Implant-associated Infections Research Articles

<i>Stenotrophomonas maltophilia</i> as a causative agent of implant-associated infection in trauma and orthopedic patients

Objective. To evaluate an etiologic significance of S. maltophilia in the development of orthopedic implant-associated infections. Materials and methods. The study involved a retrospective analysis of the frequency of excretion of S. maltophilia in patients with periprosthetic infection and osteomyelitis, using the Microbe-2 program in period of 2005–2020. Clinical isolates were excreted according to standard methods. Identification was performed via Microlatest panels using iEMS Reader MF. Antibiotic susceptibility was studied in accordance with EUCAST. Results. Over 16 years 69 strains of S. maltophilia have been identified, comprising 0.33% of all isolated pathogens (n=20631). 50% of isolates were excreted from tissue biopsies, 30% – from wound exudates. In 89% of cases, S. maltophilia was isolated in microbial associations, including 65% of cases together with Grampositive bacteria, 18% with other non-fermenting Gram-negative bacteria, and 6% with other pathogens. 63% appeared sensitive to trimethoprim/sulfamethoxazole and 25.5% of isolates were resistant. The proportion of cultures sensitive to this drug was found to increase from 63% in 2011–2014 to 81% in 2015–2019 (p = 0.08). Conclusion. S. maltophilia should be considered as a causative etiologic agent of severe chronic orthopedic infections.

Sonication protocols and their contributions to the microbiological diagnosis of implant-associated infections: a review of the current scenario.

Addressing the existing problem in the microbiological diagnosis of infections associated with implants and the current debate about the real power of precision of sonicated fluid culture (SFC), the objective of this review is to describe the methodology and analyze and compare the results obtained in current studies on the subject. Furthermore, the present study also discusses and suggests the best parameters for performing sonication. A search was carried out for recent studies in the literature (2019-2023) that addressed this research topic. As a result, different sonication protocols were adopted in the studies analyzed, as expected, and consequently, there was significant variability between the results obtained regarding the sensitivity and specificity of the technique in relation to the traditional culture method (periprosthetic tissue culture - PTC). Coagulase-negative Staphylococcus (CoNS) and Staphylococcus aureus were identified as the main etiological agents by SFC and PTC, with SFC being important for the identification of pathogens of low virulence that are difficult to detect. Compared to chemical biofilm displacement methods, EDTA and DTT, SFC also produced variable results. In this context, this review provided an overview of the most current scenarios on the topic and theoretical support to improve sonication performance, especially with regard to sensitivity and specificity, by scoring the best parameters from various aspects, including sample collection, storage conditions, cultivation methods, microorganism identification techniques (both phenotypic and molecular) and the cutoff point for colony forming unit (CFU) counts. This study demonstrated the need for standardization of the technique and provided a theoretical basis for a sonication protocol that aims to achieve the highest levels of sensitivity and specificity for the reliable microbiological diagnosis of infections associated with implants and prosthetic devices, such as prosthetic joint infections (PJIs). However, practical application and additional complementary studies are still needed.

Bacterial micro-aggregates as inoculum in animal models of implant-associated infections

Is it time to rethink the inoculum of animal models of implant-associated infections (IAI)? Traditionally, animal models of IAI are based on inoculation with metabolically active overnight cultures of planktonic bacteria or pre-grown surface-attached biofilms. However, such inoculums do not mimic the clinical initiation of IAI. Therefore, the present study aimed to develop a clinically relevant inoculum of low metabolic micro-aggregated bacteria. The porcine Staphylococcus aureus strain S54F9 was cultured in Tryptone Soya Broth (TSB) for seven days to facilitate the formation of low metabolic micro-aggregates. Subsequently, the aggregated culture underwent filtration using cell strainers of different pore sizes to separate micro-aggregates. Light microscopy was used to evaluate the aggregate formation and size in the different fractions, while isothermal microcalorimetry was used to disclose a low metabolic activity. The micro-aggregate fraction obtained with filter size 5–15 μm (actual measured mean size 32 μm) was used as inoculum in a porcine implant-associated osteomyelitis (IAO) model and compared to a standard overnight planktonic inoculum and a sham inoculum of 0.9 % saline. The micro-aggregate and planktonic inoculums caused IAO with the re-isolation of S. aureus from soft tissues, bones, and implants. However, compared to their planktonic counterpart, neither of the micro-aggregate inoculated animals showed signs of osteomyelitis, i.e., sequester, osteolysis, and pus at gross inspection. Furthermore, inoculation with low metabolic micro-aggregates resulted in a strong healing response with pronounced osteoid formation, comparable to sham animals. In conclusion, the formation and separation of low metabolic bacterial micro-aggregates into various size fractions is possible, however, planktonic bacteria were still seen in all size fractions. Inoculation with micro-aggregates caused a less-aggressive osteomyelitis i.e. combination of infected tissue and strong healing response. Therefore, the use of low metabolic micro-aggregates could be a relevant inoculum for animal models of less-aggressive and thereby slower developing IAI and add in to our understanding of the host-implant-bacteria interactions in slow-onset low-grade infections.

