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

Biocides as drivers of antibiotic resistance: A critical review of environmental implications and public health risks

The widespread and indiscriminate use of biocides poses significant threats to global health, socioeconomic development, and environmental sustainability by accelerating antibiotic resistance. Bacterial resistance development is highly complex and influenced significantly by environmental factors. Increased biocide usage in households, agriculture, livestock farming, industrial settings, and hospitals produces persistent chemical residues that pollute soil and aquatic environments. Such contaminants contribute to the selection and proliferation of resistant bacteria and antimicrobial resistance genes (ARGs), facilitating their dissemination among humans, animals, and ecosystems. In this review, we conduct a critical assessment of four significant issues pertaining to this topic. Specifically, (i) the role of biocides in exerting selective pressure within the environmental resistome, thereby promoting the proliferation of resistant microbial populations and contributing to the global spread of antimicrobial resistance genes (ARGs); (ii) the role of biocides in triggering transient phenotypic adaptations in bacteria, including efflux pump overexpression, membrane alterations, and reduced porin expression, which often result in cross-resistance to multiple antibiotics; (iii) the capacity of biocides to disrupt bacteria and make the genetic content accessible, releasing DNA into the environment that remains intact under certain conditions, facilitating horizontal gene transfer and the spread of resistance determinants; (iv) the capacity of biocides to disrupt bacterial cells, releasing intact DNA into the environment and enhancing horizontal gene transfer of resistance determinants; and (iv) the selective interactions between biocides and bacterial biofilms in the environment, strengthening biofilm cohesion, inducing resistance mechanisms, and creating reservoirs for resistant microorganisms and ARG dissemination. Collectively, this review highlights the critical environmental and public health implications of biocide use, emphasizing an urgent need for strategic interventions to mitigate their role in antibiotic resistance proliferation.

Management of Gram-positive multiresistant bacteria prosthetic joint infection: a narrative review on current and innovative strategies

BACKGROUND

Prosthetic joint infection (PJI) is a devastating complication of arthroplasty surgery, mostly caused by Gram-positive pathogens, including S. aureus and coagulase-negative staphylococci (CNS). Multidrug resistance is of major concern in this setting: i) it can negatively impact outcome, restricting the use of the most effective antimicrobials; ii) it may influence the choice of surgical strategies; and iii) it restrains the therapeutic options to newly labelled antimicrobials with limited experience in PJI.

OBJECTIVES

To provide a comprehensive overview of the clinical impact of antimicrobial resistance in Gram-positive PJI and on current and innovative therapeutic strategies.

SOURCES

The review is based on PubMed searches for relevant topics, including multiresistant staphylococci PJI and the discussed specific therapeutic approaches. Given the very few randomized trials in this setting, discussion is mostly based on observational studies and the experience and opinion of the authors.

CONTENT

Methicillin resistance is an important concern in staphylococcal PJI, especially in CNS. However, its impact on outcome is controversial. Conversely, rifampicin and/or fluoroquinolone resistance are associated with worse prognosis, and might be considered when defining difficult-to-treat pathogens in the PJI setting. There is very little experience with recently developed anti-Gram-positive antimicrobial in PJI, but evaluations of their antibiofilm activities are promising, and some of them might represent significant advances regarding antimicrobial tolerance (such as tedizolid) or PK profiles (such as dalbavancin) during long-term treatment required for PJI. Evaluation of innovative strategies in this setting is crucial, including repositioning of current surgical options using local antimicrobial delivery, PK monitoring and modelling to optimize antimicrobial therapy, suppressive antimicrobial treatment and/or phage-based approaches.

IMPLICATIONS

Prosthetic joint infections caused by resistant Gram-positive bacteria - including rifampicin- and/or fluoroquinolone-resistant staphylococci - may be associated with a poorer prognosis. It is therefore essential to optimise medical and surgical management, and to find new therapeutic alternatives.

Unconventional Therapies in Periprosthetic Joint Infections: Prevention and Treatment: A Narrative Review

BACKGROUND

as the demand for total joint arthroplasty continues to grow each year, the healthcare burden is expected to increase due to periprosthetic joint infection (PJI). This review article aims to highlight the significance of biofilms in the pathogenesis of PJI and introduce alternative therapies that prevent bacterial adhesion to implants or enhance their eradication when infection occurs.

SEARCH STRATEGY

we conducted a bibliographic search in PubMed using the following MeSH terms as follows: "no antibiotic treatment of PJI", "bacterial biofilm eradication agents", and "unconventional prevention of PJI", among others. Most important results: after an initial analysis of the literature, we selected the most significant topics on novel PJI treatment methods and prevention strategies. A second PubMed search highlighted the following therapeutic modalities: the application of hydrogels on implant surfaces, the use of phage therapy, lysostaphin and antimicrobial peptides, the implementation of two-stage debridement, irrigation, implant retention and antibiotic therapy (DAIR), the intra-articular antibiotic infusion, and the use of methylene blue for biofilm eradication.

CONCLUSIONS

the use of new cement spacers with xylitol, ammonium compounds, or silver nanoparticles is another promising technique to increase the eradication rate in two-stage revision. It is important for professionals to deeply understand the pathogenesis of PJI and the role of biofilms in its development in order to become familiar with these novel techniques that could reduce the burdens on healthcare systems.

