Combination prophylactic therapy with rifampin increases efficacy against an experimental Staphylococcus epidermidis subcutaneous implant-related infection

The pathogenicity and virulence of the opportunistic pathogen Staphylococcus epidermidis

The pervasive presence of Staphylococcus epidermidis and other coagulase-negative staphylococci on the skin and mucous membranes has long underpinned a casual disregard for the infection risk that these organisms pose to vulnerable patients in healthcare settings. Prior to the recognition of biofilm as an important virulence determinant in S. epidermidis, isolation of this microorganism in diagnostic specimens was often overlooked as clinically insignificant with potential delays in diagnosis and onset of appropriate treatment, contributing to the establishment of chronic infection and increased morbidity or mortality. While impressive progress has been made in our understanding of biofilm mechanisms in this important opportunistic pathogen, research into other virulence determinants has lagged S. aureus. In this review, the broader virulence potential of S. epidermidis including biofilm, toxins, proteases, immune evasion strategies and antibiotic resistance mechanisms is surveyed, together with current and future approaches for improved therapeutic interventions.

Duration of cefazolin prophylaxis did not impact infection risk in a murine model of joint arthroplasty

To minimize periprosthetic joint infection (PJI) risk, some clinicians prescribe extended antibiotic prophylaxis (EAP) following total joint arthroplasty (TJA). Given the limited evidence supporting EAP, we sought to evaluate impact of prophylactic antibiotic duration on PJI risk in a murine TJA model. A titanium prosthesis was implanted into the proximal tibia of 89 mice and inoculated with 102 colony forming units (cfu) of Staphylococcus aureus Xen36. Control mice (n = 20) did not receive antibiotics. Treated mice received either 24 h (n = 35) or 4 days (n = 34) of cefazolin prophylaxis. Cultures were obtained from the prostheses, tibia, femur, and knee tissues 3 weeks after surgery. All mice in the control group developed PJI. Both prophylaxis regimens reduced the rate of PJI relative to the control, with only 2/35 mice in the 24-h cohort (p < 0.0001) and 1/34 in 4-day cohort developing PJI (p < 0.0001). CFU counts from the prostheses, bone and knee tissues were reduced for the 24-h and 4-day prophylaxis cohorts relative to the control (p < 0.0001 for both). There was no difference in rates of PJI or CFU counts between the two prophylaxis cohorts (p = 0.58). Prophylactic cefazolin profoundly reduced rates of PJI in a murine model of TJA in which all control animals developed PJI. Extending cefazolin prophylaxis duration from 24 h to 4 days did not result in improved PJI rates or decreased bacterial loads in infected cases. While these results strongly support use of antibiotic prophylaxis for TJA, EAP did not appear to add benefit in the described mouse model.

A smart coating with integrated physical antimicrobial and strain-mapping functionalities for orthopedic implants

The prevalence of orthopedic implants is increasing with an aging population. These patients are vulnerable to risks from periprosthetic infections and instrument failures. Here, we present a dual-functional smart polymer foil coating compatible with commercial orthopedic implants to address both septic and aseptic failures. Its outer surface features optimum bioinspired mechano-bactericidal nanostructures, capable of killing a wide spectrum of attached pathogens through a physical process to reduce the risk of bacterial infection, without directly releasing any chemicals or harming mammalian cells. On its inner surface in contact with the implant, an array of strain gauges with multiplexing transistors, built on single-crystalline silicon nanomembranes, is incorporated to map the strain experienced by the implant with high sensitivity and spatial resolution, providing information about bone-implant biomechanics for early diagnosis to minimize the probability of catastrophic instrument failures. Their multimodal functionalities, performance, biocompatibility, and stability are authenticated in sheep posterolateral fusion model and rodent implant infection model.

