Emerging Pathogenetic Mechanisms of the Implant-Related Osteomyelitis by Staphylococcus Aureus

Interactions of Neutrophils with the Polymeric Molecular Components of the Biofilm Matrix in the Context of Implant-Associated Bone and Joint Infections

In the presence of orthopedic implants, opportunistic pathogens can easily colonize the biomaterial surfaces, forming protective biofilms. Life in biofilm is a central pathogenetic mechanism enabling bacteria to elude the host immune response and survive conventional medical treatments. The formation of mature biofilms is universally recognized as the main cause of septic prosthetic failures. Neutrophils are the first leukocytes to be recruited at the site of infection. They are highly efficient in detecting and killing planktonic bacteria. However, the interactions of these fundamental effector cells of the immune system with the biofilm matrix, which is the true interface of a biofilm with the host cells, have only recently started to be unveiled and are still to be fully understood. Biofilm matrix macromolecules consist of exopolysaccharides, proteins, lipids, teichoic acids, and the most recently described extracellular DNA. The latter can also be stolen from neutrophil extracellular traps (NETs) by bacteria, who use it to strengthen their biofilms. This paper aims to review the specific interactions that neutrophils develop when they physically encounter the matrix of a biofilm and come to interact with its polymeric molecular components.

Functionalization of 3D Printed Scaffolds Using Polydopamine and Silver Nanoparticles for Bone-Interfacing Applications

The prevention of bacterial colonization and the stimulation of osseointegration are two major requirements for bone-interfacing materials to reduce the incidence of complications and promote the restoration of the patient's health. The present investigation developed an effective, two-step functionalization of 3D printed scaffolds intended for bone-interfacing applications using a simple polydopamine (PDA) dip-coating method followed by the formation of silver nanoparticles (AgNPs) after a second coating step in silver nitrate. 3D printed polymeric substrates coated with a ∼20 nm PDA layer and 70 nm diameter AgNPs proved effective in hindering Staphylococcus aureus biofilm formation, with a 3000-8000-fold reduction in the number of bacterial colonies formed. The implementation of porous geometries significantly accelerated osteoblast-like cell growth. Microscopy characterization further elucidated homogeneity, features, and penetration of the coating inside the scaffold. A proof-of-concept coating on titanium substrates attests to the transferability of the method to other materials, broadening the range of applications both in and outside the medical sector. The antibacterial efficiency of the coating is likely to lead to a decrease in the number of bacterial infections developed after surgery in the presence of these coatings on prosthetics, thus translating to a reduction in revision surgeries and improved health outcomes.

Structural and antibacterial studies of novel ZnO and ZnxMn(1-x)O nanostructured titanium scaffolds for biomedical applications

In the biomedical field, the demand for the development of broad-spectrum biomaterials able to inhibit bacterial growth is constantly increasing. Chronic infections represent the most serious and devastating complication related to the use of biomaterials. This is particularly relevant in the orthopaedic field, where infections can lead to implant loosening, arthrodesis, amputations and sometimes death. Antibiotics are the conventional approach for implanted-associated infections, but they have the limitation of increasing antibiotic resistance, a critical worldwide healthcare issue. In this context, the development of anti-infective biomaterials and infection-resistant surfaces can be considered the more effective strategy to prevent the implant colonisation and biofilm formation by bacteria, so reducing the occurrence of implant-associated infections. In the last years, inorganic nanostructures have become extremely appealing for chemical modifications or coatings of Ti surfaces, since they do not generate antibiotic resistance issues and are featured by superior stability, durability, and full compatibility with the sterilization process. In this work, we present a simple, rapid, and cheap chemical nanofunctionalization of titanium (Ti) scaffolds with colloidal ZnO and Mn-doped ZnO nanoparticles (NPs), prepared by a sol-gel method, exhibiting antibacterial activity. ZnO NPs and Zn_xMn_(1-x)O NPs formation with a size around 10-20nm and band gap values of 3.42 eV and 3.38 eV, respectively, have been displayed by characterization studies. UV-Vis, fluorescence, and Raman investigation suggested that Mn ions acting as dopants in the ZnO lattice. Ti scaffolds have been functionalized through dip coating, obtaining ZnO@Ti and Zn_xMn_(1-x)O@Ti biomaterials characterized by a continuous nanostructured film. ZnO@Ti and Zn_xMn_(1-x)O@Ti displayed an enhanced antibacterial activity against both Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative Pseudomonas aeruginosa (P. aeruginosa) bacterial strains, compared to NPs in solution with better performance of Zn_xMn_(1-x)O@Ti respect to ZnO@Ti. Notably, it has been observed that Zn_xMn_(1-x)O@Ti scaffolds reach a complete eradication for S. aureus and 90 % of reduction for P. aeruginosa. This can be attributed to Zn²⁺ and Mn²⁺ metal ions release (as observed by ICP MS experiments) that is also maintained over time (72 h). To the best of our knowledge, this is the first study reported in the literature describing ZnO and Mn-doped ZnO NPs nanofunctionalized Ti scaffolds with improved antibacterial performance, paving the way for the realization of new hybrid implantable devices through a low-cost process, compatible with the biotechnological industrial chain method.

In Silico Genome-Scale Analysis of Molecular Mechanisms Contributing to the Development of a Persistent Infection with Methicillin-Resistant Staphylococcus aureus (MRSA) ST239

The increasing frequency of isolation of methicillin-resistant Staphylococcus aureus (MRSA) limits the chances for the effective antibacterial therapy of staphylococcal diseases and results in the development of persistent infection such as bacteremia and osteomyelitis. The aim of this study was to identify features of the MRSA_ST239 0943-1505-2016 (SA943) genome that contribute to the formation of both acute and chronic musculoskeletal infections. The analysis was performed using comparative genomics data of the dominant epidemic S. aureus lineages, namely ST1, ST8, ST30, ST36, and ST239. The SA943 genome encodes proteins that provide resistance to the host's immune system, suppress immunological memory, and form biofilms. The molecular mechanisms of adaptation responsible for the development of persistent infection were as follows: amino acid substitution in PBP2 and PBP2a, providing resistance to ceftaroline; loss of a large part of prophage DNA and restoration of the nucleotide sequence of beta-hemolysin, that greatly facilitates the escape of phagocytosed bacteria from the phagosome and formation of biofilms; dysfunction of the AgrA system due to the presence of psm-mec and several amino acid substitutions in the AgrC; partial deletion of the nucleotide sequence in genomic island vSAβ resulting in the loss of two proteases of Spl-operon; and deletion of SD repeats in the SdrE amino acid sequence.

Risk Factors for Postoperative Osteomyelitis among Patients after Bone Fracture: A Matched Case-Control Study

The healthcare burden of osteomyelitis is increasing. Postoperative and posttraumatic osteomyelitis account for 80% of all cases of osteomyelitis. The aim of this study was to find risk factors for postoperative osteomyelitis in Kazakhstan. We included 245 patients admitted to the National Scientific Center of Traumatology and Orthopedics from 2018 to 2020. Cases were matched with controls in a 1:4 ratio. Exact matching was performed by gender, ICD-10, and ICD-9 codes. The main variables included socio-demographics, diagnosis at admission, characteristics of fractures, comorbidities, complications, hospitalization milestones, and osteomyelitis characteristics. Descriptive analyses, along with bivariate analysis and multivariate conditional logistic regression, were performed. Open fracture (adjOR = 6.25; 95%CI 1.64−23.79), the presence of complications of initial fracture (adjOR = 3.46, 95%CI 1.13−10.56), comminuted fracture form (adjOR = 1.87; 95%CI 0.73−4.75), a positive history of diabetes or blood glucose >7 g/L (adjOR = 4.25; 95%CI 1.26−14.3), incision or wound length of more than 10 cm (adjOR = 6.53; 95%CI 1.1−38.6), additional implanted medical item (adjOR = 1.23; 95% CI 1.1−1.47), and unemployment or being retired (adjOR = 4.21; 95%CI 1.74−10.18) were found to be significant predictors of postoperative osteomyelitis. Almost all our findings are concordant with previous studies, except for the type of fracture. Different authors report conflicting results on the latter potential risk factor. Therefore, prospective studies on this issue are required.

What is the best technic to dislodge Staphylococcus epidermidis biofilm on medical implants?

