Oral-Only Linezolid-Rifampin Is Highly Effective Compared with Other Antibiotics for Periprosthetic Joint Infection: Study of a Mouse Model

Combination therapy delays antimicrobial resistance after adaptive laboratory evolution of Staphylococcus aureus

Antibiotic resistance, driven by misuse and overuse of antibiotics, is one of the greatest threats against human health. The antimicrobial pressure during prolonged antibiotic treatment of chronic bacterial infections selects for resistance. While antibiotic combinations may reduce resistance emergence, antibiotic-tolerant persister cells can serve as a reservoir for resistance development. Therefore, targeting these cells with anti-persister drugs might provide a novel strategy for resistance prevention. In this study, we conducted 42 days of adaptive laboratory evolution using Staphylococcus aureus exposed to rifampicin, ciprofloxacin, daptomycin, and vancomycin, alone or in combination with the anti-persister drug mitomycin C. We monitored antibiotic susceptibility daily and assessed phenotypic changes in growth and biofilm formation in evolved strains. Whole-genome sequencing revealed mutations linked to antibiotic resistance and phenotypic shifts. Rifampicin resistance developed within a few days, while ciprofloxacin and daptomycin emerged in approximately 3 weeks. Treatments with vancomycin or mitomycin C resulted in minimal changes in susceptibility. While combination therapy delayed resistance, it did not fully prevent it. Notably, the combination of rifampicin with mitomycin C maintained rifampicin susceptibility throughout the long-term evolution experiment. Sub-inhibitory antibiotic treatments selected for both previously characterized and novel mutations, including unprecedented alterations in the nucleotide excision repair system and azoreductase following mitomycin C exposure. The delayed resistance development observed with combination therapy, particularly mitomycin C's ability to suppress rifampicin resistance, suggests potential therapeutic applications. Future studies should evaluate the clinical efficacy of anti-persister drugs in preventing resistance across different bacterial pathogens and infection models.

The Application of artificial intelligence in periprosthetic joint infection

Periprosthetic joint infection (PJI) represents one of the most devastating complications following total joint arthroplasty, often necessitating additional surgeries and antimicrobial therapy, and potentially leading to disability. This significantly increases the burden on both patients and the healthcare system. Given the considerable suffering caused by PJI, its prevention and treatment have long been focal points of concern. However, challenges remain in accurately assessing individual risk, preventing the infection, improving diagnostic methods, and enhancing treatment outcomes. The development and application of artificial intelligence (AI) technologies have introduced new, more efficient possibilities for the management of many diseases. In this article, we review the applications of AI in the prevention, diagnosis, and treatment of PJI, and explore how AI methodologies might achieve individualized risk prediction, improve diagnostic algorithms through biomarkers and pathology, and enhance the efficacy of antimicrobial and surgical treatments. We hope that through multimodal AI applications, intelligent management of PJI can be realized in the future.

Ceftaroline + Rifampin Versus Vancomycin + Rifampin in the Treatment of Methicillin-Resistant Staphylococcus aureus Meningitis in an Experimental Rabbit Model

Background/Aim: To compare the effectiveness ceftaroline-rifampicin (CR) and vancomycin-rifampicin (VR), against methicillin-resistant Staphylococcus aureus (MRSA) in a rabbit meningitis model, to compare the effects on brain tissues in terms of inflammation and apoptosis and to test the antibiotics via in vitro time-kill and synergy tests. Method: Meningitis was induced using MRSA strain ATCC 43300. After 28 hours, the rabbits were split into three groups: control, VR, and CR. A CSF culture was taken at the start (T0) and end of treatment (EOT)-the 24th hour of treatment. At EOT, the animals' brain tissues were examined for inflammation and apoptosis. The study strain was tested for a 24-hour time kill assay. Results: At the EOT, statistically significant differences were observed between the treatment groups in terms of reducing the cerebrospinal fluid (CSF) bacterial count, achieving partial or complete treatment response, and exhibiting lower levels of neuronal apoptosis compared with the control group. However, there was no significant difference in all three parameters and in survival between the two treatment groups. The CR group exhibited a noticeable decrease in inflammation than the control group, but no significant difference was found between the control group versus VR and VR versus CR group. Rifampicin did not improve antibacterial efficacy in the in vitro time-kill assay. Conclusion: The CR arm showed better complete response and inflammation, but both treatments were similar in other parameters. CR combination was found as effective as VR combination for treating MRSA meningitis.

Electrophoretic Deposition of Gentamicin Into Titania Nanotubes Prevents Evidence of Infection in a Mouse Model of Periprosthetic Joint Infection

Periprosthetic joint infection (PJI) is a leading cause and major complication of joint replacement failure. As opposed to standard-of-care systemic antibiotic prophylaxis for PJI, we developed and tested titanium femoral intramedullary implants with titania nanotubes (TNTs) coated with the antibiotic gentamicin and slow-release agent chitosan through electrophoretic deposition (EPD) in a mouse model of PJI. We hypothesized that these implants would enable local gentamicin delivery to the implant surface and surgical site, effectively preventing bacterial colonization. In the mouse PJI model, C57BL/6 mice received implants with TNTs coated with chitosan (chitosan group; control group) or with TNTs coated with chitosan and gentamicin (chitosan + gentamicin group; experimental group). Following implant placement, the surgical site was inoculated with 1 × 103 CFUs of Xen36 bioluminescent Staphylococcus aureus. All the mice in the chitosan group and none in the chitosan + gentamicin group had evidence of infection based on CFU analysis and bioluminescence imaging through the 14-day assessment postsurgery. Correspondingly, scanning electron microscopy analysis at the implant surface demonstrated bacterial biofilm only in the chitosan group. Furthermore, periosteal reaction and peri-implant bone loss at the femur were significantly reduced in the chitosan + gentamicin group. The chitosan + gentamicin group had reduced pain behavior, improved weight-bearing, and increased weight compared to the chitosan-control group. This study provides preclinical evidence supporting the efficacy of implants with TNTs coated with chitosan and gentamicin through EPD for preventing bacterial colonization and biofilm formation in a mouse model of PJI.

The Role of Rifampin in Prosthetic Joint Infections: Efficacy, Challenges, and Clinical Evidence

Rifampin is a crucial antibiotic in the management of prosthetic joint infections (PJI), particularly due to its effectiveness against staphylococcal bacteria and its ability to penetrate and disrupt biofilms. This review evaluates rifampin's role by examining its mechanism of action, clinical efficacy, and integration into treatment regimens based on recent evidence and guidelines. Rifampin's synergistic effects with other antibiotics, such as β-lactams and vancomycin, enhance bacterial eradication, and some evidence shows that it improves patient outcomes. However, evidence supporting its use is limited by the scarcity of robust human clinical trials, and challenges such as potential drug interactions and resistance development necessitate careful management. Ongoing research is needed to refine its use and address existing limitations in clinical practice.

Preclinical Positron Emission Tomography (PET) of Prosthetic Joint Infection Using a Nitro-Prodrug of 2-[18F]F-p-Aminobenzoic Acid ([18F]F-PABA)

Deep-seated bacterial infections are difficult to detect and diagnose due to the lack of specific clinical imaging modalities. Therefore, the bacteria-specific positron emission tomography radiotracer 2-[18F]fluoro-4-nitrobenzoic acid ([18F]FNB) was developed, which is reduced to 2-[18F]fluoro-4-aminobenzoic acid ([18F]F-PABA) by bacterial nitroreductases and has improved pharmacokinetics compared to the parent compound. PET imaging demonstrated that the uptake of 2-[18F]fluoro-4-nitrobenzoic acid in a clinically relevant Staphylococcus aureus prosthetic joint infection model was up to ∼4-fold higher in the infected joint compared to the contralateral joint. 2-[18F]Fluoro-4-nitrobenzoic acid was also able to distinguish infection from inflammation in a surgical inflammation model. Based on the mouse radiation dosimetry results, the calculated effective dose of 2-[18F]fluoro-4-nitrobenzoic acid was well below the whole-body radiation dose limit established by the Food and Drug Administration for humans. In addition, no treatment-related microscopic changes in organ histopathology were observed in a mouse acute toxicity study. Overall, these data suggest that 2-[18F]fluoro-4-nitrobenzoic acid is a specific and effective imaging agent for noninvasively diagnosing prosthetic joint infections.