Designing Effective Antimicrobial Agents: Structural Insights into the Antibiofilm Activity of Ionic Liquids

Research concerning biofilm control is critical due to the pervasive and resilient nature of biofilms, which pose significant challenges across the industrial, environmental, and healthcare sectors. Traditional antimicrobial treatments are often ineffective against these robust structures. Here, we explore the antimicrobial properties of ionic liquids (ILs) and their efficacy in biofilm disruption. By examining the structural variations of ILs, we highlight the key role of hydrophobicity, noting that longer alkyl side chains in IL cations enhance biofilm disruption and bacterial death. However, upon reaching a certain optimal chain length─usually C12 to C14─the antimicrobial activity of ILs starts to decrease. Furthermore, the symmetry and size of anions significantly impact biofilm elimination. This Perspective addresses a critical gap in biofilm research, revealing the structure-activity relationships of ILs and providing a foundation for designing more effective biofilm-disrupting agents.

Safety and efficacy of combined intra-articular administration of vancomycin and ε-aminocaproic acid in total hip arthroplasty : a clinical study

Aims

To evaluate the concurrent use of vancomycin and ε-aminocaproic acid (EACA) in primary total hip arthroplasty (THA).

Methods

In total, 120 patients undergoing unilateral primary THA were divided into three groups: Group VE received intra-articular vancomycin and EACA; Group V received only intra-articular vancomycin; and Group E received only intra-articular EACA. Blood and joint fluids were sampled postoperatively to measure the vancomycin levels using chromatography. Blood loss and kidney function were monitored.

Results

Groups E and VE had equivalent blood loss, which was less than that in Group V. Intra-articular vancomycin levels were higher in Group VE at all intervals, with similar serum levels across the groups. Acute kidney injury, ototoxicity, and allergies were not observed, nor was a difference in rates of periprosthetic joint infection.

Conclusion

Adding intra-articular EACA to vancomycin did not affect intra-articular vancomycin levels, and maintained EACA's antifibrinolytic effects.

A novel strategy for eradication of staphylococcal biofilms using blood clots

Introduction

Infections with coagulase negative staphylococcal species (CoNS) are a major cause of mortality and morbidity in joint and heart valve replacement procedures, largely due to biofilm formation. Cells within biofilms have higher rates of antibiotic resistance than their planktonic counterparts; consequently, novel mechanisms are needed to combat these infections.

Methods

To enhance antibiotic delivery and penetration, this innovative study involved treating CoNS biofilms with murine blood clots impregnated with antibiotics. We then investigated the impact of this treatment on biofilm density, metabolism, and architecture.

Results

Our pilot study demonstrates that this method of antibiotic delivery results in improved biofilm clearance, relative to conventional exposure methods.

Discussion

Our results demonstrate that blood clot exposure has an intrinsic impact on biofilm density and potentially reduces colonization, warrenting further investigation into the mechanism.

Not All Antiseptic Solutions Are Equivalent in Removing Biofilm: A Comparison Across Different Orthopaedic Surfaces

BACKGROUND

Antiseptic solutions are commonly utilized during total joint arthroplasty (TJA) to prevent and treat periprosthetic joint infection (PJI). The purpose of this study was to investigate which antiseptic solution is most effective against methicillin-sensitive Staphylococcus aureus (MSSA) and Escherichia coli biofilms established in vitro on orthopaedic surfaces commonly utilized in total knee arthroplasty: cobalt-chromium (CC), oxidized zirconium (OxZr), and polymethylmethacrylate (PMMA).

METHODS

MSSA and E. coli biofilms were grown on CC, OxZr, and PMMA discs for 24 and 72 hours. Biofilm-coated discs were treated with control or various antiseptic solutions for 3 minutes. Solutions included 10% povidone-iodine, a 1:1 mixture of 10% povidone-iodine plus 3% hydrogen peroxide, diluted povidone-iodine, 0.05% chlorhexidine gluconate, and a surfactant-based formulation of ethanol, acetic acid, sodium acetate, benzalkonium chloride, and water. Following treatment, discs were sonicated to quantify adherent bacteria or underwent imaging with scanning electron microscopy to identify biofilm. Antiseptic solutions were considered efficacious if they produced a 3-log (1,000-fold) reduction in colony-forming units compared with controls.

RESULTS

On both OxZr and CC, 10% povidone-iodine with hydrogen peroxide eradicated all MSSA, and it achieved clinical efficacy on PMMA at both 24-hour MSSA biofilm (p < 0.0002) and 72-hour MSSA biofilm (p = 0.002). On 72-hour MSSA biofilm, 10% povidone-iodine eradicated all bacteria on OxZr and CC, and it achieved clinical efficacy on PMMA (p = 0.04). On 24-hour MSSA biofilm, 10% povidone-iodine achieved efficacy on all surfaces (all p < 0.01). The surfactant-based formulation only achieved clinical efficacy on 72-hour MSSA biofilms on CC (p = 0.04) and OxZr (p = 0.07). On 72-hour E. coli biofilm, 10% povidone-iodine with or without hydrogen peroxide achieved clinical efficacy on all surfaces. No other solution achieved clinical efficacy on either MSSA or E. coli.