Background

Bacterial biofilm can occur on all medical implanted devices and lead to infection and/or dysfunction of the device.

In this study, artificial biofilm was formed on four different medical implants (silicone, piccline, peripheral venous catheter and endotracheal tube) of interest for our daily clinical and/or research practice. We investigated the best conventional technic to dislodge the biofilm on the implants and quantified the number of bacteria. Staphylococcus epidermidis previously isolated from a breast implant capsular contracture on a patient in the university hospital of Dijon was selected for its ability to produce biofilm on the implants. Different technics (sonication, Digest-EUR®, mechanized bead mill, combination of sonication plus Digest-EUR®) were tested and compared to detach the biofilm before quantifying viable bacteria by colony counting.

Results

For all treatments, the optical and scanning electron microscope images showed substantial less biofilm biomass remaining on the silicone implant compared to non-treated implant.

This study demonstrated that the US procedure was statistically superior to the other physical treatment: beads, Digest-EUR® alone and Digest-EUR® + US (p < 0.001) for the flexible materials (picc-line, PIV, and silicone). The number of bacteria released by the US is significantly higher with a difference of 1 log on each material. The result for a rigid endotracheal tube were different with superiority for the chemical treatment dithiothreitol: Digest-EUR®. Surprisingly the combination of the US plus Digest-EUR® treatment was consistently inferior for the four materials.

Conclusions

Depending on the materials used, the biofilm dislodging technique must be adapted. The US procedure was the best technic to dislodge S. epidermidis biofilm on silicone, piccline, peripheral venous catheter but not endotracheal tube. This suggested that scientists should compare themselves different methods before designing a protocol of biofilm study on a given material.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-022-02606-x.

Micro-/Nanorobots in Antimicrobial Applications: Recent Progress, Challenges, and Opportunities

The evolution of drug-resistant pathogenic bacteria remains one of the most urgent threats to public health worldwide. Even worse, the bacterial cells commonly form biofilms through aggregation and adhesion, preventing antibiotic penetration and resisting environmental stress. Moreover, biofilms tend to grow in some hard-to-reach regions, bringing difficulty for antibiotic delivery at the infected site. The drug-resistant pathogenic bacteria and intractable biofilm give rise to chronic and recurrent infections, exacerbating the challenge in combating bacterial infections. Micro/nanorobots (MNRs) are capable of active cargo delivery, targeted treatment with high precision, and motion-assisted mechanical force, which enable transport and enhance penetration of antibacterial agents into the targeted site, thus showing great promise in emerging as an attractive alternative to conventional antibacterial therapies. This review summarizes the recent advances in micro-/nanorobots for antibacterial applications, with emphasis on those novel strategies for drug-resistance bacterium and stubborn biofilm infections. Insights on the future development of MNRs with good functionality and biosafety offer promising approaches to address infections in the clinic setting.

Construction of Antimicrobial Material-Loaded Porous Tricalcium Phosphate Beads for Treatment of Bone Infections

Due to low success rates of antibiotic therapy in most osteomyelitis diseases, continuous efforts have been made to fabricate local delivery systems with high antimicrobial effects. Here, we reported a kind of ε-polylysine(PL)/Ag-loaded porous tricalcium phosphate (TCP) bead instead of antibiotics as local delivery systems for the treatment of Staphylococcus aureus-caused osteomyelitis. Such local delivery systems were prepared by the fabrication of porous TCP beads at first and then the loading of Ag and PL in turn into porous TCP beads via in situ Ag-doping and layer-by-layer methods. In vitro experiments demonstrated that the release of PL and Ag was controllable. Especially, the release dosage of Ag could be controlled to be less than 0.05 ppm 28 days later. The surface coating of PL improved the cytocompatibility and antibacterial activity of local delivery systems. In vivo experiments demonstrated that the Ag/PL-loaded porous TCP beads displayed strong antibacterial activity and good osteoconductivity, and the combination of Ag and PL was better than the use of single antibacterial materials to treat S. aureus-caused osteomyelitis. The implantation of Ag into the infected marrow had low toxicity because Ag has been integrated into the TCP grains, which could be absorbed in marrow. Therefore, the Ag/PL-loaded porous TCP beads presented potential for treating osteomyelitis, especially sequestrum-debrided osteomyelitis.

3D-Printing of Drug-Eluting Implants: An Overview of the Current Developments Described in the Literature

The usage of 3D-printing for drug-eluting implants combines the advantages of a targeted local drug therapy over longer periods of time at the precise location of the disease with a manufacturing technique that easily allows modifications of the implant shape to comply with the individual needs of each patient. Research until now has been focused on several aspects of this topic such as 3D-printing with different materials or printing techniques to achieve implants with different shapes, mechanical properties or release profiles. This review is intended to provide an overview of the developments currently described in the literature. The topic is very multifaceted and several of the investigated aspects are not related to just one type of application. Consequently, this overview deals with the topic of 3D-printed drug-eluting implants in the application fields of stents and catheters, gynecological devices, devices for bone treatment and surgical screws, antitumoral devices and surgical meshes, as well as other devices with either simple or complex geometry. Overall, the current findings highlight the great potential of the manufacturing of drug-eluting implants via 3D-printing technology for advanced individualized medicine despite remaining challenges such as the regulatory approval of individualized implants.

Ultrasound Triggered Drug Release from Affinity-Based β-Cyclodextrin Polymers for Infection Control

This work demonstrates a slow, sustained drug delivery system that provides on-demand delivery bursts through the application of pulsed therapeutic ultrasound (TUS). Insoluble β-cyclodextrin-polymer (pCD) disks were loaded with a saturated antibiotic solution of rifampicin (RIF) and used for drug delivery studies. To obtain on-demand release from the implants, TUS was applied at an intensity of 1.8 W/cm². The therapeutic efficacy of the combination treatment was assessed in bacterial culture via an in vitro Staphylococcus aureus bioluminescence assay. The results demonstrated that the application of pulsed TUS at 3 MHz and 1.8 W/cm² to pCD implants leads to a significantly higher short-term burst in the drug release rate compared to samples not treated with TUS. The addition of TUS increased the drug release by 100% within 4 days. The pCD disk + RIF stimulated with TUS showed a comparatively higher bacterial eradication with CFU/mL of 4.277E+09, and 8.00E+08 at 1 and 24 h compared with control treated bacteria at 1.48E+10. Overall, these results suggest that the addition of pulsed TUS could be an effective technology to noninvasively expedite antibiotic release on demand at desired intervals.

The Rationale for Using Bacteriophage to Treat and Prevent Periprosthetic Joint Infections

Prosthetic joint infection (PJI) is a devastating complication after a joint replacement. PJI and its treatment have a high monetary cost, morbidity, and mortality. The lack of success treating PJI with conventional antibiotics alone is related to the presence of bacterial biofilm on medical implants. Consequently, surgical removal of the implant and prolonged intravenous antibiotics to eradicate the infection are necessary prior to re-implanting a new prosthetic joint. Growing clinical data shows that bacterial predators, called bacteriophages (phages), could be an alternative treatment strategy or prophylactic approach for PJI. Phages could further be exploited to degrade biofilms, making bacteria more susceptible to antibiotics and enabling potential combinatorial therapies. Emerging research suggests that phages may also directly interact with the innate immune response. Phage therapy may play an important, and currently understudied, role in the clearance of PJI, and has the potential to treat thousands of patients who would either have to undergo revision surgery to attempt to clear an infections, take antibiotics for a prolonged period to try and suppress the re-emerging infection, or potentially risk losing a limb.

The role of the msaABCR operon in implant-associated chronic osteomyelitis in Staphylococcus aureus USA300 LAC

BACKGROUND

The msaABCR operon regulates several staphylococcal phenotypes such as biofilm formation, capsule production, protease production, pigmentation, antibiotic resistance, and persister cells formation. The msaABCR operon is required for maintaining the cell wall integrity via affecting peptidoglycan cross-linking. The msaABCR operon also plays a role in oxidative stress defense mechanism, which is required to facilitate persistent and recurrent staphylococcal infections. Staphylococcus aureus is the most frequent cause of chronic implant-associated osteomyelitis (OM). The CA-MRSA USA300 strains are predominant in the United States and cause severe infections, including bone and joint infections.

