Establishment of a real-time, quantitative, and reproducible mouse model of Staphylococcus osteomyelitis using bioluminescence imaging

Remodeling Microenvironment for Implant-Associated Osteomyelitis by Dual Metal Peroxide

Implant-associated osteomyelitis (IAOM) is characterized by bone infection and destruction; current therapy of antibiotic treatment and surgical debridement often results in drug resistance and bone defect. It is challenging to develop an antibiotic-free bactericidal and osteogenic-enhanced strategy for IAOM. Herein, an IAOM-tailored antibacterial and osteoinductive composite of copper (Cu)-strontium (Sr) peroxide nanoparticles (CSp NPs), encapsulated in polyethylene glycol diacrylate (PEGDA) (CSp@PEGDA), is designed. The dual functional CSp NPs display hydrogen peroxide (H2O2) self-supplying and Fenton catalytic Cu2+ ions' release, generating plenty of hydroxyl radical (•OH) in a pH-responsive manner for bacterial killing, while the released Sr2+ promotes the in vitro osteogenicity regarding cell proliferation, alkaline phosphatase activity, extracellular matrix calcification, and osteo-associated genes expression. The integration of Cu2+ and Sr2+ in CSp NPs together with the coated PEGDA hydrogel ensures the stable and sustainable ion release during short- and long-term periods. Benefitted from the injectablity and photo-crosslink ability, CSp@PEGDA is able to thoroughly fill the infectious site and gelate in situ for bacterial elimination and bone regeneration, which is verified through in vivo evaluation using a clinical-simulating IAOM mouse model. These favorable abilities of CSp@PEGDA precisely meet the multiple therapeutic needs and pave a promising way for implant-associated osteomyelitis treatment.

Nanomedicine against biofilm infections: A roadmap of challenges and limitations

Microbial biofilms are complex three-dimensional structures where sessile microbes are embedded in a polymeric extracellular matrix. Their resistance toward the host immune system as well as to a diverse range of antimicrobial treatments poses a serious health and development threat, being in the top 10 global public health threats declared by the World Health Organization. In an effort to combat biofilm-related microbial infections, several strategies have been developed to independently eliminate biofilms or to complement conventional antibiotic therapies. However, their limitations leave room for other treatment alternatives, where the application of nanotechnology to biofilm eradication has gained significant relevance in recent years. Their small size, penetration efficiency, and the design flexibility that they present makes them a promising alternative for biofilm infection treatment, although they also present set-backs. This review aims to describe the main possibilities and limitations of nanomedicine against biofilms, while covering the main aspects of biofilm formation and study, and the current therapies for biofilm treatment. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Infectious Disease Toxicology and Regulatory Issues in Nanomedicine > Toxicology of Nanomaterials Toxicology and Regulatory Issues in Nanomedicine > Regulatory and Policy Issues in Nanomedicine.

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.

Nanotechnology in the Diagnosis and Treatment of Osteomyelitis

Infection remains one of the largest threats to global health. Among those infections that are especially troublesome, osteomyelitis, or inflammation of the bone, typically due to infection, is a particularly difficult condition to diagnose and treat. This difficulty stems not only from the biological complexities of opportunistic infections designed to avoid the onslaught of both the host immune system as well as exogenous antibiotics, but also from changes in the host vasculature and the heterogeneity of infectious presentations. While several groups have attempted to classify and stage osteomyelitis, controversy remains, often delaying diagnosis and treatment. Despite a host of preclinical treatment advances being incubated in academic and company research and development labs worldwide, clinical treatment strategies remain relatively stagnant, including surgical debridement and lengthy courses of intravenous antibiotics, both of which may compromise the overall health of the bone and the patient. This manuscript reviews the current methods for diagnosing and treating osteomyelitis and then contemplates the role that nanotechnology might play in the advancement of osteomyelitis treatment.

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.

Differential effects of anti-RANKL monoclonal antibody and zoledronic acid on necrotic bone in a murine model of Staphylococcus aureus-induced osteomyelitis

Osteomyelitis is characterized by progressive inflammatory bone destruction accompanied by severe pain and disability. However, with the exception of antibiotic therapies, there is no established therapy to protect the bone from infectious osteolysis. The anti-receptor activator of nuclear factor-kB ligand (RANKL) monoclonal antibody (anti-RANKL Ab) is a potential drug based on its proven effectiveness in preventing joint bone erosion in rheumatoid arthritis; however, the efficacy and adverse effects of anti-RANKL Ab in osteomyelitis remain to be investigated. In this study, we investigated the effects of anti-mouse RANKL Ab on acute osteomyelitis and compared them with those of zoledronic acid (ZA) using a murine model. Mice were inoculated with bioluminescent Staphylococcus aureus (Xen 29) on their left femur and then treated with ZA, anti-RANKL Ab, or phosphate-buffered saline as control. A 21-day longitudinal observational study using microcomputed tomography showed that both anti-RANKL Ab and ZA had an osteoprotective effect against infectious osteolysis. However, it was also demonstrated through bioluminescence imaging that ZA delayed the spontaneous reduction of bacterial load and through histology that it increased the amount of necrotic bone, while anti-RANKL Ab did not. Findings from histopathological and in vitro studies suggest that an intense inflammatory response around the necrotic bone could induce osteoclasts in a RANKL-independent manner, leading to the removal of necrotic bone, even after administration of the anti-RANKL Ab therapy. Collectively, anti-RANKL Ab may exert an osteoprotective effect without hampering the removal of the necrotic bone, which serves as a nidus for infection in osteomyelitis.

Mimicking biofilm formation and development: Recent progress in in vitro and in vivo biofilm models

Biofilm formation in living organisms is associated to tissue and implant infections, and it has also been linked to the contribution of antibiotic resistance. Thus, understanding biofilm development and being able to mimic such processes is vital for the successful development of antibiofilm treatments and therapies. Several decades of research have contributed to building the foundation for developing in vitro and in vivo biofilm models. However, no such thing as an "all fit" in vitro or in vivo biofilm models is currently available. In this review, in addition to presenting an updated overview of biofilm formation, we critically revise recent approaches for the improvement of in vitro and in vivo biofilm models.

