Staphylococcal Osteomyelitis: Disease Progression, Treatment Challenges, and Future Directions

Biomimetic Nanomedicine-Triggered in Situ Vaccination for Innate and Adaptive Immunity Activations for Bacterial Osteomyelitis Treatment

The development of bacterial vaccines for inducing an immunoresponse against infectious diseases such as osteomyelitis is of great significance and importance. However, the responsiveness of bacterial immunotherapy remains far from being satisfactory, largely due to the erratic antigen epitopes of bacteria. Herein, we report an in situ vaccination strategy for the immunotherapy of bacterial infection based on an osteomyelitis model using a biomimetic nanomedicine named as HMMP, which was constructed by engineering PpIX-encapsulated hollow MnO_x with a hybrid membrane exfoliated from both macrophage and tumor cell lines. The as-established HMMP features a burst bacterial antigen release as the in situ vaccine by the augmented sonodynamic treatment and the resultant priming of antigen-presenting cells for the following activations of both cellular and humoral adaptive immunities against bacterial infections. This treatment regimen not only triggers initial bacterial regression in the established osteomyelitis model but also simultaneously generates robust systemic antibacterial immunity against poorly immunogenic secondary osteomyelitis in the contralateral knee and additionally confers long-lasting bacteria-specific immune memory responses to prevent infection relapse. Thus, our study provides a proof of concept of in situ vaccination for the activation of both innate and adaptive antibacterial immune responses, providing an individual-independent bacterial immunotherapy.

Role of Animal Models to Advance Research of Bacterial Osteomyelitis

Osteomyelitis is an inflammatory bone disease typically caused by infectious microorganisms, often bacteria, which causes progressive bone destruction and loss. The most common bacteria associated with chronic osteomyelitis is Staphylococcus aureus. The incidence of osteomyelitis in the United States is estimated to be upwards of 50,000 cases annually and places a significant burden upon the healthcare system. There are three general categories of osteomyelitis: hematogenous; secondary to spread from a contiguous focus of infection, often from trauma or implanted medical devices and materials; and secondary to vascular disease, often a result of diabetic foot ulcers. Independent of the route of infection, osteomyelitis is often challenging to diagnose and treat, and the effect on the patient's quality of life is significant. Therapy for osteomyelitis varies based on category and clinical variables in each case. Therapeutic strategies are typically reliant upon protracted antimicrobial therapy and surgical interventions. Therapy is most successful when intensive and initiated early, although infection may recur months to years later. Also, treatment is accompanied by risks such as systemic toxicity, selection for antimicrobial drug resistance from prolonged antimicrobial use, and loss of form or function of the affected area due to radical surgical debridement or implant removal. The challenges of diagnosis and successful treatment, as well as the negative impacts on patient's quality of life, exemplify the need for improved strategies to combat bacterial osteomyelitis. There are many in vitro and in vivo investigations aimed toward better understanding of the pathophysiology of bacterial osteomyelitis, as well as improved diagnostic and therapeutic strategies. Here, we review the role of animal models utilized for the study of bacterial osteomyelitis and their critically important role in understanding and improving the management of bacterial osteomyelitis.

Engineering single-atom catalysts toward biomedical applications

Due to inherent structural defects, common nanocatalysts always display limited catalytic activity and selectivity, making it practically difficult for them to replace natural enzymes in a broad scope of biologically important applications. By decreasing the size of the nanocatalysts, their catalytic activity and selectivity will be substantially improved. Guided by this concept, the advances of nanocatalysts now enter an era of atomic-level precise control. Single-atom catalysts (denoted as SACs), characterized by atomically dispersed active sites, strikingly show utmost atomic utilization, precisely located metal centers, unique metal-support interactions and identical coordination environments. Such advantages of SACs drastically boost the specific activity per metal atom, and thus provide great potential for achieving superior catalytic activity and selectivity to functionally mimic or even outperform natural enzymes of interest. Although the size of the catalysts does matter, it is not clear whether the guideline of "the smaller, the better" is still correct for developing catalysts at the single-atom scale. Thus, it is clearly a new, urgent issue to address before further extending SACs into biomedical applications, representing an important branch of nanomedicine. This review begins by providing an overview of recent advances of synthesis strategies of SACs, which serve as a basis for the discussion of emerging achievements in improving the enzyme-like catalytic properties at an atomic level. Then, we carefully compare the structures and functions of catalysts at various scales from nanoparticles, nanoclusters, and few-atom clusters to single atoms. Contrary to conventional wisdom, SACs are not the most catalytically active catalysts in specific reactions, especially those requiring multi-site auxiliary activities. After that, we highlight the unique roles of SACs toward biomedical applications. To appreciate these advances, the challenges and prospects in rapidly growing studies of SACs-related catalytic nanomedicine are also discussed in this review.

Paediatric Osteomyelitis and Septic Arthritis Pathogen Distribution and Antimicrobial Resistance in a Single Centre: A 15-Year Retrospective Analysis

BACKGROUND

The epidemiological characteristics of the common pathogens underlying acute haematogenous osteoarticular infection (AHOI) and their resistance to drugs have temporal and regional differences.

AIMS

To determine the antimicrobial treatment most effective for culture-negative AHOI patients and those without bacterial cultures.

METHODS

Retrospective analysis of clinical data of children with AHOI who were culture positive from January 2007 to December 2021. And the distribution of the main pathogens and the drug resistance Staphylococcus aureus were analysed in different time periods, age groups and infection types.

RESULTS

A total of 188 cases met the inclusion criteria, including 97 cases of acute haematogenous osteomyelitis (AHO), 75 cases of septic arthritis (SA) and 16 cases of AHO concomitant with SA. The commonest causative pathogen in local children was S. aureus of Gram-positive cocci, followed by Streptococcus, and occasionally Gram-negative bacilli. The distribution of S. aureus had no significant correlation with age or infection type. Staphylococcus aureus accounted for 81.82%, 90.91% and 96.15% of all pathogens, and methicillin-resistant S. aureus (MRSA) accounted for 24.22%, 53.33% and 76.00% of S. aureus in 2007-11, 2012-16 and 2017-21, respectively. The frequency of MRSA infection showed an increasing trend over time.

CONCLUSION

Staphylococcus aureus is still the main pathogen of AHOI in local children. The proportion of MRSA in S. aureus has also increased over time to 76% in the last 5 years, and the increased proportion of MRSA can affect the choice of initial empirical medication.

Surface functionalization with copper endows carbonate apatite honeycomb scaffold with antibacterial, proangiogenic, and pro-osteogenic activities

Osteomyelitis is a potentially devastating inflammatory bone disease that leads to bone destruction and loss. Treatment of osteomyelitis requires the removal of residual bacteria as well as osteogenesis with angiogenesis at the site of treatment. Use of an appropriate amount of copper (Cu) in treatment scaffolds may achieve these goals without the risk of toxicity. In this study, the surface of the carbonate apatite honeycomb scaffold was functionalized with Cu through a dissolution-precipitation reaction. The resulting scaffolds retained the honeycomb structure after immersion in CuCl₂ solution, and Cu was precipitated on the surface as libethenite [Cu₂(OH)PO₄]. The surface Cu concentration was controlled by the concentration of the CuCl₂ solution. Scaffolds with a surface Cu concentration of 23.8 wt% exhibited antibacterial and cytotoxic effects, whereas those with concentrations of ≤4.6 wt% exerted antibacterial effects without negatively affecting the cellular adhesion, proliferation, differentiation, and calcification of osteoblast-like cells. Furthermore, scaffolds with a surface Cu concentration of 4.6 wt% Cu inhibited bacterial growth for at least 28 days and displayed proangiogenic and pro-osteogenic activities in vivo. These data confirm the success in functionalizing scaffolds with Cu that may be utilized as an innovative osteomyelitis therapy.