Development and Characterization of a Subcutaneous Implant-Related Infection Model in Mice to Test Novel Antimicrobial Treatment Strategies

Orthopedic-device-related infection is one of the most severe complications in orthopedic surgery. To reduce the associated morbidity and healthcare costs, new prevention and treatment modalities are continuously under development. Preclinical in vivo models serve as a control point prior to clinical implementation. This study presents a mouse model of subcutaneously implanted titanium discs, infected with Staphylococcus aureus, to fill a gap in the early-stage testing of antimicrobial biomaterials. Firstly, three different inocula were administered either pre-adhered to the implant or pipetted on top of it following implantation to test their ability to reliably create an infection. Secondly, the efficacy of low-dose (25 mg/kg) and high-dose (250 mg/kg) cefazolin administered systemically in infection prevention was assessed. Lastly, titanium implants were replaced by antibiotic-loaded bone cement (ALBC) discs to investigate the efficacy of local antibiotics in infection prevention. The efficacy in infection prevention of the low-dose perioperative antibiotic prophylaxis (PAP) depended on both the inoculum and inoculation method. Bacterial counts were significantly lower in animals receiving the high dose of PAP. ALBC discs with or without the additional PAP proved highly effective in infection prevention and provide a suitable positive control to test other prevention strategies.

A lipoglycopeptide antibiotic for Gram-positive biofilm-related infections

Drug-resistant Gram-positive bacterial infections are still a substantial burden on the public health system, with two bacteria ( Staphylococcus aureus and Streptococcus pneumoniae ) accounting for over 1.5 million drug-resistant infections in the United States alone in 2017. In 2019, 250,000 deaths were attributed to these pathogens globally. We have developed a preclinical glycopeptide antibiotic, MCC5145, that has excellent potency (MIC 90 ≤ 0.06 μg/ml) against hundreds of isolates of methicillin-resistant S. aureus (MRSA) and other Gram-positive bacteria, with a greater than 1000-fold margin over mammalian cell cytotoxicity values. The antibiotic has therapeutic in vivo efficacy when dosed subcutaneously in multiple murine models of established bacterial infections, including thigh infection with MRSA and blood septicemia with S. pneumoniae , as well as when dosed orally in an antibiotic-induced Clostridioides difficile infection model. MCC5145 exhibited reduced nephrotoxicity at microbiologically active doses in mice compared to vancomycin. MCC5145 also showed improved activity against biofilms compared to vancomycin, both in vitro and in vivo, and a low propensity to select for drug resistance. Characterization of drug action using a transposon library bioinformatic platform showed a mechanistic distinction from other glycopeptide antibiotics.

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.

Repurposing Sitafloxacin, Prulifloxacin, Tosufloxacin, and Sisomicin as Antimicrobials Against Biofilm and Persister Cells of Pseudomonas aeruginosa

Pseudomonas aeruginosa is a ubiquitous bacterium found in hospitals and the surrounding environment. The ability of P. aeruginosa to form biofilms confers high-level resistance to antibiotics, and the persister cells formed in the presence of high antibacterial drug concentrations make P. aeruginosa-related infections more refractory. Further, there rarely is an effective antimicrobial alternative when biofilm- and persister cell-targeting treatment fails. Using a high-throughput screening assay, we previously identified fluoroquinolones sitafloxacin, prulifloxacin, and tosufloxacin as well as aminoglycoside sisomicin among FDA-approved drugs with significant bactericidal activity against P. aeruginosa. In addition, in our current study, these antibiotics exhibited an effective time- and dose-dependent eradication effects against the preformed biofilms of P. aeruginosa at the concentrations of 2-4 μM. These agents also exhibited bactericidal efficacy against CCCP-induced P. aeruginosa persister cells with the viable cell count decreased from 9.14 log10 CFU/mL to 6.15 (sitafloxacin), 7.59 (prulifloxacin), 4.27 (tosufloxacin), and 6.17 (sisomicin) log10 CFU/mL, respectively, following 4 h of treatment. Furthermore, sisomicin was also effective against conventional antibiotics induced persister cells in a time-dependent manner within 24 h. In addition, we confirmed the in vivo anti-biofilm efficacy of the identified antibiotics in a subcutaneous implantation biofilm-related infection model. Tosufloxacin exhibited the greatest in vivo bactericidal activity against P. aeruginosa biofilms with a reduction of 4.54 ΔLog10 CFU/mL compared to the vehicle group, followed by prulifloxacin, sitafloxacin, and sisomicin. Taken together, our results indicate that sitafloxacin, prulifloxacin, tosufloxacin, and sisomicin have great potential as alternatives for the treatment of refractory infections caused by P. aeruginosa biofilms and persister cells.

