Recalcitrant methicillin-resistant Staphylococcus aureus infection of bone cells: Intracellular penetration and control strategies

Efficacy of Commercially Available Irrigation Solutions on Removal of Staphylococcus Aureus and Biofilm From Porous Titanium Implants: An In Vitro Study

BACKGROUND

Periprosthetic joint infection remains a major problem. The bactericidal efficacy of commercial irrigation solutions for the treatment of infection is not well established in the presence of porous titanium (Ti) implants. This study compared the in vitro efficacy of five irrigation solutions on infected three-dimensional-printed porous Ti discs.

METHODS

Titanium discs (2 × 4 mm, 400, 700, and 1,000 μm) were infected with S. aureus (1 × 106 colony-forming unit/mL) and incubated for 3 hours or 3 days to create acute or chronic infection with biofilm. Discs were irrigated with saline, antibiotic, or antiseptic solutions, then repeatedly sonicated. Sonicates were cultured for bacterial quantification. Statistical analyses were performed using one-way analysis of variance (ANOVA), followed by Tukey-Kramer post hoc testing (P < .05 significance). Biofilms were visualized by scanning electron microscopy.

RESULTS

Saline irrigation was ineffective in both groups. In acute infections with 400 μm pores, differences were found with saline versus solution #3 (P = .015) and #4 (P = .015). Solution #4 had the lowest bacterial counts for all pore sizes. For biofilm, irrigation with saline, solutions #1, #2, and #3 inadequately cleared bacteria in all pore sizes. Lower remaining concentrations were observed in #4 with 400μm pores compared to saline (P = .06) and #2 (P = .039). The scanning electron microscopy showed a reduction of biofilm in samples washed with #4.

CONCLUSIONS

Irrigation of infected porous Ti discs with saline, solutions #1 and #2 failed to reduce the bacterial load. The 400 μm discs consistently had more bacteria despite irrigation, highlighting the difficulty of removing bacteria from small pores. Solutions #3 and #4 reduced bacteria acutely, but only #4 demonstrated efficacy in clearing biofilm compared to saline. These results should be considered when treating periprosthetic joint infection in the presence of porous components and the potential presence of biofilm.

Advances in the targeted theragnostics of osteomyelitis caused by Staphylococcus aureus

Bone infections caused by Staphylococcus aureus may lead to an inflammatory condition called osteomyelitis, which results in progressive bone loss. Biofilm formation, intracellular survival, and the ability of S. aureus to evade the immune response result in recurrent and persistent infections that present significant challenges in treating osteomyelitis. Moreover, people with diabetes are prone to osteomyelitis due to their compromised immune system, and in life-threatening cases, this may lead to amputation of the affected limbs. In most cases, bone infections are localized; thus, early detection and targeted therapy may prove fruitful in treating S. aureus-related bone infections and preventing the spread of the infection. Specific S. aureus components or overexpressed tissue biomarkers in bone infections could be targeted to deliver active therapeutics, thereby reducing drug dosage and systemic toxicity. Compounds like peptides and antibodies can specifically bind to S. aureus or overexpressed disease markers and combining these with therapeutics or imaging agents can facilitate targeted delivery to the site of infection. The effectiveness of photodynamic therapy and hyperthermia therapy can be increased by the addition of targeting molecules to these therapies enabling site-specific therapy delivery. Strategies like host-directed therapy focus on modulating the host immune mechanisms or signaling pathways utilized by S. aureus for therapeutic efficacy. Targeted therapeutic strategies in conjunction with standard surgical care could be potential treatment strategies for S. aureus-associated osteomyelitis to overcome antibiotic resistance and disease recurrence. This review paper presents information about the targeting strategies and agents for the therapy and diagnostic imaging of S. aureus bone infections.

Roles of extracellular vesicles on macrophages in inflammatory bone diseases

Inflammatory bone disease is a general term for a series of diseases caused by chronic inflammation, which leads to the destruction of bone homeostasis, that is, the osteolytic activity of osteoclasts increases, and the osteogenic activity of osteoblasts decreases, leading to osteolysis. Macrophages are innate immune cell with plasticity, and their polarization is related to inflammatory bone diseases. The dynamic balance of macrophages between the M1 phenotype and the M2 phenotype affects the occurrence and development of diseases. In recent years, an increasing number of studies have shown that extracellular vesicles existing in the extracellular environment can act on macrophages, affecting the progress of inflammatory diseases. This process is realized by influencing the physiological activity or functional activity of macrophages, inducing macrophages to secrete cytokines, and playing an anti-inflammatory or pro-inflammatory role. In addition, by modifying and editing extracellular vesicles, the potential of targeting macrophages can be used to provide new ideas for developing new drug carriers for inflammatory bone diseases.

The surgical management of fracture-related infection. Surgical strategy selection and the need for early surgical intervention

The aim of this narrative review is to describe the various surgical management strategies employed in fracture-related infection (FRI), to explore how they are selected and discuss the rationale for early surgical intervention. Surgical treatment options in patients with FRI include debridement, antibiotics and implant retention (DAIR), revision (exchange) or removal. In selecting a treatment strategy, a variety of factors need to be considered, including the condition of the bone, soft tissues, host and causative microorganism. Irrespective of the selected treatment strategy, prompt surgical intervention should be considered in order to confirm the diagnosis of an FRI, to identify the causative organism, remove necrotic or non-viable tissue that can serve as a nidus for ongoing infection, ensure a healthy soft tissue envelope and to prevent the vicious cycle of infection associated with skeletal and/or implant instability. Ultimately, the objective is to prevent the establishment of a persistent infection. Urgent surgery may be indicated in case of active, progressive disease with systemic deterioration, local progression of infection, deterioration of soft tissues, or progressive fracture instability. In case of static disease, the patient should be monitored closely and surgery can be performed on an elective basis, allowing adequate time for optimisation of the host through risk factor modification, optimisation of the soft tissues and careful planning of the surgery.

Efficacy of EDTA-NS irrigation in eradicating Staphylococcus aureus biofilm-associated infection

Aims

To investigate the efficacy of ethylenediaminetetraacetic acid-normal saline (EDTA-NS) in dispersing biofilms and reducing bacterial infections.