RESULTS

The USA300 LAC strain caused significant bone damage, as evidenced by the presence of severe bone necrosis with multiple foci of sequestra and large numbers of multinucleated osteoclasts. Intraosseous survival and biofilm formation on the K-wires by USA300 LAC strains was pronounced. However, the msaABCR deletion mutant was attenuated. We observed minimal bone necrosis, with no evidence of intramedullary abscess and/or fibrosis, along reduced intraosseous bacterial population and significantly less biofilm formation on the K-wires by the msaABCR mutant. microCT analysis of infected bone showed significant bone loss and damage in the USA300 LAC and complemented strain, whereas the msaABCR mutant's effect was reduced. In addition, we observed increased osteoblasts response and new bone formation around the K-wires in the bone infected by the msaABCR mutant. Whole-cell proteomics analysis of msaABCR mutant cells showed significant downregulation of proteins, cell adhesion factors, and virulence factors that interact with osteoblasts and are associated with chronic OM caused by S. aureus.

CONCLUSION

This study showed that deletion of msaABCR operon in USA300 LAC strain lead to defective biofilm in K-wire implants, decreased intraosseous survival, and reduced cortical bone destruction. Thus, msaABCR plays a role in implant-associated chronic osteomyelitis by regulating extracellular proteases, cell adhesions factors and virulence factors. However additional studies are required to further define the contribution of msaABCR-regulated molecules in osteomyelitis pathogenesis.

α-Hemolysin suppresses osteogenesis by inducing lipid rafts accumulation in bone marrow stromal cells

α-hemolysin (Hla) is considered an essential virulent factor for Staphylococcus aureus (S. aureus) toxicity, the mechanism by which Hla affect bone metabolism is poorly understood. In this study, 2-month-old C57BL/6 mice were treated with Hla (40 μg/kg, i.p.) or S. aureus (1 × 10⁶ CFU/ml, 100 μl, i.v.) with the presence or absence of methyl-β-cyclodextrin (MβCD) (300 mg/kg, i.p.). MicroCT analysis showed progressive bone loss from week 2 to week 4 after Hla treatment, accompanied by a decreased osteoblasts and increased osteoclasts in femoral metaphysis in mice. Further, Hla stimulated the expression of Caveolin-1 in vivo and in vitro, activated lipid rafts accumulation in cell membrane of bone marrow stromal cells (BMSCs), and suppressed osteogenesis of BMSCs. Destruction of lipid rafts with MβCD or inhibition of Caveolin-1 with Daidzein blocked the detrimental effect of Hla on osteogenesis of BMSCs. Importantly, treating mice with MβCD rescued the loss of osteoblasts and increased osteoclastogenesis induced by Hla as well as the bone loss induced by S. aureus infection. Together, we demonstrate that Hla induces bone destruction directly by suppressing osteogenesis and indirectly by stimulating osteoclastogenesis, and that lipid rafts may mediate the detrimental effect of Hla and S. aureus on osteogenesis and bone formation.

Pathological and microbiological impact of a gentamicin-loaded biocomposite following limited or extensive debridement in a porcine model of osteomyelitis

Aims

CERAMENT|G is an absorbable gentamicin-loaded biocomposite used as an on-site vehicle of antimicrobials for the treatment of chronic osteomyelitis. The purpose of the present study was to investigate the sole effect of CERAMENT|G, i.e. without additional systemic antimicrobial therapy, in relation to a limited or extensive debridement of osteomyelitis lesions in a porcine model.

Methods

Osteomyelitis was induced in nine pigs by inoculation of 10⁴ colony-forming units (CFUs) of Staphylococcus aureus into a drill hole in the right tibia. After one week, the pigs were allocated into three groups. Group A (n = 3) received no treatment during the study period (19 days). Groups B (n = 3) and C (n = 3) received limited or extensive debridement seven days postinoculation, respectively, followed by injection of CERAMENT|G into the bone voids. The pigs were euthanized ten (Group C) and 12 (Group B) days after the intervention.

Results

All animals presented confirmatory signs of bone infection post-mortem. The estimated amount of inflammation was substantially greater in Groups A and B compared to Group C. In both Groups B and C, peptide nucleic acid fluorescence in situ hybridization (PNA FISH) of CERAMENT|G and surrounding bone tissue revealed bacteria embedded in an opaque matrix, i.e. within biofilm. In addition, in Group C, the maximal measured post-mortem gentamicin concentrations in CERAMENT|G and surrounding bone tissue samples were 16.6 μg/ml and 6.2 μg/ml, respectively.

Conclusion

The present study demonstrates that CERAMENT|G cannot be used as a standalone alternative to extensive debridement or be used without the addition of systemic antimicrobials.

Cite this article: Bone Joint Res 2020;9(7):394–401.

Functional State of Mesenchymal Stem Cells upon Exposure to Bioactive Coatings on Titanium Alloys

Bioactive coatings on implants affect osteogenic differentiation of mesenchymal stem cells (MSC). We studied the morphofunctional state of bone marrow MSC cultured on the surface of calcium phosphate coatings on titanium formed by plasma electrolytic oxidation (PEO). The biocompatible properties of the coatings manifested in the absence of the cytotoxic effect on cells. High expression of receptors (CD90, CD29, and CD106), enhanced synthesis of osteocalcin and osteopontin, and changes in surface architectonics of MSC adherent to the samples confirmed osteoinductive properties of the calcium phosphate PEO coating.

Dense cancellous bone as evidenced by a high HU value is predictive of late implant failure: a preliminary study

OBJECTIVES

The mechanism of late implant failure is unclear. This study examined the association between sclerosing cancellous bone images and the risk of late implant failures using multi-detector row computed tomography (CT) imaging data.

METHODS

We performed a case-control study. The study group consisted of consecutive patients with implant failures treated at Kyushu Dental University between 2001 and 2016. CT data for late failure of 36 implants in 16 patients were available. The study cohort consisted of 16 patients with 36 late failed implants and 28 patients with 113 successful implants.

RESULTS

The mean survival rate was 6.9 months for early implant failure, 76.6 months for late failure with marginal bone resorption, inflammation symptoms, and so-called peri-implantitis, and 95.0 months for late failure caused by implant fracture. The mean HU value for cases in the control group was 507 compared with 1231 for cases with late failure implants. Logistic regression was used for analysis. There were signs of high radiodensity of peri-implant cancellous bone when comparing adjusted radiodensity per 100 HU using CT data (OR 2.35; 95% CI 1.73-3.20; p < 0.001).

CONCLUSIONS

Within the limits of our study, the presence of high radiodensity and cancellous bone consolidation on imaging may be related to risk factors for late implant failure. Therefore, CT images of the host cancellous bone status for observation of visible sclerosis could be a useful diagnostic indicator for late implant failure.

Dalbavancin for treatment of implant-related methicillin-resistant Staphylococcus aureus osteomyelitis in an experimental rat model

Dalbavancin is a new semisynthetic lipoglycopeptide with improved antimicrobial activity against various gram-positive pathogens. It demonstrates an extensive plasma half-life which permits outpatient parenteral antimicrobial therapy with weekly intervals and might therefore be an excellent treatment alternative for patients requiring prolonged antimicrobial therapy. The present study investigated dalbavancin monotherapy in an experimental implant-related methicillin-resistant Staphylococcus aureus (MRSA) osteomyelitis model. A clinical MRSA isolate and a Kirschner-wire were inserted into the proximal tibia of anaesthetized Sprague-Dawley rats. Four weeks after infection 34 animals were treated over 4 weeks with either dalbavancin (20 mg/kg loading-dose; 10 mg/kg daily), vancomycin (50 mg/kg twice daily) or left untreated. Twenty-four hours after the last treatment dose tibial bones and Kirschner-wires were harvested for microbiological examination. Based on quantitative bacterial cultures of osseous tissue, dalbavancin was as effective as vancomycin and both were superior to no treatment. No emergence of an induced glycopeptide-/lipoglycopeptide- resistance was observed after a treatment period of four weeks with either dalbavancin or vancomycin. In conclusion, monotherapy with dalbavancin was shown to be as effective as vancomycin for treatment of experimental implant-related MRSA osteomyelitis in rats, but both antimicrobials demonstrated only limited efficacy. Further studies are warranted to evaluate the clinical efficacy of dalbavancin for the treatment of periprosthetic S. aureus infections.

