Osteomyelitis and the role of biofilms in chronic infection

Spinal Implants can be Retained in Patients with Deep Spine Infection: A Cohort Study

Background/Purpose

It is unclear whether implant removal is necessary when deep spine infection of spinal instrumentation occurs. This study compares mortality, relapse, and reoperation rates between such patients with and without removal of spine implants.

Methods

A total of 20 patients were retrospectively reviewed. Baseline characteristics of the implant removal and nonremoval groups were compared. Outcome measures between groups were compared using multivariable logistic regression and predictors of each outcome identified.

Results

There were no significant differences in mortality, relapse, or reoperation rates between groups. Multiple vertebral level involvement was common (85%), and the L4 (30%) and L5 (35%) levels were most commonly involved. The majority of patients had osteomyelitis/spondylodiscitis (50%) and Staphylococcus aureus infections (60%). Thoracic spine infection was associated with relapse (odds ratio = 1.26) and reoperation (odds ratio = 1.101).

Conclusion

Implant removal is not always necessary in cases of deep spine infection as retention of implants is not associated with higher mortality, relapse, or reoperation rates.

Development of mesoporous bioactive glass nanoparticles and its use in bone tissue engineering

The incidence of bone disorders, from trauma, tissue degeneration due to ageing, pathological conditions to cancer, has been increasing. The pursuit for bone graft substitutes to assist in regenerating large bone defects is ever growing as a result of the shortage in conventional autografts and allografts, in addition to the associated risks of disease transmission. However, the use of alloplastic biomaterials is limited in clinical settings, as further investigations are required to address the properties of synthetic grafts to mimic the native bone tissue and deliver desirable biomolecules to facilitate bone regeneration. This review discusses the fundamental structure and properties of bone with the emphasis on organic and inorganic components that are important for the biomaterial design. The main focus will be on the advancement and usage of bioactive glass (BG) for bone tissue engineering due to its similarity to the natural inorganic constituent of bone. The various BG synthetic processes, modifications of composition, as well as the biomolecule delivery will be discussed in great detail. As the properties of BG are tuneable according to clinical needs, it creates a new paradigm in addition to displaying its superior potential for bone tissue engineering and translational medicine in the field of orthopedic surgery. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 2878-2887, 2018.

Flash autoclave settings may influence eradication but not presence of well-established biofilms on orthopaedic implant material

Flash autoclaving is one of the most frequently utilized methods of sterilizing devices, implants or other materials. For a number of decades, it has been common practice for surgeons to remove implantable devices, flash autoclave and then reimplant them in a patient. Data have not yet indicated the potential for biofilms to survive or remain on the surface of orthopaedic-relevant materials following flash autoclave. In this study, monomicrobial and polymicrobial biofilms were grown on the surface of clinically relevant titanium materials and exposed to flash autoclave settings that included varying times and temperatures. Data indicated that when the sterilization and control temperatures of an autoclave were the same, biofilms were able to survive flash autoclaving that was performed for a short duration. Higher temperature and increased duration rendered biofilms non-viable, but none of the autoclave settings had the ability to remove or disperse the presence of biofilms from the titanium surfaces. These findings may be beneficial for facilities, clinics, or hospitals to consider if biofilms are suspected to be present on materials or devices, in particular implants that have had associated infection and are considered for re-implantation. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1543-1550, 2018.

Inhibition of Streptococcus suis Adhesion and Biofilm Formation in Vitro by Water Extracts of Rhizoma Coptidis