A Self-Transformed N-Chlorinated ε-Polylysine Coating Endows Titanium Implants with Programmed Integration of Robust Antibacterial and Pro-Osteogenic Abilities

Implant-associated infection and poor osseointegration are the main causes of orthopedic implantation failure. For a long-term successful implantation, simultaneously introducing prevention of infection and promotion of osteogenesis into implants is highly desired but remains a grand challenge. Inspired by the human immune mechanism of tissue repair under bacterial infection, we propose a self-transformed strategy for the modification of titanium with porous N-chlorinated ε-polylysine coating (Ti-PL-NCl) through pore-making, surface grafting and chlorination. The as-prepared Ti-PL-NCl exhibits an excellent antibacterial activity against S. aureus and E. coli in the presence of N-chloramine in the early stage, with an antibacterial rate as high as 95.8% and 99.4%, respectively. With the consumption of oxidative chlorine, the N─Cl groups of Ti-PL-NCl are transformed into N─H groups with moderate antibacterial yet strong pro-osteogenic abilities. The self-transformed N-chlorinated ε-polylysine coating enables Ti-PL-NCl to achieve long-lasting antibacterial activity as well as enhanced pro-osteogenesis, thus providing adaptive bioactivities for bone-implant integration. Rat implant-associated osteomyelitis model confirms that Ti-PL-NCl has excellent efficacy of infection prevention and osseointegration promotion. This work may provide a new paradigm of designing multifunctional implants to achieve long-term successful implantation.

A bioswitchable antibacterial strategy for the treatment of implant-associated infections

Implant-associated infection (IAI) remains a significant clinical challenge due to the increase of bacterial resistance and the presence of bacterial biofilm. Endowing implants with antibacterial properties and functionality by surface covalent immobilization of antimicrobial peptides (AMPs) is a highly promising approach, but suffers from poor antibacterial effect. In this study, a bioswitchable antibacterial system is flexibly designed and constructed for IAI therapy. A universal and functional coating is polymerized on the material surface by propionaldehyde plasma polymerization and then conjugated with LL-37, a human cathelicidin peptide, by Schiff base reaction. The release of LL-37 can be triggered by the acidic microenvironment results from bacterial metabolism and respiration. The conjugated LL-37 under physiological environment shows better biocompatibility than direct administration of LL-37, while responsive released LL-37 under acidic microenvironment exhibits preferrable antibacterial activity in comparison with unresponsive immobilization of LL-37. Besides, the bioswitchable coating exhibits variable immunomodulatory abilities. Further in vivo subcutaneous implant-associated infection model confirms the good protection against bacterial infection of bioswitchable antibacterial system. This design strategy of bioswitchable antibacterial system will provide a simple and universal approach for the prevention and therapy of implant-associated infection.

Diagnostic Role of Metagenomic Next-Generation Sequencing in Tubercular Orthopedic Implant-Associated Infection.

