechanism. Thus, bacterial internalization was significantly reduced after the disruption of lipid rafts with methyl-β-cyclodextrin. Confocal microscopy confirmed the colocalization of S. aureus with lipid raft markers such as ganglioside GM1 and caveolin-1. Adhesion of S. aureus to α5β1 integrin on lung epithelial cells via fibronectin-binding proteins (FnBPs) was a prerequisite for bacterial internalization. A mutant S. aureus strain deficient in the expression of alpha-hemolysin (Hla) was significantly impaired in its capacity to enter lung epithelial cells despite retaining its capacity to adhere. This suggests a direct involvement of Hla in the bacterial internalization process. Among the receptors for Hla located in lipid rafts, caveolin-1 was essential for S. aureus internalization, whereas ADAM10 was dispensable for this process. In conclusion, this study supports a significant role of lipid rafts in S. aureus internalization into human lung epithelial cells and highlights the interaction between bacterial Hla and host caveolin-1 as crucial for the internalization process.

Innovative nebulization delivery of lipid nanoparticle-encapsulated siRNA: a therapeutic advance for Staphylococcus aureus-induced pneumonia

BACKGROUND

Integrin α5β1 plays a crucial role in the invasion of nonphagocytic cells by Staphylococcus aureus (S. aureus), thereby facilitating infection development. Lipid nanoparticles (LNPs) serve as an effective vehicle for delivering small interfering ribonucleic acids (siRNA) that represent a method to knockdown integrin α5β1 in the lungs through nebulization, thereby potentially mitigating the severity of S. aureus pneumonia. The aim of this study was to harness LNP-mediated targeting to precisely knockdown integrin α5β1, thus effectively addressing S. aureus-induced pneumonia.

METHODS

C57 mice (8 week-old females) infected with S. aureus via an intratracheal nebulizing device were utilized for the experiments. The LNPs were synthesized via microfluidic mixing and characterized by their size, polydispersity index, and encapsulation efficiency. Continuous intratracheal nebulization was employed for consistent siRNA administration, with the pulmonary function metrics affirming biosafety. The therapeutic efficacy of LNP-encapsulated siRNAs against pneumonia was assessed through western blotting, bacterial count measurement, quantitative polymerase chain reaction, and histological analyses.

RESULTS

LNPs, which have an onion-like structure, retained integrity post-nebulization, ensuring prolonged siRNA stability and in vivo safety. Intratracheal nebulization delivery markedly alleviated the severity of S. aureus-induced pneumonia, as indicated by reduced bacterial load and bolstered immune response, thereby localizing the infection to the lungs and averting systemic dissemination.

CONCLUSIONS

Intratracheal nebulization of LNP-encapsulated siRNAs targeting integrin α5β1 significantly diminished the S. aureus-mediated cellular invasion and disease progression in the lungs, presenting a viable therapeutic approach for respiratory infections.

In silico testing to identify compounds that inhibit ClfA and ClfB binding to the host for the formulation of future drugs against Staphylococcus aureus colonization and infection

Introduction

Staphylococcus aureus is a highly resistant pathogen. It has multiple virulence factors, which makes it one of the most pathogenic bacteria for humankind. The vast increase in antibiotic resistance in these bacteria is a warning of existing healthcare policies. Most of the available antibiotics are ineffective due to resistance; this situation requires the development of drugs that target specific proteins and are not susceptible to resistance.

Methods

In this study, we identified a compound that acts as an antagonist of ClfA and ClfB by inhibiting their binding to host cells.

Results

The shortlisted compound's binding activity was tested by docking and molecular dynamics during its interaction with proteins. The identified compound has excellent binding energy with both ClfA (-10.11 kcal/mol) and ClfB (-11.11 kcal/mol).

Discussion

The molecular dynamics of the protein and compound were stable and promising for further in vitro and in vivo tests. The performance of our compound was tested and compared with that of the control molecule allantodapsone, which was reported in a previous study as a pan inhibitor of the clumping factor. An ADMET study of our selected compound revealed its reliable drug likeliness. This compound is an ideal candidate for in vitro studies.

Antimicrobial Biomaterials Based on Physical and Physicochemical Action

Developing effective antimicrobial biomaterials is a relevant and fast-growing field in advanced healthcare materials. Several well-known (e.g., traditional antibiotics, silver, copper etc.) and newer (e.g., nanostructured, chemical, biomimetic etc.) approaches have been researched and developed in recent years and valuable knowledge has been gained. However, biomaterials associated infections (BAIs) remain a largely unsolved problem and breakthroughs in this area are sparse. Hence, novel high risk and potential high gain approaches are needed to address the important challenge of BAIs. Antibiotic free antimicrobial biomaterials that are largely based on physical action are promising, since they reduce the risk of antibiotic resistance and tolerance. Here, selected examples are reviewed such antimicrobial biomaterials, namely switchable, protein-based, carbon-based and bioactive glass, considering microbiological aspects of BAIs. The review shows that antimicrobial biomaterials mainly based on physical action are powerful tools to control microbial growth at biomaterials interfaces. These biomaterials have major clinical and application potential for future antimicrobial healthcare materials without promoting microbial tolerance. It also shows that the antimicrobial action of these materials is based on different complex processes and mechanisms, often on the nanoscale. The review concludes with an outlook and highlights current important research questions in antimicrobial biomaterials.

Staphylococcus capitis: insights into epidemiology, virulence, and antimicrobial resistance of a clinically relevant bacterial species

SUMMARYStaphylococcus capitis is divided into two subspecies, S. capitis subsp. ureolyticus (renamed urealyticus in 1992; ATCC 49326) and S. capitis subsp. capitis (ATCC 27840), and fits with the archetype of clinically relevant coagulase-negative staphylococci (CoNS). S. capitis is a commensal bacterium of the skin in humans, which must be considered an opportunistic pathogen of interest particularly as soon as it is identified in a clinically relevant specimen from an immunocompromised patient. Several studies have highlighted the potential determinants underlying S. capitis pathogenicity, resistance profiles, and virulence factors. In addition, mobile genetic element acquisitions and mutations contribute to S. capitis genome adaptation to its environment. Over the past decades, antibiotic resistance has been identified for S. capitis in almost all the families of the currently available antibiotics and is related to the emergence of multidrug-resistant clones of high clinical significance. The present review summarizes the current knowledge concerning the taxonomic position of S. capitis among staphylococci, the involvement of this species in human colonization and diseases, the virulence factors supporting its pathogenicity, and the phenotypic and genomic antimicrobial resistance profiles of this species.

Blockade of interleukin-13 signalling improves skin barrier function and biology in patients with moderate-to-severe atopic dermatitis

BACKGROUND

Interleukin (IL)-13 is a key driver of inflammation and barrier dysfunction in atopic dermatitis (AD). While there is robust evidence that tralokinumab - a monoclonal antibody that neutralizes IL-13 - reduces inflammation and clinical disease activity, less is known about its effects on barrier function.

OBJECTIVES

To characterize the effects of tralokinumab treatment on skin barrier function.

METHODS

Transepidermal water loss (TEWL), stratum corneum hydration (SCH), natural moisturizing factor content, histopathological characteristics, biomarker expression and microbiome composition were evaluated in lesional, nonlesional and sodium lauryl sulfate-irritated skin of 16 patients with AD over the course of 16 weeks of tralokinumab treatment.

RESULTS

All clinical severity scores decreased significantly over time. At week 16, mean TEWL in target lesions decreased by 33% (P = 0.01) and SCH increased by 58% (P = 0.004), along with a histological reduction in spongiosis (P = 0.003), keratin 16 expression and epidermal thickness (P = 0.001). In parallel, there was a significant decrease in several barrier dysfunction-associated and proinflammatory proteins such as fibronectin (P = 0.006), CCL17/TARC (P = 0.03) and IL-8 (P = 0.01), with significant changes seen as early as week 8. Total bacterial load and Staphylococcus aureus abundance were significantly reduced from week 2.

CONCLUSIONS

Tralokinumab treatment improved skin physiology, epidermal pathology and dysbiosis, further highlighting the pleiotropic role of IL-13 in AD pathogenesis.