Streptococcus suis is difficult to treat and responsible for various infections in humans and pigs. It can also form biofilms and induce persistent infections. Rhizoma Coptidis is a medicinal plant widely used in Traditional Chinese Medicine. Although the inhibitory effects of Rhizoma Coptidis on biofilm formation have been investigated in several studies, the ability of Rhizoma Coptidis to inhibit S. suis biofilm formation and the underlying mechanisms have not yet been reported. In this study, we showed that sub-minimal inhibitory concentrations (25 and 50 μg mL^-1) of water extracts of Rhizoma Coptidis (Coptis deltoidea C.Y.Cheng & P.K.Hsiao, obtained from Sichuan Province) were sufficient to inhibit biofilm formation, as shown in the tissue culture plate (TCP) method and scanning electron microscopy. Real-time PCR and iTRAQ were used to measure gene and protein expression in S. suis. Sub-minimum inhibitory concentrations (25 and 50 μg mL^-1) of Rhizoma Coptidis water extracts inhibited S. suis adhesion significantly in an anti-adherence assay. Some genes, such as gapdh, sly, and mrp, and proteins, such as antigen-like protein, CPS16V, and methyltransferase H, involved in adhesion were significantly modulated in cells treated with 50 μg mL^-1 of Rhizoma Coptidis water extracts compared to untreated cells. The results from this study suggest that compounds in Rhizoma Coptidis water extracts play an important role in inhibiting adhesion of S. suis cells and, therefore, biofilm formation.

Identification of Staphylococcus aureus genes involved in the formation of structured macrocolonies

The human pathogen Staphylococcus aureus causes difficult-to-eradicate biofilm-associated infections that generally become chronic. Understanding the genetic regulation of biofilm formation in S. aureus is central to a precise definition of the conditions and genes involved in development of chronic biofilm-associated infections. Biofilm-related genes have been detected by comparing mutants using the classical submerged biofilm formation assay, in which cells adhere to the bottom of a well containing culture medium. We recently developed an alternative biofilm formation model for S. aureus, based on macrocolony formation on agar plates, comparable to an assay used to study biofilm formation in a few other bacterial species. As organism features are the result of environmental conditions as well as of genes, we used a genome-wide collection of transposon-mapped mutants in this macrocolony assay to seek S. aureus developmental genes and pathways not identified by the classical biofilm formation assay. We identified routes related to glucose and purine metabolism and clarified their regulatory link to macrocolony formation. Our study demonstrates that formation of microbial communities must be correlated to specific growth conditions, and the role of metabolism must be considered in S. aureus biofilm formation and thus, in the development of chronic infections.

Chronic Osteomyelitis - Bacterial Flora, Antibiotic Sensitivity and Treatment Challenges

Background:

Chronic osteomyelitis is a catastrophic sequel of delayed diagnosis of acute osteomyelitis.

Objectives:

The objectives of the study were to determine bacterial flora and antibiotic sensitivity, and to evaluate the outcome of an aggressive surgical approach to chronic osteomyelitis.

Methods:

This is a single surgeon, prospective cohort study on 30 consecutive patients with clinically and radiologically diagnosed chronic osteomyelitis presented to a hospital. We prospectively recorded demographic, clinical, radiological features, treatment protocol, microbiologic results of culture and sensitivity. The main treatment outcome measures were clinical signs of eradication of infection.

Results:

Microbiologic results showed that Gram-negative and mixed flora accounts for more than half of chronic osteomyelitis cases while Staphylococcus aureus was a dominating single pathogen (39%). We detected a high resistance rate to common antibiotics, e.g. 83% of S. aureus isolates were resistant to oxacillin (MRSA). The mean duration of bone infection was 4.2 years (3 months to 30 years) and the mean number of operations was 1.5 (1-5) . The mean follow-up was 15 months (12-18 months). Infection was eradicated in 95% (21 out of 22) treated by a single procedure and in all patients (n=8) by double procedure.

Conclusion:

Presented the high rate of MRSA strains is alarming and calls for updating of the antibiotic therapy guidelines in the country. Good results in treatment of chronic osteomyelitis can be achieved by a single-stage protocol including radical debridement combined with systemic and topical antibiotic.

Combined Staining Techniques for Demonstration of Staphylococcus aureus Biofilm in Routine Histopathology

Aim: Visualization of Staphylococcus aureus biofilm using histochemical staining and combined histochemistry (HC) and immunohistochemistry (IHC).