The Efficacy and Safety of an Intra-articular Dual-Acting Antibacterial Agent (TNP-2092) for Implant Infection-Associated Methicillin-Resistant Staphylococcus aureus

Owing to the presence of microbial biofilm on the implant, the eradication of biofilm-associated infections poses a challenge for antibiotic therapies. The study aimed to investigate the efficacy and safety of the novel antibiotic agent TNP-2092 in the context of implant infections. In vivo, rats with periprosthetic joint infection (PJI) treated with antibiotics showed an increase in body weight and decrease in swelling, temperature, and width of knee, compared with the control group. Meanwhile, inflammatory markers in synovium and serum were decreased in the TNP-2092 group, consistent with the pathological results. Moreover, TNP-2092 was effective in eliminating bacteria and disruption biofilm formation, and further alleviated the abnormal bone absorption and reactive bone changes around the prosthesis. In conclusion, intra-articular injection of TNP-2092 is safe and effective in treating knee PJI in a rat model. The study provides a foundation for the future utilization of TNP-2092 in the management of implant-related infections.

Self-controllable proteinic antibacterial coating with bacteria-triggered antibiotic release for prevention of periprosthetic infection

Periprosthetic infection is a devastating postimplantation complication in which a biofilm layer harboring invasive microorganisms forms around orthopedic implants, leading to severe implant failure and patient morbidity. Despite the development of several infection-triggered antibiotic release approaches, most current antibacterial coatings are susceptible to undesired antibiotic leakage or mechanical disintegration during prosthesis installation. Herein, we propose a self-controllable proteinic antibacterial coating capable of both long-lasting adherence onto titanium implant substrates over the implant fixation period and instantaneous bacterial eradication. Importantly, the pH-dependent reversible metal coordination of mussel adhesive protein (MAP) enabled bacterial concentration-dependent antibiotic delivery in response to infection-induced acidification. In addition, the MAP coating exhibited superior self-healable adhesive properties and scratch resistance, which enabled to avert issues associated with mechanical damages, including peeling and cracking, often occurring in conventional implant coating systems. The gentamicin-loaded MAP coating exhibited complete inhibition of bacterial growth in vivo against Staphylococcus aureus penetrations during implantation surgery (immediate infection) and even 4 weeks after implantation (delayed infection). Thus, our antibiotic-loaded MAP hydrogel coating can open new avenues for self-defensive antibiotic prophylaxis to achieve instant and sustainable bacteriocidal activity in orthopedic prostheses. © 2017 Elsevier Inc. All rights reserved.

Linezolid does not improve bactericidal activity of rifampin-containing first-line regimens in animal models of TB meningitis

Tuberculous meningitis (TB meningitis) is the most devastating form of tuberculosis (TB) and there is a critical need to optimize treatment. Linezolid is approved for multidrug resistant TB and has shown encouraging results in retrospective TB meningitis studies, with several clinical trials underway assessing its additive effects on high-dose (35 mg/kg/day) or standard-dose (10 mg/kg/day) rifampin-containing regimens. However, the efficacy of adjunctive linezolid to rifampin-containing first-line TB meningitis regimens and the tissue pharmacokinetics (PK) in the central nervous system (CNS) are not known. We therefore conducted cross-species studies in two mammalian (rabbits and mice) models of TB meningitis to test the efficacy of linezolid when added to the first-line TB regimen and measure detailed tissue PK (multicompartmental positron emission tomography [PET] imaging and mass spectrometry). Addition of linezolid did not improve the bactericidal activity of the high-dose rifampin-containing regimen in either animal model. Moreover, the addition of linezolid to standard-dose rifampin in mice also did not improve its efficacy. Linezolid penetration (tissue/plasma) into the CNS was compartmentalized with lower than previously reported brain and cerebrospinal fluid (CSF) penetration, which decreased further two weeks after initiation of treatment. These results provide important data regarding the addition of linezolid for the treatment of TB meningitis.

Early Staphylococcal Periprosthetic Joint Infection (PJI) Treated with Debridement, Antibiotics, and Implant Retention (DAIR): Inferior Outcomes in Patients with Staphylococci Resistant to Rifampicin

It is unknown how rifampicin resistance in staphylococci causing a periprosthetic joint infection (PJI) affects outcomes after debridement, antibiotics, and implant retention (DAIR). We thus aimed to compare the risk of relapse in DAIR-treated early PJI caused by staphylococci with or without rifampicin resistance. In total, 81 patients affected by early PJI were included, and all patients were treated surgically with DAIR. This was repeated if needed. The endpoint of relapse-free survival was estimated using the Kaplan-Meier method, and Cox regression models were fitted to assess the risk of infection relapse for patients infected with rifampicin-resistant bacteria, adjusted for age, sex, type of joint, and type of index surgery. In patients with rifampicin-resistant staphylococci, relapse was seen in 80% after one DAIR procedure and in 70% after two DAIR procedures. In patients with rifampicin-sensitive bacteria, 51% had an infection relapse after one DAIR procedure and 33% had an infection relapse after two DAIR procedures. Patients with rifampicin-resistant staphylococcal PJI thus had an increased adjusted risk of infection relapse of 1.9 (95% CI: 1.1-3.6, p = 0.04) after one DAIR procedure compared to patients with rifampicin-sensitive bacteria and a 4.1-fold (95% CI: 1.2-14.1, p = 0.03) increase in risk of infection relapse after two DAIR procedures. Staphylococcal resistance to rifampicin is associated with inferior outcomes after DAIR. These findings suggest that DAIR may not be a useful strategy in early PJI caused by rifampicin-resistant staphylococci.

A Comparison of the Minimum Inhibitory Concentration of Antibiotics in Staphylococcus Species Isolated From Orthopedic and Respiratory Medicine Infections

INTRODUCTION

Antibiotic susceptibility is very important for the successful treatment of orthopedic infections, particularly for implant-related infections. While the minimum inhibitory concentrations (MICs) of Staphylococcus species were well investigated for the isolates from the respiratory tract, investigations for orthopedic pathogens are very limited. We investigated the antibiotic MIC values of Staphylococcus species isolated from orthopedic infections and compared them with those of respiratory medicine isolates used as a control.

METHODS

The MICs of vancomycin (VCM), arbekacin (ABK), teicoplanin (TEIC), linezolid (LZD), and rifampicin (RFP) of a total of consecutive 259 (89 orthopedic and 170 respiratory) Staphylococcus speciesisolated in our laboratory from January 2013 to July 2016 were retrospectively reviewed. Differences between the MICs of each antibiotic in orthopedic and respiratory samples were determined.

RESULTS

The number of methicillin-sensitive Staphylococcus aureus (MSSA) with a VCM MIC of <0.5 μg/mL among respiratory isolates was significantly higher than that among orthopedic isolates, while those with a MIC of 2 μg/mL were significantly lower (P = 0.0078). The proportion of methicillin-resistant coagulase-negative staphylococci (MRCNS) isolates with a VCM MIC of 2 μg/mL was significantly higher in orthopedic samples than that of methicillin-resistant Staphylococcus aureus (MRSA) (P < 0.001) in respiratory isolates. The proportion of MRCNS orthopedic isolates with an RFP MIC of >2 μg/mL was significantly higher (P = 0.0058) than that of other orthopedic staphylococci.