Effects of crude oil and aromatic compounds on growth and bioluminescence of Vibrio campbellii FS5

Fifteen native luminescent bacteria were isolated from the Gulf of Thailand, and their sensitivity for the detection of toxicity of crude oil and its aromatic components was investigated. Of these isolates, Vibrio campbellii strain FS5 was one of the two most highly inhibited bacteria at all crude oil concentrations. This bacterium showed a decrease in luminescence intensity of between 10.7 and 80.2% after a 15-min exposure to 0.0001-10 mg/L of crude oil. The degree of bioluminescence inhibition increased with increasing concentrations of crude oil. The presence of crude oil at all concentrations had negative effects on the log bioluminescence per log number of viable cells after 15- to 105-min exposure. About 10 to 100 times, lower half maximal effective concentration (EC₅₀) values were observed for polycyclic aromatic hydrocarbons (PAHs) than those for benzene, toluene, ethylbenzene, and xylene (BTEX). In the presence of each individual BTEX and PAH, the bioluminescence inhibition increased with increasing exposure time (1-32 h). This indigenous bacterium can be used as a simple and general indicator of oil contamination and its impact on coastal waters as well as for assessing potential toxicity during oil bioremediation.

mRNA Transcriptome Analysis of Bone in a Mouse Model of Implant-Associated Staphylococcus aureus Osteomyelitis

To investigate the molecular pathogenesis of bone with osteomyelitis, we developed implant-associated osteomyelitis (IAOM) models in mice. An orthopedic stainless pin was surgically placed in the right femoral midshaft of mice, followed by an inoculation of Staphylococcus aureus into the medullary cavity. Typical characteristics of IAOM, like periosteal reaction and intraosseous abscess, occurred by day 14 postinfection. By day 28 postinfection, necrotic abscess, sequestrum formation, and deformity of the whole femur were observed. Transcriptional analysis identified 101 and 1,702 differentially expressed genes (DEGs) between groups by days 3 and 14 postinfection, respectively. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analyses revealed the enrichment of pathways in response to the bacterium, receptor-ligand activity, and chemokine signaling by day 3 postinfection. However, by day 14 postinfection, the enrichment switched to angiogenesis, positive regulation of cell motility and migration, skeletal system development, and cytokine-cytokine receptor interaction. Furthermore, protein-protein interaction network analysis identified 4 cytokines (interleukin 6 [IL-6], Cxcl10, gamma interferon [IFN-γ], and Cxcl9) associated with IAOM at an early stage of infection. Overall, as the pathological changes in this mouse model were consistent with those in human IAOM, our model may be used to investigate the mechanism and treatment of IAOM. Furthermore, the data for transcriptome sequencing and bioinformatic analysis will be an important resource for dissecting the molecular pathogenesis of bone with IAOM.

Development of a Murine Model of Pyogenic Flexor Tenosynovitis

BACKGROUND

Pyogenic flexor tenosynovitis is a debilitating infection of the hand flexor tendon sheath with high morbidity despite standard treatments of empiric antibiotics with irrigation and debridement. In vivo studies in the available literature have used avian models, but these models are difficult to scale and maintain. The purpose of this study was to demonstrate the plausibility of a murine model of pyogenic flexor tenosynovitis utilizing bioluminescence imaging and tissue analysis at harvest.

METHODS

A 2-μL inoculate of bioluminescent Xen29 Staphylococcus aureus or sterile phosphate-buffered saline solution (sPBS) was administered to the tendon sheath of 36 male C57BL/6J mice. The infectious course was monitored by bioluminescence imaging (BLI) via an in vivo imaging system, gross anatomic deformity, and weight change. The infected hind paws were harvested at 4 time points: 24 hours, 72 hours, 1 week, and 2 weeks for histological analysis using Alcian blue, hematoxylin, and Orange-G staining. Two-way analysis of variance with the Sidak multiple comparison test was used to assess differences in bioluminescence and weight at each time point.

RESULTS

The infected cohort displayed significantly elevated bioluminescence values, had reductions in weight, and exhibited swelling of the infected digit throughout the course of infection. By day 4, most infected mice saw a substantial decrease in BLI signal intensity; however, 2 infected mice exhibited persistent BLI intensity through day 14. Histological analysis of the infected cohort showed tissue disorganization and the presence of a cellular infiltrate in and around the flexor tendon sheath.

CONCLUSIONS

A murine model of pyogenic flexor tenosynovitis is possible and can serve as an experimental platform for further investigation of the pathophysiology of pyogenic flexor tenosynovitis.

CLINICAL RELEVANCE

This animal model can be utilized in elucidating the basic molecular and/or cellular mechanisms of pyogenic flexor tenosynovitis while simultaneously evaluating novel therapeutic strategies.

Innovations in osteomyelitis research: A review of animal models

Infection of bone tissue, or osteomyelitis, has become a growing concern in modern healthcare due in no small part to a rise in antibiotic resistance among bacteria, notably Staphylococcus aureus. The current standard of care involves aggressive, prolonged antibiotic therapy combined with surgical debridement of infected tissues. While this treatment may be sufficient for resolving a portion of cases, recurrences of the infection and associated risks including toxicity with long-term antibiotic usage have been reported. Therefore, there exists a need to produce safer, more efficacious options of treatment for osteomyelitis. In order to test treatment regimens, animal models that closely mimic the clinical condition and allow for accurate evaluation of therapeutics are necessary. Establishing a model that replicates features of osteomyelitis in humans continues to be a challenge to scientists, as there are many variables involved, including choosing an appropriate species and method to establish infection. This review addresses the refinement of animal models of osteomyelitis to reflect the clinical disease and test prospective therapeutics. The aim of this review is to explore studies regarding the use of animals for osteomyelitis therapeutics research and encourage further development of such animal models for the translation of results from the animal experiment to human medicine.

