Animal Models of Osteomyelitis

Micro-CT analysis of osteomyelitis of rabbit tibial for model establishment and biomaterials application in tissue engineering

Osteomyelitis is one of the most difficult diseases to treat in orthopedics field. The construction of animal models of osteomyelitis is now more mature but still lacks a deeper criterion other than "successful infection". In this work, rabbit tibial osteomyelitis model with S. aureus infection was established. Whole tibia, cortical bone around bone window, and tibial condyle were characterized in considerable detail using micro-CT and other means at 2/4/6 weeks, respectively. The results show that in addition to the obvious inflammatory response and bone destruction, osteomyelitis caused some other effects on compact and cancellous bone, and in particular, changes in bone mineral density after infection were of interest. Although the modeling groups all exhibited osteolysis and bone loss, their overall bone mineral density averages and those of the control groups were mostly in the range of 870 mg/cm³ to 920 mg/cm³, without statistical difference. The results suggest that overall bone mineral density is determined by both bone destruction conditions and the amount of dead bone deposition. This work provides a reference basis for the selection of time points for the subsequent animal models establishment and some valuable reference indicators of the application of biomaterials in tissue engineering.

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.

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.

Pre-Clinical Models in Implant Dentistry: Past, Present, Future

Biomedical research seeks to generate experimental results for translation to clinical settings. In order to improve the transition from bench to bedside, researchers must draw justifiable conclusions based on data from an appropriate model. Animal testing, as a prerequisite to human clinical exposure, is performed in a range of species, from laboratory mice to larger animals (such as dogs or non-human primates). Minipigs appear to be the animal of choice for studying bone surgery around intraoral dental implants. Dog models, well-known in the field of dental implant research, tend now to be used for studies conducted under compromised oral conditions (biofilm). Regarding small animal models, research studies mostly use rodents, with interest in rabbit models declining. Mouse models remain a reference for genetic studies. On the other hand, over the last decade, scientific advances and government guidelines have led to the replacement, reduction, and refinement of the use of all animal models in dental implant research. In new development strategies, some in vivo experiments are being progressively replaced by in vitro or biomaterial approaches. In this review, we summarize the key information on the animal models currently available for dental implant research and highlight (i) the pros and cons of each type, (ii) new levels of decisional procedures regarding study objectives, and (iii) the outlook for animal research, discussing possible non-animal options.

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

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

Antibiotic-loaded amphora-shaped pores on a titanium implant surface enhance osteointegration and prevent infections

Artificial prostheses for joint replacement are indispensable in orthopedic surgery. Unfortunately, the implanted surface is attractive to not only host cells but also bacteria. To enable better osteointegration, a mechanically stable porous structure was created on a titanium surface using laser treatment and metallic silver particles were embedded in a hydrophilic titanium oxide layer on top. The laser structuring resulted in unique amphora-shaped pores. Due to their hydrophilic surface conditions and capillary forces, the pores can be loaded preoperative with the antibiotic of choice/need, such as gentamicin. Cytotoxicity and differentiation assays with primary human osteoblast-like cells revealed no negative effect of the surface modification with or without gentamicin loading. An in vivo biocompatibility study showed significantly enhanced osteointegration as measured by push-out testing and histomorphometry 56 days after the implantation of the K-wires into rat femora. Using a S. aureus infection model, the porous, silver-coated K-wires slightly reduced the signs of bone destruction, while the wires were still colonized after 28 days. Loading the amphora-shaped pores with gentamicin significantly reduced the histopathological signs of bone destruction and no bacteria were detected on the wires. Taken together, this novel surface modification can be applied to new or established orthopedic implants. It enables preoperative loading with the antibiotic of choice/need without further equipment or post-coating, and supports osteointegration without a negative effect of the released dug, such as gentamicin.

Evaluation of Pseudomonas aeruginosa pathogenesis and therapeutics in military-relevant animal infection models

Modern combat-related injuries are often associated with acute polytrauma. As a consequence of severe combat-related injuries, a dysregulated immune response results in serious infectious complications. The gram-negative bacterium Pseudomonas aeruginosa is an opportunistic pathogen that often causes life-threatening bloodstream, lung, bone, urinary tract, and wound infections following combat-related injuries. The rise in the number of multidrug-resistant P. aeruginosa strains has elevated its importance to civilian clinicians and military medicine. Development of novel therapeutics and treatment options for P. aeruginosa infections is urgently needed. During the process of drug discovery and therapeutic testing, in vivo testing in animal models is a critical step in the bench-to-bedside approach, and required for Food and Drug Administration approval. Here, we review current and past literature with a focus on combat injury-relevant animal models often used to understand infection development, the interplay between P. aeruginosa and the host, and evaluation of novel treatments. Specifically, this review focuses on the following animal infection models: wound, burn, bone, lung, urinary tract, foreign body, and sepsis.