CONCLUSIONS

Antiseptic solutions vary considerably in efficacy against bacterial biofilm. The 10% povidone-iodine solution with or without hydrogen peroxide consistently removed MSSA and E. coli biofilms on multiple orthopaedic surfaces and should be considered for clinical use.

CLINICAL RELEVANCE

Clinicians should be aware of the differences in the efficacy of antiseptic solutions on different orthopaedic surfaces when treating MSSA or E. coli biofilms.

Amikacin-loaded selenium nanoparticles improved antibacterial and antibiofilm activity of amikacin against bovine mastitis-causing Staphylococcus aureus

Background

Antibiotic resistance in various microorganisms has become one of the most serious health problems worldwide. The use of nanoparticles in combination with conventional antibiotics is one of the recent efforts to overcome these challenges. This study aims to synthesize and evaluate the possibility of using amikacin-loaded selenium nanoparticles as antibacterial agent against multidrug-resistant Staphylococcus aureus, that causes bovine mastitis.

Methods

Selenium nanoparticles (SeNPs) were synthesized through chemical reduction of sodium selenite using L-cysteine. Loading of amikacin on selenium nanoparticles was done by mixing both in solution and confirmed by UV-Vis spectroscopy, XRD, SEM, and DLS. Antibacterial properties of obtained nanoparticles against S. aureus were determined using agar disc diffusion, broth micro dilution methods and also time-kill assay. Anti-biofilm properties of amikacin-loaded selenium nanoparticles was determined using microplate method and through determining the expression level of biofilm associated genes including icaA and icaD in S. aureus isolates treated with sub-MIC concentration of these nanoparticles by real-time PCR.

Results

Synthetized SeNPs and amikacin-loaded selenium nanoparticles (SeNPs@AMK) exhibited spherical appearances and 80.4 % of Se° had a diameter of 120 nm. SeNPs and SeNPs@AMK exhibited antibacterial effects against S. aureus isolates at the range of 32-128 μg/mL and 1-32 μg/mL respectively. Dependent on concentration and the exposure time, bacterial killing was promoted by the SeNPs@AMK treatment. The use of SeNPs@AMK decreased the biofilm formation of the isolates by more than 50 % and also lead to down-regulation of icaA and icaD biofilm associated gene compared to the control.

Conclusions

The results of this study suggest the antimicrobial properties of SeNPs and the reduction in the effective concentration of nanoparticle-loaded amikacin. Therefore, loading of antibiotics on the surface of nanoparticles may be used as a strategy to deal with the growing problem of drug resistance.

Povidone-iodine and silver nitrate are equally effective in eradicating staphylococcal biofilm grown on a titanium surface: an in-vitro analysis

BACKGROUND

There is no consensus on the irrigation solution and concentration that should be used when performing a debridement, antibiotics, and implant retention (DAIR) surgery.

AIM

To determine the minimum biofilm eradication concentration (MBEC) of five antibacterial solutions and to compare their efficacies in eradicating staphylococcal biofilm embedded on a titanium surface.

METHODS

Meticillin-sensitive Staphylococcus aureus (MSSA) and meticillin-resistant S. aureus (MRSA) ATCC standard strains were grown over porous Ti-6Al-4V acetabular screw-caps. Antibacterial solutions were povidone-iodine, rifampicin, silver nitrate, copper sulphate, and chlorhexidine. MBEC values were calculated for MSSA and MRSA. After 24 h, screw-caps were exposed for 3 min to each solution. Bacterial separation from each specimen was performed with vortex agitation and footprint on agar plate in triplicate. Colony forming units (cfu) were counted pre- and post-agitation, and the delta of cfu/mL was calculated for each solution. A threefold log reduction in cfu was considered a measure of solution efficacy. Comparison between groups was made with Fisher's test.

FINDINGS

MBEC values for MSSA and MRSA, respectively, were as follows: 8000 μg/mL and 16,000 μg/mL for povidone-iodine; 64 μg/mL and 128 μg/mL for rifampicin; 10,000 μg/mL and 5120 μg/mL for silver nitrate; 900 μg/mL and 900 μg/mL for copper sulphate; 16 μg/mL and 32 μg/mL for chlorhexidine. Rifampicin, copper sulphate and chlorhexidine were ineffective against MSSA and MRSA biofilm compared with povidone-iodine (P<0.01) and silver nitrate (P=0.015) that had a delta cfu reduction >8 log. Povidone-iodine and silver nitrate showed negative footprints without visible MSSA (P=0.005) and MRSA (P=0.014).

CONCLUSIONS

Povidone-iodine and silver nitrate were the only irrigating solutions capable of eradicating at least 99.9% of 24-h biofilm.

Intra-articular injection of vancomycin after arthrotomy closure following gentamicin-impregnated bone cementation in primary total knee arthroplasty provides a high intra-articular concentration while avoiding systemic toxicity: a prospective study

BACKGROUND

This study aimed to elucidate the safety and intra-articular elution profiles of vancomycin and gentamicin bone cement in patients undergoing primary total knee arthroplasty (TKA), with a focus on serum safety thresholds and therapeutic efficacy.