Locally delivered adjuvant biofilm-penetrating antibiotics rescue impaired endochondral fracture healing caused by MRSA infection

Infection is a devastating complication following an open fracture. We investigated whether local rifampin-loaded hydrogel can combat infection and improve healing in a murine model of methicillin-resistant Staphylococcus aureus (MRSA) osteomyelitis. A transverse fracture was made at the tibia midshaft of C57BL/6J mice aged 10-12 weeks and stabilized with an intramedullary pin. A total of 1 × 106 colony-forming units (CFU) of MRSA was inoculated. A collagen-based hydrogel containing low-dose (60 μg) and high-dose (300 μg) rifampin was applied before closure. Postoperative treatment response was assessed through bacterial CFU counts from tissue and hardware, tibial radiographs and microcomputed tomography (μCT), immunohistochemistry, and histological analyses. All untreated MRSA-infected fractures progressed to nonunion by 28 days with profuse MRSA colonization. Infected fractures demonstrated decreased soft callus formation on safranin O stain compared to controls. Areas of dense interleukin-1β stain were associated with poor callus formation. High-dose rifampin hydrogels reduced the average MRSA load in tissue (p < 0.0001) and implants (p = 0.041). Low-dose rifampin hydrogels reduced tissue bacterial load by 50% (p = 0.021). Among sterile models, 88% achieved union compared to 0% of those infected. Mean radiographic union scale in tibia scores improved from 6 to 8.7 with high-dose rifampin hydrogel (p = 0.024) and to 10 with combination local/systemic rifampin therapy (p < 0.0001). μCT demonstrated reactive bone formation in MRSA infection. Histology demonstrated restored fracture healing with bacterial elimination. Rifampin-loaded hydrogels suppressed osteomyelitis, prevented implant colonization, and improved healing. Systemic rifampin was more effective at eliminating infection and improving fracture healing. Further investigation into rifampin-loaded hydrogels is required to correlate these findings with clinical efficacy.

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.

Doxycycline-Coated Silicone Breast Implants Reduce Acute Surgical-Site Infection and Inflammation

BACKGROUND

Surgical-site infection after implant-based breast reconstruction remains a leading cause of morbidity. Doxycycline is an antibiotic used to treat soft-tissue infections. The authors hypothesize that doxycycline-coated breast implants will significantly reduce biofilm formation, surgical-site infection, and inflammation after bacterial infection.

METHODS

Pieces of silicone breast implants were coated in doxycycline. In vitro studies to characterize the coating include Fourier transmission infrared spectroscopy, elution data, and toxicity assays (n = 4). To evaluate antimicrobial properties, coated implants were studied after methicillin-resistant Staphylococcus aureus (MRSA) and Pseudomonas aeruginosa inoculation in vitro and in a mouse model at 3 and 7 days (n = 8). Studies included bacterial quantification, cytokine profiles, and histology.

RESULTS

Coated silicone breast implants demonstrated a color change, increased mass, and Fourier transmission infrared spectroscopy consistent with a doxycycline coating. Coated implants were nontoxic to fibroblasts and inhibited biofilm formation and bacterial adherence after MRSA and P. aeruginosa incubation in vitro, and measurable doxycycline concentrations at 24 hours were seen. In a mouse model, a significant reduction of MRSA and P. aeruginosa bacterial colonization after 3 and 7 days in the doxycycline-coated implant mice was demonstrated when compared to the control mice, control mice treated with intraperitoneal doxycycline, and control mice treated with a gentamicin/cefazolin/bacitracin wash. Decreased inflammatory cytokines and inflammatory cell infiltration were demonstrated in the doxycycline-coated mice.

