Aims. This study investigated vancomycin-microbubbles (Vm-MBs) and meropenem (Mp)-MBs with ultrasound-targeted microbubble destruction (UTMD) to disrupt biofilms and improve bactericidal efficiency, providing a new and promising strategy for the treatment of device-related infections (DRIs). Methods. A film hydration method was used to prepare Vm-MBs and Mp-MBs and examine their characterization. Biofilms of methicillin-resistant Staphylococcus aureus (MRSA) and Escherichia coli were treated with different groups. Biofilm biomass differences were determined by staining. Thickness and bacterial viability were observed with confocal laser scanning microscope (CLSM). Colony counts were determined by plate-counting. Scanning electron microscopy (SEM) observed bacterial morphology. Results. The Vm-MBs and Mp-MBs met the experimental requirements. The biofilm biomass in the Vm, Vm-MBs, UTMD, and Vm-MBs + UTMD groups was significantly lower than in the control group. MRSA and E. coli biofilms were most notably damaged in the Vm-MBs + UTMD group and Mp-MBs + UTMD group, respectively, with mean 21.55% (SD 0.08) and 19.73% (SD 1.25) remaining in the biofilm biomass. Vm-MBs + UTMD significantly reduced biofilm thickness and bacterial viability (p = 0.005 and p < 0.0001, respectively). Mp-MBs + UTMD could significantly decrease biofilm thickness and bacterial viability (allp < 0.001). Plate-counting method showed that the numbers of MRSA and E. coli bacterial colonies were significantly lower in the Vm-MBs + UTMD group and the Mp, Mp-MBs, UTMD, Mp-MBs + UTMD groups compared to the control group (p = 0.031). SEM showed that the morphology and structure of MRSA and E. coli were significantly damaged in the Vm-MBs + UTMD and Mp-MBs + UTMD groups. Conclusion. Vm-MBs or Mp-MBs combined with UTMD can effectively disrupt biofilms and protectively release antibiotics under ultrasound mediation, significantly reducing bacterial viability and improving the bactericidal effect of antibiotics. Cite this article: Bone Joint Res 2024;13(9):441–451

Aims. Periprosthetic joint infections (PJIs) are rare, but represent a great burden for the patient. In addition, the incidence of methicillin-resistant Staphylococcus aureus (MRSA) is increasing. The aim of this rat experiment was therefore to compare the antibiotics commonly used in the treatment of PJIs caused by MRSA. Methods. For this purpose, sterilized steel implants were implanted into the femur of 77 rats. The metal devices were inoculated with suspensions of two different MRSA strains. The animals were divided into groups and treated with vancomycin, linezolid, cotrimoxazole, or rifampin as monotherapy, or with combination of antibiotics over a period of 14 days. After a two-day antibiotic-free interval, the implant was explanted, and bone, muscle, and periarticular tissue were microbiologically analyzed. Results. Vancomycin and linezolid were able to significantly (p < 0.05) reduce the MRSA bacterial count at implants. No significant effect was found at the bone. Rifampin was the only monotherapy that significantly reduced the bacterial count on implant and bone. The combination with vancomycin or linezolid showed significant efficacy. Treatment with cotrimoxazole alone did not achieve a significant bacterial count reduction. The combination of linezolid plus rifampin was significantly more effective on implant and bone than the control group in both trials. Conclusion. Although rifampicin is effective as a monotherapy, it should not be used because of the high rate of resistance development. Our animal experiments showed the great importance of combination antibiotic therapies. In the future, investigations with higher case numbers, varied bacterial concentrations, and changes in individual drug dosages will be necessary to be able to draw an exact comparison, possibly within a clinical trial. Cite this article: Bone Joint Res 2022;11(3):143–151

Aims. Treatment outcomes for methicillin-resistant Staphylococcus aureus (MRSA) periprosthetic joint infection (PJI) using systemic vancomycin and antibacterial cement spacers during two-stage revision arthroplasty remain unsatisfactory. This study explored the efficacy and safety of intra-articular vancomycin injections for PJI control after debridement and cement spacer implantation in a rat model. Methods. Total knee arthroplasty (TKA), MRSA inoculation, debridement, and vancomycin-spacer implantation were performed successively in rats to mimic first-stage PJI during the two-stage revision arthroplasty procedure. Vancomycin was administered intraperitoneally or intra-articularly for two weeks to control the infection after debridement and spacer implantation. Results. Rats receiving intra-articular vancomycin showed the best outcomes among the four treatment groups, with negative bacterial cultures, increased weight gain, increased capacity for weightbearing activities, increased residual bone volume preservation, and reduced inflammatory reactions in the joint tissues, indicating MRSA eradication in the knee. The vancomycin-spacer and/or systemic vancomycin failed to eliminate the MRSA infections following a two-week antibiotic course. Serum vancomycin levels did not reach nephrotoxic levels in any group. Mild renal histopathological changes, without changes in serum creatinine levels, were observed in the intraperitoneal vancomycin group compared with the intra-articular vancomycin group, but no changes in hepatic structure or serum alanine aminotransferase or aspartate aminotransferase levels were observed. No local complications were observed, such as sinus tract or non-healing surgical incisions. Conclusion. Intra-articular vancomycin injection was effective and safe for PJI control following debridement and spacer implantation in a rat model during two-stage revision arthroplasties, with better outcomes than systemic vancomycin administration. Cite this article: Bone Joint Res 2022;11(6):371–385