Methods: The ability of S. aureus S54F9 to form biofilm was tested in vitro. Hereafter, infected bone tissue was collected from two different porcine models of osteomyelitis inoculated with S. aureus strain S54F9. The infection time was five and fifteen days, respectively. Twenty-five different histochemical staining protocols were tested in order to find the stains that could identify extracellular biofilm matrix. Protocols with an optimal visualization of biofilm extracellular matrix were combined with an immunohistochemical protocol based on a specific antibody against S. aureus. The combined protocols were applied to the tissue from the porcine models and to infected bone tissue from a child suffering from chronic staphylococcal osteomyelitis for more than a year.

Results:S. aureus S54F9 showed an ability to form biofilm in vitro. Visualization of biofilm, i.e. bacterial cells and extracellular matrix in different colours, was seen when the immunohistochemical protocol was combined with Alcian Blue pH3, Luna and Methyl-pyronin green. The bacterial cells were red to light brown and the extracellular matrix either light blue, blue or orange depending on the histochemical stain. In the porcine models and the human case 10 and 90 percent, respectively, of the bacterial aggregates in a 100x magnification field displayed both the extracellular matrix and the bacterial cells simultaneously in two different colours.

Conclusions: A combination of HC and IHC can be used to diagnose and characterise biofilm infections on a routine basis.

Staphylococcal Osteomyelitis: Disease Progression, Treatment Challenges, and Future Directions

Osteomyelitis is an inflammatory bone disease that is caused by an infecting microorganism and leads to progressive bone destruction and loss. The most common causative species are the usually commensal staphylococci, with Staphylococcus aureus and Staphylococcus epidermidis responsible for the majority of cases. Staphylococcal infections are becoming an increasing global concern, partially due to the resistance mechanisms developed by staphylococci to evade the host immune system and antibiotic treatment. In addition to the ability of staphylococci to withstand treatment, surgical intervention in an effort to remove necrotic and infected bone further exacerbates patient impairment. Despite the advances in current health care, osteomyelitis is now a major clinical challenge, with recurrent and persistent infections occurring in approximately 40% of patients. This review aims to provide information about staphylococcus-induced bone infection, covering the clinical presentation and diagnosis of osteomyelitis, pathophysiology and complications of osteomyelitis, and future avenues that are being explored to treat osteomyelitis.

Protein-mediated mineralization of edaravone into injectable, pH-sensitive microspheres used for potential minimally invasive treatment of osteomyelitis

Osteomyelitis, an infection within bone, is difficult to treat.

Porcine Models of Biofilm Infections with Focus on Pathomorphology

Bacterial biofilm formation is one of the main reasons for a negative treatment outcome and a high recurrence rate for many chronic infections in humans. The optimal way to study both the biofilm forming bacteria and the host response simultaneously is by using discriminative, reliable, and reproducible animal models of the infections. In this review, the advantages of in vivo studies are compared to in vitro studies of biofilm formation in infectious diseases. The pig is the animal of choice when developing and applying large animal models of infectious diseases due to its similarity of anatomy, physiology, and immune system to humans. Furthermore, conventional pigs spontaneously develop many of the same chronic bacterial infections as seen in humans. Therefore, in this review porcine models of five different infectious diseases all associated with biofilm formation and chronicity in humans are described. The infectious diseases are: chronic wounds, endocarditis, pyelonephritis, hematogenous osteomyelitis, and implant-associated osteomyelitis (IAO).

Impact of Staphylococcus aureus regulatory mutations that modulate biofilm formation in the USA300 strain LAC on virulence in a murine bacteremia model