Methods

EDTA-NS solutions were irrigated at different durations (1, 5, 10, and 30 minutes) and concentrations (1, 2, 5, 10, and 50 mM) to disrupt Staphylococcus aureus biofilms on Matrigel-coated glass and two materials widely used in orthopaedic implants (Ti-6Al-4V and highly cross-linked polyethylene (HXLPE)). To assess the efficacy of biofilm dispersion, crystal violet staining biofilm assay and colony counting after sonification and culturing were performed. The results were further confirmed and visualized by confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM). We then investigated the efficacies of EDTA-NS irrigation in vivo in rat and pig models of biofilm-associated infection.

Results

When 10 mM or higher EDTA-NS concentrations were used for ten minutes, over 99% of S. aureus biofilm formed on all three types of materials was eradicated in terms of absorbance measured at 595 nm and colony-forming units (CFUs) after culturing. Consistently, SEM and CSLM scanning demonstrated that less adherence of S. aureus could be observed on all three types of materials after 10 mM EDTA-NS irrigation for ten minutes. In the rat model, compared with NS irrigation combined with rifampin (Ti-6Al-4V wire-implanted rats: 60% bacteria survived; HXLPE particle-implanted rats: 63.3% bacteria survived), EDTA-NS irrigation combined with rifampin produced the highest removal rate (Ti-6Al-4V wire-implanted rats: 3.33% bacteria survived; HXLPE particle-implanted rats: 6.67% bacteria survived). In the pig model, compared with NS irrigation combined with rifampin (Ti-6Al-4V plates: 75% bacteria survived; HXLPE bearings: 87.5% bacteria survived), we observed a similar level of biofilm disruption on Ti-6Al-4V plates (25% bacteria survived) and HXLPE bearings (37.5% bacteria survived) after EDTA-NS irrigation combined with rifampin. The in vivo study revealed that the biomass of S. aureus biofilm was significantly reduced when treated with rifampin following irrigation and debridement, as indicated by both the biofilm bacterial burden and crystal violet staining. EDTA-NS irrigation (10 mM/10 min) combined with rifampin effectively removes S. aureus biofilm-associated infections both in vitro and in vivo.

Conclusion

EDTA-NS irrigation with or without antibiotics is effective in eradicating S. aureus biofilm-associated infection both ex and in vivo.

An Orthopedic Perspective on Diabetic Foot Attack - A Case Report

Introduction

Diabetic foot attack (DFA), also known as diabetic foot ulceration, is a severe and potentially limb-threatening complication of diabetes mellitus. It refers to the development of open sores or ulcers on the feet of individuals with diabetes, often leading to infections, tissue damage, and, in extreme cases, amputation. The underlying cause of DFAs is multifactorial and involves a complex interplay of various factors, including peripheral neuropathy, peripheral arterial disease, foot deformities, impaired wound healing, and poor glycemic control. This case report would be first of its kind from an orthopedic perspective.

Case Report

A 55-year-old white British gentleman, a chronic uncontrolled Type 2 diabetic, was referred by the medical team on a busy on-call night. He presented with a sudden onset pain, swelling, and difficulty in weight bearing on his left foot. He had a non-healing plantar ulcer for over a year. His inflammatory markers were abnormally high and magnetic resonance imaging of his leg and foot showed massive collection in his foot with gas extending along the posterior compartment. Diagnosis of a severe DFA was made, and urgent debridement and washout were carried out. Despite aggressive debridement, patient progressively deteriorated warranting an admission into intensive care unit. After subsequent debridement and local antibiotic therapy, he recovered and was discharged with clinic follow-up.

Conclusion

Effective management strategies for DFAs encompass a multidisciplinary approach. Preventive measures play a key role in reducing the incidence of DFAs. Regular foot examinations, self-care education, proper glycemic control, and foot hygiene are essential components of preventive strategies. Patient education regarding self-monitoring, appropriate footwear, and early recognition of foot-related complications is crucial to empower individuals with diabetes to take proactive measures.

Antibody-antibiotic conjugate targeted therapy for orthopedic implant-associated intracellular S. aureus infections

INTRODUCTION

Treating orthopedic implant-associated infections, especially those caused by Staphylococcus aureus (S. aureus), remains a significant challenge. S. aureus has the ability to invade host cells, enabling it to evade both antibiotics and immune responses during infection, which may result in clinical treatment failures. Therefore, it is critical to identify the host cell type of implant-associated intracellular S. aureus infections and to develop a strategy for highly targeted delivery of antibiotics to the host cells.

OBJECTIVES

Introduced an antibody-antibiotic conjugate (AAC) for the targeted elimination of intracellular S. aureus.

METHODS

The AAC comprises of a human monoclonal antibody (M0662) directly recognizes the surface antigen of S. aureus, Staphylococcus protein A, which is conjugated with vancomycin through cathepsin-sensitive linkers that are cleavable in the proteolytic environment of the intracellular phagolysosome. AAC, vancomycin and vancomycin combined with AAC were used in vitro intracellular infection and mice implant infection models. We then tested the effect of AAC in vivo and in vivo by fluorescence imaging, in vivo imaging, bacterial quantitative analysis and bacterial biofilm imaging.

RESULTS

In vitro, it was observed that AAC captured extracellular S. aureus and co-entered the cells, and subsequently released vancomycin to induce rapid elimination of intracellular S. aureus. In the implant infection model, AAC significantly improved the bactericidal effect of vancomycin. Scanning electron microscopy showed that the application of AAC effectively blocked the formation of bacterial biofilm. Further histochemical and micro-CT analysis showed AAC significantly reduced the level of bone marrow density (BMD) and bone volume fraction (BV/TV) reduction caused by bacterial infection in the distal femur of mice compared to vancomycin treatment alone.

CONCLUSIONS

The application of AAC in an implant infection model showed that it significantly improved the bactericidal effects of vancomycin and effectively blocked the formation of bacterial biofilms, without apparent toxicity to the host.

