A systematic review of animal models for Staphylococcus aureus osteomyelitis

Animal Models of Orthopedic Implant-Associated Infections and Revisions

Orthopedic implant-associated infections such as prosthetic joint infections (PJIs) lead to devastating complications for patients and impose significant financial burdens on the healthcare systems. Although the primary orthopedic implant associated infection rate is relatively low (0.3-9%), the reinfection rate after implant revisions can be as high as 20% to 40%. To evaluate novel therapeutic strategies for preventing and treating infections associated with primary and revision implants, it is essential to develop appropriate animal models that closely emulate clinical realities. Here we discuss existing animal models developed for orthopedic implant revision surgeries including small animal models in rats and mice, and larger animal models in rabbits, sheep, and mini-pigs. While larger animal models offer the advantage of more closely mimicking human surgical procedures, implant dimensions, and infection treatment protocols, rodent models are more cost-effective and better suited for screening experimental prophylaxes and therapeutics. Existing animal revision models have focused on primary infections established by Staphylococcal aureus (S. aureus) and revisions involving both one-stage and two-stage procedures. Further development of smaller animal implant revision models that implement more clinically relevant surgical procedures and recapitulate polymicrobial infections could facilitate the discovery and more rigorous evaluation of novel implant coating prophylaxes and therapeutics for reducing reinfection rates following implant revisions.

Development of a small animal bone-anchored limb replacement model for infection interventions

Purpose

Osseointegration-associated infections are a critical barrier to widespread implementation of osseointegrated (OI) prosthetics. To address this challenge, a preclinical animal model must exist of the human model to test potential interventions. In this article, we describe a novel rabbit model of OI implant-related infection that can act as a platform for rapid translation and development of therapeutic approaches to combat these uniquely challenging infections.

Methods

A single-stage amputation was performed by exposure, transection, reaming, and tapping of the tibia, followed by placement of a 75-mm Ti-6Al-4V cortical screw implant. Muscle and skin were closed, and a prosthetic was attached to the screw. Hematology, clinical chemistry, and imaging were performed up to 8 weeks. High-resolution microCT and histology were conducted at terminal end points. Intraosseous vancomycin delivery was compared with intravenous delivery. Serum and bone marrow collection was conducted across a period of 5 hours.

Results

Rabbits maintained normal ambulation, mobility, diet, and weight throughout the study period. Clinical chemistry results indicate normal ranges over the study course. microCT and histology demonstrate osseointegration between the threads of the implant within the medullary cavity. Pharmacokinetic data determined that intraosseous vancomycin delivery results in significantly lower vancomycin concentrations systemically compared with intravenous delivery and higher peak vancomycin concentration within the tibial canal.

Conclusion

This preclinical translational model represents a reproducible small animal model of OI transtibial amputation that successfully recreates the bone-skin-implant interface, material-bone interactions to match human OI, and a similar immune response. Preclinical efficacy of infection interventions will be further explored with establishment of this model.

Basic science review of transcutaneous osseointegration: current status, research gaps and needs, and defining future directions

Basic science research is vital for advancing the emerging field of bone-anchored limb replacement (BALR), or osseointegration (OI). This article discusses clinical challenges for BALR/OI, summarizes current basic science research regarding those challenges, identifies research gaps, and proposes future directions. OI research draws from related fields such as orthopaedic implants and dentistry. There is a need for small animal models to study critical questions related to osseointegration, including OI implant-associated infections. Small animal models are also critical to ensuring safety and efficacy of novel treatments in this vulnerable population. Key issues include infection prevention through implant surface modifications, biofilm-targeting technologies, and antimicrobial advancements. The skin-implant portal, unique to BALR, also poses significant challenges. Research on skin attachment and inflammatory processes is crucial. Noninfectious inflammatory loosening of implants, though infrequent, needs further investigation. This review emphasizes the need for collaborative efforts to develop effective preclinical models and innovative infection prevention strategies. Addressing these challenges is essential for optimizing patient outcomes and advancing this emerging field.

The Application of Rat Models in Staphylococcus aureus Infections

Staphylococcus aureus (S. aureus) is a major human pathogen and can cause a wide range of diseases, including pneumonia, osteomyelitis, skin and soft tissue infections (SSTIs), endocarditis, mastitis, bacteremia, and so forth. Rats have been widely used in the field of infectious diseases due to their unique advantages, and the models of S. aureus infections have played a pivotal role in elucidating their pathogenic mechanisms and the effectiveness of therapeutic agents. This review outlined the current application of rat models in S. aureus infections and future prospects for rat models in infectious diseases caused by S. aureus.

Rat model of recalcitrant prosthetic joint infection using biofilm inocula

Prosthetic joint infection (PJI) is a rare but devastating complication of joint arthroplasty. Biofilm formation around the prosthesis confers tolerance to antibiotics so that treatment is challenging. Most animal models of PJI use planktonic bacteria to establish the infection which fails to reproduce the pathology of chronic infection. We aimed to establish a rat model of Staphylococcus aureus PJI in male Sprague-Dawley rats using biofilm inocula and demonstrate its tolerance to frontline antibiotics. Pilot studies indicated that infection could be introduced to the knee joint by a biofilm-coated pin but that handling the prosthetic without disturbing the biofilm was difficult. We, therefore, developed a pin with a slotted end and used a miniature-biofilm reactor to develop mature biofilm in this niche. These biofilm-laden pins consistently produced infection of the bone and joint space. Treatment with high dose cefazolin, 250 mg/kg, starting the day of surgery reduced or cleared pin-adherent bioburden within 7 days, however when escalation from 25 to 250 mg/kg cefazolin treatment was delayed for 48 h, rats were unable to clear the infection. To track infections, we used bioluminescent bacteria, however, the bioluminescent signal did not accurately track the degree of infection in the bone and joint space as the signal did not penetrate the bone. In conclusion, we demonstrate that using a custom prosthetic pin, we can generate biofilm in a specific niche using a novel bioreactor setup and initiate a rat PJI that rapidly develops tolerance to supra-clinical doses of cefazolin.

In Vivo Prevention of Implant-Associated Infections Caused by Antibiotic-Resistant Bacteria through Biofunctionalization of Additively Manufactured Porous Titanium

Additively manufactured (AM) porous titanium implants may have an increased risk of implant-associated infection (IAI) due to their huge internal surfaces. However, the same surface, when biofunctionalized, can be used to prevent IAI. Here, we used a rat implant infection model to evaluate the biocompatibility and infection prevention performance of AM porous titanium against bioluminescent methicillin-resistant Staphylococcus aureus (MRSA). The specimens were biofunctionalized with Ag nanoparticles (NPs) using plasma electrolytic oxidation (PEO). Infection was initiated using either intramedullary injection in vivo or with in vitro inoculation of the implant prior to implantation. Nontreated (NT) implants were compared with PEO-treated implants with Ag NPs (PT-Ag), without Ag NPs (PT) and infection without an implant. After 7 days, the bacterial load and bone morphological changes were evaluated. When infection was initiated through in vivo injection, the presence of the implant did not enhance the infection, indicating that this technique may not assess the prevention but rather the treatment of IAIs. Following in vitro inoculation, the bacterial load on the implant and in the peri-implant bony tissue was reduced by over 90% for the PT-Ag implants compared to the PT and NT implants. All infected groups had enhanced osteomyelitis scores compared to the noninfected controls.

Anti-Staphylococcal Activity of Ligilactobacillus animalis SWLA-1 and Its Supernatant against Multidrug-Resistant Staphylococcus pseudintermedius in Novel Rat Model of Acute Osteomyelitis

Osteomyelitis caused by staphylococcal infection is a serious complication of orthopedic surgery. Staphylococcus pseudintermedius is the main causative agent of osteomyelitis in veterinary medicine. Methicillin-resistant S. pseudintermedius (MRSP) has been reported in companion animals, especially dogs. Multidrug-resistant S. pseudintermedius is an emerging pathogen and has acquired antibiotic resistance against various commercial antimicrobial agents. New antimicrobial compounds are urgently needed to address antibiotic resistance, and the development of novel agents has become an international research hotspot in recent decades. Antimicrobial compounds derived from probiotics, such as bacteriocins, are promising alternatives to classical antibiotics. In this study, the antibacterial activities of Ligilactobacillus animalis SWLA-1 and its concentrated cell-free supernatant (CCFS) were evaluated in vitro and in vivo. The CCFS of this bacterium showed no toxicity against osteoblast and myoblast cells in vitro, while significantly inhibiting the multidrug-resistant S. pseudintermedius KUVM1701GC strain in a newly established rat model. The CCFS significantly inhibited multidrug-resistant staphylococci both in vitro and in vivo. This suggests that CCFS derived from L. animalis SWLA-1 has potential as an alternative to classic antibiotics for staphylococcal infections in dogs.

