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. There is a lack of biomaterial-based carriers for the local delivery of rifampicin (RIF), one of the cornerstone second defence antibiotics for bone infections. RIF is also known for causing rapid development of antibiotic resistance when given as monotherapy. This in vitro study evaluated a clinically used biphasic calcium sulphate/hydroxyapatite (CaS/HA) biomaterial as a carrier for dual delivery of RIF with vancomycin (VAN) or gentamicin (GEN). Methods. The CaS/HA composites containing RIF/GEN/VAN, either alone or in combination, were first prepared and their injectability, setting time, and antibiotic elution profiles were assessed. Using a continuous disk diffusion assay, the antibacterial behaviour of the material was tested on both planktonic and biofilm-embedded forms of standard and clinical strains of Staphylococcus aureus for 28 days. Development of bacterial resistance to RIF was determined by exposing the biofilm-embedded bacteria continuously to released fractions of antibiotics from CaS/HA-antibiotic composites. Results. Following the addition of RIF to CaS/HA-VAN/GEN, adequate injectability and setting of the CaS/HA composites were noted. Sustained release of RIF above the minimum inhibitory concentrations of S. aureus was observed until study endpoint (day 35). Only combinations of CaS/HA-VAN/GEN + RIF exhibited antibacterial and antibiofilm effects yielding no viable bacteria at study endpoint. The S. aureus strains developed resistance to RIF when biofilms were subjected to CaS/HA-RIF alone but not with CaS/HA-VAN/GEN + RIF. Conclusion. Our in vitro results indicate that biphasic CaS/HA loaded with VAN or GEN could be used as a carrier for RIF for local delivery in clinically demanding bone infections. Cite this article: Bone Joint Res 2022;11(11):787–802

Aims. Bone regeneration during treatment of staphylococcal bone infection is challenging due to the ability of Staphylococcus aureus to invade and persist within osteoblasts. Here, we sought to determine whether the metabolic and extracellular organic matrix formation and mineralization ability of S. aureus-infected human osteoblasts can be restored after rifampicin (RMP) therapy. Methods. The human osteoblast-like Saos-2 cells infected with S. aureus EDCC 5055 strain and treated with 8 µg/ml RMP underwent osteogenic stimulation for up to 21 days. Test groups were Saos-2 cells + S. aureus and Saos-2 cells + S. aureus + 8 µg/ml RMP, and control groups were uninfected untreated Saos-2 cells and uninfected Saos-2 cells + 8 µg/ml RMP. Results. The S. aureus-infected osteoblasts showed a significant number of intracellular bacteria colonies and an unusual higher metabolic activity (p < 0.005) compared to uninfected osteoblasts. Treatment with 8 µg/ml RMP significantly eradicated intracellular bacteria and the metabolic activity was comparable to uninfected groups. The RMP-treated infected osteoblasts revealed a significantly reduced amount of mineralized extracellular matrix (ECM) at seven days osteogenesis relative to uninfected untreated osteoblasts (p = 0.007). Prolonged osteogenesis and RMP treatment at 21 days significantly improved the ECM mineralization level. Ultrastructural images of the mineralized RMP-treated infected osteoblasts revealed viable osteoblasts and densely distributed calcium crystal deposits within the extracellular organic matrix. The expression levels of prominent bone formation genes were comparable to the RMP-treated uninfected osteoblasts. Conclusion. Intracellular S. aureus infection impaired osteoblast metabolism and function. However, treatment with low dosage of RMP eradicated the intracellular S. aureus, enabling extracellular organic matrix formation and mineralization of osteoblasts at later stage. Cite this article: Bone Joint Res 2022;11(5):327–341