In situ sprayed hydrogels containing resiquimod-loaded liposomes reduce chronic osteomyelitis recurrence by intracellular bacteria clearance

At present, surgical debridement and systematic administration of antibiotics represent the mainstay of treatment for chronic osteomyelitis. However, it is now understood that Staphylococcus aureus (S. aureus) can survive within excessively polarized M2 macrophages and evade antibiotics, accounting for the high recurrence of chronic osteomyelitis. Effective treatments for intracellular infection have rarely been reported. Herein, we designed an in situ sprayed liposomes hydrogels spray with macrophage-targeted effects and the ability to reverse polarization and eradicate intracellular bacteria to reduce the recurrence of osteomyelitis. Resiquimod (R848)-loaded and phosphatidylserine (PS)-coating nanoliposomes were introduced into fibrinogen and thrombin to form the PSL-R848@Fibrin spray. Characterization and phagocytosis experiments were performed to confirm the successful preparation of the PSL-R848@Fibrin spray. Meanwhile, in vitro cell experiments validated its ability to eliminate intracellular S. aureus by reprogramming macrophages from the M2 to the M1 phenotype. Additionally, we established a chronic osteomyelitis rat model to simulate the treatment and recurrence process. Histological analysis demonstrated a significant increase in M1 macrophages and the elimination of intracellular bacteria. Imaging revealed a significant decrease in osteomyelitis recurrence. Overall, the liposome hydrogels could target macrophages to promote antibacterial properties against intracellular infection and reduce the recurrence of chronic osteomyelitis, providing the foothold for improving the outcomes of this patient population. STATEMENT OF SIGNIFICANCE: Chronic osteomyelitis remains a high recurrence although undergoing traditional treatment of debridement and antibiotics. S. aureus can survive within the excessively polarized M2 macrophages to evade the effects of antibiotics. However, few studies have sought to investigate effective intracellular bacteria eradication. Herein, we designed a macrophage-targeted R848-containing liposomes fibrin hydrogels spray (PSL-R848@Fibrin) that can reprogram polarization of macrophages and eradicate intracellular bacteria for osteomyelitis treatment. With great properties of rapid gelation, strong adhesion, high flexibility and fit-to-shape capacity, the facile-operated immunotherapeutic in-situ-spray fibrin hydrogels exhibited huge promise of reversing polarization and fighting intracellular infections. Importantly, we revealed a hitherto undocumented treatment strategy for reducing the recurrence of chronic osteomyelitis and potentially improving the prognosis of chronic osteomyelitis patients.

Parathyroid hormone therapy improves MRSA-infected fracture healing in a murine diabetic model

Introduction

Diabetes mellitus (DM) impairs fracture healing and is associated with susceptibility to infection, which further inhibits fracture healing. While intermittent parathyroid hormone (1-34) (iPTH) effectively improves fracture healing, it is unknown whether infection-associated impaired fracture healing can be rescued with PTH (teriparatide).

Methods

A chronic diet-induced type 2 diabetic mouse model was used to yield mice with decreased glucose tolerance and increased blood glucose levels compared to lean-fed controls. Methicillin-resistant Staphylococcus aureus (MRSA) was inoculated in a surgical tibia fracture model to simulate infected fracture, after which mice were treated with a combination of antibiotics and adjunctive teriparatide treatment. Fracture healing was assessed by Radiographic Union Scale in Tibial Fractures (RUST), micro-computed tomography (μCT), biomechanical testing, and histology.

Results

RUST score was significantly poorer in diabetic mice compared to their lean nondiabetic counterparts. There were concomitant reductions in micro-computed tomography (μCT) parameters of callus architecture including bone volume/total volume, trabecular thickness, and total mineral density in type 2 diabetes mellitus (T2DM) mice. Biomechanicaltesting of fractured femora demonstrated diminished torsional rigidity, stiffness, and toughness to max torque. Adjuvant teriparatide treatment with systemic antibiotic therapy improved numerous parameters of bone microarchitecture bone volume, increased connectivity density, and increased trabecular number in both the lean and T2DM group. Despite the observation that poor fracture healing in T2DM mice was further impaired by MRSA infection, adjuvant iPTH treatment significantly improved fracture healing compared to antibiotic treatment alone in infected T2DM fractures.

Discussion

Our results suggest that teriparatide may constitute a viable adjuvant therapeutic agent to improve bony union and bone microarchitecture to prevent the development of septic nonunion under diabetic conditions.

Risk Factors and Characteristics of Recalcitrant Osteomyelitis After Initial Surgical and Antibiotic Treatment

OBJECTIVES

To evaluate the injury, patient, and microbiological characteristics that place patients at risk for recalcitrant fracture-related infection and osteomyelitis despite appropriate initial treatment.

DESIGN

Retrospective chart review.

SETTING

Three level I trauma centers.

PATIENTS AND PARTICIPANTS

Two hundred and fifty-seven patients undergoing surgical debridement and antibiotic therapy for osteomyelitis from 2003 to 2019.

MAIN OUTCOME MEASUREMENTS

Patients were categorized as having undergone serial bone debridement if they had 2 separate procedures a minimum of 6 weeks apart with a full course of appropriate antibiotics in between. Patient records were reviewed for age, injury location, body mass index, smoking status, comorbidities, and culture results including the presence of multidrug-resistant organisms and culture-negative osteomyelitis.

RESULTS

A total of 257 patients were identified; 49% (n = 125) had a successful single course of treatment, and 51% (n = 132) required repeat debridement for recalcitrant osteomyelitis. At the index treatment for osteomyelitis, the most common organisms in both groups were methicillin-resistant (MRSA) and methicillin-sensitive Staphylococcus aureus (MSSA). There was no significant difference in incidence of polymicrobial infection between the 2 groups (25% vs. 20%, P = 0.49). The most common organisms cultured at the time of repeat saucerization remained MRSA and MSSA; however, the same organism was cultured from both the index and repeat procedures in only 28% (n = 37) of cases. Diabetic patients, intravenous drug use status, delay to diagnosis, and open fractures of the lower leg are independent risk factors for failure of initial treatment of posttraumatic osteomyelitis.

CONCLUSIONS

Successful eradication of fracture-related infection and posttraumatic osteomyelitis is difficult and fails 51% of the time despite standard surgical and antimicrobial therapy. Although MRSA and MSSA remain the most common organisms cultured, patients who fail initial treatment for osteomyelitis often do not culture the same organisms as those obtained at the index procedure.

LEVEL OF EVIDENCE

Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.

Repurposing Inhibitors of Phosphoinositide 3-kinase as Adjuvant Therapeutics for Bacterial Infections

The rise in antimicrobial resistance and the decline in new antibiotics has created a great need for novel approaches to treat drug resistant bacterial infections. Increasing the burden of antimicrobial resistance, bacterial virulence factors allow for survival within the host, where they can evade host killing and antimicrobial therapy within their intracellular niches. Repurposing host directed therapeutics has great potential for adjuvants to allow for more effective bacterial killing by the host and antimicrobials. To this end, phosphoinositide 3-kinase inhibitors are FDA approved for cancer therapy, but also have potential to eliminate intracellular survival of pathogens. This review describes the PI3K pathway and its potential as an adjuvant target to treat bacterial infections more effectively.