CONCLUSIONS

The VCM MICs of Staphylococcus species from orthopedic infections were higher than those of respiratory samples, particularly MRCNS from implant-related samples.

Intra-wound versus systemic vancomycin for preventing surgical site infection induced by methicillin-resistant S. aureus after spinal implant surgery in a rat model

BACKGROUND

Systemic vancomycin administration pre-operatively for the infection prophylaxis of spinal implant surgery remains unsatisfactory. This study aimed to explore the efficacy and dosage of local use of vancomycin powder (VP) in preventing surgical site infections after spinal implant surgery in a rat model.

METHODS

Systemic vancomycin (SV; intraperitoneal injection, 88 mg/kg) or intraoperative intra-wound VP (VP0.5: 44 mg/kg, VP1.0: 88 mg/kg, VP2.0: 176 mg/kg) was applied after spinal implant surgery and methicillin-resistant S. aureus (MRSA; ATCC BAA-1026) inoculation in rats. General status, blood inflammatory biomarkers, microbiological and histopathological evaluation were performed during 2 weeks post-surgery.

RESULTS

No post-surgical deaths, wound complications and obvious signs of vancomycin adverse effects were observed. Bacterial counts, blood and tissue inflammation were reduced in the VP groups compared with the SV group. VP2.0 group showed better outcomes in weight gain and tissue inflammation than the VP0.5 and VP1.0 group. Microbial counts indicated that no bacteria survived in the VP2.0 group, whereas MRSA was detected in VP0.5 and VP1.0 groups.

CONCLUSIONS

Intra-wound VP may be more effective than systemic administration in preventing infection caused by MRSA (ATCC BAA-1026) after spinal implant surgery in a rat model.

Meropenem-loaded Cement Is Effective in Preventing Gram-negative Osteomyelitis in an Animal Model

BACKGROUND

Low-dose antibiotic-loaded acrylic cement is routinely used for preventing skeletal infection or reimplantation in patients with periprosthetic joint infections. However, few reports about the selection of antibiotics in acrylic cement for antigram-negative bacteria have been proposed.

QUESTIONS/PURPOSES

(1) Does the addition of antibiotics (tobramycin, meropenem, piperacillin, ceftazidime, ciprofloxacin, and aztreonam) to acrylic cement adversely affect compressive strength before and after elution? (2) Which antibiotics have the highest cumulative release within 28 days? (3) Which antibiotics showed antimicrobial activity within 28 days? (4) Does meropenem-loaded cement improve body weight, temperature, and other inflammatory markers compared with control unloaded cement?

METHODS

This is an in vitro study that assessed the mechanical strength, antibiotic elution, and antibacterial properties of antibiotic-loaded cement, combined with an animal study in a rat model that evaluated key endpoints from the animal study. In the in vitro study, we added 2 g of tobramycin (TOB), meropenem (MEM), piperacillin (PIP), ceftazidime (CAZ), ciprofloxacin (CIP), and aztreonam (ATM) to 40 g of acrylic cement. The compressive strength, elution, and in vitro antibacterial properties of the antibiotic-loaded cement were detected. Thirty male rats were randomly divided into two groups: CON (antibiotic-unloaded cement) and MEM (meropenem-loaded cement, which had the most stable antibacterial properties of the six tested antibiotic-loaded cements in vitro within 28 days). The right tibia of all rats underwent arthroplasty and was implanted with the cement, followed by inoculation with Pseudomonas aeruginosa in the knee. General status, serum biomarkers, radiology, microbiological assay, and histopathological tests were assessed over 14 days postoperatively.

RESULTS

The compressive strength of all tested antibiotic cement combinations exceeded the 70 MPa threshold (the requirement established in ISO 5833). The cumulative release proportions of the raw antibiotic in cement were 1182.8 ± 37.9 µg (TOB), 355.6 ± 16.2 µg (MEM), 721.2 ± 40.3 µg (PIP), 477.4 ± 37.1 µg (CAZ), 146.5 ± 11.3 µg (CIP), and 372.1 ± 14.5 µg (ATM) within 28 days. Over a 28-day period, meropenem cement demonstrated antimicrobial activities against the four tested gram-negative bacteria ( Escherichia coli , P. aeruginosa , Klebsiella pneumoniae , and Proteus vulgaris ). Ciprofloxacin cement inhibited E. coli growth, ceftazidime and aztreonam cement inhibited K. pneumonia growth, and tobramycin cement inhibited P. aeruginosa . Only meropenem demonstrated antimicrobial activity against all gram-negative bacteria on agar diffusion bioassay. Rats treated with meropenem cement showed improved body weight (control: 280.1 ± 4.2 g, MEM: 288.5 ± 6.6 g, mean difference 8.4 [95% CI 4.3 to 12.6]; p < 0.001), improved knee width (control: 13.5 ± 0.3 mm, MEM: 11.8± 0.4 mm, mean difference 1.7 [95% CI 1.4 to 2.0]; p < 0.001), decreased inflammatory marker (control: 316.7 ± 45.0 mm, MEM: 116.5 ± 21.8 mm, mean difference 200.2 [95% CI 162.3 to 238.2]; p < 0.001), decreased radiographic scores (control: 17.7 ± 2.0 mm, MEM: 10.7± 1.3 mm, mean difference 7.0 [95% CI 5.4 to 8.6]; p < 0.001), improved bone volume/total volume (control: 8.7 ± 3.0 mm, MEM: 28.5 ± 5 .5 mm, mean difference 19.8 [95% CI 13.3 to 26.2]; p < 0.001), decreased Rissing scale scores of the knee gross pathology (control: 3.3 ± 0.5, MEM: 1.1 ± 0.7, mean difference 2.2 [95% CI 1.7 to 2.7]; p < 0.001), decreased Petty scale scores of knee synovium (control: 2.9 ± 0.4 mm, MEM: 0.7 ± 0.7 mm, mean difference 2.1 [95% CI 1.7 to 2.5]; p < 0.001), and decreased bacterial counts of the bone and soft tissues and negative bacterial cultures of cement (p < 0.001, p < 0.001, p < 0.001, p < 0.001, respectively).

CONCLUSION

In this current study, MEM cement had the most stable in vitro antimicrobial activities, effective in vivo activity while having acceptable mechanical and elution characteristics, and it may be an effective prophylaxis against skeletal infection caused by gram-negative bacteria.

CLINICAL RELEVANCE

Meropenem-loaded acrylic cement is a potentially effective prevention measure for skeletal infection caused by gram-negative bacteria; however, more related clinical research is needed to further evaluate the safety and efficacy.