Cell-wall-anchored proteins affect invasive host colonization and biofilm formation in Staphylococcus aureus

As a major human and animal pathogen, Staphylococcus aureus can attach to medical implants (abiotic surface) or host tissues (biotic surface), and further establish robust biofilms which enhances resistance and persistence to host immune system and antibiotics. Cell-wall-anchored proteins (CWAPs) covalently link to peptidoglycan, and largely facilitate the colonization of S. aureus on various surfaces (including adhesion and biofilm formation) and invasion into host cells (including adhesion, immune evasion, iron acquisition and biofilm formation). During biofilm formation, CWAPs function in adhesion, aggregation, collagen-like fiber network formation, and consortia formation. In this review, we firstly focus on the structural features of CWAPs, including their intracellular function and interactions with host cells, as well as the functions and ligand binding of CWAPs in different stages of S. aureus biofilm formation. Then, the roles of CWAPs in different biofilm processes with regards in development of therapeutic approaches are clarified, followed by the association between CWAPs genes and clonal lineages. By touching upon these aspects, we hope to provide comprehensive knowledge and clearer understanding on the CWAPs of S. aureus and their roles in biofilm formation, which may further aid in prevention and treatment infection and vaccine development.

Differential role of M cells in enteroid infection by Mycobacterium avium subsp. paratuberculosis and Salmonella enterica serovar Typhimurium

Infection of ruminants such as cattle with Mycobacterium avium subsp. paratuberculosis (MAP) causes Johne's disease, a disease characterized by chronic inflammation of the small intestine and diarrhoea. Infection with MAP is acquired via the faecal-to-oral route and the pathogen initially invades the epithelial lining of the small intestine. In this study we used an in vitro 3D mouse enteroid model to determine the influence of M cells in infection of the gut epithelia by MAP, in comparison with another bacterial intestinal pathogen of veterinary importance, Salmonella enterica serovar Typhimurium. The differentiation of M cells in the enteroid cultures was induced by stimulation with the cytokine receptor activator of nuclear factor-κB ligand (RANKL), and the effects on MAP and Salmonella uptake and intracellular survival were determined. The presence of M cells in the cultures correlated with increased uptake and intracellular survival of Salmonella, but had no effect on MAP. Interestingly neither pathogen was observed to preferentially accumulate within GP2-positive M cells.

Exploring the Relationship between MicroRNAs, Intratumoral Microbiota, and Breast Cancer Progression in Patients with and without Metastasis

Breast cancer (BC) continues to pose a significant burden on global cancer-related morbidity and mortality, primarily driven by metastasis. However, the combined influence of microRNAs (miRNAs) and intratumoral microbiota on BC metastasis remains largely unexplored. In this study, we aimed to elucidate the interplay between intratumoral microbiota composition, miRNA expression profiles, and their collective influence on metastasis development in BC patients by employing 16S rRNA sequencing and qPCR methodologies. Our findings revealed an increase in the expression of miR-149-5p, miR-20b-5p, and miR-342-5p in metastatic breast cancer (Met-BC) patients. The Met-BC patients exhibited heightened microbial richness and diversity, primarily attributed to diverse pathogenic bacteria. Taxonomic analysis identified several pathogenic and pro-inflammatory species enriched in Met-BC, contrasting with non-metastatic breast cancer (NonMet-BC) patients, which displayed an enrichment in potential probiotic and anti-inflammatory species. Notably, we identified and verified a baseline prognostic signature for metastasis in BC patients, with its clinical relevance further validated by its impact on overall survival. In conclusion, the observed disparities in miRNA expression and species-level bacterial abundance suggest their involvement in BC progression. The development of a prognostic signature holds promise for metastasis risk assessment, paving the way for personalized interventions and improved clinical outcomes in BC patients.

Contribution of staphylococcal virulence factors in the pathogenesis of thrombosis

Staphylococci are responsible for many infections in humans, starting with skin and soft tissue infections and finishing with invasive diseases such as endocarditis, sepsis and pneumonia, which lead to high mortality. Patients with sepsis often demonstrate activated clotting pathways, decreased levels of anticoagulants, decreased fibrinolysis, activated endothelial surfaces and activated platelets. This results in disseminated intravascular coagulation and formation of a microthrombus, which can lead to a multiorgan failure. This review describes various staphylococcal virulence factors that contribute to vascular thrombosis, including deep vein thrombosis in infected patients. The article presents mechanisms of action of different factors released by bacteria in various host defense lines, which in turn can lead to formation of blood clots in the vessels.

Staphylococcal mastitis in dairy cows

Bovine mastitis is one of the most common diseases of dairy cattle. Even though different infectious microorganisms and mechanical injury can cause mastitis, bacteria are the most common cause of mastitis in dairy cows. Staphylococci, streptococci, and coliforms are the most frequently diagnosed etiological agents of mastitis in dairy cows. Staphylococci that cause mastitis are broadly divided into Staphylococcus aureus and non-aureus staphylococci (NAS). NAS is mainly comprised of coagulase-negative Staphylococcus species (CNS) and some coagulase-positive and coagulase-variable staphylococci. Current staphylococcal mastitis control measures are ineffective, and dependence on antimicrobial drugs is not sustainable because of the low cure rate with antimicrobial treatment and the development of resistance. Non-antimicrobial effective and sustainable control tools are critically needed. This review describes the current status of S. aureus and NAS mastitis in dairy cows and flags areas of knowledge gaps.

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.

The phosphatidylinositol-5' phosphatase synaptojanin1 limits integrin-mediated invasion of Staphylococcus aureus

The gram-positive bacterium Staphylococcus aureus can invade non-professional phagocytic cells by associating with the plasma protein fibronectin to exploit host cell integrins. Integrin-mediated internalization of these pathogens is facilitated by the local production of phosphatidylinositol-4,5-bisphosphate (PI-4,5-P2) via an integrin-associated isoform of phosphatidylinositol-5' kinase. In this study, we addressed the role of PI-4,5-P2-directed phosphatases on internalization of S. aureus. ShRNA-mediated knockdown of individual phosphoinositide 5-phosphatases revealed that synaptojanin1 (SYNJ1) is counteracting invasion of S. aureus into mammalian cells. Indeed, shRNA-mediated depletion as well as genetic deletion of synaptojanin1 via CRISPR/Cas9 resulted in a gain-of-function phenotype with regard to integrin-mediated uptake. Surprisingly, the surface level of integrins was slightly downregulated in Synj1-KO cells. Nevertheless, these cells showed enhanced local accumulation of PI-4,5-P2 and exhibited increased internalization of S. aureus. While the phosphorylation level of the integrin-associated protein tyrosine kinase FAK was unaltered, the integrin-binding and -activating protein talin was enriched in the vicinity of S. aureus in synaptojanin1 knockout cells. Scanning electron microscopy revealed enlarged membrane invaginations in the absence of synaptojanin1 explaining the increased capability of these cells to internalize integrin-bound microorganisms. Importantly, the enhanced uptake by Synj1-KO cells and the exaggerated morphological features were rescued by the re-expression of the wild-type enzyme but not phosphatase inactive mutants. Accordingly, synaptojanin1 activity limits integrin-mediated invasion of S. aureus, corroborating the important role of PI-4,5-P2 during this process.IMPORTANCEStaphylococcus aureus, an important bacterial pathogen, can invade non-professional phagocytes by capturing host fibronectin and engaging integrin α5β1. Understanding how S. aureus exploits this cell adhesion receptor for efficient cell entry can also shed light on the physiological regulation of integrins by endocytosis. Previous studies have found that a specific membrane lipid, phosphatidylinositol-4,5-bisphosphate (PIP2), supports the internalization process. Here, we extend these findings and report that the local levels of PIP2 are controlled by the activity of the PIP2-directed lipid phosphatase Synaptojanin1. By dephosphorylating PIP2 at bacteria-host cell attachment sites, Synaptojanin1 counteracts the integrin-mediated uptake of the microorganisms. Therefore, our study not only generates new insight into subversion of cellular receptors by pathogenic bacteria but also highlights the role of host cell proteins acting as restriction factors for bacterial invasion at the plasma membrane.

A Staphylococcus epidermidis strain inhibits the uptake of Staphylococcus aureus derived from atopic dermatitis skin into the keratinocytes

BACKGROUND

Various bacterial species form a microbiome in the skin. In the past, dead Staphylococcus aureus derived from atopic dermatitis (AD) are taken up by keratinocytes; however, whether live S. aureus can be taken up by keratinocytes is unknown.

OBJECTIVE

This study aimed to examine whether live AD strains of S. aureus internalize into the keratinocytes and how the internalization changes under conditions in which other bacterial species including S. epidermidis are present.