Size-dependent gold nanoparticles induce macrophage M2 polarization and promote intracellular clearance of Staphylococcus aureus to alleviate tissue infection

Tissue infection typically results from blood transmission or the direct inoculation of bacteria following trauma. The pathogen-induced destruction of tissue prevents antibiotics from penetrating the infected site, and severe inflammation further impairs the efficacy of conventional treatment. The current study describes the size-dependent induction of macrophage polarization using gold nanoparticles. Gold nanoparticles with a diameter of 50 ​nm (Au50) can induce M2 polarization in macrophages by inhibiting the NF-κB signaling pathway and stimulate an inflammatory response in the environment by inhibiting the MAPK signaling pathway LPS. Furthermore, the induced polarization and anti-inflammatory effects of the Au50 nanoparticles promoted the osteogenic differentiation of BMSCs in vitro. In addition, the overexpression of TREM2 in macrophage induced by Au50 nanoparticles was found to promote macrophage phagocytosis of Staphylococcus aureus, enhance the fusion of autophagosomes and lysosomes, accelerate the intracellular degradation of S. aureus, in addition to achieving an effective local treatment of osteomyelitis and infectious skin defects in conjunction with inflammatory regulation and accelerating bone regeneration. The findings, therefore, demonstrate that Au50 nanoparticles can be utilized as a promising nanomaterial for in vivo treatment of infections.

Positron Emission Tomography-Computed Tomography and Magnetic Resonance Imaging Assessments in a Mouse Model of Implant-Related Bone and Joint Staphylococcus aureus Infection

Osteomyelitis is an infection of the bone, associated with an inflammatory process. Imaging plays an important role in establishing the diagnosis and the most appropriate patient management. However, data are lacking regarding the use of preclinical molecular imaging techniques to assess osteomyelitis progression in experimental models. This study aimed to compare structural and molecular imaging to assess disease progression in a mouse model of implant-related bone and joint infections caused by Staphylococcus aureus. In SWISS mice, the right femur was implanted with a resorbable filament impregnated with S. aureus (infected group, n = 10) or sterile culture medium (uninfected group, n = 6). Eight animals (5 infected, 3 uninfected) were analyzed with magnetic resonance imaging (MRI) at 1, 2, and 3 weeks postintervention, and 8 mice were analyzed with [18F]fluorodeoxyglucose (FDG)-positron emission tomography (PET)-computed tomography (CT) at 48 h and at 1, 2, and 3 weeks postintervention. In infected animals, CT showed bone lesion progression, mainly in the distal epiphysis, although some uninfected animals presented evident bone sequestra at 3 weeks. MRI showed a lesion in the articular area that persisted for 3 weeks in infected animals. This lesion was smaller and less evident in the uninfected group. At 48 h postintervention, FDG-PET showed higher joint uptake in the infected group than in the uninfected group (P = 0.025). Over time, the difference between groups increased. These results indicate that FDG-PET imaging was much more sensitive than MRI and CT for differentiating between infection and inflammation at early stages. FDG-PET clearly distinguished between infection and postsurgical bone healing (in uninfected animals) from 48 h to 3 weeks after implantation. IMPORTANCE Our results encourage future investigations on the utility of the model for testing different therapeutic procedures for osteomyelitis.

Local Antibiotic Delivery Ceramic Bone Substitutes for the Treatment of Infected Bone Cavities and Bone Regeneration: A Systematic Review on What We Have Learned from Animal Models

AIMS

the focus of this study is to evaluate if the combination of an antibiotic with a ceramic biomaterial is effective in treating osteomyelitis in an infected animal model and to define which model and protocol are best suited for in vivo experiments of local bone infection treatment.

METHODS

a systematic review was carried out based on PRISMA statement guidelines. A PubMed search was conducted to find original papers on animal models of bone infections using local antibiotic delivery systems with the characteristics of bone substitutes. Articles without a control group, differing from the experimental group only by the addition of antibiotics to the bone substitute, were excluded.

RESULTS

a total of 1185 records were retrieved, and after a three-step selection, 34 papers were included. Six manuscripts studied the effect of antibiotic-loaded biomaterials on bone infection prevention. Five articles studied infection in the presence of foreign bodies. In all but one, the combination of an antibiotic with bioceramic bone substitutes tended to prevent or cure bone infection while promoting biomaterial osteointegration.

CONCLUSIONS

this systematic review shows that the combination of antibiotics with bioceramic bone substitutes may be appropriate to treat bone infection when applied locally. The variability of the animal models, time to develop an infection, antibiotic used, way of carrying and releasing antibiotics, type of ceramic material, and endpoints limits the conclusions on the ideal therapy, enhancing the need for consistent models and guidelines to develop an adequate combination of material and antimicrobial agent leading to an effective human application.

Murine models of orthopedic infection featuring Staphylococcus aureus biofilm

Introduction: Osteomyelitis remains a major clinical challenge. Many published rodent fracture infection models are costly compared with murine models for rapid screening and proof-of-concept studies. We aimed to develop a dependable and cost-effective murine bone infection model that mimics bacterial bone infections associated with biofilm and metal implants. Methods: Tibial drilled hole (TDH) and needle insertion surgery (NIS) infection models were compared in C57BL/6 mice (female, N = 150 ). Metal pins were inserted selectively into the medullary canal adjacent to the defect sites on the metaphysis. Free Staphylococcus aureus (ATCC 12600) or biofilm suspension (ATCC 25923) was locally inoculated. Animals were monitored for physiological or radiographic evidence of infection without prophylactic antibiotics for up to 14 d. At the end point, bone swabs, soft-tissue biopsies, and metal pins were taken for cultures. X-ray and micro-CT scans were performed along with histology analysis. Results: TDH and NIS both achieved a 100 % infection rate in tibiae when a metal implant was present with injection of free bacteria. In the absence of an implant, inoculation with a bacterial biofilm still induced a 40 %-50 % infection rate. In contrast, freely suspended bacteria and no implant consistently showed lower or negligible infection rates. Micro-CT analysis confirmed that biofilm infection caused local bone loss even without a metal implant as a nidus. Although a metal surface permissive for biofilm formation is impermeable to create progressive bone infections in animal models, the metal implant can be dismissed if a bacterial biofilm is used. Conclusion: These models have a high potential utility for modeling surgery-related osteomyelitis, with NIS being simpler to perform than TDH.

In vitro and in vivo assessment of caprine origin Staphylococcus aureus ST398 strain UTCVM1 as an osteomyelitis pathogen

Staphylococcus aureus (SA) is a significant and well-recognized causative organism of bacterial osteomyelitis. Osteomyelitis is an inflammatory bone disease characterized by progressive bone destruction and loss. This disease causes significant morbidity and mortality to the patient and poses therapeutic challenges for clinicians. To improve the efficacy of therapeutic strategies to combat bacterial osteomyelitis, there is a need to define the molecular epidemiology of bacterial organisms more clearly and further the understanding of the pathogenesis of SA osteomyelitis. We conducted in vitro characterization of the pathogenic capabilities of an isolate of SA ST398 derived from a clinical case of osteomyelitis in a goat. We also report a rodent mandibular defect model to determine the ability of ST398 to cause reproducible osteomyelitis. Our results indicate that ST398 can invade and distort pre-osteoblastic cells in culture, induce significant inflammation and alter expression of osteoregulatory cytokines. We also demonstrate the ability of ST398 to induce osteomyelitis in a rat mandibular model. When compiled, these data support ST398 as a competent osteomyelitis pathogen.