Aim. There is a theoretical advantage for immediate postoperative start of rifampicin after debridement, antibiotics and implant retention (DAIR). Anti-biofilm treatment may be mostly needed during the first postoperative days in order to prevent new biofilm formation. However, there are concerns with regard to development of rifampicin resistance if rifampicin is started too early. Rifampicin monotherapy will rapidly result in rifampicin resistance, but this may not occur when prescribed as part of combination antimicrobial therapy and after thorough surgical debridement. We hypothesized that in this setting the probability of development of rifampicin resistance is very low. We evaluated the frequency of development of rifampicin resistance in patients with acute staphylococcal PJI who were treated with DAIR followed by immediate postoperative start of rifampicin in combination with a betalactam or glycopeptide. Method. During 2003–2014, all patients with an acute staphylococcal PJI were treated with five days of high-dose rifampicin (600mg bid) in combination with at least 6 weeks of betalactam or glycopeptide antibiotics, both started immediately postoperative after DAIR. Clinical outcome and development of rifampicin resistance in patients who failed were monitored. Susceptibility testing for rifampicin was performed by Vitek 2 (Biomerieux). Until 2014, Clinical and Laboratory Standards Institute (CLSI) criteria for rifampicin resistance were applied (S ≤ 1), from 2014 EUCAST criteria (S ≤ 0.06) were applied. Results. Forty-one patients with acute staphylococcal hip (22) of knee (19) PJI were included. Comorbidities were rheumatoid arthritis (22%), diabetes (10%), a tumor prosthesis due to malignancy (34%) and corticosteroid use (27%). Fifteen patients (37%) developed a failure after DAIR. Eight failures were caused by the same staphylococcal species as the initial PJI (six Staphylococcus aureus, two Coagulase-negative staphylococci). In all failures, rifampicin susceptibility of the isolate had not changed. One patient was started on chronic suppressive treatment (not including rifampicin) and had a prosthetic joint removal 18 months later. In this patient, one out of five positive cultures with S. aureus from the removed prosthesis showed a rifampicin resistant strain. In all failures, mean duration between the initial DAIR and failure was 208 days (range 7–636 days). Conclusions. Immediate postoperative start of high-dose rifampicin in combination with betalactam or glycopeptide did not result in rifampicin resistant staphylococci among patient who had a failure with the same staphylococci. These results strongly indicate that immediate postoperative start of rifampicin is safe. Larger studies are needed to prove the clinical benefit of this strategy

Aims. Poly(methyl methacrylate) (PMMA)-based bone cements are the industry standard in orthopaedics. PMMA cement has inherent disadvantages, which has led to the development and evaluation of a novel silorane-based biomaterial (SBB) for use as an orthopaedic cement. In this study we test both elution and mechanical properties of both PMMA and SBB, with and without antibiotic loading. Methods. For each cement (PMMA or SBB), three formulations were prepared (rifampin-added, vancomycin-added, and control) and made into pellets (6 mm × 12 mm) for testing. Antibiotic elution into phosphate-buffered saline was measured over 14 days. Compressive strength and modulus of all cement pellets were tested over 14 days. Results. The SBB cement was able to deliver rifampin over 14 days, while PMMA was unable to do so. SBB released more vancomycin overall than did PMMA. The mechanical properties of PMMA were significantly reduced upon rifampin incorporation, while there was no effect to the SBB cement. Vancomycin incorporation had no effect on the strength of either cement. Conclusion. SBB was found to be superior in terms of rifampin and vancomycin elution. Additionally, the incorporation of these antibiotics into SBB did not reduce the strength of the resultant SBB cement composite whereas rifampin substantially attenuates the strength of PMMA. Thus, SBB emerges as a potential weight-bearing alternative to PMMA for the local delivery of antibiotics. Cite this article: Bone Joint Res 2021;10(4):277–284

Background. With promising antibiofilm properties, rifampicin is considered as a cornerstone in the complementary treatment of bone and joint infections. But, achieving an adequate concentration of rifampicin long-term in bone tissue is a challenge. Long-term systemic administration also comes with concomitant side effects. Thus, local delivery of rifampicin in a carrier to ensure the high local concentration of antibiotic in surgical site after intervention due to infection could be a valuable alternative. However, an ideal platform for local delivery of rifampicin is still lacking. A calcium sulphate/hydroxyapatite (CaS/HA) (Cerament, Bonesupport AB, Sweden) biomaterial was used as a local delivery platform. Here we aimed 1) to evaluate the injectability of CaS/HA hand-mixed with rifampicin at various concentrations up to maximum one daily dose used systemically in clinical practice 2) to test a clinically used and commercially available mixing device containing the biphasic ceramic with rifampicin. Materials & Methods. Three different concentrations (100 mg, 300 mg and 600 mg) of rifampicin powder (Rifampicin Ebb, Sanofi S.P.A, Italy) diluted in 5 mL of mixing solution (C-TRU, Bonesupport AB, Sweden) were used. Rifampicin solution was mixed to the CaS/HA powder and the injectability of the CaS/HA plus rifampicin composite was evaluated by extruding 250 µL of paste manually through a graduated 1 mL syringe connected to an 18G needle (Ø=1.2 mm, L=4 cm). Mixing was done with a spatula for 30 s at 22°C ±1°C. Total weight of the paste before and after extrusion were measured. To normalize the amount of composite that remained in the needle and syringe tip after injection, the mean of the paste extruded from the syringe at 3 min was calculated for the tested concentrations (normalized value). Injectability (%) was calculated by dividing the weight of the paste extruded from the syringe with normalized value. Each test was repeated for three times at various time points (3, 5, 7 and 9 min). Additionally, 300 mg rifampicin was chosen to mix with the CaS/HA in a commercially available mixing system, which is used clinically. Results. All three combinations of CaS/HA plus rifampicin (100 mg, 300 mg & 600 mg) could be completely extruded from 1 mL syringes at 3 min. At 5 min, 100 mg & 300 mg could still be injected, whereas 600 mg was uninjectable or solidified. At 7 min, rifampicin 100 mg & 300 mg showed 34% and 11% of injectability respectively. At 9 min, no injectability was observed. The material was completely set within 15 minutes with all concentrations. With commercial mixing system, at the recommended injection time of 4 min, 78% of the CaS/HA plus rifampicin (300 mg) composite could be injected. Conclusions. The injectability was reduced with the increasing concentration of rifampicin. CaS/HA plus rifampicin (100 mg and/or 300 mg) could be used by hand mixing and transferred to a syringe or by using an available mixing system containing the ceramic. For higher concentrations of rifampicin, the rheological properties of the ceramics have to be modified for injectability