CONCLUSIONS

A method to coat silicone implants with doxycycline was developed. The authors' doxycycline-coated silicone implants significantly reduced biofilm formation, surgical-site infections, and inflammation. Further studies are needed to evaluate the long-term implications.

Antibiotic eluting poly(ester urea) films for control of a model cardiac implantable electronic device infection

Cardiac implantable electronic device (CIED) infections acquired during or after surgical procedures are a major complication that are challenging to treat therapeutically, resulting in chronic and sometimes fatal infections. Localized delivery of antibiotics at the surgical site could be used to supplement traditional systemic administration as a preventative measure. Herein, we investigate a cefazolin-eluting l-valine poly(ester urea) (PEU) films as a model system for localized antibiotic delivery for CIEDs. Poly(1-VAL-8) PEU was used to fabricate a series of antibiotic-loaded films with varied loading concentrations (2%, 5%, 10% wt/wt) and thicknesses (40 µm, 80 µm, 140 µm). In vitro release measurements show thickness and loading concentration influence the amount and rate of cefazolin release. Group 10%-140 µm (load-thickness) showed 22.5% release of active pharmaceutical ingredient (API) in the first 24 h and 81.2% of cumulative percent release through day 14 and was found most effective in bacterial clearance in vitro. This group was also effective in clearing a bacterial infection in a model in vivo rat study while eliciting a limited inflammatory response. Our results suggest the feasibility of cefazolin-loaded PEU films as an effective sustained release matrix for localized delivery of antibiotics. SIGNIFICANCE STATEMENT: Implant-associated infections acquired during surgical procedures are a major complication that have proven a challenge to treat clinically, resulting in chronic and sometimes fatal infections. In this manuscript, we investigate an antibiotic-eluting L-valine poly(ester urea) (PEU) films as a model system for localized delivery of cefazolin. Significantly, we demonstrate a wide variation in temporal delivery and dosing within this family of PEUs and show that the delivery can be extended by varying the film thickness. The in vivo results show efficacy in an infected wound model and suggest antibiotic loaded PEU films function as an effective sustained release matrix for localized delivery of antibiotics across a number of clinical indications.

The Use of a Novel Antimicrobial Implant Coating In Vivo to Prevent Spinal Implant Infection

STUDY DESIGN

A controlled, interventional animal study.

OBJECTIVE

Spinal implant infection (SII) is a devastating complication. The objective of this study was to evaluate the efficacy of a novel implant coating that has both a passive antibiotic elution and an active-release mechanism triggered in the presence of bacteria, using an in vivo mouse model of SII.

SUMMARY OF BACKGROUND DATA

Current methods to minimize the frequency of SII include local antibiotic therapy (vancomycin powder), betadine irrigation, silver nanoparticles, and passive release from antibiotic-loaded poly(methyl methacrylate) cement beads, all of which have notable weaknesses. A novel implant coating has been developed to address some of these limitations but has not been tested in the environment of a SII.

METHODS

A biodegradable coating using branched poly(ethylene glycol)-poly(propylene sulfide) (PEG-PPS) polymer was designed to deliver antibiotics. The in vivo performance of this coating was tested in the delivery of either vancomycin or tigecycline in a previously established mouse model of SII. Noninvasive bioluminescence imaging was used to quantify the bacterial burden, and implant sonication was used to determine bacterial colony-forming units (CFUs) from the implant and surrounding bone and soft tissue.

RESULTS

The PEG-PPS-vancomycin coating significantly lowered the infection burden from postoperative day 3 onwards (P < 0.05), whereas PEG-PPS-tigecycline only decreased the infection on postoperative day 5 to 10 (P < 0.05). CFUs were lower on PEG-PPS-vancomycin pins than PEG-PPS-tigecycline and PEG-PPS pins alone on both the implants (2.4 × 10, 8.5 × 10, and 1.0 × 10 CFUs, respectively) and surrounding bone and soft tissue (1.3 × 10, 4.8 × 10, and 5.4 × 10 CFUs, respectively) (P < 0.05).