The diagnosis of tubercular orthopedic implant-associated infection (TB-IAI) is challenging. This study evaluated the value of metagenomic next-generation sequencing (mNGS) for the diagnosis of TB-IAI and developed a standardized diagnostic procedure for TB-IAI. The records of all patients with TB-IAI diagnosed and treated at our institution between December 2018 and September 2022 were retrospectively reviewed. Patient demographic characteristics, medical history, laboratory test, microbial culture, histopathology, and mNGS results, and time to diagnosis were recorded. The diagnostic efficiency of mNGS for TB-IAI was assessed by comparing the results and diagnostic time with that of other diagnostic modalities. Ten patients were included in the analysis, including eight with prosthetic joint infections and two with fracture-related infections. The mNGS positivity rate was 100% (10/10), which was higher than that of TB-antibody (11%, 1/9), real-time quantitative polymerase chain reaction (22%, 2/9), T-SPOT.TB (25%, 2/8), purified protein derivative (50%, 4/8), microbial culture (50%, 5/10), and histopathology (20%, 2/10). mNGS shortened the time to diagnosis of TB-IAI. A standardized diagnostic procedure for TB-IAI was developed based on the findings. mNGS is useful for the diagnosis of TB-IAI. mNGS is recommended in cases where it is difficult to identify a pathogen using routine diagnostic tests. The standardized diagnostic procedure might improve TB-IAI diagnosis. TB-IAI is a rare infection, which occurs after orthopedic surgery and hard to diagnose microbiologically. mNGS is a new detection technique not yet discussed in current literature as a means for TB-IAI diagnostics. Here we describe a cohort of patients with TB-IAI diagnosed by mNGS show high efficiency of mNGS for detection of this pathology and present a clinical algorithm supplementing conventional methods for TB-IAI assessment.

An In Vitro Study on the Application of Silver-Doped Platelet-Rich Plasma in the Prevention of Post-Implant-Associated Infections.

Implant therapy is a common treatment option in dentistry and orthopedics, but its application is often associated with an increased risk of microbial contamination of the implant surfaces that cause bone tissue impairment. This study aims to develop two silver-enriched platelet-rich plasma (PRP) multifunctional scaffolds active at the same time in preventing implant-associated infections and stimulating bone regeneration. Commercial silver lactate (L) and newly synthesized silver deoxycholate:β-Cyclodextrin (B), were studied in vitro. Initially, the antimicrobial activity of the two silver soluble forms and the PRP enriched with the two silver forms has been studied on microbial planktonic cells. At the same time, the biocompatibility of silver-enriched PRPs has been assessed by an MTT test on human primary osteoblasts (hOBs). Afterwards, an investigation was conducted to evaluate the activity of selected concentrations and forms of silver-enriched PRPs in inhibiting microbial biofilm formation and stimulating hOB differentiation. PRP-L (0.3 µg/mm2) and PRP-B (0.2 µg/mm2) counteract Staphylococcus aureus, Staphylococcus epidermidis and Candida albicans planktonic cell growth and biofilm formation, preserving hOB viability without interfering with their differentiation capability. Overall, the results obtained suggest that L- and B-enriched PRPs represent a promising preventive strategy against biofilm-related implant infections and demonstrate a new silver formulation that, together with increasing fibrin binding protecting silver in truncated cone-shaped cyclic oligosaccharides, achieved comparable inhibitory results on prokaryotic cells at a lower concentration.

Factors affecting the course and prognosis of implant-associated infection caused by Klebsiella spp.

Background. The outcome of complex treatment of implant-associated infection (IAI) depends on various factors, but one of the most important is the etiology of the inflammatory process. Treatment of orthopedic infection caused by gram-negative microorganisms in general and representatives of the Enterobacteria family in particular causes many difficulties, one of which is the rapid growth of antibiotic resistance. Aim of the stydy - to evaluate the factors affecting the course and prognosis of IAI caused by Klebsiella spp. Methods. A retrospective case history of 85 patients who were treated in the clinical departments of the center from January 1, 2017 to December 31, 2021 for the treatment of IAI caused by Klebsiella spp was performed. According to the results of the telephone survey, the patients were divided into 2 main groups depending on the outcome of the 2-year follow-up period determined according to the Delphi criteria. The groups were comparable in terms of gender, age and anthropometric data. Further, in the IBM SPSS STATISTICS program (version 26), a statistical analysis of the impact on the outcome of various parameters was carried out: anamnesis data, laboratory studies, type of surgical intervention, the course of the postoperative period, antibiotic therapy at the inpatient and outpatient stages. Results. During the studied period, it was found that the prognosis was significantly worsened by the number of sanitizing surgical interventions in the anamnesis (p=0.022), the need for sanitizing intervention in the early postoperative period (p0.001) and the presence of Klebsiella spp. growth in postoperative crops (p=0.002), hypoalbuminemia on 7-14 days after the operation (p=0.008). At the same time, the appointment of trimethoprim-sulfamethoxazole for the outpatient period significantly improved the outcome (p=0.038).