Comparing the efficacy of different antibiotic regimens on osteomyelitis: A network meta-analysis of animal studies

Background

Despite the surge in the number of antibiotics used to treat preclinical osteomyelitis (OM), their efficacy remains inadequately assessed.

Objective

To establish network comparisons on the efficacy of antibiotic regimens on OM in animal studies.

Methods

PubMed, Embase, Web of Science, and The Cochrane Library were searched from inception to March 2022 for relevant articles. Odds ratios (ORs) were generated for dichotomous variants, and the standard mean difference (SMD) was calculated for constant variables. The predominant outcomes were the effective rate of sterility, also known as sterility rates, as well as the bacterial counts at the end of the experiments and antibiotic concentrations in serum or bone. All the network meta-analyses were performed using STATA MP 16.0. This study was registered in the International Prospective Register of Systematic Reviews (PROSPERO; no. CRD42022316544).

Results

A total of 28 eligible studies with 1,488 animals were included for data analysis, including 13 antibiotic regimens. Regarding the effective rate of sterility, glycopeptides (GLY), linezolid (LIN), rifampicin (RIF)+β-Lactam, and β-Lactam showed significant efficacy compared with placebo (OR ranging from 0.01 to 0.08). For radiological grade, only RIF+GLY (SMD: −5.92, 95%CI: −11.65 to −0.19) showed significant efficacy compared with placebo. As for reducing bacteria count, fosfomycin (FOS), tigecycline (TIG), GLY, LIN, RIF, RIF+β-Lactam, RIF+GLY, aminoglycosides (AMI), and clindamycin (CLI) showed significant efficacy compared with placebo (SMD ranging from −6.32 to −2.62). Moreover, the bone concentrations of GLY were higher 1 h after administration and the higher blood concentrations were higher after 1 h and 4 h compared with the other antibiotics.

Conclusion

Multiple antibiotic regimens showed significant efficacy in animals with OM, including increasing effective rates of sterility, reducing bacterial counts, and lowering radiological scores. Among them, RIF+GLY was the most promising treatment regimen owing to its optimal efficacy. Based on the preclinical studies included in our meta-analysis, head-to-head clinical randomized controlled trials are required to confirm these findings in humans.

The Medium Composition Impacts Staphylococcus aureus Biofilm Formation and Susceptibility to Antibiotics Applied in the Treatment of Bone Infections

The biofilm-associated infections of bones are life-threatening diseases, requiring application of dedicated antibiotics in order to counteract the tissue damage and spread of microorganisms. The in vitro analyses on biofilm formation and susceptibility to antibiotics are frequently carried out using methods that do not reflect conditions at the site of infection. To evaluate the influence of nutrient accessibility on Staphylococcus aureus biofilm development in vitro, a cohesive set of analyses in three different compositional media was performed. Next, the efficacy of four antibiotics used in bone infection treatment, including gentamycin, ciprofloxacin, levofloxacin, and vancomycin, against staphylococcal biofilm, was also assessed. The results show a significant reduction in the ability of biofilm to grow in a medium containing elements occurring in the serum, which also translated into the diversified changes in the efficacy of used antibiotics, compared to the setting in which conventional media were applied. The differences indicate the need for implementation of adequate in vitro models that closely mimic the infection site. The results of the present research may be considered an essential step toward the development of in vitro analyses aiming to accurately indicate the most suitable antibiotic to be applied against biofilm-related infections of bones.

Developing a third-degree burn model of rats using the Delphi method

Animal experiments play an essential role in advances in the research and treatment of burns. Currently, researchers often rely on personal experience or the literature to complete the construction of animal disease models, which may lead to a lack of scientific rigor and a wide range of animal disease models with reference value. The purposes of this study were to establish a third-degree burn model of rats using the Delphi method to provide a reference. Two rounds of a Delphi expert consultation survey were conducted on experts (n = 13) in this study, and then the boundary value method was used to screen, modify and supplement the indicators. Next, the indicator weight was determined by dividing the boundary value, and finally, the index system of the rat model of third-degree burns was established. The statistical analysis results show that the positive coefficients of the two rounds of expert consultation are 100% and 88.67% respectively. The expert authority coefficient values were 0.73 and 0.67, respectively, and the expert coordination coefficient test was P < 0.001. According to the experts' suggestion, the third-degree burn model of rats with 8 first-degree indexes, 14 second-degree indexes and 46 third-degree indexes was finally established. According to the characteristics and quality requirements of animal models, this study constructs a rat model of third degree burns, which is expected to expressively improve the overall proficiency of burn research quality.

Role of animal models in biomedical research: a review

The animal model deals with the species other than the human, as it can imitate the disease progression, its’ diagnosis as well as a treatment similar to human. Discovery of a drug and/or component, equipment, their toxicological studies, dose, side effects are in vivo studied for future use in humans considering its’ ethical issues. Here lies the importance of the animal model for its enormous use in biomedical research. Animal models have many facets that mimic various disease conditions in humans like systemic autoimmune diseases, rheumatoid arthritis, epilepsy, Alzheimer’s disease, cardiovascular diseases, Atherosclerosis, diabetes, etc., and many more. Besides, the model has tremendous importance in drug development, development of medical devices, tissue engineering, wound healing, and bone and cartilage regeneration studies, as a model in vascular surgeries as well as the model for vertebral disc regeneration surgery. Though, all the models have some advantages as well as challenges, but, present review has emphasized the importance of various small and large animal models in pharmaceutical drug development, transgenic animal models, models for medical device developments, studies for various human diseases, bone and cartilage regeneration model, diabetic and burn wound model as well as surgical models like vascular surgeries and surgeries for intervertebral disc degeneration considering all the ethical issues of that specific animal model. Despite, the process of using the animal model has facilitated researchers to carry out the researches that would have been impossible to accomplish in human considering the ethical prohibitions.

A Journey into Animal Models of Human Osteomyelitis: A Review

Osteomyelitis is an infection of the bone characterized by progressive inflammatory destruction and apposition of new bone that can spread via the hematogenous route (hematogenous osteomyelitis (HO)), contiguous spread (contiguous osteomyelitis (CO)), and direct inoculation (osteomyelitis associated with peripheral vascular insufficiency (PVI)). Given the significant financial burden posed by osteomyelitis patient management, the development of new preventive and treatment methods is warranted. To achieve this objective, implementing animal models (AMs) of infection such as rats, mice, rabbits, avians, dogs, sheep, goats, and pigs might be of the essence. This review provides a literature analysis of the AMs developed and used to study osteomyelitis. Historical relevance and clinical applicability were taken into account to choose the best AMs, and some study methods are briefly described. Furthermore, the most significant strengths and limitations of each species as AM are discussed, as no single model incorporates all features of osteomyelitis. HO's clinical manifestation results in extreme variability between patients due to multiple variables (e.g., age, sex, route of infection, anatomical location, and concomitant diseases) that could alter clinical studies. However, these variables can be controlled and tested through different animal models.

Assessment of listing and categorisation of animal diseases within the framework of the Animal Health Law (Regulation (EU) No 2016/429): antimicrobial-resistant Staphylococcus aureus in cattle and horses

Staphylococcus aureus (S. aureus) was identified among the most relevant antimicrobial-resistant (AMR) bacteria in the EU for cattle and horses in previous scientific opinions. Thus, it has been assessed according to the criteria of the Animal Health Law (AHL), in particular criteria of Article 7 on disease profile and impacts, Article 5 on its eligibility to be listed, Annex IV for its categorisation according to disease prevention and control rules as in Article 9, and Article 8 for listing animal species related to the bacterium. The assessment has been performed following a methodology previously published. The outcome is the median of the probability ranges provided by the experts, which indicates whether each criterion is fulfilled (lower bound ≥ 66%) or not (upper bound ≤ 33%), or whether there is uncertainty about fulfilment. Reasoning points are reported for criteria with uncertain outcome. According to the assessment here performed, it is uncertain whether AMR S. aureus can be considered eligible to be listed for Union intervention according to Article 5 of the AHL (60-90% probability). According to the criteria in Annex IV, for the purpose of categorisation related to the level of prevention and control as in Article 9 of the AHL, the AHAW Panel concluded that the bacterium does not meet the criteria in Sections 1, 2 and 4 (Categories A, B and D; 1-5%, 5-10% and 10-33% probability of meeting the criteria, respectively) and the AHAW Panel was uncertain whether it meets the criteria in Sections 3 and 5 (Categories C and E, 33-90% and 60-90% probability of meeting the criteria, respectively). The animal species to be listed for AMR S. aureus according to Article 8 criteria include mainly mammals, birds, reptiles and fish.