METHODS

HaCaT cells were cultured with live S. aureus and S. epidermidis (live or heat-treated) or their culture supernatants. After coculture, the change in the amount of S. aureus in the cytoplasm of HaCaT cells was analyzed using, a high-throughput imaging system, Opera Phenix™.

RESULTS

Live S. aureus were taken up in the cytoplasm of HaCaT cells. Coculturing live S. aureus with live S. epidermidis or the culture supernatants decreased the abundance of S. aureus in the cytoplasm. The heat-treated culture supernatants of live S. epidermidis or culture supernatants of other S. strains did not decrease the abundance of S. aureus in the cytoplasm.

CONCLUSION

Live S. aureus was internalized into the cytoplasm of HaCaT cells as does heat-treated S. aureus. In addition, the heat-sensitive substances secreted by coculture with S. epidermidis and keratinocytes inhibited the uptake of S. aureus by keratinocytes.

Genomic features and pathophysiological impact of a multidrug-resistant Staphylococcus warneri variant in murine mastitis

Non-aureus staphylococci (NAS) represent a major etiological agent in dairy animal mastitis, yet their role and impact remain insufficiently studied. This study aimed to elucidate the genomic characteristics of a newly identified multidrug-resistant NAS strain, specifically Staphylococcus warneri G1M1F, isolated from murine feces in an experimental mastitis model. Surprisingly, NAS species accounted for 54.35 % of murine mastitis cases, with S. warneri being the most prevalent at 40.0 %. S. warneri G1M1F exhibited resistance to 10 major antibiotics. Whole-genome sequencing established a genetic connection between G1M1F and S. warneri strains isolated previously from various sources including mastitis milk in dairy animals, human feces and blood across diverse geographical regions. Genomic analysis of S. warneri G1M1F unveiled 34 antimicrobial resistance genes (ARGs), 30 virulence factor genes (VFGs), and 278 metabolic features. A significant portion of identified ARGs (64 %) conferred resistance through antibiotic efflux pumps, while VFGs primarily related to bacterial adherence and biofilm formation. Inoculation with G1M1F in mice resulted in pronounced inflammatory lesions in mammary and colon tissues, indicating pathogenic potential. Our findings highlight distinctive genomic traits in S. warneri G1M1F, signifying the emergence of a novel multidrug-resistant NAS variant. These insights contribute to understanding NAS-related mastitis pathophysiology and inform strategies for effective treatment in dairy animals.

Biofilm Producing Methicillin-Resistant Staphylococcus aureus (MRSA) Infections in Humans: Clinical Implications and Management

Since its initial description in the 1960s, methicillin-resistant Staphylococcus aureus (MRSA) has developed multiple mechanisms for antimicrobial resistance and evading the immune system, including biofilm production. MRSA is now a widespread pathogen, causing a spectrum of infections ranging from superficial skin issues to severe conditions like osteoarticular infections and endocarditis, leading to high morbidity and mortality. Biofilm production is a key aspect of MRSA's ability to invade, spread, and resist antimicrobial treatments. Environmental factors, such as suboptimal antibiotics, pH, temperature, and tissue oxygen levels, enhance biofilm formation. Biofilms are intricate bacterial structures with dense organisms embedded in polysaccharides, promoting their resilience. The process involves stages of attachment, expansion, maturation, and eventually disassembly or dispersion. MRSA's biofilm formation has a complex molecular foundation, involving genes like icaADBC, fnbA, fnbB, clfA, clfB, atl, agr, sarA, sarZ, sigB, sarX, psm, icaR, and srtA. Recognizing pivotal genes for biofilm formation has led to potential therapeutic strategies targeting elemental and enzymatic properties to combat MRSA biofilms. This review provides a practical approach for healthcare practitioners, addressing biofilm pathogenesis, disease spectrum, and management guidelines, including advances in treatment. Effective management involves appropriate antimicrobial therapy, surgical interventions, foreign body removal, and robust infection control practices to curtail spread within healthcare environments.

Eliminating the invading extracellular and intracellular FnBp+ bacteria from respiratory epithelial cells by autophagy mediated through FnBp-Fn-Integrin α5β1 axis

Background

We previously found that the respiratory epithelial cells could eliminate the invaded group A streptococcus (GAS) through autophagy induced by binding a fibronectin (Fn) binding protein (FnBp) expressed on the surface of GAS to plasma protein Fn and its receptor integrin α5β1 of epithelial cells. Is autophagy initiated by FnBp+ bacteria via FnBp-Fn-Integrin α5β1 axis a common event in respiratory epithelial cells?

Methods

We chose Staphylococcus aureus (S. aureus/S. a) and Listeria monocytogenes (L. monocytogenes/L. m) as representatives of extracellular and intracellular FnBp+ bacteria, respectively. The FnBp of them was purified and the protein function was confirmed by western blot, viable bacteria count, confocal and pull-down. The key molecule downstream of the action axis was detected by IP, mass spectrometry and bio-informatics analysis.

Results

We found that different FnBp from both S. aureus and L. monocytogenes could initiate autophagy through FnBp-Fn-integrin α5β1 axis and this could be considered a universal event, by which host tries to remove invading bacteria from epithelial cells. Importantly, we firstly reported that S100A8, as a key molecule downstream of integrin β1 chain, is highly expressed upon activation of integrin α5β1, which in turn up-regulates autophagy.

Conclusions

Various FnBp from FnBp+ bacteria have the ability to initiate autophagy via FnBp-Fn-Integrin α5β1 axis to promote the removal of invading bacteria from epithelial cells in the presence of fewer invaders. S100A8 is a key molecule downstream of Integrin α5β1 in this autophagy pathway.

Emerging novel sequence types of Staphylococcus aureus in Pakistan

BACKGROUND

Despite an increasing incidence of Staphylococcus aureus infection and dissemination in Pakistan, the epidemiology of different Staphylococcus aureus research clones has been the subject of only a small number of investigations. By analyzing the collected data sequence, this study was designed to study the epidemiology of Staphylococcus aureus in the area using multilocus sequence typing (MLST).

METHODS

A total of 1015 staphylococcus strains collected from the city's tertiary care facilities were biochemically screened, followed by antimicrobial susceptibility testing against a panel of 13 antibiotics. Analyzed methicillin-resistant Staphylococcus aureus (MRSA) was subjected to molecular characterization using multilocus sequence typing (MLST), clonal complex analysis, recombination testing, and phylogenetic analysis.

RESULTS

Approximately 421 bacteria were verified as Staphylococcus aureus by biochemical analysis. 57% of the isolates exhibited multidrug resistance, of which 89% were found to be methicillin-resistant Staphylococcus aureus (MRSA). MLST results in a total of 39 sequence types (ST) and 5 clonal complexes (CC), out of which twenty-two STs were newly documented worldwide. The most common CC identified was CC8. The direct sequencing data also revealed significant shifts at MLST loci, with point mutations resulting in the aroE-343 and tpi-278 alleles.

CONCLUSIONS

This study concludes that there is high diversity in the locally circulating clones of Staphylococcus aureus present in nature and that they are defined by their geographic epidemiology. These findings have practical implications for public health, including the need for tailored infection control strategies, antibiotic stewardship, global surveillance, and a deeper understanding of bacterial evolution.

Understanding Staphylococcus aureus internalisation and induction of antimicrobial tolerance

INTRODUCTION

Staphylococcus aureus, a human commensal, is also one of the most common and serious pathogens for humans. In recent years, its capacity to survive and replicate in phagocytic and non-phagocytic cells has been largely demonstrated. In these intracellular niches, bacteria are shielded from the immune response and antibiotics, turning host cells into long-term infectious reservoirs. Moreover, neutrophils carry intracellular bacteria in the bloodstream, leading to systemic spreading of the disease. Despite the serious threat posed by intracellular S. aureus to human health, the molecular mechanisms behind its intracellular survival and subsequent antibiotic treatment failure remain elusive.

AREA COVERED

We give an overview of the killing mechanisms of phagocytes and of the impressive arsenal of virulence factors, toxins and stress responses deployed by S. aureus as a response. We then discuss the different barriers to antibiotic activity in this intracellular niche and finally describe innovative strategies to target intracellular persisting reservoirs.

EXPERT OPINION

Intracellular niches represent a challenge in terms of diagnostic and treatment. Further research using ad-hoc in-vivo models and single cell approaches are needed to better understand the molecular mechanisms underlying intracellular survival and tolerance to antibiotics in order to identify strategies to eliminate these persistent bacteria.

