Establishment of a new methicillin resistant Staphylococcus aureus animal model of osteomyelitis

Prosthetic Joint Infection Research Models in NZW Rabbits: Opportunities for Standardization-A Systematic Review

Prosthetic joint infection (PJI) is a major complication following total arthroplasty. Rising antimicrobial resistance (AMR) to antibiotics will further increase therapeutic insufficiency. New antibacterial technologies are being developed to prevent PJI. In vivo models are still needed to bridge the translational gap to clinical implementation. Though rabbit models have been used most frequently, there is no consensus about methodology and measured outcomes. The PubMed, Scopus, and EMBASE databases were searched for literature on PJI in rabbit models. Data extraction included bias control, experimental design, and outcome measures of the NZW rabbit models in the articles. A total of 60 articles were included in this systematic literature review. The articles were divided into six groups based on the PJI intervention: no intervention used (21%), revision surgery (14%), prevention with only antibiotics (21%), prevention with surface modifications (7%), prevention with coatings (23%), and others (14%). Despite the current availability of guidelines and recommendations regarding experimental design, bias control, and outcome measures, many articles neglect to report on these matters. Ultimately, this analysis aims to assist researchers in determining suitable clinically relevant methodologies and outcome measures for in vivo PJI models using NZW rabbits to test new antimicrobial technologies.

3D printed PLGA scaffold with nano-hydroxyapatite carrying linezolid for treatment of infected bone defects

BACKGROUND

Linezolid has been reported to protect against chronic bone and joint infection. In this study, linezolid was loaded into the 3D printed poly (lactic-co-glycolic acid) (PLGA) scaffold with nano-hydroxyapatite (HA) to explore the effect of this composite scaffold on infected bone defect (IBD).

METHODS

PLGA scaffolds were produced using the 3D printing method. Drug release of linezolid was analyzed by elution and high-performance liquid chromatography assay. PLGA, PLGA-HA, and linezolid-loaded PLGA-HA scaffolds, were implanted into the defect site of a rabbit radius defect model. Micro-CT, H&E, and Masson staining, and immunohistochemistry were performed to analyze bone infection and bone healing. Evaluation of viable bacteria was performed. The cytocompatibility of 3D-printed composite scaffolds in vitro was detected using human bone marrow mesenchymal stem cells (BMSCs). Long-term safety of the scaffolds in rabbits was evaluated.

RESULTS

The linezolid-loaded PLGA-HA scaffolds exhibited a sustained release of linezolid and showed significant antibacterial effects. In the IBD rabbit models implanted with the scaffolds, the linezolid-loaded PLGA-HA scaffolds promoted bone healing and attenuated bone infection. The PLGA-HA scaffolds carrying linezolid upregulated the expression of osteogenic genes including collagen I, runt-related transcription factor 2, and osteocalcin. The linezolid-loaded PLGA-HA scaffolds promoted the proliferation and osteogenesis of BMSCs in vitro via the PI3K/AKT pathway. Moreover, the rabbits implanted with the linezolid-loaded scaffolds showed normal biochemical profiles and normal histology, which suggested the safety of the linezolid-loaded scaffolds.

CONCLUSION

Overall, the linezolid-loaded PLGA-HA scaffolds fabricated by 3D printing exerts significant bone repair and anti-infection effects.

Microbiological aspects of osteomyelitis in veterinary medicine: drawing parallels to the infection in human medicine

Osteomyelitis is a challenging infectious disease affecting humans and animals. It is difficult to diagnose because, in many cases, symptoms are non-specific and, for example in implant-related cases, can appear long time after surgery. In addition to this, it is also difficult to treat due to the need to find the appropriate antibiotic regime and delivery system to reach the site of infection and to avoid development of bacterial resistance. The central purpose of this review is to compare the microbiological aspects of osteomyelitis in human and veterinary medicine, with the aim of improving the microbiological diagnosis and treatment of this infection in animals. Furthermore, the study of osteomyelitis in animals may help to improve the development of animal models for testing new treatments in humans. Host factors and underlying conditions have been studied mainly in humans, although aspects as immunodeficiency have been described in some veterinary cases. Even when Staphylococcus aureus is still considered the most prevalent causing microorganism, this prevalence should be reviewed using molecular diagnostic techniques, and this could affect treatment options. New approaches to treatment include local delivery of antibiotics using different biomaterials, antimicrobial photodynamic therapy, and new antimicrobial compounds. We would like to remark the need of large, high-quality clinical trials and of the development of guides for the diagnosis and treatment of osteomyelitis in different animal species.