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.

Decompression effects on bone healing in rat mandible osteomyelitis

Osteomyelitis (OM) of the jaw is usually caused by a chronic odontogenic infection. Decompression is the release the intraluminal pressure in the cystic cavity allowing gradual bone growth from the periphery. The aim of this study was to analyze the effectiveness of decompression in an OM jaw model. A 4-mm-diameter defect was made on mandibles of fourteen Sprague-Dawley rats and inoculated with S. aureus (20 μl of 1 × 10⁷ CFU/ml) injection. Two weeks later, four groups were made as non-treatment (C1), only curettage (C2), curettage and decompression (E1), and curettage and decompression with normal saline irrigation (E2). After four weeks, each group was analyzed. Most micro-CT parameters, including bone mineral density [0.87 (± 0.08) g/cm³] with bone volume [0.73 (± 0.08) mm³] was higher in E2 group than that of C1 group (p = 0.04, p = 0.05, respectively). E2 group in histology showed the highest number of osteocytes than those of control groups, 91.00 (± 9.90) (p = 0.002). OPN were expressed strongly in the E1 ("5": 76-100%) that those of other groups. Decompression drains induced advanced bone healing compared to that of curettage alone. Therefore, it could be recommended to use decompressive drain for enhancing the jaw OM management.

Anti-Periprosthetic Infection Strategies: From Implant Surface Topographical Engineering to Smart Drug-Releasing Coatings

Despite advanced implant sterilization and aseptic surgical techniques, periprosthetic bacterial infection remains a major challenge for orthopedic and dental implants. Bacterial colonization/biofilm formation around implants and their invasion into the dense skeletal tissue matrices are difficult to treat and could lead to implant failure and osteomyelitis. These complications require major revision surgeries and extended antibiotic therapies that are associated with high treatment cost, morbidity, and even mortality. Effective preventative measures mitigating risks for implant-related infections are thus in dire need. This review focuses on recent developments of anti-periprosthetic infection strategies aimed at either reducing bacterial adhesion, colonization, and biofilm formation or killing bacteria directly in contact with and/or in the vicinity of implants. These goals are accomplished through antifouling, quorum-sensing interfering, or bactericidal implant surface topographical engineering or surface coatings through chemical modifications. Surface topographical engineering of lotus leaf mimicking super-hydrophobic antifouling features and cicada wing-mimicking, bacterium-piercing nanopillars are both presented. Conventional physical coating/passive release of bactericidal agents is contrasted with their covalent tethering to implant surfaces through either stable linkages or linkages labile to bacterial enzyme cleavage or environmental perturbations. Pros and cons of these emerging anti-periprosthetic infection approaches are discussed in terms of their safety, efficacy, and translational potentials.

Non-rodent animal models of osteosarcoma: A review

Osteosarcoma is extremely malignant, and the most common cancer that affects bone. Current treatments involve surgical resection of the affected area and multi-agent chemotherapy, though survival rate is generally poor for those affected by metastases. As treatment for osteosarcoma has remained unchanged for the past few decades, there is a need for further advancements in the understanding of osteosarcoma biology and therapeutics. Thus, reliable animal models that can accurately recapitulate the disease are required. Though rodents represent the most popular animal model of osteosarcoma, they may not model the disease best. This review analyzes emerging alternative non-rodent animal models of osteosarcoma, such as the chick chorioallantoic membrane (CAM) assay, pigs, and canines. Each of these alternatives offer advantages over classic rodent models for pre-clinical research. Research of these cross-species platforms imparts knowledge of metastases biology and potential new treatments for osteosarcoma.

Guideline for Preclinical Studies of Bone Infections in Large Animals Based on a Systematic Review of 316 Non-Rodent Models

BACKGROUND

In recent years, animal models of bone infections have been used with increased frequency in order to evaluate novel diagnostic and anti-infective technologies, like antibacterial coating of bone implants or local antibiotic carrier products. Therefore, it is highly relevant to evaluate the scientific quality of existing bone infection models.

METHODS

We conducted a systematic review of 316 studies of large non-rodent animal models of bone infection (254 rabbit, 16 pig, 23 dog, 11 goat, and 12 sheep) and extracted data on study design, methodological quality, and postmortem evaluation of infection with respect to reporting and quantification of pathology and microbiology.

RESULTS

The review demonstrated a substantial lack of study-design information, which hampers reproducibility and continuation of the established work. Furthermore, the methodological study quality was found to be low, as the definition of infection, randomization, power analysis, and blinding were only seldomly reported. The use of histology increased in recent years, but a semi-quantitative scoring of the lesions was often missing, i.e. no objective quantification of outcome. Most of the studies focused on whether the inoculated bacteria were present within the bone tissue post mortem or not. However, very often the bacterial burden was not quantified. In many of the models, different antimicrobial interventions were examined and, although antimicrobial effects were commonly described, a lack of complete sterile outcome was observed in many models. On the basis of the systematic review, we established a study template providing a guideline for the standard reporting of animal models of bone infections, including details related to the animal, pathogen, infected animal, and postmortem analysis that are of crucial importance for validation of results and reproducibility.