Geometric constraint-triggered collagen expression mediates bacterial-host adhesion

Cells living in geometrically confined microenvironments are ubiquitous in various physiological processes, e.g., wound closure. However, it remains unclear whether and how spatially geometric constraints on host cells regulate bacteria-host interactions. Here, we reveal that interactions between bacteria and spatially constrained cell monolayers exhibit strong spatial heterogeneity, and that bacteria tend to adhere to these cells near the outer edges of confined monolayers. The bacterial adhesion force near the edges of the micropatterned monolayers is up to 75 nN, which is ~3 times higher than that at the centers, depending on the underlying substrate rigidities. Single-cell RNA sequencing experiments indicate that spatially heterogeneous expression of collagen IV with significant edge effects is responsible for the location-dependent bacterial adhesion. Finally, we show that collagen IV inhibitors can potentially be utilized as adjuvants to reduce bacterial adhesion and thus markedly enhance the efficacy of antibiotics, as demonstrated in animal experiments.

Nanoparticles of Lactiplantibacillus plantarum K8 Reduce Staphylococcus aureus Respiratory Infection and Tumor Necrosis Factor Alpha- and Interferon Gamma-Induced Lung Inflammation

Multiple studies have confirmed that Lactiplantibacillus plantarum has beneficial effects in respiratory diseases, including respiratory tract infections, asthma, and chronic obstructive pulmonary disease. However, the role of L. plantarum lysates in respiratory diseases is unclear. Staphylococcus aureus infects the lungs of mice, recruits immune cells, and induces structural changes in alveoli. Lung diseases can be further aggravated by inflammatory cytokines such as CCL2 and interleukin (IL)-6. In in vivo studies, L. plantarum K8 nanoparticles (K8NPs) restored lung function and prevented lung damage caused by S. aureus infection. They inhibited the S. aureus infection and the infiltration of immune cells and prevented the increase in goblet cell numbers in the lungs of S. aureus-infected mice. K8NPs suppressed the expression of CCL2 and IL-6, which were increased by the combination treatment of tumor necrosis factor alpha and interferon gamma (TI), in a dose-dependent manner. In in vitro studies, the anti-inflammatory effect of K8NPs in TI-treated A549 cells and TI-injected mice occurred through the reduction in activated mitogen-activated protein kinases and nuclear factor kappa-B. These findings suggest that the efficacy of K8NPs in controlling respiratory inflammation and infection can be used to develop functional materials that can prevent or alleviate respiratory diseases.

Verma S, Panda PK, Jerman I. Boosting Copper Biocidal Activity by Silver Decoration and Few-Layer Graphene in Coatings on Textile Fibers

The outbreak of the Coronavirus disease 2019 (COVID-19) pandemic has highlighted the importance of developing antiviral surface coatings that are capable of repelling pathogens and neutralizing them through self-sanitizing properties. In this study, a novel coating design based on few-layer graphene (FLG) is proposed and silver-decorated micro copper flakes (CuMF) that exhibit both antibacterial and antiviral properties. The role of sacrificial anode surfaces and intrinsic graphene defects in enhancing the release of metal ions from CuMF embedded in water-based binders is investigated. In silico analysis is conducted to better understand the molecular interactions of pathogen-repelling species with bacterial or bacteriophage proteins. The results show that the optimal amount of CuMF/FLG in the coating leads to a significant reduction in bacterial growth, with reductions of 3.17 and 9.81 log for Staphylococcus aureus and Escherichia coli, respectively. The same coating also showed high antiviral efficacy, reducing bacteriophage phi6 by 5.53 log. The antiviral efficiency of the coating is find to be doubled compared to either micro copper flakes or few-layer graphene alone. This novel coating design is versatile and can be applied to various substrates, such as personal protective clothing and face masks, to provide biocidal activity against both bacterial and viral pathogens.

CD9 co-operation with syndecan-1 is required for a major staphylococcal adhesion pathway

Epithelial colonization is a critical first step in bacterial pathogenesis. Staphylococcus aureus can utilize several host factors to associate with cells, including α5β1 integrin and heparan sulfate proteoglycans, such as the syndecans. Here, we demonstrate that a partner protein of both integrins and syndecans, the host membrane adapter protein tetraspanin CD9, is essential for syndecan-mediated staphylococcal adhesion. Fibronectin is also essential in this process, while integrins are only critical for post-adhesion entry into human epithelial cells. Treatment of epithelial cells with CD9-derived peptide or heparin caused significant reductions in staphylococcal adherence, dependent on both CD9 and syndecan-1. Exogenous fibronectin caused a CD9-dependent increase in staphylococcal adhesion, whereas blockade of β1 integrins did not affect adhesion but did reduce the subsequent internalization of adhered bacteria. CD9 disruption or deletion increased β1 integrin-mediated internalization, suggesting that CD9 coordinates sequential staphylococcal adhesion and internalization. CD9 controls staphylococcal adhesion through syndecan-1, using a mechanism that likely requires CD9-mediated syndecan organization to correctly display fibronectin at the host cell surface. We propose that CD9-derived peptides or heparin analogs could be developed as anti-adhesion treatments to inhibit the initial stages of staphylococcal pathogenesis. IMPORTANCE Staphylococcus aureus infection is a significant cause of disease and morbidity. Staphylococci utilize multiple adhesion pathways to associate with epithelial cells, including interactions with proteoglycans or β1 integrins through a fibronectin bridge. Interference with another host protein, tetraspanin CD9, halves staphylococcal adherence to epithelial cells, although CD9 does not interact directly with bacteria. Here, we define the role of CD9 in staphylococcal adherence and uptake, observing that CD9 coordinates syndecan-1, fibronectin, and β1 integrins to allow efficient staphylococcal infection. Two treatments that disrupt this action are effective and may provide an alternative to antibiotics. We provide insights into the mechanisms that underlie staphylococcal infection of host cells, linking two known adhesion pathways together through CD9 for the first time.

Colonization of methicillin-resistant Staphylococcus species in healthy and sick pets: prevalence and risk factors

BACKGROUND

The characterization of staphylococcal species that colonize pets is important to maintain animal health and to minimize the risk of transmission to owners. Here, the prevalence of Staphylococcus spp. and methicillin resistance was investigated in canine and feline isolates, and risk factors of staphylococcal colonization were determined. Pets were examined and separated into four groups: (1) healthy dogs, (2) healthy cats, and (3) dogs and (4) cats with clinical signs of bacterial infections of skin, mucous membranes, or wounds. Specimens were collected by a veterinary physician from six anatomic sites (external ear canal, conjunctival sacs, nares, mouth, skin [groin], and anus). In total, 274 animals (cats n = 161, dogs n = 113) were enrolled.

RESULTS

Staphylococcus species were highly diverse (23 species; 3 coagulase-positive and 20 coagulase-negative species), with the highest variety in healthy cats (19 species). The most frequent feline isolates were S. felis and S. epidermidis, while S. pseudintermedius was the most prevalent isolate in dogs. Risk factors of staphylococcal colonization included the presence of other animals in the same household, medical treatment within the last year, and a medical profession of at least one owner. Methicillin resistance was higher in coagulase-negative (17.86%) compared to coagulase-positive (1.95%) staphylococci. The highest prevalence of methicillin-resistant CoNS colonization was observed in animals kept in homes as the most common (dogs and cats).

CONCLUSIONS

The association of methicillin-resistant CoNS colonization with animals most often chosen as pets, represents a high risk of transmission between them and owners. The importance of nosocomial transmission of CoNS was also confirmed. This information could guide clinical decisions during the treatment of veterinary bacterial infections. In conclusion, the epidemiologic characteristics of CoNS and their pathogenicity in pets and humans require further research.

Exploring differentially expressed genes of Staphylococcus aureus exposed to human tonsillar cells using RNA sequencing

BACKGROUND

The nose and the throat are the most predominant colonizing sites of Staphylococcus aureus, and colonization is a risk factor for infection. Nasal colonization is well described; however, we have limited knowledge about S. aureus throat colonization. The main objective of this study was to explore differentially expressed genes (DEGs) in S. aureus throat isolate TR145 exposed to human tonsil epithelial cells (HTEpiC) by using RNA sequencing (RNA-seq) and pathway analysis. DEGs in S. aureus at 1 or 3 hours (h) interaction with its host were explored.