CONCLUSION

The biodegradable PEG-PPS coating demonstrates promise in decreasing bacterial burden and preventing SII. The vancomycin coating outperformed the tigecycline coating in this model compared to prior work in arthroplasty models, highlighting the uniqueness of the paraspinal infection microenvironment.

LEVEL OF EVIDENCE

N/A.

Direct Microscopic Observation of Human Neutrophil-Staphylococcus aureus Interaction In Vitro Suggests a Potential Mechanism for Initiation of Biofilm Infection on an Implanted Medical Device

The ability of human neutrophils to clear newly attached Staphylococcus aureus bacteria from a serum-coated glass surface was examined in vitro using time-lapse confocal scanning laser microscopy. Quantitative image analysis was used to measure the temporal change in bacterial biomass, neutrophil motility, and fraction of the surface area policed by neutrophils. In control experiments in which the surface was inoculated with bacteria but no neutrophils were added, prolific bacterial growth was observed. Neutrophils were able to control bacterial growth but only consistently when the neutrophil/bacterium number ratio exceeded approximately 1. When preattached bacteria were given a head start and allowed to grow for 3 h prior to neutrophil addition, neutrophils were unable to maintain control of the nascent biofilm. In these head-start experiments, aggregates of bacterial biofilm with areas of 50 μm² or larger formed, and the growth of such aggregates continued even when multiple neutrophils attacked a cluster. These results suggest a model for the initiation of a biofilm infection in which a delay in neutrophil recruitment to an abiotic surface allows surface-attached bacteria time to grow and form aggregates that become protected from neutrophil clearance. Results from a computational model of the neutrophil-biofilm surface contest supported this conceptual model and highlighted the stochastic nature of the interaction. Additionally, we observed that both neutrophil motility and clearance of bacteria were impaired when oxygen tension was reduced to 0% or 2% O₂.

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.

Ultra-dense polymer brush coating reduces Staphylococcus epidermidis biofilms on medical implants and improves antibiotic treatment outcome

Staphylococcal biofilm formation is a severe complication of medical implants, leading to high antibiotic tolerance and treatment failure. Ultra-dense poly(ethylene glycol) (udPEG) coating resists adsorption of proteins, polysaccharides and extracellular DNA. It is therefore uniquely resistant to attachment by Staphylococcus epidermidis, which remains loosely adhered to the surface. Our aim was to determine if S. epidermidis remains susceptible to antibiotics when adhering to udPEG, and if udPEG coatings can improve the treatment outcome for implant-associated infections. We tested the in vitro efficacy of vancomycin treatment on recently adhered S. epidermidis AUH4567 on udPEG, conventional PEG or titanium surfaces using live/dead staining and microscopy. udPEG was then applied to titanium implants and inserted subcutaneously in mice and inoculated with S. epidermidis to induce infection. Mice were given antibiotic prophylaxis or a short antibiotic treatment. One group was given immunosuppressive therapy. After five days, implants and surrounding tissue were harvested for CFU enumeration. Only few S. epidermidis cells adhered to udPEG compared to conventional PEG and uncoated titanium, and a much lower fraction of cells on udPEG survived antibiotic treatment in vitro. In vivo, the bacterial load on implants in mice receiving vancomycin treatment was significantly lower on udPEG-coated compared to uncoated implants, also in neutropenic mice. Our results suggest that the improved outcome results from the coating's anti-adhesive properties that leads to less biofilm and increased efficacy of antibiotic treatment. Thus, the combination of udPEG with antibiotics is a promising strategy to prevent acute implant-associated infections that arise due to perioperative contaminations.