An antibacterial coated polymer prevents biofilm formation and implant-associated infection

To prevent infections associated with medical implants, various antimicrobial silver-coated implant materials have been developed. However, these materials do not always provide consistent antibacterial effects in vivo despite having dramatic antibacterial effects in vitro, probably because the antibacterial effects involve silver-ion-mediated reactive oxygen species generation. Additionally, the silver application process often requires extremely high temperatures, which damage non-metal implant materials. We recently developed a bacteria-resistant coating consisting of hydroxyapatite film on which ionic silver is immobilized via inositol hexaphosphate chelation, using a series of immersion and drying steps performed at low heat. Here we applied this coating to a polymer, polyetheretherketone (PEEK), and analyzed the properties and antibacterial activity of the coated polymer in vitro and in vivo. The ionic silver coating demonstrated significant bactericidal activity and prevented bacterial biofilm formation in vitro. Bio-imaging of a soft tissue infection mouse model in which a silver-coated PEEK plate was implanted revealed a dramatic absence of bacterial signals 10 days after inoculation. These animals also showed a strong reduction in histological features of infection, compared to the control animals. This innovative coating can be applied to complex structures for clinical use, and could prevent infections associated with a variety of plastic implants.

Development of systemic immune dysregulation in a rat trauma model of biomaterial-associated infection

Orthopedic biomaterial-associated infections remain a major clinical challenge, with Staphylococcus aureus being the most common pathogen. S. aureus biofilm formation enhances immune evasion and antibiotic resistance, resulting in a local, indolent infection that can persist long-term without symptoms before eventual hardware failure, bone non-union, or sepsis. Immune modulation is an emerging strategy to combat host immune evasion by S. aureus. However, most immune modulation strategies are focused on local immune responses at the site of infection, with little emphasis on understanding the infection-induced and orthopedic-related systemic immune responses of the host, and their role in local infection clearance and tissue regeneration. This study utilized a rat bone defect model to investigate how implant-associated infection affects the systemic immune response. Long-term systemic immune dysregulation was observed with a significant systemic decrease in T cells and a concomitant increase in immunosuppressive myeloid-derived suppressor cells (MDSCs) compared to non-infected controls. Further, the control group exhibited a regulated and coordinated systemic cytokine response, which was absent in the infection group. Multivariate analysis revealed high levels of MDSCs to be most correlated with the infection group, while high levels of T cells were most correlated with the control group. Locally, the infection group had attenuated macrophage infiltration and increased levels of MDSCs in the local soft tissue compared to non-infected controls. These data reveal the widespread impacts of an orthopedic infection on both the local and the systemic immune responses, uncovering promising targets for diagnostics and immunotherapies that could optimize treatment strategies and ultimately improve patient outcomes.

Surface-grafted zwitterionic polymers improve the efficacy of a single antibiotic injection in suppressing S. aureus periprosthetic infections

Implant-associated bacterial infections are difficult to treat due to the tendency of biofilm formation on implant surfaces, which protects embedded pathogens from host defense and impedes antibiotic penetration, rendering systemic antibiotic injections ineffective. Here, we test the hypothesis that implant coatings that reduce bacterial colonization would make planktonic bacteria within the periprosthetic environment more susceptible to conventional systemic antibiotic treatment. We covalently grafted zwitterionic polymer brushes poly(sulfobetaine methacryate) from Ti6Al4V surface to increase the substrate surface hydrophilicity and reduce staphylococcus aureus (S. aureus) adhesion. Using a mouse femoral intramedullary (IM) canal infection model, we showed that the anti-fouling coating applied to Ti6Al4V IM implants, when combined with a single vancomycin systemic injection, significantly suppressed both bacterial colonization on implant surfaces and the periprosthetic infections, outperforming either treatment alone. This work supports the hypothesis that grafting anti-fouling polymers to implant surfaces improves the efficacy of systemic antibiotic injections to combat periprosthetic infections.

Potential osteomyelitis biomarkers identified by plasma metabolome analysis in mice

Osteomyelitis, which often arises from a surgical-site infection, is a serious problem in orthopaedic surgery. However, there are no specific biomarkers for osteomyelitis. Here, to identify specific plasma biomarkers for osteomyelitis, we conducted metabolome analyses using a mouse osteomyelitis model and bioluminescence imaging. We divided adult male pathogen-free BALB/C mice into control, sham-control, and infected groups. In the infected group, a bioluminescent Staphylococcus aureus strain was inoculated into the femur, and osteomyelitis was detected by bioluminescence imaging. We next analysed the metabolome, by comprehensively measuring all of the small molecules. This analysis identified 279 metabolites, 12 of which were significantly higher and 45 were significantly lower in the infected group than in the sham-control and control groups. Principal component analysis identified sphingosine as the highest loading factor. Several acyl carnitines and fatty acids, particularly ω-3 and ω-6 polyunsaturated fatty acids, were significantly lower in the infected group. Several metabolites in the tricarboxylic acid cycle were lower in the infected group than in the other groups. Thus, we identified two sphingolipids, sphinganine and sphingosine, as positive biomarkers for mouse osteomyelitis, and two components in the tricarboxylic acid cycle, two-oxoglutarate and succinic acid, as negative biomarkers.

Significant Suppression of Staphylococcus aureus Colonization on Intramedullary Ti6Al4V Implants Surface-Grafted with Vancomycin-Bearing Polymer Brushes

Orthopedic implant-associated bacterial infection presents a major health threat due to tendency for periprosthetic bacterial colonization/biofilm formation that protects bacteria from host immune response and conventional antibiotic treatment. Using surface-initiated atom transfer radical polymerization and copper-catalyzed azide-alkyne cycloaddition (CuAAC), alkynylated vancomycin is conjugated to azido-functionalized side chains of polymethacrylates grafted from Ti6Al4V. High-efficiency CuAAC across the substrate is confirmed by complete surface conversion of azides by X-ray photoelectron spectroscopy (XPS) and elemental mapping of changing characteristic elements. The vancomycin-modified surface (Ti-pVAN) significantly reduces in vitro adhesion and colonization of Staphylococcus aureus (S. aureus), a main bacterial pathogen responsible for periprosthetic infection and osteomyelitis, compared to untreated Ti6Al4V, supporting retained antibacterial properties of the covalently conjugated antibiotics. When the surface-modified intramedullary Ti-pVAN pins are inserted into mouse femoral canals infected by bioluminescent Xen29 S. aureus, significantly reduced local bioluminescence along with mitigated blood markers for infection are detected compared to untreated Ti6Al4V pins over 21 days. Ti-pVAN pins retrieved after 21 days are confirmed with ∼20-fold reduction in adherent bacteria counts compared to untreated control, supporting the ability of surface-conjugated vancomycin in inhibiting periprosthetic S. aureus adhesion and colonization.