Long non-coding RNA KCNQ1OT1 overexpression promotes osteogenic differentiation of staphylococcus aureus-infected human bone mesenchymal stem cells by sponging microRNA miR-29b-3p

Osteomyelitis (OM) is an orthopedic disease caused by bone infections in the bone cortex, bone marrow, periosteum, and surrounding soft tissues. Recent studies have implicated non-coding RNAs (ncRNAs) in the development of OM. However, little is known about the role of ncRNAs in the osteogenic differentiation during bone infection. In the present study, we investigated the role of KCNQ1OT1/miR-29b-3p axis in osteogenic differentiation in staphylococcus aureus (SpA)-infected human bone mesenchymal stem cells (hBMSCs). We first examined the expression of lncRNA KCNQ1OT1 and miR-29b-3p in the serum samples of OM patients and healthy controls. We also infected hBMSCs with different concentrations of SpA and studied the osteogenic differentiation after infection. Our results revealed that KCNQ1OT1 was downregulated while miR-29b-3p was upregulated in the serum samples of OM patients, as well as in SpA-infected hBMSCs. Overexpression of KCNQ1OT1 ameliorated the damage in hBMSCs caused by SpA infection. KCNQ1OT1 could support hBMSCs osteogenic differentiation by enhancing ALP activity, alizarin red S accumulation, expressions of osteogenic markers, and attenuating inflammatory responses after SpA infection. We further showed that miR-29b-3p was a downstream target of KCNQ1OT1, mediating the osteogenic differentiation of hBMSCs during SpA infection. Our data suggest that KCNQ1OT1 could ameliorate the SpA-induced suppression of osteogenic differentiation in hBMSCs by sponging miR-29b-3p. Modulating KCNQ1OT1 expression may serve as a strategy to ameliorate osteomyelitis.

Role of Implantable Drug Delivery Devices with Dual Platform Capabilities in the Prevention and Treatment of Bacterial Osteomyelitis

As medicine advances and physicians are able to provide patients with innovative solutions, including placement of temporary or permanent medical devices that drastically improve quality of life of the patient, there is the persistent, recurring problem of chronic bacterial infection, including osteomyelitis. Osteomyelitis can manifest as a result of traumatic or contaminated wounds or implant-associated infections. This bacterial infection can persist as a result of inadequate treatment regimens or the presence of biofilm on implanted medical devices. One strategy to mitigate these concerns is the use of implantable medical devices that simultaneously act as local drug delivery devices (DDDs). This classification of device has the potential to prevent or aid in clearing chronic bacterial infection by delivering effective doses of antibiotics to the area of interest and can be engineered to simultaneously aid in tissue regeneration. This review will provide a background on bacterial infection and current therapies as well as current and prospective implantable DDDs, with a particular emphasis on local DDDs to combat bacterial osteomyelitis.

Ultrasonic Interfacial Engineering of MoS2 -Modified Zn Single-Atom Catalysts for Efficient Osteomyelitis Sonodynamic Ion Therapy

Osteomyelitis is considered as the most serious bone infection, which can lead to the bone destruction or fatal sepsis. Clinical treatments through frequent antibiotics administration and surgical debridement bring inevitable side effects including drug-resistance and disfigurements. It is urgent to develop an antibiotics-free and rapid strategy to treat osteomyelitis. Herein, a bifunctional sonosensitizer that consists of porphyrin-like Zn single-atom catalysts (g-ZnN₄ ) and MoS₂ quantum dots is developed, which exhibits excellent sonodynamic antibacterial efficiency and osteogenic ability. It is found that the construction of heterogeneous interfaces of g-ZnN₄ -MoS₂ fully activates the adsorbed O₂ due to the increased interface charge transfer, enhanced spin-flip, and reduced activation energy of O₂ . The generated ¹ O₂ can kill methicillin-resistant Staphylococcus aureus (MRSA) with an antibacterial efficiency of 99.58% under 20 min of ultrasound (US) irradiation. The Zn single atoms immobilized in g-ZnN₄ can be released steadily in the form of Zn²⁺ for 28 days within safe concentration, realizing the great osteoinductive ability of such a sonosensitizer. For the treatment of MRSA-infected osteomyelitis, the inflammation and bone loss can be significantly suppressed through sonodynamic ion therapy. This work provides another strategy for developing high efficiency sonosensitizer through ultrasound interfacial engineering.

Erythrocyte Membrane-Enveloped Molybdenum Disulfide Nanodots for Biofilm Elimination on Implants via Toxin Neutralization and Immune Modulation

Implant-related infections (IRIs) caused by bacterial biofilms remain a prevalent but tricky clinical issue, which are characterized by drug resistance, toxin impairment and immunity suppression. Recently, antimicrobial therapies based on...

Changes of Migration, Immunoregulation and Osteogenic Differentiation of Mesenchymal Stem Cells in Different Stages of Inflammation

Bone infection has always been the focus of orthopedic research. Mesenchymal stem cells (MSCs) are the natural progenitors of osteoblasts, and the process of osteogenesis is triggered in response to different signals from the extracellular matrix. MSCs exert important functions including secretion and immune regulation and also play a key role in bone regeneration. The biological behavior of MSCs in acute and chronic inflammation, especially the transformation between acute inflammation and chronic inflammation, has aroused great interest among researchers. This paper reviews the recent literature and summarizes the behavior and biological characteristics of MSCs in acute and chronic inflammation to stimulate further research on MSCs and treatment of bone diseases.

In Vivo Antibacterial Efficacy of Nanopatterns on Titanium Implant Surface: A Systematic Review of the Literature

Background: Bionic surface nanopatterns of titanium (Ti) materials have excellent antibacterial effects in vitro for infection prevention. To date, there is a lack of knowledge about the in vivo bactericidal outcomes of the nanostructures on the Ti implant surfaces. Methods: A systematic review was performed using the PubMed, Embase, and Cochrane databases to better understand surface nanoscale patterns’ in vivo antibacterial efficacy. The inclusion criteria were preclinical studies (in vivo) reporting the antibacterial activity of nanopatterns on Ti implant surface. Ex vivo studies, studies not evaluating the antibacterial activity of nanopatterns or surfaces not modified with nanopatterns were excluded. Results: A total of five peer-reviewed articles met the inclusion criteria. The included studies suggest that the in vivo antibacterial efficacy of the nanopatterns on Ti implants’ surfaces seems poor. Conclusions: Given the small number of literature results, the variability in experimental designs, and the lack of reporting across studies, concluding the in vivo antibacterial effectiveness of nanopatterns on Ti substrates’ surfaces remains a big challenge. Surface coatings using metallic or antibiotic elements are still practical approaches for this purpose. High-quality preclinical data are still needed to investigate the in vivo antibacterial effects of the nanopatterns on the implant surface.

Recent advances in the local antibiotics delivery systems for management of osteomyelitis

Chronic osteomyelitis is a challenging disease due to its serious rates of mortality and morbidity while the currently available treatment strategies are suboptimal. In contrast to the adopted systemic treatment approaches after surgical debridement in chronic osteomyelitis, local drug delivery systems are receiving great attention in the recent decades. Local drug delivery systems using special carriers have the pros of enhancing the feasibility of penetration of antimicrobial agents to bone tissues, providing sustained release and localized concentrations of the antimicrobial agents in the infected area while avoiding the systemic side effects and toxicity. Most important, the incorporation of osteoinductive and osteoconductive materials in these systems assists bones proliferation and differentiation, hence the generation of new bone materials is enhanced. Some of these systems can also provide mechanical support for the long bones during the healing process. Most important, if the local systems are designed to be injectable to the affected site and biodegradable, they will reduce the level of invasion required for implantation and can win the patients’ compliance and reduce the healing period. They will also allow multiple injections during the course of therapy to guard against the side effect of the long-term systemic therapy. The current review presents different available approaches for delivering antimicrobial agents for the treatment of osteomyelitis focusing on the recent advances in researches for local delivery of antibiotics.