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.

Preventing Staphylococcus aureus stainless steel-associated infections in orthopedics. A systematic review and meta-analysis of animal literature

Surgical site infection in the presence of orthopedic implants poses significant healthcare and socioeconomic burden. To assess the potential of various prevention strategies against Staphylococcus-induced stainless steel-associated infections, a review of animal evidence was designed. The databases of PubMed, Embase, and CENTRAL were searched until March 10, 2020, for articles including animal models with stainless steel instrumentation and techniques to prevent Staphylococcus infection. We conducted a random-effects meta-analysis of standardized mean differences (SMD) with subgroup analysis linked to various protection strategies and we recorded complications. Quality was assessed with the SYRCLE's risk of bias tool. Twenty-five studies were included. Combined active coating (featuring organic antibacterial compound release) and degradable passive finishing (lipid- or polymer-based structure modification reducing bacterial adhesion) was favored over untreated controls (SMDs for methicillin-sensitive Staphylococcus aureus [MSSA] and methicillin-resistant Staphylococcus aureus [MRSA] were -3.46, 95% CI [-4.53 to -2.4], p < .001 [n = 4 head-to-head comparisons]; and -6.67, 95% CI [-10.53 to -3], p < .001 [n = 5 head-to-head comparisons], respectively). Systemic vitamin D supplementation and systemic antibiotic administration with or without local antibiotics demonstrated favorable outcomes against MSSA infection. On the contrary, no benefit was seen following vaccination. Of note, no side effects were documented. On the basis of data gathered from eight studies, which comprised 294 animals, a bioresorbable polymer- or lipid-based surface modification supplemented with organic coating yielded improved infection-related outcomes against MSSA and MRSA stainless steel infections, and therefore, this strategy could be further investigated in human research.

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.

Infection Responsive Smart Delivery of Antibiotics Using Recombinant Spider Silk Nanospheres

Frequent and inappropriate usage of antibiotics has changed the natural evolution of bacteria by reducing susceptibility and increasing resistance towards antibacterial agents. New resistance mechanisms evolved in the response to host defenses and pharmaceutical interventions are threatening our ability to treat common infections, resulting in increased mortality. In the face of this rising epidemic, antibiotic drug discovery, which has long been overlooked by big pharma, is reaching a critical low. Thus, the development of an infection-responsive drug delivery system, which may mitigate multidrug resistance and preserve the lifetime of our current antibiotic arsenal, has garnered the attention of both popular science and funding agencies. The present work describes the development of a thrombin-sensitive linker embedded into a recombinant spider silk copolymer to create a nanosphere drug delivery vehicle. Recent studies have suggested that there is an increase in thrombin-like activity during Staphylococcus aureus infection; thus, drug release from this new "smart" nanosphere can be triggered in the presence of infection. A thrombin sensitive peptide (TSP) was synthesized, and the thrombin cleavage sensitivity was determined by HPLC. The results showed no cleavage of the peptide when exposed to human serum whereas the peptide was cleaved when incubated with S. aureus exudate. Subsequently, the peptide was coupled with a silk copolymer via EDC-NHS chemistry and formulated into nanospheres encapsulating antibiotic vancomycin. These nanospheres were evaluated for in vitro infection-responsive drug release and antimicrobial activity. Finally, the drug responsive nanospheres were assessed for efficacy in an in vivo septic arthritis model. Our study provides evidence that the protein conjugate was enzyme responsive and can be used to formulate targeted drug release to combat infections against multidrug-resistant bacterial strains.

Ceramic composite with gentamicin decreases persistent infection and increases bone formation in a rat model of debrided osteomyelitis

Introduction: Current methods of managing osteomyelitic voids after debridement are inadequate and result in significant morbidity to patients. Synthetic ceramic void fillers are appropriate for non-infected bone defects but serve as a nidus of re-infection in osteomyelitis after debridement. CERAMENT G (CG) is an injectable ceramic bone void filler which contains gentamicin and is currently being evaluated for use in osteomyelitic environments after debridement due to its theoretical ability to serve as a scaffold for healing while eliminating residual bacteria after debridement through the elution of antibiotics. The goal of this study was to evaluate (1) the rate of persistent infection and (2) new bone growth of a debrided osteomyelitic defect in a rat model which has been treated with either gentamicin-impregnated ceramic cement (CERAMENT G) or the same void filler without antibiotics (CERAMENT, CBVF). Methods: Osteomyelitis was generated in the proximal tibia of Sprague Dawley rats, subsequently debrided, and the defect filled with either (1) CG ( n = 20 ), (2) CBVF ( n = 20 ), or (3) nothing ( n = 20 ). Each group was euthanized after 6 weeks. Infection was detected through bacterial culture and histology. Bone growth was quantified using microCT. Results: Infection was not detected in defects treated with CG as compared with 35 % of defects ( 7 / 20 ) treated with CBVF and 50 % ( 10 / 20 ) of empty defects ( p = 0.001 ). Bone volume in the defect of CG-treated rats was greater than the CBVF (0.21 vs. 0.17, p = 0.021 ) and empty groups (0.21 vs. 0.11, p < 0.001 ) at 6 weeks after implantation. Conclusions: Ceramic void filler with gentamicin (CERAMENT G) decreased the rate of persistent infection and increased new bone growth as compared to the same void filler without antibiotics (CERAMENT) and an empty defect in a rat model of debrided osteomyelitis.

2021 Frank Stinchfield Award: A novel cemented hip hemiarthroplasty infection model with real-time in vivo imaging in rats : an animal study

AIMS

The aims of this study were to develop an in vivo model of periprosthetic joint infection (PJI) in cemented hip hemiarthroplasty, and to monitor infection and biofilm formation in real-time.

METHODS

Sprague-Dawley rats underwent cemented hip hemiarthroplasty via the posterior approach with pre- and postoperative gait assessments. Infection with Staphylococcus aureus Xen36 was monitored with in vivo photoluminescent imaging in real-time. Pre- and postoperative gait analyses were performed and compared. Postmortem micro (m) CT was used to assess implant integration; field emission scanning electron microscopy (FE-SEM) was used to assess biofilm formation on prosthetic surfaces.

RESULTS

All animals tolerated surgery well, with preservation of gait mechanics and weightbearing in control individuals. Postoperative in vivo imaging demonstrated predictable evolution of infection with logarithmic signal decay coinciding with abscess formation. Postmortem mCT qualitative volumetric analysis showed high contact area and both cement-bone and cement-implant interdigitation. FE-SEM revealed biofilm formation on the prosthetic head.

CONCLUSION

This study demonstrates the utility of a new, high-fidelity model of in vivo PJI using cemented hip hemiarthroplasty in rats. Inoculation with bioluminescent bacteria allows for non-invasive, real-time monitoring of infection. Cite this article: Bone Joint J 2021;103-B(7 Supple B):9-16.

