Recent lessons for the management of bone and joint infections

A remotely controlled nanotherapeutic with immunomodulatory property for MRSA-induced bone infection

Osteomyelitis is a deep bone tissue infection caused by pathogenic microorganisms, with the primary pathogen being methicillin-resistant Staphylococcus aureus (MRSA). Due to the tendency of the infection site to form biofilms that shield drugs and immune cells to kill bacteria, combined with the severe local inflammatory response causing bone tissue destruction, the treatment of osteomyelitis poses a significant challenge. Herein, we developed a remotely controlled nanotherapeutic (TLBA) with immunomodulatory to treat MRSA-induced osteomyelitis. TLBA, combined with baicalin and gold nanorods, is positively charged to actively target and penetrate biofilms. Near-infrared light (808 nm) triggers spatiotemporal, controllable drug release, while bacteria are eliminated through synergistic interaction of non-antibiotic drugs and photothermal therapy, enhancing bactericidal efficiency and minimizing drug resistance. TLBA eliminated nearly 100 % of planktonic bacteria and dispersed 90 % of biofilms under NIR light stimulation. In MRSA-induced osteomyelitis rat models, laser irradiation raised the infection site temperature to 50 °C, effectively eradicating bacteria, promoting M2 macrophage transformation, inhibiting bone inflammation, curbing bone destruction, and fostering bone tissue repair. In summary, TLBA proposes a more comprehensive treatment strategy for the two characteristic pathological changes of bacterial infection and bone tissue damage in osteomyelitis.

Applications of biocompatible polymeric nanomaterials in three-dimensional (3D) scaffolds: Bacterial infections and diabetes

Printed form of polymeric nanomaterials in formation, crosslinking, structure, properties, toxicity and biocompatibility refers to the application of nanotechnology and 3D printing techniques to fabricate polymeric nanomaterials with specific physicochemical and biomedical features. In this regard, applications of 3D printing techniques, specifically for production of 3D scaffold have received huge attention in diabetes and bacterial infections. This review has tried to address recent advances and challenges related to applications of biocompatible polymeric nanomaterials in 3D printing techniques to ameliorate bacterial infections and diabetes. The applications of metal/metal oxide such as silver, gold, zinc, and titanium dioxide, and polymeric nanoparticles can augment the antimicrobial and degradation characteristics of 3D-printed scaffolds. The rapid advancements in 3D bio-printed scaffolds, specifically by artificial intelligence (AI) present a transformative landscape for diabetes treatment, addressing the complex challenges associated with impaired wound healing and tissue regeneration in individuals with diabetes mellitus.

Predictors of Methicillin-resistant Staphylococcus aureus infection in children with acute osteomyelitis

BACKGROUND

This study aims to identify risk factors associated with Methicillin-resistant Staphylococcus aureus (MRSA) infection in children diagnosed with acute osteomyelitis (AO) and to elucidate the laboratory characteristics of these MRSA-infected children to enhance early targeted therapeutic interventions.

METHODS

We conducted a retrospective analysis involving 123 children with acute osteomyelitis treated at our hospital. Upon admission, we measured white blood cell (WBC) counts, C-reactive protein (CRP) levels, erythrocyte sedimentation rates (ESR), and platelet counts. Patients were categorized into two groups: the non-MRSA group (n = 73) and the MRSA group (n = 50), with values assigned as follows (non-MRSA group = 0, MRSA group = 1).

RESULTS

The MRSA group had a significantly higher average age compared to the non-MRSA group (P < 0.05). Notably, the incidence of suppurative arthritis was significantly lower in the MRSA group (P < 0.05). At the time of admission, CRP levels in the MRSA group were markedly elevated compared to those in the non-MRSA group (P < 0.01). After three days of empirical therapy, both WBC and CRP levels remained significantly higher in the MRSA group compared to the non-MRSA group (P < 0.05).

CONCLUSIONS

In children newly admitted with acute osteomyelitis, a CRP level exceeding 73.23 µg/mL may indicate a high likelihood of MRSA infection. For children with AO who have been hospitalized for three days on empirical therapy, the presence of WBC > 10.95 × 10^9/L, CRP > 49.56 µg/mL, age > 3.5 years, and the absence of suppurative arthritis suggests a heightened risk of MRSA infection.

3D Printed Multifunctional Biomimetic Bone Scaffold Combined with TP-Mg Nanoparticles for the Infectious Bone Defects Repair

Infected bone defects are one of the most challenging problems in the treatment of bone defects due to the high antibiotic failure rate and the lack of ideal bone grafts. In this paper, inspired by clinical bone cement filling treatment, α-c phosphate (α-TCP) with self-curing properties is composited with β-tricalcium phosphate (β-TCP) and constructed a bionic cancellous bone scaffolding system α/β-tricalcium phosphate (α/β-TCP) by low-temperature 3D printing, and gelatin is preserved inside the scaffolds as an organic phase, and later loaded with a metal-polyphenol network structure of tea polyphenol-magnesium (TP-Mg) nanoparticles. The scaffolds mimic the structure and components of cancellous bone with high mechanical strength (>100 MPa) based on α-TCP self-curing properties through low-temperature 3D printing. Meanwhile, the scaffolds loaded with TP-Mg exhibit significant inhibition of Staphylococcus aureus (S.aureus) and promote the transition of macrophages from M1 pro-inflammatory to M2 anti-inflammatory phenotype. In addition, the composite scaffold also exhibits excellent bone-enhancing effects based on the synergistic effect of Mg2+ and Ca2+. In this study, a multifunctional ceramic scaffold (α/β-TCP@TP-Mg) that integrates anti-inflammatory, antibacterial, and osteoinduction is constructed, which promotes late bone regenerative healing while modulating the early microenvironment of infected bone defects, has a promising application in the treatment of infected bone defects.

Melatonin-loaded mesoporous zinc- and gallium-doped hydroxyapatite nanoparticles to control infection and bone repair

Effective treatment of infected bone defects resulting from multi-drug resistant bacteria (MDR) has emerged as a significant clinical challenge, highlighting the pressing demand for potent antibacterial bone graft substitutes. Mesoporous nanoparticles have been introduced as a promising class of biomaterials offering significant properties for treating bone infections. Herein, we synthesize antibacterial mesoporous hydroxyapatite substituted with zinc and gallium (Zn-Ga:mHA) nanoparticles using a facile sol-gel method. The resulting mesoporous nanoparticles are applied for the controlled release of melatonin (Mel). Zn-Ga:mHA nanoparticles with an average particle size of 36 ± 3 nm and pore size of 10.6 ± 0.4 nm reveal a Mel loading efficiency of 58 ± 1%. Results show that 50% of Mel is released within 20 h and its long-term release is recorded up to 50 h. The Zn-Ga:mHA nanoparticles exhibit highly effective antibacterial performance as reflected by a 19 ± 1% and 8 ± 2% viability reduction in Escherichia coli and Staphylococcus bacteria, respectively. Noticeably, Mel-loaded Zn-Ga:mHA nanoparticles are also cytocompatible and stimulate in vitro osteogenic differentiation of human mesenchymal stem cells (hMSCs) without any osteoinductive factor. In vivo studies in a rabbit skull also show significant regeneration of bone during 14 days. In summary, Mel-loaded Zn-Ga:mHA nanoparticles provide great potential as an antibacterial and osteogenic component in bone substitutes like hydrogels, scaffolds, and coatings.

Recent development and fighting strategies for lincosamide antibiotic resistance

SUMMARYLincosamides constitute an important class of antibiotics used against a wide range of pathogens, including methicillin-resistant Staphylococcus aureus. However, due to the misuse of lincosamide and co-selection pressure, the resistance to lincosamide has become a serious concern. It is urgently needed to carefully understand the phenomenon and mechanism of lincosamide resistance to effectively prevent and control lincosamide resistance. To date, six mobile lincosamide resistance classes, including lnu, cfr, erm, vga, lsa, and sal, have been identified. These lincosamide resistance genes are frequently found on mobile genetic elements (MGEs), such as plasmids, transposons, integrative and conjugative elements, genomic islands, and prophages. Additionally, MGEs harbor the genes that confer resistance not only to antimicrobial agents of other classes but also to metals and biocides. The ultimate purpose of discovering and summarizing bacterial resistance is to prevent, control, and combat resistance effectively. This review highlights four promising strategies, including chemical modification of antibiotics, the development of antimicrobial peptides, the initiation of bacterial self-destruct program, and antimicrobial stewardship, to fight against resistance and safeguard global health.