Serratiopeptidase reduces the invasion of osteoblasts by Staphylococcus aureus

Finding new strategies to counteract periprosthetic infection and implant failure is a main target in orthopedics. Staphylococcus aureus, the leading etiologic agent of orthopedic implant infections, is able to enter and kill osteoblasts, to stimulate pro-inflammatory chemokine secretion, to recruit osteoclasts, and to cause inflammatory osteolysis. Moreover, by entering eukaryotic cells, staphylococci hide from the host immune defenses and shelter from the extracellular antibiotics. Thus, infection persists, inflammation thrives, and a highly destructive osteomyelitis occurs around the implant. The ability of serratiopeptidase (SPEP), a metalloprotease by Serratia marcescens, to control S. aureus invasion of osteoblastic MG-63 cells and pro-inflammatory chemokine MCP-1 secretion was evaluated. Human osteoblast cells were infected with staphylococcal strains in the presence and in the absence of SPEP. Cell proliferation and cell viability were also evaluated. The release of pro-inflammatory chemokine MCP-1 was evaluated after the exposure of the osteoblast cells to staphylococcal strains. The significance of the differences in the results of each test and the relative control values was determined with Student's t-test. SPEP impairs their invasiveness into osteoblasts, without affecting the viability and proliferation of bone cells, and tones down their production of MCP-1. We recognize SPEP as a potential tool against S. aureus bone infection and destruction.

Detection of Bacteria Colonizing Titanium Spinal Implants in Children

BACKGROUND

Bacterial colonization of spinal implants may cause severe complications in patients with early-onset scoliosis. Correct diagnosis and detection of microbiologic formation is crucial to prevent delayed infections caused by bacterial colonization. The purposes of this study were to estimate the rate and risk factors of colonization of vertical expandable prosthetic titanium rib (VEPTR) implants in children and to compare the different methods for detecting microbiologic formation on the spinal implants.

METHODS

We evaluated prospectively a group of 42 children with spinal deformities with an overall of 95 lengthening surgeries and applied different methods to detect potential bacterial colonization of VEPTR implants: swab of the implant, swab with culture of tissue, analysis of the removed lock, polymerase chain reaction (PCR), and confocal microscopy. Potential risk factors were evaluated.

RESULTS

Of 42 patients, 17 (40%) were rated positive for bacterial colonization with Propionibacterium acnes and coagulase-negative staphylococci being the most commonly found bacteria. Risk factors for colonization were increasing age, body height, and weight. The swab with culture of removed tissue yielded most positive results, whereas direct microscopy and PCR were the least sensitive detection methods. Furthermore, commonly used infectious blood parameters were inconclusive.

CONCLUSIONS

Although the impact of bacterial colonized implants on the health of the patients is not fully elucidated, clinicians aim for prevention of microbiologic formation on implanted devices. Therefore, reliable, inexpensive, and easy to apply diagnostic tools are indispensable to detect colonization. Based on our data, the swab together with tissue culture has the potential to become the method of choice for future diagnosis.

Staphylococcal biofilm gene expression on biomaterials - A methodological study

The combination of increased healthcare access, universal aging, and infallible therapy demands, synergistically drive the need for the development of biomaterial technologies that mitigate the challenge of biomaterial-associated infections (BAI). Staphylococcus epidermidis and Staphylococcus aureus account for the majority of BAI due to their ability to accumulate in adherent multilayered biofilm. This investigation details the development of gene expression assays to evaluate the genetic processes of attachment, accumulation, maturation, and dispersal phases of biofilms on biomaterials in vitro, while abiding by the Minimum Information for Publication of Quantitative Real-Time PCR Experiments (MIQE) guidelines. The biofilm formation of S. epidermidis on polyurethane (PU) central venous catheters and S. aureus on machined titanium (Ti) was examined in terms of gene expression at early and late time points. The results provided insight into how each stage of biofilm formation is orchestrated over time on these biomaterials in vitro. Furthermore, the results suggested that mechanical RNA extraction, organic solvents, elimination of genomic DNA, and preamplification are advisable strategies to implement for biofilm gene expression analysis. It is concluded that this method can be employed for the assessment of biofilm-biomaterial interactions at the molecular level. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 3400-3412, 2017.

Monocyclic β-lactams loaded on hydroxyapatite: new biomaterials with enhanced antibacterial activity against resistant strains

The development of biomaterials able to act against a wide range of bacteria, including antibiotic resistant bacteria, is of great importance since bacterial colonization is one of the main causes of implant failure. In this work, we explored the possibility to functionalize hydroxyapatite (HA) nanocrystals with some monocyclic N-thio-substituted β-lactams. To this aim, a series of non-polar azetidinones have been synthesized and characterized. The amount of azetidinones loaded on HA could be properly controlled on changing the polarity of the loading solution and it can reach values up to 17 wt%. Data on cumulative release in aqueous solution show different trends which can be related to the lipophilicity of the molecules and can be modulated by suitable groups on the azetidinone. The examined β-lactams-HA composites display good antibacterial activity against reference Gram-positive and Gram-negative bacteria. However, the results of citotoxicity and antibacterial tests indicate that HA loaded with 4-acetoxy-1-(methylthio)-azetidin-2-one displays the best performance. In fact, this material strongly inhibited the bacterial growth of both methicillin resistant and methicillin susceptible clinical isolates of S. aureus from surgical bone biopsies, showing to be a very good candidate as a new functional biomaterial with enhanced antibacterial activity.

[Effect of staphylococcal lipoteichoic acid on differentiation of RAW264.7 cells into osteoclasts]

Objective

To investigate the effect of staphylococcal lipoteichoic acid (LTA-sa) on RAW264.7 cells differentiation into osteoclasts.

Methods

RAW264.7 cells were cultured with LTA-sa of 100 ng/mL (group A), LTA-sa of 200 ng/mL (group B), LTA-sa of 400 ng/mL (group C), receptor activator of nuclear factor κB (NF-κB) ligand (RANKL) of 100 ng/mL as positive control (group D), and equal volume of PBS as blank control (group E) respectively for 5 days. And then, tartrate resistant acid phosphatase staining (TRAP) was used to detect the formation of osteoclast-like cells, Image-Pro Plus 6.0 software to measure the areas of bone resorption pits in Corning Osteo Assay Surface (COAS) wells, and MTT assay to observe the proliferation activity of RAW264.7 cells in group A, B, C, and E.

Results

After cultured for 5 days, the formation of osteoclast-like cells and bone resorption pits were observed in all groups. The number of osteoclast-like cells and the area of bone resorption pits in groups A, B, C, and D were more than those in group E. And with the increased concentration of LTA-sa, the indexes in groups A, B, and C increased gradually, but were lower than those in group D, and differences were significant between groups ( P<0.05). At 5 days after culture, there was no significant difference in absorbance value among the experimental groups (groups A, B, C, and E) ( P>0.05).

Conclusion

LTA-sa has promoting effect on RAW264.7 cells differentiation into osteoclasts.

Fosfomycin Addition to Poly(D,L-Lactide) Coating Does Not Affect Prophylaxis Efficacy in Rat Implant-Related Infection Model, But That of Gentamicin Does

Gentamicin is the preferred antimicrobial agent used in implant coating for the prevention of implant-related infections (IRI). However, the present heavy local and systemic administration of gentamicin can lead to increased resistance, which has made its future use uncertain, together with related preventive technologies. Fosfomycin is an alternative antimicrobial agent that lacks the cross-resistance presented by other classes of antibiotics. We evaluated the efficacy of prophylaxis of 10% fosfomycin-containing poly(D,L-lactide) (PDL) coated K-wires in a rat IRI model and compared it with uncoated (Control 1), PDL-coated (Control 2), and 10% gentamicin-containing PDL-coated groups with a single layer of coating. Stainless steel K-wires were implanted and methicillin-resistant Staphylococcus aureus (ATCC 43300) suspensions (103 CFU/10 μl) were injected into a cavity in the left tibiae. Thereafter, K-wires were removed and cultured in tryptic soy broth and then 5% sheep blood agar mediums. Sliced sections were removed from the tibiae, stained with hematoxylin-eosin, and semi-quantitatively evaluated with X-rays. The addition of fosfomycin into PDL did not affect the X-ray and histopathological evaluation scores; however, the addition of gentamicin lowered them. The addition of gentamicin showed a protective effect after the 28th day of X-ray evaluations. PDL-only coating provided no protection, while adding fosfomycin to PDL offered a 20% level protection and adding gentamicin offered 80%. Furthermore, there were 103 CFU level growths in the gentamicin-added group, while the other groups had 105. Thus, the addition of fosfomycin to PDL does not affect the efficacy of prophylaxis, but the addition of gentamicin does. We therefore do not advise the use of fosfomycin as a single antimicrobial agent in coating for IRI prophylaxis.