Advanced antibacterial activity of biocompatible tantalum nanofilm via enhanced local innate immunity

Tantalum (Ta) has been shown to enhance osseointegration in clinical practice, yet little is known about whether Ta nanofilms can be used as antimicrobial coatings in vivo. A highly biocompatible Ta nanofilm was developed using magnetron sputtering technology to further study the mechanism of its antibacterial effects in vivo and elucidate its potential for clinical translation. The Ta nanofilms exhibited effective antimicrobial activity against soft tissue infections but did not show an intrinsic antimicrobial effect in vitro. This inconsistency between the in vivo and in vitro antimicrobial effects was further investigated using ex vivo models. The Ta nanofilms could enhance the phagocytosis of bacteria by polymorphonuclear neutrophils (PMNs, neutrophils), reduce the lysis of neutrophils and enhance the proinflammatory cytokine release of macrophages. This accumulative enhancement of the local host defenses contributed to the favorable antibacterial effect in vivo. The alleviated osteolysis observed in the presence of the Ta nanofilms in the osteomyelitis model further proved the practicality of this antibacterial strategy in the orthopedic field. In summary, Ta nanofilms show excellent biocompatibility and in vivo antimicrobial activity mediated by the enhancement of local innate immunity and are promising for clinical application. STATEMENT OF SIGNIFICANCE: In this study, Ta nanofilms were deposited on titanium substrate by magnetron sputtering. Ta nanofilms exhibited excellent in vivo and in vitro biocompatibility. In vivo antimicrobial effects of Ta nanofilms were revealed by soft tissue infection and osteomyelitis models, while no direct antibacterial activity was observed in vitro. Comprehensive ex vivo models revealed that Ta nanofilms could enhance the phagocytosis of bacteria by neutrophils, reduce the lysis of neutrophils and promote the release of proinflammatory cytokines from macrophages. This immunomodulatory effect helps host to eliminate bacteria. In contrast to traditional antimicrobial nanocoatings which apply toxic materials to kill bacteria, this work proposes a safe, practical and effective Ta nanofilm immunomodulatory antimicrobial strategy with clinical translational prospect.

Inhibition of pyroptosis attenuates Staphylococcus aureus-induced bone injury in traumatic osteomyelitis

Background

Osteomyelitis is a severe bone infection and typically leads to progressive bone resorption, destruction and dysfunction. Pyroptosis is a form of programmed cell death involved in various infectious diseases. However, the identification of pyroptosis and the role it plays in osteomyelitis remains to be clarified. In this study, we investigated the expression of pyroptosis-associated proteins in osteomyelitis and the effects of inhibiting pyroptosis on S. aureus-induced osteomyelitis both in vitro and in vivo.

Methods

The expression of pyroptosis-associated protein-NLRP3 (NLR Family Pyrin Domain Containing 3), Caspase1 and GSDMD (GasderminD) were examined in murine and human infectious bone fragments by western blot. Bone destruction was evaluated by microcomputed tomography (µCT). The concentration of inflammatory factors was tested by Enzyme linked Immunosorbent Assay (ELISA). The expression of pyroptosis-associated gene was detected by real-time quantitative polymerase chain reaction (RT-qPCR).

Results

The expression of pyroptosis-associated proteins in infectious bone fragments from patients with osteomyelitis was significantly higher than uninfected bone. Additionally, in S. aureus-induced murine osteomyelitis model, higher expression of pyroptosis-associated proteins was noticed. Furthermore, the inhibitors of pyroptosis-associated proteins alleviated S. aureus-induced pyroptosis both in vivo and in vitro. More importantly, the inhibition of pyroptosis restored the bone formative property, attenuated the aberrant activation of osteoclast in vitro and reversed bone injury in vivo.

Conclusions

Our study identified pyroptosis as a key pathway in osteomyelitis and elaborated that the inhibition of pyroptosis could attenuate S. aureus-induced bone destruction in osteomyelitis, providing a potential treatment target to osteomyelitis.

In vivo efficacy of tobramycin-loaded synthetic calcium phosphate beads in a rabbit model of staphylococcal osteomyelitis

Background

Osteomyelitis is an acute or chronic inflammatory process of the bone following infection with pyogenic organisms like Staphylococcus aureus. Tobramycin (TOB) is a promising aminoglycoside antibiotic used to treat various bacterial infections, including S. aureus. The aim of this study was to investigate the efficacy of tobramycin-loaded calcium phosphate beads (CPB) in a rabbit osteomyelitis model.

Methods

Tobramycin (30 mg/mL) was incorporated into CPB by dipping method and the efficacy of TOB-loaded CPB was studied in a rabbit osteomyelitis model. For juxtaposition, CPB with and without TOB were prepared. Twenty-five New Zealand white rabbits were grouped (n = 5) as sham (group 1), TOB-loaded CPB without S. aureus (group 2), S. aureus only (group 3), S. aureus + CPB (group 4), and S. aureus + TOB-loaded CPB (group 5). Groups infected with S. aureus followed by CPB implantation were immediately subjected to surgery at the mid-shaft of the tibia. After 28 days post-surgery, all rabbits were euthanized and the presence or absence of chronic osteomyelitis and the extent of architectural destruction of the bone were assessed by radiology, bacteriology and histological studies.

Results

Tobramycin-loaded CPB group potentially inhibited the growth of S. aureus causing 3.2 to 3.4 log₁₀ reductions in CFU/g of bone tissue compared to the controls. Untreated groups infected with S. aureus showed signs of chronic osteomyelitis with abundant bacterial growth and alterations in bone architecture. The sham group and TOB-loaded CPB group showed no evidence of bacterial growth.

Conclusions

TOB-incorporated into CPB for local bone administration was proven to be more successful in increasing the efficacy of TOB in this rabbit osteomyelitis model and hence could represent a good alternative to other formulations used in the treatment of osteomyelitis.