Longitudinal intravital imaging of the bone marrow for analysis of the race for the surface in a murine osteomyelitis model

Critical knowledge gaps of orthopedic infections pertain to bacterial colonization. The established dogma termed the Race for the Surface posits that contaminating bacteria compete with host cells for the implant post-op, which remains unproven without real-time in vivo evidence. Thus, we modified the murine longitudinal intravital imaging of the bone marrow (LIMB) system to allow real-time quantification of green fluorescent protein (GFP+) host cells and enhanced cyan fluorescent protein (ECFP+) or red fluorescent protein (RFP+) methicillin-resistant Staphylococcus aureus (MRSA) proximal to a transfemoral implant. Following inoculation with ~105 CFU, an L-shaped metal implant was press-fit through the lateral cortex at a 90° angle ~0.150 mm below a gradient refractive index (GRIN) lens. We empirically derived a volume of interest (VOI) = 0.0161 ± 0.000675 mm3 during each imaging session by aggregating the Z-stacks between the first (superior) and last (inferior) in-focus LIMB slice. LIMB postimplantation revealed very limited bacteria detection at 1 h, but by 3 h, 56.8% of the implant surface was covered by ECFP+ bacteria, and the rest were covered by GFP+ host cells. 3D volumetric rendering of the GFP+ and ECFP+ or RFP+ voxels demonstrated exponential MRSA growth between 3 and 6 h in the Z-plane, which was validated with cross-sectional ex vivo bacterial burden analyses demonstrating significant growth by ~2 × 104 CFU/h on the implant from 2 to 12 h post-op (p < 0.05; r2  > 0.98). Collectively, these results show the competition at the surface is completed by 3 h in this model and demonstrate the potential of LIMB to elucidate mechanisms of bacterial colonization, the host immune response, and the efficacy of antimicrobials.

Antimicrobial and Biodegradable 3D Printed Scaffolds for Orthopedic Infections

In bone tissue engineering, the performance of scaffolds underpins the success of the healing of bone. Microbial infection is the most challenging issue for orthopedists. The application of scaffolds for healing bone defects is prone to microbial infection. To address this challenge, scaffolds with a desirable shape and significant mechanical, physical, and biological characteristics are crucial. 3D printing of antibacterial scaffolds with suitable mechanical strength and excellent biocompatibility is an appealing strategy to surmount issues of microbial infection. The spectacular progress in developing antimicrobial scaffolds, along with beneficial mechanical and biological properties, has sparked further research for possible clinical applications. Herein, the significance of antibacterial scaffolds designed by 3D, 4D, and 5D printing technologies for bone tissue engineering is critically investigated. Materials such as antibiotics, polymers, peptides, graphene, metals/ceramics/glass, and antibacterial coatings are used to impart the antimicrobial features for the 3D scaffolds. Polymeric or metallic biodegradable and antibacterial 3D-printed scaffolds in orthopedics disclose exceptional mechanical and degradation behavior, biocompatibility, osteogenesis, and long-term antibacterial efficiency. The commercialization aspect of antibacterial 3D-printed scaffolds and technical challenges are also discussed briefly. Finally, the discussion on the unmet demands and prevailing challenges for ideal scaffold materials for fighting against bone infections is included along with a highlight of emerging strategies in this field.

Approaching prosthesis infection environment: Development of an innovative in vitro Staphylococcus aureus biofilm model

The major role and implication of bacterial biofilms in the case of bone and prosthesis infections have been highlighted and often linked to implant colonization. Management strategies of these difficult-to-treat infections consist in surgeries and antibiotic treatment, but the rate of relapse remains high, especially if Staphylococcus aureus, a high-virulent pathogen, is involved. Therapeutic approaches are not adapted to the specific features of biofilm in bone context whereas infectious environment is known to importantly influence biofilm structure. In the present study, we aim to characterize S. aureus SH1000 (methicillin-sensitive strain, MSSA) and USA300 (methicillin-resistant strain, MRSA) biofilm on different surfaces mimicking the periprosthetic environment. As expected, protein adsorption on titanium enhanced the number of adherent bacteria for both strains. On bone explant, USA300 adhered more than SH1000. The simultaneous presence of two different surfaces was also found to change the bacterial behaviour. Thus, proteins adsorption on titanium and bone samples (from bank or directly recovered after an arthroplasty) were found to be key parameters that influence S. aureus biofilm formation: adhesion, matrix production and biofilm-related gene regulation. These results highlighted the need for new biofilm models, more relevant with the infectious environment by using adapted culture medium and presence of surfaces that are representative of in situ conditions to better evaluate therapeutic strategies against biofilm.

Thermosensitive Nanotherapeutics for Localized Photothermal Ablation of MRSA-Infected Osteomyelitis Combined with Chemotherapy

Chronic osteomyelitis is an inflammatory skeletal disease caused by a bacterial infection that affects the periosteum, bone, and bone marrow. Methicillin-resistant Staphylococcus aureus (MRSA) is the most common causative agent. The bacterial biofilm formed on the necrotic bone is a considerable challenge to treating MRSA-infected osteomyelitis. Here, we developed an all-in-one cationic thermosensitive nanotherapeutic (TLCA) for treating MRSA-infected osteomyelitis. The prepared TLCA particles were positively charged and <230 nm in size, which allowed them to diffuse effectively into the biofilm. The positive charges of the nanotherapeutic accurately targeted the biofilm, and it subsequently regulated the drug release under near-infrared (NIR) light irradiation, thereby efficiently exerting the synergistic effect of NIR light-driven photothermal sterilization and chemotherapy. More than 80% of the antibiotics were abruptly released at 50 °C, which dispersed the biofilm by up to 90%. When applied to MRSA-infected osteomyelitis, with a localized temperature of 50 °C induced by 808 nm laser irradiation, it not only eliminated the bacteria and controlled infection but also inhibited the bone tissue inflammatory response, significantly reducing TNF-α, IL-1β, and IL-6 levels. In conclusion, we constructed an all-in-one antimicrobial treatment modality that provides a new and effective strategy for the topical treatment of chronic osteomyelitis.

Treating methicillin-resistant Staphylococcus aureus (MRSA) bone infection with focused ultrasound combined thermally sensitive liposomes

OBJECTIVE

Chronic bone infection caused by Staphylococcus aureus biofilms in children and adults is characterized by reduced antibiotic sensitivity. In this study, we assessed 'heat-targeted, on-demand' antibiotic delivery for S. aureus killing by combining ciprofloxacin (CIP)-laden low-temperature sensitive liposomes (LTSLs) with local high-intensity focused ultrasound (HIFU) induced bone heating in a rat model of bone infection.

METHODS

CIP-LTSLs were prepared using the thin-film hydration and extrusion method. Bone infection was established by surgically implanting an orthopedic K-wire colonized with methicillin-resistant S. aureus (MRSA) strain into rat's femurs. For bone heating, ultrasound-guided HIFU exposures were performed to achieve a local temperature of 40-42 °C (∼15 min) concurrently with intravenous injection of CIP-LTSLs or CIP. CIP biodistribution was determined spectrophotometrically and therapeutic efficacy was determined by bacteriological, histological and scanning electron microscopy (SEM) analyses.

RESULTS

CIP-LTSLs in the range of 183.5 nm ± 1.91 showed an encapsulation efficiency of >70% at 37 °C and a complete release at ∼42 °C. The metal implantation method yielded medullary osteomyelitis characterized by suppurative changes (bacterial and pus pockets) by day 10 in bones and adjoining muscle tissues. HIFU heating significantly improved CIP delivery from LTSLs in bones, resulting in a significant reduction in MRSA load compared to HIFU and CIP alone groups. These were also verified by histology and SEM, wherein a distinct reduction in S. aureus population in the infected metal wires and tissues from the combinatorial therapy was noted.

CONCLUSION

HIFU improved CIP delivery to bones, achieving clearance of hard-to-treat MRSA biofilms.