Aims. Biofilm formation is intrinsic to prosthetic joint infection (PJI). In the current study, we evaluated the effects of silver-containing hydroxyapatite (Ag-HA) coating and vancomycin (VCM) on methicillin-resistant Staphylococcus aureus (MRSA) biofilm formation. Methods. Pure titanium discs (Ti discs), Ti discs coated with HA (HA discs), and 3% Ag-HA discs developed using a thermal spraying were inoculated with MRSA suspensions containing a mean in vitro 4.3 (SD 0.8) x 10. 6. or 43.0 (SD 8.4) x 10. 5. colony-forming units (CFUs). Immediately after MRSA inoculation, sterile phosphate-buffered saline or VCM (20 µg/ml) was added, and the discs were incubated for 24 hours at 37°C. Viable cell counting, 3D confocal laser scanning microscopy with Airyscan, and scanning electron microscopy were then performed. HA discs and Ag HA discs were implanted subcutaneously in vivo in the dorsum of rats, and MRSA suspensions containing a mean in vivo 7.2 (SD 0.4) x 10. 6.   or 72.0 (SD 4.2) x 10. 5.   CFUs were inoculated on the discs. VCM was injected subcutaneously daily every 12 hours followed by viable cell counting. Results. Biofilms that formed on HA discs were thicker and larger than those on Ti discs, whereas those on Ag-HA discs were thinner and smaller than those on Ti discs. Viable bacterial counts in vivo revealed that Ag-HA combined with VCM was the most effective treatment. Conclusion. Ag-HA with VCM has a potential synergistic effect in reducing MRSA biofilm formation and can thus be useful for preventing and treating PJI. Cite this article:Bone Joint Res. 2020;9(5):211–218

Aims. Methicillin-resistant Staphylococcus aureus (MRSA) can cause wound infections via a ‘Trojan Horse’ mechanism, in which neutrophils engulf intestinal MRSA and travel to the wound, releasing MRSA after apoptosis. The possible role of intestinal MRSA in prosthetic joint infection (PJI) is unknown. Methods. Rats underwent intestinal colonization with green fluorescent protein (GFP)-tagged MRSA by gavage and an intra-articular wire was then surgically implanted. After ten days, the presence of PJI was determined by bacterial cultures of the distal femur, joint capsule, and implant. We excluded several other possibilities for PJI development. Intraoperative contamination was excluded by culturing the specimen obtained from surgical site. Extracellular bacteraemia-associated PJI was excluded by comparing with the infection rate after intravenous injection of MRSA or MRSA-carrying neutrophils. To further support this theory, we tested the efficacy of prophylactic membrane-permeable and non-membrane-permeable antibiotics in this model. Results. After undergoing knee surgery eight or 72 hours after colonization, five out of 20 rats (25.0%) and two out of 20 rats (10.0%) developed PJI, respectively. Strikingly, 11 out of 20 rats (55.0%) developed PJI after intravenous injection of MRSA-carrying neutrophils that were isolated from rats with intestinal MRSA colonization. None of the rats receiving intravenous injections of MRSA developed PJI. These results suggest that intestinal MRSA carried by neutrophils could cause PJI in our rat model. Ten out of 20 (50.0%) rats treated with non-membrane-permeable gentamicin developed PJI, whereas only one out of 20 (5.0%) rats treated with membrane-permeable linezolid developed PJI. Conclusion. Neutrophils as carriers of intestinal MRSA may play an important role in PJI development. Cite this article:Bone Joint Res. 2020;9(4):152–161