Objectives. The objective of this study was to characterize the effect of rifampin incorporation into poly(methyl methacrylate) (PMMA) bone cement. While incompatibilities between the two materials have been previously noted, we sought to identify and quantify the cause of rifampin’s effects, including alterations in curing properties, mechanical strength, and residual monomer content. Methods. Four cement groups were prepared using commercial PMMA bone cement: a control; one with 1 g of rifampin; and one each with equimolar amounts of ascorbic acid or hydroquinone relative to the amount of rifampin added. The handling properties, setting time, exothermic output, and monomer loss were measured throughout curing. The mechanical strength of each group was tested over 14 days. A radical scavenging assay was used to assess the scavenging abilities of rifampin and its individual moieties. Results. Compared with control, the rifampin-incorporated cement had a prolonged setting time and a reduction in exothermic output during polymerization. The rifampin cement showed significantly reduced strength and was below the orthopaedic weight-bearing threshold of 70 MPa. Based on the radical scavenging assay and strength tests, the hydroquinone structure within rifampin was identified as the polymerization inhibitor. Conclusion. The incorporation of rifampin into PMMA bone cement interferes with the cement’s radical polymerization. This interference is due to the hydroquinone moiety within rifampin. This combination alters the cement’s handling and curing properties, and lowers the strength below the threshold for weight-bearing applications. Additionally, the incomplete polymerization leads to increased toxic monomer output, which discourages its use even in non-weight-bearing applications. Cite this article: G. A. Funk, E. M. Menuey, K. A. Cole, T. P. Schuman, K. V. Kilway, T. E. McIff. Radical scavenging of poly(methyl methacrylate) bone cement by rifampin and clinically relevant properties of the rifampin-loaded cement. Bone Joint Res 2019;8:81–89. DOI: 10.1302/2046-3758.82.BJR-2018-0170.R2

Aim. Pyogenic spondylodiscitis remains a therapeutic challenge, as demonstrated by divergent treatment guidelines. The combination of moxifloxacin and rifampicin may be an attractive treatment option for cases caused by staphylococci; however, previous studies have reported a reduction in plasma concentrations of moxifloxacin when co-administered with rifampicin. The magnitude of this reduction in spinal tissues is not known. We aimed to investigate the interaction of rifampicin on moxifloxacin tissue concentrations in vertebral cancellous bone, intervertebral disc and subcutaneous adipose tissue in steady-state conditions using microdialysis in a porcine model. Method. Twenty female pigs were randomized into two groups of ten pigs: Group A received moxifloxacin 400 mg orally once daily for three days preoperatively. Group B received moxifloxacin 400 mg orally for three days preoperatively combined with rifampicin 450 mg twice daily for seven days preoperatively. Measurements were obtained from plasma, vertebral cancellous bone, intervertebral disc and subcutaneous adipose tissue for 24 h. Microdialysis was applied for sampling in solid tissues. Results. Co-administration of moxifloxacin and rifampicin demonstrated a reduction of free moxifloxacin concentrations in spinal tissues. The peak drug concentration (C. max. ) and the area under the concentration-time curve (AUC. 0–24. ) in all tissue compartments decreased in the range of 66–79% and 65–76%, respectively. Conclusions. Using microdialysis, we demonstrated a significant reduction of moxifloxacin C. max. and AUC. 0–24. in the spinal tissues when co-administered with rifampicin. Further studies are warranted to understand the clinical implications of this finding for the treatment of pyogenic spondylodiscitis