Effect of the Biopolymer Carrier on Staphylococcus aureus Bacteriophage Lytic Activity

The use of implant materials is always associated with the risk of infection. Moreover, the effectiveness of antibiotics is reduced due to antibiotic-resistant pathogens. Thus, selecting the appropriate alternative antimicrobials for local delivery systems is correlated with successful infection management. We evaluated immobilization of the S. aureus specific bacteriophages in clinically recognized biopolymers, i.e., chitosan and alginate, to control the release profile of the antimicrobials. The high-titre S. aureus specific bacteriophages were prepared from commercial bacteriophage cocktails. The polymer mixtures with the propagated bacteriophages were then prepared. The stability of the S. aureus bacteriophages in the biopolymer solutions was assessed. In the case of chitosan, no plaques indicating the presence of the lytic bacteriophages were observed. The titre reduction of the S. aureus bacteriophages in the Na-alginate was below 1 log unit. Furthermore, the bacteriophages retained their lytic activity in the alginate after crosslinking with Ca2+ ions. The release of the lytic S. aureus bacteriophages from the Ca-alginate matrices in the TRIS-HCl buffer solution (pH 7.4 ± 0.2) was determined. After 72 h-0.292 ± 0.021% of bacteriophages from the Ca-alginate matrices were released. Thus, sustained release of the lytic S. aureus bacteriophages can be ensured.

Anti-infective composite cryogel scaffold treats osteomyelitis and augments bone healing in rat femoral condyle

Bone and joint infections pose a serious challenge in the orthopedic medical condition which presents a major health care problem and economic burden to the patients. The current treatment strategies adopted have a very limited successful outcome in majority of the cases and need serious reconsiderations in terms of management, diagnosis and effective treatment approach. Herein, we have developed a composite cryogel scaffold from nanohydroxyapatite and collagen mimicking natural bone composition for the local delivery of antibiotic to treat osteomyelitis. The biomimetic and biodegradable antibiotic-loaded composite scaffold was found to be biocompatible with potent osteogenic capacity and anti-infective characteristics under in vitro conditions. Moreover, the anti-infective potency of the antibiotic-loaded composite cryogel was also evaluated in rat osteomyelitis model to cure the infection and promote bone healing. It was observed that anti-infective collagen-nanohydroxyapatite composite cryogel when loaded with bone morphogenetic protein-2 (BMP-2) and zoledronic acid (ZA) could completely eradicate the infection in rat femoral condyle and simultaneously, accelerate bone healing at the dead space created during surgical procedures. The approach developed in this study is the development of biomimetic and bioactive composite carrier of antibiotics for the treatment of bone infection. The findings of this study insinuate that this antibiotic-loaded composite cryogel scaffold could potentially be used as an anti-infective biomaterial for the treatment of bone infections which will simultaneosuly promote bone healing at the dead space created during surgical procedures.

Systemic IL-27 administration prevents abscess formation and osteolysis via local neutrophil recruitment and activation

Interleukin-27 is a pleiotropic cytokine whose functions during bacterial infections remain controversial, and its role in patients with S. aureus osteomyelitis is unknown. To address this knowledge gap, we completed a clinical study and observed elevated serum IL-27 levels (20-fold higher, P < 0.05) in patients compared with healthy controls. Remarkably, IL-27 serum levels were 60-fold higher in patients immediately following septic death than in uninfected patients (P < 0.05), suggesting a pathogenic role of IL-27. To test this hypothesis, we evaluated S. aureus osteomyelitis in WT and IL-27Rα-/- mice with and without exogenous IL-27 induction by intramuscular injection of rAAV-IL-27p28 or rAAV-GFP, respectively. We found that IL-27 was induced at the surgical site within 1 day of S. aureus infection of bone and was expressed by M0, M1 and M2 macrophages and osteoblasts but not by osteoclasts. Unexpectedly, exogenous IL-27p28 (~2 ng·mL-1 in serum) delivery ameliorated soft tissue abscesses and peri-implant bone loss during infection, accompanied by enhanced local IL-27 expression, significant accumulation of RORγt+ neutrophils at the infection site, a decrease in RANK+ cells, and compromised osteoclast formation. These effects were not observed in IL-27Rα-/- mice compared with WT mice, suggesting that IL-27 is dispensable for immunity but mediates redundant immune and bone cell functions during infection. In vitro studies and bulk RNA-seq of infected tibiae showed that IL-27 increased nos1, nos2, il17a, il17f, and rorc expression but did not directly stimulate chemotaxis. Collectively, these results identify a novel phenomenon of IL-27 expression by osteoblasts immediately following S. aureus infection of bone and suggest a protective role of systemic IL-27 in osteomyelitis.

Evidence of Neutralizing and Non-Neutralizing Anti-Glucosaminidase Antibodies in Patients With S. Aureus Osteomyelitis and Their Association With Clinical Outcome Following Surgery in a Clinical Pilot

Staphylococcus aureus osteomyelitis remains a very challenging condition; recent clinical studies have shown infection control rates following surgery/antibiotics to be ~60%. Additionally, prior efforts to produce an effective S. aureus vaccine have failed, in part due to lack of knowledge of protective immunity. Previously, we demonstrated that anti-glucosaminidase (Gmd) antibodies are protective in animal models but found that only 6.7% of culture-confirmed S. aureus osteomyelitis patients in the AO Clinical Priority Program (AO-CPP) Registry had basal serum levels (>10 ng/ml) of anti-Gmd at the time of surgery (baseline). We identified a small subset of patients with high levels of anti-Gmd antibodies and adverse outcomes following surgery, not explained by Ig class switching to non-functional isotypes. Here, we aimed to test the hypothesis that clinical cure following surgery is associated with anti-Gmd neutralizing antibodies in serum. Therefore, we first optimized an in vitro assay that quantifies recombinant Gmd lysis of the M. luteus cell wall and used it to demonstrate the 50% neutralizing concentration (NC50) of a humanized anti-Gmd mAb (TPH-101) to be ~15.6 μg/ml. We also demonstrated that human serum deficient in anti-Gmd antibodies can be complemented by TPH-101 to achieve the same dose-dependent Gmd neutralizing activity as purified TPH-101. Finally, we assessed the anti-Gmd physical titer and neutralizing activity in sera from 11 patients in the AO-CPP Registry, who were characterized into four groups post-hoc. Group 1 patients (n=3) had high anti-Gmd physical and neutralizing titers at baseline that decreased with clinical cure of the infection over time. Group 2 patients (n=3) had undetectable anti-Gmd antibodies throughout the study and adverse outcomes. Group 3 (n=3) had high titers +/- neutralizing anti-Gmd at baseline with adverse outcomes. Group 4 (n=2) had low titers of non-neutralizing anti-Gmd at baseline with delayed high titers and adverse outcomes. Collectively, these findings demonstrate that both neutralizing and non-neutralizing anti-Gmd antibodies exist in S. aureus osteomyelitis patients and that screening for these antibodies could have a value for identifying patients in need of passive immunization prior to surgery. Future prospective studies to test the prognostic value of anti-Gmd antibodies to assess the potential of passive immunization with TPH-101 are warranted.

Recent Advances in Multifunctional Hydrogels for the Treatment of Osteomyelitis

Osteomyelitis (OM), a devastating disease caused by microbial infection of bones, remains a major challenge for orthopedic surgeons. Conventional approaches for prevention and treatment of OM are unsatisfactory. Various alternative strategies have been proposed, among which, hydrogel-based strategies have demonstrated potential due to their unique properties, including loadable, implantable, injectable, printable, degradable, and responsive to stimuli. Several protocols, including different hydrogel designs, selection of antimicrobial agent, co-administration of bone morphogenetic protein 2 (BMP 2), and nanoparticles, have been shown to improve the biological properties, including antimicrobial effects, osteo-induction, and controlled drug delivery. In this review, we describe the current and future directions for designing hydrogels and their applications to improve the biological response to OM in vivo.

Is Early Surgical Intervention Necessary for Acute Neonatal Humeral Epiphyseal Osteomyelitis: A Retrospective Study of 31 Patients

Objective: To review the treatment experience of neonatal humeral epiphyseal osteomyelitis retrospectively. Study design: Retrospective cohort study of infants with neonatal humeral epiphyseal osteomyelitis. Patients were divided into conservative group and surgical group, and the surgical group was subdivided into early and delayed surgical group. Results: In total, there were 7 patients in the conservative group and 24 in the surgical group. The length of hospital stay and intravenous course of antibiotic therapy were both significantly shorter in the surgical group (p < 0.001). The full recovery rate was also higher in the surgical group (83.3%) than the conservative group (14.3%) (p < 0.001). Early surgery group (n = 14) had an insignificantly higher positive rate of pus/aspirate culture and full recovery rate than delayed surgery group (n = 10). Conclusion: Surgical treatment for neonatal humeral epiphyseal osteomyelitis demonstrated significantly higher rates of positive culture for the pathogen, a shorter course of intravenous oral antibiotics, and lower incidence of growth abnormality than conservative treatment. In our institution, most of culture outcome Gram-positive bacteria, and early surgical treatment was recommended with better outcome than delayed surgical group. Empirical antibiotics should be tailored to the epidemiological characteristics of local virulent bacteria.