Targeted Drug Delivery Systems for Eliminating Intracellular Bacteria

The intracellular survival of pathogenic bacteria requires a range of survival strategies and virulence factors. These infections are a significant clinical challenge, wherein treatment frequently fails because of poor antibiotic penetration, stability, and retention in host cells. Drug delivery systems (DDSs) are promising tools to overcome these shortcomings and enhance the efficacy of antibiotic therapy. In this review, the classification and the mechanisms of intracellular bacterial persistence are elaborated. Furthermore, the systematic design strategies applied to DDSs to eliminate intracellular bacteria are also described, and the strategies used for internalization, intracellular activation, bacterial targeting, and immune enhancement are highlighted. Finally, this overview provides guidance for constructing functionalized DDSs to effectively eliminate intracellular bacteria.

Construction and evaluation of a clinically relevant model of septic arthritis

Despite the creation of several experimental animal models for the study of septic arthritis, a protocol detailing the development of a reliable and easily reproducible animal model has not yet been reported. The experimental protocol described herein for the development of a clinically relevant mouse model of septic arthritis includes two main study stages: the first stage consisting of the preparation of the mice and of the methicillin-resistant Staphylococcus aureus (MRSA) cultures, followed by direct inoculation of MRSA into the knee joints of C57BL/6J mice (25-40 min); and a second study stage consisting of multiple sample collection and data analysis (1-3 days). This protocol may be carried out by researchers skilled in mouse care and trained to work with biosafety-level-2 agents such as MRSA. The model of septic arthritis described here has demonstrated clinical relevance in developing intra-articular inflammation and cartilage destruction akin to that of human patients. Moreover, we describe methods for serum, synovial fluid and knee joint tissue analysis that were used to confirm the development of septic arthritis in this model, and to test potential treatments. This protocol confers the advantages of enabling granular evaluation of the pathophysiology of MRSA infection and of the efficacy of therapeutic medications; it may also be employed to study a range of native joint diseases beyond inflammatory pathologies alone.

Concurrent targeting of glycolysis in bacteria and host cell inflammation in septic arthritis

Intracellular infiltration of bacteria into host cells complicates medical and surgical treatment of bacterial joint infections. Unlike soft tissue infections, septic arthritis and infection-associated inflammation destroy cartilage that does not regenerate once damaged. Herein, we show that glycolytic pathways are shared by methicillin-resistant Staphylococcus aureus (MRSA) proliferation and host inflammatory machinery in septic arthritis. MRSA readily penetrates host cells and induces proinflammatory cascades that persist after conventional antibiotic treatment. The glycolysis-targeting drug dimethyl fumarate (DMF) showed both bacteriostatic and anti-inflammatory effects by hindering the proliferation of intracellular MRSA and dampening excessive intraarticular inflammation. Combinatorial treatment with DMF and vancomycin further reduced the proliferation and re-emergence of intracellular MRSA. Combinatorial adjuvant administration of DMF with antibiotics alleviated clinical symptoms of septic arthritis by suppressing bacterial burden and curbing inflammation to protect cartilage and bone. Our results provide mechanistic insight into the regulation of glycolysis in the context of infection and host inflammation toward development of a novel therapeutic paradigm to ameliorate joint bioburden and destruction in septic arthritis.

The osteoblast secretome in Staphylococcus aureus osteomyelitis

Osteomyelitis (OM) is an infectious disease of the bone predominantly caused by the opportunistic bacterium Staphylococcus aureus (S. aureus). Typically established upon hematogenous spread of the pathogen to the musculoskeletal system or contamination of the bone after fracture or surgery, osteomyelitis has a complex pathogenesis with a critical involvement of both osteal and immune components. Colonization of the bone by S. aureus is traditionally proposed to induce functional inhibition and/or apoptosis of osteoblasts, alteration of the RANKL/OPG ratio in the bone microenvironment and activation of osteoclasts; all together, these events locally subvert tissue homeostasis causing pathological bone loss. However, this paradigm has been challenged in recent years, in fact osteoblasts are emerging as active players in the induction and orientation of the immune reaction that mounts in the bone during an infection. The interaction with immune cells has been mostly ascribed to osteoblast-derived soluble mediators that add on and synergize with those contributed by professional immune cells. In this respect, several preclinical and clinical observations indicate that osteomyelitis is accompanied by alterations in the local and (sometimes) systemic levels of both pro-inflammatory (e.g., IL-6, IL-1α, TNF-α, IL-1β) and anti-inflammatory (e.g., TGF-β1) cytokines. Here we revisit the role of osteoblasts in bacterial OM, with a focus on their secretome and its crosstalk with cellular and molecular components of the bone microenvironment and immune system.

Extended local release and improved bacterial eradication by adding rifampicin to a biphasic ceramic carrier containing gentamicin or vancomycin

Aims

There is a lack of biomaterial-based carriers for the local delivery of rifampicin (RIF), one of the cornerstone second defence antibiotics for bone infections. RIF is also known for causing rapid development of antibiotic resistance when given as monotherapy. This in vitro study evaluated a clinically used biphasic calcium sulphate/hydroxyapatite (CaS/HA) biomaterial as a carrier for dual delivery of RIF with vancomycin (VAN) or gentamicin (GEN).

Methods

The CaS/HA composites containing RIF/GEN/VAN, either alone or in combination, were first prepared and their injectability, setting time, and antibiotic elution profiles were assessed. Using a continuous disk diffusion assay, the antibacterial behaviour of the material was tested on both planktonic and biofilm-embedded forms of standard and clinical strains of Staphylococcus aureus for 28 days. Development of bacterial resistance to RIF was determined by exposing the biofilm-embedded bacteria continuously to released fractions of antibiotics from CaS/HA-antibiotic composites.

Results

Following the addition of RIF to CaS/HA-VAN/GEN, adequate injectability and setting of the CaS/HA composites were noted. Sustained release of RIF above the minimum inhibitory concentrations of S. aureus was observed until study endpoint (day 35). Only combinations of CaS/HA-VAN/GEN + RIF exhibited antibacterial and antibiofilm effects yielding no viable bacteria at study endpoint. The S. aureus strains developed resistance to RIF when biofilms were subjected to CaS/HA-RIF alone but not with CaS/HA-VAN/GEN + RIF.

Conclusion

Our in vitro results indicate that biphasic CaS/HA loaded with VAN or GEN could be used as a carrier for RIF for local delivery in clinically demanding bone infections. Cite this article: Bone Joint Res 2022;11(11):787–802.