HIGHLIGHTS

Chronic osteomyelitis is a challenging disease due to its serious mortality and morbidity rates and limited effective treatment options.

Local drug delivery systems are receiving great attention in the recent decades.

Osteoinductive and osteoconductive materials in the local systems assists bones proliferation and differentiation

Local systems can be designed to provide mechanical support for the long bones during the healing process.

Designing the local system to be injectable to the affected site and biodegradable will reduces the level of invasion and win the patients’ compliance.

Injectable polyelectrolyte complex-nascent HAP biodegradable antibiotic delivery system for the treatment of osteomyelitis

An injectable osteoconductive polyelectrolyte complex -hydroxyapatite formulation capable of controlled delivery of ciprofloxacin has been developed from a novel biodegradable polyelectrolyte complex and antibiotic loaded nascent hydroxyapatite (n-HAP) for the treatment of osteomyelitis. A single source (chitosan) derived polyelectrolytes were complexed in situ in the presence of n-HAP, pre-loaded with ciprofloxacin. The PEC- (n-HAP) nanoformulation (HPEC) was characterized by FT-IR, XRD, TGA and TEM analyses. HPEC combines functionalities of n-HAP (crystallinity and osteoconductivity) as well as PEC (biodegradable hydrophilic electrostatically bound macromolecular network) imparting better control over swelling and degradation kinetics favourable for drug release and transport of micronutrients. MTT assay and cytoskeleton staining (MG 63 cells) established cytocompatibility of HPEC. Early biomimetic mineralization of apatite was manifested under simulated physiological condition with a Ca/P of 1.23 (day 3) and 1.55 (day 6) complimented by in vitro biomineralization of MG-63 and Human Osteosarcoma (HOS) cells in a week (Alizarin Red S staining), which was further validated by calcium quantification. Antibacterial efficacy of HPEC has been evaluated by delivery kinetics of ciprofloxacin and by disc diffusion method against S. aureus and E. coli. The injectable system therefore possesses unique combination of functionalities: osteoconduction enriched with early biomineralization, antibacterial activity and is biodegradable; hence highly suitable for osteomyelitis treatment.

Current opinions on the mechanism, classification, imaging diagnosis and treatment of post-traumatic osteomyelitis

Post-traumatic osteomyelitis (PTO) is a worldwide problem in the field of orthopaedic trauma. So far, there is no ideal treatment or consensus-based gold standard for its management. This paper reviews the representative literature focusing on PTO, mainly from the following four aspects: (1) the pathophysiological mechanism of PTO and the interaction mechanism between bacteria and the body, including fracture stress, different components of internal fixation devices, immune response, occurrence and development mechanisms of inflammation in PTO, as well as the occurrence and development mechanisms of PTO in skeletal system; (2) clinical classification, mainly the etiological classification, histological classification, anatomical classification and the newly proposed new classifications (a brief analysis of their scope and limitations); (3) imaging diagnosis, including non-invasive examination and invasive examination (this paper discusses their advantages and disadvantages respectively, and briefly compares the sensitivity and effectiveness of the current examinations); and (4) strategies, including antibiotic administration, surgical choices and other treatment programs. Based on the above-mentioned four aspects, we try to put forward some noteworthy sections, in order to make the existing opinions more specific.

Staphylococcal infection prevention using antibiotic-loaded mannitol-chitosan paste in a rabbit model of implant-associated osteomyelitis

Antibiotic-loaded chitosan pastes have shown advantages in the treatment and coverage of complex musculoskeletal defects. We added mannitol, previously shown to increase antibiotic susceptibility of biofilm, to an injectable chitosan/polyethylene glycol paste for delivery of antibiotics. Ground sponges (0.85% acetic acid solution, 1% chitosan, 0% or 2% mannitol, 1% polyethylene glycol) were hydrated using phosphate-buffered saline with 10 mg/ml amikacin and 10 mg/ml vancomycin added to form pastes. We inoculated rabbit radial defects with 10⁵ colony-forming units of Staphylococcus aureus (UAMS-1) and inserted titanium pins into the cortical bone. Groups compared included mannitol blend pastes, non-mannitol blends, antibiotic-loaded bone cement, vancomycin powder, and no treatment controls. We harvested tissue samples and retrieved the pins retrieved at 3 weeks. All antibiotic-loaded groups lowered bacterial growth and colony-forming unit counts in soft and bone tissue and on titanium pins in in vivo studies. The results indicate this biomaterial is capable of eluting active antibiotics at concentrations that reduce bacterial growth on biomaterials and tissue, which, in turn, may prevent biofilm formation. Blends of chitosan and mannitol may be useful in prevention and treatment of osteomyelitis and implant-associated infections.

Neutralization of IL-17 and treatment with IL-2 protects septic arthritis by regulating free radical production and antioxidant enzymes in Th17 and Tregs: An immunomodulatory TLR2 versus TNFR response

Septic arthritis is a destructive joint disease caused by Staphylococcus aureus. Synovial inflammation involved Th17 proliferation and down regulation of Treg population, thus resolution of inflammation targeting IL-17 may be important to control arthritis. Endogenous inhibition of IL-17 to regulate arthritic inflammation correlating with Th17/Treg cells TLR2 and TNFRs are not done. The role of SOD, CAT and GRx in relation to ROS production during arthritis along with expression of TLR2, TNFR1/TNFR2 in Th17/Treg cells of mice treated with IL-17A Ab/ IL-2 were studied. Increased ROS, reduced antioxidant enzyme activity was found in Th17 cells of SA infected mice whereas Treg cells of IL-17A Ab/ IL-2 treated group showed opposite effects. Neutralization of IL-17 after arthritis cause decreased TNFR1 and increased TNFR2 expression in Treg cells. Thus, neutralization of IL-17 or IL-2 treatment regulates septic arthritis by enhancing anti-inflammatory properties of Treg via antioxidant balance and modulating TLR2/TNFR response.

Biomaterials and nanomedicine for bone regeneration: Progress and future prospects

Bone defects pose a heavy burden on patients, orthopedic surgeons, and public health resources. Various pathological conditions cause bone defects including trauma, tumors, inflammation, osteoporosis, and so forth. Auto- and allograft transplantation have been developed as the most commonly used clinic treatment methods, among which autologous bone grafts are the golden standard. Yet the repair of bone defects, especially large-volume defects in the geriatric population or those complicated with systemic disease, is still a challenge for regenerative medicine from the clinical perspective. The fast development of biomaterials and nanomedicine favors the emergence and promotion of efficient bone regeneration therapies. In this review, we briefly summarize the progress of novel biomaterial and nanomedical approaches to bone regeneration and then discuss the current challenges that still hinder their clinical applications in treating bone defects.