Aims. To characterize the intracellular penetration of osteoblasts and osteoclasts by methicillin-resistant Staphylococcus aureus (MRSA) and the antibiotic and detergent susceptibility of MRSA in bone. Methods. Time-lapse confocal microscopy was used to analyze the interaction of MRSA strain USA300 with primary murine osteoblasts and osteoclasts. The effects of early and delayed antibiotic treatments on intracellular and extracellular bacterial colony formation and cell death were quantified. We tested the effects of cefazolin, gentamicin, vancomycin, tetracycline, rifampicin, and ampicillin, as well as agents used in surgical preparation and irrigation. Results. MRSA infiltrated bone-resident cells within 15 to 30 minutes. Penetration was most effectively prevented with early (i.e. 30 minutes) antibiotic administration. The combined administration of rifampicin with other antibiotics potentiated their protective effects against MRSA-induced cytotoxicity and most significantly reduced extracellular bacterial bioburden. Gentamicin-containing compounds were most effective in reducing intracellular MRSA bioburden. Of the surgical preparation agents evaluated, betadine reduced in vitro MRSA growth to the greatest extent. Conclusion. The standard of care for open fractures involves debridement and antibiotics within the first six hours of injury but does not account for the window in which bacteria penetrate cells. Antibiotics must be administered as early as possible after injury or prior to incision to prevent intracellular infestation. Rifampicin can potentiate the capacity of antibiotic regimens to reduce MRSA-induced cytotoxicity. Cite this article:Bone Joint Res. 2020;9(2):49–59

Objectives. Vancomycin and fosfomycin are antibiotics commonly used to treat methicillin-resistant Staphylococcus aureus (MRSA) infection. This study compares the in vitro inhibitory effects against MRSA of articulating cement spacers impregnated with either vancomycin or fosfomycin. Methods. Vancomycin-impregnated articulating cement spacers and fosfomycin-impregnated articulating cement spacers were immersed in sterile phosphate-buffered saline (PBS) solutions and then incubated. Samples were collected for bioactivity evaluation. The aliquots were tested for MRSA inhibition with the disc diffusion method, and the inhibition zone diameters were measured. The inhibition zone differences were evaluated using the Wilcoxon Rank Sum Test. Results. The vancomycin group had significantly larger inhibition zones than the fosfomycin group from day three through to completion of the fourth week of incubation (p < 0.001). The vancomycin group exhibited a MRSA inhibition zone up to four weeks but the fosfomycin group showed an inhibition zone for only three days and after that did not show the the potential to inhibit MRSA. Conclusion. This in vitro study found that the inhibitory effect of vancomycin-impregnated articulating cement spacers against MRSA outperformed fosfomycin-impregnated articulating cement spacers. Further comparing our results to other published reports suggests there might be a limitation of the disc diffusion bioassay to show a large inhibitory zone in a high concentration of a highly soluble antibiotic. Cite this article: V. Yuenyongviwat, N. Ingviya, P. Pathaburee, B. Tangtrakulwanich. Inhibitory effects of vancomycin and fosfomycin on methicillin-resistant Staphylococcus aureus from antibiotic-impregnated articulating cement spacers. Bone Joint Res 2017;6:132–136. DOI: 10.1302/2046-3758.63.2000639

Local antimicrobial therapy is an integral aspect of treating orthopaedic device related infection (ODRI), which is conventionally administered via polymethylmethacrylate (PMMA) bone cement. PMMA, however, is limited by a suboptimal antibiotic release profile and a lack of biodegradability. In this study, we compare the efficacy of PMMA versus an antibioticloaded hydrogel in a single- stage revision for chronic methicillin-resistant Staphylococcus aureus (MRSA) ODRI in. sheep. Antibiofilm activity of the antibiotic combination (gentamicin and vancomycin) was determined in vitro. Swiss alpine sheep underwent a single-stage revision of a tibial intramedullary nail with MRSA infection. Local gentamicin and vancomycin therapy was delivered via hydrogel or PMMA (n = 5 per group), in conjunction with systemic antibiotic therapy. In vivo observations included: local antibiotic tissue concentration, renal and liver function tests, and quantitative microbiology on tissues and hardware post-mortem. There was a nonsignificant reduction in biofilm with an increasing antibiotic concentration in vitro (p = 0.12), confirming the antibiotic tolerance of the MRSA biofilm. In the in vivo study, four out of five sheep from each treatment group were culture negative. Antibiotic delivery via hydrogel resulted in 10–100 times greater local concentrations for the first 2–3 days compared with PMMA and were comparable thereafter. Systemic concentrations of gentamicin were minimal or undetectable in both groups, while renal and liver function tests were within normal limits. This study shows that a single-stage revision with hydrogel or PMMA is equally effective, although the hydrogel offers certain practical benefits over PMMA, which make it an attractive proposition for clinical use