Nickel nitride-mediated nitric oxide generation for combating implant-associated infections

NiTi alloys are widely used in the fabrication of biomedical implants, and it is essential to endow them with selective antibacterial properties to avoid implant-associated infection. In this study, nickel nitride (Ni3N), as a promising new inorganic nitric oxide (NO) donor, was in situ constructed on the surface of NiTi alloys through a straightforward two-step plasma immersion ion implantation (PIII) strategy. Nickel sites were first exposed by physical bombardment with argon or metal plasma, followed by reaction with nitrogen plasma to form Ni3N. Ni3N can disrupt the transmembrane proton electrochemical gradient by capturing protons to produce ammonia species (NHx), resulting in the accumulation of reactive oxygen species (ROS) as a result of bacterial metabolic disruption. On the other hand, the generated NHx can further react with ROS to produce NO and reactive nitrogen species (RNS). As a result, the Ni3N films exhibited more than 99 % antibacterial efficiency against both gram-negative and gram-positive bacteria. They also demonstrated effective antibacterial properties in a rat subcutaneous implant model. In addition, the modified NiTi alloys exhibit good corrosion resistance and cytocompatibility. This study provides a green, safe, and inexpensive method for constructing metal nitride films on implant surfaces and offers new ideas for the clinical design and fabrication of novel antibacterial implants.

Synthesis and preclinical evaluation of novel 18F-vancomycin-based tracers for the detection of bacterial infections using positron emission tomography.

Bacterial infections are a major problem in medicine, and the rapid and accurate detection of such infections is essential for optimal patient outcome. Bacterial infections can be diagnosed by nuclear imaging, but most currently available modalities are unable to discriminate infection from sterile inflammation. Bacteria-targeted positron emission tomography (PET) tracers have the potential to overcome this hurdle. In the present study, we compared three 18F-labelled PET tracers based on the clinically applied antibiotic vancomycin for targeted imaging of Gram-positive bacteria. [18F]FB-NHS and [18F]BODIPY-FL-NHS were conjugated to vancomycin. The resulting conjugates, together with our previously developed [18F]PQ-VE1-vancomycin, were tested for stability, lipophilicity, selective binding to Gram-positive bacteria, antimicrobial activity and biodistribution. For the first time, the pharmacokinetic properties of all three tracers were compared in healthy animals to identify potential binding sites. [18F]FB-vancomycin, [18F]BODIPY-FL-vancomycin, and [18F]PQ-VE1-vancomycin were successfully synthesized with radiochemical yields of 11.7%, 2.6%, and 0.8%, respectively. [18F]FB-vancomycin exhibited poor in vitro and in vivo stability and, accordingly, no bacterial binding. In contrast, [18F]BODIPY-FL-vancomycin and [18F]PQ-VE1-vancomycin showed strong and specific binding to Gram-positive bacteria, including methicillin-resistant Staphylococcus aureus (MRSA), which was outcompeted by unlabeled vancomycin only at concentrations exceeding clinically relevant vancomycin blood levels. Biodistribution showed renal clearance of [18F]PQ-VE1-vancomycin and [18F]BODIPY-FL-vancomycin with low non-specific accumulation in muscles, fat and bones. Here we present the synthesis and first evaluation of the vancomycin-based PET tracers [18F]BODIPY-FL-vancomycin and [18F]PQ-VE1-vancomycin for image-guided detection of Gram-positive bacteria. Our study paves the way towards real-time bacteria-targeted diagnosis of soft tissue and implant-associated infections that are oftentimes caused by Gram-positive bacteria, even after prophylactic treatment with vancomycin.

Human T-Cell Responses to Metallic Ion-Doped Bioactive Glasses.