Preclinical Testing of Radiopharmaceuticals for the Detection and Characterization of Osteomyelitis: Experiences from a Porcine Model

The development of new and better radioactive tracers capable of detecting and characterizing osteomyelitis is an ongoing process, mainly because available tracers lack selectivity towards osteomyelitis. An integrated part of developing new tracers is the performance of in vivo tests using appropriate animal models. The available animal models for osteomyelitis are also far from ideal. Therefore, developing improved animal osteomyelitis models is as important as developing new radioactive tracers. We recently published a review on radioactive tracers. In this review, we only present and discuss osteomyelitis models. Three ethical aspects (3R) are essential when exposing experimental animals to infections. Thus, we should perform experiments in vitro rather than in vivo (Replacement), use as few animals as possible (Reduction), and impose as little pain on the animal as possible (Refinement). The gain for humans should by far exceed the disadvantages for the individual experimental animal. To this end, the translational value of animal experiments is crucial. We therefore need a robust and well-characterized animal model to evaluate new osteomyelitis tracers to be sure that unpredicted variation in the animal model does not lead to a misinterpretation of the tracer behavior. In this review, we focus on how the development of radioactive tracers relies heavily on the selection of a reliable animal model, and we base the discussions on our own experience with a porcine model.

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.

Silver ion-doped calcium phosphate-based bone-graft substitute eliminates chronic osteomyelitis: An experimental study in animals

Despite the latest technologies and advances in microbiology and orthopedic surgery, chronic osteomyelitis is still a challenging disorder. Antibiotic resistance and bacterially induced bone destruction can have very serious consequences. We hypothesized that calcium phosphate-based bone graft substitution with silver ion doping would simultaneously treat bone infection and the bony defect in the chronic osteomyelitis. An unicortical 10-mm-diameter bone was harvested in the proximal tibial metaphysis of 24 rabbits. After contaminating the wounds with an infective dose of methicillin-resistant Staphylococcus aureus (MRSA), osteomyelitis was proven radiographically and microbiologically in all rabbits. Animals were than divided into three groups. The first group received vancomycin-impregnated bone cement beads (comparative control group), the second/experimental group received silver ion-doped calcium phosphate beads and the third group received pure calcium phosphate beads (negative controls). Radiographs, intraosseous cultures, and histopathological examinations were performed on postoperative Week 10. The cultures showed no evidence of intramedullary infection in the silver ion-doped calcium phosphate beads group, but they were positive for MRSA in four of the six rabbits in the vancomycin- impregnated bone cement beads group and in all of the eight rabbits in the pure calcium phosphate beads group. Quantitative assessment of histopathological examination showed lowest total damage score in silver ion-doped calcium phosphate beads group (p < .001). Percentage of osteoid tissue + bony tissue was also higher in this group compared with other groups. In the final radiological examinations, it was observed that the changes caused by osteomyelitis in the bone tissue in the silver ion-doped calcium phosphate beads group were much improved compared with the vancomycin-impregnated bone cement beads group. Silver ion doped calcium phosphate-based bone-graft substitute offer the ability to stimulate bone growth, combat infection, and, ultimately, treat experimental chronic osteomyelitis in an animal model.

Zebrafish: An Attractive Model to Study Staphylococcus aureus Infection and Its Use as a Drug Discovery Tool

Non-mammalian in vivo disease models are particularly popular in early drug discovery. Zebrafish (Danio rerio) is an attractive vertebrate model, the success of which is driven by several advantages, such as the optical transparency of larvae, the small and completely sequenced genome, the small size of embryos and larvae enabling high-throughput screening, and low costs. In this review, we highlight zebrafish models of Staphyloccoccus aureus infection, which are used in drug discovery and for studying disease pathogenesis and virulence. Further, these infection models are discussed in the context of other relevant zebrafish models for pharmacological and toxicological studies as part of early drug profiling. In addition, we examine key differences to commonly applied models of S.aureus infection based on invertebrate organisms, and we compare their frequency of use in academic research covering the period of January 2011 to January 2021.

Establishment of a localized acute implant-associated Staphylococcus aureus bone infection model in sheep

Orthopedic implant-associated bacterial infections with Staphylococcus aureus constitute a major clinical problem, and large pre-clinical animal models remain scarce. The aim of this study was to establish a standardized method of a localized, acute S. aureus bone infection in the presence of complex implanted devices in a sheep model. Four sheep underwent surgery receiving a complex implanted metallic device with a component stabilizing a bone defect created in the left tibial metaphysis, and an attached component placed in adjacent soft tissue. The bone defect was inoculated with S. aureus strain ATCC25293 (1 × 104 CFU). Twenty one days later, the surgery site was macroscopically evaluated, tissue samples and implants harvested for bacterial cell count quantification and tissue samples histologically analyzed. The animals exhibited clinical signs of localized infection (e.g. swelling, lameness, pain) but did not develop symptoms of sepsis. After euthanasia, macroscopic assessment revealed a localized bone and soft tissue infection at the surgery site. Histologically, an acute inflammation with neutrophils but also signs of bone destruction with necrosis was noted. An ovine model of a localized, acute S. aureus bone infection with complex implants was successfully established and could be used to test novel treatments against orthopedic implant-associated infections.

Infectious Osteomyelitis: Marrying Bone Biology and Microbiology to Shed New Light on a Persistent Clinical Challenge

Infections of bone occur in a variety of clinical settings, ranging from spontaneous isolated infections arising from presumed hematogenous spread to those associated with skin and soft tissue wounds or medical implants. The majority are caused by the ubiquitous bacterium Staphyloccocus (S.) aureus, which can exist as a commensal organism on human skin as well as an invasive pathogen, but a multitude of other microbes are also capable of establishing bone infections. While studies of clinical isolates and small animal models have advanced our understanding of the role of various pathogen and host factors in infectious osteomyelitis (iOM), many questions remain unaddressed. Thus, there are many opportunities to elucidate host-pathogen interactions that may be leveraged toward treatment or prevention of this troublesome problem. Herein, we combine perspectives from bone biology and microbiology and suggest that interdisciplinary approaches will bring new insights to the field. © 2021 American Society for Bone and Mineral Research (ASBMR).

A Hyaluronic Acid Hydrogel Loaded with Gentamicin and Vancomycin Successfully Eradicates Chronic Methicillin-Resistant Staphylococcus aureus Orthopedic Infection in a Sheep Model

Implantable orthopedic devices have had an enormously positive impact on human health; however, despite best practice, patients are prone to developing orthopedic device-related infections (ODRI) that have high treatment failure rates. One barrier to the development of improved treatment options is the lack of an animal model that may serve as a robust preclinical assessment of efficacy. We present a clinically relevant large animal model of chronic methicillin-resistant Staphylococcus aureus (MRSA) ODRI that persists despite current clinical practice in medical and surgical treatment at rates equivalent to clinical observations. Furthermore, we showed that an injectable, thermoresponsive, hyaluronic acid-based hydrogel loaded with gentamicin and vancomycin outperforms current clinical practice treatment in this model, eliminating bacteria from all animals. These results confirm that local antibiotic delivery with an injectable hydrogel can dramatically increase treatment success rates beyond current clinical practice, with efficacy proven in a robust animal model.

Humanized Mice Exhibit Exacerbated Abscess Formation and Osteolysis During the Establishment of Implant-Associated Staphylococcus aureus Osteomyelitis

Staphylococcus aureus is the predominant pathogen causing osteomyelitis. Unfortunately, no immunotherapy exists to treat these very challenging and costly infections despite decades of research, and numerous vaccine failures in clinical trials. This lack of success can partially be attributed to an overreliance on murine models where the immune correlates of protection often diverge from that of humans. Moreover, S. aureus secretes numerous immunotoxins with unique tropism to human leukocytes, which compromises the targeting of immune cells in murine models. To study the response of human immune cells during chronic S. aureus bone infections, we engrafted non-obese diabetic (NOD)-scid IL2Rγ^null (NSG) mice with human hematopoietic stem cells (huNSG) and analyzed protection in an established model of implant-associated osteomyelitis. The results showed that huNSG mice have increases in weight loss, osteolysis, bacterial dissemination to internal organs, and numbers of Staphylococcal abscess communities (SACs), during the establishment of implant-associated MRSA osteomyelitis compared to NSG controls (p < 0.05). Flow cytometry and immunohistochemistry demonstrated greater human T cell numbers in infected versus uninfected huNSG mice (p < 0.05), and that T-bet⁺ human T cells clustered around the SACs, suggesting S. aureus-mediated activation and proliferation of human T cells in the infected bone. Collectively, these proof-of-concept studies underscore the utility of huNSG mice for studying an aggressive form of S. aureus osteomyelitis, which is more akin to that seen in humans. We have also established an experimental system to investigate the contribution of specific human T cells in controlling S. aureus infection and dissemination.

