UV-killed Staphylococcus aureus enhances adhesion and differentiation of osteoblasts on bone-associated biomaterials

Evaluation of the collagen-binding properties and virulence of killed Streptococcus mutans in a silkworm model

Streptococcus mutans, a major pathogen of dental caries, is also known as a causative agent of cardiovascular disease. A 120 kDa collagen-binding protein (Cnm) of S. mutans is an important contributor to the pathogenicity of cardiovascular disease. Although dead bacteria have been detected in cardiovascular specimens by molecular biological methods, the pathogenicity of the bacteria remains unknown. Here, we analyzed the pathogenicity of killed S. mutans by focusing on collagen-binding ability and the effects on silkworms. In live S. mutans, Cnm-positive S. mutans had high collagen-binding activity, while Cnm-negative S. mutans had no such activity. After treatment with killed Cnm-positive S. mutans, amoxicillin-treated bacteria still had collagen-binding ability, while lysozyme-treated bacteria lost this ability. When live and amoxicillin-treated S. mutans strains were administered to silkworms, the survival rates of the silkworms were reduced; this reduction was more pronounced in Cnm-positive S. mutans infection than in Cnm-negative S. mutans infection. However, the administration of any of the lysozyme-treated bacteria did not reduce the survival rate of the silkworms. These results suggest that amoxicillin-killed Cnm-positive S. mutans strains maintain collagen-binding properties and pathogenicity in the silkworm model, and are possibly associated with pathogenicity in cardiovascular diseases.

Drug infused Al2O3-bioactive glass coatings toward the cure of orthopedic infection

A unique implant coated substrate with dual-drug-eluting system exhibiting antibacterial, anti-inflammatory, and bone regenerative capacity has been fabricated using spray pyrolysis deposition (SPD) method. Bioglass (BG) and BG-alumina (BG-Al) composites coatings with different concentrations of Al incorporated on BG network over the Cp-Ti substrate were fabricated using SPD technique. Phase purity of BG and BG-Al composites were analyzed by XRD in which Na₂Ca₂Si₃O₉ and β-Na₂Ca₄(PO₄)₂SiO₄) and Na_7.15(Al_7.2Si_8.8O₃₂) phases were formed. Surface morphology of the coated substrates was analyzed by SEM. Uniformity of the coatings were evaluated by surface profilometer and the uniform distribution the nanoparticles were confirmed with Elemental mapping. Systematically, each apatite layer formation on coated substrate was confirmed by immersing the samples for 1, 3, and 7 days in simulated body fluid and the needle-like structure was characterized using SEM. Cumulative release of Tetracycline hydrochloride (Tet) antibiotic and Dexamethasone (Dex) anti-inflammatory drug-loaded BG-Al and BG-Al composite-coated substrate were studied for 24 h. Antibacterial activity of the coated substrates were evaluated by time-dependent growth inhibition and minimal inhibitory concentration (MIC) assays in which BG-Al and BG-Al composite loaded with Tet showed considerable growth inhibition against S. aureus. Osteoblast-like cells (MG-63) exhibited profound proliferation with no cytotoxic effects which was due to release of Dex drug-coated substrates. Thus, surface modification of Cp-Ti substrate with BG, BG-Al composites coatings loaded with Tet and Dex drug can be considered for post-operative orthopedic implant infection application.

Wnt3a and ASCs are capable of restoring mineralization in staph aureus-infected primary murine osteoblasts

INTRODUCTION

Bone infections are one of the main reasons for impaired bone regeneration and non-union formation. In previous experimental animal studies we could already demonstrate that bone defects due to prior infections showed a markedly reduced healing capacity, which could effectively be enhanced via application of Wnt3a and Adipose-derived stromal cells (ASCs). For a more in-depth analysis, we investigated proliferation and mineralization of cultured osteoblasts infected with staph aureus and sought to investigate effects of Wnt3a and ASCs on infected osteoblasts.