Biomaterials are extensively used as replacements for damaged tissue with bioactive glasses standing out as bone substitutes for their intrinsic osteogenic properties. However, biomaterial implantation has the following risks: the development of implant-associated infections and adverse immune responses. Thus, incorporating metallic ions with known antimicrobial properties can prevent infection, but should also modulate the immune response. Therefore, we selected silver, copper and tellurium as doping for bioactive glasses and evaluated the immunophenotype and cytokine profile of human T-cells cultured on top of these discs. Results showed that silver significantly decreased cell viability, copper increased the T helper (Th)-1 cell percentage while decreasing that of Th17, while tellurium did not affect either cell viability or immune response, as evaluated via multiparametric flow cytometry. Multiplex cytokines assay showed that IL-5 levels were decreased in the copper-doped discs, compared with its undoped control, while IL-10 tended to be lower in the doped glass, compared with the control (plastic) while undoped condition showed lower expression of IL-13 and increased MCP-1 and MIP-1β secretion. Overall, we hypothesized that the Th1/Th17 shift, and specific cytokine expression indicated that T-cells might cross-activate other cell types, potentially macrophages and eosinophils, in response to the scaffolds.

Surface Modification of Hydroxyapatite Coating for Enhanced Antibiotic Therapy

A major strategy to combat implant-associated infections is to develop implant coatings with intrinsic antibacterial activity. Since hydroxyapatite (HAp) coatings and antibiotic administration are commonly used in clinical settings, developing HAp-coated implants with localized antibiotic-releasing properties has attracted popularity. Considering the antibacterial metal species (Ag, Zn, Cu, etc.) in metal–organic frameworks and their drug delivery capacity, in this study, a gentamicin-loaded zeolitic imidazolate framework-8 nanolayer was deposited on a plasma-sprayed HAp coating (HAp/ZIF-8@Gent), which served as a Gent and Zn2+ reservoir. The investigation on the binding interaction between ZIF-8 and HAp indicated that the growth of ZIF-8 was through a Zn2+ seed layer on the HAp coating via an adsorption–replacement mechanism, instead of simple physical adsorption. The HAp/ZIF-8@Gent coating exhibited a sustained drug-release property, and the cumulative concentration of released Gent reached 239.8 ± 7.1 μg/mL on day 8. Compared to the HAp-Zn and HAp/ZIF-8 coatings, the HAp/ZIF-8@Gent coating exhibited significantly higher antibacterial activity against E. coli. This was ascribed to the combined antibacterial effects of Zn2+ and Gent. The cytocompatibility of the HAp/ZIF-8@Gent coating was confirmed via cell proliferation. Above all, the ZIF-8-modified HAp coating with localized delivery of Gent and Zn2+ possessed excellent antibacterial activity and acceptable cytocompatibility, showing potential in mitigating implant-associated infections.

Multifaceted Materials for Enhanced Osteogenesis and Antimicrobial Properties on Bioplastic Polyetheretherketone Surfaces: A Review.

Implant-associated infections and the increasing number of bone implants loosening and falling off after implantation have become urgent global challenges, hence the need for intelligent alternative solutions to combat implant loosening and falling off. The application of polyetheretherketone (PEEK) in biomedical and medical therapy has aroused great interest, especially because its elastic modulus close to bone provides an effective alternative to titanium implants, thereby preventing the possibility of bone implants loosening and falling off due to the mismatch of elastic modulus. In this Review, we provide a comprehensive overview of recent advances in surface modifications to prevent bone binding deficiency and bacterial infection after implantation of bone implants, starting with inorganics for surface modification, followed by organics that can effectively promote bone integration and antimicrobial action. In addition, surface modifications derived from cells and related products of biological activity have been proposed, and there is increasing evidence of clinical potential. Finally, the advantages and future challenges of surface strategies against medical associated poor osseointegration and infection are discussed, with promising prospects for developing novel osseointegration and antimicrobial PEEK materials.