METHODS

Consecutive patients who underwent unilateral primary TKA were prospectively enrolled. The implants were fixed using gentamicin-impregnated bone cement, and after arthrotomy closure, 1000 mg of vancomycin suspended in 25 mL of normal saline was directly injected into the joint. Peripheral venous blood and drain fluid samples were collected 2, 8, and 24 h postoperatively. The serum and intra-articular concentrations of vancomycin and gentamicin were analyzed using liquid chromatography-tandem mass spectrometry within 24 h.

RESULTS

Clinical data reflecting renal and liver function were recorded preoperatively, and at 24 and 72 h postoperatively. A total of 100 patients were included. At 2, 8, and 24 h postoperatively, the serum vancomycin concentration was 7.0 ± 2.0, 5.7 ± 1.8, and 3.6 ± 1.4 µg/mL, respectively, while the intra-articular concentration was 468.5 (interquartile range [IQR] 286.0 to 774.8), 139.5 (IQR 52.0 to 295.3), and 34.4 (IQR 22.2 to 56.8) µg/mL, respectively; 33.2 (IQR 19.5 to 80.5) mg vancomycin was lost in drainage fluid at 24 h postoperatively. For gentamicin, the overall intra-articular concentration was 70.4 (IQR 35.4 to 109.2), 33.8 (IQR 17.8 to 73.9), and 21.1 (IQR 12.2 to 36.0) µg/mL at 2, 8, and 24 h postoperatively, respectively, with an undetectable serum concentration. No cases of acute renal injury, liver injury, ototoxicity, or anaphylaxis were observed.

CONCLUSIONS

Intra-articular injection of 1000 mg vancomycin after arthrotomy closure combined with gentamicin-impregnated bone cement provided a therapeutic intra-articular concentration while avoiding systemic toxicity over the initial 24 h after primary TKA. Therefore, intra-articular vancomycin administration may offer a safer alternative to intravenous antibiotics, reducing systemic toxicity; however, further large-scale studies are necessary.

TRIAL REGISTRATION

ClinicalTrials. Gov (registration number: NCT05338021).

Investigating the Translational Value of Periprosthetic Joint Infection Models to Determine the Risk and Severity of Staphylococcal Biofilms

With the advent of antibiotic-eluting polymeric materials for targeting recalcitrant infections, using preclinical models to study biofilms are crucial for improving the treatment efficacy in periprosthetic joint infections. The stratification of risk and severity of infections is needed to develop an effective clinical dosing framework with better treatment outcomes. We use in vivo and in vitro implant-associated infection models to demonstrate that methicillin-sensitive and resistant Staphylococcus aureus (MSSA and MRSA) have model-dependent distinct implant and peri-implant tissue colonization patterns. The maturity of biofilms and the location (implant vs tissue) were found to influence the antibiotic susceptibility evolution profiles of MSSA and MRSA, and the models could capture the differing host-microbe interactions in vivo. Gene expression studies revealed the molecular heterogeneity of colonizing bacterial populations. The comparison and stratification of the risk and severity of infection across different preclinical models provided in this study can guide clinical dosing to prevent or treat PJI effectively.

Microneedles Constructed by Swellable Hydrogels Loaded with Celastrol for Efficient Treatment of Skin Infections Induced by Drug-Resistant Bacterial Strains

The urgent need for new antimicrobial drugs arises from the limited efficacy of traditional antibiotics against emerging drug-resistant strains. Celastrol (CSL) demonstrates an exceptional antibacterial property that remains unaffected by bacterial resistance, but its poor water solubility limits its wide applications. This study uses the hydrophobic inner cavity of mono-(6-diethylenetriamine-6-deoxy)-β-cyclodextrin (mβ-CD) (a derivative of cyclodextrin) to encapsulate CSL, constructing an inclusion complex (CSL@mβ-CD) to enhance the water solubility of CSL. The obtained inclusion complex is further incorporated into a swellable hydrogel microneedle (MN) to obtain CSL@mβ-CD/MN. The fabricated CSL@mβ-CD/MN can enable the sustained release of CSL, achieving effective bacterial eradication at infected sites. In vivo experiments demonstrate that CSL@mβ-CD/MN has a remarkable efficacy in the treatment of methicillin-resistant Staphylococcus aureus-induced subcutaneous abscesses and wound infections. Specifically, CSL@mβ-CD/MN can effectively penetrate the stratum corneum of the skin to realize rapid elimination of the bacteria in wounds. Moreover, CSL@mβ-CD/MN can efficiently scavenge reactive oxygen species, promote M2 polarization of macrophages, and relieve local inflammation at the wound sites. These results reveal that CSL@mβ-CD/MN holds great promise in the clinical treatment of acute skin infections induced by drug-resistant bacteria.