The Novel Oxazolidinone TBI-223 Is Effective in Three Preclinical Mouse Models of Methicillin-Resistant Staphylococcus aureus Infection

Staphylococcus aureus is an important cause of various infections in humans, including bacteremia, skin and soft tissue infections, and infections associated with implanted medical devices. The emergence of hospital- and community-acquired methicillin-resistant Staphylococcus aureus (MRSA) underscores the urgent and unmet need to develop novel, safe, and effective antibiotics against these multidrug-resistant clinical isolates. Oxazolidinone antibiotics such as linezolid have excellent oral bioavailability and provide coverage against MRSA infections. However, their widespread and long-term use is often limited by adverse effects, especially myelosuppression. TBI-223 is a novel oxazolidinone with potentially reduced myelosuppression, compared to linezolid, but its efficacy against MRSA infections is unknown. Therefore, the preclinical efficacy of TBI-223 (80 and 160 mg/kg twice daily) was compared with that of linezolid (40 and 80 mg/kg twice daily) and sham treatment in mouse models of MRSA bacteremia, skin wound infection, and orthopedic-implant-associated infection. The dosage was selected based on mouse pharmacokinetic analysis of both linezolid and TBI-223, as well as measurement of the MICs. In all three models, TBI-223 and linezolid had comparable dose-dependent efficacies in reducing bacterial burden and disease severity, compared with sham-treated control mice. Taken together, these findings indicate that TBI-223 represents a novel oxazolidinone antibiotic that may provide an additional option against MRSA infections. Future studies in larger animal models and clinical trials are warranted to translate these findings to humans. IMPORTANCE Staphylococcus aureus is the predominant cause of bloodstream, skin, and bone infections in humans. Resistance to commonly used antibiotics is a growing concern, making it more difficult to treat staphylococcal infections. Use of the oxazolidinone antibiotic linezolid against resistant strains is hindered by high rates of adverse reactions during prolonged therapy. Here, a new oxazolidinone named TBI-223 was tested against S. aureus in three mouse models of infection, i.e., bloodstream infection, skin infection, and bone infection. We found that TBI-223 was as effective as linezolid in these three models. Previous data suggest that TBI-223 has a better safety profile than linezolid. Taken together, these findings indicate that this new agent may provide an additional option against MRSA infections. Future studies in larger animal models and clinical trials are warranted to translate these findings to humans.

Felodipine enhances aminoglycosides efficacy against implant infections caused by methicillin-resistant Staphylococcus aureus, persisters and biofilms

Methicillin-resistant Staphylococcus aureus (MRSA), biofilms, and persisters are three major factors leading to recurrent and recalcitrant implant infections. Although antibiotics are still the primary treatment for chronic implant infections in clinical, only few drugs are effective in clearing persisters and formed biofilms. Here, felodipine, a dihydropyridine calcium channel blocker, was reported for the first time to have antibacterial effects against MRSA, biofilm, and persisters. Even after continuous exposure to sub-lethal concentrations of felodipine, bacteria are less likely to develop resistance. Besides, low doses of felodipine enhances the antibacterial activity of gentamicin by inhibiting the expression of protein associated with aminoglycoside resistance (aacA-aphD). Next, biofilm eradication test and persisters killing assay suggested felodipine has an excellent bactericidal effect against formed biofilms and persisters. Furthermore, the result of protein profiling, and quantitative metabonomics analysis indicated felodipine reduce MRSA virulence (agrABC), biofilm formation and TCA cycle. Then, molecular docking showed felodipine inhibit the growth of persisters by binding to the H pocket of ClpP protease, which could lead to substantial protein degradation. Furthermore, murine infection models suggested felodipine in combination with gentamicin alleviate bacterial burden and inflammatory response. In conclusion, low dose of felodipine might be a promising agent for biomaterial delivery to enhance aminoglycosides efficacy against implant infections caused by MRSA, biofilm, and persisters.

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Felodipine inhibits MRSA gene expression associated with aminoglycoside resistance and biofilm formation.

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Felodipine eradicates formed biofilm and persisters on the surface of implants.

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Felodipine induces proteolysis of MRSA and decreases energy metabolism.

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Felodipine in combination with gentamicin alleviates murine periprosthetic joint infection.

Estimation of Minimum Biofilm Eradication Concentration (MBEC) on In Vivo Biofilm on Orthopedic Implants in a Rodent Femoral Infection Model

The formation of a biofilm on the implant surface is a major cause of intractable implant-associated infection. To investigate the antibiotic concentration needed to eradicate the bacteria inside a biofilm, the minimum biofilm eradication concentration (MBEC) has been used, mostly against in vitro biofilms on plastic surfaces. To produce a more clinically relevant environment, an MBEC assay against biofilms on stainless-steel implants formed in a rat femoral infection model was developed. The rats were implanted with stainless steel screws contaminated by two Staphylococcus aureus strains (UAMS-1, methicillin-sensitive Staphylococcus aureus; USA300LAC, methicillin-resistant Staphylococcus aureus) and euthanized on days 3 and 14. Implants were harvested, washed, and incubated with various concentrations (64–4096 μg/mL) of gentamicin (GM), vancomycin (VA), or cefazolin (CZ) with or without an accompanying systemic treatment dose of VA (20 μg/mL) or rifampicin (RF) (1.5 μg/mL) for 24 h. The implant was vortexed and sonicated, the biofilm was removed, and the implant was re-incubated to determine bacterial recovery. MBEC on the removed biofilm and implant was defined as in vivo MBEC and in vivo implant MBEC, respectively, and the concentrations of 100% and 60% eradication were defined as MBEC₁₀₀ and MBEC₆₀, respectively. As for in vivo MBEC, MBEC₁₀₀ of GM was 256–1024 μg/mL, but that of VA and CZ ranged from 2048–4096 μg/mL. Surprisingly, the in vivo implant MBEC was much higher, ranging from 2048 μg/mL to more than 4096 μg/mL. The addition of RF, not VA, as a secondary antibiotic was effective, and MBEC₆₀ on day 3 USA300LAC biofilm was reduced from 1024 μg/mL with GM alone to 128 μg/mL in combination with RF and the MBEC₆₀ on day 14 USA300LAC biofilm was reduced from 2048 μg/mL in GM alone to 256 μg/mL in combination with RF. In conclusion, a novel MBEC assay for in vivo biofilms on orthopedic implants was developed. GM was the most effective against both methicillin-sensitive and methicillin-resistant Staphylococcus aureus, in in vivo biofilms, and the addition of a systemic concentration of RF reduced MBEC of GM. Early initiation of treatment is desired because the required concentration of antibiotics increases with biofilm maturation.

Intra-articular versus systemic vancomycin for the treatment of periprosthetic joint infection after debridement and spacer implantation in a rat model

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.

Rifampicin induced fever during treatment against Staphylococcal biofilm in a patient with periprosthetic joint infection

Periprosthetic joint infection (PJI) after total knee arthroplasty remains a challenging complication. The treatment options for PJI include different procedures; however, regardless of the strategy, antibiotics are required. The combination of different antibiotics increased the rates of PJI eradication. For almost three decades, rifampicin has been used as part of antibiotic therapy for PJI. Drug fever, a febrile response that coincides with the onset of drug administration and disappears after drug discontinuation in the absence of other underlying conditions that could cause fever, is frequently misdiagnosed. Case presentation: We present the case of a 72-year-old man with PJI six months after total knee arthroplasty. Two-stage revision surgery was followed by culture-directed antibiotic treatment (ciprofloxacin and rifampicin) against Staphylococcus aureus isolated from the periprosthetic tissue. On the fifth day of antibiotic treatment, the patient became febrile, and in the next five days, he had an intermittent fever of up to 40 °C, although he showed clinical improvement. The patient was normotensive without a maculopapular rash, urticaria, or clotting abnormalities. A drug fever was suspected, and rifampicin was discontinued. A re-challenge test was performed, and the fever recurred. Antibiotic treatment with ciprofloxacin was continued, and after 12 months of follow-up, the patient was doing well. Conclusion: Clinicians should be aware that fever could be a clinical presentation of drug fever. If it occurs during an infection, drug fever could necessitate additional diagnostic procedures for further evaluation, inadequate antibiotic therapy, and prolonged hospitalisation.

11C-Para-aminobenzoic acid PET imaging of S. aureus and MRSA infection in preclinical models and humans

Tools for noninvasive detection of bacterial pathogens are needed but are not currently available for clinical use. We have previously shown that para-aminobenzoic acid (PABA) rapidly accumulates in a wide range of pathogenic bacteria, motivating the development of related PET radiotracers. In this study, ¹¹C-PABA PET imaging was used to accurately detect and monitor infections due to pyogenic bacteria in multiple clinically relevant animal models. ¹¹C-PABA PET imaging selectively detected infections in muscle, intervertebral discs, and methicillin-resistant Staphylococcus aureus–infected orthopedic implants. In what we believe to be first-in-human studies in healthy participants, ¹¹C-PABA was safe, well-tolerated, and had a favorable biodistribution, with low background activity in the lungs, muscles, and brain. ¹¹C-PABA has the potential for clinical translation to detect and localize a broad range of bacteria.

