Microscopic detection of viable Staphylococcus epidermidis in peri-implant tissue in experimental biomaterial-associated infection, identified by bromodeoxyuridine incorporation

Spatial Resolution for X-ray Excited Luminescence Chemical Imaging (XELCI)

Measuring chemical concentrations at the surface of implanted medical devices is important for elucidating the local biochemical environment, especially during implant infection. Although chemical indicator dyes enable chemical measurements in vitro, they are usually ineffective when measuring through tissue because the background obscures the dye signal and scattering dramatically reduces the spatial resolution. X-ray excited luminescent chemical imaging (XELCI) is a recent imaging modality which overcomes these limitations using a focused X-ray beam to excite a small spot of red light on scintillator-coated medical implants with well-defined location (because X-rays are minimally scattered) and low background. A spectrochemical indicator film placed over the scintillator layer, e.g., a polymer film containing pH-indicator dyes, absorbs some of the luminescence according to the local chemical environment, and this absorption is then detected by measuring the light intensity/spectrum passing through the tissue. A focused X-ray beam is used to scan point-by-point with a spatial resolution mainly limited by the X-ray beam width with minimum increase from X-ray absorption and scattering in the tissue. X-ray resolution, implant surface specificity, and chemical sensitivity are the three key features of XELCI. Here, we study spatial resolution using optically absorptive targets. For imaging a series of lines, the 20-80% knife-edge resolution was ∼285 (±15) μm with no tissue and 475 ± 18 and 520 ± 34 μm, respectively, through 5 and 10 mm thick tissue. Thus, doubling the tissue depth did not appreciably change the spatial resolution recorded through the tissue. This shows the promise of XELCI for submillimeter chemical imaging through tissue.

Role of Resident Microbial Communities in Biofilm-Related Implant Infections: Recent Insights and Implications

The use of medical implants continues to grow as the population ages. Biofilm-related implant infection is the leading cause of medical implant failure and remains difficult to diagnose and treat. Recent technologies have enhanced our understanding of the composition and complex functions of microbiota occupying various body site niches. In this review, we leverage data from molecular sequencing technologies to explore how silent changes in microbial communities from various sites can influence the development of biofilm-related infections. Specifically, we address biofilm formation and recent insights of the organisms involved in biofilm-related implant infections; how composition of microbiomes from skin, nasopharyngeal, and nearby tissue can impact biofilm-formation, and infection; the role of the gut microbiome in implant-related biofilm formation; and therapeutic strategies to mitigate implant colonization.

Non-invasive sampling procedure revealing the molecular events at different abutments of bone-anchored hearing systems–A prospective clinical pilot study

Purpose

To investigate the molecular activities in different compartments around the bone-anchored hearing system (BAHS) with either electropolished or machined abutments and to correlate these activities with clinical and microbiological findings.

Materials and methods

Twelve patients received machined or electropolished abutments after implant installation of BAHS. Peri-abutment fluid and tissue were collected from baseline to 12 months. Gene expression of cytokines and factors related to tissue healing and inflammation, regeneration and remodelling, as well as bacterial recognition were determined using quantitative-polymerase chain reaction (qPCR). The clinical status was evaluated using the Holgers scoring system, and bacterial colonisation was investigated by culturing.

Results

The gene expression of inflammatory cytokines (IL-8, IL-1β, and IL-10) and bacteria-related Toll-like receptors (2 and 4) was higher in the peri-abutment fluid than at baseline and in the peri-abutment tissue at 3 and 12 months. Conversely, the expression of genes related to tissue regeneration (Coll1a1 and FOXO1) was higher in the tissue samples than in the peri-abutment fluid at 3 and 12 months. Electropolished abutments triggered higher expression of inflammatory cytokines (IL-8 and IL-1β) (in peri-abutment fluid) and regeneration factor FOXO1 (in peri-abutment tissue) than machined abutments. Several cytokine genes in the peri-abutment fluid correlated positively with the detection of aerobes, anaerobes and Staphylococcus species, as well as with high Holger scores.