Electronic supplementary material

The online version of this article (10.1186/s12941-018-0296-3) contains supplementary material, which is available to authorized users.

In-vivo monitoring of infectious diseases in living animals using bioluminescence imaging

Traditional methods of localizing and quantifying the presence of pathogenic microorganisms in living experimental animal models of infections have mostly relied on sacrificing the animals, dissociating the tissue and counting the number of colony forming units. However, the discovery of several varieties of the light producing enzyme, luciferase, and the genetic engineering of bacteria, fungi, parasites and mice to make them emit light, either after administration of the luciferase substrate, or in the case of the bacterial lux operon without any exogenous substrate, has provided a new alternative. Dedicated bioluminescence imaging (BLI) cameras can record the light emitted from living animals in real time allowing non-invasive, longitudinal monitoring of the anatomical location and growth of infectious microorganisms as measured by strength of the BLI signal. BLI technology has been used to follow bacterial infections in traumatic skin wounds and burns, osteomyelitis, infections in intestines, Mycobacterial infections, otitis media, lung infections, biofilm and endodontic infections and meningitis. Fungi that have been engineered to be bioluminescent have been used to study infections caused by yeasts (Candida) and by filamentous fungi. Parasitic infections caused by malaria, Leishmania, trypanosomes and toxoplasma have all been monitored by BLI. Viruses such as vaccinia, herpes simplex, hepatitis B and C and influenza, have been studied using BLI. This rapidly growing technology is expected to continue to provide much useful information, while drastically reducing the numbers of animals needed in experimental studies.

Novel rat tail discitis model using bioluminescent Staphylococcus aureus

Management of spondylodiscitis is a challenging clinical problem requiring medical and surgical treatment strategies. The purpose of this study was to establish a rat model of spondylodiscitis that utilizes bioluminescent Staphylococcus aureus (S. aureus), thus permitting in vivo surveillance of infection intensity. Inocula of the bioluminescent S. aureus strain XEN36 were created in concentrations of 10² CFU/0.1 ml, 10⁴  CFU/0.1 ml, and 10⁶  CFU/0.1 ml. Three groups of rats were injected with the bacteria in the most proximal intervertebral tail segment. The third most proximal tail segment was injected with saline as a control. Bioluminescence was measured at baseline, 3 days, and weekly for a total of 6 weeks. Detected bioluminescence for each group peaked at day 3 and returned to baseline in 21 days. The average intensity was highest for the experimental group injected with the most concentrated bacterial solution (10⁶  CFU/0.1 ml). Radiographic analysis revealed loss of intervertebral disc space and evidence of osseous bridging. Saline-injected spaces exhibited no decrease in intervertebral spacing as compared to distal sites. Histologic analysis revealed neutrophilic infiltrates, destruction of the annulus fibrosus and nucleus pulposus, destruction of vertebral endplates, and osseous bridging. Saline-injected discs exhibited preserved annulus fibrosus and nucleus pulposus on histology. This study demonstrates that injection of bioluminescent S. aureus into the intervertebral disc of a rat tail is a viable animal model for spondylodiscitis research. This model allows for real-time, in vivo quantification of infection intensity, which may decrease the number of animals required for infection studies of the intervertebral disc. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2075-2081, 2017.

Nano-layered magnesium fluoride reservoirs on biomaterial surfaces strengthen polymorphonuclear leukocyte resistance to bacterial pathogens

Biomaterial-related bacterial infections cause patient suffering, mortality and extended periods of hospitalization, imposing a substantial burden on medical systems. In this context, understanding of nanomaterials-bacteria-cells interactions is of both fundamental and clinical significance. Herein, nano-MgF₂ films were deposited on titanium substrate via magnetron sputtering. Using this platform, the antibacterial behavior and mechanism of the nano-MgF₂ films were investigated in vitro and in vivo. It was found that, for S. aureus (CA-MRSA, USA300) and S. epidermidis (RP62A), the nano-MgF₂ films possessed excellent anti-biofilm activity, but poor anti-planktonic bacteria activity in vitro. Nevertheless, both the traditional SD rat osteomyelitis model and the novel stably luminescent mouse infection model demonstrated that nano-MgF₂ films exerted superior anti-infection effect in vivo, which cannot be completely explained by the antibacterial activity of the nanomaterial itself. Further, using polymorphonuclear leukocytes (PMNs), the critical immune cells of innate immunity, a complementary investigation of MgF₂-bacteria-PMNs co-culturing revealed that the nano-MgF₂ films improved the antibacterial effect of PMNs through enhancing their phagocytosis and stability. To our knowledge, this is the first time of exploring the antimicrobial mechanism of nano-MgF₂ from the perspective of innate immunity both in vitro and in vivo. Based on the research results, a plausible mechanism is put forward for the predominant antibacterial effect of nano-MgF₂in vivo, which may originate from the indirect immune enhancement effect of nano-MgF₂ films. In summary, this study of surface antibacterial design using MgF₂ nanolayer is a meaningful attempt, which can promote the host innate immune response to bacterial pathogens. This may give us a new understanding towards the antibacterial behavior and mechanism of nano-MgF₂ films and pave the way towards their clinical applications.

Staphylococcus aureus-dependent septic arthritis in murine knee joints: local immune response and beneficial effects of vaccination

Staphylococcus aureus is the major cause of human septic arthritis and osteomyelitis, which deserve special attention due to their rapid evolution and resistance to treatment. The progression of the disease depends on both bacterial presence in situ and uncontrolled disruptive immune response, which is responsible for chronic disease. Articular and bone infections are often the result of blood bacteremia, with the knees and hips being the most frequently infected joints showing the worst clinical outcome. We report the development of a hematogenous model of septic arthritis in murine knees, which progresses from an acute to a chronic phase, similarly to what occurs in humans. Characterization of the local and systemic inflammatory and immune responses following bacterial infection brought to light specific signatures of disease. Immunization of mice with the vaccine formulation we have recently described (4C-Staph), induced a strong antibody response and specific CD4+ effector memory T cells, and resulted in reduced bacterial load in the knee joints, a milder general inflammatory state and protection against bacterial-mediated cellular toxicity. Possible correlates of protection are finally proposed, which might contribute to the development of an effective vaccine for human use.