MATERIALS AND METHODS

Primary murine osteoblasts were isolated from calvariae and infected with staph aureus. Infected osteoblasts received treatment via application of recombinant Wnt3a, ASC conditioned medium and were furthermore cocultured with ASCs. Osteoblasts were evaluated by Alamar blue assay for metabolic activity, TUNEL-assay for apoptosis, ALP and Alizarin Red staining for mineralization. In addition, immunoflourescent staining (IF) and qRT-PCR analyses were performed.

RESULTS

Infected osteoblasts showed a markedly reduced ability for mineralization and increased apoptosis, which could be restored to physiological levels by Wnt3a and ASC treatment. Interestingly, metabolic activity of osteoblasts seemed to be unaffected by staph aureus infection. Additional analyses of Wnt-pathway activity revealed effective enhancement of canonical Wnt-pathway activity in Wnt3a-treated osteoblasts.

CONCLUSIONS

In summary, we gained further osteoblast-related insights into pathomechanisms of reduced bone healing capacity upon infections.

Membrane perturbation, altered morphology and killing of Staphylococcus epidermidis upon contact with a cytocompatible peptide-based antibacterial surface

One possibility to prevent prosthetic infections is to produce biomaterials resistant to bacterial colonization by anchoring membrane active antimicrobial peptides (AMPs) onto the implant surface. In this perspective, a deeper understanding of the mode of action of the immobilized peptides should improve the development of AMP-inspired infection-resistant biomaterials. The aim of the present study was to characterize the bactericidal mechanism against Staphylococcus epidermidis of the AMP BMAP27(1-18), immobilized on titanium disks and on a model resin support, by applying viability counts, Field Emission Scanning Electron Microscopy (FE-SEM), and a fluorescence microplate assay with a membrane potential-sensitive dye. The cytocompatibility to osteoblast-like MG-63 cells was investigated in monoculture and in co-culture with bacteria. The impact of peptide orientation was explored by using N- and C- anchored analogues. On titanium, the ∼50 % drop in bacteria viability and dramatically affected morphology indicate a contact-killing action exerted by the N- and C-immobilized peptides to the same extent. As further shown by the fluorescence assay with the resin-anchored peptides, the bactericidal effect was mediated by rapid membrane perturbation, similar to free peptides. However, at peptide MBC resin equivalents the C-oriented analogue proved more effective with more than 99 % killing and maximum fluorescence increase, compared to half-maximum fluorescence with more than 90 % killing produced by the N-orientation. Confocal microscopy analyses revealed 4-5 times better MG-63 cell adhesion on peptide-functionalized titanium both in monoculture and in co-culture with bacteria, regardless of peptide orientation, thus stimulating further studies on the effects of the immobilized BMAP27(1-18) on osteoblast cells.

Pathogenic characteristics of Staphylococcus aureus isolates from arthroplasty infections

BACKGROUND

Staphylococcus aureus has a great ability to form biofilms on implant-related biomaterials. This study aimed to investigate the resistance, biofilm and molecular characteristics of S. aureus strains isolated from patients with postoperative infections after arthroplasty in two Chinese tertiary care hospitals during 2017 to 2018.

METHODS

Antimicrobial susceptibility was determined by the agar dilution method. Bacterial biofilm formation was determined by crystal violet staining. The genes related to biofilm formation and molecular typing were analyzed by PCR amplification.

RESULTS

A total of 33 isolates were collected, 21 of which were from Henan. The strains were completely sensitive to vancomycin, linezolid, and nitrofurantoin. All the isolates had adhesion ability and could produce biofilms. Of the isolates, 75.0% from Chongqing and 85.7% from Henan had stronger biofilm formation abilities. The strains from Henan had slightly higher resistance, adhesion and biofilm-forming abilities than those from Chongqing. The strains in both hospitals carried at least two genes related to biofilm formation, and the ica and fnb genes were the most frequently detected genes. Three SCCmec types and seven sequence types (STs) were found in Henan, and two SCCmec types and six STs were found in Chongqing. ST239-SCCmec III was the main epidemic clone in the two hospitals.