Conclusion

This study provides unprecedented molecular information on the biological processes of BAHS. Despite being apparently healed, the peri-abutment fluid harbours prolonged inflammatory activity in conjunction with the presence of different bacterial species. An electropolished abutment surface appears to be associated with stronger proinflammatory activity than that with a machined surface. The analysis of the peri-abutment fluid deserves further verification as a non-invasive sampling and diagnostic procedure of BAHS.

Combating Implant Infections: Shifting Focus from Bacteria to Host

The widespread use of biomaterials to support or replace body parts is increasingly threatened by the risk of implant-associated infections. In the quest for finding novel anti-infective biomaterials, there generally has been a one-sided focus on biomaterials with direct antibacterial properties, which leads to excessive use of antibacterial agents, compromised host responses, and unpredictable effectiveness in vivo. This review sheds light on how host immunomodulation, rather than only targeting bacteria, can endow biomaterials with improved anti-infective properties. How antibacterial surface treatments are at risk to be undermined by biomaterial features that dysregulate the protection normally provided by critical immune cell subsets, namely, neutrophils and macrophages, is discussed. Accordingly, how the precise modification of biomaterial surface biophysical cues, or the incorporation of immunomodulatory drug delivery systems, can render biomaterials with the necessary immune-compatible and immune-protective properties to potentiate the host defense mechanisms is reviewed. Within this context, the protective role of host defense peptides, metallic particles, quorum sensing inhibitors, and therapeutic adjuvants is discussed. The highlighted immunomodulatory strategies may lay a foundation to develop anti-infective biomaterials, while mitigating the increasing threat of antibacterial drug resistance.

Noninvasively Imaging pH at the Surface of Implanted Orthopedic Devices with X-ray Excited Luminescence Chemical Imaging

Implanted medical device-associated infections are a leading cause of fixation failure, and early diagnosis is the key to successful treatment. During infection, acidosis near the implant plays a role in antibiotic resistance and low pH is a potential infection indicator. Herein, we describe a pH sensor which attaches to the implants to noninvasively image local pH with high spatial resolution. The sensor has two layers: a scintillator layer which emits 620 and 700 nm light upon X-ray irradiation and a pH indicator layer containing bromocresol green dye that absorbs 620 nm luminescence in neutral/basic pH and passes 700 nm light at all pHs. We also developed a dedicated imaging system capable of scanning relatively large specimens through thick tissues. A focused X-ray beam irradiates one spot on the sensor, and the 620 to 700 nm peak ratio is measured to determine the local pH; images are acquired by scanning the X-ray beam across the surface and measuring the pH point-by-point. The sensor was covered with varying thickness slices of chicken breast tissue (0-19 mm) to evaluate how the tissue affects the peak intensity and ratio. Thick tissues attenuated both 620 and 700 nm light, with more attenuation at 620 nm than 700 nm. Although this spectral distortion shifted the pH calibration curve, the effect could be corrected for using a scintillator film region with no pH indicator layer as a spectral reference. The sensor was attached to an orthopedic plate affixed to a human cadaveric tibia and imaged through tissue. This approach provides both high spatial resolution from focused X-ray excitation and surface chemical specificity from the indicator dye, providing a tool for imaging local pH through tissue.

2018 international consensus meeting on musculoskeletal infection: Summary from the biofilm workgroup and consensus on biofilm related musculoskeletal infections