Development of a large animal rabbit model for chronic periprosthetic joint infection

Aims

Periprosthetic joint infections (PJIs) and osteomyelitis are clinical challenges that are difficult to eradicate. Well-characterized large animal models necessary for testing and validating new treatment strategies for these conditions are lacking. The purpose of this study was to develop a rabbit model of chronic PJI in the distal femur.

Methods

Fresh suspensions of Staphylococcus aureus (ATCC 25923) were prepared in phosphate-buffered saline (PBS) (1 × 10⁹ colony-forming units (CFUs)/ml). Periprosthetic osteomyelitis in female New Zealand white rabbits was induced by intraosseous injection of planktonic bacterial suspension into a predrilled bone tunnel prior to implant screw placement, examined at five and 28 days (n = 5/group) after surgery, and compared to a control aseptic screw group. Radiographs were obtained weekly, and blood was collected to measure ESR, CRP, and white blood cell (WBC) counts. Bone samples and implanted screws were harvested on day 28, and processed for histological analysis and viability assay of bacteria, respectively.

Results

Intraosseous periprosthetic introduction of planktonic bacteria induced an acute rise in ESR and CRP that subsided by day 14, and resulted in radiologically evident periprosthetic osteolysis by day 28 accompanied by elevated WBC counts and histological evidence of bacteria in the bone tunnels after screw removal. The aseptic screw group induced no increase in ESR, and no lysis developed around the implants. Bacterial viability was confirmed by implant sonication fluid culture.

Conclusion

Intraosseous periprosthetic introduction of planktonic bacteria reliably induces survivable chronic PJI in rabbits.

Cite this article: Bone Joint Res 2021;10(3):156–165.

Staphylococcus aureus Internalization in Osteoblast Cells: Mechanisms, Interactions and Biochemical Processes. What Did We Learn from Experimental Models?

Bacterial internalization is a strategy that non-intracellular microorganisms use to escape the host immune system and survive inside the human body. Among bacterial species, Staphylococcus aureus showed the ability to interact with and infect osteoblasts, causing osteomyelitis as well as bone and joint infection, while also becoming increasingly resistant to antibiotic therapy and a reservoir of bacteria that can make the infection difficult to cure. Despite being a serious issue in orthopedic surgery, little is known about the mechanisms that allow bacteria to enter and survive inside the osteoblasts, due to the lack of consistent experimental models. In this review, we describe the current knowledge about S. aureus internalization mechanisms and various aspects of the interaction between bacteria and osteoblasts (e.g., best experimental conditions, bacteria-induced damages and immune system response), focusing on studies performed using the MG-63 osteoblastic cell line, the best traditional (2D) model for the study of this phenomenon to date. At the same time, as it has been widely demonstrated that 2D culture systems are not completely indicative of the dynamic environment in vivo, and more recent 3D models—representative of bone infection—have also been investigated.

An injectable and antibacterial calcium phosphate scaffold inhibiting Staphylococcus aureus and supporting stem cells for bone regeneration

Staphylococcus aureus (S. aureus) is the major pathogen for osteomyelitis, which can lead to bone necrosis and destruction. There has been no report on antibacterial calcium phosphate cement (CPC) against S. aureus. The aims of this study were to: (1) develop novel antibacterial CPC-chitosan-alginate microbead scaffold; (2) investigate mechanical and antibacterial properties of CPC-chitosan-penicillin-alginate scaffold; (3) evaluate the encapsulation and delivery of human umbilical cord mesenchymal stem cells (hUCMSCs). Flexural strength, elastic modulus and work-of-fracture of the CPC-chitosan-penicillin-alginate microbeads scaffold and CPC-chitosan scaffold were evaluated. Penicillin release profile and antibacterial effects on S. aureus were determined. The hUCMSC delivery and release from penicillin-alginate microbeads were investigated. Injectable CPC-chitosan-penicillin-alginate microbeads scaffold was developed for the first time. CPC-chitosan-penicillin-alginate microbeads scaffold had a flexural strength of 3.16 ± 0.55 MPa, matching that of cancellous bone. With sustained penicillin release, the new scaffold had strong antibacterial effects on S. aureus, with an inhibition zone diameter of 32.2 ± 2.5 mm, greater than that of penicillin disk control (15.1 ± 2.0 mm) (p < 0.05). Furthermore, this injectable and antibacterial scaffold had no toxic effects, yielding excellent hUCMSC viability, which was similar to that of CPC control without antibacterial activity (p > 0.05). CPC-chitosan-penicillin-microbeads scaffold had injectability, good strength, strong antibacterial effects, and good biocompatibility to support stem cell viability for osteogenesis. CPC-chitosan-penicillin-microbeads scaffold is promising for dental, craniofacial and orthopedic applications to combat infections and promote bone regeneration.

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.

Antibacterial, proangiogenic, and osteopromotive nanoglass paste coordinates regenerative process following bacterial infection in hard tissue

Bacterial infection raises serious concerns in tissue repair settings involved with implantable biomaterials, devastating the regenerative process and even life-threatening. When hard tissues are infected with bacteria (called 'osteomyelitis'), often the cases in open fracture or chronic inflammation, a complete restoration of regenerative capacity is significantly challenging even with highly-dosed antibiotics or surgical intervention. The implantable biomaterials are thus needed to be armored to fight bacteria then to relay regenerative events. To this end, here we propose a nanoglass paste made of ~200-nm-sized silicate-glass (with Ca, Cu) particles that are hardened in contact with aqueous medium and multiple-therapeutic, i.e., anti-bacterial, pro-angiogenic and osteopromotive. The nanoglass paste self-hardened via networks of precipitated nano-islands from leached ions to exhibit ultrahigh surface area (~300 m²/g), amenable to fill tunable defects with active biomolecular interactions. Also, the nanoglass paste could release multiple ions (silicate, calcium, and copper) at therapeutically relevant doses and sustainably (for days to weeks), implying possible roles in surrounding cells/tissues as a therapeutic-ions reservoir. The osteopromotive effects of nanoglass paste were evidenced by the stimulated osteogenic differentiation of MSCs. Also, the nanoglass paste promoted angiogenesis of endothelial cells in vitro and vasculature formation in vivo. Furthermore, the significant bactericidal effect of nanoglass paste, as assessed with E. coli and S. aureus, highlighted the role of copper played in elevating ROS level and destroying homeostasis, which salvaged tissue cells from co-cultivated bacteria contamination. When administered topically to rat tibia osteomyelitis defects, the nanoglass paste enhanced in vivo bone healing and fracture resistance. The developed nanoglass paste, given its self-setting property and the coordinated therapeutic actions, is considered to be a promising drug-free inorganic biomaterial platform for the regenerative therapy of bacteria-infected hard tissues.

Longitudinal time-lapse in vivo micro-CT reveals differential patterns of peri-implant bone changes after subclinical bacterial infection in a rat model

Subclinical infection associated with orthopedic devices can be challenging to diagnose. The goal of this study was to evaluate longitudinal, microcomputed tomography (microCT) imaging in a rat model of subclinical orthopedic device-related infection caused by Staphylococcus epidermidis and four different Cutibacterium (previously Propionibacterium) acnes strains, and compare outcomes with non-inoculated and historical S. aureus-inoculated controls. Sterile screws or screws colonized with bacteria were placed in the tibia of 38 adult Wistar rats [n = 6 sterile screws; n = 6 S. epidermidis-colonized screws; n = 26 C. acnes-colonized screws (covering all three main subspecies)]. Regular microCT scans were taken over 28 days and processed for quantitative time-lapse imaging with dynamic histomorphometry. At euthanasia, tissues were processed for semiquantitative histopathology or quantitative bacteriology. All rats receiving sterile screws were culture-negative at euthanasia and displayed progressive bony encapsulation of the screw. All rats inoculated with S. epidermidis-colonized screws were culture-positive and displayed minor changes in peri-implant bone, characteristic of subclinical infection. Five of the 17 rats in the C. acnes inoculated group were culture positive at euthanasia and displayed bone changes at the interface of the screw and bone, but not deeper in the peri-implant bone. Dynamic histomorphometry revealed significant differences in osseointegration, bone remodeling and periosteal reactions between groups that were not measurable by visual observation of still microCT images. Our study illustrates the added value of merging 3D microCT data from subsequent timepoints and producing inherently richer 4D data for the detection and characterization of subclinical orthopedic infections, whilst also reducing animal use.