RESULTS

S. aureus was co-cultured in absence and presence of tonsillar cells at 1 or 3 h. Over the 3 h time frame, the bacteria multiplied, but still caused only minor cytotoxicity. Upon exposure to tonsillar cell line, S. aureus changed its transcriptomic profile. A total of 508 DEGs were identified including unique (1 h, 160 DEGs and 3 h, 78 DEGs) and commonly shared genes (1 and 3 h, 270 DEGs). Among the DEGs, were genes encoding proteins involved in adhesion and immune evasion, as well as iron acquisition and transport. Reverse transcription qPCR was done on selected genes, and the results correlated with the RNA-seq data.

CONCLUSION

We have shown the suitability of using HTEpiC as an in vitro model for investigating key determinants in S. aureus during co-incubation with host cells. Several DEGs were unique after 1 or 3 h exposure to host cells, while others were commonly expressed at both time points. As their expression is induced upon meeting with the host, they might be explored further for future targets for intervention to prevent either colonization or infection in the throat.

Protein Disulfide Isomerase and Extracellular Adherence Protein Cooperatively Potentiate Staphylococcal Invasion into Endothelial Cells

Invasion of host cells is an important feature of Staphylococcus aureus. The main internalization pathway involves binding of the bacteria to host cells, e.g., endothelial cells, via a fibronectin (Fn) bridge between S. aureus Fn binding proteins and α5β1-integrin, followed by phagocytosis. The secreted extracellular adherence protein (Eap) has been shown to promote this cellular uptake pathway of not only S. aureus, but also of bacteria otherwise poorly taken up by host cells, such as Staphylococcus carnosus. The exact mechanisms are still unknown. Previously, we demonstrated that Eap induces platelet activation by stimulation of the protein disulfide isomerase (PDI), a catalyst of thiol-disulfide exchange reactions. Here, we show that Eap promotes PDI activity on the surface of endothelial cells, and that this contributes critically to Eap-driven staphylococcal invasion. PDI-stimulated β1-integrin activation followed by increased Fn binding to host cells likely accounts for the Eap-enhanced uptake of S. aureus into non-professional phagocytes. Additionally, Eap supports the binding of S. carnosus to Fn-α5β1 integrin, thereby allowing its uptake into endothelial cells. To our knowledge, this is the first demonstration that PDI is crucial for the uptake of bacteria into host cells. We describe a hitherto unknown function of Eap-the promotion of an enzymatic activity with subsequent enhancement of bacterial uptake-and thus broaden mechanistic insights into its importance as a driver of bacterial pathogenicity. IMPORTANCE Staphylococcus aureus can invade and persist in non-professional phagocytes, thereby escaping host defense mechanisms and antibiotic treatment. The intracellular lifestyle of S. aureus contributes to the development of infection, e.g., in infective endocarditis or chronic osteomyelitis. The extracellular adherence protein secreted by S. aureus promotes its own internalization as well as that of bacteria that are otherwise poorly taken up by host cells, such as Staphylococcus carnosus. In our study, we demonstrate that staphylococcal uptake by endothelial cells requires catalytic disulfide exchange activity by the cell-surface protein disulfide isomerase, and that this critical enzymatic function is enhanced by Eap. The therapeutic application of PDI inhibitors has previously been investigated in the context of thrombosis and hypercoagulability. Our results add another intriguing possibility: therapeutically targeting PDI, i.e., as a candidate approach to modulate the initiation and/or course of S. aureus infectious diseases.

Staphylococcus aureus from Atopic Dermatitis Patients: Its Genetic Structure and Susceptibility to Phototreatment

We characterized the population of Staphylococcus aureus from patients with atopic dermatitis (AD) in terms of (i) genetic diversity, (ii) presence and functionality of genes encoding important virulence factors: staphylococcal enterotoxins (sea, seb, sec, sed), toxic shock syndrome 1 toxin (tsst-1), and Panton-Valentine leukocidin (lukS/lukF-PV) by spa typing, PCR, drug resistance profile determination, and Western blot. We then subjected the studied population of S. aureus to photoinactivation based on a light-activated compound called rose bengal (RB) to verify photoinactivation as an approach to effectively kill toxin-producing S. aureus. We have obtained 43 different spa types that can be grouped into 12 clusters, indicating for the first-time clonal complex (CC) 7 as the most widespread. A total of 65% of the tested isolates had at least one gene encoding the tested virulence factor, but their distribution differed between the group of children and adults, and between patients with AD and the control group without atopy. We detected a 3.5% frequency of methicillin-resistant strains (MRSA) and no other multidrug resistance. Despite genetic diversity and production of various toxins, all isolates tested were effectively photoinactivated (bacterial cell viability reduction ≥ 3 log10 units) under safe conditions for the human keratinocyte cell line, which indicates that photoinactivation can be a good option in skin decolonization. IMPORTANCE Staphylococcus aureus massively colonizes the skin of patients with atopic dermatitis (AD). It is worth noting that the frequency of detection of multidrug-resistant S. aureus (MRSA) in AD patients is higher than the healthy population, which makes treatment much more difficult. Information about the specific genetic background of S. aureus accompanying and/or causing exacerbations of AD is of great importance from the point of view of epidemiological investigations and the development of possible treatment options.

Catch Bond-Mediated Adhesion Drives Staphylococcus aureus Host Cell Invasion

Various viruses and pathogenic bacteria interact with annexin A2 to invade mammalian cells. Here, we show that Staphylococcus aureus engages in extremely strong catch bonds for host cell invasion. By means of single-molecule atomic force microscopy, we find that bacterial surface-located clumping factors bind annexin A2 with extraordinary strength, indicating that these bonds are extremely resilient to mechanical tension. By determining the lifetimes of the complexes under increasing mechanical stress, we demonstrate that the adhesins form catch bonds with their ligand that are capable to sustain forces of 1500-1700 pN. The force-dependent adhesion mechanism identified here provides a molecular framework to explain how S. aureus pathogens tightly attach to host cells during invasion and shows promise for the design of new therapeutics against intracellular S. aureus.

Invasion of intestinal cells by Staphylococcus warneri, a member of the human gut microbiota

Coagulase negative staphylococci (CoNS) are a heterogeneous group of bacteria that colonize different types of human epithelia. These bacteria have a highly variable pathogenic potential ranging from avirulent species to major nosocomial pathogens. Staphylococcus warneri is a CoNS species considered to be nonpathogenic. Here, we identify that S. warneri is a natural member of both human and mouse gut microbiota. In addition, we demonstrate that this bacterium is able to get internalized into human cells. We show that S. warneri efficiently invades several human cell types and, more specifically, intestinal epithelial cells, using actin-dependent mechanisms. In contrast to bona fide pathogens, S. warneri does not actively replicate within intestinal cells or resist killing by macrophages. Together, our results highlight that bacteria from the human gut microbiota that are not associated with a high pathogenic potential, can actively invade intestinal cells and may, in this way, impact intestinal physiology.

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.

Review on skeletal disorders caused by Staphylococcus spp. in poultry

Lameness or leg weakness is the main cause of poor poultry welfare and serious economic losses in meat-type poultry production worldwide. Disorders related to the legs are often associated with multifactorial aetiology which makes diagnosis and proper treatment difficult. Among the infectious agents, bacteria of genus Staphylococcus are one of the most common causes of bone infections in poultry and are some of the oldest bacterial infections described in poultry. Staphylococci readily infect bones and joints and are associated with bacterial chondronecrosis with osteomyelitis (BCO), spondylitis, arthritis, tendinitis, tenosynovitis, osteomyelitis, turkey osteomyelitis complex (TOC), bumblefoot, dyschondroplasia with osteomyelitis and amyloid arthropathy. Overall, 61 staphylococcal species have been described so far, and 56% of them (34/61) have been isolated from clinical cases in poultry. Although Staphylococcus aureus is the principal cause of poultry staphylococcosis, other Staphylococcus species, such as S. agnetis, S. cohnii, S. epidermidis, S. hyicus, S. simulans, have also been isolated from skeletal lesions. Antimicrobial treatment of staphylococcosis is usually ineffective due to the location and type of lesion, as well as the possible occurrence of multidrug-resistant strains. Increasing demand for antibiotic-free farming has contributed to the use of alternatives to antibiotics. Other prevention methods, such as better management strategies, early feed restriction or use of slow growing broilers should be implemented to avoid rapid growth rate, which is associated with locomotor problems. This review aims to summarise and address current knowledge on skeletal disorders associated with Staphylococcus spp. infection in poultry.