Compounds Containing 2,3-Bis(phenylamino) Quinoxaline Exhibit Activity Against Methicillin-Resistant Staphylococcus aureus, Enterococcus faecalis, and Their Biofilms

Antimicrobial resistance remains a global issue, hindering the control of bacterial infections. This study examined the antimicrobial properties of 2,3-N,N-diphenyl quinoxaline derivatives against Gram-positive, Gram-negative, and Mycobacterium species. Two quinoxaline derivatives (compounds 25 and 31) exhibited significant activity against most strains of Staphylococcus aureus, Enterococcus faecium, and Enterococcus faecalis tested, with MIC values ranging from 0.25 to 1 mg/L. These compounds also showed effective antibacterial activity against methicillin-resistant S. aureus (MRSA) and vancomycin-resistant E. faecium/E. faecalis (VRE) strains. They demonstrated comparable or superior activity to four current antibiotics (vancomycin, teicoplanin, daptomycin, and linezolid) against a wide range of clinically relevant isolates. Additionally, they were more effective in preventing S. aureus and E. faecalis biofilm formation compared to several other antibiotics. In summary, these two quinoxaline derivatives have potential as new antibacterial agents.

Unlocking the potential of lactic acid bacteria mature biofilm extracts as antibiofilm agents

The continuous growth of biofilm infections and their resilience to conventional cleaning methods and antimicrobial agents pose a worldwide challenge across diverse sectors. This persistent medical, industrial, and environmental issue contributes to treatment challenges and chronic diseases. Lactic acid bacteria have garnered global attention for their substantial antimicrobial effects against pathogens and established beneficial roles. Notably, their biofilms are also predicted to show a promising control strategy against pathogenic biofilm formation. The prevalence of biofilm-related problems underscores the need for extensive research and innovative solutions to tackle this global challenge. This novel study investigates the effect of different extracts (external, internal, and mixed extracts) obtained from Lactobacillus rhamnosus GG biofilm on pathogenic-formed biofilms. Subsequently, external extracts presented an important eradication effectiveness. Furthermore, a 6-fold concentration of these extracts led to eradication percentages of 57%, 67%, and 76% for Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa biofilms, respectively, and around 99.9% bactericidal effect of biofilm cells was observed for the three strains. The results of this research could mark a significant breakthrough in the field of anti-biofilm and antimicrobial strategies. Further studies and molecular research will be necessary to detect the molecules secreted by the biofilm, and their mechanisms of action engaged in new anti-biofilm strategies.

Effective biofilm eradication in MRSA isolates with aminoglycoside-modifying enzyme genes using high-concentration and prolonged gentamicin treatment

Bone and soft tissue infections caused by biofilm-forming bacteria, such as methicillin-resistant Staphylococcus aureus (MRSA), remain a significant clinical challenge. While the control of local infection is necessary, systemic treatment is also required, and biofilm eradication is a critical target for successful management. Topical antibiotic treatments, such as antibiotic-loaded bone cement (ALBC), have been used for some time, and continuous local antibiotic perfusion therapy, a less invasive method, has been developed by our group. However, the optimal antibiotics and concentrations for biofilms of clinical isolates are still not well understood. We examined the efficacy of high concentrations of gentamicin against MRSA biofilms and the role of gentamicin resistance genes in biofilm eradication. We collected 101 MRSA samples from a hospital in Japan and analyzed their gene properties, including methicillin and gentamicin resistance, and their minimum biofilm eradication concentration (MBEC) values. Our results showed that high concentrations of gentamicin are effective against MRSA biofilms and that even concentrations lower than the MBEC value could eliminate biofilms after prolonged exposure. We also identified three aminoglycoside/gentamicin resistance genes [aac(6')-aph(2″), aph(3')-III, and ant(4')-IA] and found that the presence or absence of these genes may inform the selection of treatments. It was also found that possession of the aac(6')-aph(2″) gene correlated with the minimum inhibitory concentration/MBEC values of gentamicin. Although this study provides insight into the efficacy of gentamicin against MRSA biofilms and the role of gentamicin resistance genes, careful selection of the optimal treatment strategy is needed for clinical application.

IMPORTANCE

Our analysis of 101 MRSA clinical isolates has provided valuable insights that could enhance treatment selection for biofilm infections in orthopedics. We found that high concentrations of gentamicin were effective against MRSA biofilms, and even prolonged exposure to concentrations lower than the minimum biofilm eradication concentration (MBEC) value could eliminate biofilms. The presence of the aac(6')-aph(2″) gene, an aminoglycoside resistance gene, was found to correlate with the minimum inhibitory concentration (MIC) and MBEC values of gentamicin, providing a potential predictive tool for treatment susceptibility. These results suggest that extended high concentrations of local gentamicin treatment could effectively eliminate MRSA biofilms in orthopedic infections. Furthermore, testing for gentamicin MIC or the possession of the aac(6')-aph(2″) gene could help select treatment, including topical gentamicin administration and surgical debridement.

In Vivo Intra-Articular Antibiotic Concentrations at 24 Hours After TKA Fall Below the Minimum Inhibitory Concentration for Most Bacteria: A Randomized Study of Commercially Available Bone Cement

BACKGROUND

The use of antibiotic-loaded bone cement (ALBC) to help reduce the risk of infection after primary total knee arthroplasty (TKA) is controversial. There is a paucity of in vivo data on the elution characteristics of ALBC. We aimed to determine whether the antibiotic concentrations of 2 commercially available ALBCs met the minimum inhibitory concentration (MIC) and minimum biofilm eradication concentration (MBEC) for common infecting organisms.