Delayed Propionibacterium acnes surgical site infections occur only in the presence of an implant

Whether Propionibacterium acnes (P. acnes) causes surgical-site infections (SSI) after orthopedic surgery is controversial. We previously reported that we frequently find P. acnes in intraoperative specimens, yet none of the patients have clinically apparent infections. Here, we tracked P. acnes for 6 months in a mouse osteomyelitis model. We inoculated P. acnes with an implant into the mouse femur in the implant group; the control group was treated with the bacteria but no implant. We then observed over a 6-month period using optical imaging system. During the first 2 weeks, bacterial signals were detected in the femur in the both groups. The bacterial signal completely disappeared in the control group within 28 days. Interestingly, in the implant group, bacterial signals were still present 6 months after inoculation. Histological and scanning electron-microscope analyses confirmed that P. acnes was absent from the control group 6 months after inoculation, but in the implant group, the bacteria had survived in a biofilm around the implant. PCR analysis also identified P. acnes in the purulent effusion from the infected femurs in the implant group. To our knowledge, this is the first report showing that P. acnes causes SSI only in the presence of an implant.

A novel hydroxyapatite film coated with ionic silver via inositol hexaphosphate chelation prevents implant-associated infection

Various silver-coated implants have been developed to prevent implant-associated infections, and have shown dramatic effects in vitro. However, the in vivo results have been inconsistent. Recent in vitro studies showed that silver exerts antibacterial activity by mediating the generation of reactive oxygen species in the presence of oxygen. To maintain its antibacterial activity in vivo, the silver should remain in an ionic state and be stably bound to the implant surface. Here, we developed a novel bacteria-resistant hydroxyapatite film in which ionic silver is immobilized via inositol hexaphosphate chelation using a low-heat immersion process. This bacteria-resistant coating demonstrated significant antibacterial activity both in vitro and in vivo. In a murine bioluminescent osteomyelitis model, no bacteria were detectable 21 days after inoculation with S. aureus and placement of this implant. Serum interleukin-6 was elevated in the acute phase in this model, but it was significantly lower in the ionic-silver group than the control group on day 2. Serum C-reactive protein remained significantly higher in the control group than the ionic-silver group on day 14. Because this coating is produced by a low-heat immersion process, it can be applied to complex structures of various materials, to provide significant protection against implant-associated infections.

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.

Quantifying the natural history of biofilm formation in vivo during the establishment of chronic implant-associated Staphylococcus aureus osteomyelitis in mice to identify critical pathogen and host factors

While it is well known that Staphylococcus aureus establishes chronic implant-associated osteomyelitis by generating and persisting in biofilm, research to elucidate pathogen, and host specific factors controlling this process has been limited due to the absence of a quantitative in vivo model. To address this, we developed a murine tibia implant model with ex vivo region of interest (ROI) imaging analysis by scanning electron microscopy (SEM). Implants were coated with Staphylococcus aureus strains (SH1000, UAMS-1, USA300LAC) with distinct in vitro biofilm phenotypes, were used to infect C57BL/6 or Balb/c mice. In contrast to their in vitro biofilm phenotype, results from all bacteria strains in vivo were similar, and demonstrated that biofilm on the implant is established within the first day, followed by a robust proliferation phase peaking on Day 3 in Balb/c mice, and persisting until Day 7 in C57BL/6 mice, as detected by SEM and bioluminescent imaging. Biofilm formation peaked at Day 14, covering ∼40% of the ROI coincident with massive agr-dependent bacterial emigration, as evidenced by large numbers of empty lacunae with few residual bacteria, which were largely culture negative (80%) and PCR positive (87.5%), supporting the clinical relevance of this implant model.

Infected animal models for tissue engineering

Infection is one of the most common complications associated with medical interventions and implants. As tissue engineering strategies to replace missing or damaged tissue advance, the focus on prevention and treatment of concomitant infection has also begun to emerge as an important area of research. Because the in vivo environment is a complex interaction between host tissue, implanted materials, and native immune system that cannot be replicated in vitro, animal models of infection are integral in evaluating the safety and efficacy of experimental treatments for infection. In this review, considerations for selecting an animal model, established models of infection, and areas that require further model development are discussed with regard to cutaneous, fascial, and orthopedic infections.

Scaffold-based anti-infection strategies in bone repair

Bone fractures and non-union defects often require surgical intervention where biomaterials are used to correct the defect, and approximately 10% of these procedures are compromised by bacterial infection. Currently, treatment options are limited to sustained, high doses of antibiotics and surgical debridement of affected tissue, leaving a significant, unmet need for the development of therapies to combat device-associated biofilm and infections. Engineering implants to prevent infection is a desirable material characteristic. Tissue engineered scaffolds for bone repair provide a means to both regenerate bone and serve as a base for adding antimicrobial agents. Incorporating anti-infection properties into regenerative medicine therapies could improve clinical outcomes and reduce the morbidity and mortality associated with biomaterial implant-associated infections. This review focuses on current animal models and technologies available to assess bone repair in the context of infection, antimicrobial agents to fight infection, the current state of antimicrobial scaffolds, and future directions in the field.

A modified chronic infection model for testing treatment of Staphylococcus aureus biofilms on implants

Bacterial biofilms causing implant-associated osteomyelitis is a severe complication with limited antimicrobial therapy options. We designed an animal model, in which implant associated osteomyelitis arise from a Staphylococcus aureus biofilm on a tibia implant. Two bioluminescently engineered (luxA-E transformed), strains of S. aureus were utilized, Xen29 and Xen31. Biofilm formation was assessed with epifluorescence microscopy. Quantitative measurements were performed day 4, 6, 8, 11 and 15 post-surgery. Bacteria were extracted from the biofilm by sonication and the bacterial load quantified by culturing. Biofilm formation was evident from day 6 post-implantation. Mean bacterial load from implants was ∼1×10(4) CFU/implant, while mean bacterial load from infected tibias were 1×10(6) CFU/bone. Bioluminesence imaging revealed decreasing activity throughout the 15-day observation period, with signal intensity for both strains reaching that of the negative control by day 15 while there was no significant reduction in bacterial load. The model is suitable for testing antimicrobial treatment options for implant associated OM, as treatment efficacy on both biofilm and viable counts can be assessed.