Retention of the well-fixed implant in the single-stage exchange for chronic infected total hip arthroplasty: an average of five years of follow-up

PURPOSE

Removal of an infected prosthesis was considered the gold standard for eradication of infection. However, removal of well-fixed components can result in structural bone damage and compromised reconstruction. In these situations we questioned whether the infection after the total hip arthroplasty could be treated effectively and retain the well-fixed implant in a single-stage exchange.

METHODS

A retrospective analysis which included 31 patients with chronic infected THA who underwent major partial single-stage revision, including routinely exchanged femoral head and liner components, aggressive soft tissue debridement, removal of the femoral stem or acetabular cup and retention of the well-fixed component, thorough exposed component brushing, and adequate surgical soaking. Powdered Vancomycin was poured into the surgical area and the infection control rate and clinical outcomes were evaluated. The failure to treat the infection was defined as a recurrence of infection in the same hip. The average follow-up was five years (2-15 years).

RESULT

There were four (12.9 %) failures during the study period at an average of 15 months (9-21 months) after partial single-stage revision. Of the 31 patients, 27 (87.1 %) patients had a satisfactory outcome and required no additional surgical or medical treatment for recurrence of infection. Acetabular cups were revised in 22 patients and femoral stems in nine patients. The mean post-operative Harris hip score at the most recent assessment was 74.6 (68-82).

CONCLUSIONS

Treatment of chronic infected THA with retention of the well-fixed implant in a single-stage exchange can be fairly effective in the treatment of infection and achieving acceptable functional outcomes, which indicated that this may be an attractive alternative in highly selected patients.

LEVEL OF EVIDENCE

Level IV, therapeutic study.

A Novel Nanosilver/Nanosilica Hydrogel for Bone Regeneration in Infected Bone Defects

Treating bone defects in the presence of infection is a formidable clinical challenge. The use of a biomaterial with the dual function of bone regeneration and infection control is a novel therapeutic approach to this problem. In this study, we fabricated an innovative, dual-function biocomposite hydrogel containing nanosilver and nanosilica (nAg/nSiO2) particles and evaluated its characteristics using FT-IR, SEM, swelling ratio, and stiffness assays. The in vitro antibacterial analysis showed that this nAg/nSiO2 hydrogel inhibited both Gram-positive and Gram-negative bacteria. In addition, this nontoxic material could promote osteogenic differentiation of rat bone marrow stromal cells (BMSCs). We then created infected bone defects in rat calvaria in order to evaluate the function of the hydrogel in vivo. The hydrogel demonstrated effective antibacterial ability while promoting bone regeneration in these defects. Our results indicate that this nAg/nSiO2 hydrogel has the potential to both control infection and to promote bone healing in contaminated defects.

Antimicrobial activity of four cationic peptides immobilised to poly-hydroxyethylmethacrylate

The objective of this study was to immobilise and characterise a variety of antimicrobial peptides (AMPs) onto poly-hydroxyethylmethacrylate (pHEMA) surfaces to achieve an antibacterial effect. Four AMPs, viz. LL-37, melimine, lactoferricin and Mel-4 were immobilised on pHEMA by 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) which assisted covalent attachment. Increasing concentrations of AMPs were immobilised to determine the effect on the adhesion of Pseudomonas aeruginosa and Staphylococcus aureus. The AMP immobilised pHEMAs were characterised by X-ray photoelectron spectroscopy (XPS) to determine the surface elemental composition and by amino acid analysis to determine the total amount of AMP attached. In vitro cytotoxicity of the immobilised pHEMA samples to mouse L929 cells was investigated. Melimine and Mel-4 when immobilised at the highest concentrations showed 3.1 ± 0.6 log and 1.3 ± 0.2 log inhibition against P. aeruginosa, and 3.9 ± 0.6 log and 2.4 ± 0.5 log inhibition against S. aureus, respectively. Immobilisation of LL-37 resulted in up to 2.6 ± 1.0 log inhibition against only P. aeruginosa, but no activity against S. aureus. LFc attachment showed no antibacterial activity. Upon XPS analysis, immobilised melimine, LL-37, LFc and Mel-4 had 1.57 ± 0.38%, 1.13 ± 1.36%, 0.66 ± 0.47% and 0.73 ± 0.32% amide nitrogen attached to pHEMA compared to 0.12 ± 0.14% in the untreated controls. Amino acid analysis determined that the total amount of AMP attachment to pHEMA was 44.3 ± 7.4 nmol, 3.8 ± 0.2 nmol, 6.5 ± 0.6 nmol and 48.9 ± 2.3 nmol for the same peptides respectively. None of the AMP immobilised pHEMA surfaces showed any toxicity towards mouse L929 cells. The immobilisation of certain AMPs at nanomolar concentration to pHEMA is an effective option to develop a stable antimicrobial surface.

Staphylokinase and ABO group phenotype: new players in Staphylococcus aureus implant-associated infections development

Aim: To identify bacterial and/or clinical features involved in the pathogenesis of Staphylococcus aureus implant-associated infections (IAI). Materials & methods: In total, 57 IAI S. aureus and 31 nasal carriage (NC) S. aureus isolates were studied. Staphylococcus aureus genetic background was obtained by microarray analysis. Multilocus sequence typing was performed to determine clonal complexes (CC). Biofilm production was investigated by resazurin and crystal violet methods. Results: Staphylokinase gene was associated with the occurrence of S. aureus IAI. Patients’ ABO blood group phenotype was associated with IAI S. aureus genetic background. CC8 S. aureus strains produce more biofilm than others and carry particular alleles of bbp gene. Conclusion: This study identifies some predictive markers for S. aureus IAI.

Immunomodulatory Peptide IDR-1018 Decreases Implant Infection and Preserves Osseointegration

BACKGROUND

Innate defense regulator peptide-1018 (IDR-1018) is a 12-amino acid, synthetic, immunomodulatory host defense peptide that can reduce soft tissue infections and is less likely to induce bacterial resistance than conventional antibiotics. However, IDRs have not been tested on orthopaedic infections and the immunomodulatory effects of IDR-1018 have only been characterized in response to lipopolysacharide, which is exclusively produced by Gram-negative bacteria.

QUESTIONS/PURPOSES

We sought (1) to more fully characterize the immunomodulatory effects of IDR-1018, especially in response to Staphylococcus aureus; and (2) to determine whether IDR-1018 decreases S aureus infection of orthopaedic implants in mice and thereby protects the implants from failure to osseointegrate.

METHODS

In vitro effects of IDR-1018 on S aureus were assessed by determining minimum inhibitory concentrations in bacterial broth without and with supplementation of physiologic ion levels. In vitro effects of IDR-1018 on macrophages were determined by measuring production of monocyte chemoattractant protein-1 (MCP-1) and proinflammatory cytokines by enzyme-linked immunosorbent assay. In vivo effects of IDR-1018 were determined in a murine model of S aureus implant infection by quantitating bacterial burden, macrophage recruitment, MCP-1, proinflammatory cytokines, and osseointegration in nine mice per group on Day 1 postimplantation and 20 mice per group on Day 15 postimplantation.

RESULTS

IDR-1018 demonstrated antimicrobial activity by directly killing S aureus even in the presence of physiologic ion levels, increasing recruitment of macrophages to the site of infections by 40% (p = 0.036) and accelerating S aureus clearance in vivo (p = 0.008) with a 2.6-fold decrease in bacterial bioburden on Day 7 postimplantation. In vitro immunomodulatory activity of IDR-1018 included inducing production of MCP-1 in the absence of other inflammatory stimuli and to potently blunt excess production of proinflammatory cytokines and MCP-1 induced by lipopolysaccharide. Higher concentrations of IDR-1018 were required to blunt production of proinflammatory cytokines and MCP-1 in the presence S aureus. The largest in vivo immunomodulatory effect of IDR-1018 was to reduce tumor necrosis factor-α levels induced by S aureus by 60% (p = 0.006). Most importantly, IDR-1018 reduced S aureus-induced failures of osseointegration by threefold (p = 0.022) and increased osseointegration as measured by ultimate force (5.4-fold, p = 0.033) and average stiffness (4.3-fold, p = 0.049).