Biofilm-associated implant-related bone and joint infections are clinically important due to the extensive morbidity, cost of care and socioeconomic burden that they cause. Research in the field of biofilms has expanded in the past two decades, however, there is still an immense knowledge gap related to many clinical challenges of these biofilm-associated infections. This subject was assigned to the Biofilm Workgroup during the second International Consensus Meeting on Musculoskeletal Infection held in Philadelphia USA (ICM 2018) (https://icmphilly.com). The main objective of the Biofilm Workgroup was to prepare a consensus document based on a review of the literature, prepared responses, discussion, and vote on thirteen biofilm related questions. The Workgroup commenced discussing and refining responses prepared before the meeting on day one using Delphi methodology, followed by a tally of responses using an anonymized voting system on the second day of ICM 2018. The Working group derived consensus on information about biofilms deemed relevant to clinical practice, pertaining to: (1) surface modifications to prevent/inhibit biofilm formation; (2) therapies to prevent and treat biofilm infections; (3) polymicrobial biofilms; (4) diagnostics to detect active and dormant biofilm in patients; (5) methods to establish minimal biofilm eradication concentration for biofilm bacteria; and (6) novel anti-infectives that are effective against biofilm bacteria. It was also noted that biomedical research funding agencies and the pharmaceutical industry should recognize these areas as priorities. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.

Antibiofilm Peptides and Peptidomimetics with Focus on Surface Immobilization

Bacterial biofilms pose a major threat to public health, as they are associated with at least two thirds of all infections. They are highly resilient and render conventional antibiotics inefficient. As a part of the innate immune system, antimicrobial peptides have drawn attention within the last decades, as some of them are able to eradicate biofilms at sub-minimum inhibitory concentration (MIC) levels. However, peptides possess a number of disadvantages, such as susceptibility to proteolytic degradation, pH and/or salinity-dependent activity and loss of activity due to binding to serum proteins. Hence, proteolytically stable peptidomimetics were designed to overcome these drawbacks. This paper summarizes the current peptide and peptidomimetic strategies for combating bacteria-associated biofilm infections, both in respect to soluble and surface-functionalized solutions.

Antimicrobial Peptides in Biomedical Device Manufacturing

Over the past decades the use of medical devices, such as catheters, artificial heart valves, prosthetic joints, and other implants, has grown significantly. Despite continuous improvements in device design, surgical procedures, and wound care, biomaterial-associated infections (BAI) are still a major problem in modern medicine. Conventional antibiotic treatment often fails due to the low levels of antibiotic at the site of infection. The presence of biofilms on the biomaterial and/or the multidrug-resistant phenotype of the bacteria further impair the efficacy of antibiotic treatment. Removal of the biomaterial is then the last option to control the infection. Clearly, there is a pressing need for alternative strategies to prevent and treat BAI. Synthetic antimicrobial peptides (AMPs) are considered promising candidates as they are active against a broad spectrum of (antibiotic-resistant) planktonic bacteria and biofilms. Moreover, bacteria are less likely to develop resistance to these rapidly-acting peptides. In this review we highlight the four main strategies, three of which applying AMPs, in biomedical device manufacturing to prevent BAI. The first involves modification of the physicochemical characteristics of the surface of implants. Immobilization of AMPs on surfaces of medical devices with a variety of chemical techniques is essential in the second strategy. The main disadvantage of these two strategies relates to the limited antibacterial effect in the tissue surrounding the implant. This limitation is addressed by the third strategy that releases AMPs from a coating in a controlled fashion. Lastly, AMPs can be integrated in the design and manufacturing of additively manufactured/3D-printed implants, owing to the physicochemical characteristics of the implant material and the versatile manufacturing technologies compatible with antimicrobials incorporation. These novel technologies utilizing AMPs will contribute to development of novel and safe antimicrobial medical devices, reducing complications and associated costs of device infection.

Gentamicin-Loaded Polysaccharide Membranes for Prevention and Treatment of Post-operative Wound Infections in the Skeletal System

PURPOSE

To develop polysaccharide-based membranes that allow controlled and localized delivery of gentamicin for the treatment of post-operative bone infections.

METHODS

Membranes made of gellan gum (GUM), sodium alginate (ALG), GUM and ALG crosslinked with calcium ions (GUM + Ca and ALG + Ca, respectively) as well as reference collagen (COL) were produced by freeze-drying. Mechanical properties, drug release, antimicrobial activity and cytocompatibility of the membranes were assessed.