Aim. Rifampin is considered as the antibiotic corner stone in the treatment of acute staphylococcal periprosthetic joint infections (PJI). However, if, when, and how to use rifampin has been questioned. We evaluated the outcome of patients treated with and without rifampin, and analysed the influence of timing, dose and co-antibiotic. Method. Acute staphylococcal PJIs treated with surgical debridement between 1999 and 2017, and a minimal follow-up of 1 year were evaluated. Treatment failure was defined as the need for any further surgical procedure related to infection, PJI-related death, or the need for suppressive antimicrobial treatment. Results. A total of 669 patients were analysed. Treatment failure was 32.2% (131/407) in patients treated with rifampin and 54.2% (142/262) in whom rifampin was withheld (P < 0.001). The most prominent effect of rifampin was observed in knees (treatment failure 28.6% versus 63.9%, respectively, P < 0.001). The use of rifampin was an independent predictor of treatment success in the multi-variate analysis (OR 0.30, 95% CI 0.20 – 0.45). In the rifampin group, the use of a co-antibiotic other than a fluoroquinolone (OR 7.73, 95% CI 4.26 – 14.0) and the start of rifampin within 5 days after surgical debridement (OR 1.88, 95% CI 1.05 – 3.35) were predictors of treatment failure. Clindamycin demonstrated similar efficacy as co-antibiotic. The dosing of rifampin had no effect on outcome. Conclusions. Our data supports the use of rifampin in acute staphylococcal PJIs treated with surgical debridement, particularly in knees. Immediate start of rifampin after surgical debridement should probably be discouraged

Aim. Bone regeneration following the treatment of Staphylococcal bone infection or osteomyelitis is challenging due to the ability of Staphylococcus aureus to invade and persist within bone cells, which could possibly lead to antimicrobial tolerance and incessant bone destruction. Here, we investigated the influence of Staphylococcal bone infection on osteoblasts metabolism and function, with the underlying goal of determining whether Staphylococcus aureus-infected osteoblasts retain their ability to produce extracellular mineralized organic matrix after antibiotic treatment. Method. Using our in vitro infection model, human osteoblasts-like Saos-2 cells were infected with high-grade Staphylococcus aureus EDCC 5055 strain, and then treated with 8 µg/ml rifampicin and osteogenic stimulators up to 21-days. Results. Immunofluorescence and transmission electron microscopic (TEM) imaging demonstrated the presence of intracellular bacteria within the infected osteoblasts as early as 2 hours post-infection. TEM micrographs revealed intact intracellular bacteria with dividing septa indicative of active replication. The infected osteoblasts showed significant amounts of intracellular bacteria colonies and alteration in metabolic activity compared to the uninfected osteoblasts (p≤0.001). Treatment of S. aureus-infected osteoblasts with a single dose of 8 µg/ml rifampicin sufficiently restored the metabolic activity comparative to the uninfected groups. Alizarin red staining and quantification of the rifampicin-treated infected osteoblasts revealed significantly lower amount of mineralized extracellular matrix after 7-days osteogenesis (p<0.05). Interestingly, prolonged osteogenic stimulation and rifampicin-treatment up to 21 days improved the extracellular matrix mineralization level comparable to the rifampicin-treated uninfected group. However, the untreated (native) osteoblasts showed significantly more quantity of mineral deposits (p≤0.001). Ultrastructural analysis of the rifampicin-treated infected osteoblasts at 21-days osteogenesis revealed active osteoblasts and newly differentiated osteocytes, with densely distributed calcium crystal deposits within the extracellular organic matrix. Moreover, residual colony of dead bacteria bodies and empty vacuoles of the fully degraded bacteria embedded within the mineralized extracellular matrix. Gene expression level of prominent bone formation markers, namely RUNX2, COL1A1, ALPL, BMP-2, SPARC, BGLAP, OPG/RANKL showed no significant difference between the infected and uninfected osteoblast at 21-days of osteogenesis. Conclusions. Staphylococcus aureus bone infection can drastically impair osteoblasts metabolism and function. However, treatment with potent intracellular penetrating antibiotics, namely rifampicin restored the metabolic and bone formation activity of surviving osteoblasts. Delay in early osteogenesis caused by the bacterial infection was significantly improved over time after successful intracellular bacteria eradication

Aim. The demonstration of the in vivo bactericidal efficacy of a new bone cement with rifampicin contained in microcapsules and its intra-articular release profile. Method. Fifteen New Zealand White rabbits were employed to reproduce periprosthetic infection by intra-articular inoculation of 10. 5. CFU/mL of Staphylococcus aureus ATCC® 29213 using as a target implant a 3D printed stainless steel tibial insert. 7 days after inoculation, the first stage of the two stage exchange was carried out and at this time the animals were divided into two study groups: group C (7 rabbits) that received a spacer with gentamicin and group R (8 rabbits) that received a spacer with gentamicin and rifampicin microcapsules. Response to infection was monitored by clinical (weight and temperature), hematological (leukocyte, lymphocyte and platelet counts) and biochemical (erythrocyte sedimentation rate) analyses at the time of inoculation, at the first stage of exchange, 4 days after first stage and weekly until the fourth week when animals were euthanized. Microbiological counts were performed at the first stage of exchange and at the end of the study. Results. 14/15 animals (93.3%) developed a PJI 1 week after the inoculation. A statistically significant elevation of the leukocyte and platelet count and a decrease in the percentage of lymphocytes (p=0.0001) was found and positive microbiological cultures. Four weeks after the placement of the spacer, no bacterial growth was found in the soft tissue or bone samples of the group with rifampicin microcapsules (group R), being these differences statistically significant with p=0.01 and 0.03 respectively. The rifampicin intra-articular release kinetics showed concentrations above the staphylococcal MIC at all time points. Conclusions. The bone cement with microencapsulated rifampicin is effective in the in vivo treatment of prosthetic joint infection due to biofilm-forming S. aureus