A novel mouse model of soft-tissue infection using bioluminescence imaging allows noninvasive, real-time monitoring of bacterial growth

Musculoskeletal infections, including surgical-site and implant-associated infections, often cause progressive inflammation and destroy areas of the soft tissue. Treating infections, especially those caused by multi-antibiotic resistant bacteria such as methicillin-resistant Staphylococcus aureus (MRSA) remains a challenge. Although there are a few animal models that enable the quantitative evaluation of infection in soft tissues, these models are not always reproducible or sustainable. Here, we successfully established a real-time, in vivo, quantitative mouse model of soft-tissue infection in the superficial gluteus muscle (SGM) using bioluminescence imaging. A bioluminescent strain of MRSA was inoculated into the SGM of BALB/c adult male mice, followed by sequential measurement of bacterial photon intensity and serological and histological analyses of the mice. The mean photon intensity in the mice peaked immediately after inoculation and remained stable until day 28. The serum levels of interleukin-6, interleukin-1 and C-reactive protein at 12 hours after inoculation were significantly higher than those prior to inoculation, and the C-reactive protein remained significantly elevated until day 21. Histological analyses showed marked neutrophil infiltration and abscesses containing necrotic and fibrous tissues in the SGM. With this SGM mouse model, we successfully visualized and quantified stable bacterial growth over an extended period of time with bioluminescence imaging, which allowed us to monitor the process of infection without euthanizing the experimental animals. This model is applicable to in vivo evaluations of the long-term efficacy of novel antibiotics or antibacterial implants.

Does PGE₁ vasodilator prevent orthopaedic implant-related infection in diabetes? Preliminary results in a mouse model

BACKGROUND

Implant-related infections are characterized by bacterial colonization and biofilm formation on the prosthesis. Diabetes represents one of the risk factors that increase the chances of prosthetic infections because of related severe peripheral vascular disease. Vasodilatation can be a therapeutic option to overcome diabetic vascular damages and increase the local blood supply. In this study, the effect of a PGE₁ vasodilator on the incidence of surgical infections in diabetic mice was investigated.

METHODOLOGY

A S. aureus implant-related infection was induced in femurs of diabetic mice, then differently treated with a third generation cephalosporin alone or associated with a PGE₁ vasodilator. Variations in mouse body weight were evaluated as index of animal welfare. The femurs were harvested after 28 days and underwent both qualitative and quantitative analysis as micro-CT, histological and microbiological analyses.

RESULTS

The analysis performed in this study demonstrated the increased host response to implant-related infection in diabetic mice treated with the combination of a PGE₁ and antibiotic. In this group, restrained signs of infections were identified by micro-CT and histological analysis. On the other hand, the diabetic mice treated with the antibiotic alone showed a severe infection and inability to successfully respond to the standard antimicrobial treatment.

CONCLUSIONS

The present study revealed interesting preliminary results in the use of a drug combination of antibiotic and vasodilator to prevent implant-related Staphylococcus aureus infections in a diabetic mouse model.

A systematic review of animal models for Staphylococcus aureus osteomyelitis

Staphylococcus aureus (S. aureus) osteomyelitis is a significant complication for orthopaedic patients undergoing surgery, particularly with fracture fixation and arthroplasty. Given the difficulty in studying S. aureus infections in human subjects, animal models serve an integral role in exploring the pathogenesis of osteomyelitis, and aid in determining the efficacy of prophylactic and therapeutic treatments. Animal models should mimic the clinical scenarios seen in patients as closely as possible to permit the experimental results to be translated to the corresponding clinical care. To help understand existing animal models of S. aureus, we conducted a systematic search of PubMed and Ovid MEDLINE to identify in vivo animal experiments that have investigated the management of S. aureus osteomyelitis in the context of fractures and metallic implants. In this review, experimental studies are categorised by animal species and are further classified by the setting of the infection. Study methods are summarised and the relevant advantages and disadvantages of each species and model are discussed. While no ideal animal model exists, the understanding of a model's strengths and limitations should assist clinicians and researchers to appropriately select an animal model to translate the conclusions to the clinical setting.

Comparison of 3 real-time, quantitative murine models of staphylococcal biofilm infection by using in vivo bioluminescent imaging

Biofilm formation represents a unique mechanism by which Staphylococcus aureus and other microorganisms avoid antimicrobial clearance and establish chronic infections. Treatment of these infections can be challenging, because the bacteria in the biofilm state are often resistant to therapies that are effective against planktonic bacteria of the same species. Effective animal models for the study of biofilm infections and novel therapeutics are needed. In addition, there is substantial interest in the use of noninvasive, in vivo data collection techniques to decrease the animal numbers required for the execution of infectious disease studies. To ad- dress these needs, we evaluated 3 murine models of implant-associated biofilm infection by using in vivo bioluminescent imaging techniques. The goal of these studies was to identify the model that was most amenable to development of sustained infections that could be imaged repeatedly in vivo by using bioluminescent technology. We found that the subcutaneous mesh and tibial intramedullary pin models both maintained consistent levels of bioluminescence for as long as 35 d after infection, with no implant loss experienced in either model. In contrast, a subcutaneous catheter model demonstrated significant incidence of incisional ab- scessation and implant loss by day 20 after infection. The correlation of bioluminescent measurements and bacterial enumeration was strongest with the subcutaneous mesh model. Among the 3 models we evaluated, the subcutaneous mesh model is the most appropriate animal model for prolonged study of biofilm infections by using bioluminescent imaging.

Molecular imaging: an innovative force in musculoskeletal radiology

OBJECTIVE

A review of the innovative role molecular imaging plays in musculoskeletal radiology is provided. Musculoskeletal molecular imaging is under development in four key areas: imaging the activity of osteoblasts and osteoclasts, imaging of molecular and cellular biomarkers of arthritic joint destruction, cellular imaging of osteomyelitis, and imaging generators of musculoskeletal pain.