METHODS

Forty-five patients undergoing TKA were randomized to receive 1 of the following: bone cement without antibiotic (the negative control; n = 5), a commercially available formulation containing 1 g of tobramycin (n = 20), or a commercially available formulation containing 0.5 g of gentamicin (n = 20). Intra-articular drains were placed, and fluid was collected at 4 and 24 hours postoperatively. An automated immunoassay measuring antibiotic concentration was performed, and the results were compared against published MIC and MBEC thresholds.

RESULTS

The ALBC treatment groups were predominantly of White (65%) or Black (32.5%) race and were 57.5% female and 42.4% male. The mean age (and standard deviation) was 72.6 ± 7.2 years in the gentamicin group and 67.6 ± 7.4 years in the tobramycin group. The mean antibiotic concentration in the tobramycin group was 55.1 ± 37.7 μg/mL at 4 hours and 19.5 ± 13.0 μg/mL at 24 hours, and the mean concentration in the gentamicin group was 38.4 ± 25.4 μg/mL at 4 hours and 17.7 ± 15.4 μg/mL at 24 hours. Time and antibiotic concentration had a negative linear correlation coefficient (r = -0.501). Most of the reference MIC levels were reached at 4 hours. However, at 24 hours, a considerable percentage of patients had concentrations below the MIC for many common pathogens, including Staphylococcus epidermidis (gentamicin: 65% to 100% of patients; tobramycin: 50% to 85%), methicillin-sensitive Staphylococcus aureus (gentamicin: 5% to 90%; tobramycin: 5% to 50%), methicillin-resistant S . aureus (gentamicin: 5% to 65%; tobramycin: 50%), Streptococcus species (gentamicin: 10% to 100%), and Cutibacterium acnes (gentamicin: 10% to 65%; tobramycin: 100%). The aforementioned ranges reflect variation in the MIC among different strains of each organism. Gentamicin concentrations reached MBEC threshold values at 4 hours only for the least virulent strains of S . aureus and Escherichia coli. Tobramycin concentrations did not reach the MBEC threshold for any of the bacteria at either time point.

CONCLUSIONS

The elution of antibiotics from commercially available ALBC decreased rapidly following TKA, and only at 4 hours postoperatively did the mean antibiotic concentrations exceed the MIC for most of the pathogens. Use of commercially available ALBC may not provide substantial antimicrobial coverage following TKA.

LEVEL OF EVIDENCE

Therapeutic Level I . See Instructions for Authors for a complete description of levels of evidence.

Pathogens in FRI - Do bugs matter? - An analysis of FRI studies to assess your enemy

Fracture-related infection (FRI) is a devasting complication for both patients and their treating Orthopaedic surgeon that can lead to loss of limb function or even amputation. The unique and unpredictable features of FRI make its diagnosis and treatment a significant challenge. It has substantial morbidity and financial implications for patients, their families and healthcare providers. In this article, we perform an in-depth and comprehensive review of FRI through recent and seminal literature to highlight evolving definitions, diagnostic and treatment approaches, focusing on common pathogens such as Staphylococcus aureus, polymicrobial infections and multi-drug-resistant organisms (MDRO). Furthermore, multiple resistance mechanisms and adaptations for microbial survival are discussed, as well as modern evidence-based medical and surgical advancements in treatment strategies in combating FRI.

Designed De Novo α-Sheet Peptides Destabilize Bacterial Biofilms and Increase the Susceptibility of E. coli and S. aureus to Antibiotics

Biofilm-associated microbes are 10-1000 times less susceptible to antibiotics. An emerging treatment strategy is to target the structural components of biofilm to weaken the extracellular matrix without introducing selective pressure. Biofilm-associated bacteria, including Escherichia coli and Staphylococcus aureus, generate amyloid fibrils to reinforce their extracellular matrix. Previously, de novo synthetic α-sheet peptides designed in silico were shown to inhibit amyloid formation in multiple bacterial species, leading to the destabilization of their biofilms. Here, we investigated the impact of inhibiting amyloid formation on antibiotic susceptibility. We hypothesized that combined administration of antibiotics and α-sheet peptides would destabilize biofilm formation and increase antibiotic susceptibility. Two α-sheet peptides, AP90 and AP401, with the same sequence but inverse chirality at every amino acid were tested: AP90 is L-amino acid dominant while AP401 is D-amino acid dominant. For E. coli, both peptides increased antibiotic susceptibility and decreased the biofilm colony forming units when administered with five different antibiotics, and AP401 caused a greater increase in all cases. For S. aureus, increased biofilm antibiotic susceptibility was also observed for both peptides, but AP90 outperformed AP401. A comparison of the peptide effects demonstrates how chirality influences biofilm targeting of gram-negative E. coli and gram-positive S. aureus. The observed increase in antibiotic susceptibility highlights the role amyloid fibrils play in the reduced susceptibility of bacterial biofilms to specific antibiotics. Thus, the co-administration of α-sheet peptides and existing antibiotics represents a promising strategy for the treatment of biofilm infections.