RESULTS

The most appropriate handling and mechanical properties (Young's modulus, E = 92 ± 4 MPa and breaking force, F _MAX  = 2.6 ± 0.1 N) had GUM + Ca membrane. In contrast, COL membrane showed F _MAX  = 0.14 ± 0.02 N, E = 1.0 ± 0.3 MPa and was deemed to be unsuitable for antibiotic delivery. The pharmacokinetic data demonstrated a uniform and sustainable delivery of gentamicin from GUM + Ca (44.4 ± 1.3% within 3 weeks), while for COL, ALG and ALG + Ca membranes the most of the drug was released within 24 h (55.3 ± 1.9%, 52.5 ± 1.5% and 37.5 ± 1.8%, respectively). Antimicrobial activity against S. aureus and S. epidermidis was confirmed for all the membranes. GUM + Ca and COL membranes supported osteoblasts growth, whereas on ALG and ALG + Ca membranes cell growth was reduced.

CONCLUSIONS

GUM + Ca membrane holds promise for effective treatment of bone infections thanks to favorable pharmacokinetics, bactericidal activity, cytocompatibility and good mechanical properties.

Site-specific gene expression analysis of implant-near cells in a soft tissue infection model - Application of laser microdissection to study biomaterial-associated infection

Analysis of the implant-tissue interface is important for an understanding of the cellular response to biomaterials with different surface characteristics. However, inaccessibility to the site has restricted the detailed evaluation of the tissue surrounding the implant. Laser microdissection enables the isolation of specific cells and tissues for subsequent DNA, RNA, or protein analysis. The present experimental study employed laser microdissection to analyze tissue-specific differences in gene expression in cells around infected or control titanium implants 72 h after subcutaneous implantation in a rat model. Three different tissue zones located 0-800 μm away from the implant-tissue interface were analyzed. Implant sites challenged with a dose of 10⁶  CFU Staphylococcus epidermidis demonstrated higher gene expression of selected markers for inflammation (TNF-α, IL-6), cell recruitment (MCP-1, IL-8, IL-8 R), infection (TLR2), and tissue remodeling (MMP-9) compared with control implants. Furthermore, the gene expression analysis of the three extracted tissue zones revealed marked spatial differences, depending on the distance to the implant. Control implants continuously induced higher cell gene expression in the implant-tissue interface compared with cells 200-800 μm away from the implant, whereas the sites inoculated with S. epidermidis resulted in high gene expression further away from the implant as well. In conclusion, this study demonstrates that laser microdissection is an interesting tool, revealing both gene- and site-specific gene expression patterns in the implant-tissue interface. The technique provides an opportunity for detailed molecular dissection of the biological events related to the implant but occurring at different distances from the implant. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 2210-2217, 2017.

Antimicrobial peptides and their interaction with biofilms of medically relevant bacteria

Biofilm-associated infections represent one of the major threats of modern medicine. Biofilm-forming bacteria are encased in a complex mixture of extracellular polymeric substances (EPS) and acquire properties that render them highly tolerant to conventional antibiotics and host immune response. Therefore, there is a pressing demand of new drugs active against microbial biofilms. In this regard, antimicrobial peptides (AMPs) represent an option taken increasingly in consideration. After dissecting the peculiar biofilm features that may greatly affect the development of new antibiofilm drugs, the present article provides a general overview of the rationale behind the use of AMPs against biofilms of medically relevant bacteria and on the possible mechanisms of AMP-antibiofilm activity. An analysis of the interactions of AMPs with biofilm components, especially those constituting the EPS, and the obstacles and/or opportunities that may arise from such interactions in the development of new AMP-based antibiofilm strategies is also presented and discussed. This article is part of a Special Issue entitled: Antimicrobial Peptides edited by Karl Lohner and Kai Hilpert.