CONCLUSION

The resistance phenotype and molecular characteristics of S. aureus strains varied in different hospitals. The results reflect the potential risks of S. aureus infection in postoperative arthroplasty patients. Our study provides a powerful basis for the clinical treatment, infection control and monitoring of outbreaks of epidemic strains.

Tantalum-coated pedicle screws enhance implant integration

Because titanium alloy (Ti) has the natural advantage of a low elastic modulus, it has become the most commonly used material for the manufacturing of pedicle screws. However, its poor shear strength and osteogenic ability are undesirable properties. The superior osteoinductivity demonstrated by tantalum (Ta) in oral and maxillofacial surgery and joint surgery leads us to assume that the tantalum-coated pedicle screws may have better osteogenic properties and bone anchoring strength. To verify this hypothesis, MC3T3-E1 cells and human mesenchymal stem cells (hBMSCs) were seeded on the surface of Ta and Ti disks to compare the effects of two different metals on cell adhesion, proliferation, and differentiation. At the same time, we observed the inhibitory effect of Ta on osteoclasts. As an in vivo study, conventional Ti pedicle screws and Ta-coated screws were implanted in bilateral pedicles of Bama pigs. The results showed that compared to titanium, tantalum promoted greater cell adhesion and proliferation and improved the level of hBMSC mineralization, and Ta-coated screws exerted an inhibitory effect on osteoclasts. More importantly, we found that the effect of tantalum on osteogenic differentiation was mediated through the Wnt/β-catenin and TGF-β/smad signaling pathways. Ta-coated screws significantly promoted trabecular bone growth compared with Ti as evidenced by micro-CT, histology and biomechanical examination. Our study clearly indicated that tantalum was a superior promoter of osteogenesis and proved that tantalum coating is an effective improvement for titanium alloy implants.

In vivo bactericidal efficacy of the Ti6Al4V surface after ultraviolet C treatment

Background

Biomaterial-associated infections are one of the most important complications in orthopedic surgery. The main goal of this study was to demonstrate the in vivo bactericidal effect of ultraviolet (UV) irradiation on Ti6Al4V surfaces.

Materials and methods

An experimental model of device-related infections was developed by direct inoculation of Staphylococcus aureus into the canal of both femurs of 34 rats. A UV-irradiated Ti6Al4V pin was press-fit into the canal by retrograde insertion in one femur and the control pin was inserted into the contralateral femur. To assess the efficacy of UV radiation, the mean colony counts after inoculation in the experimental subjects and the control group were compared at different times of sacrifice and at different inoculum doses.

Results

At 72 h, the mean colony counts after inoculation in experimental femurs were significantly lower than those of the control group, with a reduction percentage of 76 % (p = 0.041). A similar difference between control and experimental pins was observed at 24 h using an inoculum dose <10⁴ colony-forming units (CFU), for which the reduction percentage was 70.48 % (p = 0.017).

Conclusion

The irradiated surface of Ti6Al4V is able to reduce early bacterial colonization of Ti6AlV pins located in the medullar channel and in the surrounding femur. The reductions depend on the initial inoculums used to cause infection in the animals and the greatest effects are detected for inoculums <10⁴ CFU.

Level of evidence

Not applicable.

Staphylococcus aureus vs. Osteoblast: Relationship and Consequences in Osteomyelitis

Bone cells, namely osteoblasts and osteoclasts work in concert and are responsible for bone extracellular matrix formation and resorption. This homeostasis is, in part, altered during infections by Staphylococcus aureus through the induction of various responses from the osteoblasts. This includes the over-production of chemokines, cytokines and growth factors, thus suggesting a role for these cells in both innate and adaptive immunity. S. aureus decreases the activity and viability of osteoblasts, by induction of apoptosis-dependent and independent mechanisms. The tight relationship between osteoclasts and osteoblasts is also modulated by S. aureus infection. The present review provides a survey of the relevant literature discussing the important aspects of S. aureus and osteoblast interaction as well as the ability for antimicrobial peptides to kill intra-osteoblastic S. aureus, hence emphasizing the necessity for new anti-infectious therapeutics.