Identification and Characterization of Staphylococcus delphini Internalization Pathway in Nonprofessional Phagocytic Cells

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.

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 internalization impairs osteoblastic activity and early differentiation process

Staphylococcus aureus is the most frequent aetiology of bone and joint infections (BJI) and can cause relapsing and chronic infections. One of the main factors involved in the chronicization of staphylococcal BJIs is the internalization of S. aureus into osteoblasts, the bone-forming cells. Previous studies have shown that S. aureus triggers an impairment of osteoblasts function that could contribute to bone loss. However, these studies focused mainly on the extracellular effects of S. aureus. Our study aimed at understanding the intracellular effects of S. aureus on the early osteoblast differentiation process. In our in vitro model of osteoblast lineage infection, we first observed that internalized S. aureus 8325-4 (a reference lab strain) significantly impacted RUNX2 and COL1A1 expression compared to its non-internalized counterpart 8325-4^∆fnbAB (with deletion of fnbA and fnbB). Then, in a murine model of osteomyelitis, we reported no significant effect for S. aureus 8325-4 and 8325-4^∆fnbAB on bone parameters at 7 days post-infection whereas S. aureus 8325-4 significantly decreased trabecular bone thickness at 14 days post-infection compared to 8325-4^∆fnbAB. When challenged with two clinical isogenic strains isolated from initial and relapse phase of the same BJI, significant impairments of bone parameters were observed for both initial and relapse strain, without differences between the two strains. Finally, in our in vitro osteoblast infection model, both clinical strains impacted alkaline phosphatase activity whereas the expression of bone differentiation genes was significantly decreased only after infection with the relapse strain. Globally, we highlighted that S. aureus internalization into osteoblasts is responsible for an impairment of the early differentiation in vitro and that S. aureus impaired bone parameters in vivo in a strain-dependent manner.

The Multivalent Role of Fibronectin-Binding Proteins A and B (FnBPA and FnBPB) of Staphylococcus aureus in Host Infections

Staphylococcus aureus, one of the most important human pathogens, is the causative agent of several infectious diseases including sepsis, pneumonia, osteomyelitis, endocarditis and soft tissue infections. This pathogenicity is due to a multitude of virulence factors including several cell wall-anchored proteins (CWA). CWA proteins have modular structures with distinct domains binding different ligands. The majority of S. aureus strains express two CWA fibronectin (Fn)-binding adhesins FnBPA and FnBPB (Fn-binding proteins A and B), which are encoded by closely related genes. The N-terminus of FnBPA and FnBPB comprises an A domain which binds ligands such as fibrinogen, elastin and plasminogen. The A domain of FnBPB also interacts with histones and this binding results in the neutralization of the antimicrobial activity of these molecules. The C-terminal moiety of these adhesins comprises a long, intrinsically disordered domain composed of 11/10 fibronectin-binding repeats. These repetitive motifs of FnBPs promote invasion of cells that are not usually phagocytic via a mechanism by which they interact with integrin α₅β₁ through a Fn mediated-bridge. The FnBPA and FnBPB A domains engage in homophilic cell-cell interactions and promote biofilm formation and enhance platelet aggregation. In this review we update the current understanding of the structure and functional properties of FnBPs and emphasize the role they may have in the staphylococcal infections.