A novel soft tissue model for biomaterial-associated infection and inflammation - bacteriological, morphological and molecular observations

Infection constitutes a major risk for implant failure, but the reasons why biomaterial sites are more vulnerable than normal tissue are not fully elucidated. In this study, a soft tissue infection model was developed, allowing the analysis of cellular and molecular responses in each of the sub-compartments of the implant-tissue interface (on the implant surface, in the surrounding exudate and in the tissue). Smooth and nanostructured titanium disks with or without noble metal chemistry (silver, gold, palladium), and sham sites, were inoculated with Staphylococcus epidermidis and analysed with respect to number of viable bacteria, number, viability and gene expression of host cells, and using different morphological techniques after 4 h, 24 h and 72 h. Non-infected rats were controls. Results showed a transient inflammatory response at control sites, whereas bacterial administration resulted in higher recruitment of inflammatory cells (mainly polymorphonuclear), higher, continuous cell death and higher gene expression of tumour necrosis factor-alpha, interleukin-6, interleukin-8, Toll-like receptor 2 and elastase. At all time points, S. epidermidis was predominantly located in the interface zone, extra- and intracellularly, and lower levels were detected on the implants compared with surrounding exudate. This model allows detailed analysis of early events in inflammation and infection associated to biomaterials in vivo leading to insights into host defence mechanisms in biomaterial-associated infections.

Staphylococcus epidermidis originating from titanium implants infects surrounding tissue and immune cells

Infection is a major cause of failure of inserted or implanted biomedical devices (biomaterials). During surgery, bacteria may adhere to the implant, initiating biofilm formation. Bacteria are also observed in and recultured from the tissue surrounding implants, and may even reside inside host cells. Whether these bacteria originate from biofilms is not known. Therefore, we investigated the fate of Staphylococcus epidermidis inoculated on the surface of implants as adherent planktonic cells or as a biofilm in mouse experimental biomaterial-associated infection. In order to discriminate the challenge strain from potential contaminating mouse microflora, we constructed a fully virulent green fluorescent S. epidermidis strain. S. epidermidis injected along subcutaneous titanium implants, pre-seeded on the implants or pre-grown as biofilm, were retrieved from the implants as well as the surrounding tissue in all cases after 4days, and in histology bacteria were observed in the tissue co-localizing with macrophages. Thus, bacteria adherent to or in a biofilm on the implant are a potential source of infection of the surrounding tissue, and antimicrobial strategies should prevent both biofilm formation and tissue colonization.

Development of a standardized and safe airborne antibacterial assay, and its evaluation on antibacterial biomimetic model surfaces

Bacterial infection of biomaterials is a major concern in medicine, and different kinds of antimicrobial biomaterial have been developed to deal with this problem. To test the antimicrobial performance of these biomaterials, the airborne bacterial assay is used, which involves the formation of biohazardous bacterial aerosols. We here describe a new experimental set-up which allows safe handling of such pathogenic aerosols, and standardizes critical parameters of this otherwise intractable and strongly user-dependent assay. With this new method, reproducible, thorough antimicrobial data (number of colony forming units and live-dead-stain) was obtained. Poly(oxonorbornene)-based Synthetic Mimics of Antimicrobial Peptides (SMAMPs) were used as antimicrobial test samples. The assay was able to differentiate even between subtle sample differences, such as different sample thicknesses. With this new set-up, the airborne bacterial assay was thus established as a useful, reliable, and realistic experimental method to simulate the contamination of biomaterials with bacteria, for example in an intraoperative setting.