Novel calcium phosphate cement with biofilm-inhibition and platelet lysate delivery to enhance osteogenesis of encapsulated human periodontal ligament stem cells

Osteomyelitis is caused by Staphylococcus aureus (S. aureus), with associated progressive bone loss. This study developed for the first time a calcium phosphate cement (CPC) for delivery of doxycycline (DOX) and human platelet lysate (hPL) to fight against S. aureus infection and enhance the osteogenesis of human periodontal ligament stem cells (hPDLSCs). Chitosan-containing CPC scaffolds were fabricated in the absence (CPCC) or presence of DOX (CPCC+DOX). In addition, hPL was encapsulated in alginate microbeads and incorporated into CPCC+DOX (CPCC+DOX+ hPL). Flexural strength of CPCC+DOX + hPL was (5.56 ± 0.55) MPa, lower than (8.26 ± 1.6) MPa of CPCC+DOX (p < 0.05), but exceeding the reported strength of cancellous bone. CPCC+DOX and CPCC+DOX + hPL exhibited strong antibacterial activity against S. aureus, reducing biofilm CFU by 4 orders of magnitude. The hPDLSCs encapsulated in microbeads were co-cultured with the CPCs. The hPDLSCs were able to be released from the microbeads and showed a high proliferation rate, increasing by about 8 folds at 14 days for all groups. The hPL was released from the scaffold and promoted the osteogenic differentiation of hPDLSCs. ALP activity was 28.07 ± 5.15 mU/mg for CPCC+DOX + hPL, higher than 17.36 ± 2.37 mU/mg and 1.34 ± 0.37 mU/mg of CPCC+DOX and CPCC, respectively (p < 0.05). At 7 days, osteogenic genes (ALP, RUNX2, COL-1, and OPN) in CPCC+DOX + hPL were 3-10 folds those of control. The amount of hPDLSC-synthesized bone mineral with CPCC+DOX + hPL was 3.8 folds that of CPCC (p < 0.05). In summary, the novel CPC + DOX + hPL-hPDLSCs scaffold exhibited strong antibacterial activity, excellent cytocompatibility and hPDLSC osteogenic differentiation, showing a promising approach for treatment and prevention of bone infection and enhancement of bone regeneration.

Molecular Cloning, Functional and Biophysical Characterization of an Antimicrobial Peptide from Rhizosphere Soil

AIM

This study was designed to screen and identify an antimicrobial peptide from rhizosphere soil. The study was further focused towards overexpression, purification and characterization of this antimicrobial peptide, and to functionally validate its efficiency and efficacy as an antimicrobial agent. Yet the study was further aimed at corroborating structural and functional studies using biophysical tools.

BACKGROUND

Antimicrobial resistance is emerging as one of the top 10 global health crisis, it is multifaceted and is the second largest cause of mortality. According to the World Health Organization (WHO), around the world, an estimated 700,000 people die each year from infection caused by antibiotic-resistant microbes. Antimicrobial peptides offers best alternative to combat and overcome this crisis. In this manuscript, we report cloning, expression, purification and characterization of an antimicrobial peptide discovered from rhizosphere soil.

OBJECTIVE

Objectives of this study includes construction, screening and identification of antimicrobial peptide from metagenome followed by its expression, purification and functional and biophysical investigation. Yet another objective of the study was to determine antimicrobial efficacy and efficiency as an antimicrobial peptide towards MRSA strains.

METHODS

In this study, we used array of molecular biology tools that include genetic engineering, PCR amplification, construction of an expression construct and NI-NTA based purification of the recombinant peptide. We have also carried out antimicrobial activity assay to determine MIC and IC50 values of antimicrobial peptide. To establish structural and functional relationship, circular dichroism, and both extrinsic and intrinsic fluorescence spectroscopy studies were carried out.

RESULTS

Screening of metagenomic library resulted in identification of gene (~500bp) harbouring an open reading frame (ORF) consisting of 282 bp. Open reading frame identified in gene encodes an antimicrobial peptide which had shared ~95% sequence similarity with the antimicrobial peptide of Bacillus origin. Purification of recombinant protein using Ni-NTA column chromatography demonstrated a purified protein band of ~11 kDa on 14% SDS-PAGE which is well corroborated to theoretical deduced molecular weight of peptide from its amino acids sequence. Interestingly, the peptide exhibited antimicrobial activity in broad range of pH and temperature. MIC (minimum inhibitory concentration) determined against gram positive Bacillus sp. was found to be 0.015mg/ml, whereas in case of gram negative E. coli, it was calculated to be 0.062mg/ml. The peptide exhibited IC50 values corresponding to ~0.25mg/ml against Bacillus and ~0.5 mg/ml against E. coli. Antimicrobial susceptibility assay performed against methicillin resistant Staphylococcus aureus strain ATCC 3412 and standard strain of Staphylococcus aureus ATCC 9144 revealed its strong inhibitory activity against MRSA, whereby we observed a ~16mm clearance zone at higher peptide concentrations ~2mg/ml (~181.8µM). Biophysical investigation carried out using Trp fluorescence, ANS fluorescence and circular dichroism spectroscopy further revealed conformational stability in its secondary and tertiary structure at wide range of temperature and pH.

CONCLUSION

Altogether, the peptide discovered from rhizosphere metagenome hold potential in inhibiting the growth of both the gram positive and gram negative bacteria, and was equally effective in inhibiting the multidrug resistant pathogenic strains (MRSA).

Accuracy and Impact on Patient Management of New Tools for Diagnosis of Sepsis: Experience with the T2 Magnetic Resonance Bacteria Panel

The rapid and accurate identification of pathogens responsible for sepsis is essential for prompt and effective antimicrobial therapy. Molecular technologies have been developed to detect the most common causative agents, with high sensitivity and short time to result (TTR). T2 Bacteria Panel (T2), based on a combination of PCR and T2 magnetic resonance, can identify directly in blood samples Escherichia coli, Staphylococcus aureus, Klebsiella pneumoniae, Pseudomonas aeruginosa, Enterococcus faecium, and Acinetobacter baumannii pathogens. This study evaluates the role of T2 in the diagnosis of sepsis and its impact on patient management, specifically in terms of TTR and the switch from empirical to directed therapy, comparing results of blood culture (BC) and T2 assay in 82 patients with sepsis. T2 significantly improved the detection of the causative agents of sepsis. For pathogens included in the panel, T2 sensitivity was 100% (95% CI 86.3–100.0), significantly higher than that of BC (54.8%, 95% CI 36.0–72.7). The TTR (median, IQR) of positive T2 (3.66 h, 3.59–4.31) was significantly shorter than that of the positive BC (37.58 h, 20.10–47.32). A significant reduction in the duration of empiric therapy and an increase in the percentage of patients with switched therapy was observed in patients with a positive T2 result. In conclusion, T2 can shorten and improve the etiological diagnosis of sepsis with a positive impact on patient management.

Characterization of an osteomyelitis case caused by dalbavancin, ceftaroline, and vancomycin non-susceptible methicillin-resistant Staphylococcus aureus

We report a case of osteomyelitis due to methicillin-resistant Staphylococcus aureus (MRSA) that is also non-susceptible to vancomycin, dalbavancin, ceftaroline, and ceftobiprole, in the absence of exposure to the latter three antibiotics. It was isolated from a patient with a 26-year history of cranial surgeries and episodes of osteomyelitis. Whole-genome sequencing was performed. It was found to belong to ST247 and the mecA gene was detected within the SSCmec type I (1B) gene cassette that lacked the E447K mutation known to produce resistance to ceftobiprole and ceftaroline. However, mutations in other genes related to resistance to these antibiotics were found.

The Potential Role of RP105 in Regulation of Inflammation and Osteoclastogenesis During Inflammatory Diseases

Inflammatory diseases have a negative impact on bone homeostasis via exacerbated local and systemic inflammation. Bone resorbing osteoclasts are mainly derived from hematopoietic precursors and bone marrow monocytes. Induced osteoclastogenesis during inflammation, autoimmunity, metabolic diseases, and cancers is associated with bone loss and osteoporosis. Proinflammatory cytokines, pathogen-associated molecular patterns, or endogenous pathogenic factors induce osteoclastogenic differentiation by binding to the Toll-like receptor (TLR) family expressed on surface of osteoclast precursors. As a non-canonical member of the TLRs, radioprotective 105 kDa (RP105 or CD180) and its ligand, myeloid differentiation protein 1 (MD1), are involved in several bone metabolic disorders. Reports from literature had demonstrated RP105 as an important activator of B cells, bone marrow monocytes, and macrophages, which regulates inflammatory cytokines release from immune cells. Reports from literature had shown the association between RP105 and other TLRs, and the downstream signaling mechanisms of RP105 with different “signaling-competent” partners in immune cells during different disease conditions. This review is focused to summarize: (1) the role of RP105 on immune cells’ function and inflammation regulation (2) the potential regulatory roles of RP105 in different disease-mediated osteoclast activation and the underlying mechanisms, and (3) the different “signaling-competent” partners of RP105 that regulates osteoclastogenesis.