Orthopedic Device-Related Infections (ODRIs) are a major medical challenge, particularly due to the involvement of biofilm-encased and multidrug-resistant bacteria. Current treatments, based on antibiotic administration, have proven to be ineffective. Consequently, there is a need for antibiotic-free alternatives. Antimicrobial peptides (AMPs) are a promising solution due to their broad-spectrum of activity, high efficacy at very low concentrations, and low propensity to induce resistance. We aim to develop a new AMP-based chitosan nanogel to be injected during orthopedic device implantation to prevent ODRIs. Chitosan was functionalized with norbornenes (NorChit) through the reaction with carbic anhydride and then, a cysteine-modified AMP, Dhvar5, a peptide with potent antibacterial activity, even against methicillin-resistant Staphylococcus aureus (MRSA), was covalently conjugated to NorChit (NorChit- Dhvar5), through a thiol-norbornene photoclick chemistry (UV= 365 nm). For NorChit-Dhvar5 nanogels production, the NorChit-Dhvar5 solution (0.15% w/v) and Milli-Q water were injected separately into microfluidic system. The nanogels were characterized regarding size, concentration, and shape, using Transmission Electron Microscopy (TEM), Nanoparticle Tracking Analysis (NTA) and Dynamic light scattering (DLS). The nanogels antibacterial properties were assessed in Phosphate Buffer (PBS) for 6 h, against four relevant microorganisms (Pseudomonas aeruginosa, S. aureus and MRSA, and in Muller- Hinton Broth (MHB), 50% (v/v) in PBS, supplemented with human plasma (1% (v/v)), for 6 and 24 h against MRSA. The obtained NorChit-Dhvar5 nanogels, presented a round-shaped and ∼100 nm. NorChit- Dhvar5 nanogels in a concentration of 10. 10. nanogels/mL in PBS were capable of reducing the initial inoculum of P. aeruginosa by 99%, S. aureus by 99%, and MRSA by 90%. These results were corroborated by a 99% MRSA reduction, after 24 h in medium. Furthermore, NorChit-Dhvar5 nanogels do not demonstrate signs of cytotoxicity against MC3T3-E1 cells (a pre-osteoblast cell line) after 14 days, having high potential to prevent antibiotic-resistant infection in the context of ODRIs

Aim. Bacteriophages are remerging as alternative and adjunctive therapy for fracture-related infection (FRI). However, current administration protocols involve prolonged retention of a percutaneous draining tube with potential risk of developing superinfection. In this study, we applied a cocktail of in vitro evolved biofilm-targeting phages for Methicillin-resistant Staphylococcus aureus (MRSA) in a hydrogel platform co-delivering vancomycin. In vitro synergy and antibiofilm activity was assessed and a subsequent in vivo study was performed in a mouse FRI model with MRSA. Method. Two evolved bacteriophages (MRSA-R14 and COL-R23) with improved antibiofilm activity against a clinical isolate (MRSA3) were tested in combination with vancomycin and a carboxymethylcellulose (CMC) hydrogel in vitro and in vivo. MRSA3 bacterial biofilms were formed on sterile 4 mm sintered porous glass beads at 37 °C for 24 h. Biofilms were exposed to i-phage cocktail (10. 7. PFU/ml), ii-vancomycin at concentrations of 0.5, 1, 10 and 100 times the MIC, or iii-combination of phage cocktail and vancomycin. Recovered biofilm cells, were quantified by colony counting. The stability and release profiles of phage cocktail and vancomycin in co-delivery hydrogel were assessed in vitro for 8 days and 72 hrs, respectively, and subsequently tested in the treatment of 5-day-old MRSA3 infection of a femoral plate osteotomy in mice. Results. In vitro: The cocktail of evolved phages (10. 7. PFU/ml, 1:1) combined with 0.5 MIC vancomycin achieved 99.72% reduction in MRSA3 biofilm in vitro compared to the growth control. This combination was stable in the co-delivery hydrogel over 8 days. The release profile showed that 57% of phages and 80% of vancomycin were released after 72hrs, which was identical to the performance for gels loaded with phage or antibiotic alone. In the in vivo study, the bacterial load from animals that received co-delivery hydrogel and systemic vancomycin was significantly reduced compared to controls, animals that received systemic vancomycin and animals that received co-delivery hydrogel alone (p<0.05). Conclusions. Our study demonstrates the potential of using evolved phages in combination with vancomycin and hydrogel delivery systems for the treatment of MRSA-related infections. Further research in this area may lead to the development of specific therapies for biofilm-related infection