CONCLUSIONS

As the aim of many bone infection models is to examine the effect of an intervention, the guideline emphasizes the importance of objective quantification of outcome, e.g., blinded quantitative scoring of histological findings and quantification of bacterial burden within tissue and on inserted implants. Less than 5% of the analyzed studies adhered completely to the ideal form presented in the study template.

CLINICAL RELEVANCE

Anti-infective interventions must be tested in preclinical animal models before implementation in human patients, and optimal design and validation is essential for a high translational value.

Development of bone regeneration strategies using human periosteum-derived osteoblasts and oxygen-releasing microparticles in mandibular osteomyelitis model of miniature pig

Hypoxia and limited vascularization inhibit bone growth and recovery after surgical debridement to treat osteomyelitis. Similarly, despite significant efforts to create functional tissue-engineered organs, clinical success is often hindered by insufficient oxygen diffusion and poor vascularization. To overcome these shortcomings, we previously used the oxygen carrier perfluorooctane (PFO) to develop PFO emulsion-loaded hollow microparticles (PFO-HPs). PFO-HPs act as a local oxygen source that increase cell viability and maintains the osteogenic differentiation potency of human periosteum-derived cells (hPDCs) under hypoxic conditions. In the present study, we used a miniature pig model of mandibular osteomyelitis to investigate bone regeneration using hPDCs seeded on PFO-HPs (hPDCs/PFO-HP) or hPDCs seeded on phosphate-buffered saline (PBS)-HPs (hPDCs/PBS-HP). Osteomyelitis is characterized by a series of microbial invasion, vascular disruption, bony necrosis, and sequestrum formation due to impaired host defense response. Sequential plain radiography, computed tomography (CT), and 3D reconstructed CT images revealed new bone formation was more advanced in defects that had been implanted with the hPDCs/PFO-HPs than in defects implanted with the hPDCs/PBS-HP. Thus, PFO-HPs are a promising tissue engineering approach to repair challenging bone defects and regenerate structurally organized bone tissue with 3D architecture.

Animal models of orthopaedic infections. A review of rabbit models used to induce long bone bacterial infections

The development of infections is one of the main complications in orthopaedics, especially in the presence of implants for the osteosynthesis of compound fractures and joint prosthesis. Indeed, foreign materials and implants act as substrates for the adhesion and proliferation of bacterial strains able to produce biofilm, causing peri-implant osteomyelitis. The eradication of biofilm remains a great challenge for the host immune system, as well as for medical and surgical approaches, thus imposing the need for new prophylactic and/or therapeutic strategies in which animal models have an essential role. In vivo orthopaedic models have mainly been used to study the pathogenesis of infections, biofilm behaviour and the efficacy of antimicrobial strategies, to select diagnostic techniques and test the efficacy of novel materials or surface modifications to impede both the establishment of bone infections and the associated septic loosening of implants. Among several models of osteomyelitis and implant-related infections described in small rodents and large animals, the rabbit has been widely used as a reliable and reproducible model of orthopaedic infections. This review examines the relevance of rabbits for the development of clinically representative models by analysing the pros and cons of the different approaches published in the literature. This analysis will aid in increasing our knowledge concerning orthopaedic infections by using this species. This review will be a tool for researchers who need to approach pre-clinical studies in the field of bone infection and have to identify the most appropriate animal model to verify their scientific hypothesis.

In vivo efficiency of antimicrobial inorganic bone grafts in osteomyelitis treatments

The purpose of the present work was to evaluate in vivo different antimicrobial therapies to eradicate osteomyelitis created in the femoral head of New Zealand rabbits. Five phosphate-based cements were evaluated: calcium phosphate cements (CPC) and calcium phosphate foams (CPF), both in their pristine form and loaded with doxycycline hyclate, and an intrinsic antimicrobial magnesium phosphate cement (MPC; not loaded with an antibiotic). The cements were implanted in a bone previously infected with Staphylococcus aureus to discern the effects of the type of antibiotic administration (systemic vs. local), porosity (microporosity, i.e. <5 μm vs. macroporosity, i.e. >5 μm) and type of antimicrobial mechanism (release of antibiotic vs. intrinsic antimicrobial activity) on the improvement of the health state of the infected animals. A new method was developed, with a more comprehensive composite score that integrates 5 parameters of bone infection, 4 parameters of bone structural integrity and 4 parameters of bone regeneration. This method was used to evaluate the health state of the infected animals, both before and after osteomyelitis treatment. The results showed that the composite score allows to discern statistically significant differences between treatments that individual evaluations were not able to identify. Despite none of the therapies completely eradicated the infection, it was observed that macroporous materials (CPF and CPFd, the latter loaded with doxycycline hyclate) and intrinsic antimicrobial MPC allowed a better containment of the osteomyelitis. This study provides novel insights to understand the effect of different antimicrobial therapies in vivo, and a promising comprehensive methodology to evaluate the health state of the animals was developed. We expect that the implementation of such methodology could improve the criteria to select a proper antimicrobial therapy.