Recent Advances in the Evaluation of Antimicrobial Materials for Resolution of Orthopedic Implant-Associated Infections In Vivo

While orthopedic implant-associated infections are rare, revision surgeries resulting from infections incur considerable healthcare costs and represent a substantial research area clinically, in academia, and in industry. In recent years, there have been numerous advances in the development of antimicrobial strategies for the prevention and treatment of orthopedic implant-associated infections which offer promise to improve the limitations of existing delivery systems through local and controlled release of antimicrobial agents. Prior to translation to in vivo orthopedic implant-associated infection models, the properties (e.g., degradation, antimicrobial activity, biocompatibility) of the antimicrobial materials can be evaluated in subcutaneous implant in vivo models. The antimicrobial materials are then incorporated into in vivo implant models to evaluate the efficacy of using the material to prevent or treat implant-associated infections. Recent technological advances such as 3D-printing, bacterial genomic sequencing, and real-time in vivo imaging of infection and inflammation have contributed to the development of preclinical implant-associated infection models that more effectively recapitulate the clinical presentation of infections and improve the evaluation of antimicrobial materials. This Review highlights the advantages and limitations of antimicrobial materials used in conjunction with orthopedic implants for the prevention and treatment of orthopedic implant-associated infections and discusses how these materials are evaluated in preclinical in vivo models. This analysis serves as a resource for biomaterial researchers in the selection of an appropriate orthopedic implant-associated infection preclinical model to evaluate novel antimicrobial materials.

Dynamic PET-facilitated modeling and high-dose rifampin regimens for Staphylococcus aureus orthopedic implant-associated infections

Staphylococcus aureus is a major human pathogen causing serious implant–associated infections. Combination treatment with rifampin (10 to 15 mg/kg per day), which has dose-dependent activity, is recommended to treat S. aureus orthopedic implant–associated infections. Rifampin, however, has limited bone penetration. Here, dynamic 11C-rifampin positron emission tomography (PET) performed in prospectively enrolled patients with confirmed S. aureus bone infection (n = 3) or without orthopedic infection (n = 12) demonstrated bone/plasma area under the concentration-time curve ratio of 0.14 (interquartile range, 0.09 to 0.19), exposures lower than previously thought. PET-based pharmacokinetic modeling predicted rifampin concentration-time profiles in bone and facilitated studies in a mouse model of S. aureus orthopedic implant infection. Administration of high-dose rifampin (human equipotent to 35 mg/kg per day) substantially increased bone concentrations (2 mg/liter versus <0.2 mg/liter with standard dosing) in mice and achieved higher bacterial killing and biofilm disruption. Treatment for 4 weeks with high-dose rifampin and vancomycin was noninferior to the recommended 6-week treatment of standard-dose rifampin with vancomycin in mice (risk difference, −6.7% favoring high-dose rifampin regimen). High-dose rifampin treatment ameliorated antimicrobial resistance (0% versus 38%; P = 0.04) and mitigated adverse bone remodeling (P < 0.01). Last, whole-genome sequencing demonstrated that administration of high-dose rifampin in mice reduced selection of bacterial mutations conferring rifampin resistance (rpoB) and mutations in genes potentially linked to persistence. These data suggest that administration of high-dose rifampin is necessary to achieve optimal bone concentrations, which could shorten and improve treatments for S. aureus orthopedic implant infections.

Intra-articular vancomycin for the prophylaxis of periprosthetic joint infection caused by methicillin-resistant S. aureus after total knee arthroplasty in a rat model: the dosage, efficacy, and safety

Although intra-articular vancomycin powder (VP) is sometimes applied before the closure of the incision to prevent periprosthetic joint infection (PJI) after joint replacement, the dosage, efficacy and safety remain controversial. This study aimed to explore the dosage, efficacy, and safety of intra-articular VP in the prophylaxis of infection after total knee arthroplasty (TKA) in a rat model. Sixty male rats were randomly divided into five groups after receiving TKA surgery: Control (no antibiotics); systemic vancomycin (SV) (intraperitoneal injection, 88 mg/kg, equal to 1g in a patient weighted 70kg); VP0.5, VP1.0 and VP2.0 (44 mg/kg, 88 mg/kg and 176 mg/kg respectively, intra-articular). All animals were inoculated in the knee with methicillin-resistant S. aureus (MRSA). General status, serum biomarkers, radiology, microbiological assay and histopathological tests were assessed within 14 days post-operatively. Compared with the Control and SV groups, bacterial counts, knee-width, tissue inflammation, and osteolysis were reduced in the VP0.5, VP1.0 and VP2.0 groups, without notable bodyweight loss and incision complications. Among all the VP groups, VP1.0 and VP2.0 groups presented superior outcomes in the knee-width and tissue inflammation than the VP0.5 group. Microbial culture indicated that no MRSA survived in the knee of VP1.0 and VP2.0 groups, while bacteria growth was observed in VP0.5 group. No obvious changes in the structure and functional biomarkers of liver and kidney were observed in both SV and VP groups. Therefore, intra-articular vancomycin powder at the dosage from 88 mg/kg to 176 mg/kg may be effective and safe in preventing PJI induced by methicillin-resistant S. aureus in the rat TKA model.

Predilection for developing a hematogenous orthopaedic implant-associated infection in older versus younger mice

Background

The pathogenesis of hematogenous orthopaedic implant-associated infections (HOIAI) remains largely unknown, with little understanding of the influence of the physis on bacterial seeding. Since the growth velocity in the physis of long bones decreases during aging, we sought to evaluate the role of the physis on influencing the development of Staphylococcus aureus HOIAI in a mouse model comparing younger versus older mice.

Methods

In a mouse model of HOIAI, a sterile Kirschner wire was inserted retrograde into the distal femur of younger (5–8-week-old) and older (14–21-week-old) mice. After a 3-week convalescent period, a bioluminescent Staphylococcus aureus strain was inoculated intravenously. Bacterial dissemination to operative and non-operative legs was monitored longitudinally in vivo for 4 weeks, followed by ex vivo bacterial enumeration and X-ray analysis.

Results

In vivo bioluminescence imaging and ex vivo CFU enumeration of the bone/joint tissue demonstrated that older mice had a strong predilection for developing a hematogenous infection in the operative legs but not the non-operative legs. In contrast, this predilection was less apparent in younger mice as the infection occurred at a similar rate in both the operative and non-operative legs. X-ray imaging revealed that the operative legs of younger mice had decreased femoral length, likely due to the surgical and/or infectious insult to the more active physis, which was not observed in older mice. Both age groups demonstrated substantial reactive bone changes in the operative leg due to infection.

Conclusions

The presence of an implant was an important determinant for developing a hematogenous orthopaedic infection in older but not younger mice, whereas younger mice had a similar predilection for developing periarticular infection whether or not an implant was present. On a clinical scale, diagnosing HOIAI may be difficult particularly in at-risk patients with limited examination or other data points. Understanding the influence of age on developing HOIAI may guide clinical surveillance and decision-making in at-risk patients.