Aim. Antibiotics have limited activity in the treatment of multidrug-resistant or chronic biofilm-associated infections, in particular when implants cannot be removed. Lytic bacteriophages can rapidly and selectively kill bacteria, and can be combined with antibiotics. However, clinical experience in patients with surgical infections is limited. We investigated the outcome and safety of local application of bacteriophages in addition to antimicrobial therapy. Method. 8 patients (2 female and 6 male) with complex orthopedic and cardiovascular infections were included, in whom standard treatment was not feasible or impossible. The treatment was performed in agreement with the Article 37 of the Declaration of Helsinki. Commercial or individually prepared bacteriophages were provided by ELIAVA Institute in Tbilisi, Georgia. Bacteriophages were applied during surgery and continued through drains placed during surgery three times per day for the following 5–14 days. Follow-up ranged from 1 to 28 months. Results. Median age was 57 years, range 33–75 years. Two patients were diagnosed with a persistent knee arthrodesis infection, one chronic periprosthetic joint infection (PJI), one cardiovascular implantable electronic device (CIED) infection and four patients with left ventricular assist device (LVAD) infection. The isolated pathogens were multi-drug-resistant Pseudomonas aeruginosa (n=3), methicillin-sensitive Staphylococcus aureus (n=4), methicillin-resistant Staphylococcus aureus (MRSA) (n=1) and methicillin-resistant Staphylococcus epidermidis (MRSE) (n=1). 4 infections were polymicrobial. 5 patients underwent surgical debridement with retention of the implant, 1 patient with PJI underwent the exchange of the prosthesis and one patient with LVAD infection was treated conservatively. All patients received intravenous and oral antibiotic therapy and local application of bacteriophages. At follow-up of 12 month, 5 patients were without signs or symptoms of infection, whereas in one patient with LVAD infection, a relapse was observed with emergence of phage-resistant Pseudomonas aeruginosa. In this patient, no surgical revision was performed. Conclusions. Bacteriophage therapy may represent a valid additional approach, when standard antimicrobial and surgical treatment is not possible or feasible, including in difficult-to-treat infections. In our case series, 5 of 6 patients were infection free after 1 year. Further studies need to address the optimal bacteriophage administration route, concentration, duration of treatment and combination with antimicrobials

Aim. The rise of multidrug-resistant bacteria and the decreasing efficacy of antibiotic therapy in successfully treating biofilm-associated infections are prompting the exploration of alternative treatment options. This study investigates the efficacy of different bioactive glass (BAG) formulations - alone or combined with vancomycin - to eradicate biofilm. Further, we study the influence of BAG on pH and osmotic pressure as important factors limiting bacterial growth. Method. Different BAG-S53P4 formulations were used for this study, including (a) BAG-powder (<45 μm), (b) BAG-granules (500–800 μm), (c) a cone-shaped BAG-scaffold and (d) two kinds of BAG-putty containing granules, with no powder (putty-A) or with additional powder (putty-B), and a synthetic binder. Inert glass beads were included as control. All formulations were tested in a concentration of 1750 g/ml in Müller-Hinton-Broth. Targeted bacteria included methicillin-resistant Staphylococcus aureus (MRSA) and epidermidis (MRSE). Vancomycin was tested at the minimum-inhibitory-concentration for each strain (1 µg/ml for MRSA; 2 μg/ml for MRSE). To investigate the antibiofilm effect of BAG alone or combined with vancomycin, 3 hour-old MRSA or MRSE biofilms were formed on porous glass beads and exposed to BAG ± vancomycin for 24h, 72h and 168h. After co-incubation, biofilm-beads were deep-washed in phosphate-buffered saline and placed in glass vials containing fresh medium. Recovering biofilm bacteria were detected by measuring growth-related heat production at 37°C for 24h by isothermal microcalorimetry. Changes in pH and osmotic pressure over time were assessed after co-incubation of each BAG formulation in Müller-Hinton-Broth for 0h, 24h, 72h and 168h. Results. All BAG formulations showed antibiofilm activity against MRSA and MRSE in a time-dependent manner, where longer incubation times revealed higher antibiofilm activity. BAG-powder and BAG-putty-B were the most effective formulations suppressing biofilm, followed by BAG-granules, BAG-scaffold and finally BAG-putty-A. The addition of vancomycin had no substantial impact on biofilm suppression. An increase in pH and osmotic pressure over time could be observed for all BAG formulations. BAG-powder reached the highest pH value of 12.5, whereas BAG-putty-A resulted in the lowest pH of 9. Both BAG-putty formulations displayed the greatest increase on osmotic pressure. Conclusions. BAG-S53P4 has demonstrated efficient biofilm suppression against MRSA and MRSE, especially in powder-containing formulations. Our data indicates no additional antibiofilm improvement with addition of vancomycin. Moreover, high pH appears to have a larger antimicrobial impact than high osmolarity. Acknowledgements. This work was supported by PRO-IMPLANT Foundation (Berlin, Germany). The tested materials were provided by Bonalive Biomaterials Ltd (Turku, Finland)