STATEMENT OF SIGNIFICANCE

Infections of medical implants is an ever-present danger. Here, bacteria develop biofilms that cannot be eradicated with antibiotics. By using an ultra-dense polymer-brush coating (udPEG), bacterial attachment and the subsequent biofilm formation can be reduced, resulting in increased antibiotic susceptibility of bacteria surrounding the implant. udPEG combined with antibiotics proved to significantly reduce bacteria on implants inserted into mice, in our animal model. As the coating is not antibacterial per se, it does not induce antimicrobial resistance and its effect is independent of the bacterial species. Our results are encouraging for the prospect of preventing and treating implant-associated infections that arise due to perioperative contaminations.

Combinatory antibiotic therapy increases rate of bacterial kill but not final outcome in a novel mouse model of Staphylococcus aureus spinal implant infection

Background

Management of spine implant infections (SII) are challenging. Explantation of infected spinal hardware can destabilize the spine, but retention can lead to cord compromise and biofilm formation, complicating management. While vancomycin monotherapy is commonly used, in vitro studies have shown reduced efficacy against biofilm compared to combination therapy with rifampin. Using an established in vivo mouse model of SII, we aim to evaluate whether combination therapy has increased efficacy compared to both vancomycin alone and infected controls.

Methods

An L-shaped, Kirschner-wire was transfixed into the L4 spinous process of 12-week-old C57BL/6 mice, and inoculated with bioluminescent Staphylococcus aureus. Mice were randomized into a vancomycin group, a combination group with vancomycin plus rifampin, or a control group receiving saline. Treatment began on post-operative day (POD) 7 and continued through POD 14. In vivo imaging was performed to monitor bioluminescence for 35 days. Colony-forming units (CFUs) were cultured on POD 35.

Results

Bioluminescence peaked around POD 7 for all groups. The combination group had a 10-fold decrease in signal by POD 10. The vancomycin and control groups reached similar levels on POD 17 and 21, respectively. On POD 25 the combination group dropped below baseline, but rebounded to the same level as the other groups, demonstrating a biofilm-associated infection by POD 35. Quantification of CFUs on POD 35 confirmed an ongoing infection in all three groups.

Conclusions

Although both therapies were initially effective, they were not able to eliminate implant biofilm bacteria, resulting in a rebound infection after antibiotic cessation. This model shows, for the first time, why histologic-based, static assessments of antimicrobials can be misleading, and the importance of longitudinal tracking of infection. Future studies can use this model to test combinations of antibiotic therapies to see if they are more effective in eliminating biofilm prior to human trials.

Is the prognosis the same for periprosthetic joint infections due to Staphylococcus aureus versus coagulase-negative staphylococci? A retrospective study of 101 patients with 2-year minimum follow-up

BACKGROUND

Staphylococcus aureus (SA) and Coagulase-negative staphylococci (CoNS) are often responsible for infections of total hip arthroplasty (THA) and total knee arthroplasty (TKA). One of the main differences between these two microorganisms is their virulence, with SA presumed to be more virulent; however, few studies have specifically investigated the impact of this virulence. This inspired us to carry out a retrospective study to evaluate whether the healing rate differed between SA and CoNS infections.

HYPOTHESIS

We hypothesised that the healing rate is lower for SA prosthetic joint infections.

MATERIALS AND METHODS

This was a retrospective study of 101 consecutive Staphylococcus infection cases that occurred between 2007 and 2011. There were 56 men and 45 women with an average age of 69 years (range 23-95). The infection was associated with TKA in 38 cases and THA in 63 cases. Thirty-two percent of patients had one or more comorbidities with infectious potential. In our cohort, there were 32 SA infections (31.7 %) and 69 CoNS infections (68.3 %) with 58 of the infections being methicillin-resistant (15 SA and 43 CoNS); there were 27 polymicrobial infections (26.7 %).

RESULTS

With a minimum 24-month follow-up after the end of antibiotic treatment, the healing rate was 70.3 % overall (71 patients). The healing rate was 75 % in the SA group (24 patients) versus 68.1 % (47 patients) in the CoNS group (P = 0.42).

CONCLUSION

Our hypothesis was not confirmed: the healing rate of SA prosthetic joint infections was not lower than that of CoNS infections.

LEVEL OF EVIDENCE

III, retrospective case-control study.