Plasma-Activated Saline Promotes Antibiotic Treatment of Systemic Methicillin-Resistant Staphylococcus aureus Infection

Systemic infections caused by methicillin-resistant Staphylococcus aureus (MRSA) are life-threatening due to their strong multidrug resistance, especially since the biofilms formed by MRSA are more difficult to inactivate by antibiotics, causing long term recurrence of infection. Plasma-activated saline (PAS), a derived form of cold atmospheric-pressure plasma, can effectively inactivate bacteria and cancer cells and has been applied to sterilization and cancer treatment. Previous studies have demonstrated that the pretreatment of MRSA with PAS could promote the action of antibiotics. Here, the PAS was used as an antibiotic adjuvant to promote the inactivation of MRSA biofilms by rifampicin and vancomycin, and the combined treatment reduced approximately 6.0-log₁₀ MRSA cells in biofilms. The plasma-activated saline and rifampicin synergistically and effectively reduced the systemic infection in the murine model. The histochemical analysis and the blood hematological and biochemical test demonstrated that the combined treatment with plasma-activated saline and rifampicin improved the blood hematological and biochemical parameters of infected mice by reducing the infection. Therefore, PAS based on plasma technology represents a new strategy for the treatment of infectious disease caused by multidrug-resistant bacteria and alleviating antibiotic resistance.

The limitations of mono- and combination antibiotic therapies on immature biofilms in a murine model of implant-associated osteomyelitis

Treatment of implant-associated orthopedic infections remains challenging, partly because antimicrobial treatment is ineffective after a mature biofilm covers the implant surface. Currently, the relative efficacy of systemic mono- and combination standard-of-care (SOC) antibiotic therapies over the course of mature biofilm formation is unknown. Thus, we assessed the effects of cefazoline (CEZ), gentamicin (GM), and vancomycin, with or without rifampin (RFP), on Staphylococcus aureus biofilm formation during the establishment of implant-associated osteomyelitis in a murine tibia model. Quantitative scanning electron microscopy of the implants harvested on Days 0, 3, and 7 revealed that all treatments except CEZ monotherapy significantly reduced biofilm formation when antibiotics started at Day 0 (0.46- to 0.25-fold; p < 0.05). When antibiotics commenced 3 days after the infection, only GM monotherapy significantly inhibited biofilm growth (0.63-fold; p < 0.05), while all antibiotics inhibited biofilm formation in combination with RFP (0.56- to 0.44-fold; p < 0.05). However, no treatment was effective when antibiotics commenced on Day 7. To confirm these findings, we assessed bacterial load via colony-forming unit and histology. The results showed that GM monotherapy and all combination therapies reduced the colony-forming unit in the implant (0.41- to 0.23-fold; p < 0.05); all treatments except CEZ monotherapy reduced the colony-forming unit and staphylococcus abscess communities in the tibiae (0.40- to 0.10-fold; p < 0.05). Collectively, these findings demonstrate that systemic SOC antibiotics can inhibit biofilm formation within 3 days but not after 7 days of infection. The efficacy of SOC monotherapies, CEZ particularly, is very limited. Thus, combination treatment with RFP may be necessary to inhibit implant-associated osteomyelitis.

A Glimmer of Hope: Maintain Mitochondrial Homeostasis to Mitigate Alzheimer's Disease

Mitochondria are classically known to be cellular energy producers. Given the high-energy demanding nature of neurons in the brain, it is essential that the mitochondrial pool remains healthy and provides a continuous and efficient supply of energy. However, mitochondrial dysfunction is inevitable in aging and neurodegenerative diseases. In Alzheimer’s disease (AD), neurons experience unbalanced homeostasis like damaged mitochondrial biogenesis and defective mitophagy, with the latter promoting the disease-defining amyloid β (Aβ) and p-Tau pathologies impaired mitophagy contributes to inflammation and the aggregation of Aβ and p-Tau-containing neurotoxic proteins. Interventions that restore defective mitophagy may, therefore, alleviate AD symptoms, pointing out the possibility of a novel therapy. This review aims to illustrate mitochondrial biology with a focus on mitophagy and propose strategies to treat AD while maintaining mitochondrial homeostasis.

Interleukin-1β and tumor necrosis factor are essential in controlling an experimental orthopedic implant-associated infection

Orthopedic implant-associated infection (OIAI) is a major complication that leads to implant failure. In preclinical models of Staphylococcus aureus OIAI, osteomyelitis and septic arthritis, interleukin-1α (IL-1α), IL-1β, and tumor necrosis factor (TNF) are induced, but whether they have interactive or distinctive roles in host defense are unclear. Herein, a S. aureus OIAI model was performed in mice deficient in IL-1α, IL-1β, or TNF. Mice deficient in IL-1β or TNF (to a lesser extent) but not IL-1α had increased bacterial burden at the site of the OIAI throughout the 28-day experiment. IL-1β and TNF had a combined and critical role in host defense as mice deficient in both IL-1R and TNF (IL-1R/TNF-deficient mice) had a 40% mortality rate, which was associated with markedly increased bacterial burden at the site of the OIAI infection. Finally, IL-1α- and IL-1β-deficient mice had impaired neutrophil recruitment whereas IL-1β-, TNF-, and IL-1R/TNF-deficient mice all had impaired recruitment of both neutrophils and monocytes. Therefore, IL-1β and TNF contributed to host defense against S. aureus OIAI and neutrophil recruitment was primarily mediated by IL-1β and monocyte recruitment was mediated by both IL-1β and TNF.

Clinical use of linezolid in periprosthetic joint infections - a systematic review

Introduction: The most common causative organism in periprosthetic joint infections (PJIs) is Gram-positive bacteria that are increasingly drug resistant. In these cases the use of linezolid may be warranted. However, there are conflicting reports regarding its role in antibiotic treatment of PJIs. The aim of this review is to gather and analyze clinical results and treatment details on linezolid in patients with PJIs. Methods: In August 2019, a comprehensive literature search using MEDLINE (Pubmed and Ovid) and Cochrane Library was performed. A total of 504 records were screened, and a total of 16 studies including 372 patients treated with linezolid for a PJI were included in this review based on the PRISMA criteria and after quality analysis using the MINOR score and Newcastle–Ottawa scale, as well as assessing level of evidence. Pooling analysis as well as descriptive analysis was performed. Results: Based on the results from the studies included, infection control was achieved in 80 % (range 30 %–100 %) of patients after a mean follow-up period of 25 (range 2–66) months. The mean duration of treatment was 58 d intravenous and orally at a median dose of 600 mg bis in die (b.i.d.) (range 400–900 b.i.d.). A combination therapy with rifampicin was used in 53 % of patients. MRSA (methicillin-resistant Staphylococcus aureus) infections were present in 29 % and resistant CoNS (coagulase-negative Staphylococcus) in 46 %. Adverse effects occurred in 33 % of cases, mostly anemia, thrombocytopenia and gastrointestinal complaints leading to treatment discontinuation in 9 %. However, great heterogeneity was found with respect to surgical treatment, diagnosis of infection and indication for linezolid. Discussion: Linezolid is an appropriate option for treatment of resistant Gram-positive organisms in PJIs. Most commonly 600 mg b.i.d. is used, and a combination with rifampicin appears feasible although one must consider individual increases in doses in these cases. However, adverse effects are common and there are limited data for long-term use and optimal antibiotic combinations or individual doses.

The combination of silver-containing hydroxyapatite coating and vancomycin has a synergistic antibacterial effect on methicillin-resistant Staphylococcus aureus biofilm formation

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 10⁶ or 43.0 (SD 8.4) x 10⁵ 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 10⁶  or 72.0 (SD 4.2) x 10⁵  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.