Novel FtsZ inhibitor with potent activity against Staphylococcus aureus

OBJECTIVES

FtsZ is an essential bacterial protein and an unexplored target for the development of antibacterial drugs. The development of a novel inhibitor targeting FtsZ offers a potential opportunity to combat drug resistance. DS01750413, a new derivative of PC190723, is a novel FtsZ inhibitor with improved in vitro and in vivo activity. The objective of this study was to investigate the efficacy of DS01750413 against Staphylococcus spp., including MRSA, in in vitro and in vivo models.

METHODS

In vitro activities of DS01750413 and standard-of-care antibiotics were evaluated against clinical isolates of Gram-positive pathogens. The in vivo efficacy was evaluated in a murine systemic infection model caused by MRSA.

RESULTS

DS01750413 showed potent in vitro activity against MRSA clinical isolates with MIC ranges of 0.5-1 mg/L and also demonstrated concentration-dependent bactericidal killing. In the murine bacteraemia infection model of MRSA, treatment with DS01750413 resulted in prolonged survival of animals compared with placebo-treated animals and exhibited a significant reduction in the bacterial load in liver, spleen, lungs and kidneys.

CONCLUSIONS

DS01750413 showed encouraging in vitro and in vivo activity against MRSA. As a novel chemical class, DS01750413 has the potential to become clinically viable antibiotics to address the drug resistance problem by its unique novel targeting mechanism of action.

Modification of polyetheretherketone implants: From enhancing bone integration to enabling multi-modal therapeutics

Polyetheretherketone (PEEK) is a popular thermoplastic material widely used in engineering applications due to its favorable mechanical properties and stability at high temperatures. With the first implantable grade PEEK being commercialized in 1990s, the use of PEEK has since grown exponentially in the biomedical field and has rapidly transformed a large section of the medical devices landscape. Nowadays, PEEK is a standard biomaterial used across a wide range of implant applications, however, its bioinertness remains a limitation for bone repair applications. The increasing demand for enhanced treatment efficacy/improved patient quality of life, calls for next-generation implants that can offer fast bone integration as well as other desirable therapeutic functions. As such, modification of PEEK implants has progressively shifted from offering desirable mechanical properties, enhancing bioactivity/fast osteointegration, to more recently, tackling post-surgery bacterial infection/biofilm formation, modulation of inflammation and management of bone cancers. Such progress is also accompanied by the evolution of the PEEK manufacturing technologies, to meet the ever increasing demand for more patient specific devices. However, no review has comprehensively covered the recently engaged application areas to date. This paper provides an up-to-date review on the development of PEEK-based biomedical devices in the past 10 years, with particularly focus on modifying PEEK for multi-modal therapeutics. The aim is to provide the peers with a timely update, which may guide and inspire the research and development of next generation PEEK-based healthcare products. STATEMENT OF SIGNIFICANCE: Significant progress has been made in PEEK processing and modification techniques in the past decades, which greatly contributed to its wide applications in the biomedical field. Despite the high volume of published literature on PEEK implant related research, there is a lack of review on its emerging applications in multi-modal therapeutics, which involve bone regeneration, anti-bacteria/anti-inflammation, and cancer inhibition, etc. This timely review covers the state-of-the-art in these exciting areas and provides the important guidance for next generation PEEK based biomedical device research and development.

Effect of Gold Nanoparticles and Silicon on the Bioactivity and Antibacterial Properties of Hydroxyapatite/Chitosan/Tricalcium Phosphate-Based Biomicroconcretes

Bioactive, chemically bonded bone substitutes with antibacterial properties are highly recommended for medical applications. In this study, biomicroconcretes, composed of silicon modified (Si-αTCP) or non-modified α-tricalcium phosphate (αTCP), as well as hybrid hydroxyapatite/chitosan granules non-modified and modified with gold nanoparticles (AuNPs), were designed. The developed biomicroconcretes were supposed to combine the dual functions of antibacterial activity and bone defect repair. The chemical and phase composition, microstructure, setting times, mechanical strength, and in vitro bioactive potential of the composites were examined. Furthermore, on the basis of the American Association of Textile Chemists and Colorists test (AATCC 100), adapted for chemically bonded materials, the antibacterial activity of the biomicroconcretes against S. epidermidis, E. coli, and S. aureus was evaluated. All biomicroconcretes were surgically handy and revealed good adhesion between the hybrid granules and calcium phosphate-based matrix. Furthermore, they possessed acceptable setting times and mechanical properties. It has been stated that materials containing AuNPs set faster and possess a slightly higher compressive strength (3.4 ± 0.7 MPa). The modification of αTCP with silicon led to a favorable decrease of the final setting time to 10 min. Furthermore, it has been shown that materials modified with AuNPs and silicon possessed an enhanced bioactivity. The antibacterial properties of all of the developed biomicroconcretes against the tested bacterial strains due to the presence of both chitosan and Au were confirmed. The material modified simultaneously with AuNPs and silicon seems to be the most promising candidate for further biological studies.

3D Cocultures of Osteoblasts and Staphylococcus aureus on Biomimetic Bone Scaffolds as a Tool to Investigate the Host-Pathogen Interface in Osteomyelitis

Osteomyelitis (OM) is an infectious disease of the bone primarily caused by the opportunistic pathogen Staphylococcus aureus (SA). This Gram-positive bacterium has evolved a number of strategies to evade the immune response and subvert bone homeostasis, yet the underlying mechanisms remain poorly understood. OM has been modeled in vitro to challenge pathogenetic hypotheses in controlled conditions, thus providing guidance and support to animal experimentation. In this regard, traditional 2D models of OM inherently lack the spatial complexity of bone architecture. Three-dimensional models of the disease overcome this limitation; however, they poorly reproduce composition and texture of the natural bone. Here, we developed a new 3D model of OM based on cocultures of SA and murine osteoblastic MC3T3-E1 cells on magnesium-doped hydroxyapatite/collagen I (MgHA/Col) scaffolds that closely recapitulate the bone extracellular matrix. In this model, matrix-dependent effects were observed in proliferation, gene transcription, protein expression, and cell–matrix interactions both of the osteoblastic cell line and of bacterium. Additionally, these had distinct metabolic and gene expression profiles, compared to conventional 2D settings, when grown on MgHA/Col scaffolds in separate monocultures. Our study points to MgHA/Col scaffolds as biocompatible and bioactive matrices and provides a novel and close-to-physiology tool to address the pathogenetic mechanisms of OM at the host–pathogen interface.

Recent Advances in Research on Antibacterial Metals and Alloys as Implant Materials

Implants are widely used in orthopedic surgery and are gaining attention of late. However, their use is restricted by implant-associated infections (IAI), which represent one of the most serious and dangerous complications of implant surgeries. Various strategies have been developed to prevent and treat IAI, among which the closest to clinical translation is designing metal materials with antibacterial functions by alloying methods based on existing materials, including titanium, cobalt, tantalum, and biodegradable metals. This review first discusses the complex interaction between bacteria, host cells, and materials in IAI and the mechanisms underlying the antibacterial effects of biomedical metals and alloys. Then, their applications for the prevention and treatment of IAI are highlighted. Finally, new insights into their clinical translation are provided. This review also provides suggestions for further development of antibacterial metals and alloys.