Novel porcine model of implant-associated osteomyelitis: A comprehensive analysis of local, regional, and systemic response

Pigs are favorable experimental animals for infectious diseases in humans. However, implant-associated osteomyelitis (IAO) models in pigs have only been evaluated using high-inoculum infection (>10⁸ CFU) models in 1975 and 1993. Therefore, the aim of this paper was to present a new low inoculum porcine model of human IAO based on 42 experimental pigs. The model was created by drilling an implant cavity in the tibial bone followed by insertion of a small steel implant and simultaneous inoculation of Staphylococcus aureus bacteria (n = 32) or saline (n = 10). The infected pigs were either inoculated with 10⁴ CFU (n = 26) or 10² and 10³ CFU (n = 6). All animals were euthanized 5 days after insertion of implants. Pigs receiving the high-inoculum infections showed a significantly higher volume of bone lesion, number of neutrophils around the implant, concentrations of acute phase proteins in serum, and enlargement of regional lymph nodes. A positive correlation was present between a high number of surrounding neutrophils and high values of all other parameters. Furthermore, a threshold of 40 neutrophils per 10 high power fields for the histopathological diagnosis of high grade IAO was defined.

IN CONCLUSION

This paper describes a novel low-inoculum S. aureus porcine model of IAO which was demonstrated to be reliable, reproducible and discriminative to human IAO, and represents a requested and valuable tool in orthopedic research. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2211-2221, 2017.

A resorbable antibiotic-eluting polymer composite bone void filler for perioperative infection prevention in a rabbit radial defect model

Nearly 1.3 million total joint replacement procedures are performed in the United States annually, with numbers projected to rise exponentially in the coming decades. Although finite infection rates for these procedures remain consistently low, device-related infections represent a significant cause of implant failure, requiring secondary or revision procedures. Revision procedures manifest several-fold higher infection recurrence rates. Importantly, many revision surgeries, infected or not, require bone void fillers to support the host bone and provide a sufficient tissue bed for new hardware placement. Antibiotic-eluting bone void fillers (ABVF), providing both osteoconductive and antimicrobial properties, represent one approach for reducing rates of orthopedic device-related infections. Using a solvent-free, molten-cast process, a polymer-controlled antibiotic-eluting calcium carbonate hydroxyapatite (HAP) ceramic composite BVF (ABVF) was fabricated, characterized, and evaluated in vivo using a bacterial challenge in a rabbit radial defect window model. ABVF loaded with tobramycin eliminated the infectious burden in rabbits challenged with a clinically relevant strain of Staphylococcus aureus (inoculum as high as 10⁷ CFU). Histological, microbiological, and radiographic methods were used to detail the effects of ABVF on microbial challenge to host bone after 8 weeks in vivo. In contrast to the HAP/BVF controls, which provided no antibiotic protection and required euthanasia 3 weeks post-operatively, tobramycin-releasing ABVF animals showed no signs of infection (clinical, microbiological, or radiographic) when euthanized at the 8-week study endpoint. ABVF sites did exhibit fibrous encapsulation around the implant at 8 weeks. Local antibiotic release from ABVF to orthopedic sites requiring bone void fillers eliminated the periprosthetic bacterial challenge in this 8-week in vivo study, confirming previous in vitro results.

Foreign Body Infection Models to Study Host-Pathogen Response and Antimicrobial Tolerance of Bacterial Biofilm

The number of implanted medical devices is steadily increasing and has become an effective intervention improving life quality, but still carries the risk of infection. These infections are mainly caused by biofilm-forming staphylococci that are difficult to treat due to the decreased susceptibility to both antibiotics and host defense mechanisms. To understand the particular pathogenesis and treatment tolerance of implant-associated infection (IAI) animal models that closely resemble human disease are needed. Applications of the tissue cage and catheter abscess foreign body infection models in the mouse will be discussed herein. Both models allow the investigation of biofilm and virulence of various bacterial species and a comprehensive insight into the host response at the same time. They have also been proven to serve as very suitable tools to study the anti-adhesive and anti-infective efficacy of different biomaterial coatings. The tissue cage model can additionally be used to determine pharmacokinetics, efficacy and cytotoxicity of antimicrobial compounds as the tissue cage fluid can be aspirated repeatedly without the need to sacrifice the animal. Moreover, with the advance in innovative imaging systems in rodents, these models may offer new diagnostic measures of infection. In summary, animal foreign body infection models are important tools in the development of new antimicrobials against IAI and can help to elucidate the complex interactions between bacteria, the host immune system, and prosthetic materials.