Each year more than 70 billion standard units of antibiotic are prescribed to treat bacterial infections worldwide. In addition, at least 63,000 tons of antibiotics are consumed by livestock for growth promotion and disease prevention. The result of this overuse of antibiotics is a spiraling increase in resistance. In the United States and Europe, antibiotic resistant bacteria are responsible for more than 4 million infections and approximately 50,000 deaths annually. In addition, bacteria such as methicillin-resistant Staphylococcus aureus (MRSA) have increased in prevalence in hospitals over the last three decades. Such bacteria are particularly problematic in postoperative infections, exacerbating treatment through the development of biofilms, especially on medical implants which are virtually impossible to treat without removal and replacement of the device. This presentation will show how non-invasive preclinical imaging (optical, PET and CT) is being used to better understand the establishment and development of bacterial infections in vivo, and how best to treat them. In particular, data will be shown as to how preclinical imaging can be used to monitor bacterial infections on orthopaedic implants, and how this technology might be translated into the clinic

Aims. Prosthetic joint infection (PJI) remains the most severe complication of arthroplasty. Failure of intensive, long-term antibiotic treatment for PJI often requires removal of the implant. Antibiotic failure is thought to be caused by biofilm and persister formation. Novel anti-biofilm and anti-persister strategies are urgently needed. Here, we investigated the effects of several antimicrobial peptides on the bacteria within antibiotic-treated biofilms in an in vitro mature biofilm model on abiotic surfaces. Methods. On polystyrene, a mature (7 day-old) methicillin-resistant Staphylococcus aureus (MRSA) biofilm was developed. Thereafter, bacteria in the biofilm were exposed to rifampicin and ciprofloxacin (both 10× >MIC) for three days. Surviving bacteria in the antibiotic-treated biofilm, presumed to include persisters, were exposed to increasing doses of the antimicrobial peptides SAAP-148, acyldepsipeptide 4 (ADEP4), LL-37 and pexiganan. SAAP-148 was further tested on antibiotic-treated mature biofilms on titanium/aluminium/niobium (TAN) discs and prosthetic joint liners. Results. Daily exposure of the mature biofilm for seven days with antibiotics resulted in a 4-log reduction of MRSA without elimination of the bacteria. The surviving bacteria within the biofilm were eliminated upon subsequent exposure to SAAP-148 and pexiganan but not with LL-37 ad ADEP4. Antibiotic treatment of mature biofilms on TAN discs followed by SAAP-148 also resulted in eradication of bacteria within the biofilm. SAAP-148 also fully eliminated bacteria within antibiotic-treated mature MRSA biofilms on an ex vivo liner of a prosthetic joint. Conclusions. A novel mature biofilm model has been developed in which the efficacy of antimicrobial peptides against bacteria, including persisters, residing within a biofilm was investigated. SAAP-148 and pexiganan were highly effective against the bacteria residing in antibiotic-exposed mature MRSA biofilms. This in vitro model system will be used to analyze the effects of novel antibiotic strategies and other anti-PJI agents

Aim. To investigate the ability of the bacteriophage Sb-1 to treat and prevent implant-associated infections due to methicillin-resistant Staphylococcus aureus (MRSA) in Galleria mellonella larvae implanted with a K-wire. Method. The stability of Sb-1 in G. mellonella larvae was investigated by injecting a phage titer of 10. 8. PFU and evaluating the presence of Sb-1 in hemolymph at different time points. For infection experiments, sterile stainless-steel K-wires (4 mm, 0.6 mm Ø) were implanted into larvae. Two days after implant, larvae were infected with MRSA ATCC 43300 (1×10. 5. CFU) and incubated at 37°C for further 2 days. Implanted-infected larvae were thus treated for 2 days (3×/day) with 10µL of: i) PBS; ii) Sb-1 (10. 7. PFU); iii) Daptomycin (4mg/kg), iv) PBS (24h)/Daptomycin(24h); v) Sb-1(24h)/Daptomycin(24h). To evaluate the prophylactic efficacy of Sb-1, an experiment based on phages or vancomycin (10mg/kg) administration, followed by MRSA infection of implanted larvae was performed. Both two days post-infection and post-treatment, K-wires were explanted, and the material was sonicated and plated for MRSA colony counting. Results. Sb-1 titer resulted stable in hemolymph of G. mellonella larvae for 6–8 h post-administration. Two days post-infection of K-wire implanted larvae, ≈5×10. 7. CFU/ml MRSA were found on the material. K-wires from larvae treated with Sb-1 or Daptomycin showed a MRSA CFU/ml reduction of ≈1 log compared to the CFU/ml values of the untreated control. The staggered administration Sb-1/Daptomycin determined higher CFU reduction (≈ 3.5 log). Prophylaxis with Sb-1 prevented MRSA infection of 7out of 10 larvae similarly to vancomycin. Conclusions. G. mellonella larvae implanted with K-wires are a suitable model to test antibiofilm formulations in vivo. Sb-1 phage is able to prevent implant-associated infection due to MRSA in larvae. Sequential combination of Sb-1 and Daptomycin strongly reduces the MRSA load on implanted K-wires