Chronic osteomyelitis caused by Achromobacter xylosoxidans following orthopaedic trauma: A case report and review of the literature

Background

Achromobacter xylosoxidans is an opportunistic environmental aerobe. In cases where A. xylosoxidans infects humans, it most commonly manifests as bacteraemia in the immunosuppressed. A. xylosoxidans causing chronic osteomyelitis is rare, particularly in the immunocompetent and young.

Case

We present the case of a 23-year-old man with chronic osteomyelitis of the right femur caused by co-infection of A. xylosoxidans and Staphylococcus aureus. Five years earlier, he had sustained a right femur fracture and was treated with intramedullary fixation at a peripheral hospital in a developing nation. Past medical history was otherwise unremarkable. Management comprised of surgical debridement and culture-directed antibiotic therapy, resulting in clinical cure.

Conclusion

In the context of local trauma and previous surgery, osteomyelitis caused by atypical pathogens must be considered. A multidisciplinary approach commensurate with duration and severity of infection and tailored to the causative organism is paramount.

Single-Atom Catalysis for Efficient Sonodynamic Therapy of Methicillin-Resistant Staphylococcus aureus-Infected Osteomyelitis

Osteomyelitis, as a severe bone disease caused by bacterial infection, can result in lifelong disability or fatal sepsis. Considering that the infection is stubborn and deep-sited in bone tissue, in situ and rapid treatments for osteomyelitis remain a significant challenge. Herein, we prepare an ultrasound (US)-activated single-atom catalyst that consists of a Au nanorod (NRs)-actuated single-atom-doped porphyrin metal-organic framework (HNTM-Pt@Au) and red cell membrane (RBC), which can efficiently treat methicillin-resistant Staphylococcus aureus (MRSA)-infected osteomyelitis under US. Besides the outstanding performance in the field of photocatalysis, we find that single atoms (such as Pt, Au, Cu) also improve the sonocatalytic ability of the sonosensitizer. Due to the strong electron-trapping and oxygen adsorption capacity, the Pt single atom endows RBC-HNTM-Pt@Au with an excellent sonocatalytic activity. It shows an excellent antibacterial performance with an antibacterial efficiency of 99.9% toward MRSA under 15 min of US irradiation. Meanwhile, the RBC-HNTM-Pt@Au can be propelled directionally under US and thus dynamically neutralize the secreted toxins. The MRSA-infected osteomyelitis in rat tibia was successfully treated, which shows negligible bone loss, reduced inflammation response, and great biocompatibility. This work presents an efficient sonodynamic therapy for the treatment of deep tissue infections via a multifunctional single-atom catalyst.

Pathogenesis of Gram-Negative Bacteremia

Gram-negative bacteremia is a devastating public health threat, with high mortality in vulnerable populations and significant costs to the global economy. Concerningly, rates of both Gram-negative bacteremia and antimicrobial resistance in the causative species are increasing. Gram-negative bacteremia develops in three phases. First, bacteria invade or colonize initial sites of infection. Second, bacteria overcome host barriers, such as immune responses, and disseminate from initial body sites to the bloodstream. Third, bacteria adapt to survive in the blood and blood-filtering organs. To develop new therapies, it is critical to define species-specific and multispecies fitness factors required for bacteremia in model systems that are relevant to human infection. A small subset of species is responsible for the majority of Gram-negative bacteremia cases, including Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Acinetobacter baumannii The few bacteremia fitness factors identified in these prominent Gram-negative species demonstrate shared and unique pathogenic mechanisms at each phase of bacteremia progression. Capsule production, adhesins, and metabolic flexibility are common mediators, whereas only some species utilize toxins. This review provides an overview of Gram-negative bacteremia, compares animal models for bacteremia, and discusses prevalent Gram-negative bacteremia species.

Astragalus polysaccharide attenuates LPS-related inflammatory osteolysis by suppressing osteoclastogenesis by reducing the MAPK signalling pathway

Bacterial products can stimulate inflammatory reaction and activate immune cells to enhance the production of inflammatory cytokines, and finally promote osteoclasts recruitment and activity, leading to bone destruction. Unfortunately, effective preventive and treatment measures for inflammatory osteolysis are limited and usually confuse the orthopedist. Astragalus polysaccharide (APS), the main extractive of Astragali Radix, has been widely used for treating inflammatory diseases. In the current study, in vitro and in vivo experimental results demonstrated that APS notably inhibited osteoclast formation and differentiation dose-dependently. Moreover, we found that APS down-regulated RANKL-related osteoclastogenesis and levels of osteoclast marker genes, such as NFATC1, TRAP, c-FOS and cathepsin K. Further underlying mechanism investigation revealed that APS attenuated activity of MAPK signalling pathways (eg ERK, JNK and p38) and ROS production induced by RANKL. Additionally, APS was also found to suppress LPS-related inflammatory osteolysis by decreasing inflammatory factors' production in vivo. Overall, our findings demonstrate that APS effectively down-regulates inflammatory osteolysis due to osteoclast differentiation and has the potential to become an effective treatment of the disorders associated with osteoclast.

A New Optical Fiber Probe-Based Quantum Dots Immunofluorescence Biosensors in the Detection of Staphylococcus aureus

Staphylococcus aureus (S. aureus) is one of the most common clinical pathogenic bacteria with strong pathogenicity and usually leads to various suppurative infections with high fatality. Traditional bacterial culture for the detection of S. aureus is prone to diagnosis and antimicrobial treatment delays because of its long-time consumption and low sensitivity. In this study, we successfully developed a quantum dots immunofluorescence biosensor for S. aureus detection. The biosensor combined the advantages of biosensors with the high specificity of antigen-antibody immune interactions and the high sensitivity and stability of quantum dots fluorescence. The results demonstrated that the biosensor possessed high specificity and high sensitivity for S. aureus detection. The detection limit of S. aureus reached 1 × 10⁴ CFU/ml or even 1 × 10³ CFU/ml, and moreover, the fluorescence intensity had a significant positive linear correlation relationship with the logarithm of the S. aureus concentration in the range of 10³–10⁷ CFU/ml (correlation coefficient R² = 0.9731, P = 0.011). A specificity experiment showed that this biosensor could effectively distinguish S. aureus (1 × 10⁴ CFU/ml and above) from other common pathogenic (non-S. aureus) bacteria in nosocomial infections, such as Klebsiella pneumoniae, Pseudomonas aeruginosa, Acinetobacter baumannii and Escherichia coli. Additionally, the whole detection procedure spent only 2 h. In addition, the biosensor in this study may not be affected by the interference of the biofilm or other secretions since the clinical biological specimens are need to be fully liquefied to digest and dissolve viscous secretions such as biofilms before the detection procedure of the biosensor in this study. In conclusion, the biosensor could meet the need for rapid and accurate S. aureus detection for clinical application.

Fabrication and Characterization of Cinnamaldehyde-Loaded Mesoporous Bioactive Glass Nanoparticles/PHBV-Based Microspheres for Preventing Bacterial Infection and Promoting Bone Tissue Regeneration

Polyhydroxybutyrate-co-hydroxyvalerate (PHBV) is considered a suitable polymer for drug delivery systems and bone tissue engineering due to its biocompatibility and biodegradability. However, the lack of bioactivity and antibacterial activity hinders its biomedical applications. In this study, mesoporous bioactive glass nanoparticles (MBGN) were incorporated into PHBV to enhance its bioactivity, while cinnamaldehyde (CIN) was loaded in MBGN to introduce antimicrobial activity. The blank (PHBV/MBGN) and the CIN-loaded microspheres (PHBV/MBGN/CIN5, PHBV/MBGN/CIN10, and PHBV/MBGN/CIN20) were fabricated by emulsion solvent extraction/evaporation method. The average particle size and zeta potential of all samples were investigated, as well as the morphology of all samples evaluated by scanning electron microscopy. PHBV/MBGN/CIN5, PHBV/MBGN/CIN10, and PHBV/MBGN/CIN20 significantly exhibited antibacterial activity against Staphylococcus aureus and Escherichia coli in the first 3 h, while CIN releasing behavior was observed up to 7 d. Human osteosarcoma cell (MG-63) proliferation and attachment were noticed after 24 h cell culture, demonstrating no adverse effects due to the presence of microspheres. Additionally, the rapid formation of hydroxyapatite on the composite microspheres after immersion in simulated body fluid (SBF) during 7 d revealed the bioactivity of the composite microspheres. Our findings indicate that this system represents an alternative model for an antibacterial biomaterial for potential applications in bone tissue engineering.