(68)Ga-DOTA-Siglec-9 PET/CT imaging of peri-implant tissue responses and staphylococcal infections

Background

Staphylococcus epidermidis (S. epidermidis) has emerged as one of the leading pathogens of biomaterial-related infections. Vascular adhesion protein-1 (VAP-1) is an inflammation-inducible endothelial molecule controlling extravasation of leukocytes. Sialic acid-binding immunoglobulin-like lectin 9 (Siglec-9) is a leukocyte ligand of VAP-1. We hypothesized that ⁶⁸Ga-labeled 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid-conjugated Siglec-9 motif containing peptide (⁶⁸Ga-DOTA-Siglec-9) could detect inflammatory response due to S. epidermidis peri-implant infection by positron emission tomography (PET).

Methods

Thirty Sprague-Dawley rats were randomized into three groups. A sterile catheter was implanted into the medullary canal of the left tibia. In groups 1 and 2, the implantation was followed by peri-implant injection of S. epidermidis or Staphylococcus aureus (S. aureus) with adjunct injections of aqueous sodium morrhuate. In group 3, sterile saline was injected instead of bacteria and no aqueous sodium morrhuate was used. At 2 weeks after operation, ⁶⁸Ga-DOTA-Siglec-9 PET coupled with computed tomography (CT) was performed with the measurement of the standardized uptake value (SUV). The presence of the implant-related infection was verified by microbiological analysis, imaging with fluorescence microscope, and histology. The in vivo PET results were verified by ex vivo measurements by gamma counter.

Results

In group 3, the tibias with implanted sterile catheters showed an increased local uptake of ⁶⁸Ga-DOTA-Siglec-9 compared with the intact contralateral bones (SUV_ratio +29.5%). ⁶⁸Ga-DOTA-Siglec-9 PET detected inflammation induced by S. epidermidis and S. aureus catheter-related bone infections (SUV_ratio +58.1% and +41.7%, respectively). The tracer uptake was significantly higher in the S. epidermidis group than in group 3 without bacterial inoculation, but the difference between S. epidermidis and S. aureus groups was not statistically significant. The difference between the S. aureus group and group 3 was neither statistically significant.

Conclusion

PET/CT imaging with novel ⁶⁸Ga-DOTA-Siglec-9 tracer was able to detect inflammatory tissue response induced by catheter implantation and staphylococcal infections.

A novel knee prosthesis model of implant-related osteomyelitis in rats

BACKGROUND AND PURPOSE

There have been numerous reports of animal models of osteomyelitis. Very few of these have been prosthesis models that imitate human conditions. We have developed a new rat model of implant-related osteomyelitis that mimics human osteomyelitis, to investigate the pathology of infection after orthopedic implant surgery.

METHODS

2 wild-type strains of Staphylococcus aureus, MN8 and UAMS-1, and their corresponding mutants that are unable to produce poly-N-acetyl glucosamine (PNAG) (ica::tet) were injected into the medullary canals of the femur and tibia at 3 different doses: 10(2), 10(3), and > 10(4) CFU/rat. We measured clinical signs, inflammatory markers, radiographic signs, histopathology, and bacteriology in the infected animals.

RESULTS

An inoculum of at least 10(4) cfu of either wild-type bacterial strain resulted in histological, bacteriological, and radiographic signs of osteomyelitis with loosening of the prosthesis. An inoculum of 10(3) CFU gave signs of osteomyelitis but the prosthesis remained in situ. Bacterial inocula of 10(2) cfu gave no signs of osteolysis.

INTERPRETATION

We have established a new knee prosthesis model that is suitable for reliable induction of experimental implant-associated osteomyelitis with the prosthesis in situ, using a small inoculum of S. aureus. At a dose of 10(3) CFU/rat, bacteria unable to produce PNAG (ica::tet) had only minor defects in their virulence.

In vivo models of bone repair

This review is aimed at clinicians appraising preclinical trauma studies and researchers investigating compromised bone healing or novel treatments for fractures. It categorises the clinical scenarios of poor healing of fractures and attempts to match them with the appropriate animal models in the literature.

We performed an extensive literature search of animal models of long bone fracture repair/nonunion and grouped the resulting studies according to the clinical scenario they were attempting to reflect; we then scrutinised them for their reliability and accuracy in reproducing that clinical scenario.

Models for normal fracture repair (primary and secondary), delayed union, nonunion (atrophic and hypertrophic), segmental defects and fractures at risk of impaired healing were identified. Their accuracy in reflecting the clinical scenario ranged greatly and the reliability of reproducing the scenario ranged from 100% to 40%.