Aim. S. aureus and coagulase-negative staphylococci are the most frequent bacteria responsible for PJI. In patients with acute PJI (i.e. <1 month following the implantation), DAIR with exchange of removal components followed by a combination of antibiotics that includes rifampin (particularly rifampin+fluoroquinolone) are recommended. Unfortunately, some patients could not receive rifampin due to drug-drug interaction or stopped it due to an adverse event. Finally, it was unclear if the dose and the duration of rifampin influenced the prognosis. Method. We performed a retrospective cohort study in 4 hospitals and included patients with staphylococcal acute post-operative (< 1 month) PJI treated with DAIR in 2011–2016 period. Univariate and multivariate Cox analysis and Kaplan Meier curves were used to determine the risk factors for treatment failure (persistence of clinical signs, new surgery w/o persistence or superinfection, infection-related death). Results. 79 patients were included (median age: 71 years IQR 53–89]; 55 men [69.6 %]; median ASA score: 2 [IQR 2–3]). Bacterial cultures revealed 65 S. aureus (82.3 %) and 15 coagulase-negative staphylococci (19.0 %) infections, including 14 methicillin-resistant isolates (17.7 %). Among all isolates, only 2 (2.5 %) were resistant to rifampin and 16 (20.3 %) were resistant to fluoroquinolone. The median duration of antimicrobial therapy was 92 days (IQR 31–152). Only 59 patients received rifampin (74.7 %), and 35 (44.3 %) the combination rifampin + fluoroquinolone. Median duration of rifampin was 56.5 days (IQR 15.8–86.0) and median dose 14.6mg/kg/d (IQR 13.0–16.7). Forty patients (50.6 %) received rifampin in the first 2 weeks and 43 patients (54.4 %) received at least 2 weeks of rifampin. Six patients (7.6 %) developed an adverse event leading to rifampin interruption. During a median follow-up of 443 days (IQR 219.5–790.5), 21 patients (26.6 %) experienced a treatment failure including 12 persistence of the initial pathogen (57.1 %) and 9 superinfections (42.9 %). An ASA score >2 (HR 2.8; 95%CI 1.26–6.15), the use of rifampin (HR 0.4; 95% CI 0.17–0.95) and the duration of rifampin treatment (HR 0.83; 95%CI 0.75–0.92 per additional week of treatment) were significant determinants of the outcome (but not methicillin-resistance). Receiving >2 weeks of rifampin prevented the failure, but an introduction during the first 2 weeks did not influence the outcome. Conclusions. In patients with staphylococcal acute PJI, the use of rifampin and its duration strongly influenced the prognosis. As 25% of patients could not receive rifampin, new drugs with anti-biofilm activity are required

Aim. This study investigated if co-administration of rifampicin with moxifloxacin led to a decrease in moxifloxacin concentrations in relevant tissues in a porcine model of implant-associated osteomyelitis caused S. aureus. Pharmacokinetics were measured using microdialysis and treatment effect was measured by quantifying bacterial load from implant and periprosthetic bone following a 1-stage revision and antibiotics. Method. 15 female pigs received a stainless-steel implant in the right proximal tibia and were randomized into two groups. Infection was introduced by inoculating the implant with Staphylococcus aureus as previously described. 1. On day 7 post surgery, all pigs were revised with implant removal, debridement of implant cavity and insertion of a sterile implant. 7 days of treatment was then initiated with either moxifloxacin 400 mg iv q.d. (M) or moxifloxacin and rifampicin 450 mg iv b.i.d. (RM). At day 14, animals were sedated and microdialysis was applied for continuous sampling of moxifloxacin concentrations during 8 h in five compartments: the implant cavity, cancellous bone in both the infected and non-infected proximal tibia, and adjacent subcutaneous tissue on both the infected and non-infected side using a previously described setup. 2. Venous blood samples were collected. Implant and adjacent bone were removed for analysis. Results. Comparable cure rates (sterilization of both implant and bone) were observed with 5/8 pigs in the RM group compared to 3/7 in the M group, p= 0.62 (Fisher's exact test). Due to the small number of samples with growth, median log CFU/ml was 0 for implant and bones in both groups. AUC. 0-last. was significantly smaller in plasma for the RM group, 407; 315 – 499 min µg/mL vs 625; 536 – 724 min µg/mL (mean;95% CI), p= 0.002 (Student's t-test). For the implant cavity, there was a trend toward a lower AUC. 0-last. 425; 327 – 524 min µg/ml vs 297; 205 – 389 min µg/ml in the RM group compared to M, yet this difference was not statistically different, p = 0.06. For the other compartments for other parameters (C. max. and T. max. ) across all compartments, there was no difference. Conclusions. While the AUC. 0-last. was lower in plasma for animals treated with RM, both the concentrations at the site of infection and treatment outcomes were comparable between groups