CONCLUSIONS

IDR-1018 is potentially useful to reduce orthopaedic infections by directly killing bacteria and by recruiting macrophages to the infection site.

CLINICAL RELEVANCE

These findings make IDR-1018 an attractive candidate to explore in larger animal models to ascertain whether its effects in our in vitro and mouse experiments can be replicated in more clinically relevant settings.

Bacterial adherence and biofilm formation on medical implants: a review

Biofilms are a complex group of microbial cells that adhere to the exopolysaccharide matrix present on the surface of medical devices. Biofilm-associated infections in the medical devices pose a serious problem to the public health and adversely affect the function of the device. Medical implants used in oral and orthopedic surgery are fabricated using alloys such as stainless steel and titanium. The biological behavior, such as osseointegration and its antibacterial activity, essentially depends on both the chemical composition and the morphology of the surface of the device. Surface treatment of medical implants by various physical and chemical techniques are attempted in order to improve their surface properties so as to facilitate bio-integration and prevent bacterial adhesion. The potential source of infection of the surrounding tissue and antimicrobial strategies are from bacteria adherent to or in a biofilm on the implant which should prevent both biofilm formation and tissue colonization. This article provides an overview of bacterial biofilm formation and methods adopted for the inhibition of bacterial adhesion on medical implants.

Contribution of Reduced Interleukin-10 Levels to the Pathogenesis of Osteomyelitis in Children with Sickle Cell Disease

Osteomyelitis is a significant complication of sickle cell disease (SCD), and several factors contribute to its pathogenesis, including altered expression of proinflammatory and anti-inflammatory cytokines. In view of the role of interleukin-10 (IL-10) as an anti-inflammatory cytokine, we tested the notion that SCD osteomyelitis is associated with a reduction in IL-10 secretion and, hence, precipitation of a proinflammatory state. Study subjects comprised 52 SCD patients with confirmed diagnosis of osteomyelitis and 165 age- and gender-matched SCD patients with negative histories of osteomyelitis. Results obtained showed that IL-10 serum levels in SCD osteomyelitis patients were significantly lower than those of control SCD patients. Receiver operating characteristic (ROC) analysis demonstrated that altered IL-10 serum levels predicted the development of osteomyelitis, and the mean area under ROC curves of IL-10 was 0.810 among SCD patients with osteomyelitis. A systematic shift in IL-10 serum levels toward lower values was seen in osteomyelitis cases, with an increased osteomyelitis risk associated with decreased IL-10 levels. Multivariate logistic regression analyses confirmed the independent association of reduced IL-10 with osteomyelitis after controlling for sickle hemoglobin (HbS), fetal hemoglobin (HbF), platelet count, and white blood cell (WBC) count. These data support the strong association of decreased IL-10 levels with osteomyelitis, thereby supporting a role for IL-10 in osteomyelitis follow-up.

In Vivo MicroCT Monitoring of Osteomyelitis in a Rat Model

Infection associated with orthopedic implants often results in bone loss and requires surgical removal of the implant. The aim of this study was to evaluate morphological changes of bone adjacent to a bacteria-colonized implant, with the aim of identifying temporal patterns that are characteristic of infection. In an in vivo study with rats, bone changes were assessed using in vivo microCT at 7 time points during a one-month postoperative period. The rats received either a sterile or Staphylococcus aureus-colonized polyetheretherketone screw in the tibia. Bone-implant contact, bone fraction, and bone changes (quiescent, resorbed, and new bone) were calculated from consecutive scans and validated against histomorphometry. The screw pullout strength was estimated from FE models and the results were validated against mechanical testing. In the sterile group, bone-implant contact, bone fraction, and mechanical fixation increased steadily until day 14 and then plateaued. In the infected group, they decreased rapidly. Bone formation was reduced while resorption was increased, with maximum effects observed within 6 days. In summary, the model presented is capable of evaluating the patterns of bone changes due to implant-related infections. The combined use of longitudinal in vivo microCT imaging and image-based finite element analysis provides characteristic signs of infection within 6 days.

Staphylococcus epidermidis serine--aspartate repeat protein G (SdrG) binds to osteoblast integrin alpha V beta 3

Staphylococcus epidermidis is the leading etiologic agent of orthopaedic implant infection. Contamination of the implanted device during insertion allows bacteria gain entry into the sterile bone environment leading to condition known as osteomyelitis. Osteomyelitis is characterised by weakened bones associated with progressive bone loss. The mechanism through which S. epidermidis interacts with bone cells to cause osteomyelitis is poorly understood. We demonstrate here that S. epidermidis can bind to osteoblasts in the absence of matrix proteins. S. epidermidis strains lacking the cell wall protein SdrG had a significantly reduced ability to bind to osteoblasts. Consistent with this, expression of SdrG in Lactococcus lactis resulted in significantly increased binding to the osteoblasts. Protein analysis identified that SdrG contains a potential integrin recognition motif. αVβ3 is a major integrin expressed on osteoblasts and typically recognises RGD motifs in its ligands. Our results demonstrate that S. epidermidis binds to recombinant purified αVβ3, and that a mutant lacking SdrG failed to bind. Blocking αVβ3 on osteoblasts significantly reduced binding to S. epidermidis. These studies are the first to identify a mechanism through which S. epidermidis binds to osteoblasts and potentially offers a mechanism through which implant infection caused by S. epidermidis leads to osteomyelitis.

Nanostructured platforms for the sustained and local delivery of antibiotics in the treatment of osteomyelitis

This article provides a critical view of the current state of the development of nanoparticulate and other solid-state carriers for the local delivery of antibiotics in the treatment of osteomyelitis. Mentioned are the downsides of traditional means for treating bone infection, which involve systemic administration of antibiotics and surgical debridement, along with the rather imperfect local delivery options currently available in the clinic. Envisaged are more sophisticated carriers for the local and sustained delivery of antimicrobials, including bioresorbable polymeric, collagenous, liquid crystalline, and bioglass- and nanotube-based carriers, as well as those composed of calcium phosphate, the mineral component of bone and teeth. A special emphasis is placed on composite multifunctional antibiotic carriers of a nanoparticulate nature and on their ability to induce osteogenesis of hard tissues demineralized due to disease. An ideal carrier of this type would prevent the long-term, repetitive, and systemic administration of antibiotics and either minimize or completely eliminate the need for surgical debridement of necrotic tissue. Potential problems faced by even hypothetically "perfect" antibiotic delivery vehicles are mentioned too, including (i) intracellular bacterial colonies involved in recurrent, chronic osteomyelitis; (ii) the need for mechanical and release properties to be adjusted to the area of surgical placement; (iii) different environments in which in vitro and in vivo testings are carried out; (iv) unpredictable synergies between drug delivery system components; and (v) experimental sensitivity issues entailing the increasing subtlety of the design of nanoplatforms for the controlled delivery of therapeutics.

Biofilm-based implant infections in orthopaedics

The demand for joint replacement surgery is continuously increasing with rising costs for hospitals and healthcare systems. Staphylococci are the most prevalent etiological agents of orthopedic infections. After an initial adhesin-mediated implant colonization, Staphylococcus aureus and Staphylococcus epidermidis produce biofilm. Biofilm formation proceeds as a four-step process: (1) initial attachment of bacterial cells; (2) cell aggregation and accumulation in multiple cell layers; (3) biofilm maturation and (4) detachment of cells from the biofilm into a planktonic state to initiate a new cycle of biofilm formation elsewhere. The encasing of bacteria in biofilms gives rise to insuperable difficulties not only in the treatment of the infection, but also in assessing the state and the nature of the infection using traditional cultural methods. Therefore, DNA-based molecular methods have been developed to provide rapid identification of all microbial pathogens. To combat biofilm-centered implant infections, new strategies are being developed, among which anti-infective or infective-resistant materials are at the forefront. Infection-resistant materials can be based on different approaches: (i) modifying the biomaterial surface to give anti-adhesive properties, (ii) doping the material with antimicrobial substances, (iii) combining anti-adhesive and antimicrobial effects in the same coating, (iv) designing materials able to oppose biofilm formation and support bone repair.