CONCLUSION

Together, these applications suggest that next-generation musculoskeletal radiology will facilitate quantitative visualization of molecular and cellular biomarkers, an advancement that appeared futuristic just a decade ago.

Diabetic mouse model of orthopaedic implant-related Staphylococcus aureus infection

Background

Periprosthetic bacterial infections represent one of the most challenging orthopaedic complications that often require implant removal and surgical debridement and carry high social and economical costs. Diabetes is one of the most relevant risk factors of implant-related infection and its clinical occurrence is growing worldwide. The aim of the present study was to test a model of implant-related infection in the diabetic mouse, with a view to allow further investigation on the relative efficacy of prevention and treatment options in diabetic and non-diabetic individuals.

Methodology

A cohort of diabetic NOD/ShiLtJ mice was compared with non-diabetic CD1 mice as an in vivo model of S. aureus orthopaedic infection of bone and soft tissues after femur intramedullary pin implantation. We tested control and infected groups with 1×10³ colony-forming units of S. aureus ATCC 25923 strain injected in the implant site. At 4 weeks post-inoculation, host response to infection, microbial biofilm formation, and bone damage were assessed by traditional diagnostic parameters (bacterial culture, C-reactive protein and white blood cell count), histological analysis and imaging techniques (micro computed tomography and scanning electron microscopy).

Results

Unlike the controls and the CD1 mice, all the diabetic mice challenged with a single inoculum of S. aureus displayed severe osteomyelitic changes around the implant.

Conclusions

Our findings demonstrate for the first time that the diabetic mouse can be successfully used in a model of orthopaedic implant-related infection. Furthermore, the same bacteria inoculum induced periprosthetic infection in all the diabetic mice but not in the controls. This animal model of implant-related infection in diabetes may be a useful tool to test in vivo treatments in diabetic and non-diabetic individuals.

From in vitro to in vivo Models of Bacterial Biofilm-Related Infections

The influence of microorganisms growing as sessile communities in a large number of human infections has been extensively studied and recognized for 30–40 years, therefore warranting intense scientific and medical research. Nonetheless, mimicking the biofilm-life style of bacteria and biofilm-related infections has been an arduous task. Models used to study biofilms range from simple in vitro to complex in vivo models of tissues or device-related infections. These different models have progressively contributed to the current knowledge of biofilm physiology within the host context. While far from a complete understanding of the multiple elements controlling the dynamic interactions between the host and biofilms, we are nowadays witnessing the emergence of promising preventive or curative strategies to fight biofilm-related infections. This review undertakes a comprehensive analysis of the literature from a historic perspective commenting on the contribution of the different models and discussing future venues and new approaches that can be merged with more traditional techniques in order to model biofilm-infections and efficiently fight them.

Blue light eliminates community-acquired methicillin-resistant Staphylococcus aureus in infected mouse skin abrasions

BACKGROUND AND OBJECTIVE

Bacterial skin and soft tissue infections (SSTI) affect millions of individuals annually in the United States. Treatment of SSTI has been significantly complicated by the increasing emergence of community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) strains. The objective of this study was to demonstrate the efficacy of blue light (415 ± 10 nm) therapy for eliminating CA-MRSA infections in skin abrasions of mice.

METHODS

The susceptibilities of a CA-MRSA strain (USA300LAC) and human keratinocytes (HaCaT) to blue light inactivation were compared by in vitro culture studies. A mouse model of skin abrasion infection was developed using bioluminescent USA300LAC::lux. Blue light was delivered to the infected mouse skin abrasions at 30 min (acute) and 24 h (established) after the bacterial inoculation. Bioluminescence imaging was used to monitor in real time the extent of infection in mice.

RESULTS

USA300LAC was much more susceptible to blue light inactivation than HaCaT cells (p=0.038). Approximately 4.75-log10 bacterial inactivation was achieved after 170 J/cm(2) blue light had been delivered, but only 0.29 log10 loss of viability in HaCaT cells was observed. Transmission electron microscopy imaging of USA300LAC cells exposed to blue light exhibited disruption of the cytoplasmic content, disruption of cell walls, and cell debris. In vivo studies showed that blue light rapidly reduced the bacterial burden in both acute and established CA-MRSA infections. More than 2-log10 reduction of bacterial luminescence in the mouse skin abrasions was achieved when 41.4 (day 0) and 108 J/cm(2) (day 1) blue light had been delivered. Bacterial regrowth was observed in the mouse wounds at 24 h after the blue light therapy.

CONCLUSIONS

There exists a therapeutic window of blue light for bacterial infections where bacteria are selectively inactivated by blue light while host tissue cells are preserved. Blue light therapy has the potential to rapidly reduce the bacterial load in SSTI.

A novel mouse model of Staphylococcus aureus chronic osteomyelitis that closely mimics the human infection: an integrated view of disease pathogenesis

Osteomyelitis is a serious bone infection typically caused by Staphylococcus aureus. The pathogenesis of osteomyelitis remains poorly understood, mainly for lack of experimental models that closely mimic human disease. We describe a novel murine model of metastatic chronic osteomyelitis initiated after intravenous inoculation of S. aureus microorganisms. The bacteria entered bones through the bloodstream and, after an acute phase with progressive growth (first 2 weeks after infection), they remained at constant numbers for up to 56 days (chronic phase). Clinical signs of illness and systemic inflammation were apparent only during the acute phase. Bone destruction and remodeling processes were readily detectable by magnetic resonance and X-ray imaging 3 weeks after infection, and high levels of bone deformation were observed during the chronic phase. Histological examination of infected bones demonstrated suppurative inflammation with foci of intense bacterial multiplication and necrosis during acute infection and osteoclastic resorption accompanied by new woven bone formation during chronic infection. Transmission electron microscopy revealed S. aureus microorganisms forming microcolonies within the nonmineralized collagen matrix or located intracellularly within neutrophils. In summary, our mouse model of staphylococcal hematogenous osteomyelitis precisely reproduces most features of the human disease. Although the extent of lesions in the chronic phase was subject to variation, this model is ideal for testing and monitoring novel treatment modalities via noninvasive imaging.