Experimental reproduction of periprosthetic joint infection: Developing a representative animal model

BACKGROUND

Infection after arthroplasty (prosthetic joint infection; PJI) is a devastating complication that can lead to functional loss of the affected limb. The purpose of the present study is to develop an animal model of PJI using a three-dimensional printed species-specific implant, which is a step forward for future research to develop new therapeutic strategies.

METHODS

Fifteen New Zealand White rabbits were employed to reproduce PJI by intra-articular inoculation of 10⁵ cfu/ml of Staphylococcus aureus ATCC® 29213. Three-dimensional printing technology was used to design a species-specific four-millimeter-thick implant maintaining the anatomical irregularities of the tibial-articular surface. Response to bacterial inoculation was monitored by clinical (weight and temperature), hematological (leukocyte, lymphocyte and platelet counts) and biochemical (erythrocyte sedimentation rate) analyses at the time of inoculation and seven days thereafter, when microbiological samples for culture were also taken.

RESULTS

All animals recovered from surgery and all displayed full weight-bearing four days postoperatively. Fourteen of the 15 tested animals (93.3%) presented positive microbiological cultures. A statistically significant increase was found in the number of platelets and leukocytes, as well as a significant decrease in the percentage of lymphocytes, with P = 0.0001 in all cases.

CONCLUSIONS

An experimental model faithfully reproducing the periprosthetic infection environment and achieving a high rate of infection has been designed. The use of three-dimensional printed species-specific implants allows rapid postoperative recovery of animals and the development of a stable biofilm. These characteristics make it an interesting model to study its pathogenesis and possible therapeutic strategies.

The Antistaphylococcal Activity of Amoxicillin/Clavulanic Acid, Gentamicin, and 1,8-Cineole Alone or in Combination and Their Efficacy through a Rabbit Model of Methicillin-Resistant Staphylococcus aureus Osteomyelitis

The aim of this research paper is to test the antistaphylococcal effect of 1,8-cineole, amoxicillin/clavulanic acid (AMC), and gentamicin, either separately or in combination against three Staphylococcus aureus strains isolated from patients suffering from osteomyelitis. This activity was tested in vitro by using the microdilution method and the checkerboard assay. The efficacy of these three antibacterial agents was then tested in vivo by using an experimental model of methicillin-resistant S. aureus osteomyelitis in rabbits. This efficacy was assessed after four days of treatment by counting the number of bacteria in the bone marrow. The obtained results in vitro showed that the combination of the AMC with gentamicin did not induce a synergistic effect, whereas the combination of the two antibiotics with 1,8-cineole did. This effect is stronger when AMC is combined with 1,8-cineole as a total synergistic effect was obtained on the three strains used (FIC ≤ 0.5). In vivo, a significant reduction was noted in the number of colonies in the bone marrow when rabbits were treated with AMC associated with either 1,8-cineole or gentamicin compared to rabbits treated with AMC, gentamicin, or 1,8-cineole alone. These results demonstrated that 1,8-cineole showed a synergistic effect in combination with both AMC and gentamicin, which offer possibilities for reducing antibiotic usage. Also, the AMC associated with 1,8-cineole could be used to treat MRSA osteomyelitis.

A new small animal model for simulating a two-stage-revision procedure in implant-related methicillin-resistant Staphylococcus aureus bone infection

BACKGROUND

Implant-related bone infections with methicillin-resistant Staphylococcus aureus (MRSA) remain a challenge for orthopedic surgeons. This devasting complication may lead to functional impairment and loss of the affected limbs. High failure rates in treatment make improvement of surgical treatment necessary. Beside an already established demanding and costly large animal model, a small animal model of a two-stage revision does not exist, yet. Thus, the purpose of this study was to establish a preclinical small animal model to simulate a two-stage revision in implant-related MRSA infection.