Nanoantibiotics Based in Mesoporous Silica Nanoparticles: New Formulations for Bacterial Infection Treatment

This review focuses on the design of mesoporous silica nanoparticles for infection treatment. Written within a general context of contributions in the field, this manuscript highlights the major scientific achievements accomplished by professor Vallet-Regí's research group in the field of silica-based mesoporous materials for drug delivery. The aim is to bring out her pivotal role on the envisage of a new era of nanoantibiotics by using a deep knowledge on mesoporous materials as drug delivery systems and by applying cutting-edge technologies to design and engineer advanced nanoweapons to fight infection. This review has been divided in two main sections: the first part overviews the influence of the textural and chemical properties of silica-based mesoporous materials on the loading and release of antibiotic molecules, depending on the host-guest interactions. Furthermore, this section also remarks on the potential of molecular modelling in the design and comprehension of the performance of these release systems. The second part describes the more recent advances in the use of mesoporous silica nanoparticles as versatile nanoplatforms for the development of novel targeted and stimuli-responsive antimicrobial nanoformulations for future application in personalized infection therapies.

Serum antibodies against Staphylococcus aureus can prognose treatment success in patients with bone infections

Prognosing life-threatening orthopedic infections caused by Staphylococcus aureus remains a major clinical challenge. To address this, we developed a multiplex assay to assess the humoral immune proteome against S. aureus in patients with musculoskeletal infections. We found initial evidence that antibodies against some antigens (autolysins: Amd, Gmd; secreted immunotoxins: CHIPS, SCIN, Hla) were associated with protection, whereas antibodies against the iron-regulated surface determinant (Isd) proteins (IsdA, IsdB, IsdH) were aligned with adverse outcomes. To formally test this, we analyzed antibody levels and 1-year clinical outcomes of 194 patients with confirmed S. aureus bone infections (AO Trauma Clinical Priority Program [CPP] Bone Infection Registry). A staggering 20.6% of the enrolled patients experienced adverse clinical outcomes (arthrodesis, reinfection, amputation, and septic death) after 1-year. At enrollment, anti-S. aureus immunoglobulin G (IgG) levels in patients with adverse outcomes were 1.35-fold lower than those in patients whose infections were successfully controlled (p < 0.0001). Overall, there was a 51%-69% reduction in adverse outcome risk for every 10-fold increase in initial IgG concentration against Gmd, Amd, IsdH, CHIPS, SCIN, and Hla (p < 0.05). Notably, anti-IsdB antibodies remained elevated in patients with adverse outcomes; for every 10-fold change in the ratio of circulating anti-Isd to anti-Atl IgG at enrollment, there was a trending 2.6-fold increased risk (odds ratio = 2.555) of an adverse event (p = 0.105). Moreover, antibody increases over time correlated with adverse outcomes and decreases with positive outcomes. These studies demonstrate the potential of the humoral immune response against S. aureus as a prognostic indicator for assessing treatment success and identifying patients requiring additional interventions.

Gallium Porphyrin and Gallium Nitrate Reduce the High Vancomycin Tolerance of MRSA Biofilms by Promoting Extracellular DNA-Dependent Biofilm Dispersion

Biofilms, structured communities of bacterial cells embedded in a self-produced extracellular matrix (ECM) which consists of proteins, polysaccharide intercellular adhesins (PIAs), and extracellular DNA (eDNA), play a key role in clinical infections and are associated with an increased morbidity and mortality by protecting the embedded bacteria against drug and immune response. The high levels of antibiotic tolerance render classical antibiotic therapies impractical for biofilm-related infections. Thus, novel drugs and strategies are required to reduce biofilm tolerance and eliminate biofilm-protected bacteria. Here, we showed that gallium, an iron mimetic metal, can lead to nutritional iron starvation and act as dispersal agent triggering the reconstruction and dispersion of mature methicillin-resistant Staphylococcus aureus (MRSA) biofilms in an eDNA-dependent manner. The extracellular matrix, along with the integral bacteria themselves, establishes the integrated three-dimensional structure of the mature biofilm. The structures and compositions of gallium-treated mature biofilms differed from those of natural or antibiotic-survived mature biofilms but were similar to those of immature biofilms. Similar to immature biofilms, gallium-treated biofilms had lower levels of antibiotic tolerance, and our in vitro tests showed that treatment with gallium agents reduced the antibiotic tolerance of mature MRSA biofilms. Thus, the sequential administration of gallium agents (gallium porphyrin and gallium nitrate) and relatively low concentrations of vancomycin (16 mg/L) effectively eliminated mature MRSA biofilms and eradicated biofilm-enclosed bacteria within 1 week. Our results suggested that gallium agents may represent a potential treatment for refractory biofilm-related infections, such as prosthetic joint infections (PJI) and osteomyelitis, and provide a novel basis for future biofilm treatments based on the disruption of normal biofilm-development processes.

Fusobacterial Pelvic Osteomyelitis with Brodie's Abscess in a 10-Year-Old Boy Requiring Surgical Evacuation: A Case Report

CASE

A 10-year-old boy presented with pain in the lateral hip and buttock area and fever. Magnetic resonance imaging revealed osteomyelitis of the pelvis with extensive Brodie's abscess (2.6 × 4.5 × 10.0 cm) continuing into the pelvic cavity. Surgical evacuation through the ilioinguinal approach was performed. In prolonged culture and in polymerase chain reaction of pus, the Fusobacterium nucleatum was found.

CONCLUSION

Pelvic osteomyelitis caused by Fusobacterium is very rare. In this case, surgical treatment was required after conservative treatment with antibiotics was ineffective.

Toward Bactericidal Enhancement of Additively Manufactured Titanium Implants

Implant-associated infections (IAIs) are among the most intractable and costly complications in implant surgery. They can lead to surgery failure, a high economic burden, and a decrease in patient quality of life. This manuscript is devoted to introducing current antimicrobial strategies for additively manufactured (AM) titanium (Ti) implants and fostering a better understanding in order to pave the way for potential modern high-throughput technologies. Most bactericidal strategies rely on implant structure design and surface modification. By means of rational structural design, the performance of AM Ti implants can be improved by maintaining a favorable balance between the mechanical, osteogenic, and antibacterial properties. This subject becomes even more important when working with complex geometries; therefore, it is necessary to select appropriate surface modification techniques, including both topological and chemical modification. Antibacterial active metal and antibiotic coatings are among the most commonly used chemical modifications in AM Ti implants. These surface modifications can successfully inhibit bacterial adhesion and biofilm formation, and bacterial apoptosis, leading to improved antibacterial properties. As a result of certain issues such as drug resistance and cytotoxicity, the development of novel and alternative antimicrobial strategies is urgently required. In this regard, the present review paper provides insights into the enhancement of bactericidal properties in AM Ti implants.

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

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

Emerging electron microscopy and 3D methodologies to interrogate Staphylococcus aureus osteomyelitis in murine models

Recent breakthroughs in our understanding of orthopaedic infections have come from advances in transmission electron microscopy (TEM) imaging of murine models of bone infection, most notably Staphylococcus aureus invasion and colonization of osteocyte-lacuno canalicular networks of live cortical bone during the establishment of chronic osteomyelitis. To further elucidate this microbial pathogenesis and evaluate the mechanism of action of novel interventions, additional advances in TEM imaging are needed. Here we present detailed protocols for fixation, decalcification, and epoxy embedment of bone tissue for standard TEM imaging studies, as well as the application of immunoelectron microscopy to confirm S. aureus occupation within sub-micron canaliculi. We also describe the first application of the novel Automated-Tape-UltraMicrotome system with three-dimensional reconstruction and volumetric analyses to quantify S. aureus occupation within the osteocyte-lacuno canalicular networks. Reconstruction of the three-dimensional volume broadened our perspective of S. aureus colonization of the canalicular network and, surprisingly, revealed adjacent noninfected canaliculi. This observation has led us to hypothesize that viable osteocytes of the osteocyte-lacuno canalicular networks respond and resist infection, opening future research directions to explain the paradox of adjacent uninfected canaliculi and life-long deep bone infection in patients with chronic osteomyelitis.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