Background. Vancomycin and fosfomycin are antibiotic commonly used in Methicillin-resistant Staphylococcus aureus (MRSA) infection. This study compares the efficacy of articulating cement spacer implegnated with vancomycin and articulating cement spacer implegnated with fosfomycin to inhibit MRSA. Methods. Vancomycin implegnated articulating cement spacers and Fosfomycin implegnated articulating cement spacers were immersed in sterile phosphate buffered saline(PBS) and then incubated at 37 C. The samples were collected and change daily. Aliquots were tested for MRSA inhibition by disc diffusion method. The inhibition zones diameters were measured. Results. Vancomycin group showed an MRSA inhibition zone up to four weeks. However, Fosfomycin group showed inhibition zone in day 3 in some samples but after that no sample had the potential to inhibit MRSA. Conclusion. In this experiment. Vancomycin impregnated articulating cement spacers showed longer efficacy to inhibit MRSA when compared to Fosfomycin

Aim. The increasing incidence of orthopaedic methicillin-resistant Staphylococcus aureus (MRSA) infections represents a significant therapeutic challenge. Being effective against MRSA, the role of vancomycin may become more important in the orthopaedic setting in the years to come. Nonetheless, vancomycin bone and soft tissue penetration during infection remains unclear. We assessed the effect of a traumatically induced, implant-associated acute osteomyelitis on vancomycin bone penetration in a porcine model. Method. In eight pigs, implant-associated osteomyelitis was induced on day 0, using a Staphylococcus aureus strain. Following administration of 1,000 mg of vancomycin on day 5, vancomycin concentrations were obtained with microdialysis for eight hours in the implant bone cavity, in cancellous bone adjacent to the implant cavity, in subcutaneous adipose tissue (SCT) adjacent to the implant cavity, and in healthy cancellous bone and healthy SCT in the contralateral leg. Venous blood samples were also obtained. The extent of infection and inflammation was evaluated by post-mortem computed tomography scans, C-reactive protein serum levels and cultures of blood and swabs. Results. In relation to all the implant cavities, bone destruction was found. Ranging from 0.20 to 0.74, tissue penetration, expressed as the ratio of tissue to plasma area under the concentration-time curve from 0 to the last measured value, was incomplete for all compartments except for healthy SCT. The lowest penetration was found in the implant cavity. Conclusions. Staphylococcus aureus implant-associated osteomyelitis was found to reduce vancomycin bone penetration, especially in the implant cavity. These findings suggest that it may be unsafe to rely solely on vancomycin therapy when treating acute osteomyelitis. Particularly when metaphyseal cavities are present, surgical debridement seems necessary

Aim. Implant-associated osteomyelitis is a devastating complication with poor outcomes following treatment, especially when caused by antibiotic-resistant bacteria such as methicillin-resistant Staphylococcus aureus (MRSA). A large animal model of a two-stage revision to treat MRSA implant-associated osteomyelitis has been developed to assess novel treatments. A bioresorbable, thermo-responsive hyaluronan hydrogel (THH) loaded with antibiotics has been developed and our aim was to investigate it´s in vivo efficacy as a local antibiotic carrier compared to the current standard of care i.e. antibiotic-loaded polymethylmethacrylate (PMMA) bone cement. Method. 12 female, 2 to 4 year old, Swiss Alpine Sheep were inoculated with MRSA at the time of intramedullary nail insertion in the tibia to develop chronic osteomyelitis. After 8 weeks sheep received a 2-stage revision protocol, with local and systemic antibiotics. Group 1 received the gold standard clinical treatment: systemic vancomycin (2 weeks) followed by rifampicin plus trimethoprim/sulfamethoxazole (4 weeks), and local gentamicin/vancomycin via PMMA. Group 2 received local gentamicin/vancomycin delivered via THH at both revision surgeries and identical systemic therapy to group 1. Sheep were euthanized 2 weeks following completion of antibiotic therapy. At euthanasia, soft tissue, bone, and sonicate fluid from the hardware was collected for quantitative bacteriology. Results. Sheep tolerated the surgeries and both local and systemic antibiotics well. Gold standard of care successfully treated 3/6 sheep with a total of 10/30 culture-positive samples. All 6 sheep receiving antibiotic-loaded THH were successfully treated with 0/30 culture-positive samples, p=0.0008 gold-standard vs. hydrogel (Fisher's Exact). Conclusions. The clinical gold standard treatment was successful in 50% of sheep, consistent with outcomes reported in the literature treating MRSA infection. The antibiotic-loaded THH clearly outperformed the gold standard in this model. Superior efficacy of the THH is likely due to 1) the ability to administer local antibiotics at the both revision surgies due to the bioresorbable nature of the hydrogel, and 2) complete antibiotic release compared to bone cement, which is known to retain antibiotics. Our results highlight the potential of local delivered, biodegradable systems for antibiotics for eradicating implant-related infection caused by antibiotic-resistant pathogens. Acknowledgement. Funding provided by AO Trauma