Microscopy-based phenotypic profiling of infection by Staphylococcus aureus clinical isolates reveals intracellular lifestyle as a prevalent feature

Staphylococcus aureus is increasingly recognized as a facultative intracellular pathogen, although the significance and pervasiveness of its intracellular lifestyle remain controversial. Here, we applied fluorescence microscopy-based infection assays and automated image analysis to profile the interaction of 191 S. aureus isolates from patients with bone/joint infections, bacteremia, and infective endocarditis, with four host cell types, at five times post-infection. This multiparametric analysis revealed that almost all isolates are internalized and that a large fraction replicate and persist within host cells, presenting distinct infection profiles in non-professional vs. professional phagocytes. Phenotypic clustering highlighted interesting sub-groups, including one comprising isolates exhibiting high intracellular replication and inducing delayed host death in vitro and in vivo. These isolates are deficient for the cysteine protease staphopain A. This study establishes S. aureus intracellular lifestyle as a prevalent feature of infection, with potential implications for the effective treatment of staphylococcal infections.

YAP promotes cell-autonomous immune responses to tackle intracellular Staphylococcus aureus in vitro

Transcriptional cofactors YAP/TAZ have recently been found to support autophagy and inflammation, which are part of cell-autonomous immunity and are critical in antibacterial defense. Here, we studied the role of YAP against Staphylococcus aureus using CRISPR/Cas9-mutated HEK293 cells and a primary cell-based organoid model. We found that S. aureus infection increases YAP transcriptional activity, which is required to reduce intracellular S. aureus replication. A 770-gene targeted transcriptomic analysis revealed that YAP upregulates genes involved in autophagy/lysosome and inflammation pathways in both infected and uninfected conditions. The YAP-TEAD transcriptional activity promotes autophagic flux and lysosomal acidification, which are then important for defense against intracellular S. aureus. Furthermore, the staphylococcal toxin C3 exoenzyme EDIN-B was found effective in preventing YAP-mediated cell-autonomous immune response. This study provides key insights on the anti-S. aureus activity of YAP, which could be conserved for defense against other intracellular bacteria.

Comparative genomics study of Staphylococcus aureus isolated from cattle and humans reveals virulence patterns exclusively associated with bovine clinical mastitis strains

Staphylococcus aureus causes nosocomial and intramammary infections in humans and cattle, respectively. A large number of virulence factors are thought to play important roles in the pathogenesis of this bacterium. Currently, genome-wide and data-analysis studies are being used to better understand its epidemiology. In this study, we conducted a genome wide comparison and phylogenomic analyses of S. aureus to find specific virulence patterns associated with clinical and subclinical mastitis strains in cattle and compare them with those of human origin. The presence/absence of key virulence factors such as adhesin, biofilm, antimicrobial resistance, and toxin genes, as well as the phylogeny and sequence type of the isolates were evaluated. A total of 248 genomes (27 clinical mastitis, 43 subclinical mastitis, 21 milk, 53 skin-related abscesses, 49 skin infections, and 55 pus from cellulitis) isolated from 32 countries were evaluated. We found that the cflA, fnbA, ebpS, spa, sdrC, coa, emp, vWF, atl, sasH, sasA, and sasF adhesion genes, as well as the aur, hglA, hglB, and hglC toxin genes were highly associated in clinical mastitis strains. The strains had diverse genetic origins (72 protein A and 48 sequence types with ST97, ST8 and ST152 being frequent in isolates from clinical mastitis, abscess, and skin infection, respectively). Further, our phylogenomic analyses suggested that zoonotic and/or zooanthroponotic transmission may have occurred. These findings contribute to a better understanding of S. aureus epidemiology and the relationships between adhesion mechanisms, biofilm formation, antimicrobial resistance, and toxins and could aid in the development of improved vaccines and strain genotyping methods.

RNA-Sequencing of Heterorhabditis nematodes to identify factors involved in symbiosis with Photorhabdus bacteria

Background

Nematodes are a major group of soil inhabiting organisms. Heterorhabditis nematodes are insect-pathogenic nematodes and live in a close symbiotic association with Photorhabdus bacteria. Heterorhabditis-Photorhabdus pair offers a powerful and genetically tractable model to study animal-microbe symbiosis. It is possible to generate symbiont bacteria free (axenic) stages in Heterorhabditis. Here, we compared the transcriptome of symbiotic early-adult stage Heterorhabditis nematodes with axenic early-adult nematodes to determine the nematode genes and pathways involved in symbiosis with Photorhabdus bacteria.

Results

A de-novo reference transcriptome assembly of 95.7 Mb was created for H. bacteriophora by using all the reads. The assembly contained 46,599 transcripts with N50 value of 2,681 bp and the average transcript length was 2,054 bp. The differentially expressed transcripts were identified by mapping reads from symbiotic and axenic nematodes to the reference assembly. A total of 754 differentially expressed transcripts were identified in symbiotic nematodes as compared to the axenic nematodes. The ribosomal pathway was identified as the most affected among the differentially expressed transcripts. Additionally, 12,151 transcripts were unique to symbiotic nematodes. Endocytosis, cAMP signalling and focal adhesion were the top three enriched pathways in symbiotic nematodes, while a large number of transcripts coding for various responses against bacteria, such as bacterial recognition, canonical immune signalling pathways, and antimicrobial effectors could also be identified.

Conclusions

The symbiotic Heterorhabditis nematodes respond to the presence of symbiotic bacteria by expressing various transcripts involved in a multi-layered immune response which might represent non-systemic and evolved localized responses to maintain mutualistic bacteria at non-threatening levels. Subject to further functional validation of the identified transcripts, our findings suggest that Heterorhabditis nematode immune system plays a critical role in maintenance of symbiosis with Photorhabdus bacteria.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08952-4.

In Silico Identification of Potential Insect Peptides against Biofilm-Producing Staphylococcus aureus

Biofilm-producing Staphylococcus aureus (SA) strains are frequently found in medical environments, from surgical/ wound sites, medical devices. These biofilms reduce the efficacy of applied antibiotics during the treatment of several infections, such as cystic fibrosis, endocarditis, or urinary tract infections. Thus, the development of potential therapeutic agents to destroy the extra protective biofilm layers or to inhibit the biofilm-producing enzymes is urgently needed. Advanced and cost-effective bioinformatics tools are advantageous in locating and speeding up the selection of antibiofilm candidates. Based on the potential drug characteristics, we have selected one-hundred thirty-three antibacterial peptides derived from insects to assess for their antibiofilm potency via molecular docking against five putative biofilm formation and regulated target enzymes: the staphylococcal accessory regulator A or SarA (PDB ID: 2FRH), 4,4'-diapophytoene synthase or CrtM (PDB ID: 2ZCQ), clumping factor A or ClfA (PDB ID: 1N67) and serine-aspartate repeat protein C or SdrC (PDB ID: 6LXH) and sortase A or SrtA (PDB ID: 1T2W) of SA bacterium. In this study, molecular docking was performed using HPEPDOCK and HDOCK servers, and molecular interactions were examined using BIOVIA Discovery Studio Visualizer-2019. The docking score (kcal/mol) range of five promising antibiofilm peptides against five targets was recorded as follows: diptericin A (-215.52 to -303.31), defensin (-201.11 to -301.92), imcroporin (-212.08 to -287.64), mucroporin (-228.72 to -286.76), apidaecin II (-203.90 to -280.20). Among these five, imcroporin and mucroporin were 13 % each, while defensin contained only 1 % of positive net charged residues (Arg+Lys) projected through ProtParam and NetWheels tools. Similarly, imcroporin, mucroporin and apidaecin II were 50 %, while defensin carried 21.05 % of hydrophobic residues predicted by the tool PEPTIDE. 2.0. Most of the peptides exhibited potential characteristics to inhibit S. aureus-biofilm formation via disrupting the cell membrane and cytoplasmic integrity. In summary, the proposed hypothesis can be considered a cost-effective platform for selecting the most promising bioactive drug candidates within a limited timeframe with a greater chance of success in experimental and clinical studies.