Can intracellular Staphylococcus aureus in osteomyelitis be treated using current antibiotics? A systematic review and narrative synthesis

Approximately 40% of treatments of chronic and recurrent osteomyelitis fail in part due to bacterial persistence. Staphylococcus aureus, the predominant pathogen in human osteomyelitis, is known to persist by phenotypic adaptation as small-colony variants (SCVs) and by formation of intracellular reservoirs, including those in major bone cell types, reducing susceptibility to antibiotics. Intracellular infections with S. aureus are difficult to treat; however, there are no evidence-based clinical guidelines addressing these infections in osteomyelitis. We conducted a systematic review of the literature to determine the demonstrated efficacy of all antibiotics against intracellular S. aureus relevant to osteomyelitis, including protein biosynthesis inhibitors (lincosamides, streptogramins, macrolides, oxazolidines, tetracyclines, fusidic acid, and aminoglycosides), enzyme inhibitors (fluoroquinolones and ansamycines), and cell wall inhibitors (beta-lactam inhibitors, glycopeptides, fosfomycin, and lipopeptides). The PubMed and Embase databases were screened for articles related to intracellular S. aureus infections that compared the effectiveness of multiple antibiotics or a single antibiotic together with another treatment, which resulted in 34 full-text articles fitting the inclusion criteria. The combined findings of these studies were largely inconclusive, most likely due to the plethora of methodologies utilized. Therefore, the reported findings in the context of the models employed and possible solutions for improved understanding are explored here. While rifampicin, oritavancin, linezolid, moxifloxacin and oxacillin were identified as the most effective potential intracellular treatments, the scientific evidence for these is still relatively weak. We advocate for more standardized research on determining the intracellular effectiveness of antibiotics in S. aureus osteomyelitis to improve treatments and patient outcomes.

Enhancement of Impaired MRSA-Infected Fracture Healing by Combinatorial Antibiotics and Modulation of Sustained Inflammation

Fracture healing is impaired in the setting of infection, which begets protracted inflammation. The most problematic causative agent of musculoskeletal infection is methicillin-resistant Staphylococcus aureus (MRSA). We hypothesized that modulation of excessive inflammation combined with cell-penetrating antibiotic treatments facilitates fracture healing in a murine MRSA-infected femoral fracture model. Sterile and MRSA-contaminated open transverse femoral osteotomies were induced in 10-week-old male C57BL/6 mice and fixed via intramedullary nailing. In the initial therapeutic cohort, empty, vancomycin (V), rifampin (R), vancomycin-rifampin (VR), or vancomycin-rifampin-trametinib (VRT) hydrogels were applied to the fracture site intraoperatively. Rifampin was included because of its ability to penetrate eukaryotic cells to target intracellular bacteria. Unbiased screening demonstrated ERK activation was upregulated in the setting of MRSA infection. As such, the FDA-approved mitogen-activated protein kinase kinase (MEK)1-pERK1/2 inhibitor trametinib was evaluated as an adjunctive therapeutic agent to selectively mitigate excessive inflammation after infected fracture. Two additional cohorts were created mimicking immediate and delayed postoperative antibiotic administration. Systemic vancomycin or VR was administered for 2 weeks, followed by 2 weeks of VRT hydrogel or oral trametinib therapy. Hematologic, histological, and cytokine analyses were performed using serum and tissue isolates obtained at distinct postoperative intervals. Radiography and micro-computed tomography (μCT) were employed to assess fracture healing. Pro-inflammatory cytokine levels remained elevated in MRSA-infected mice with antibiotic treatment alone, but increasingly normalized with trametinib therapy. Impaired callus formation and malunion were consistently observed in the MRSA-infected groups and was partially salvaged with systemic antibiotic treatment alone. Mice that received VR alongside adjuvant MEK1-pERK1/2 inhibition displayed the greatest restoration of bone and osseous union. A combinatorial approach involving adjuvant cell-penetrating antibiotic treatments alongside mitigation of excessive inflammation enhanced healing of infected fractures. © 2022 American Society for Bone and Mineral Research (ASBMR).

Treating 'Septic' With Enhanced Antibiotics and 'Arthritis' by Mitigation of Excessive Inflammation

Bacterial infection within the synovial joint, commonly known as septic arthritis, remains a clinical challenge as it presents two concurrent therapeutic goals of reducing bacterial burden and preservation of articular cartilage from destructive host inflammation. We hypothesized that mitigation of MRSA-induced inflammatory signaling could diminish destruction of articular cartilage in the setting of septic arthritis when used in conjunction with antibiotics. Herein, we provide evidence which supports a new therapeutic notion that concurrent antimicrobial therapy to address the ‘septic’ component of the disease with inflammation mitigation to manage the destructive ‘arthritis’ component. We established a murine model to mimic septic knee arthritis, as well as a variety of other inflammatory joint conditions. This murine septic arthritis model, in conjunction with in vitro and ex-vivo models, was utilized to characterize the inflammatory profile seen in active septic arthritis, as well as post-antibiotic treatment, via transcriptomic and histologic studies. Finally, we provided the clinical rationale for a novel therapeutic strategy combining enhanced antibiotic treatment with rifampin and adjuvant immunomodulation to inhibit post-infectious, excess chondrolysis and osteolysis. We identified that septic arthritis secondary to MRSA infection in our murine model led to increased articular cartilage damage compared to various types of inflammatory arthritis. The activation of the pERK1/2 signaling pathway, which is implicated with the mounting of an immune response and generation of inflammation, was increased in intracellular MRSA-infected synovial tissue and persisted despite antibiotic treatment. Trametinib, an inhibitor of ERK signaling through suppression of MEK1/2, alleviated the inflammation produced by the addition of intra-articular, heat-killed MRSA. Further, when combined with vancomycin and rifampin, mitigation of inflammation by pERK1/2 targeting improved outcomes for MRSA septic arthritis by conferring chondroprotection to articular cartilage and diminishing inflammatory osteolysis within bone. Our results support a new therapeutic notion that cell/biofilm-penetrating antibiotics alongside adjuvant mitigation of excessive intra-articular inflammation accomplish distinct therapeutic goals: reduction of bacterial burden and preservation of articular cartilage integrity.