Aim. This study aims to describe our department experience with single stage revision (SSR) for chronic prosthetic-joint infection (PJI) after total hip arthroplasty (THA) between 2005 and 2014 and to analyze success rates and morbidity results of patients submitted to SSR for infected THA according to pathogen. Method. We retrospectively reviewed our 10 years of results (2005–2014) of patients submitted to SSR of the hip combined with IV and oral antibiotic therapy for treatment of chronic PJI (at least 4 weeks of symptoms), with a minimum follow-up of four years (n=26). Patients were characterized for demographic data, comorbidities, identified germ and antibiotic therapy applied (empiric and/or targeted). Outcomes analyzed were re-intervention rate (infection-related or aseptic), success rate (clinical and laboratory assessment), length of stay, morbidity and mortality outcomes. Results. In this period, 26 single-stage revisions for chronic PJI of the hip were performed. Patients average age was 72 years (range 44–82). Ten patients were women. The average time of follow up was 69 months (range 4 to 12 years). The most commonly isolated bacteria were coagulase-negative Staphylococci (30%), methicillin-resistant Staphylococcus aureus (MRSA) (18%) and methicillin-sensitive Staphylococcus aureus (15%). It wasn't possible to identify the germ in 19% of the patients and other 23% were polymicrobial. Targeted antibiotic therapy was administered to 73% of patients and the most used targeted antibiotics were Vancomycin (53%), Linezolid (32%) and Rifampicin (21%). Mean length of stay was 25 days. In the follow-up period, 9 patients (35%) required a re-intervention for infection relapse. Two patients (8%) needed surgery because of persistent instability. During the follow-up period, the infection-free survival was 65% (33% for MRSA; 82% for coagulase-negative Staphylococci) and the surgery-free survival was 62%. Six patients (23%) died during the follow-up, all due to other medical conditions not related to hip infection. Conclusions. Our experience suggests that SSR is associated with good outcomes and low re-intervention rate, except in the case of infection due to MRSA. In this last group, the results were significantly poorer, what leads to suggest that a two-stage revision may be a better option. The potential advantages of a SSR include good rates of infection eradication, a decrease in surgical morbidity and mortality as well as a decrease in healthcare and global economic costs. As such, a one-stage aggressive surgical attitude in addition to targeted antibiotherapy seems to be a suitable solution in selected patients

Aim. We aimed to compare the in vitro antibacterial activity of Bioactive Glass (BAG) S53P4, which is a compound showing local antibacterial activity, to that of antibiotic-loaded polymethylmethacrylate (PMMA) against multidrug resistant bacteria from osteomyelitis (OM) and prosthetic joint infection (PJI) isolates. Method. We studied convenience samples of multidrug resistant (MDR) microorganisms obtained from patients presenting OM and prosthetic joint infection (PJI). Mixtures containing tryptic soy broth (TSB) and inert glass beads (2mm), BAG-S53P4 granules (0.5–0.8mm and <45 mm) and Gentamicin or Vancomycin-loaded PMMA beads were inoculated with methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-resistant coagulase-negative Staphylococcus (MR-CoNS), Pseudomonas aeruginosa or Klebsiella pneumoniae isolates. Glass beads (2.0mm) were used as a control. Antibacterial activity was evaluated by means of time-kill curve, through seeding the strains on blood agar plates, and subsequently performing colony counts after 24, 48, 72, 96, 120 and 168 hours of incubation. Differences between groups were evaluated by means of two-way analysis of variance (ANOVA) and Bonferroni's t test. Results. Inhibition of bacterial growth started soon after 48 hours of incubation, reached zero CFU/ml between 120 and 168 hours of incubation for both antibiotic-loaded PMMA and BAG S53P4 groups, in comparison with inert glass (p< 0.05). No difference regarding time-kill curves between antibiotic-loaded PMMA and BAG S53P4 was observed. Moreover, despite no difference was observed between both Vancomycin - or Gentamicin-loaded PMMA and BAG groups, there was statistical difference between the effectiveness of all treatments (BAG included) against gram-positive cocci and gram-negative bacilli, the latter of which requiring longer time frames for the cultures to yield no bacterial growth. Conclusions. BAG S53P4 presented antibacterial properties as much as antibiotic-loaded PMMA for MDR bacteria producing OM and PJI, although presenting differences between its effectiveness against different bacterial groups