Lysostaphin-coated titan-implants preventing localized osteitis by Staphylococcus aureus in a mouse model

The increasing incidence of implant-associated infections induced by Staphylococcus aureus (SA) in combination with growing resistance to conventional antibiotics requires novel therapeutic strategies. In the current study we present the first application of the biofilm-penetrating antimicrobial peptide lysostaphin in the context of bone infections. In a standardized implant-associated bone infection model in mice beta-irradiated lysostaphin-coated titanium plates were compared with uncoated plates. Coating of the implant was established with a poly(D,L)-lactide matrix (PDLLA) comprising lysostaphin formulated in a stabilizing and protecting solution (SPS). All mice were osteotomized and infected with a defined count of SA. Fractures were fixed with lysostaphin-coated locking plates. Plates uncoated or PDLLA-coated served as controls. All mice underwent debridement and lavage on Days 7, 14, 28 to determine the bacterial load and local immune reaction. Fracture healing was quantified by conventional radiography. On Day 7 bacterial growth in the lavages of mice with lysostaphin-coated plates showed a significantly lower count to the control groups. Moreover, in the lysostaphin-coated plate groups complete fracture healing were observed on Day 28. The fracture consolidation was accompanied by a diminished local immune reaction. However, control groups developed an osteitis with lysis or destruction of the bone and an evident local immune response. The presented approach of terminally sterilized lysostaphin-coated implants appears to be a promising therapeutic approach for low grade infection or as prophylactic strategy in high risk fracture care e.g. after severe open fractures.

The interaction of bacteria with engineered nanostructured polymeric materials: a review

Bacterial infections are a leading cause of morbidity and mortality worldwide. In spite of great advances in biomaterials research and development, a significant proportion of medical devices undergo bacterial colonization and become the target of an implant-related infection. We present a review of the two major classes of antibacterial nanostructured materials: polymeric nanocomposites and surface-engineered materials. The paper describes antibacterial effects due to the induced material properties, along with the principles of bacterial adhesion and the biofilm formation process. Methods for antimicrobial modifications of polymers using a nanocomposite approach as well as surface modification procedures are surveyed and discussed, followed by a concise examination of techniques used in estimating bacteria/material interactions. Finally, we present an outline of future sceneries and perspectives on antibacterial applications of nanostructured materials to resist or counteract implant infections.

Silver deposition on titanium surface by electrochemical anodizing process reduces bacterial adhesion of Streptococcus sanguinis and Lactobacillus salivarius

OBJECTIVES

The aim of this study was to determine the antibacterial properties of silver-doped titanium surfaces prepared with a novel electrochemical anodizing process.

MATERIAL AND METHODS

Titanium samples were anodized with a pulsed process in a solution of silver nitrate and sodium thiosulphate at room temperature with stirring. Samples were processed with different electrolyte concentrations and treatment cycles to improve silver deposition. Physicochemical properties were determined by X-ray photoelectron spectroscopy, contact angle measurements, white-light interferometry, and scanning electron microscopy. Cellular cytotoxicity in human fibroblasts was studied with lactate dehydrogenase assays. The in vitro effect of treated surfaces on two oral bacteria strains (Streptococcus sanguinis and Lactobacillus salivarius) was studied with viable bacterial adhesion measurements and growth curve assays. Nonparametric statistical Kruskal-Wallis and Mann-Whitney U-tests were used for multiple and paired comparisons, respectively. Post hoc Spearman's correlation tests were calculated to check the dependence between bacteria adhesion and surface properties.

RESULTS

X-ray photoelectron spectroscopy results confirmed the presence of silver on treated samples and showed that treatments with higher silver nitrate concentration and more cycles increased the silver deposition on titanium surface. No negative effects in fibroblast cell viability were detected and a significant reduction on bacterial adhesion in vitro was achieved in silver-treated samples compared with control titanium.

CONCLUSIONS

Silver deposition on titanium with a novel electrochemical anodizing process produced surfaces with significant antibacterial properties in vitro without negative effects on cell viability.

Cutaneous Immune Defenses Against Staphylococcus aureus Infections

Staphylococcus aureus (S. aureus) is a virulent bacterium that abundantly colonizes inflammatory skin diseases. Since S. aureus infections occur in an impaired skin barrier, it is important to understand the protective mechanism through cutaneous immune responses against S. aureus infections and the interaction with Staphylococcal virulence factors. In this review, we summarize not only the pathogenesis and key elements of S. aureus skin infections, but also the cutaneous immune system against its infections and colonization. The information obtained from this area may provide the groundwork for further immunomodulatory therapies or vaccination strategies to prevent S. aureus infections.

Efficacy of antibacterial-loaded coating in an in vivo model of acutely highly contaminated implant

Purpose

The purpose of this study was to test the ability of DAC®, a fast resorbable, antibacterial-loaded hydrogel coating, to prevent acute bacterial colonization in an in vivo model of an intra-operatively highly contaminated implant.

Methods

A histocompatibility study was performed in 10 adult New Zealand rabbits. Then, methicillin-resistant Staph. aureus were inoculated in the femur of 30 adult New Zealand rabbits at the time of intra-medullary nailing; vancomycin-loaded DAC® coated nails were compared to controls regarding local and systemic infection development.

Results

Histocompatibility study showed no detrimental effect of DAC® hydrogel on bone tissue after 12 weeks from implant. After seven days from implant, none of the rabbits receiving vancomycin-loaded DAC® nail showed positive blood cultures, compared to all the controls; vancomycin-loaded DAC® coating was associated with local bacterial load reduction ranging from 72 to 99 %, compared to controls.

Conclusions

Vancomycin-loaded DAC® coating is able to significantly reduce bacterial colonization in an animal model of an intra-operatively highly contaminated implant, without local or general side effect.

A rabbit osteomyelitis model for the longitudinal assessment of early post-operative implant infections

BACKGROUND

Implant infection is one of the most severe complications within the field of orthopaedic surgery, associated with an enormous burden for the healthcare system. During the last decades, attempts have been made to lower the incidence of implant-related infections. In the case of cemented prostheses, the use of antibiotic-containing bone cement can be effective. However, in the case of non-cemented prostheses, osteosynthesis and spinal surgery, local antibacterial prophylaxis is not a standard procedure. For the development of implant coatings with antibacterial properties, there is a need for a reliable animal model to evaluate the preventive capacity of such coatings during a specific period of time. Existing animal models generally present a limited follow-up, with a limited number of outcome parameters and relatively large animal numbers in multiple groups.

METHODS

To represent an early post-operative implant infection, we established an acute tibial intramedullary nail infection model in rabbits by contamination of the tibial nail with 3.8 × 10⁵ colony forming units of Staphylococcus aureus. Clinical, haematological and radiological parameters for infection were weekly assessed during a 6-week follow-up with post-mortem bacteriological and histological analyses.

RESULTS

S. aureus implant infection was confirmed by the above parameters. A saline control group did not develop osteomyelitis. By combining the clinical, haematological, radiological, bacteriological and histological data collected during the experimental follow-up, we were able to differentiate between the control and the infected condition and assess the severity of the infection at sequential timepoints in a parameter-dependent fashion.

CONCLUSION

We herein present an acute early post-operative rabbit implant infection model which, in contrast to previously published models, combines improved in-time insight into the development of an implant osteomyelitis with a relatively low amount of animals.

An overview of the methodological approach to the in vitro study of anti-infective biomaterials

Biomaterial-associated infections have an enormous impact in terms of morbidity of the patients and costs to national health systems. Perioperative antibiotics and aseptic procedures have not proved sufficient to eradicate the occurrence of this type of infections which often lead to devastating effects. Adjunctive strategies for preventing the establishment of infections are increasingly being centered on the development of new biomaterials with anti-infective properties. The creation of new anti-infective biomaterials can be obtained by alternative approaches oriented to achieve either bacteria-repellent surfaces or bioactive surfaces expressing self-sterilizing properties when not even able to treat pre-existing infections in the surrounding tissues. Here, we offer a short overview of the currently available in vitro methods that can be used to investigate and assess the performance of anti-infective biomaterials, with special emphasis on those whose mechanism of action is based on bacteria-repellent surfaces.