It is vital to know the limitations and success of each model when considering its application.

Biofilm formation in Staphylococcus implant infections. A review of molecular mechanisms and implications for biofilm-resistant materials

Implant infections in orthopaedics, as well as in many other medical fields, are chiefly caused by staphylococci. The ability of growing within a biofilm enhances the chances of staphylococci to protect themselves from host defences, antibiotic therapies, and biocides. Advances in scientific knowledge on structural molecules (exopolysaccharide, proteins, teichoic acids, and the most recently described extracellular DNA), on the synthesis and genetics of staphylococcal biofilms, and on the complex network of signal factors that intervene in their control are here presented, also reporting on the emerging strategies to disrupt or inhibit them. The attitude of polymorphonuclear neutrophils and macrophages to infiltrate and phagocytise biofilms, as well as the ambiguous behaviour exhibited by these innate immune cells in biofilm-related implant infections, are here discussed. Research on anti-biofilm biomaterials is focused, reviewing materials loaded with antibacterial substances, or coated with anti-adhesive/anti-bacterial immobilized agents, or surfaced with nanostructures. Latter approaches appear promising, since they avoid the spread of antibacterial substances in the neighbouring tissues with the consequent risk of inducing bacterial resistance.

Development of an interlocked nail for segmental defects in the rabbit tibia

Previous animal models have been developed to study intramedullary nailing for challenging segmental defects in the tibia. In large animals, interlocked nail fixation created a stable environment suitable to study new bone growth technologies placed in the defect. To our knowledge, there are no comparable interlocked tibial defect models for the rabbit in which new technologies could be evaluated. Such a model would be helpful since the rabbit is a popular initial model for orthopedic research studies owing to its wide availability and low cost. While numerous studies have nailed the rabbit tibia, all were non-locked implants that allowed some degree of instability between the fracture fragments. In addition, the non-locked nails were constructed of stainless steel, whereas human nails are increasingly made from titanium alloy. In the current study, an interlocked titanium nail was developed for the rabbit tibia. It was implanted in cadaver tibiae and subjected to fatigue cycling in combined compression and bending at physiologic levels to 21,061 cycles. This duration is estimated to represent 12 weeks of gait by the animal. Before and after fatigue cycling, monotonic testing was performed in compression and bending at physiologic levels. The intact contralateral limbs served as controls. All limbs completed the cycling; the instrumented limbs exhibited interfragmentary cyclic strain amplitudes during fatigue (616 ± 139 microstrain), which was significantly greater than the control limbs (136 ± 35 microstrain). Monotonic strain amplitudes for the test limbs in bending and compression were 4839 ± 1028 and 542 ± 122 microstrain, respectively; corresponding values for the control bones were 407 ± 118 and 95 ± 38 microstrain, respectively. These data are similar to those presented in prior studies in larger bone models. The current study presents one method for interlocked nail fixation for this complex tibial shaft fracture in a small animal.

Hydrophobic polycationic coatings that inhibit biofilms and support bone healing during infection

Adhesion of microorganisms to biomaterials with subsequent formation of biofilms on such foreign bodies as orthopedic trauma hardware is a critical factor in implant-associated infections; once a biofilm has been established, its microorganisms become recalcitrant to the host's immune surveillance and markedly resistant to drugs. We have previously reported that painting with the hydrophobic polycation N,N-dodecyl,methyl-PEI (PEI = polyethylenimine) renders solid surfaces bactericidal in vitro. Herein we observe that N,N-dodecyl,methyl-PEI-derivatized titanium and stainless steel surfaces resist biofilm formation by Staphylococcus aureus compared to the untreated ones. Using imaging, microbiology-, histopathology-, and scanning electron microscopy (SEM) experiments in a clinically relevant large-animal (sheep) trauma model, we subsequently demonstrate in vivo that orthopedic fracture hardware painted with N,N-dodecyl,methyl-PEI not only prevents implant colonization with biofilm but also promotes bone healing. Functionalizing orthopedic hardware with hydrophobic polycations thus holds promise in supporting bone healing in the presence of infection in veterinary and human orthopedic patients.

Animal models of external traumatic wound infections

BACKGROUND

Despite advances in traumatic wound care and management, infections remain a leading cause of mortality,morbidity and economic disruption in millions of wound patients around the world. Animal models have become standard tools for studying a wide array of external traumatic wound infections and testing new antimicrobial strategies.

RESULTS

Animal models of external traumatic wound infections reported by different investigators vary in animal species used, microorganism strains, the number of microorganisms applied, the size of the wounds and for burn infections, the length of time the heated object or liquid is in contact with the skin.

METHODS

This review covers experimental infections in animal models of surgical wounds, skin abrasions, burns, lacerations,excisional wounds and open fractures.