Selective Activation of MST1/2 Kinases by Retinoid Agonist Adapalene Abrogates AURKA-Regulated Septic Arthritis

Septic arthritis is a chronic inflammatory disorder caused by Staphylococcus aureus invasion of host synovium, which often progresses to impairment of joint functions. Although it is known that disease progression is intricately dependent on dysregulated inflammation of the knee joint, identification of molecular events mediating such imbalance during S. aureus-induced septic arthritis still requires detailed investigation. In this article, we report that Aurora kinase A (AURKA) responsive WNT signaling activates S. aureus infection-triggered septic arthritis, which results in inflammation of the synovium. In this context, treatment with adapalene, a synthetic retinoid derivative, in a mouse model for septic arthritis shows significant reduction of proinflammatory mediators with a simultaneous decrease in bacterial burden and prevents cartilage loss. Mechanistically, adapalene treatment inhibits WNT signaling with concomitant activation of HIPPO signaling, generating alternatively activated macrophages. Collectively, we establish adapalene as a promising strategy to suppress S. aureus-induced irreversible joint damage.

Staphylococcus aureus clones causing osteomyelitis: a literature review (2000-2020)

OBJECTIVES

Staphylococcus aureus is the most common causative organism of osteomyelitis (OM). Nevertheless, the molecular epidemiology of S. aureus causing OM remains ill-defined. This study aimed to address the global epidemiology of S. aureus clones from OM patients.

METHODS

Literature databases were searched for studies reporting the molecular typing of S. aureus involved in OM published between 1 January 2000 and 29 July 2020. Data from 32 articles that fulfilled the inclusion criteria were analysed for year of publication, country of patients, methicillin susceptibility and genotypic characteristics of S. aureus isolates.

RESULTS

Pandemic clones CC5, CC8, CC22, CC30 and CC45 were the most common in OM. The distribution of clones differed greatly among studies owing to the local epidemiology of S. aureus and the MSSA heterogeneity. PVL-positive MRSA clones belonging to ST80/CC80 and ST8/CC8/USA300 were the most common among paediatric patients in Europe and the USA; greater variability was observed in the adult population. In Europe, MRSA belonged to PVL-negative CC5, CC8 and CC22 indicating a nosocomial origin of infections; in Asia PVL-positive ST59/CC59 MRSA was the most frequent. PVL-positive clones were often detected in haematogenous OM in children and adults. Although MSSA were polyclonal, PVL-negative ST398/CC398 MSSA was the most prevalent clone in diabetic foot OM.

CONCLUSION

All major S. aureus clones circulating both in hospital and community settings appear to be capable of causing OM. Future studies reporting molecular typing and genomic data will provide more insights into the epidemiology and pathobiology of S. aureus clones causing OM.

How not to miss infective causes of hip pain in children

A referral from accident and emergency for a child with hip pain is a scenario commonly faced by orthopaedic juniors on call. The list of differentials is vast and can make assessment and diagnosis challenging, with severe consequences if diagnosis is delayed or missed. Three common causes of paediatric hip pain are septic arthritis, transient synovitis and osteomyelitis. These can all present as a child with atraumatic hip pain, irritability, fever and refusal to weight bear. Differentiating between them can be challenging. A thorough history and examination, combined with appropriate investigations and imaging, is essential. Early diagnosis and prompt treatment are key to reducing irreversible secondary sequelae of joint destruction and long-term functional impairment.

Mesoporous Silica-Bioglass Composite Pellets as Bone Drug Delivery System with Mineralization Potential

For decades, local bone drug delivery systems have been investigated in terms of their application in regenerative medicine. Among them, inorganic polymers based on amorphous silica have been widely explored. In this work, we combined two types of amorphous silica: bioglass and doxycycline-loaded mesoporous silica MCM-41 into the form of spherical granules (pellets) as a bifunctional bone drug delivery system. Both types of silica were obtained in a sol-gel method. The drug adsorption onto the MCM-41 was performed via adsorption from concentrated doxycycline hydrochloride solution. Pellets were obtained on a laboratory scale using the wet granulation-extrusion-spheronization method and investigated in terms of physical properties, drug release, antimicrobial activity against Staphylococcus aureus, mineralization properties in simulated body fluid, and cytotoxicity towards human osteoblasts. The obtained pellets were characterized by satisfactory mechanical properties which eliminated the risk of pellets cracking during further investigations. The biphasic drug release from pellets was observed: burst stage (44% of adsorbed drug released within the first day) followed by prolonged release with zero-order kinetics (estimated time of complete drug release was 19 days) with maintained antimicrobial activity. The progressive biomimetic apatite formation on the surface of the pellets was observed. No cytotoxic effect of pellets towards human osteoblasts was noticed.

Anti-biofilm activity of dalbavancin against methicillin-resistant Staphylococcus aureus (MRSA) isolated from human bone infection

The presence of methicillin-resistant Staphylococcus aureus (MRSA) in bone infections difficults its treatment and is a sign of concern. The aim of this study was to evaluate in vitro activity of dalbavancin on pre-established adhered cells and 24 h old biofilms of MRSA strains isolated from a human bone infection. Thirty-three MRSA were isolated from osteomyelitis episodes. The antimicrobial susceptibility of these strains was assessed by the Kirby-Bauer disc diffusion method and the presence of resistance genes was screened by PCR. MRSA planktonic minimum inhibitory concentration and minimum bactericidal concentration were assessed. Minimum biofilm eradication concentration (MBEC) was performed by the microtiter biofilm formation assay. All 33 MRSA strains were classified as multidrug-resistant strains and susceptible to dalbavancin. Dalbavancin inhibited the growth of 54.6% and 52% of strains at the concentrations of 0.05 µg/mL and 1 µg/mL, respectively. The MBEC values up to 0.4 µg/mL demonstrated that dalbavancin was active against most strains in pre-established adhered cells and 24 h old biofilms. The current results show that dalbavancin is active against adhered cells and biofilms in vitro, suggesting that this antimicrobial agent may be an option for the treatment of bone infections caused by MRSA.

Long-Acting Lipoglycopeptides for the Treatment of Bone and Joint Infections

Background: The long-acting lipoglycopeptides dalbavancin and oritavancin possess excellent microbiologic activity against gram-positive bacteria and provide prolonged tissue exposure at sites of infection. Moreover, these antibiotics are well tolerated and do not require therapeutic drug monitoring. Methods: Pharmacokinetic/pharmacodynamic experiments ascertained that one to two doses of these long-acting agents can provide an extended period (≥6 weeks) of antimicrobial therapy. Results: Clinical studies subsequently found that microbiologic and clinical response rates with these agents were comparable to standard antibiotic agents used in the treatment of bone and joint infections. In addition, pharmacoeconomic analyses have discovered cost savings with the use of these antimicrobial agents in the treatment of serious deep-seated bacterial infections. Conclusions: Thus, these long-acting lipoglycopeptides offer potential for cost-effective outpatient parenteral antibiotic therapy of difficult to treat infections, such as osteomyelitis.