Prolactin regulates H3K9ac and H3K9me2 epigenetic marks and miRNAs expression in bovine mammary epithelial cells challenged with Staphylococcus aureus

Epigenetic mechanisms are essential in the regulation of immune response during infections. Changes in the levels of reproductive hormones, such as prolactin, compromise the mammary gland’s innate immune response (IIR); however, its effect on epigenetic marks is poorly known. This work explored the epigenetic regulation induced by bovine prolactin (bPRL) on bovine mammary epithelial cells (bMECs) challenged with Staphylococcus aureus. In this work, bMECs were treated as follows: (1) control cells without any treatment, (2) bMECs treated with bPRL (5 ng/ml) at different times (12 or 24 h), (3) bMECs challenged with S. aureus for 2 h, and (4) bMECs treated with bPRL at different times (12 or 24 h), and then challenged with S. aureus 2 h. By western blot analyses of histones, we determined that the H3K9ac mark decreased (20%) in bMECs treated with bPRL (12 h) and challenged with S. aureus, while the H3K9me2 mark was increased (50%) in the same conditions. Also, this result coincided with an increase (2.3-fold) in HDAC activity analyzed using the cellular histone deacetylase fluorescent kit FLUOR DE LYS^®. ChIP-qPCRs were performed to determine if the epigenetic marks detected in the histones correlate with enriched marks in the promoter regions of inflammatory genes associated with the S. aureus challenge. The H3K9ac mark was enriched in the promoter region of IL-1β, IL-10, and BNBD10 genes (1.5, 2.5, 7.5-fold, respectively) in bMECs treated with bPRL, but in bMECs challenged with S. aureus it was reduced. Besides, the H3K9me2 mark was enriched in the promoter region of IL-1β and IL-10 genes (3.5 and 2.5-fold, respectively) in bMECs challenged with S. aureus but was inhibited by bPRL. Additionally, the expression of several miRNAs was analyzed by qPCR. Let-7a-5p, miR-21a, miR-30b, miR-155, and miR-7863 miRNAs were up-regulated (2, 1.5, 10, 1.5, 3.9-fold, respectively) in bMECs challenged with S. aureus; however, bPRL induced a down-regulation in the expression of these miRNAs. In conclusion, bPRL induces epigenetic regulation on specific IIR elements, allowing S. aureus to persist and evade the host immune response.

Antibiofilm, AntiAdhesive and Anti-Invasive Activities of Bacterial Lysates Extracted from Pediococcus acidilactici against Listeria monocytogenes

This study aimed to investigate whether bacterial lysates (BLs) extracted from Pediococcus acidilactici reduce Listeria monocytogenes biofilm formation, as well as adhesion to and invasion of human intestinal epithelial cells. Pretreatment with P. acidilactici BLs (20, 40, and 80 μg/mL) significantly inhibited L. monocytogenes biofilm formation on the surface of polystyrene (p < 0.05). Fluorescence and scanning-electron-microscopic analyses indicated that L. monocytogenes biofilm comprised a much less dense layer of more-dispersed cells in the presence of P. acidilactici BLs. Moreover, biofilm-associated genes, such as flaA, fliG, flgE, motB, degU, agrA, and prfA, were significantly downregulated in the presence of P. acidilactici BLs (p < 0.05), suggesting that P. acidilactici BLs prevent L. monocytogenes biofilm development by suppressing biofilm-associated genes. Although P. acidilactici BLs did not dose-dependently inhibit L. monocytogenes adhesion to and invasion of intestinal epithelial cells, the BLs effectively inhibited adhesion and invasion at 40 and 80 μg/mL (p < 0.05). Supporting these findings, P. acidilactici BLs significantly downregulated L. monocytogenes transcription of genes related to adhesion and invasion, specifically fbpA, ctaP, actA, lapB, ami, and inlA. Collectively, these results suggest that P. acidilactici BLs have the potential to reduce health risks from L. monocytogenes.

Annexin A2 regulates Mycoplasma bovis adhesion and invasion to embryo bovine lung cells affecting molecular expression essential to inflammatory response

Mycoplasma bovis (M. bovis) is an important pathogen of the bovine respiratory disease complex, invading lower respiratory tracts and causing severe pneumonia. However, its molecular mechanism largely remains unknown. Host annexin A2 (ANXA2) is a calcium-dependent phospholipid-binding protein. The current study sought to determine whether ANXA2 could mediate M. bovis adhesion and invasion thereby affecting its induction of inflammatory response. ANXA2 expression was upregulated in M. bovis-infected bovine lung epithelial cells (EBL), and blocking ANXA2 with an anti-ANXA2 antibody reduced M. bovis adhesion to EBL. Compared with uninfected cells, more ANXA2 was translocated from the cytoplasm to the cell surface after M. bovis infection. Furthermore, RNA interference knockdown of ANXA2 expression in EBL cells resulted in a significant decrease in M. bovis invasion and F-actin polymerization. Next, the transcriptomic study of M. bovis-infected EBL cells with and without ANXA2 knockdown were performed. The data exhibited that ANXA2 knockdown EBL cells had 2487 differentially expressed genes (DEGs), with 1175 upregulated and 1312 downregulated compared to control. According to GO and KEGG analyses, 50 genes potentially linked to inflammatory responses, 23 involved in extracellular matrix (ECM) receptor interaction, and 48 associated with PI3K-AKT signal pathways were upregulated, while 38 mRNA binding genes, 16 mRNA 3′-UTR binding genes, and 34 RNA transport genes were downregulated. Furthermore, 19 genes with various change-folds were selected for qPCR verification, and the results agreed with the RNA-seq findings. Above all, the transcription of two chemokines (IL-8 and CXCL5) and a key bovine β-defensin TAP in IL-17 signaling pathway were significantly increased in ANXA2 knockdown cells. Moreover, ANXA2 knockdown or knockout could increase NF-κB and MAPK phosphorylation activity in response to M. bovis infection. Additionally, ANXA2 knockdown also significantly decreased the CD44 transcripts via exon V3 and V7 skipping after M. bovis infection. We concluded that M. bovis borrowed host ANXA2 to mediate its adhesion and invasion thereby negatively regulating molecular expression essential to IL-17 signal pathway. Furthermore, CD44 V3 and V7 isoforms might contribute to this ANXA2 meditated processes in M. bovis infected EBL cells. These findings revealed a new understanding of pathogenesis for M. bovis infection.

Short Chain Fatty Acids (SCFAs) Are the Potential Immunomodulatory Metabolites in Controlling Staphylococcus aureus-Mediated Mastitis

Mastitis is an emerging health concern in animals. An increased incidence of mastitis in dairy cows has been reported in the last few years across the world. It is estimated that up to 20% of cows are suffering from mastitis, causing incompetency in the mucosal immunity and resulting in excessive global economic losses in the dairy industry. Staphylococcus aureus (S. aureus) has been reported as the most common bacterial pathogen of mastitis at clinical and sub-clinical levels. Antibiotics, including penicillin, macrolides, lincomycin, cephalosporins, tetracyclines, chloramphenicol, and methicillin, were used to cure S. aureus-induced mastitis. However, S. aureus is resistant to most antibiotics, and methicillin-resistant S. aureus (MRSA) especially has emerged as a critical health concern. MRSA impairs immune homeostasis leaving the host more susceptible to other infections. Thus, exploring an alternative to antibiotics has become an immediate requirement of the current decade. Short chain fatty acids (SCFAs) are the potent bioactive metabolites produced by host gut microbiota through fermentation and play a crucial role in host/pathogen interaction and could be applied as a potential therapeutic agent against mastitis. The purpose of this review is to summarize the potential mechanism by which SCFAs alleviate mastitis, providing the theoretical reference for the usage of SCFAs in preventing or curing mastitis.

Air pollution induces Staphylococcus aureus USA300 respiratory tract colonization mediated by specific bacterial genetic responses involving the global virulence gene regulators Agr and Sae

Exposure to particulate matter (PM), a major component of air pollution, is associated with exacerbation of chronic respiratory disease, and infectious diseases such as community-acquired pneumonia. Although PM can cause adverse health effects through direct damage to host cells, our previous study showed that PM can also impact bacterial behaviour by promoting in vivo colonization. In this study we describe the genetic mechanisms involved in the bacterial response to exposure to black carbon (BC), a constituent of PM found in most sources of air pollution. We show that Staphylococcus aureus strain USA300 LAC grown in BC prior to inoculation showed increased murine respiratory tract colonization and pulmonary invasion in vivo, as well as adhesion and invasion of human epithelial cells in vitro. Global transcriptional analysis showed that BC has a widespread effect on S. aureus transcriptional responses, altering the regulation of the major virulence gene regulators Sae and Agr and causing increased expression of genes encoding toxins, proteases and immune evasion factors. Together these data describe a previously unrecognized causative mechanism of air pollution-associated infection, in that exposure to BC can increase bacterial colonization and virulence factor expression by acting directly on the bacterium rather than via the host.