CONCLUSIONS

As antibiotic resistance continues to increase,more new antimicrobial approaches are urgently needed.These should be tested using standard protocols for infections in external traumatic wounds in animal models.

A new animal model for implant-related infected non-unions after intramedullary fixation of the tibia in rats with fluorescent in situ hybridization of bacteria in bone infection

There is no adequate animal model to mimic the difficult clinical situation of infected non-union of the tibia after intramedullary stabilization. The purpose was to establish an animal model of implant-related infected non-unions of the tibia in rats. Furthermore, it was evaluated if detection of bacteria by fluorescent in situ hybridisation (FISH) technique is possible in bone infection. 17 rats were used in which osteotomy of the midshaft tibia was performed and stabilized with an intramedullary device. Two groups were tested: group 1: contamination of the osteotomy site with 10(4) colony forming units (CFUs) of Staphylococcus aureus (11 animals), group 2: no bacterial contamination (6 animals). The animals were sacrificed after 42 days and bone healing and infection were assessed clinically, by X-ray, micro-CT, and microbiological methods including FISH technique using EUB and STAPHY probes. Histology and scanning electron microscopy (SEM) for biofilm formation were performed. All animals of the control group showed uneventful bone healing after 6 weeks without any signs of local infections. 10 of 11 (90.9%) animals of group 1 with bacterial contamination exhibited infected non-union formation with positive clinical, radiological and microbiological infection signs of the tibia but without any systemic infection signs. FISH technique was able to identify bacteria in the infected bone. All intramedullary implants from the infected animals showed positive biofilm formation in SEM. This work presents the first animal model for the induction of intramedullary device-related infected non-union in the tibia and detection of bacteria by FISH technique in infected bone.

Development of a fracture osteomyelitis model in the rat femur

Osteomyelitis contributes significantly to fracture morbidity. Our objective was to develop a model of induced implant-associated osteomyelitis following fracture repair by modifying an existing rat femur fracture model. Thirty male Sprague-Dawley rats were divided into three groups (Control, Staphylococcus aureus, S. aureus + ceftriaxone). The closed femur fracture model (right femur), stabilized with an intramedullary pin, was combined with inoculation of 10(4) colony-forming units (CFU) of S. aureus. Radiographs were obtained immediately after surgery and at weeks 1, 2, and 3 and were evaluated by individuals blinded to treatment group. At necropsy the CFU of S. aureus per femur and pin were determined and synovial tissue and blood were cultured. The fractured femur from two rats in each group was evaluated histologically. A statistically significant difference in the CFU/femur and CFU/pin was found across treatment groups, with the highest CFU in the S. aureus group and the lowest in the Control group. Cultures of synovial tissue were positive in 11/19 of inoculated limbs. Osteomyelitis was present both radiographically and histopathologically in both S. aureus groups but not in the controls. No rats were systemically ill or had positive blood cultures at the study endpoint. This model will be useful for the evaluation of treatments or prophylactics designed for use in implant-associated osteomyelitis.

A porcine model of acute, haematogenous, localized osteomyelitis due to Staphylococcus aureus: a pathomorphological study

A porcine model of acute, haematogenous, localized osteomyelitis was established. Serial dilutions of Staphylococcus aureus [5-50-500-5000-50 000 CFU/kg body weight (BW) suspended in saline or saline alone] were inoculated into the right brachial artery of pigs (BW 15 kg) separated into six groups of two animals. During the infection, blood was collected for cultivation, and after the animals were killed from day 5 to 15, they were necropsied and tissues were sampled for histopathology. Animals receiving ≤500 CFU/kg BW were free of lesions. Pigs inoculated with 5000 and 50 000 CFU/kg BW only developed microabscesses in bones of the infected legs. In the centre of microabscesses, S. aureus was regularly demonstrated together with necrotic neutrophils. Often, bone lesions resulted in trabecular osteonecrosis. The present localized model of acute haematogenous osteomyelitis revealed a pattern of development and presence of lesions similar to the situation in children. Therefore, this model should be reliably applied in studies of this disease with respect to e.g. pathophysiology and pathomorphology. Moreover, because of the regional containment of the infection to a defined number of bones, the model should be applicable also for screening of new therapy strategies.