Synthesis and evaluation of a novel vancomycin-infused, biomimetic bone graft using a rat model of spinal implant-associated infection

BackgroundPostoperative infection is a complication of spinal fusion surgery resulting in increased patient morbidity. Strategies including intraoperative application of powdered vancomycin have been proposed to reduce the incidence of infection; however, such antimicrobial effects are short-lived. MethodsInstrumentation of the L4–L5 vertebrae was performed mimicking pedicle screw and rod fixation in 30 rats. Titanium instrumentation inoculated with either PBS or 1×105 CFU bioluminescent MRSA, along with biomimetic bone grafts infused with varying concentrations of vancomycin and 125 µg of rhBMP-2 (BioMim-rhBMP-2-VCM) were implanted prior to closure. Infection was quantified during the six-week postoperative period using bioluminescent imaging. Arthrodesis was evaluated using micro-CT. ResultsInfected animals receiving a bone graft infused with low-dose (0.18 mg/g) or high-dose vancomycin (0.89 mg/g) both exhibited significantly lower bioluminescent signal over the six-week postoperative period than control animals inoculated with MRSA and implanted with bone grafts lacking vancomycin (p=.019 and p=.007, respectively). Both low and high-dose vancomycin-infused grafts also resulted in a statistically significant reduction in average bioluminescence when compared to control animals (p=.027 and p=.047, respectively), independent of time. MicroCT analysis of animals from each group revealed pseudoarthrosis only in the control group, suggesting a correlation between infection and pseudoarthrosis. MRSA-inoculated control animals also had significantly less bone volume formation on micro-CT than the PBS-inoculated control cohort (p<.001), the MRSA+low-dose vancomycin-infused bone graft cohort (p<.001), and the MRSA+high-dose vancomycin-infused bone graft cohort (p<.001). ConclusionBioMim-rhBMP-2-VCM presents a novel tissue engineering approach to simultaneously promoting arthrodesis and antimicrobial prophylaxis in spinal fusion. Despite mixed evidence of potential osteotoxicity of vancomycin reported in literature, BioMim-rhBMP-2-VCM preserved arthrodesis and osteogenesis with increasing vancomycin loading doses due to the graft's osteoinductive composition.

Infection Microenvironment-Responsive Coating on Titanium Surfaces for On-Demand Release of Therapeutic Gas and Antibiotic.

Aseptic loosening and bacterial infection pose significant challenges in the clinical application of titanium (Ti) orthopedic implants, which are primarily caused by insufficient osseointegration and bacterial contamination. To address these issues, a responsive coating on Ti surface is constructed, which achieves enhanced osseointegration and infection elimination by on-demand release of therapeutic gas hydrogen sulfide (H2S) and antibiotic. TiO2 nanotubes (TNT) are anodized on the Ti surface to enhance its bioactivity and serve as reservoirs for the antibiotic. An infection microenvironment-responsive macromolecular H2S donor layer is coated on top of TNT to inhibit premature leakage of antibiotic. This layer exhibits a sustained release of low-dosage H2S, which is capable of promoting the osteogenic differentiation and migration of cells. Moreover, the compactness of the macromolecular H2S donor layer could be broken by bacterial invasion, leading to rapid antibiotic release thus preventing infection. In vitro antibacterial experiments validates significant antibacterial activity of the coating against both Gram-negative (Escherichia coli) and Gram-positive bacteria (Staphylococcus aureus). Crucially, this coating effectively suppresses implant-associated infection with 98.7% antibacterial efficiency in a rat femoral bone defect model, mitigates inflammation at the defect site and promotes osseointegration of the Ti orthopedic implant.

CXCR2 perturbation promotes Staphylococcus aureus implant-associated infection.