Rifampicin restores extracellular organic matrix formation and mineralization of osteoblasts after intracellular Staphylococcus aureus infection

Aims

Bone regeneration during treatment of staphylococcal bone infection is challenging due to the ability of Staphylococcus aureus to invade and persist within osteoblasts. Here, we sought to determine whether the metabolic and extracellular organic matrix formation and mineralization ability of S. aureus-infected human osteoblasts can be restored after rifampicin (RMP) therapy.

Methods

The human osteoblast-like Saos-2 cells infected with S. aureus EDCC 5055 strain and treated with 8 µg/ml RMP underwent osteogenic stimulation for up to 21 days. Test groups were Saos-2 cells + S. aureus and Saos-2 cells + S. aureus + 8 µg/ml RMP, and control groups were uninfected untreated Saos-2 cells and uninfected Saos-2 cells + 8 µg/ml RMP.

Results

The S. aureus-infected osteoblasts showed a significant number of intracellular bacteria colonies and an unusual higher metabolic activity (p < 0.005) compared to uninfected osteoblasts. Treatment with 8 µg/ml RMP significantly eradicated intracellular bacteria and the metabolic activity was comparable to uninfected groups. The RMP-treated infected osteoblasts revealed a significantly reduced amount of mineralized extracellular matrix (ECM) at seven days osteogenesis relative to uninfected untreated osteoblasts (p = 0.007). Prolonged osteogenesis and RMP treatment at 21 days significantly improved the ECM mineralization level. Ultrastructural images of the mineralized RMP-treated infected osteoblasts revealed viable osteoblasts and densely distributed calcium crystal deposits within the extracellular organic matrix. The expression levels of prominent bone formation genes were comparable to the RMP-treated uninfected osteoblasts.

Conclusion

Intracellular S. aureus infection impaired osteoblast metabolism and function. However, treatment with low dosage of RMP eradicated the intracellular S. aureus, enabling extracellular organic matrix formation and mineralization of osteoblasts at later stage.

Cite this article: Bone Joint Res 2022;11(5):327–341.

The intersection of fracture healing and infection: Orthopaedics research society workshop 2021

Infection is a common cause of impaired fracture healing. In the clinical setting, definitive fracture treatment and infection are often treated separately and sequentially, by different clinical specialties. The ability to treat infection while promoting fracture healing will greatly reduce the cost, number of procedures, and patient morbidity associated with infected fractures. In order to develop new therapies, scientists and engineers must understand the clinical need, current standards of care, pathologic effects of infection on fractures, available preclinical models, and novel technologies. One of the main causes of poor fracture healing is infection; unfortunately, bone regeneration and infection research are typically approached independently and viewed as two separate disciplines. Here, we aim to bring these two groups together in an educational workshop to promote research into the basic and translational science that will address the clinical challenge of delayed fracture healing due to infection. Statement of clinical significance: Infection and nonunion are each feared outcomes in fracture care, and infection is a significant driver of nonunion. The impact of nonunions on patie[Q2]nt well-being is substantial. Outcome data suggests a long bone nonunion is as impactful on health-related quality of life measures as a diagnosis of type 1 diabetes and fracture-related infection has been shown to significantly l[Q3]ower a patient's quality of life for over 4 years.  Although they frequently are associated with one another, the treatment approaches for infections and nonunions are not always complimentary and cannot be performed simultaneously without accepting tradeoffs. Furthermore, different clinical specialties are often required to address the problem, the orthopedic surgeon treating the fracture and an infectious disease specialist addressing the sources of infection. A sequential approach that optimizes treatment parameters requires more time, more surgeries, and thus confers increased morbidity to the patient. The ability to solve fracture healing and infection clearance simultaneously in a contaminated defect would benefit both the patient and the health care system.

Platelets mediate trained immunity against bone and joint infections in a mouse model

AIMS

Trained immunity confers non-specific protection against various types of infectious diseases, including bone and joint infection. Platelets are active participants in the immune response to pathogens and foreign substances, but their role in trained immunity remains elusive.

METHODS

We first trained the innate immune system of C57BL/6 mice via intravenous injection of two toll-like receptor agonists (zymosan and lipopolysaccharide). Two, four, and eight weeks later, we isolated platelets from immunity-trained and control mice, and then assessed whether immunity training altered platelet releasate. To better understand the role of immunity-trained platelets in bone and joint infection development, we transfused platelets from immunity-trained mice into naïve mice, and then challenged the recipient mice with Staphylococcus aureus or Escherichia coli.

RESULTS

After immunity training, the levels of pro-inflammatory cytokines (tumour necrosis factor alpha (TNF-α), interleukin (IL)-17A) and chemokines (CCL5, CXCL4, CXCL5, CXCL7, CXCL12) increased significantly in platelet releasate, while the levels of anti-inflammatory cytokines (IL-4, IL-13) decreased. Other platelet-secreted factors (e.g. platelet-derived growth factor (PDGF)-AA, PDGF-AB, PDGF-BB, cathepsin D, serotonin, and histamine) were statistically indistinguishable between the two groups. Transfusion of platelets from trained mice into naïve mice reduced infection risk and bacterial burden after local or systemic challenge with either S. aureus or E. coli.

CONCLUSION

Immunity training altered platelet releasate by increasing the levels of inflammatory cytokines/chemokines and decreasing the levels of anti-inflammatory cytokines. Transfusion of platelets from immunity-trained mice conferred protection against bone and joint infection, suggesting that alteration of platelet releasate might be an important mechanism underlying trained immunity and may have clinical implications. Cite this article: Bone Joint Res 2022;11(2):73-81.

In vitro antibiotic activity against intraosteoblastic Staphylococcus aureus: a narrative review of the literature

Staphylococcus aureus – a major aetiological agent of bone and joint infection (BJI) – is associated with a high risk of relapse and chronicity, in part due to its ability to invade and persist in non-professional phagocytic bone cells such as osteoblasts. This intracellular reservoir protects S. aureus from the action of the immune system and most antibiotics. To date, the choice of antimicrobial strategies for BJI treatment mostly relies on standard susceptibility testing, bone penetration of antibiotics and their ‘antibiofilm’ activity. Despite the role of intracellular persistent S. aureus in the development of chronic infection, the ability of antibiotics to target the S. aureus intraosteoblastic reservoir is not considered in therapeutic choices but might represent a key determinant of treatment outcome. This review provides an overview of the intracellular pharmacokinetics of antistaphylococcal drugs used in the treatment of BJI and of their ability to target intraosteoblastic S. aureus. Thirteen studies focusing on the intraosteoblastic activity of antibiotics against S. aureus were reviewed, all relying on in vitro models of osteoblast infection. Despite varying incubation times, multiplicities of infection, bacterial strains, and the types of infected cell lines, rifamycins and fluoroquinolones remain the two most potent antimicrobial classes for intraosteoblastic S. aureus eradication, consistent with clinical data showing a superiority of this combination therapy in S. aureus orthopaedic device-related infections.