LEVEL OF EVIDENCE

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

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

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

Staphylococcus aureus ATP Synthase Promotes Biofilm Persistence by Influencing Innate Immunity

Staphylococcus aureus is a major cause of prosthetic joint infection (PJI), which is characterized by biofilm formation. S. aureus biofilm skews the host immune response toward an anti-inflammatory profile by the increased recruitment of myeloid-derived suppressor cells (MDSCs) that attenuate macrophage proinflammatory activity, leading to chronic infection. A screen of the Nebraska Transposon Mutant Library identified several hits in the ATP synthase operon that elicited a heightened inflammatory response in macrophages and MDSCs, including atpA, which encodes the alpha subunit of ATP synthase. An atpA transposon mutant (ΔatpA) had altered growth kinetics under both planktonic and biofilm conditions, along with a diffuse biofilm architecture that was permissive for leukocyte infiltration, as observed by confocal laser scanning microscopy. Coculture of MDSCs and macrophages with ΔatpA biofilm elicited significant increases in the proinflammatory cytokines interleukin 12p70 (IL-12p70), tumor necrosis factor alpha (TNF-α), and IL-6. This was attributed to increased leukocyte survival resulting from less toxin and protease production by ΔatpA biofilm as determined by liquid chromatography with tandem mass spectrometry (LC-MS/MS). The enhanced inflammatory response elicited by ΔatpA biofilm was cell lysis-dependent since it was negated by polyanethole sodium sulfanate treatment or deletion of the major autolysin, Atl. In a mouse model of PJI, ΔatpA-infected mice had decreased MDSCs concomitant with increased monocyte/macrophage infiltrates and proinflammatory cytokine production, which resulted in biofilm clearance. These studies identify S. aureus ATP synthase as an important factor in influencing the immune response during biofilm-associated infection and bacterial persistence.IMPORTANCE Medical device-associated biofilm infections are a therapeutic challenge based on their antibiotic tolerance and ability to evade immune-mediated clearance. The virulence determinants responsible for bacterial biofilm to induce a maladaptive immune response remain largely unknown. This study identified a critical role for S. aureus ATP synthase in influencing the host immune response to biofilm infection. An S. aureus ATP synthase alpha subunit mutant (ΔatpA) elicited heightened proinflammatory cytokine production by leukocytes in vitro and in vivo, which coincided with improved biofilm clearance in a mouse model of prosthetic joint infection. The ability of S. aureus ΔatpA to augment host proinflammatory responses was cell lysis-dependent, as inhibition of bacterial lysis by polyanethole sodium sulfanate or a ΔatpAΔatl biofilm did not elicit heightened cytokine production. These studies reveal a critical role for AtpA in shaping the host immune response to S. aureus biofilm.

Daptomycin for Pediatric Gram-Positive Acute Hematogenous Osteomyelitis

BACKGROUND

We prospectively evaluated efficacy and safety of daptomycin versus active comparator in children with acute hematogenous osteomyelitis (AHO).

METHODS

Randomized, controlled, double-blind, global, multicenter, phase 3 trial. Patients 1-17 years of age with suspected/confirmed AHO requiring hospitalization and intravenous therapy were randomized 1:1 to intravenous daptomycin (once-daily, age-adjusted doses) or comparator (vancomycin, nafcillin or equivalent) ≥4 days, followed by oral therapy (14-42 days total). Primary endpoint: protocol-defined clinical improvement by Day 5 in the modified intention-to-treat (MITT) population (confirmed AHO, ≥1 dose of study treatment); differences between study arms were evaluated using a prespecified 15% noninferiority margin for daptomycin.

RESULTS

Seventy-three patients per arm received treatment. Pathogens were isolated from 62% of patients (83% methicillin-susceptible Staphylococcus aureus, 9% methicillin-resistant S. aureus [MRSA]). Clinical improvement by Day 5 was observed in 55/71 (78%) daptomycin- and 58/70 (83%) comparator-treated MITT patients (95% confidence interval [CI]: -19.4, 7.4). This difference was not statistically significant; however, daptomycin did not meet the prespecified 15% noninferiority margin, since the lower bound of the 95% CI extended below 15%. Overall, 82% of daptomycin and 87% of comparator patients achieved clinical cure at the test-of-cure visit (secondary endpoint). More comparator patients had treatment-emergent (63% vs. 46%) and treatment-related (18% vs. 7%) adverse events.

CONCLUSIONS

Differences between daptomycin and comparator for the primary endpoint were not statistically significant; however, prespecified noninferiority criteria for daptomycin were not met. With insufficient cases of confirmed MRSA, we could not evaluate daptomycin for MRSA AHO. Our nonvalidated protocol design yields valuable information for implementing future trials in AHO (ClinicalTrials.gov NCT01922011).

Characteristics of Pyogenic Musculoskeletal Infections in Older Children and Adolescents

The characteristics and clinical consequences of pyogenic bone and joint infections in older children and adolescents have received little attention. This study evaluated the presentation and complications of musculoskeletal infections involving the pelvis and extremities in children older than 10 years. Thirty patients 10 to 17 years old (mean, 12.7 years old) were treated for musculoskeletal infections. Mean time to diagnosis was 9.2 days. Prior to correct diagnosis, 83% were assessed by at least 1 outpatient provider. At the time of admission, 55% were weight bearing and 93% were afebrile. Twenty-eight percent had a multifocal infection. More than one-third had serious medical complications or orthopedic sequelae; compared with patients without complications, this group had a significantly higher admission C-reactive protein and longer hospital stay. Symptoms of musculoskeletal infection common among young children may be absent in adolescents. Axial imaging is recommended to identify adjacent or multifocal disease. The Kocher criteria are less sensitive for septic hip arthritis in the adolescent population. Prompt recognition and treatment are critical to avoid medical and musculoskeletal complications. [Orthopedics. 2020;43(4):e291-e298.].

Biomaterials against Bone Infection

Chronic bone infection is considered as one of the most problematic biofilm-related infections. Its recurrent and resistant nature, high morbidity, prolonged hospitalization, and costly medical care expenses have driven the efforts of the scientific community to develop new therapies to improve the standards used today. There is great debate on the management of this kind of infection in order to establish consistent and agreed guidelines in national health systems. The scientific research is oriented toward the design of anti-infective biomaterials both for prevention and cure. The properties of these materials must be adapted to achieve better anti-infective performance and good compatibility, which allow a good integration of the implant with the surrounding tissue. The objective of this review is to study in-depth the antibacterial biomaterials and the strategies underlying them. In this sense, this manuscript focuses on antimicrobial coatings, including the new technological advances on surface modification; scaffolding design including multifunctional scaffolds with both antimicrobial and bone regeneration properties; and nanocarriers based on mesoporous silica nanoparticles with advanced properties (targeting and stimuli-response capabilities).

A Bioinformatic Approach to Utilize a Patient's Antibody-Secreting Cells against Staphylococcus aureus to Detect Challenging Musculoskeletal Infections

Noninvasive diagnostics for Staphylococcus aureus musculoskeletal infections (MSKI) remain challenging. Abs from newly activated, pathogen-specific plasmablasts in human blood, which emerge during an ongoing infection, can be used for diagnosing and tracking treatment response in diabetic foot infections. Using multianalyte immunoassays on medium enriched for newly synthesized Abs (MENSA) from Ab-secreting cells, we assessed anti-S. aureus IgG responses in 101 MSKI patients (63 culture-confirmed S. aureus, 38 S. aureus-negative) and 52 healthy controls. MENSA IgG levels were assessed for their ability to identify the presence and type of S. aureus MSKI using machine learning and multivariate receiver operating characteristic curves. Eleven S. aureus-infected patients were presented with prosthetic joint infections, 15 with fracture-related infections, 5 with native joint septic arthritis, 15 with diabetic foot infections, and 17 with suspected orthopedic infections in the soft tissue. Anti-S. aureus MENSA IgG levels in patients with non-S. aureus infections and healthy controls were 4-fold (***p = 0.0002) and 8-fold (****p < 0.0001) lower, respectively, compared with those with culture-confirmed S. aureus infections. Comparison of MENSA IgG responses among S. aureus culture-positive patients revealed Ags predictive of active MSKI (IsdB, SCIN, Gmd) and Ags predictive of MSKI type (IsdB, IsdH, Amd, Hla). When combined, IsdB, IsdH, Gmd, Amd, SCIN, and Hla were highly discriminatory of S. aureus MSKI (area under the ROC curve = 0.89 [95% confidence interval 0.82-0.93, p < 0.01]). Collectively, these results demonstrate the feasibility of a bioinformatic approach to use a patient's active immune proteome against S. aureus to diagnose challenging MSKI.