Introduction. Staphylococcus aureus is the leading cause of acute medical implant infections, representing a significant modern medical concern. The success of S. aureus as a pathogen in these cases resides in its arsenal of virulence factors, resistance to multiple antimicrobials, mechanisms of immune modulation, and ability to rapidly form biofilms associated with implant surfaces. S. aureus device-associated, biofilm-mediated infections are often persistent and notoriously difficult to treat, skewing innate immune responses to promote chronic reoccurring infections. While relatively little is known of the role neutrophils play in response to acute S. aureus biofilm infections, these effector cells must be efficiently recruited to sites of infection via directed chemotaxis. Here we investigate the effects of modulating CXC chemokine receptor 2 (CXCR2) activity, predominantly expressed on neutrophils, during S. aureus implant-associated infection.Hypothesis. We hypothesize that modulation of CXCR2 expression and/or signalling activities during S. aureus infection, and thus neutrophil recruitment, extravasation and antimicrobial activity, will affect infection control and bacterial burdens in a mouse model of implant-associated infection.Aim. This investigation aims to elucidate the impact of altered CXCR2 activity during S. aureus biofilm-mediated infection that may help develop a framework for an effective novel strategy to prevent morbidity and mortality associated with implant infections.Methodology. To examine the role of CXCR2 during S. aureus implant infection, we employed a mouse model of indwelling subcutaneous catheter infection using a community-associated methicillin-resistant S. aureus (MRSA) strain. To assess the role of CXCR2 induction or inhibition during infection, treatment groups received daily intraperitoneal doses of either Lipocalin-2 (Lcn2) or AZD5069, respectively. At the end of the study, catheters and surrounding soft tissues were analysed for bacterial burdens and dissemination, and Cxcr2 transcription within the implant-associated tissues was quantified.Results. Mice treated with Lcn2 developed higher bacterial burdens within the soft tissue surrounding the implant site, which was associated with increased Cxcr2 expression. AZD5069 treatment also resulted in increased implant- and tissues-associated bacterial titres, as well as enhanced Cxcr2 expression.Conclusion. Our results demonstrate that CXCR2 plays an essential role in regulating the severity of S. aureus implant-associated infections. Interestingly, however, perturbation of CXCR2 expression or signalling both resulted in enhanced Cxcr2 transcription and elevated implant-associated bacterial burdens. Thus, CXCR2 appears finely tuned to efficiently recruit effector cells and mediate control of S. aureus biofilm-mediated infection.

Surface modification of a commercial bone plate (Ti6Al4V) implant for improved antibacterial and cytocompatibility via thermal dewetting of a silver thin film

The high demand for bone grafts has motivated the development of implants with excellent osteogenic activity, whereas the risk of implant-associated infection, particularly given the rise of antimicrobial resistance, has compelled the development of implants with innovative antimicrobial strategies in which a small amount of bactericidal agent can effectively kill a wide range of bacteria. To induce antibacterial property, the surface of Grade-5 bone plate titanium implants used in clinical applications was modified using direct current (DC) sputter coating followed by thermal annealing. The 15 nm silver film-coated implants were thermally annealed in the furnace for 15 min at 750 °C. The modified implant surface’s antibacterial efficacy against Escherichia coli (E. coli), Staphylococcus aureus (S. aureus), Salmonella typhi, and Methicillin-resistant staphylococcus aureus bacteria has been assessed using a colony-forming assay. On the modified implant surface, the growth of E. coli and S. aureus bacteria is reduced by 99.72%, while highly drug-resistant bacteria are inhibited by 96.59%. The MTT assay was used to assess the cytotoxicity of the modified bone-implant surface against NIH3T3 mouse fibroblast cells. The modified bone-implant surface promoted fibroblast growth and demonstrated good cytocompatibility. Furthermore, the mechanical properties of the implant were not harmed by this novel surface modification method. This method is simple and provides new insight into surface modification of commercial metallic implants to have effective antibacterial properties against various classes of bacteria.

409 Evaluation of a Novel Vancomycin-Infused, Biomimetic Bone Graft in a Rat model of Spinal Implant-Associated Infection

INTRODUCTION: Postoperative infection is a complication of spinal fusion surgery resulting in increased patient morbidity. Strategies including intraoperative application of powdered vancomycin have been proposed to reduce the incidence of infection, however such antimicrobial effects are short-lived. METHODS: Instrumentation of the L4-L5 vertebrae was performed mimicking pedicle screw and rod fixation in 30 rats. Titanium inoculated with PBS or 1x105 CFU bioluminescent MRSA and biomimetic bone grafts infused with varying concentrations of vancomycin were inserted before closure. Infection was quantified during the six-week postoperative period using IVIS bioluminescent imaging. Arthrodesis was evaluated using micro-CT. Histological analysis was utilized to evaluate fusion and leukocyte infiltration. RESULTS: Infected animals receiving a bone graft infused with high-dose vancomycin (0.89 mg/g) exhibited significantly lower bioluminescent signal over the six-week postoperative infection period (p = 0.032) than control animals inoculated with MRSA and implanted with bone grafts lacking vancomycin. Both high and low-dose (0.18 mg/g) vancomycin-infused grafts resulted in a statistically significant reduction in average bioluminescence when compared to control animals (p = 0.018 and p = 0.027, respectively), independent of time. MicroCT analysis of animals from each group revealed pseudoarthrosis only in the control group, suggesting a correlation between infection and pseudoarthrosis. Histology revealed the formation of fusion masses in all animals receiving vancomycin infused-bone grafts regardless of MRSA inoculation, with clearance of infection indicated by lack of abscess formation. MRSA-inoculated control animals receiving no vancomycin within the bone graft demonstrated significant abscess formation and lack of fusion mass. CONCLUSIONS: The novel vancomycin-infused, biomimetic bone graft effectively mitigated implant-associated infection while promoting fusion in a rat model of instrumented lumbar fusion.