Uptake of Staphylococcus aureus by keratinocytes is reduced by interferon-fibronectin pathway and filaggrin expression

Staphylococcus aureus (S. aureus) is frequently detected in the skin of patients with atopic dermatitis (AD). AD skin-derived strains of S. aureus (AD strain) are selectively internalized into keratinocytes (HaCaT cells) compared to standard strains. However, the mechanism of AD strain internalization by keratinocytes and effect of the skin environment on internalization remain unclear. HaCaT cells were exposed to heat-killed AD or standard strains of fluorescently labeled S. aureus, with or without interferon (IFN)-γ, interleukin (IL)-4, and IL-13 cytokines, for 24 h. Filaggrin and fibronectin expression in HaCaT cells was knocked down using small interfering RNA. The amount of internalized S. aureus was evaluated using a cell imaging system. The effects of INF-γ, IL-4, and S. aureus exposure on mRNA expression in HaCaT cells were analyzed using single-cell RNA sequencing. AD strains adhered to HaCaT cells in approximately 15 min and were increasingly internalized for up to 3 h (2361 ± 467 spots/100 cells, mean ± SD), whereas the standard strain was not (991 ± 71 spots/100 cells). In the presence of IFN-γ, both the number of internalized strains and fibronectin expression significantly decreased compared to in the control, whereas Th2 cytokines had no significant effects. The number of internalized AD strains was significantly higher in filaggrin knockdown and lower in fibronectin knockdown HaCaT cells compared to in the control. RNA sequencing revealed that IFN-γ decreased both fibronectin and filaggrin expression. Keratinocyte internalization of the AD strain may be predominantly mediated by the INF-γ-fibronectin pathway and partially regulated by filaggrin expression.

Pharmacological Approaches for the Prevention of Breast Implant Capsular Contracture

Capsular contracture is a common complication associated with breast implants following reconstructive or aesthetic surgery in which a tight or constricting scar tissue capsule forms around the implant, often distorting the breast shape and resulting in chronic pain. Capsulectomy (involving full removal of the capsule surrounding the implant) and capsulotomy (where the capsule is released and/or partly removed to create more space for the implant) are the most common surgical procedures used to treat capsular contracture. Various structural modifications of the implant device (including use of textured implants, submuscular placement of the implant, and the use of polyurethane-coated implants) and surgical strategies (including pre-operative skin washing and irrigation of the implant pocket with antibiotics) have been and/or are currently used to help reduce the incidence of capsular contracture. In this article, we review the pharmacological approaches-both commonly practiced in the clinic and experimental-reported in the scientific and clinical literature aimed at either preventing or treating capsular contracture, including (i) pre- and post-operative intravenous administration of drug substances, (ii) systemic (usually oral) administration of drugs before and after surgery, (iii) modification of the implant surface with grafted drug substances, (iv) irrigation of the implant or peri-implant tissue with drugs prior to implantation, and (v) incorporation of drugs into the implant shell or filler prior to surgery followed by drug release in situ after implantation.

The Role of Nanoscale Distribution of Fibronectin in the Adhesion of Staphylococcus aureus Studied by Protein Patterning and DNA-PAINT

Staphylococcus aureus is a widespread and highly virulent pathogen that can cause superficial and invasive infections. Interactions between S. aureus surface receptors and the extracellular matrix protein fibronectin mediate the bacterial invasion of host cells and is implicated in the colonization of medical implant surfaces. In this study, we investigate the role of distribution of both fibronectin and cellular receptors on the adhesion of S. aureus to interfaces as a model for primary adhesion at tissue interfaces or biomaterials. We present fibronectin in patches of systematically varied size (100-1000 nm) in a background of protein and bacteria rejecting chemistry based on PLL-g-PEG and studied S. aureus adhesion under flow. We developed a single molecule imaging assay for localizing fibronectin binding receptors on the surface of S. aureus via the super-resolution DNA points accumulation for imaging in nanoscale topography (DNA-PAINT) technique. Our results indicate that S. aureus adhesion to fibronectin biointerfaces is regulated by the size of available ligand patterns, with an adhesion threshold of 300 nm and larger. DNA-PAINT was used to visualize fibronectin binding receptor organization in situ at ∼7 nm localization precision and with a surface density of 38-46 μm^-2, revealing that the engagement of two or more receptors is required for strong S. aureus adhesion to fibronectin biointerfaces.

Investigation of the pathophysiology of bacterial mastitis using precision-cut bovine udder slices

Mastitis in cattle is a major health problem as well as incurring high costs for the dairy industry. To assess the suitability of precision-cut bovine udder slices (PCBUS) for bovine mastitis studies, we infected PCBUS with 2 different Staphylococcus aureus strains. Accordingly, we investigated both the tissue response to infection based on immune mediators at the mRNA and protein levels and the invasion of bacteria within the tissue. The studied proteins represent immune mediators of early inflammation [IL-1β, tumor necrosis factor-α (TNF-α), prostaglandin E₂ (PGE₂)] and showed a time-dependent increase in concentration. Infection of PCBUS with S. aureus resulted in increased expression of proinflammatory cytokines and chemokines such as TNF-α, C-C motif chemokine ligand 20 (CCL20), IL-1β, IL-6, and IL-10, but not C-X-C motif chemokine ligand 8 (CXCL8), lingual antimicrobial peptide (LAP), or S100 calcium binding protein A9 (S100A9) at the mRNA level. To compare the data acquired with this model, we carried out investigations on primary bovine mammary epithelial cells. Our results showed that the immune responses of both models-PCBUS and primary bovine mammary epithelial cells-were similar. In addition, investigations using PCBUS enabled us to demonstrate adherence of bacteria in the physiological cell network. These findings support the use of PCBUS in studies designed to further understand the complex pathophysiological processes of infection and inflammation in bovine mastitis and to investigate alternative therapies for mastitis.

Binding of the extracellular matrix laminin-1 to Clostridioides difficile strains

BACKGROUND

Clostridioides difficile is the most common cause of nosocomial diarrhea associated with antibiotic use. The disease’s symptoms are caused by enterotoxins, but other surface adhesion factors also play a role in the pathogenesis. These adhesins will bind to components of extracellular matrix.

OBJECTIVE

There is a lack of knowledge on MSCRAMM, this work set-out to determine the adhesive properties of several C. difficile ribotypes (027, 133, 135, 014, 012) towards laminin-1 (LMN-1).

METHODS

A binding experiment revealed that different ribotypes have distinct adhesion capabilities. To identify this adhesin, an affinity chromatography column containing LMN-1 was prepared and total protein extracts were analysed using mass spectrometry.

FINDINGS

Strains from ribotypes 012 and 027 had the best adhesion when incubated with glucose supplementations (0.2%, 0.5%, and 1%), while RT135 had a poor adherence. The criteria were not met by RT014 and RT133. In the absence of glucose, there was no adhesion for any ribotype, implying that glucose is required and plays a significant role in adhesion.

MAIN CONCLUSIONS

These findings show that in the presence of glucose, each C. difficile ribotype interacts differently with LMN-1, and the adhesin responsible for recognition could be SlpA protein.

Staphylococcus aureus adhesion to the host

Staphylococcus aureus is a pathobiont capable of colonizing and infecting most tissues within the human body, resulting in a multitude of different clinical outcomes. Adhesion of S. aureus to the host is crucial for both host colonization and the establishment of infections. Underlying the pathogen's success is a complex and diverse arsenal of adhesins. In this review, we discuss the different classes of adhesins, including a consideration of the various adhesion sites throughout the body and the clinical outcomes of each infection type. The development of therapeutics targeting the S. aureus host-pathogen interaction is a relatively understudied area. Due to the increasing global threat of antimicrobial resistance, it is crucial that innovative and alternative approaches are considered. Neutralizing virulence factors, through the development of antivirulence agents, could reduce bacterial pathogenicity and the ever-increasing burden of S. aureus infections. This review provides insight into potentially efficacious adhesion-associated targets for the development of novel decolonizing and antivirulence strategies.

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.