Staphylococcus aureus Osteomyelitis: Bone, Bugs, and Surgery

Osteomyelitis, or inflammation of bone, is most commonly caused by invasion of bacterial pathogens into the skeleton. Bacterial osteomyelitis is notoriously difficult to treat, in part because of the widespread antimicrobial resistance in the preeminent etiologic agent, the Gram-positive bacterium Staphylococcus aureus Bacterial osteomyelitis triggers pathological bone remodeling, which in turn leads to sequestration of infectious foci from innate immune effectors and systemically delivered antimicrobials. Treatment of osteomyelitis therefore typically consists of long courses of antibiotics in conjunction with surgical debridement of necrotic infected tissues. Even with these extreme measures, many patients go on to develop chronic infection or sustain disease comorbidities. A better mechanistic understanding of how bacteria invade, survive within, and trigger pathological remodeling of bone could therefore lead to new therapies aimed at prevention or treatment of osteomyelitis as well as amelioration of disease morbidity. In this minireview, we highlight recent developments in our understanding of how pathogens invade and survive within bone, how bacterial infection or resulting innate immune responses trigger changes in bone remodeling, and how model systems can be leveraged to identify new therapeutic targets. We review the current state of osteomyelitis epidemiology, diagnostics, and therapeutic guidelines to help direct future research in bacterial pathogenesis.

Sonography of musculoskeletal infection in children

Musculoskeletal infection, especially in young children, often presents with non-specific clinical signs and symptoms necessitating early imaging to identify the source of infection. While MRI is the investigation of choice to demonstrate bone infection, it is expensive and often requires a general anaesthetic in the young child. Ultrasound can be a useful tool in the initial assessment due to its easy availability and portable equipment. It does not involve ionising radiation and is used to guide aspiration and drainage procedures. This review explains sonographic features of septic arthritis, osteomyelitis, pyomyositis and soft tissue infection in children and highlights advantages and limitations of sonography when assessing the child with suspected musculoskeletal infection.

Investigation of synovial fluid induced Staphylococcus aureus aggregate development and its impact on surface attachment and biofilm formation

Periprosthetic joint infections (PJIs) are a devastating complication that occurs in 2% of patients following joint replacement. These infections are costly and difficult to treat, often requiring multiple corrective surgeries and prolonged antimicrobial treatments. The Gram-positive bacterium Staphylococcus aureus is one of the most common causes of PJIs, and it is often resistant to a number of commonly used antimicrobials. This tolerance can be partially attributed to the ability of S. aureus to form biofilms. Biofilms associated with the surface of indwelling medical devices have been observed on components removed during chronic infection, however, the development and localization of biofilms during PJIs remains unclear. Prior studies have demonstrated that synovial fluid, in the joint cavity, promotes the development of bacterial aggregates with many biofilm-like properties, including antibiotic resistance. We anticipate these aggregates have an important role in biofilm formation and antibiotic tolerance during PJIs. Therefore, we sought to determine specifically how synovial fluid promotes aggregate formation and the impact of this process on surface attachment. Using flow cytometry and microscopy, we quantified the aggregation of various clinical S. aureus strains following exposure to purified synovial fluid components. We determined that fibrinogen and fibronectin promoted bacterial aggregation, while cell free DNA, serum albumin, and hyaluronic acid had minimal effect. To determine how synovial fluid mediated aggregation affects surface attachment, we utilized microscopy to measure bacterial attachment. Surprisingly, we found that synovial fluid significantly impeded bacterial surface attachment to a variety of materials. We conclude from this study that fibrinogen and fibronectin in synovial fluid have a crucial role in promoting bacterial aggregation and inhibiting surface adhesion during PJI. Collectively, we propose that synovial fluid may have conflicting protective roles for the host by preventing adhesion to surfaces, but by promoting bacterial aggregation is also contributing to the development of antibiotic tolerance.

Declining Prevalence of Methicillin-Resistant Staphylococcus aureus Septic Arthritis and Osteomyelitis in Children: Implications for Treatment

This study sought to assess clinical characteristics and differences in outcomes between children with Methicillin-resistant Staphylococcus aureus (MRSA) and Methicillin-sensitive Staphylococcus aureus (MSSA) osteomyelitis or septic arthritis and whether initial antibiotic regimen affects patient outcomes. We analyzed records of children ages 15 days to 18 years admitted between 2009 and 2016 to two tertiary children's hospitals who were diagnosed with an osteoarticular infection and had a microorganism identified. A total of 584 patients met inclusion criteria, of which 365 (62.5%) had a microbiological diagnosis. MSSA was the most common pathogen identified (45.5%), followed by MRSA (31.2%). Compared to MSSA, patients with MRSA had a higher initial C-reactive protein and longer hospitalization. Patients whose initial antibiotic regimens included vancomycin had a longer hospitalization than those initiated on clindamycin without vancomycin, even after removing sicker patients admitted to the pediatric intensive care unit. While MRSA was associated with increased severity of osteoarticular infections compared to MSSA, the incidence of MRSA has been declining at our institution. Patients with longer lengths of stay were more likely to be on vancomycin. Clindamycin should be considered in the initial antibiotic regimen for osteomyelitis and septic arthritis with ongoing surveillance of local microbiology and outcomes.

Mechanisms of Immune Evasion and Bone Tissue Colonization That Make Staphylococcus aureus the Primary Pathogen in Osteomyelitis

PURPOSE OF REVIEW

Staphylococcus aureus is the primary pathogen responsible for osteomyelitis, which remains a major healthcare burden. To understand its dominance, here we review the unique pathogenic mechanisms utilized by S. aureus that enable it to cause incurable osteomyelitis.

RECENT FINDINGS

Using an arsenal of toxins and virulence proteins, S. aureus kills and usurps immune cells during infection, to produce non-neutralizing pathogenic antibodies that thwart adaptive immunity. S. aureus also has specific mechanisms for distinct biofilm formation on implants, necrotic bone tissue, bone marrow, and within the osteocyte lacuno-canicular networks (OLCN) of live bone. In vitro studies have also demonstrated potential for intracellular colonization of osteocytes, osteoblasts, and osteoclasts. S. aureus has evolved a multitude of virulence mechanisms to achieve life-long infection of the bone, most notably colonization of OLCN. Targeting S. aureus proteins involved in these pathways could provide new targets for antibiotics and immunotherapies.

Kingella kingae and Osteoarticular Infections

OBJECTIVES

In this study, we aimed to contrast the bacteriologic epidemiology of osteoarticular infections (OAIs) between 2 patient groups in successive 10-year periods, before and after the extensive use of nucleic acid amplification assays in the diagnostic process.

METHODS

Epidemiologic data and bacteriologic etiologies of all children presenting with OAIs on admission to our institution over 20 years (1997-2016) were assessed retrospectively. The population was divided into 2 cohorts, using the standardized use of polymerase chain reaction as the cutoff point (2007). The conventional cohort included children with OAIs mainly investigated by using classic cultures, whereas the molecular cohort referred to patients also investigated by using molecular assays.

RESULTS

Kingella kingae was the most frequently isolated pathogen, responsible for 51% of OAIs, whereas other classic pathogens were responsible for 39.7% of cases in the molecular cohort. A statistically significant increase in the mean incidence of OAIs was observed, as was a decrease in the mean age at diagnosis after 2007. After 2007, the pathogen remained unidentified in 21.6% of OAIs in our pediatric population.

CONCLUSIONS

Extensive use of nucleic acid amplification assays improved the detection of fastidious pathogens and has increased the observed incidence of OAI, especially in children aged between 6 and 48 months. We propose the incorporation of polymerase chain reaction assays into modern diagnostic algorithms for OAIs to better identify the bacteriologic etiology of OAIs.