Lack of Humoral Immunity Against Glucosaminidase Is Associated with Postoperative Complications in Staphylococcus aureus Osteomyelitis

BACKGROUND

Glucosaminidase (Gmd) is known to be a protective antigen in animal models of Staphylococcus aureus osteomyelitis. We compared the endogenous anti-Gmd antibody levels in sera of patients with culture-confirmed S. aureus bone infections to their sera at 1 year after operative treatment of the infection.

METHODS

A novel global biospecimen registry of 297 patients with deep-wound culture-confirmed S. aureus osteomyelitis was analyzed to assess relationships between baseline anti-Gmd serum titers (via custom Luminex assay), known host risk factors for infection, and 1-year postoperative clinical outcomes (e.g., infection control, inconclusive, refracture, persistent infection, septic nonunion, amputation, and septic death).

RESULTS

All patients had measurable humoral immunity against some S. aureus antigens, but only 20 patients (6.7%; p < 0.0001) had high levels of anti-Gmd antibodies (>10 ng/mL) in serum at baseline. A subset of 194 patients (65.3%) who completed 1 year of follow-up was divided into groups based on anti-Gmd level: low (<1 ng/mL, 54 patients; 27.8%), intermediate (<10 ng/mL, 122 patients; 62.9%), and high (>10 ng/mL, 18 patients; 9.3%), and infection control rates were 40.7%, 50.0%, and 66.7%, respectively. The incidence of adverse outcomes in these groups was 33.3%, 16.4%, and 11.1%, respectively. Assessing anti-Gmd level as a continuous variable showed a 60% reduction in adverse-event odds (p = 0.04) for every tenfold increase in concentration. No differences in patient demographics, body mass index of >40 kg/m, diabetes status, age of ≥70 years, male sex, Charlson Comorbidity Index of >1, or Cierny-Mader host type were observed between groups, and these risk factors were not associated with adverse events. Patients with low anti-Gmd titer demonstrated a significant 2.68-fold increased odds of adverse outcomes (p = 0.008).

CONCLUSIONS

Deficiency in circulating anti-Gmd antibodies was associated serious adverse outcomes following operative treatment of S. aureus osteomyelitis. At 1 year, high levels of anti-Gmd antibodies were associated with a nearly 3-fold increase in infection-control odds. Additional prospective studies clarifying Gmd immunization for osteomyelitis are needed.

LEVEL OF EVIDENCE

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

An antibacterial and injectable calcium phosphate scaffold delivering human periodontal ligament stem cells for bone tissue engineering

Osteomyelitis and post-operative infections are major problems in orthopedic, dental and craniofacial surgeries. It is highly desirable for a tissue engineering construct to kill bacteria, while simultaneously delivering stem cells and enhancing cell function and tissue regeneration. The objectives of this study were to: (1) develop a novel injectable calcium phosphate cement (CPC) scaffold containing antibiotic ornidazole (ORZ) while encapsulating human periodontal ligament stem cells (hPDLSCs), and (2) investigate the inhibition efficacy against Staphylococcus aureus (S. aureus) and the promotion of hPDLSC function for osteogenesis for the first time. ORZ was incorporated into a CPC-chitosan scaffold. hPDLSCs were encapsulated in alginate microbeads (denoted hPDLSCbeads). The ORZ-loaded CPCC+hPDLSCbeads scaffold was fully injectable, and had a flexural strength of 3.50 ± 0.92 MPa and an elastic modulus of 1.30 ± 0.45 GPa, matching those of natural cancellous bone. With 6 days of sustained ORZ release, the CPCC+10ORZ (10% ORZ) scaffold had strong antibacterial effects on S. aureus, with an inhibition zone of 12.47 ± 1.01 mm. No colonies were observed in the CPCC+10ORZ group from 3 to 7 days. ORZ-containing scaffolds were biocompatible with hPDLSCs. CPCC+10ORZ+hPDLSCbeads scaffold with osteogenic medium had 2.4-fold increase in alkaline phosphatase (ALP) activity and bone mineral synthesis by hPDLSCs, as compared to the control group (p < 0.05). In conclusion, the novel antibacterial construct with stem cell delivery had injectability, good strength, strong antibacterial effects and biocompatibility, supporting osteogenic differentiation and bone mineral synthesis of hPDLSCs. The injectable and mechanically-strong CPCC+10ORZ+hPDLSCbeads construct has great potential for treating bone infections and promoting bone regeneration.

Preparation of lysozyme loaded gelatin microcryogels and investigation of their antibacterial properties

Antibacterial micron-sized cryogels, so-called microcryogels, were prepared by cryogelation of gelatin and integration of lysozyme. Gelation yield, specific surface area, macro-porosity and swelling degree of the microcryogels were examined in order to characterize their physical properties. MTT method was utilized to measure cell viability of the gelatin microcryogels with a period of 24, 48, and 72 h and no significant decrease was observed at 72 h. Apoptotic staining assay also showed high viability at 24, 48, 72 h in parallel with the control group. The antibacterial performances of the gelatin microcryogels against Bacillus subtilis, Staphylococcus aureus, and Escherichia coli were examined. The results showed that the incorporation of lysozyme into gelatin microcryogels exhibited the antibacterial activity against S. aureus, B. subtilis, and E. coli, that may provide great potential for various applications in the biomedical industry.

IsdB antibody-mediated sepsis following S. aureus surgical site infection

Staphylococcus aureus is prevalent in surgical site infections (SSI) and leads to death in approximately 1% of patients. Phase IIB/III clinical trial results have demonstrated that vaccination against the iron-regulated surface determinant protein B (IsdB) is associated with an increased mortality rate in patients with SSI. Thus, we hypothesized that S. aureus induces nonneutralizing anti-IsdB antibodies, which facilitate bacterial entry into leukocytes to generate "Trojan horse" leukocytes that disseminate the pathogen. Since hemoglobin (Hb) is the primary target of IsdB, and abundant Hb-haptoglobin (Hb-Hp) complexes in bleeding surgical wounds are normally cleared via CD163-mediated endocytosis by macrophages, we investigated this mechanism in vitro and in vivo. Our results demonstrate that active and passive IsdB immunization of mice renders them susceptible to sepsis following SSI. We also found that a multimolecular complex containing S. aureus protein A-anti-IsdB-IsdB-Hb-Hp mediates CD163-dependent bacterial internalization of macrophages in vitro. Moreover, IsdB-immunized CD163-/- mice are resistant to sepsis following S. aureus SSI, as are normal healthy mice given anti-CD163-neutralizing antibodies. These genetic and biologic CD163 deficiencies did not exacerbate local infection. Thus, anti-IsdB antibodies are a risk factor for S. aureus sepsis following SSI, and disruption of the multimolecular complex and/or CD163 blockade may intervene.

Staphylococcus aureus Host Tropism and Its Implications for Murine Infection Models

Staphylococcus aureus (S. aureus) is a pathobiont of humans as well as a multitude of animal species. The high prevalence of multi-resistant and more virulent strains of S. aureus necessitates the development of new prevention and treatment strategies for S. aureus infection. Major advances towards understanding the pathogenesis of S. aureus diseases have been made using conventional mouse models, i.e., by infecting naïve laboratory mice with human-adapted S.aureus strains. However, the failure to transfer certain results obtained in these murine systems to humans highlights the limitations of such models. Indeed, numerous S. aureus vaccine candidates showed promising results in conventional mouse models but failed to offer protection in human clinical trials. These limitations arise not only from the widely discussed physiological differences between mice and humans, but also from the lack of attention that is paid to the specific interactions of S. aureus with its respective host. For instance, animal-derived S. aureus lineages show a high degree of host tropism and carry a repertoire of host-specific virulence and immune evasion factors. Mouse-adapted S.aureus strains, humanized mice, and microbiome-optimized mice are promising approaches to overcome these limitations and could improve transferability of animal experiments to human trials in the future.