Aims. Here we used a mature seven-day biofilm model of Staphylococcus aureus, exposed to antibiotics up to an additional seven days, to establish the effectiveness of either mechanical cleaning or antibiotics or non-contact induction heating, and which combinations could eradicate S. aureus in mature biofilms. Methods. Mature biofilms of S. aureus (ATCC 29213) were grown on titanium alloy (Ti6Al4V) coupons for seven days and were subjected to the following treatments or their combinations: antibiotics, mechanical cleaning, or heat shock by induction heating of 60°C for one minute. Experiments were repeated at least five times. Results. In the untreated biofilm, growth up to 1.8×10. 11. colony-forming units (CFU)/cm. 2. was observed. Treatment with ciprofloxacin, flucloxacillin, vancomycin, cefuroxime, and amoxicillin all with rifampicin gave 6.0 log, 6.1 log, 1.4 log, 4.8 log, and 3.6 log reduction in CFU/cm. 2. , respectively. Mechanical cleaning alone resulted in 4.9 log reduction and induction heating in 7.3 log reduction. There was an additional effect of ciprofloxacin, flucloxacillin, and induction heating when used in combinations. There was no additional effect for mechanical cleaning. No bacterial growth could be detected after induction heating followed by seven days of ciprofloxacin with rifampicin. Conclusion. Mechanical cleaning, antibiotics, and non-contact induction heating reduced the bacterial load of mature S. aureus biofilms with approximately 5 log or more as a single treatment. The effect of mechanical cleaning on mature S. aureus biofilms was limited when used in combination with antibiotics and/or induction heating. Cite this article: Bone Joint Res 2022;11(9):629–638

Aim. The treatment of a chronic prosthetic joint infection (PJI) is a combination of the bacteria's identification, a «carcinological» surgery and an appropriate antibiotherapy. In case of gram positive cocci infection, rifampicin is often used. The aim of this study is to determine which factors are responsible for the development of resistance to rifampicine. Method. All patients had a total hip (THA) or knee (TKA) arthroplasty with a chronic infection. They were treated with a two-time surgery. All of them received a bi-antibiotic treatment. In case of gram positive cocci infection, and according to the susceptibility test, they received rifampicin. The 221 patients were operated from July 1997 to November 2013 in 3 university centers (one Belgian and two French) and were retrospectively analysed. The demographical, clinical and bacterial data as well as the antibiotic treatment were collected. The healing was defined as the absence of recurrence during the 2 years following surgery. Results. Among the 221 patients (from 22 to 91 years old, median age: 67), 133 (60%) had a THA infection. 22% of the peroperative samples collected during the first time surgery were sterile. 64% were mono-microbial and 14% were poly-microbial. For 69% of them, gentamycin-impregnated spacers were used and for 26% of them vancomycin and gentamycin-impregnated spacers were used. The median delay for the second time surgery was 52 days (15 to 221 days). The healing was higher for the patients treated by an antibiotic combination with rifampicin than the others (86 vs 72%; p=0.02). In the same way, the healing rate was higher in patients where the delay between the two surgeries was less than one month (91 vs 77%; p=0.09). There were more recurrence in TKA than in THA (30% vs 13%, p=0.006). 12 % of the patients showed a persistence of the germ or the emergence of a new microorganism with a comparable antibiogram. A resistance to rifampicin during the second surgery appears in 9 % of cases. Conclusions. Theses study results suggest the benefit of the use of rifampicin for the treatment of gram positive cocci prosthetic joint infections treated by a two time surgery. In all cases, intravenous antibiotic therapy was maintained until the wound was closed to decrease the emergence of resistance