The effectiveness of the controlled release of gentamicin from polyelectrolyte multilayers in the treatment of Staphylococcus aureus infection in a rabbit bone model

While the infection rate of orthopedic implants is low, the required treatment, which can involve six weeks of antibiotic therapy and two additional surgical operations, is life threatening and expensive, and thus motivates the development of a one-stage re-implantation procedure. Polyelectrolyte multilayers incorporating gentamicin were fabricated using the layer-by-layer deposition process for use as a device coating to address an existing bone infection in a direct implant exchange operation. The films eluted about 70% of their payload in vitro during the first three days and subsequently continued to release drug for more than four additional weeks, reaching a total average release of over 550 microg/cm(2). The coatings were demonstrated to be bactericidal against Staphylococcus aureus, and degradation products were generally nontoxic towards MC3T3-E1 murine preosteoblasts. Film-coated titanium implants were compared to uncoated implants in an in vivo S. aureus bone infection model. After a direct exchange procedure, the antimicrobial-coated devices yielded bone homogenates with a significantly lower degree of infection than uncoated devices at both day four (p < 0.004) and day seven (p < 0.03). This study has demonstrated that a self-assembled ultrathin film coating is capable of effectively treating an experimental bone infection in vivo and lays the foundation for development of a multi-therapeutic film for optimized, synergistic treatment of pain, infection, and osteomyelitis.

A novel canine model of acute pyogenic spondylodiscitis

New, appropriate in vivo animal models are needed for the study of the pathogenesis of spinal infections and the development of novel anti-infection strategies. The purpose of this study was to develop a canine model of acute pyogenic spondylodiscitis which can best mimic the human spinal infection process, characterized by separately inoculating bacterial suspension into the lumbar intervertebral spaces of a single animal. A total of 14 dogs were used in this study. An inoculation containing Staphylococcus aureus and sodium morrhuate was injected into the intervertebral spaces. Two pilot studies were carried out to determine the most appropriate concentration of the bacterium inoculum. Before the inoculation, the intervertebral disks were partially removed and the end plates of the adjacent two vertebrae were deliberately curetted out to make space for the inoculum and to more thoroughly expose the neighboring vertebrae to the bacterial inoculum. The dogs were euthanized at 14 days postimplantation. The bacterial loads of the infected tissues were assayed. Spondylodiscitis of the lumbar spinal column was consistently produced in 90% (nine out of ten) of the sites challenged with 10(2) colony-forming units (CFU) of S. aureus. Liver biopsy and blood culture did not show signs of systematic infections at 14 days postsurgery. Two out of four animals implanted with the suspension at a concentration higher than 10(3) CFUs were dead within 3 days postimplantation. The results indicate that this new canine model of acute pyogenic spondylodiscitis could be used to test the efficacy of different anti-infection strategies.

Preliminary investigations on a new gentamicin and vancomycin-coated PMMA nail for the treatment of bone and intramedullary infections: An experimental study in the rabbit

To evaluate a new gentamicin-vancomycin- impregnated (2:1) PMMA coating nail as a drug delivery device to treat bone and intramedullary infections, methicillin-resistant Staphylococcus aureus (MRSA) was used to induce femoral osteomyelitis in 20 New Zealand male rabbits. Four weeks after inoculum, the animals were submitted to debridement of infected femur canal, divided into four groups of five animals each and treated according to the following protocols: Group 1, insertion of a steel AISI316 intramedullary nail; Group 2, insertion of a gentamicin-vancomycin-impregnated PMMA nail; Group 3, no therapy; and Group 4 no fixation device and 1-week systemic antibiotic therapy with teicoplanin i.m. At 7 weeks after inoculum, the femurs were explanted sterilely. The radiological score showed that the lowest and best radiological score was observed in Group 2 that was significantly different from the other groups. The highest bacterial load in the femoral canal was found in Group 1, which was significantly different from Group 2 and Group 4 (p < 0.05). Histology showed that Group 2 produced a marked improvement (p < 0.005) of the bone injuries induced by the osteomyelitis in comparison with the other groups (Smeltzer score). The current findings showed that tested device might effectively lead to MRSA infection healing after surgical debridement and immediate implantation.

Assessing infection risk in implanted tissue-engineered devices

Peri-operative contamination is the major cause of biomaterial-associated infections, highly complicating surgical patient outcomes. While this risk in traditional implanted biomaterials is well-recognised, newer cell-seeded, biologically conducive tissue-engineered (TE) constructs now targeted for human use have not been assessed for this possibility. We investigated infection incidence of implanted, degradable polyester TE scaffold biomaterials in rabbit knee osteochondral defects. Sterile, polyester copolymer scaffolds of different compositions and cell-accessible pore volumes were surgically inserted into rabbit osteochondral defects for periods of 3 weeks up to 9 months, either with or without initial seeding with autologous or allogeneic chondrocytes. Infection assessment included observation of pus or abscesses in or near the knee joint and post-mortem histological evaluation. Of 228 implanted TE scaffolds, 10 appeared to be infected: 6 scaffolds without cell seeding (3.6%) and 4 cell-seeded scaffolds (6.3%). These infections were evident across all scaffold types, independent of polymer composition or available pore volume, and up to 9 months. We conclude that infections in TE implants pose a serious problem with incidences similar to current biomaterials-associated infections. Infection control measures should be developed in tissue engineering to avoid further complications when TE devices emerge clinically.