Preclinical Models and Methodologies for Monitoring Staphylococcus aureus Infections Using Noninvasive Optical Imaging

In vivo whole-animal optical (bioluminescence and fluorescence) imaging of Staphylococcus aureus infections has provided the opportunity to noninvasively and longitudinally monitor the dynamics of the bacterial burden and ensuing host immune responses in live anesthetized animals. Herein, we describe several different mouse models of S. aureus skin infection, skin inflammation, incisional/excisional wound infections, as well as mouse and rabbit models of orthopedic implant infection, which utilized this imaging technology. These animal models and imaging methodologies provide insights into the pathogenesis of these infections and innate and adaptive immune responses, as well as the preclinical evaluation of diagnostic and treatment modalities. Noninvasive approaches to investigate host-pathogen interactions are extremely important as virulent community-acquired methicillin-resistant S. aureus strains (CA-MRSA) are spreading through the normal human population, becoming more antibiotic resistant and creating a serious threat to public health.

Development of a Staphylococcus aureus reporter strain with click beetle red luciferase for enhanced in vivo imaging of experimental bacteremia and mixed infections

In vivo bioluminescence imaging has been used to monitor Staphylococcus aureus infections in preclinical models by employing bacterial reporter strains possessing a modified lux operon from Photorhabdus luminescens. However, the relatively short emission wavelength of lux (peak 490 nm) has limited tissue penetration. To overcome this limitation, the gene for the click beetle (Pyrophorus plagiophtalamus) red luciferase (luc) (with a longer >600 emission wavelength), was introduced singly and in combination with the lux operon into a methicillin-resistant S. aureus strain. After administration of the substrate D-luciferin, the luc bioluminescent signal was substantially greater than the lux signal in vitro. The luc signal had enhanced tissue penetration and improved anatomical co-registration with infected internal organs compared with the lux signal in a mouse model of S. aureus bacteremia with a sensitivity of approximately 3 × 10⁴ CFU from the kidneys. Finally, in an in vivo mixed bacterial wound infection mouse model, S. aureus luc signals could be spectrally unmixed from Pseudomonas aeruginosa lux signals to noninvasively monitor the bacterial burden of both strains. Therefore, the S. aureus luc reporter may provide a technological advance for monitoring invasive organ dissemination during S. aureus bacteremia and for studying bacterial dynamics during mixed infections.

Preclinical Optical Imaging to Study Pathogenesis, Novel Therapeutics and Diagnostics Against Orthopaedic Infection

Preclinical in vivo optical imaging includes bioluminescence imaging (BLI) and fluorescence imaging (FLI), which provide noninvasive and longitudinal monitoring of biological processes in an in vivo context. In vivo BLI involves the detection of photons of light from bioluminescent bacteria engineered to naturally emit light in preclinical animal models of infection. Meanwhile, in vivo FLI involves the detection of photons of a longer emission wavelength of light after exposure of a fluorophore to a shorter excitation wavelength of light. In vivo FLI has been used in preclinical animal models to detect fluorescent-labeled host proteins or cells (often in engineered fluorescent reporter mice) to understand host-related processes, or to detect injectable near-infrared fluorescent probes as a novel approach for diagnosing infection. This review describes the use of in vivo optical imaging in preclinical models of orthopaedic implant-associated infection (OIAI), including (i) pathogenesis of the infectious course, (ii) monitoring efficacy of antimicrobial prophylaxis and therapy and (iii) evaluating novel near-infrared fluorescent probes for diagnosing infection. Finally, we describe optoacoustic imaging and fluorescence image-guided surgery, which are recent technologies that have the potential to translate to diagnosing and treating OIAI in humans. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:2269-2277, 2019.

Linezolid use in German acute care hospitals: results from two consecutive national point prevalence surveys

Background

Linezolid belongs to a reserve group of antibiotics. In recent years, reports on linezolid resistance in gram-positive cocci have become more frequent. Overuse of linezolid is a relevant factor for resistance development. The objective of this study was to describe current prescription practices of linezolid in German hospitals and identify targets for antimicrobial stewardship interventions.

Methods

We analyzed all linezolid prescriptions from the datasets of the consecutive national point prevalence surveys performed in German hospitals in 2011 and 2016. In both surveys, data on healthcare-associated infections and antimicrobial use were collected following the methodology of the European Centre for Disease Prevention and Control.

Results

Overall, the percentage of linezolid among all documented antimicrobials increased significantly from 2011 to 2016 (p < 0.01). In 2011, 0.3% (119 of 41,539) patients received linezolid, in 2016 this proportion was significantly higher (0.4%; 255 of 64,412 patients; p < 0.01). In 2016, intensive care units (ICUs) were the wards most frequently prescribing linezolid. The largest proportion of patients receiving linezolid were non-ICU patients. Roughly 38% of linezolid prescriptions were for treatment of skin/soft tissue and respiratory tract infections. In 2016, linezolid was administered parenterally in 70% (n = 179) of cases. Multivariable analysis showed that the ward specialty ICU posed an independent risk factor, while Northern and Southwestern regions in Germany were independent protective factors for a high rate of linezolid prescriptions.

Conclusions

In conclusion, we detected potentials for improving linezolid prescription practices in German hospitals. Given the emergence of linezolid resistance, optimization of linezolid use must be a target of future antimicrobial stewardship activities.

A novel bispecific antibody platform to direct complement activity for efficient lysis of target cells

Harnessing complement-mediated cytotoxicity by therapeutic antibodies has been limited because of dependency on size and density of antigen, structural constraints resulting from orientation of antibody binding, and blockade of complement activation by inhibitors expressed on target cells. We developed a modular bispecific antibody platform that directs the complement-initiating protein C1q to target cells, increases local complement deposition and induces cytotoxicity against target antigens with a wide-range of expression. The broad utility of this approach to eliminate both prokaryotic and eukaryotic cells was demonstrated by pairing a unique C1q-recruiting arm with multiple targeting arms specific for Staphylococcus aureus, Pseudomonas aeruginosa, B-cells and T-cells, indicating applicability for diverse indications ranging from infectious diseases to cancer. Generation of C1q humanized mice allowed for demonstration of the efficacy of this approach to clear disease-inducing cells in vivo. In summary, we present a novel, broadly applicable, and versatile therapeutic modality for targeted cell depletion.

Efficacy of a Multimechanistic Monoclonal Antibody Combination against Staphylococcus aureus Surgical Site Infections in Mice

Surgical site infections (SSIs) are commonly caused by Staphylococcus aureus We report that a combination of three monoclonal antibodies (MEDI6389) that neutralize S. aureus alpha-toxin, clumping factor A, and four leukocidins (LukSF, LukED, HlgAB, and HlgCB) plus vancomycin had enhanced efficacy compared with control antibody plus vancomycin in two mouse models of S. aureus SSI. Therefore, monoclonal antibody-based neutralization of multiple S. aureus virulence factors may provide an adjunctive perioperative approach to combat S. aureus SSIs.

Comparison of Methicillin-Resistant Staphylococcus aureus Isolates from Cellulitis and from Osteomyelitis in a Taiwan Hospital, 2016-2018

Methicillin-resistant Staphylococcus aureus (MRSA) causes superficial infections such as cellulitis or invasive infections such as osteomyelitis; however, differences in MRSA isolates from cellulitis (CL-MRSA) and from osteomyelitis (OM-MRSA) at the same local area remain largely unknown. A total of 221 MRSA isolates including 106 CL-MRSA strains and 115 OM-MRSA strains were collected at Chang-Gung Memorial Hospital in Taiwan between 2016 and 2018, and their genotypic and phenotypic characteristics were compared. We found that OM-MRSA isolates significantly exhibited higher rates of resistance to multiple antibiotics than CL-MRSA isolates. Genotypically, OM-MRSA isolates had higher proportions of the SCCmec type III, the sequence type ST239, and the spa type t037 than CL-MRSA isolates. Besides the multidrug-resistant lineage ST239-t037-SCCmecIII more prevalent in OM-MRSA, higher antibiotic resistance rates were also observed in several other prevalent lineages in OM-MRSA as compared to the same lineages in CL-MRSA. Furthermore, when prosthetic joint infection (PJI) associated and non-PJI-associated MRSA strains in osteomyelitis were compared, no significant differences were observed in antibiotic resistance rates between the two groups, albeit more diverse genotypes were found in non-PJI-associated MRSA. Our findings therefore suggest that deep infections may allow MRSA to evade antibiotic attack and facilitate the convergent evolution and selection of multidrug-resistant lineages.