There is a lack of carriers for the local delivery of rifampicin (RIF), one of the cornerstone second defence antibiotic for Staphylococcus aureus deep bone infections (DBIs). RIF is also associated with systemic side effects, and known for causing rapid development of antibiotic resistance when given as monotherapy. We evaluated a clinically usedbi-phasic calcium sulphate/hydroxyapatite (CaS/HA) biomaterial as a carrier for dual delivery of RIF with vancomycin (VAN) or gentamicin (GEN). It was hypothesized that this combined approach could provide improved biofilm eradication and prevent the development of RIF resistance. Methods: 1) Biofilm eradication: Using a modified crystal violet staining biofilm quantification method, the antibiotics released at different time points (Day 1, 3, 7, 14, 21, 28 and 35) from the hemispherical pellets of CaS/HA(500 mg)-VAN (24.57 mg) / GEN (10.35 mg) composites with or without RIF (8.11 mg) were tested for their ability to disrupt the preformed 48-h old biofilms of S. aureus ATCC 25923, and S. aureus clinical strain P-3 in 96-well microtitre plate. For each tested group of antibiotic fractions, five separate wells were used (n=5). 2) Testing for resistance development: Similar to the method mentioned above the 48-h biofilm embeded bacteria exposed to antibiotic fractions from different time points continuously for 7 days. The biofilms remained were then tested for RIF resistant strains of bacteria. Overall, there was clear antibiofilm biofilm activity observed with CaS/HA-VAN/GEN+RIF combinations compared with CaS/HA-VAN/GEN alone. The S. aureus strains developed resistance to RIF when biofilms were subjected to CaS/HA-RIF alone but not with combinations of CaS/HA-VAN/GEN+RIF. Enhanced antibiofilm effects without development of RIF resistance indicates that biphasic CaS/HA loaded with VAN or GEN could be used as a carrier for RIF for additional local delivery in clinically demanding DBIs. Acknowledgement: We deeply acknowledge the Royal Fysiographic Society of Lund, Landshövding Per Westlings Minnesfond and the Stina and Gunnar Wiberg fond for financial support

Introduction: Data on intralesional concentrations of modern anti-tuberculosis drugs isoniazid (H), rifampin (R) and pyrazinamid (Z) in tuberculous pleural effusions and psoas abscesses are scarce. Insight into drug penetration is important since subtherapeutic drug concentrations may result in the selection of a resistant bacterial population and lead to treatment failure. Material and Methods: Intralesional concentrations were measured 2 hours after drug administration in 6 patients with pleural effusions, and 10 with psoas abscesses. Results: Concentrations were variable. The same range was found for pleural effusions and psoas abscesses. Concentrations were below MIC values in none of 15 patients for H, in 2 of 13 for R, and in 8 of 9 for Z. Cmax:MIC ratio was always > 4 for H, in 4 of 13 for R, and in none of 9 for Z. In 5:8 patients receiving all 3 drugs both R and Z had Cmax:MIC ratios < 4, indicating subtherapeutic drug levels. Conclusion: Intralesional drug concentrations of isoniazid (H), rifampin (R), and pyrazinamid (Z) were variable. The same range was found for pleural effusions and psoas abscesses. Cmax:MIC ratio for H was always sufficient, for R in most cases below the desired ratio, and for Z on average 10 times too low. In 5 of 8 patients receiving all 3 drugs, both R and Z had Cmax:MIC ratios below 4, indicating intralesional subtherapeutic drug levels for R and Z. This local monotherapy with H may result in the selection of a resistant bacterial population and lead to failure of treatment. Drainage as additional therapy seems indicated

Aims. To investigate the efficacy of ethylenediaminetetraacetic acid-normal saline (EDTA-NS) in dispersing biofilms and reducing bacterial infections. Methods. EDTA-NS solutions were irrigated at different durations (1, 5, 10, and 30 minutes) and concentrations (1, 2, 5, 10, and 50 mM) to disrupt Staphylococcus aureus biofilms on Matrigel-coated glass and two materials widely used in orthopaedic implants (Ti-6Al-4V and highly cross-linked polyethylene (HXLPE)). To assess the efficacy of biofilm dispersion, crystal violet staining biofilm assay and colony counting after sonification and culturing were performed. The results were further confirmed and visualized by confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM). We then investigated the efficacies of EDTA-NS irrigation in vivo in rat and pig models of biofilm-associated infection. Results. When 10 mM or higher EDTA-NS concentrations were used for ten minutes, over 99% of S. aureus biofilm formed on all three types of materials was eradicated in terms of absorbance measured at 595 nm and colony-forming units (CFUs) after culturing. Consistently, SEM and CSLM scanning demonstrated that less adherence of S. aureus could be observed on all three types of materials after 10 mM EDTA-NS irrigation for ten minutes. In the rat model, compared with NS irrigation combined with rifampin (Ti-6Al-4V wire-implanted rats: 60% bacteria survived; HXLPE particle-implanted rats: 63.3% bacteria survived), EDTA-NS irrigation combined with rifampin produced the highest removal rate (Ti-6Al-4V wire-implanted rats: 3.33% bacteria survived; HXLPE particle-implanted rats: 6.67% bacteria survived). In the pig model, compared with NS irrigation combined with rifampin (Ti-6Al-4V plates: 75% bacteria survived; HXLPE bearings: 87.5% bacteria survived), we observed a similar level of biofilm disruption on Ti-6Al-4V plates (25% bacteria survived) and HXLPE bearings (37.5% bacteria survived) after EDTA-NS irrigation combined with rifampin. The in vivo study revealed that the biomass of S. aureus biofilm was significantly reduced when treated with rifampin following irrigation and debridement, as indicated by both the biofilm bacterial burden and crystal violet staining. EDTA-NS irrigation (10 mM/10 min) combined with rifampin effectively removes S. aureus biofilm-associated infections both in vitro and in vivo. Conclusion. EDTA-NS irrigation with or without antibiotics is effective in eradicating S. aureus biofilm-associated infection both ex and in vivo. Cite this article: Bone Joint Res 2024;13(1):40–51