Dual therapeutic targeting of intra-articular inflammation and intracellular bacteria enhances chondroprotection in septic arthritis

Bacterial infections involving joints and vital organs represent a challenging clinical problem because of the two concurrent therapeutic goals of bacterial eradication and tissue preservation. In the case of septic arthritis, permanent destruction of articular cartilage by intense host inflammation is commonly seen even after successful treatment of bacterial infection. Here, we provide scientific evidence of a novel treatment modality that can protect articular cartilage and enhanced eradication of causative bacteria in septic arthritis. Locally delivered cell-penetrating antibiotics such as rifampicin effectively eradicate intracellular reservoirs of methicillin-resistant Staphylococcus aureus within joint cells. Furthermore, mitigation of intra-articular inflammation by targeting the NLRP3 (nucleotide-binding oligomerization domain-, leucine-rich repeat- and pyrin domain-containing 3) inflammasome protects articular cartilage from damage in a murine model of knee septic arthritis. Together, concurrent mitigation of intra-articular inflammation and local adjuvant targeting of intracellular bacteria represents a promising new therapeutic strategy for septic arthritis.

An Antisense yycF RNA Modulates Biofilm Organization of Methicillin-Resistant Staphylococcus aureus and Pathogenicity in a Rat Model of Osteomyelitis

Staphylococcus aureus (S. aureus) is one of most common opportunistic pathogens and is attributed to several human infections. The increasing incidence of methicillin-resistant S. aureus (MRSA) is a serious clinical threat for osteomyelitis crisis. The YycFG two-component system of S. aureus regulates genes associated with biofilm formation. To investigate the potential role of an antisense yycF RNA in the regulation of transcription levels of yycF and associated effects on biofilm formation and pathogenicity, antisense yycF (ASyycF) RNA was detected by RT-PCR and 5′ RACE assays. ASyycF overexpression mutants were constructed, and the biofilm biomass was determined by crystal violet microtiter assay and scanning electron microscopy (SEM). Quantitative RT-PCR and Western blotting analyses were used to detect whether ASyycF overexpression inhibited the transcription and translation of biofilm-related genes. Then, a rat tibial infective model was used to evaluate the pathogenicity of ASyycF overexpression in vivo. ASyycF transcription led to reductions in YycF production and biofilm formation. Overexpression of ASyycF inhibited the transcription and translation of biofilm-related genes. The sensitivity to vancomycin was improved in ASyycF-overexpressing MRSA. Furthermore, ASyycF inhibited MRSA invasion in a rat tibial infection model. From this study, the expression of the YycF protein was found to be inversely correlated with different levels of ASyycF transcription. The biofilm biomass and pathogenicity decreased in the ASyycF-overexpressing mutant. Thus, the current evidence may support ASyycF as a supplementary strategy for managing S. aureus and MRSA infections.

Efficacy of common antiseptic solutions against clinically relevant microorganisms in biofilm

AIMS

Periprosthetic joint infections (PJIs) are among the most devastating complications after joint arthroplasty. There is limited evidence on the efficacy of different antiseptic solutions on reducing biofilm burden. The purpose of the present study was to test the efficacy of different antiseptic solutions against clinically relevant microorganisms in biofilm.

METHODS

We conducted an in vitro study examining the efficacy of several antiseptic solutions against clinically relevant microorganisms. We tested antiseptic irrigants against nascent (four-hour) and mature (three-day) single-species biofilm created in vitro using a drip-flow reactor model.

RESULTS

With regard to irrigant efficacy against biofilms, Povidone-iodine treatment resulted in greater reductions in nascent MRSA biofilms (logarithmic reduction (LR) = 3.12; p < 0.001) compared to other solutions. Bactisure treatment had the greatest reduction of mature Pseudomonas aeruginosa biofilms (LR = 1.94; p = 0.032) and a larger reduction than Vashe or Irrisept for mature Staphylococcus epidermidis biofilms (LR = 2.12; p = 0.025). Pooled data for all biofilms tested resulted in Bactisure and Povidone-iodine with significantly greater reductions compared to Vashe, Prontosan, and Irrisept solutions (p < 0.001).

CONCLUSION

Treatment failure in PJI is often due to failure to clear the biofilm; antiseptics are often used as an adjunct to biofilm clearance. We tested irrigants against clinically relevant microorganisms in biofilm in vitro and showed significant differences in efficacy among the different solutions. Further clinical outcome data is necessary to determine whether these solutions can impact PJI outcome in vivo. Cite this article: Bone Joint J 2021;103-B(5):908-915.

Moxifloxacin-loaded in situ synthesized Bioceramic/Poly(L-lactide-co-ε-caprolactone) composite scaffolds for treatment of osteomyelitis and orthopedic regeneration

High local intraosseous levels of antimicrobial agents are required for adequate long-term treatment of chronic osteomyelitis (OM). In this study, biodegradable composite scaffolds of poly-lactide-co-ε-caprolactone/calcium phosphate (CaP) were in-situ synthesized using two different polymer grades and synthesis pathways and compared to composites prepared by pre-formed (commercially available) CaP for delivery of the antibiotic moxifloxacin hydrochloride (MOX). Phase identification and characterization by Fourier transform infra-red (FTIR) spectroscopy, X-ray powder diffraction (XRPD) and scanning electron microscope (SEM) confirmed the successful formation of different CaP phases within the biodegradable polymer matrix. The selected in-situ formed CaP scaffold showed a sustained release for MOX for six weeks and adequate porosity. Cell viability study on MG-63 osteoblast-like cells revealed that the selected composite scaffold maintained the cellular proliferation and differentiation. Moreover, it was able to diminish the bacterial load, inflammation and sequestrum formation in the bones of OM-induced animals. The results of the present work deduce that the selected in-situ formed CaP composite scaffold is a propitious candidate for OM treatment, and further clinical experiments are recommended.