Haem toxicity provides a competitive advantage to the clinically relevant Staphylococcus aureus small colony variant phenotype

Microorganisms encounter toxicities inside the host. Many pathogens exist as subpopulations to maximize survivability. Subpopulations of Staphylococcus aureus include antibiotic-tolerant small colony variants (SCVs). These mutants often emerge following antibiotic treatment but can be present in infections prior to antibiotic exposure. We hypothesize that haem toxicity in the host selects for respiration-deficient S. aureus SCVs in the absence of antibiotics. We demonstrate that some but not all respiration-deficient SCV phenotypes are more protective than the haem detoxification system against transient haem exposure, indicating that haem toxicity in the host may contribute to the dominance of menaquinone-deficient and haem-deficient SCVs prior to antibiotic treatment.

Liposomes as a Nanoplatform to Improve the Delivery of Antibiotics into Staphylococcus aureus Biofilms

Staphylococcus aureus biofilm-associated infections are a major public health concern. Current therapies are hampered by reduced penetration of antibiotics through biofilm and low accumulation levels at infected sites, requiring prolonged usage. To overcome these, repurposing antibiotics in combination with nanotechnological platforms is one of the most appealing fast-track and cost-effective approaches. In the present work, we assessed the potential therapeutic benefit of three antibiotics, vancomycin, levofloxacin and rifabutin (RFB), through their incorporation in liposomes. Free RFB displayed the utmost antibacterial effect with MIC and MBIC₅₀ below 0.006 µg/mL towards a methicillin susceptible S. aureus (MSSA). RFB was selected for further in vitro studies and the influence of different lipid compositions on bacterial biofilm interactions was evaluated. Although positively charged RFB liposomes displayed the highest interaction with MSSA biofilms, RFB incorporated in negatively charged liposomes displayed lower MBIC₅₀ values in comparison to the antibiotic in the free form. Preliminary safety assessment on all RFB formulations towards osteoblast and fibroblast cell lines demonstrated that a reduction on cell viability was only observed for the positively charged liposomes. Overall, negatively charged RFB liposomes are a promising approach against biofilm S. aureus infections and further in vivo studies should be performed.

Mechanisms of Antibiotic Failure During Staphylococcus aureus Osteomyelitis

Staphylococcus aureus is a highly successful Gram-positive pathogen capable of causing both superficial and invasive, life-threatening diseases. Of the invasive disease manifestations, osteomyelitis or infection of bone, is one of the most prevalent, with S. aureus serving as the most common etiologic agent. Treatment of osteomyelitis is arduous, and is made more difficult by the widespread emergence of antimicrobial resistant strains, the capacity of staphylococci to exhibit tolerance to antibiotics despite originating from a genetically susceptible background, and the significant bone remodeling and destruction that accompanies infection. As a result, there is a need for a better understanding of the factors that lead to antibiotic failure in invasive staphylococcal infections such as osteomyelitis. In this review article, we discuss the different non-resistance mechanisms of antibiotic failure in S. aureus. We focus on how bacterial niche and destructive tissue remodeling impact antibiotic efficacy, the significance of biofilm formation in promoting antibiotic tolerance and persister cell formation, metabolically quiescent small colony variants (SCVs), and potential antibiotic-protected reservoirs within the substructure of bone.

Bacterial toxins in musculoskeletal infections

Musculoskeletal infections (MSKIs) remain a major health burden in orthopaedics. Bacterial toxins are foundational to pathogenesis in MSKI, but poorly understood by the community of providers that care for patients with MSKI, inducing an international group of microbiologists, infectious diseases specialists, orthopaedic surgeons and biofilm scientists to review the literature in this field to identify key topics and compile the current knowledge on the role of toxins in MSKI, with the goal of illuminating potential impact on biofilm formation and dispersal as well as therapeutic strategies. The group concluded that further research is needed to maximize our understanding of the effect of toxins on MSKIs, including: (i) further research to identify the roles of bacterial toxins in MSKIs, (ii) establish the understanding of the importance of environmental and host factors and in vivo expression of toxins throughout the course of an infection, (iii) establish the principles of drug-ability of antitoxins as antimicrobial agents in MSKIs, (iv) have well-defined metrics of success for antitoxins as antiinfective drugs, (v) design a cocktail of antitoxins against specific pathogens to (a) inhibit biofilm formation and (b) inhibit toxin release. The applicability of antitoxins as potential antimicrobials in the era of rising antibiotic resistance could meet the needs of day-to-day clinicians.

The limitations of mono- and combination antibiotic therapies on immature biofilms in a murine model of implant-associated osteomyelitis

Treatment of implant-associated orthopedic infections remains challenging, partly because antimicrobial treatment is ineffective after a mature biofilm covers the implant surface. Currently, the relative efficacy of systemic mono- and combination standard-of-care (SOC) antibiotic therapies over the course of mature biofilm formation is unknown. Thus, we assessed the effects of cefazoline (CEZ), gentamicin (GM), and vancomycin, with or without rifampin (RFP), on Staphylococcus aureus biofilm formation during the establishment of implant-associated osteomyelitis in a murine tibia model. Quantitative scanning electron microscopy of the implants harvested on Days 0, 3, and 7 revealed that all treatments except CEZ monotherapy significantly reduced biofilm formation when antibiotics started at Day 0 (0.46- to 0.25-fold; p < 0.05). When antibiotics commenced 3 days after the infection, only GM monotherapy significantly inhibited biofilm growth (0.63-fold; p < 0.05), while all antibiotics inhibited biofilm formation in combination with RFP (0.56- to 0.44-fold; p < 0.05). However, no treatment was effective when antibiotics commenced on Day 7. To confirm these findings, we assessed bacterial load via colony-forming unit and histology. The results showed that GM monotherapy and all combination therapies reduced the colony-forming unit in the implant (0.41- to 0.23-fold; p < 0.05); all treatments except CEZ monotherapy reduced the colony-forming unit and staphylococcus abscess communities in the tibiae (0.40- to 0.10-fold; p < 0.05). Collectively, these findings demonstrate that systemic SOC antibiotics can inhibit biofilm formation within 3 days but not after 7 days of infection. The efficacy of SOC monotherapies, CEZ particularly, is very limited. Thus, combination treatment with RFP may be necessary to inhibit implant-associated osteomyelitis.

Transcriptome sequencing profiling identifies miRNA-331-3p as an osteoblast-specific miRNA in infected bone nonunion

Bone nonunion caused by bacterial infection accounts for bone fractures, bone trauma and bone transplantation surgeries. Severe consequences include delayed unions and amputation and result in functional limitations, work disability, and poor quality of life. However, the mechanism of bone nonunion remains unknown. In this study, we aimed to screen the miRNA biomarkers of bacterial bone infection and investigated whether miRNAs regulate the osteoblasts and thus contribute to bone nonunion. We established a miRNA-mRNA network based on high-throughput RNA sequencing to compare the model rabbits infected with Staphylococcus aureus with the control rabbits. After validation experiments, miRNA-331-3p and fibroblast growth factor 23 (FGF23) were found to be inversely correlated with the pathways of osteoblast mineralization and pathology of infected bone nonunion. In in vitro experiments, miRNA-331-3p was downregulated and FGF23 was upregulated in lipopolysaccharide (LPS)-induced mouse calvarial osteoblasts. Further studies of the mechanism showed that mutated of putative miRNA-331-3p can bind to FGF23 3'-untranslated region sites. MiRNA-331-3p acted as an osteoblast mineralization promoter by directly targeting FGF23. Downregulation of miRNA-331-3p led to inhibition of osteoblast mineralization by regulating the DKK1/β-catenin mediated signaling. Thus, we established an improved animal model and identified new bone-related biomarkers in the infected bone nonunion. The miRNA-331-3p biomarker was demonstrated to regulate osteoblast mineralization by targeting FGF23. The novel mechanism can be used as potential diagnostic biomarkers and therapeutic targets in the infected bone nonunion and other inflammatory bone disorders.