Aim. Rifampicin as a biofilm-active antibiotic drug has a significant role in the treatment of periprosthetic joint infection (PJI). However, rifampicin resistance is an increasing threat to PJI treatment. This study aimed to evaluate the prevalence of rifampicin resistant staphylococci over time and its association with infection-free survival after PJI in a single centre in Sweden. Methods. We included 238 PJIs in 238 patients who had undergone PJI revision surgery from 2001 to 2020 on whom the causative bacteria were staphylococci, and the agent was tested for rifampicin resistance. Data regarding agents, rifampicin resistance, treatment and outcome was obtained. Kaplan-Meier survival analysis and a Cox regression model with adjustment for age, sex, localisation (hip or knee) and type of prosthesis (primary or revision) were used to calculate infection-free survival rates and adjusted risk ratios (HRs) of the risk of treatment failure. Treatment failure was defined as any reoperation or suppression treatment with antibiotics due to prolonged infection. Results. Among the included 238 PJIs, 40 rifampicin-resistant staphylococci [93% Coagulase Negative Staphylococci (CoNS)] and 29 treatment failures were identified. The proportion of rifampicin resistant agents decreased from 25% in 2010–2015 to 12% in 2016–2020. The 2-year infection-free survival rates were 79.0% (95% CI 0.66–0.92) for the rifampicin resistant and 90% (95% CI 0.86–0.94) for the rifampicin sensitive group. Patients with PJI caused by rifampicin resistant bacteria had a significantly higher risk of treatment failure than those caused by sensitive bacteria (HR 2.5; 95% CI 1.0–6.2). Conclusions. The incidence of PJI caused by rifampicin resistant staphylococci decreased in Uppsala, Sweden over the past 20 years. PJI caused by rifampicin-resistant staphylococci has a two-fold risk for treatment failure compared to PJI caused by rifampicin-sensitive staphylococci, which stresses the importance of retaining rifampicin resistance low. Additionally, the increased risk of treatment failure when PJI is caused by a rifampicin-resistant bacteria warrants consideration of a more conservative treatment strategy

Background. Treatment of staphylococcal prosthetic joint infection (PJI) usually consists of surgical debridement and prolonged rifampicin combination therapy. Tailored antimicrobial treatment alternatives are needed due to frequent side effects and drug-drug interactions with rifampicin combination therapy. We aimed to assess the effectiveness of several alternative antibiotic strategies in patients with staphylococcal PJI. Methods. In this prospective, multicenter registry-based study, all consecutive patients with a staphylococcal PJI, treated with DAIR or one-stage revision surgery between January 1. st. , 2015 and November 3. rd. , 2020, were included. Patients were treated according to a predefined protocol for PJI. Antimicrobial treatment strategies differed between centers, which was accepted and used as pseudorandomization. Depending on the hospital patients were admitted to, they were treated with either a long-term rifampicin strategy (consisting of 12 weeks rifampicin combination therapy) ore one of several short-term rifampicin strategies, consisting of only five days of rifampicin combination treatment, started immediately postoperative, followed by clindamycin, flucloxacillin or vancomycin monotherapy. Patients were stratified in different groups, depending on the used antimicrobial strategy. Cox proportional hazards models were used to compare outcome between the groups. Results. Two hundred patients were included and, based on the antimicrobial treatment, stratified in one long-term rifampicin group (n=23) or one of the three short-term rifampicin groups: clindamycin (n=56), flucloxacillin (n=47), vancomycin (n=26), other (n=48). Outcome of PJI after DAIR or one-stage exchange was not statistically different between patients treated with long-term rifampicin combination therapy and patients treated with clindamycin or flucloxacillin monotherapy including only five days of rifampicin combination therapy. Moreover, treatment duration was four weeks shorter in the clindamycin-based and flucloxacillin-based groups. Adjusted hazard ratios for failure for patients treated with either flucloxacillin or clindamycin were almost equal to patients treated with long-term rifampicin combination therapy (aHR 1.21, 95%CI 0.34–4.40). Conclusions. A short-term rifampicin strategy with either clindamycin or flucloxacillin and only five days of rifampicin was found to be as effective as traditional long-term rifampicin combination therapy. A randomized controlled trial is needed to further address efficacy and safety of alternative treatment strategies for staphylococcal PJI