MATERIALS AND METHODS

In twelve rabbits Steel K-wires were implanted into the intramedullary canal of the left tibia, followed by inoculation with MRSA. Two different clinical isolates of MRSA-strains were used in two different concentrations (CFUs; 10⁵ and 10⁷ colony forming units (CFUs). This led to four groups of three rabbits each. Eleven rabbits survived the whole study period. After four weeks the inoculated K-wires were removed and replaced with vancomycin loaded PMMA-spacers (stage 1). Twenty-eight days later new K-wire implants were placed intramedullary (stage 2). After 84 days all animals were sacrificed. Tibiae were analyzed microbiologically, radiologically and histologically.

RESULTS

In every rabbit K-wire associated infection could be established within the first four weeks. After irrigation and debridement at revision one (stage 1), infection could be eradicated in 67% of group I, in 50% of group II and in 33% of group III and IV. Recurrence of the infection could be determined in all animals of group I and IV at day 84. X-ray analysis and histology both demonstrated clear signs of osteomyelitis after twelve weeks. Survival, clinical observations and weight assessment confirmed the ethical justifiable stress of the animals during the experiment.

CONCLUSION

The presented small animal model of a two-stage revision in implant-related infection is a promising preclinical set-up for assessment of new treatment strategies of implant-related infections. Both high survival as well as reinfection rates were possible by simulating the clinical gold standard of two-stage revision surgery in an MRSA implant-related infection model. Therefore, the model can be deemed suitable for further preclinical in vivo testing.

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.

3D printing in experimental orthopaedic surgery: do it yourself

INTRODUCTION

Periprosthetic infection is considered an increasing incidence pathology whose therapeutic strategies can be defined as unsatisfactory. Currently, animal models are employed to study its physiopathology and strategic therapies, but non-species-specific materials are implanted as foreign bodies. The use of these implants implies intrinsic instability, which hinders the development of a biofilm on their surfaces and complicates the post-operative recovery of the animal. The objective of the present study is the design of a species-specific implant for the New Zealand white (NZW) rabbit by means of 3D printing.

MATERIALS AND METHODS

A CT scan of the knee of a NZW rabbit was performed, and the tibial surface was reconstructed in order to fabricate a species-specific tibial plateau using Horos^® and Autodesk^® Meshmixer™ software. This implant was inserted in fifteen NZW rabbits, and the assessment of its stability was based on the position of the limb at rest and the animal weight-bearing capacity. Biofilm formation on the surface was demonstrated by crystal violet staining.

RESULTS

A 1.81 cm × 1 cm × 1.24 cm stainless steel implant was designed. It consisted of a 4-mm-thick tibial plate with a rough surface and an eccentric metaphyseal anchoring. All of the animals exhibited hyperflexion of the operated limb immediately post-operative, and 100% could apply full weight bearing from day 5 after surgery.

CONCLUSIONS

The species-specific design of implants in experimental surgery encourages rapid recovery of the animal and the development of a biofilm on their surfaces, making them ideal for the study of the physiopathology and for establishing possible therapeutic targets for prosthetic infection.

Polylactic-co-glycolic acid microspheres added to fixative cements and its role on bone infected architecture

Joint prostheses are an essential element to improve quality of life. However, prostheses may fail due to several factors, including the most frequent cause, Staphylococcus aureus infection. The identification of new fixing bone cements with less reactivity on bone tissue and an adequate response to infection remains a primary challenge. The aim of this study is to evaluate the response of bone tissue in rabbits after introduction of a hydroxyapatite‐coated titanium rod with a commercial fixative cement (Palacos®) compared to a modified experimental cement (EC) containing polylactic‐co‐glycolic acid (PLGA) microspheres in the presence or absence of contaminating germs. This study used 20 New Zealand rabbits which were divided into four groups (n = 5) depending on the presence or absence of S. aureus and the use of commercial (Palacos®) or EC. A histological method, based on bone architecture damage, was proposed to evaluate from 1 to 9 the histological results and the response of the infected tissue. The macrophage response was also evaluated using monoclonal antibody RAM‐11. The study showed better bone conservation with the use of EC with PLGA microspheres against the Palacos® commercial cement, including the noncontaminated and contaminated groups. © 2019 The Authors. Journal of Biomedical Materials Research Part B: Applied Biomaterials published by Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B:2517–2526, 2019.