Investigating the translational value of Periprosthetic Joint Infection (PJI) models to determine the risk and severity of Staphylococcal biofilms

With the advent of antibiotic-eluting polymeric materials for targeting recalcitrant infections, using preclinical models to study biofilm is crucial for improving the treatment efficacy in periprosthetic joint infections. The stratification of risk and severity of infections is needed to develop an effective clinical dosing framework with better outcomes. Here, using in-vivo and in-vitro implant-associated infection models, we demonstrate that methicillin-sensitive and resistant Staphylococcus aureus (MSSA and MRSA) have model-dependent distinct implant and peri-implant tissue colonization patterns. The maturity of biofilms and the location (implant vs tissue) were found to influence the antibiotic susceptibility evolution profiles of MSSA and MRSA and the models could capture the differing host-microbe interactions in vivo. Gene expression studies revealed the molecular heterogeneity of colonizing bacterial populations. The comparison and stratification of the risk and severity of infection across different preclinical models provided in this study can guide clinical dosing to effectively prevent or treat PJI.

A review on antimicrobial strategies in mitigating biofilm-associated infections on medical implants

Biomedical implants are crucial in providing support and functionality to patients with missing or defective body parts. However, implants carry an inherent risk of bacterial infections that are biofilm-associated and lead to significant complications. These infections often result in implant failure, requiring replacement by surgical restoration. Given these complications, it is crucial to study the biofilm formation mechanism on various biomedical implants that will help prevent implant failures. Therefore, this comprehensive review explores various types of implants (e.g., dental implant, orthopedic implant, tracheal stent, breast implant, central venous catheter, cochlear implant, urinary catheter, intraocular lens, and heart valve) and medical devices (hemodialyzer and pacemaker) in use. In addition, the mechanism of biofilm formation on those implants, and their pathogenesis were discussed. Furthermore, this article critically reviews various approaches in combating implant-associated infections, with a special emphasis on novel non-antibiotic alternatives to mitigate biofilm infections.

Efficacy of the bee-venom antimicrobial peptide Osmin against sensitive and carbapenem-resistant Klebsiella pneumoniae strains

The emergence of multidrug-resistant (MDR) Klebsiella pneumoniae strains causes severe problems in the treatment of bacterial infections owing to limited treatment options. Especially, carbapenem-resistant Klebsiella pneumoniae (CRKP) is rapidly spreading worldwide and is emerging as a new cause of drug-resistant healthcare-associated infections. CRKP also has been announced by the Centers for Disease Control and Prevention (CDC) and the World Health Organization (WHO) as one of the most pressing antibiotic resistance threats. Antimicrobial peptides (AMPs) are drawing considerable attention as ideal antibiotic alternative candidates to combat MDR bacterial infections. In a previous study, Osmin is composed of 17 amino acids and is isolated from solitary bee (Osmia rufa) venom. Herein, we evaluated the potential of Osmin to be used against drug-resistant K. pneumoniae as an alternative to conventional antibiotics. Osmin exhibited significant antimicrobial and anti-biofilm activity and lower toxicity than melittin, a well-known bee venom peptide. Additionally, we confirmed that it possesses a bactericidal mechanism that rapidly destroys bacterial membranes. Osmin was relatively more stable than melittin under the influence of various environmental factors and unlike conventional antibiotics, it exhibited a low bacterial resistance risk. During in vivo tests, Osmin reduced bacterial growth and the expression of pro-inflammatory cytokines and fibrosis-related genes in mice with CRKP-induced sepsis. Overall, our results indicate a high potential for Osmin to be used as a valuable therapeutic agent against drug-resistant K. pneumoniae infections.

The potential of suspended chitosan nanoparticles as a surgical irrigation fluid

In this study, we sought to synthesize chitosan nanoparticles (CS-NPs) and characterize their morphology, efficacy in inhibiting bacterial attachment, and efficacy in eradicating bacteria established on implantable hardware. CS-NPs possess desirable properties, including antibacterial properties in biofilm-mediated infections. CS-NPs were produced using ionic gelation and characterized via scanning electron microscope imaging. Staphylococcus aureus was incubated with CS-NPs at various concentrations and compared to a 1% povidone-iodine with 1% H2 O2 control in 24-well plates. Stainless steel bone screws were placed in six-well plates and inoculated with S. aureus. After 24 h, the screws were transferred to one of three solutions (saline, 40 mg/mL CS-NP, or 1% povidone-iodine with 1% H2 O2 ). Four screws from each group were vortexed in saline and plated. The remaining screw from each group was prepped and imaged to map the location of persistent bacteria. Synthesized CS-NPs had a mean diameter of 0.39 ± 0.13 μm and circularity of 0.87 ± 0.05. The percent inhibition of bacterial attachment was 73% at 20 mg/mL, 73% at 30 mg/mL, 75% at 40 mg/mL, 79% at 50 mg/mL, and 78% at 60 mg/mL. When compared to saline, the 40 mg/mL CS-NP solution reduced bacteria on the screws by 76%. No bacteria were retrieved from the 1% povidone-iodine with 1% H2 O2 group. This study demonstrated that CS-NP solution effectively inhibited S. aureus bacterial attachment and was more effective than saline in eradicating bacteria from orthopedic hardware, suggesting that CS-NPs have the potential for prevention and treatment of musculoskeletal infections as a component of an intraoperative surgical irrigation solution.