A tailored positively-charged hydrophobic surface reduces the risk of implant associated infections

Implant-associated infections is one of the most challenging post-operative complications in bone-related implantations. To tackle this clinical issue, we developed a low-cost and durable surface coating for medical grade titanium implants that uses positively charged silane molecules. The in vitro antimicrobial tests revealed that the titanium surface coated with (3-aminopropyl) triethoxysilane, which has the appropriate length of hydrophobic alkyl chain and positive charged amino group, suppressed more than 90% of the initial bacterial adhesion of S. aureus, P. aeruginosa, and E. coli after 30 min of incubation. In terms of growth inhibitory rate, the treated surface was able to reduce 75.7% ± 11.9% of bacterial growth after a 24-hour culturing, thereby exhibiting superior anti-biofilm formation in the late stage. When implanted into the rat model infected by S. aureus, the treated surface eliminated the implant-associated infection through the mechanism of inhibition of bacterial adhesion on the implant surface. Additionally, the treated surface was highly compatible with mammalian cells. In general, our design demonstrated its potential for human clinical trials as a low-cost and effective antibacterial strategy to minimize post-operative implant-related bacterial infection.

Treatment of contaminated radial fracture in Sprague-Dawley rats by application of a degradable polymer releasing gentamicin

Fracture-related infections remain a leading cause of morbidity and mortality. We aimed to establish a simple contaminated radial osteotomy model to assess the efficacy of a biodegradable polymer poly(sebacic-co-ricinoleic acid) [p(SA-RA)] containing 20% w/w gentamicin. A unilateral transverse osteotomy was induced in Sprague-Dawley (SD) rats, followed by application of Staphylococcus aureus suspension over the fracture. After successfully establishing the contaminated open fracture model, we treated the rats either systemically (intraperitoneal cefuroxime), locally with p(SA-RA) containing gentamicin, or both. Control groups included non-contaminated group and contaminated groups that were either untreated or treated with the polymer alone. After 4 weeks, the bones were subjected to micro-CT scanning and microbiological and histopathology evaluations. Micro-CT analysis revealed similar changes in the group subjected to both local and systemic treatment as in the non-contaminated control group. Lack of detectable bacterial growth was noted in most animals of the group subjected to both local and systemic treatment, and all samples were negative for S. aureus. Histopathological evaluation revealed that all treatment modalities containing antibiotics were highly effective in reducing infection and promoting callus repair, resulting in early bone healing. While p(SA-RA) containing gentamicin treatment showed better results than cefuroxime, the combination of local and systemic treatment displayed the highest therapeutic potential in this model.

Rapid Determination of Benzylpenicillin Resistance in Staphylococcus aureus Bacteraemia Model

Rapid determination of antimicrobial susceptibility/resistance is an important factor in selecting an appropriate antimicrobial treatment and eradicating infections promptly. Conventional antimicrobial susceptibility tests (ASTs) are very time consuming. Thus, we developed a liquid chromatography-mass spectrometry (LC-MS/MS) method for rapidly determining the resistance of Staphylococcus aureus to penicillin-G in an animal-infection model. This technique will be able to detect those resistant strains whose resistance mechanism specifically controlled by penicillinase. The resistance status of S. aureus against penicillin-G was determined by conventional AST. Cultured S. aureus cells were inoculated to chicken for developing bacteraemia. The solution of penicillin-G was intravenously administered (10 mg/kg b.w.) to chickens just after infection detection. Blood samples were collected at different intervals after drug administration. The concentration of active penicillin-G and its metabolites were determined from the bacteria-free blood supernatant by utilizing the LC-MS/MS method. Evidence of infection in chicken was observed within 5 h of bacterial inoculation. The penicillinase enzyme generated by S. aureus transforms the active penicillin-G to an inactive metabolite by hydrolysis, which is evident by the mass shift from 335.10600 to 353.11579 Da as quantified using liquid chromatography quadrupole time-of-flight mass spectrometry (LC/Q-TOF/MS). The signal intensity of inactive/hydrolysed penicillin-G is several-fold greater than that of the active penicillin-G in the blood sample of chicken infected with resistant strain and treated with penicillin-G. The antimicrobial resistance index (ARI) value of resistant S. aureus strain was more than 1, demonstrating the penicillin-G-resistance pattern of that strain. This method is able to determine the extent of β-lactam antimicrobial resistance within 1.5 h from the patient's blood and is complementary with those existing AST methods which are usually practicing in the evaluation of β-lactam antibiotic resistance.

A new sequential animal model for infection-related non-unions with segmental bone defect

BACKGROUND

The treatment of fracture-related infections (FRI) is still a challenge for orthopedic surgeons. The prevalence of FRI is particularly high in open fractures with extensive soft-tissue damage. This study aimed to develop a new two-step animal model for non-unions with segmental bone defects, which could be used to evaluate new innovative bone substitutes to improve the therapeutic options in humans with FRI and bone defects.

METHODS

After randomization to infected or non-infected groups, 30 Sprague-Dawley rats underwent a transverse osteotomy of the mid-shaft femur with a 5 mm defect. Additionally, the periosteum at the fracture zone was cauterized at both sides. After intramedullary inoculation with 10³ CFU Staphylococcus aureus (infected group) or PBS (non-infected group), a fracture stabilization was done by intramedullary K-wires. After 5 weeks, the bone healing process was evaluated, and revision surgery was performed in order to obtain increased bone healing. The initial K-wires were removed, and debridement of the osteotomy-gap was done followed by a more stable re-osteosynthesis with an angle-stable plate. After further 8 weeks all rats were euthanized and the bone consolidation was tested biomechanically and the callus formation quantitatively by micro-CT analysis.

RESULTS

We developed and presented a new two-stage non-union animal model through a targeted S. aureus infection. After 5 weeks, all animals showed a non-union irrespective of assignment to the infected and non-infected group. Lane and Sandhu score showed a higher callus formation in the infected group. In all infected animals, the inoculated S. aureus strain was detected in the revision surgery. The second surgery did not improve bone healing, as shown by the Lane Sandhu score and in the μ-CT analysis. Similarly, biomechanical testing showed in both groups a significantly lower maximum torque as compared to the contralateral side (p < 0.0001).

CONCLUSIONS

We were able to successfully develop a new two-stage non-union animal model, which reflects a genuine clinical situation of an infection-related non-union model with segmental bone defects. This model could be used to evaluate various therapeutic anti-infectious and osteoinductive strategies in FRIs.

Antimicrobial Silver Multilayer Coating for Prevention of Bacterial Colonization of Orthopedic Implants

Due to increasing rates of periprosthetic joint infections (PJI), new approaches are needed to minimize the infection risk. The first goal of this study was to modify a well-established infection model to test surface-active antimicrobial systems. The second goal was to evaluate the antimicrobial activity of a silver multilayer (SML) coating. In vitro tests with SML items showed a >4 Log reduction in a proliferation assay and a 2.2 Log reduction in an agar immersion test (7 d). In the in vivo model blank and SML coated K-wires were seeded with ~2 × 104 CFU of a methicillin-sensitive Staphylococcus epidermidis (MSSE) and inserted into the intramedullary tibial canal of rabbits. After 7 days, the animals were sacrificed and a clinical, microbiological and histological analysis was performed. Microbiology showed a 1.6 Log pathogen reduction on the surface of SML items (p = 0.022) and in loosely attached tissue (p = 0.012). In the SML group 7 of 12 SML items were completely free of pathogens (cure rate = 58%, p = 0.002), while only 1 of 12 blank items were free of pathogens (cure rate = 8%, p = 0.110). No silver was detected in the blood or urine of the SML treated animals and only scarcely in the liver or adjacent lymph nodes. In summary, an in vivo infection model to test implants with bacterial pre-incubation was established and the antimicrobial activity of the SML coating was successfully proven.