Foreign Body Infection Models to Study Host-Pathogen Response and Antimicrobial Tolerance of Bacterial Biofilm

The number of implanted medical devices is steadily increasing and has become an effective intervention improving life quality, but still carries the risk of infection. These infections are mainly caused by biofilm-forming staphylococci that are difficult to treat due to the decreased susceptibility to both antibiotics and host defense mechanisms. To understand the particular pathogenesis and treatment tolerance of implant-associated infection (IAI) animal models that closely resemble human disease are needed. Applications of the tissue cage and catheter abscess foreign body infection models in the mouse will be discussed herein. Both models allow the investigation of biofilm and virulence of various bacterial species and a comprehensive insight into the host response at the same time. They have also been proven to serve as very suitable tools to study the anti-adhesive and anti-infective efficacy of different biomaterial coatings. The tissue cage model can additionally be used to determine pharmacokinetics, efficacy and cytotoxicity of antimicrobial compounds as the tissue cage fluid can be aspirated repeatedly without the need to sacrifice the animal. Moreover, with the advance in innovative imaging systems in rodents, these models may offer new diagnostic measures of infection. In summary, animal foreign body infection models are important tools in the development of new antimicrobials against IAI and can help to elucidate the complex interactions between bacteria, the host immune system, and prosthetic materials.

Propionibacterium acnes and Staphylococcus lugdunensis cause pyogenic osteomyelitis in an intramedullary nail model in rabbits

Propionibacterium acnes and coagulase-negative staphylococci (CoNS) are opportunistic pathogens implicated in prosthetic joint and fracture fixation device-related infections. The purpose of this study was to determine whether P. acnes and the CoNS species Staphylococcus lugdunensis, isolated from an "aseptically failed" prosthetic hip joint and a united intramedullary nail-fixed tibial fracture, respectively, could cause osteomyelitis in an established implant-related osteomyelitis model in rabbits in the absence of wear debris from the implant material. The histological features of P. acnes infection in the in vivo rabbit model were consistent with localized pyogenic osteomyelitis, and a biofilm was present on all explanted intramedullary (IM) nails. The animals displayed no outward signs of infection, such as swelling, lameness, weight loss, or elevated white blood cell count. In contrast, infection with S. lugdunensis resulted in histological features consistent with both pyogenic osteomyelitis and septic arthritis, and all S. lugdunensis-infected animals displayed weight loss and an elevated white blood cell count despite biofilm detection in only two out of six rabbits. The differences in the histological and bacteriological profiles of the two species in this rabbit model of infection are reflective of their different clinical presentations: low-grade infection in the case of P. acnes and acute infection for S. lugdunensis. These results are especially important in light of the growing recognition of chronic P. acnes biofilm infections in prosthetic joint failure and nonunion of fracture fixations, which may be currently reported as "aseptic" failure.

Biomaterial-associated infection: locating the finish line in the race for the surface

Biomaterial-associated infections occur on both permanent implants and temporary devices for restoration or support of human functions. Despite increasing use of biomaterials in an aging society, comparatively few biomaterials have been designed that effectively reduce the incidence of biomaterial-associated infections. This review provides design guidelines for infection-reducing strategies based on the concept that the fate of biomaterial implants or devices is a competition between host tissue cell integration and bacterial colonization at their surfaces.

Advances in biomaterials and surface technologies

Tremendous advances in quality, reliability, performance, and versatility of surgical instrumentation and devices have been achieved over the past 50 years using biomaterials. The global orthopaedic implant industry is expected to grow to $41.8 billion by 2016, driven primarily by advancements in implant designs, including materials that provide improved biocompatibility, durability, and expanded clinical applications. Biomaterials have evolved through 3 clinical "generations": (1) "bio-inert materials," (2) materials with intrinsic bioactivity and degradability, and (3) biomaterials that stimulate specific biological host responses. In all cases, surface modifications, including coatings, represent a key strategy for improvements in tissue-contacting properties. Surfaces continue to be a focus for many device improvements and for tissue interfacing, especially for many orthopaedic structural implants comprising metal and metal alloys. Progress in implant materials processing, coating technologies, and coating combinations with therapeutic agents provide new properties and functionalities to improve device-tissue integration and reduce foreign body reactions and infections. Performance criteria for these surface modifications success in clinical practice are daunting, and translation of several technologies from in vitro proof-of-concept to in vivo applications has proven challenging.