Dissolvable alginate hydrogel-based biofilm microreactors for antibiotic susceptibility assays

Biofilms are found in many infections in the forms of surface-adhering aggregates on medical devices, small clumps in tissues, or even in synovial fluid. Although antibiotic resistance genes are studied and monitored in the clinic, the structural and phenotypic changes that take place in biofilms can also lead to significant changes in how bacteria respond to antibiotics. Therefore, it is important to better understand the relationship between biofilm phenotypes and resistance and develop approaches that are compatible with clinical testing. Current methods for studying antimicrobial susceptibility are mostly planktonic or planar biofilm reactors. In this work, we develop a new type of biofilm reactor-three-dimensional (3D) microreactors-to recreate biofilms in a microenvironment that better mimics those in vivo where bacteria tend to form surface-independent biofilms in living tissues. The microreactors are formed on microplates, treated with antibiotics of 1000 times of the corresponding minimal inhibitory concentrations (1000 × MIC), and monitored spectroscopically with a microplate reader in a high-throughput manner. The hydrogels are dissolvable on demand without the need for manual scraping, thus enabling measurements of phenotypic changes. Bacteria inside the biofilm microreactors are found to survive exposure to 1000 × MIC of antibiotics, and subsequent comparison with plating results reveals no antibiotic resistance-associated phenotypes. The presented microreactor offers an attractive platform to study the tolerance and antibiotic resistance of surface-independent biofilms such as those found in tissues.

Rat model of recalcitrant prosthetic joint infection using biofilm inocula

Prosthetic joint infection (PJI) is a rare but devastating complication of joint arthroplasty. Biofilm formation around the prosthesis confers tolerance to antibiotics so that treatment is challenging. Most animal models of PJI use planktonic bacteria to establish the infection which fails to reproduce the pathology of chronic infection. We aimed to establish a rat model of Staphylococcus aureus PJI in male Sprague-Dawley rats using biofilm inocula and demonstrate its tolerance to frontline antibiotics. Pilot studies indicated that infection could be introduced to the knee joint by a biofilm-coated pin but that handling the prosthetic without disturbing the biofilm was difficult. We, therefore, developed a pin with a slotted end and used a miniature-biofilm reactor to develop mature biofilm in this niche. These biofilm-laden pins consistently produced infection of the bone and joint space. Treatment with high dose cefazolin, 250 mg/kg, starting the day of surgery reduced or cleared pin-adherent bioburden within 7 days, however when escalation from 25 to 250 mg/kg cefazolin treatment was delayed for 48 h, rats were unable to clear the infection. To track infections, we used bioluminescent bacteria, however, the bioluminescent signal did not accurately track the degree of infection in the bone and joint space as the signal did not penetrate the bone. In conclusion, we demonstrate that using a custom prosthetic pin, we can generate biofilm in a specific niche using a novel bioreactor setup and initiate a rat PJI that rapidly develops tolerance to supra-clinical doses of cefazolin.

Antimicrobial Treatment of Staphylococcus aureus Biofilms

Staphylococcus aureus is a microorganism frequently associated with implant-related infections, owing to its ability to produce biofilms. These infections are difficult to treat because antimicrobials must cross the biofilm to effectively inhibit bacterial growth. Although some antibiotics can penetrate the biofilm and reduce the bacterial load, it is important to understand that the results of routine sensitivity tests are not always valid for interpreting the activity of different drugs. In this review, a broad discussion on the genes involved in biofilm formation, quorum sensing, and antimicrobial activity in monotherapy and combination therapy is presented that should benefit researchers engaged in optimizing the treatment of infections associated with S. aureus biofilms.

Extended local release and improved bacterial eradication by adding rifampicin to a biphasic ceramic carrier containing gentamicin or vancomycin

Aims

There is a lack of biomaterial-based carriers for the local delivery of rifampicin (RIF), one of the cornerstone second defence antibiotics for bone infections. RIF is also known for causing rapid development of antibiotic resistance when given as monotherapy. This in vitro study evaluated a clinically used biphasic calcium sulphate/hydroxyapatite (CaS/HA) biomaterial as a carrier for dual delivery of RIF with vancomycin (VAN) or gentamicin (GEN).

Methods

The CaS/HA composites containing RIF/GEN/VAN, either alone or in combination, were first prepared and their injectability, setting time, and antibiotic elution profiles were assessed. Using a continuous disk diffusion assay, the antibacterial behaviour of the material was tested on both planktonic and biofilm-embedded forms of standard and clinical strains of Staphylococcus aureus for 28 days. Development of bacterial resistance to RIF was determined by exposing the biofilm-embedded bacteria continuously to released fractions of antibiotics from CaS/HA-antibiotic composites.

Results

Following the addition of RIF to CaS/HA-VAN/GEN, adequate injectability and setting of the CaS/HA composites were noted. Sustained release of RIF above the minimum inhibitory concentrations of S. aureus was observed until study endpoint (day 35). Only combinations of CaS/HA-VAN/GEN + RIF exhibited antibacterial and antibiofilm effects yielding no viable bacteria at study endpoint. The S. aureus strains developed resistance to RIF when biofilms were subjected to CaS/HA-RIF alone but not with CaS/HA-VAN/GEN + RIF.

Conclusion

Our in vitro results indicate that biphasic CaS/HA loaded with VAN or GEN could be used as a carrier for RIF for local delivery in clinically demanding bone infections. Cite this article: Bone Joint Res 2022;11(11):787–802.