Chronic infection and infected non-union of the long bones in paediatric patients: preliminary results of bone versus beta-tricalcium phosphate grafting after induced membrane formation

PURPOSE

Chronic infection (CO) and infected non-union of the long bones are relatively rare conditions in paediatric patients. Large bone defects secondary to these conditions can be managed with the induced membrane technique. The technique requires grafting of the bone void, although it is not yet established what bone substitute is the best option. The aim of this work was to evaluate the outcome and efficacy of treatment in children with CO and infected non-union of the long bones using the induced membrane technique and bone (BG) versus beta-tricalcium phosphate (BTP) grafting.

METHODS

Eight skeletally immature patients with CO and infected non-union of the long bones were treated surgically between 2010 and 2017 by a combination of resection of necrotic infected bone, debridement of surrounding soft tissue, osteosynthesis using a stable internal fixation when needed, and application of antibiotic-laden cement (ALC) spacer inducing new membrane before final bone reconstruction with bone substitutes: BTP in five cases, BG (allograft and/or autologous graft) in three cases. A second surgical step, once inflammatory markers had normalized, consisted of ALC spacer removal, application of BG or BTP graft and concomitant stable osteosynthesis, if needed, if this had not been done during the first surgical stage. All the patients underwent clinical, laboratory and imaging evaluation before and after surgery. Antibiotics were adjusted according to culture and sensitivity.

RESULTS

Mean patient age at time of diagnosis was 13 ± four years (range, 4-16) and all had at least a 12-month follow-up (range 12-60). Estimated time for induced membrane formation was significantly shorter in patients treated with BTP compared with BG: 3±1 vs. 10±2 (p = 0.02). This result was confirmed by multivariate analysis (p = 0.044) taking into account adjustment for age of patients and time after initial surgery. Time of final union was about 5.5 ± 4.1 months (range 2-66). At the last follow-up visit, bone had healed and all the patients had resumed daily living and sports activities.

CONCLUSION

The induced membrane technique with BG or BTP graft can achieve bone healing in large bone defects secondary to CO and infected non-union in children and adolescents. The choice of bone substitute is important. Our preliminary results show graft integration and bone healing can be expected sooner if BTP is used as bone void filler.

Influence of implant properties and local delivery systems on the outcome in operative fracture care

Fracture fixation devices are implanted into a growing number of patients each year. This may be attributed to an increase in the popularity of operative fracture care and the development of ever more sophisticated implants, which may be used in even the most difficult clinical cases. Furthermore, as the general population ages, fragility fractures become more frequent. With the increase in number of surgical interventions, the absolute number of complications of these surgical treatments will inevitably rise. Implant-related infection and compromised fracture healing remain the most challenging and prevalent complications in operative fracture care. Any strategy that can help to reduce these complications will not only lead to a faster and more complete resumption of activities, but will also help to reduce the socio-economic impact. In this review we describe the influence of implant design and material choice on complication rates in trauma patients. Furthermore, we discuss the importance of local delivery systems, such as implant coatings and bone cement, and how these systems may have an impact on the prevalence, prevention and treatment outcome of these complications.

Surgical Debridement Is Superior to Sole Antibiotic Therapy in a Novel Murine Posttraumatic Osteomyelitis Model

Introduction

Bone infections after trauma, i.e. posttraumatic osteomyelitis, pose one of the biggest problems of orthopedic surgery. Even after sufficient clinical therapy including vast debridement of infected bone and antibiotic treatment, regeneration of postinfectious bone seems to be restricted. One explanation includes the large sized defects resulting from sufficient debridement. Furthermore, it remains unclear if inflammatory processes after bone infection do affect bone regeneration. For continuing studies in this field, an animal model is needed where bone regeneration after sufficient treatment can be studied in detail.

Methods

For this purpose we created a stable infection in murine tibiae by Staphylococcus aureus inoculation. Thereafter, osteomyelitic bones were debrided thoroughly and animals were subsequently treated with antibiotics. Controls included debrided, non-infected, as well as infected animals exclusively treated with antibiotics. To verify sufficient treatment of infected bone, different assessments detecting S. aureus were utilized: agar plates, histology and RT-qPCR.