In Vivo Bioluminescence Imaging in a Rabbit Model of Orthopaedic Implant-Associated Infection to Monitor Efficacy of an Antibiotic-Releasing Coating

BACKGROUND

In vivo bioluminescence imaging (BLI) provides noninvasive monitoring of bacterial burden in animal models of orthopaedic implant-associated infection (OIAI). However, technical limitations have limited its use to mouse and rat models of OIAI. The goal of this study was to develop a larger, rabbit model of OIAI using in vivo BLI to evaluate the efficacy of an antibiotic-releasing implant coating.

METHODS

A nanofiber coating loaded with or without linezolid-rifampin was electrospun onto a surgical-grade locking peg. To model OIAI in rabbits, a medial parapatellar arthrotomy was performed to ream the femoral canal, and a bright bioluminescent methicillin-resistant Staphylococcus aureus (MRSA) strain was inoculated into the canal, followed by retrograde insertion of the coated implant flush with the articular surface. In vivo BLI signals were confirmed by ex vivo colony-forming units (CFUs) from tissue, bone, and implant specimens.

RESULTS

In this rabbit model of OIAI (n = 6 rabbits per group), implants coated without antibiotics were associated with significantly increased knee width and in vivo BLI signals compared with implants coated with linezolid-rifampin (p < 0.001 and p < 0.05, respectively). On day 7, the implants without antibiotics were associated with significantly increased CFUs from tissue (mean [and standard error of the mean], 1.4 × 10 ± 2.1 × 10 CFUs; p < 0.001), bone (6.9 × 10 ± 3.1 × 10 CFUs; p < 0.05), and implant (5.1 × 10 ± 2.2 × 10 CFUs; p < 0.05) specimens compared with implants with linezolid-rifampin, which demonstrated no detectable CFUs from any source.

CONCLUSIONS

By combining a bright bioluminescent MRSA strain with modified techniques, in vivo BLI in a rabbit model of OIAI demonstrated the efficacy of an antibiotic-releasing coating.

CLINICAL RELEVANCE

The new capability of in vivo BLI for noninvasive monitoring of bacterial burden in larger-animal models of OIAI may have important preclinical relevance.

Role of Rifampin against Staphylococcal Biofilm Infections In Vitro, in Animal Models, and in Orthopedic-Device-Related Infections

Rifampin has been used as an agent in combination therapy in orthopedic device-related infections (ODRI) for almost three decades. The aim of this review is to provide data regarding the role of rifampin against biofilm infection in vitro, in animal models, and in clinical ODRI. Available data are gathered in order to present the rational use of rifampin combinations in patients with periprosthetic joint infection (PJI). The role of rifampin is well defined in patients with PJI and is indicated in those who fulfill the Infectious Diseases Society of America criteria for debridement and implant retention or one-stage exchange. It should be used with care because of the danger of rapid emergence of resistance. Potential drug interactions should be considered.

A Review of Novel Antibiotic Regimens for the Treatment of Orthopedic Infections

As a result of the increasing numbers of joint replacement surgeries and other implant-associated procedures performed, the incidences of periprosthetic joint infections and osteomyelitis are on the rise. Antibiotic resistance to gram-positive species, which are mostly isolated from such infections, is a significant obstacle in clinical practice. Promising clinical outcomes have been reported with the use of novel antibiotics for patients with periprosthetic joint infections and osteomyelitis. Further research is necessary for the establishment of these novel antibiotic therapies in routine clinical practice. [Orthopedics. 2018; 41(6):323-328.].

Mouse model of Gram-negative prosthetic joint infection reveals therapeutic targets

Bacterial biofilm infections of implantable medical devices decrease the effectiveness of antibiotics, creating difficult-to-treat chronic infections. Prosthetic joint infections (PJI) are particularly problematic because they require prolonged antibiotic courses and reoperations to remove and replace the infected prostheses. Current models to study PJI focus on Gram-positive bacteria, but Gram-negative PJI (GN-PJI) are increasingly common and are often more difficult to treat, with worse clinical outcomes. Herein, we sought to develop a mouse model of GN-PJI to investigate the pathogenesis of these infections and identify potential therapeutic targets. An orthopedic-grade titanium implant was surgically placed in the femurs of mice, followed by infection of the knee joint with Pseudomonas aeruginosa or Escherichia coli. We found that in vitro biofilm-producing activity was associated with the development of an in vivo orthopedic implant infection characterized by bacterial infection of the bone/joint tissue, biofilm formation on the implants, reactive bone changes, and inflammatory immune cell infiltrates. In addition, a bispecific antibody targeting P. aeruginosa virulence factors (PcrV and Psl exopolysaccharide) reduced the bacterial burden in vivo. Taken together, our findings provide a preclinical model of GN-PJI and suggest the therapeutic potential of targeting biofilm-associated antigens.

Vancomycin-Loaded Polymethylmethacrylate Spacers Fail to Eradicate Periprosthetic Joint Infection in a Clinically Representative Mouse Model

BACKGROUND

Periprosthetic joint infection (PJI) remains a devastating complication following total joint arthroplasty. Current animal models of PJI do not effectively recreate the clinical condition and thus provide limited help in understanding why treatments fail. We developed a mouse model of the first-stage surgery of a 2-stage revision for PJI involving a 3-dimensionally printed Ti-6Al-4V implant and a mouse-sized cement spacer that elutes vancomycin.

METHODS

Vancomycin was mixed with polymethylmethacrylate (PMMA) cement and inserted into custom-made mouse-sized spacer molds. Twenty C57BL/6 mice received a proximal tibial implant and an intra-articular injection of 3 × 10 colony-forming units of Staphylococcus aureus Xen36. At 2 weeks, 9 mice underwent irrigation and debridement of the leg with revision of the implant to an articulating vancomycin-loaded PMMA spacer. Postoperatively, mice underwent radiography and serum inflammatory-marker measurements. Following euthanasia of the mice at 6 weeks, bone and soft tissues were homogenized to quantify bacteria within periprosthetic tissues. Implants and articulating spacers were either sonicated to quantify adherent bacteria or examined under scanning electron microscopy (SEM) to characterize the biofilm.

RESULTS

Vancomycin-loaded PMMA spacers eluted vancomycin for ≤144 hours and retained antimicrobial activity. Control mice had elevated levels of inflammatory markers, radiographic evidence of septic loosening of the implant, and osseous destruction. Mice treated with a vancomycin-loaded PMMA spacer had significantly lower levels of inflammatory markers (p < 0.01), preserved tibial bone, and no intra-articular purulence. Retrieved vancomycin-loaded spacers exhibited significantly lower bacterial counts compared with implants (p < 0.001). However, bacterial counts in periprosthetic tissue did not significantly differ between the groups. SEM identified S. aureus encased within biofilm on control implants, while vancomycin-loaded spacers contained no bacteria.

CONCLUSIONS

This animal model is a clinically representative model of PJI treatment. The results suggest that the antimicrobial effects of PMMA spacers are tightly confined to the articular space and must be utilized in conjunction with thorough tissue debridement and systemic antibiotics.

CLINICAL RELEVANCE

These data provide what we believe to be the first insight into the effect of antibiotic-loaded cement spacers in a clinically relevant animal model and justify the adjunctive use of intravenous antibiotics when performing a 2-stage revision for PJI.