Evolving concepts in bone infection: redefining "biofilm", "acute vs. chronic osteomyelitis", "the immune proteome" and "local antibiotic therapy"

Osteomyelitis is a devastating disease caused by microbial infection of bone. While the frequency of infection following elective orthopedic surgery is low, rates of reinfection are disturbingly high. Staphylococcus aureus is responsible for the majority of chronic osteomyelitis cases and is often considered to be incurable due to bacterial persistence deep within bone. Unfortunately, there is no consensus on clinical classifications of osteomyelitis and the ensuing treatment algorithm. Given the high patient morbidity, mortality, and economic burden caused by osteomyelitis, it is important to elucidate mechanisms of bone infection to inform novel strategies for prevention and curative treatment. Recent discoveries in this field have identified three distinct reservoirs of bacterial biofilm including: Staphylococcal abscess communities in the local soft tissue and bone marrow, glycocalyx formation on implant hardware and necrotic tissue, and colonization of the osteocyte-lacuno canalicular network (OLCN) of cortical bone. In contrast, S. aureus intracellular persistence in bone cells has not been substantiated in vivo, which challenges this mode of chronic osteomyelitis. There have also been major advances in our understanding of the immune proteome against S. aureus, from clinical studies of serum antibodies and media enriched for newly synthesized antibodies (MENSA), which may provide new opportunities for osteomyelitis diagnosis, prognosis, and vaccine development. Finally, novel therapies such as antimicrobial implant coatings and antibiotic impregnated 3D-printed scaffolds represent promising strategies for preventing and managing this devastating disease. Here, we review these recent advances and highlight translational opportunities towards a cure.

Clinical Features and Outcomes of Children with Culture-Negative Septic Arthritis

BACKGROUND

Septic arthritis is a serious infection, but the results of blood and joint fluid cultures are often negative in children. We describe here the clinical features and management of culture-negative septic arthritis in children at our hospital and their outcomes.

METHODS

We performed a retrospective review of a cohort of children with septic arthritis who were hospitalized at Children's Hospital of Philadelphia between January 2002 and December 2014. Culture-negative septic arthritis was defined as a joint white blood cell count of >50000/μL with associated symptoms, a clinical diagnosis of septic arthritis, and a negative culture result. Children with pretreatment, an intensive case unit admission, Lyme arthritis, immunodeficiency, or surgical hardware were excluded. Treatment failure included a change in antibiotics, surgery, and/or reevaluation because of a lack of improvement/worsening.

RESULTS

We identified 157 children with septic arthritis. The patients with concurrent osteomyelitis (n = 28) had higher inflammatory marker levels at presentation, had a longer duration of symptoms (median, 4.5 vs 3 days, respectively; P < .001), and more often had bacteremia (46.4% vs 6.2%, respectively; P < .001). Among children with septic arthritis without associated osteomyelitis, 69% (89 of 129) had negative culture results. These children had lower C-reactive protein levels (median, 4.0 vs 7.3 mg/dL, respectively; P = .001) and erythrocyte sedimentation rates (median, 39 vs 51 mm/hour, respectively; P = .01) at admission and less often had foot/ankle involvement (P = .02). Among the children with culture-negative septic arthritis, the inpatient treatment failure rate was 9.1%, and treatment failure was more common in boys than in girls (17.1% vs 3.8%, respectively; P = .03). We found no association between treatment failure and empiric antibiotics or patient age. No outpatient treatment failures occurred during the 6-month follow-up period, although 17% of the children discharged with a peripherally inserted central catheter line experienced complications, including 3 with bacteremia.

CONCLUSIONS

The majority of septic arthritis infections at our institution were culture negative. Among patients with culture-negative infection, empiric antibiotics failed for 9% and necessitated a change in therapy. More sensitive diagnostic testing should be implemented to elucidate the causes of culture-negative septic arthritis in children.

An in vitro platform for elucidating the molecular genetics of S. aureus invasion of the osteocyte lacuno-canalicular network during chronic osteomyelitis

Staphylococcus aureus osteomyelitis is a devasting disease that often leads to amputation. Recent findings have shown that S. aureus is capable of invading the osteocyte lacuno-canalicular network (OLCN) of cortical bone during chronic osteomyelitis. Normally a 1 μm non-motile cocci, S. aureus deforms smaller than 0.5 μm in the sub-micron channels of the OLCN. Here we present the μSiM-CA (Microfluidic - Silicon Membrane - Canalicular Array) as an in vitro screening platform for the genetic mechanisms of S. aureus invasion. The μSiM-CA platform features an ultrathin silicon membrane with defined pores that mimic the openings of canaliculi. While we anticipated that S. aureus lacking the accessory gene regulator (agr) quorum-sensing system would not be capable of invading the OLCN, we found no differences in propagation compared to wild type in the μSiM-CA. However the μSiM-CA proved predictive as we also found that the agr mutant strain invaded the OLCN of murine tibiae.

2018 International Consensus Meeting on Musculoskeletal Infection: Research Priorities from the General Assembly Questions

Musculoskeletal infections (MSKI) remain the bane of orthopedic surgery, and result in grievous illness and inordinate costs that threaten healthcare systems. As prevention, diagnosis, and treatment has remained largely unchanged over the last 50 years, a 2nd International Consensus Meeting on Musculoskeletal Infection (ICM 2018, https://icmphilly.com) was completed. Questions pertaining to all areas of MSKI were extensively researched to prepare recommendations, which were discussed and voted on by the delegates using the Delphi methodology. The questions, including the General Assembly (GA) results, have been published (GA questions). However, as critical outcomes include: (i) incidence and cost data that substantiate the problems, and (ii) establishment of research priorities; an ICM 2018 research workgroup (RW) was assembled to accomplish these tasks. Here, we present the result of the RW consensus on the current and projected incidence of infection, and the costs per patient, for all orthopedic subspecialties, which range from 0.1% to 30%, and $17,000 to $150,000. The RW also identified the most important research questions. The Delphi methodology was utilized to initially derive four objective criteria to define a subset of the 164 GA questions that are high priority for future research. Thirty-eight questions (23% of all GA questions) achieved the requisite > 70% agreement vote, and are highlighted in this Consensus article within six thematic categories: acute versus chronic infection, host immunity, antibiotics, diagnosis, research caveats, and modifiable factors. Finally, the RW emphasizes that without appropriate funding to address these high priority research questions, a 3rd ICM on MSKI to address similar issues at greater cost is inevitable.

Acute Hematogenous Osteomyelitis in Children

Background: The epidemiology of acute hematogenous osteomyelitis (AHO) in children has changed. Methods: We reviewed the current literature regarding the epidemiology, microbiology, pathogenesis, clinical presentation, diagnosis, and antimicrobial management of AHO in children. Results: Staphylococcus aureus is the most common microorganism causing pediatric AHO, followed by group A Streptococcus (GAS). AHO due to community-associated methicillin-resistant Staphylococcus aureus (MRSA) can cause severe and complicated disease. Pathogen isolation by culture is key for targeted antibiotic therapy. Polymerase chain reaction assay in tissue sample or joint fluid may enhance the yield of Kingella kingae. C-reactive protein is useful in diagnosis and monitoring the course of AHO. Magnetic resonance imaging is the preferred diagnostic imaging study for AHO. Clindamycin or vancomycin (for serious disease) is recommended for empiric therapy of suspected AHO due to MRSA depending on the geographic prevalence. Penicillinase-stable penicillins or first-generation cephalosporins are preferred antibiotics to treat methicillin-sensitive S aureus (MSSA) infection. Beta-lactam agents are the drugs of choice for treating AHO due to K kingae, GAS, or Streptococcus pneumoniae. For uncomplicated AHO due to MSSA, a short parenteral antibiotic course followed by oral therapy for a minimum total duration of 3-4 weeks is adequate. Complicated AHO due to MRSA may warrant prolonged therapy with surgical intervention. Conclusion: Given the evolution of pathogens, the variability in clinical presentations and course ranging from simple to complex disease, and response to treatment, the management of AHO continues to evolve and warrants an individualized, multidisciplinary approach.

Staphylococcus aureus Evasion of Host Immunity in the Setting of Prosthetic Joint Infection: Biofilm and Beyond

PURPOSE OF REVIEW

The incidence of complications from prosthetic joint infection (PJI) is increasing, and treatment failure remains high. We review the current literature with a focus on Staphylococcus aureus pathogenesis and biofilm, as well as treatment challenges, and novel therapeutic strategies.

RECENT FINDINGS

S. aureus biofilm creates a favorable environment that increases antibiotic resistance, impairs host immunity, and increases tolerance to nutritional deprivation. Secreted proteins from bacterial cells within the biofilm and the quorum-sensing agr system contribute to immune evasion. Additional immunoevasive properties of S. aureus include the formation of staphylococcal abscess communities (SACs) and canalicular invasion. Novel approaches to target biofilm and increase resistance to implant colonization include novel antibiotic therapy, immunotherapy, and local implant treatments. Challenges remain given the diverse mechanisms developed by S. aureus to alter the host immune responses. Further understanding of these processes should provide novel therapeutic mechanisms to enhance eradication after PJI.