Surgical management of the acute severely infected diabetic foot - The 'infected diabetic foot attack'. An instructional review

Diabetic Foot Infection (DFI), in its severest form the acute infected 'diabetic foot attack', is a limb and life threatening condition if untreated. Acute infection may lead to tissue necrosis and rapid spread through tissue planes, in the patient with poorly controlled diabetes facilitated by the host status. A combination of soft tissue infection and osteomyelitis may co-exist, in particular if chronic osteomyelitis serves as a persistent source for recurrence of soft tissue infection. This "diabetic foot attack" is characterised by acutely spreading infection and substantial soft tissue necrosis. In the presence of ulceration, the condition is classified by the Infectious Diseases Society of America/International Working Group on the Diabetic Foot (IDSA/IWGDF Class 3 or 4) presentation requiring an urgent surgical intervention by radical debridement of the infection. Thus, 'time is tissue', referring to tissue salvage and maximal limb preservation. Emergent treatment is important for limb salvage and may be life-saving. We provide a narrative current treatment practices in managing severe DFI with severe soft tissue and osseous infection. We address the role of surgery and its adjuvants, the long term outcomes, potential complications and possible future treatment strategies.

Locally delivered adjuvant biofilm-penetrating antibiotics rescue impaired endochondral fracture healing caused by MRSA infection

Infection is a devastating complication following an open fracture. We investigated whether local rifampin-loaded hydrogel can combat infection and improve healing in a murine model of methicillin-resistant Staphylococcus aureus (MRSA) osteomyelitis. A transverse fracture was made at the tibia midshaft of C57BL/6J mice aged 10-12 weeks and stabilized with an intramedullary pin. A total of 1 × 106 colony-forming units (CFU) of MRSA was inoculated. A collagen-based hydrogel containing low-dose (60 μg) and high-dose (300 μg) rifampin was applied before closure. Postoperative treatment response was assessed through bacterial CFU counts from tissue and hardware, tibial radiographs and microcomputed tomography (μCT), immunohistochemistry, and histological analyses. All untreated MRSA-infected fractures progressed to nonunion by 28 days with profuse MRSA colonization. Infected fractures demonstrated decreased soft callus formation on safranin O stain compared to controls. Areas of dense interleukin-1β stain were associated with poor callus formation. High-dose rifampin hydrogels reduced the average MRSA load in tissue (p < 0.0001) and implants (p = 0.041). Low-dose rifampin hydrogels reduced tissue bacterial load by 50% (p = 0.021). Among sterile models, 88% achieved union compared to 0% of those infected. Mean radiographic union scale in tibia scores improved from 6 to 8.7 with high-dose rifampin hydrogel (p = 0.024) and to 10 with combination local/systemic rifampin therapy (p < 0.0001). μCT demonstrated reactive bone formation in MRSA infection. Histology demonstrated restored fracture healing with bacterial elimination. Rifampin-loaded hydrogels suppressed osteomyelitis, prevented implant colonization, and improved healing. Systemic rifampin was more effective at eliminating infection and improving fracture healing. Further investigation into rifampin-loaded hydrogels is required to correlate these findings with clinical efficacy.

Antibiofilm efficacy of focused high-energy extracorporeal shockwaves and antibiotics in vitro

Aims

Biofilm formation is one of the primary reasons for the difficulty in treating implant-related infections (IRIs). Focused high-energy extracorporeal shockwave therapy (fhESWT), which is a treatment modality for fracture nonunions, has been shown to have a direct antibacterial effect on planktonic bacteria. The goal of the present study was to investigate the effect of fhESWT on Staphylococcus aureus biofilms in vitro in the presence and absence of antibiotic agents.

Methods

S. aureus biofilms were grown on titanium discs (13 mm × 4 mm) in a bioreactor for 48 hours. Shockwaves were applied with either 250, 500, or 1,000 impulses onto the discs surrounded by either phosphate-buffered saline or antibiotic (rifampin alone or in combination with nafcillin). The number of viable bacteria was determined by quantitative culture after sonication. Representative samples were taken for scanning electron microscopy.

Results

The application of fhESWT led to a ten-fold reduction in bacterial counts on the metal discs for all impulse numbers compared to the control (p < 0.001). Increasing the number of impulses did not further reduce bacterial counts in the absence of antibiotics (all p > 0.289). Antibiotics alone reduced the number of bacteria on the discs; however, the combined application of the fhESWT and antibiotic administration further reduced the bacterial count compared to the antibiotic treatment only (p = 0.032).

Conclusion

The use of fhESWT significantly reduced the colony-forming unit (CFU) count of a S. aureus biofilm in our model independently, and in combination with antibiotics. Therefore, the supplementary application of fhESWT could be a helpful tool in the treatment of IFIs in certain cases, including infected nonunions.

Cite this article: Bone Joint Res 2021;10(1):77–84.

Optimal concentration of ethylenediaminetetraacetic acid as an irrigation solution additive to reduce infection rates in rat models of contaminated wound

AIMS

In wound irrigation, 1 mM ethylenediaminetetraacetic acid (EDTA) is more efficacious than normal saline (NS) in removing bacteria from a contaminated wound. However, the optimal EDTA concentration remains unknown for different animal wound models.

METHODS

The cell toxicity of different concentrations of EDTA dissolved in NS (EDTA-NS) was assessed by Cell Counting Kit-8 (CCK-8). Various concentrations of EDTA-NS irrigation solution were compared in three female Sprague-Dawley rat models: 1) a skin defect; 2) a bone exposed; and 3) a wound with an intra-articular implant. All three models were contaminated with Staphylococcus aureus or Escherichia coli. EDTA was dissolved at a concentration of 0 (as control), 0.1, 0.5, 1, 2, 5, 10, 50, and 100 mM in sterile NS. Samples were collected from the wounds and cultured. The bacterial culture-positive rate (colony formation) and infection rate (pus formation) of each treatment group were compared after irrigation and debridement.

RESULTS

Cell viability intervened below 10 mM concentrations of EDTA-NS showed no cytotoxicity. Concentrations of 1, 2, and 5 mM EDTA-NS had lower rates of infection and positive cultures for S. aureus and E. coli compared with other concentrations in the skin defect model. For the bone exposed model, 0.5, 1, and 2 mM EDTA-NS had lower rates of infection and positive cultures. For intra-articular implant models 10 and 50 mM, EDTA-NS had the lowest rates of infection and positive cultures.

CONCLUSION

The concentrations of EDTA-NS below 10 mM are safe for irrigation. The optimal concentration of EDTA-NS varies by type of wound after experimental inoculation of three types of wound. Cite this article: Bone Joint Res 2021;10(1):68-76.