Results

All three detection methods revealed massive reduction or eradication of S. aureus within debrided bones 1 and 2 weeks postoperatively, whereas sole antibiotic therapy could not provide sufficient treatment of osteomyelitic bones. Debrided, previously infected bones showed significantly decreased bone formation, compared to debrided, non-infected controls.

Discussion

Thus, the animal model presented herein provides a reliable and fascinating tool to study posttraumatic osteomyelitis for clinical therapies.

Synergistic effect of a biodegradable Mg–Zn alloy on osteogenic activity and anti-biofilm ability: an in vitro and in vivo study

It is desirable for orthopaedic implants to possess good osteointegration and anti-biofilm ability simultaneously for the prevention of implant associated infections and promotion of osteointegration.

A doxycycline-loaded polymer-lipid encapsulation matrix coating for the prevention of implant-related osteomyelitis due to doxycycline-resistant methicillin-resistant Staphylococcus aureus

Implant-associated bone infections caused by antibiotic-resistant pathogens pose significant clinical challenges to treating physicians. Prophylactic strategies that act against resistant organisms, such as methicillin-resistant Staphylococcus aureus (MRSA), are urgently required. In the present study, we investigated the efficacy of a biodegradable Polymer-Lipid Encapsulation MatriX (PLEX) loaded with the antibiotic doxycycline as a local prophylactic strategy against implant-associated osteomyelitis. Activity was tested against both a doxycycline-susceptible (doxy(S)) methicillin-susceptible S. aureus (MSSA) as well as a doxycycline-resistant (doxy(R)) methicillin-resistant S. aureus (MRSA). In vitro elution studies revealed that 25% of the doxycycline was released from the PLEX-coated implants within the first day, followed by a 3% release per day up to day 28. The released doxycycline was highly effective against doxy(S) MSSA for at least 14days in vitro. A bolus injection of doxycycline mimicking a one day release from the PLEX-coating reduced, but did not eliminate, mouse subcutaneous implant-associated infection (doxy(S) MSSA). In a rabbit intramedullary nail-related infection model, all rabbits receiving a PLEX-doxycycline-coated nail were culture negative in the doxy(S) MSSA-group and the surrounding bone displayed a normal physiological appearance in both histological sections and radiographs. In the doxy(R) MRSA inoculated rabbits, a statistically significant reduction in the number of culture-positive samples was observed for the PLEX-doxycycline-coated group when compared to the animals that had received an uncoated nail, although the reduction in bacterial burden did not reach statistical significance. In conclusion, the PLEX-doxycycline coating on titanium alloy implants provided complete protection against implant-associated MSSA osteomyelitis, and resulted in a significant reduction in the number of culture positive samples when challenged with a doxycycline-resistant MRSA.

Coating with a novel gentamicinpalmitate formulation prevents implant-associated osteomyelitis induced by methicillin-susceptible Staphylococcus aureus in a rat model

PURPOSE

Implant-associated osteomyelitis still represents a demanding challenge due to unfavourable biological conditions, bacterial properties and incremental resistance to antibiotic treatment. Therefore different bactericide or bacteriostatic implant coatings have been developed recently to control local intramedullary infections. Controlled local release of gentamicin base from a highly lipophilic gentamicin palmitate compound achieves extended intramedullary retention times and thus may improve its bactericide effect.

METHODS

Forty male Sprague-Dawley rats were divided into two groups receiving an intramedullary femoral injection of 10(2) colony-forming units (CFU) of a common methicillin susceptible Staphylococcus aureus strain (MSSA Rosenbach) and either an uncoated femur nail (Group I) or a nail coated with gentamicin palmitate (Group II). Animals were observed for 28 and 42 days. Serum haptoglobin and relative weight gain were assessed as well as rollover cultures of explanted femur nails and histological scores of periprosthetic infection in dissected femurs.

RESULTS

Implants coated with gentamicin palmitate significantly reduced periprosthetic bacterial growth as well as signs of systemic inflammation compared with uncoated implants.

CONCLUSIONS

Gentamicin palmitate appears to be a viable coating for the prevention of implant-associated infections. These findings will have to be confirmed in larger animal models as well as in clinical trials.