Evaluation of the current use of imaging modalities and pathogen detection in children with acute osteomyelitis and septic arthritis

Diagnostic tools for the management of acute osteomyelitis (OM) and septic arthritis (SA) have improved over the last decade. To investigate the influence and availability of magnetic resonance imaging (MRI) and nucleic acid testing (NAT), a retrospective cohort study was done. Patients admitted with acute OM or SA between 2005 and 2014 were identified using ICD-10 discharge codes. Ninety-six children were identified: OM, n = 45; SA, n = 42; and OM + SA, n = 9. Diagnostic imaging was performed in 100% of OM or OM + SA and 95% of SA patients. MRI was performed in 85% of OM patients, 26% of SA patients and 100% OM + SA patients. In patients with OM or SA, concomitant joint/bone involvement was detected in 24 and 36% of patients, respectively. In 58% of patients, a pathogen was detected (Staphylococcus aureus, Streptococcus pyogenes and Streptococcus pneumoniae being most common). Blood and tissue culture were positive in 41 and 86% for OM patients and in 14 and 41%, respectively, for SA patients. In 42% of patients, no pathogen was identified, of which 40% had no material for blood or tissue culture/NAT taken.

CONCLUSION

Optimal use of imaging modalities including MRI and systematic pathogen detection including NAT should be advocated to limit use of broad spectrum antibiotics and treatment duration. What is Known: • Magnetic resonance imaging and sonography have the best sensitivity for detection of acute osteomyelitis and septic arthritis in children. • Systematic use of blood cultures, tissue cultures and nucleic acid testing improves pathogen detection in children with acute osteomyelitis and septic arthritis. What is New: • The added value of imaging modalities other than magnetic resonance and sonography for detection of osteomyelitis and septic arthritis is limited, and their routine use should be questioned. • Despite availability of optimal pathogen detection methods, missed opportunities to improve pathogen detection are frequent.

Imaging of Kingella kingae musculoskeletal infections in children: a series of 5 cases

PURPOSE

Kingella kingae musculoskeletal infections continue to be under-diagnosed and there remains a paucity of literature on its imaging features. The purpose of this manuscript is to review the imaging, clinical, and laboratory findings of microbiology-proven K. kingae infections.

MATERIALS AND METHODS

A retrospective review of musculoskeletal infections between January 1, 2013 and Dec 31, 2016 yielded 134 patients from whom 5 patients had confirmed K. kingae infections (3 boys and 2 girls, mean age of 16 months, range 9-38 months). Picture archiving and communication system and electronic medical records were reviewed.

RESULTS

At presentation, none of the patients had a fever and not all patients had abnormal inflammatory markers. Three patients had septic arthritis (2 knee and 1 sternomanubrial joints), one had epiphyseal osteomyelitis, and one had lumbar spondylodiscitis. The case of epiphyseal osteomyelitis of the distal humerus also had elbow joint involvement. A combination of radiography (n = 4), ultrasound (n = 2), and magnetic resonance (MR) imaging (n = 5) were performed. Prominent synovial thickening was observed for both knee and elbow joints and extensive regional myositis for all except for the patient with sternomanubrial joint infection. The diagnosis of K. kingae infection resulted in a change in the antibiotic regimen in 80% of the patients.

CONCLUSION

Disproportionate synovial thickening, prominent peri-articular myositis, and/or characteristic sites of involvement demonstrating imaging features of infection or inflammation in a young child with mild infectious symptoms and elevated inflammatory markers should invoke the possibility of an underlying K. kingae infection.

Interleukin-33 Receptor (ST2) Deficiency Improves the Outcome of Staphylococcus aureus-Induced Septic Arthritis

The ST2 receptor is a member of the Toll/IL-1R superfamily and interleukin-33 (IL-33) is its agonist. Recently, it has been demonstrated that IL-33/ST2 axis plays key roles in inflammation and immune mediated diseases. Here, we investigated the effect of ST2 deficiency in Staphylococcus aureus-induced septic arthritis physiopathology. Synovial fluid samples from septic arthritis and osteoarthritis individuals were assessed regarding IL-33 and soluble (s) ST2 levels. The IL-33 levels in samples from synovial fluid were significantly increased, whereas no sST2 levels were detected in patients with septic arthritis when compared with osteoarthritis individuals. The intra-articular injection of 1 × 10⁷ colony-forming unity/10 μl of S. aureus American Type Culture Collection 6538 in wild-type (WT) mice induced IL-33 and sST2 production with a profile resembling the observation in the synovial fluid of septic arthritis patients. Data using WT, and ST2 deficient (^−/−) and interferon-γ (IFN-γ)^−/− mice showed that ST2 deficiency shifts the immune balance toward a type 1 immune response that contributes to eliminating the infection due to enhanced microbicide effect via NO production by neutrophils and macrophages. In fact, the treatment of ST2^−/− bone marrow-derived macrophage cells with anti-IFN-γ abrogates the beneficial phenotype in the absence of ST2, which confirms that ST2 deficiency leads to IFN-γ expression and boosts the bacterial killing activity of macrophages against S. aureus. In agreement, WT cells achieved similar immune response to ST2 deficiency by IFN-γ treatment. The present results unveil a previously unrecognized beneficial effect of ST2 deficiency in S. aureus-induced septic arthritis.

EPIDEMIOLOGICAL STUDY OF OSTEOARTICULAR INFECTIONS IN CHILDREN

OBJECTIVE

To analyze the characteristics of patients diagnosed with pediatric osteoarticular infections treated in a level III trauma center in São Paulo, Brazil.

METHODS

We retrospectively analyzed patients admitted between September 2012 and August 2014. The outcomes analyzed were: age, sex, diagnosis, etiologic agent, anatomic location, time to diagnosis, history of previous trauma and infection, laboratory tests, treatment, and complications.

RESULTS

Twenty patients were included, 50% with septic arthritis, 35% with osteomyelitis, and 15% with both. Boys were predominant (80%), and the mean age was 6.6 years. The most common etiologic agent was Staphylococcus aureus. C-reactive protein value and erythrocyte sedimentation rate were elevated. The infections were treated with antibiotic therapy (intravenous and oral) and oxacillin was most frequently used. Most patients underwent at least one surgical procedure, and 35% of patients had complications.

CONCLUSION

This epidemiological mapping identified clinical and demographic characteristics which are useful for improving preparation for care. Future prospective studies with longer patient follow-up and the development of treatment protocols are needed to improve therapeutic decision-making and the prognosis of children with suspected osteoarticular infections. Evidence Level II; Prognostic studies - Investigation of the effect of patient characteristics on the outcome of the disease.

The Contemporary Bacteriologic Epidemiology of Osteoarticular Infections in Children in Switzerland

OBJECTIVES

To assess the contemporary bacteriologic epidemiology of pediatric osteoarticular infection with particular regard to children's ages, because Kingella kingae has gained increasing recognition as the predominant pathogen for osteoarticular infection in young children.

STUDY DESIGN

Retrospective file review of enrolled children from 0 to 15 years of age, admitted to our institution from 2007 to 2015 for suspected osteoarticular infection (217 cases). Information on age, sex, the bone or joint infected, imaging studies, and laboratory data (including bacterial investigations) were collected for analysis.

RESULTS

Microorganism identification was possible for 138 infected children (63.6%), through blood (cultures or polymerase chain reaction [PCR]) and/or operative samples (cultures or PCR). Thirty-one patients (14.3%) were found to both have positive blood cultures and operative samples. The results of positive bacteriology specimens identified the most common causative pathogen for osteoarticular infection as K kingae (47.8% of microbiologically confirmed osteoarticular infections of all ages, and 87.7% in children between the ages of 6 and 48 months), significantly more common than Staphylococcus aureus (35.5% of microbiologically confirmed osteoarticular infections of all ages, and 78.2% in children >4 years of age).

CONCLUSIONS

Use of the appropriate PCR assays demonstrated that K kingae currently is the major bacterial cause of pediatric osteoarticular infection, especially in children <4 years of age in whom K kingae is more common than S aureus. PCR assays should be used in routine microbiologic laboratory evaluation to improve diagnostic performance. However, despite the use of molecular methods, there are many osteoarticular infections in which no microorganism is detected, which suggests that these infections may be caused by other as yet unrecognized fastidious microorganisms.