Dual-functional polyetheretherketone surface modification for enhanced osseointegration and antibacterial activity in pH-responsive manner

Polyetheretherketone (PEEK) has been recognized for its immense potential in hard tissue repair applications due to its mechanical properties resembling those of natural bones. However, the inherent bioinertness of pristine PEEK results in insufficient osseointegration. Moreover, implant-associated infection (IAI) has become a serious threat in orthopedic surgery. These risks usually lead to implant loosening, delayed healing, and even the failure of implantation, hampering many clinical applications of PEEK. In this study, we present a facile strategy to endow PEEK implants with enhanced osseointegration and pH-responsive antibacterial activity. Briefly, pristine PEEK was first treated with mixed acids to obtain a porous structure (referred to as SNPEEK), and then the metal-phenolic networks (MPN) coating was prepared using layer-by-layer (LbL) assembly consisting of Sr2+ and tannin acid (TA) (referred to as ST coating). The results demonstrated that the dual-functional PEEK displayed enhanced antibacterial activity in pH-responsive manner. At pH 7.4, the antibacterial ratios were 71.72% and 66.79% against Staphylococcus aureus (MSSA, ATCC 25,923) and methicillin-resistant Staphylococcus aureus (MRSA, ATCC BAA-40), respectively. Remarkably, at pH 5.5, the antibacterial activities significantly increased, resulting in killing ratios of 99.98% and 100%, respectively. Furthermore, the dual-functional PEEK promoted osteogenic differentiation of pre-osteoblasts (MC3T3-E1) and migration of human umbilical vascular endothelial cells (HUVECs). In addition, the dual-functional PEEK demonstrated effective anti-infection ability and desirable new bone formation ability in vivo compared to both pristine PEEK and SNPEEK implants. Overall, this study provides a promising strategy to endow PEEK implants with effective osseointegration and anti-infective ability, representing a prospective solution to address current clinical challenges associated with PEEK implants.

Potential of diallyl sulfide from bulbs of Allium parvum to inhibit the growth and biofilm formation in Malassezia furfur MTCC 1374

The bulbs of Allium parvum are used as a flavoring agent in diet and are conventionally assumed to treat skin infections. The current study evaluates the phytochemicals from organic extract of A. parvum and their antifungal activity against biofilm-forming dermatophytic fungi Malassezia furfur MTCC 1374, yeast found in the normal flora of the skin, causes superficial infections, systemic infections like pulmonary infections, fungemia, etc., and implant-associated infection by biofilm formation. Biofilm formation enables the fungi to escape from antifungal agents and renders resistance to antifungal agents. The phytochemical assay for the organic extract of the onion bulb documented that A. parvum contains phenol (58 + 0.1 mg GAE/g), flavonoids (112 + 0.12 mg QE/g), saponins (1.45 + 0.1 mg AE/g), and tannins (4.1 + 0.03 g TA/g). The FT-IR and GC-MS analysis revealed the presence of specific compounds, alkaloids such as glycosides and quinolones, plant flavonoids such as 4H-Pyran-4-one, 2,3-dihydro-3,5-dihydroxy-6-methyl-ester, phenolics, saponins such as butanoic acid and gluconic acid, and organic sulfur compounds such as diallyl sulfide, thiopyran tetrahydro-ester, allyl methyl trisulfide, and allyl methyl di sulfide. These compounds inhibited the growth of M. furfur at a minimum inhibitory concentration (MIC) value of 6.25 mg/ml and its biofilm at a minimum biofilm inhibitory concentration (MBIC) value of 12.5 mg/ml. Further studies required to explore the possible mechanism in controlling the biofilm, so, as to recommend as fungal control agent in medical sector.