Immobilized antibiotics to prevent orthopaedic implant infections

Many surgical procedures require the placement of an inert or tissue-derived implant deep within the body cavity. While the majority of these implants do not become colonized by bacteria, a small percentage develops a biofilm layer that harbors invasive microorganisms. In orthopaedic surgery, unresolved periprosthetic infections can lead to implant loosening, arthrodeses, amputations and sometimes death. The focus of this review is to describe development of an implant in which an antibiotic tethered to the metal surface is used to prevent bacterial colonization and biofilm formation. Building on well-established chemical syntheses, studies show that antibiotics can be linked to titanium through a self-assembled monolayer of siloxy amines. The stable metal-antibiotic construct resists bacterial colonization and biofilm formation while remaining amenable to osteoblastic cell adhesion and maturation. In an animal model, the antibiotic modified implant resists challenges by bacteria that are commonly present in periprosthetic infections. While the long-term efficacy and stability is still to be established, ongoing studies support the view that this novel type of bioactive surface has a real potential to mitigate or prevent the devastating consequences of orthopaedic infection.

Non-typeable Haemophilus influenzae invasion and persistence in the human respiratory tract

Non-typeable Haemophilus influenzae (NTHI) is an opportunistic bacterial pathogen of the human respiratory tract and is a leading cause of respiratory infections in children and adults. NTHI is considered to be an extracellular pathogen, but has consistently been observed within and between human respiratory epithelial cells and macrophages, in vitro and ex vivo. Until recently, few studies have examined the internalization, trafficking, and fate of NTHI in host cells. It is important to clarify this interaction because of a possible correlation between intracellular NTHI and symptomatic infection, and because NTHI infections frequently persist and recur despite antibiotic therapy and the development of bactericidal antibodies, suggesting a possible intracellular state or reservoir for NTHI. How does NTHI enter host cells? Can NTHI survive intracellularly and, if so, for how long? Strides have been made in the identification of host receptors, signaling, endocytosis, and trafficking pathways involved in the entry and persistence of NTHI in the respiratory tract.

Effects of coagulase-negative staphylococci and fibrin on breast capsule formation in a rabbit model

BACKGROUND

The etiology and ideal clinical treatment of capsular contracture (CC) remain unresolved. Bacteria, especially coagulase-negative staphylococci, have been previously shown to accelerate the onset of CC. The role of fibrin in capsule formation has also been controversial.

OBJECTIVE

The authors investigate whether fibrin and coagulase-negative staphylococci (CoNS) modulate the histological, microbiological, and clinical outcomes of breast implant capsule formation in a rabbit model and evaluate contamination during the surgical procedure.

METHODS

Thirty-one New Zealand white female rabbits were each implanted with one tissue expander and two breast implants. The rabbits received (1) untreated implants and expanders (control; n = 10), (2) two implants sprayed with 2 mL of fibrin and one expander sprayed with 0.5 mL of fibrin (fibrin; n = 11), or (3) two implants inoculated with 100 µL of a CoNS suspension (10(8)CFU/mL-0.5 density on the McFarland scale) and one expander inoculated with a CoNS suspension of 2.5 × 10(7) CFU/mL (CoNS; n = 10). Pressure/volume curves and histological and microbiological evaluations were performed. Operating room air samples and contact skin samples were collected for microbiological evaluation. The rabbits were euthanized at four weeks.

RESULTS

In the fibrin group, significantly decreased intracapsular pressures, thinner capsules, loose/dense (<25%) connective tissue, and negative/mild angiogenesis were observed. In the CoNS group, increased capsular thicknesses and polymorph-type inflammatory cells were the most common findings. Similar bacteria in capsules, implants, and skin were cultured from all the study groups. One Baker grade IV contracture was observed in an implant infected with Micrococcus spp.

CONCLUSIONS

Fibrin was associated with reduced capsule formation in this preclinical animal model, which makes fibrin an attractive potential therapeutic agent in women undergoing breast augmentation procedures. Clinical strategies for preventing bacterial contamination during surgery are crucial, as low pathogenic agents may promote CC.