Osteogenic and antimicrobial nanoparticulate calcium phosphate and poly-(D,L-lactide-co-glycolide) powders for the treatment of osteomyelitis

Development of a material for simultaneous sustained and localized delivery of antibiotics and induction of spontaneous regeneration of hard tissues affected by osteomyelitis stands for an important clinical need. In this work, a comparative analysis of the bacterial and osteoblastic cell response to two different nanoparticulate carriers of clindamycin, an antibiotic commonly prescribed in the treatment of bone infection, one composed of calcium phosphate and the other comprising poly-(D,L-lactide-co-glycolide)-coated calcium phosphate, was carried out. Three different non-cytotoxic phases of calcium phosphate, exhibiting dissolution and drug release profiles in the range of one week to two months to one year, respectively, were included in the analysis: monetite, amorphous calcium phosphate and hydroxyapatite. Spherical morphologies and narrow size distribution of both types of nanopowders were confirmed in transmission and scanning electron microscopic analyses. The antibiotic-containing powders exhibited sustained drug release contingent upon the degradation rate of the carrier. Assessment of the antibacterial performance of the antibiotic-encapsulated powders against Staphylococcus aureus, the most common pathogen isolated from infected bone, yielded satisfactory results both in broths and on blood agar plates for all the analyzed powders. In contrast, no cytotoxic behavior was detected upon the incubation of the antibiotic powders with the osteoblastic MC3T3-E1 cell line for up to three weeks. The cells were shown to engage in a close contact with the antibiotic-containing particles, irrespective of their internal or surface phase composition, polymeric or mineral. At the same time, both types of particles upregulated the expression of osteogenic markers osteocalcin, osteopontin, Runx2 and protocollagen type I, suggesting their ability to promote osteogenesis and enhance remineralization of the infected site in addition to eliminating the bacterial source of infection.

Staphylococcus aureus biofilms decrease osteoblast viability, inhibits osteogenic differentiation, and increases bone resorption in vitro

Background

Osteomyelitis is a severe and often debilitating disease characterized by inflammatory destruction of bone. Despite treatment, chronic infection often develops which is associated with increased rates of treatment failure, delayed osseous-union, and extremity amputation. Within affected bone, bacteria exist as biofilms, however the impact of biofilms on osteoblasts during disease are unknown. Herein, we evaluated the effect of S. aureus biofilms on osteoblast viability, osteogenic potential, and the expression of the pro-osteoclast factor, receptor activator of NF-kB ligand (RANK-L).

Methods

Osteoblasts were exposed to biofilm conditioned media (BCM) from clinical wound isolates of Staphylococcus aureus under normal growth and osteogenic conditions to assess cellular viability and osteoblast differentiation, respectively. Cell viability was evaluated using a live/dead assay and by quantifying total cellular DNA at days 0, 1, 3, 5, and 7. Apoptosis following treatment with BCM was measured by flow-cytometry using the annexin V-FITC/PI apoptosis kit. Osteogenic differentiation was assessed by measuring alkaline phosphatase activity and intracellular accumulation of calcium and osteocalcin for up to 21 days following exposure to BCM. Expression of genes involved in osteogenic differentiation and osteoclast regulation, were also evaluated by quantitative real-time PCR.

Results

BCM from clinical strains of S. aureus reduced osteoblast viability which was accompanied by an increase in apoptosis. Osteogenic differentiation was significantly inhibited following treatment with BCM as indicated by decreased alkaline phosphatase activity, decreased intracellular accumulation of calcium and inorganic phosphate, as well as reduced expression of transcription factors and genes involved in bone mineralization in viable cells. Importantly, exposure of osteoblasts to BCM resulted in up-regulated expression of RANK-L and increase in the RANK-L/OPG ratio compared to the untreated controls.

Conclusions

Together these studies suggest that soluble factors produced by S. aureus biofilms may contribute to bone loss during chronic osteomyelitis simultaneously by: (1) reducing osteoblast viability and osteogenic potential thereby limiting new bone growth and (2) promoting bone resorption through increased expression of RANK-L by osteoblasts. To our knowledge these are the first studies to demonstrate the impact of staphylococcal biofilms on osteoblast function, and provide an enhanced understanding of the pathogenic role of staphylococcal biofilms during osteomyelitis.

Nanomaterials and synergistic low-intensity direct current (LIDC) stimulation technology for orthopedic implantable medical devices

Nanomaterials play a significant role in biomedical research and applications because of their unique biological, mechanical, and electrical properties. In recent years, they have been utilized to improve the functionality and reliability of a wide range of implantable medical devices ranging from well-established orthopedic residual hardware devices (e.g., hip implants) that can repair defects in skeletal systems to emerging tissue engineering scaffolds that can repair or replace organ functions. This review summarizes the applications and efficacies of these nanomaterials that include synthetic or naturally occurring metals, polymers, ceramics, and composites in orthopedic implants, the largest market segment of implantable medical devices. The importance of synergistic engineering techniques that can augment or enhance the performance of nanomaterial applications in orthopedic implants is also discussed, the focus being on a low-intensity direct electric current (LIDC) stimulation technology to promote the long-term antibacterial efficacy of oligodynamic metal-based surfaces by ionization, while potentially accelerating tissue growth and osseointegration. While many nanomaterials have clearly demonstrated their ability to provide more effective implantable medical surfaces, further decisive investigations are necessary before they can translate into medically safe and commercially viable clinical applications. The article concludes with a discussion about some of the critical impending issues with the application of nanomaterials-based technologies in implantable medical devices, and potential directions to address these.

Osteomyelitis: an overview of antimicrobial therapy

Osteomyelitis is an inflammatory bone disorder caused by infection, leading to necrosis and destruction of bone. It can affect all ages, involve any bone, become a chronic disease and cause persistent morbidity. Treatment of osteomyelitis is challenging particularly when complex multiresistant bacterial biofilm has already been established. Bacteria in biofilm persist in a low metabolic phase, causing persistent infection due to increased resistance to antibiotics. Staphylococcus aureus and Staphylococcus epidermidis are the most common causative organism responsible for more than 50% of osteomyelitis cases. Osteomyelitis treatment implies the administration of high doses of antibiotics (AB) by means of endovenous and oral routes and should take a period of at least 6 weeks. Local drug delivery systems, using non-biodegradable (polymethylmethacrylate) or biodegradable and osteoactive materials such as calcium orthophosphates bone cements, have been shown to be promising alternatives for the treatment of osteomyelitis. These systems allow the local delivery of AB in situ with bactericidal concentrations for long periods of time and without the toxicity associated with other means of administration. This review examines the most recent literature evidence on the causes, pathogeneses and pharmacological treatment of osteomyelitis. The study methodology consisted of a literature review in Google Scholar, Science Direct, Pubmed, Springer link, B-on. Papers from 1979 till present were reviewed and evaluated.

Recurrence of pelvic abscess from Panton-Valentine leukocidin-positive community-acquired ST30 methicillin-resistant Staphylococcus aureus

A 17-year-old female patient (a basketball player) suffered from recurrent pelvic abscesses from methicillin-resistant Staphylococcus aureus (MRSA). The first episode, from strain NN12, occurred in October 2004. Her cutaneous abscesses complicated into systemic progression to osteomyelitis and multifocal pelvic abscesses, adjacent to the sacroiliac joint. The second episode, abscesses at tissues adjacent to the sacroiliac joint from strain NN31A, occurred late in February 2005. The third episode, from strain NN31B, occurred on July 30, 2005, repeating the second episode. Three MRSA strains were identical in terms of genotypes (belonging to Panton-Valentine leukocidin [PVL]-positive ST30 community-acquired MRSA, CA-MRSA), pulsed-field gel electrophoresis patterns, and peptide cytolysin gene (psmα) expression levels. The three MRSA strains exhibited superior THP-1 cell invasion ability over hospital-acquired MRSA (New York/Japan clone). The data suggest that PVL-positive ST30 CA-MRSA, with high levels of cell invasion and peptide cytolysins, causes recurrence of pelvic abscesses in a healthy adolescent.