Staphylococcus aureus causes acute and chronic forms of infection, the latter often associated with formation of a biofilm. It has previously been demonstrated that mutation of atl, codY, rot, sarA, and sigB limits biofilm formation in the USA300 strain LAC while mutation of agr, fur, and mgrA has the opposite effect. Here we used a murine sepsis model to assess the impact of these same loci in acute infection. Mutation of agr, atl, and fur had no impact on virulence, while mutation of mgrA and rot increased virulence. In contrast, mutation of codY, sarA, and sigB significantly attenuated virulence. Mutation of sigB resulted in reduced accumulation of AgrA and SarA, while mutation of sarA resulted in reduced accumulation of AgrA, but this cannot account for the reduced virulence of sarA or sigB mutants because the isogenic agr mutant was not attenuated. Indeed, as assessed by accumulation of alpha toxin and protein A, all of the mutants we examined exhibited unique phenotypes by comparison to an agr mutant and to each other. Attenuation of the sarA, sigB and codY mutants was correlated with increased production of extracellular proteases and global changes in extracellular protein profiles. These results suggest that the inability to repress the production of extracellular proteases plays a key role in attenuating the virulence of S. aureus in acute as well as chronic, biofilm-associated infections, thus opening up the possibility that strategies aimed at the de-repression of protease production could be used to broad therapeutic advantage. They also suggest that the impact of codY, sarA, and sigB on protease production occurs via an agr-independent mechanism.

Surface topography of silicon nitride affects antimicrobial and osseointegrative properties of tibial implants in a murine model

While silicon nitride (Si₃ N₄ ) is an antimicrobial and osseointegrative orthopaedic biomaterial, the contribution of surface topography to these properties is unknown. Using a methicillin-resistant strain of Staphylococcus aureus (MRSA), this study evaluated Si₃ N₄ implants in vitro utilizing scanning electron microscopy (SEM) with colony forming unit (CFU) assays, and later in an established in vivo murine tibia model of implant-associated osteomyelitis. In vitro, the "as-fired" Si₃ N₄ implants displayed significant reductions in adherent bacteria versus machined Si₃ N₄ (2.6 × 10⁴ vs. 8.7 × 10⁴ CFU, respectively; p < 0.0002). Moreover, SEM imaging demonstrated that MRSA cannot directly adhere to native as-fired Si₃ N₄ . Subsequently, a cross-sectional study was completed in which sterile or MRSA contaminated as-fired and machined Si₃ N₄ implants were inserted into the tibiae of 8-week old female Balb/c mice, and harvested on day 1, 3, 5, 7, 10, or 14 post-operatively for SEM. The findings demonstrated that the antimicrobial activity of the as-fired implants resulted from macrophage clearance of the bacteria during biofilm formation on day 1, followed by osseointegration through the apparent recruitment of mesenchymal stem cells on days 3-5, which differentiated into osteoblasts on days 7-14. In contrast, the antimicrobial behavior of the machined Si₃ N₄ was due to repulsion of the bacteria, a phenomenon that also limited osteogenesis, as host cells were also unable to adhere to the machined surface. Taken together, these results suggest that the in vivo biological behavior of Si₃ N₄ orthopaedic implants is driven by critical features of their surface nanotopography. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 3413-3421, 2017.

Cell differentiation defines acute and chronic infection cell types in Staphylococcus aureus

A central question to biology is how pathogenic bacteria initiate acute or chronic infections. Here we describe a genetic program for cell-fate decision in the opportunistic human pathogen Staphylococcus aureus, which generates the phenotypic bifurcation of the cells into two genetically identical but different cell types during the course of an infection. Whereas one cell type promotes the formation of biofilms that contribute to chronic infections, the second type is planktonic and produces the toxins that contribute to acute bacteremia. We identified a bimodal switch in the agr quorum sensing system that antagonistically regulates the differentiation of these two physiologically distinct cell types. We found that extracellular signals affect the behavior of the agr bimodal switch and modify the size of the specialized subpopulations in specific colonization niches. For instance, magnesium-enriched colonization niches causes magnesium binding to S. aureusteichoic acids and increases bacterial cell wall rigidity. This signal triggers a genetic program that ultimately downregulates the agr bimodal switch. Colonization niches with different magnesium concentrations influence the bimodal system activity, which defines a distinct ratio between these subpopulations; this in turn leads to distinct infection outcomes in vitro and in an in vivo murine infection model. Cell differentiation generates physiological heterogeneity in clonal bacterial infections and helps to determine the distinct infection types.

While in hospital, patients can be unwittingly exposed to bacteria that can cause disease. These hospital-associated bacteria can lead to potentially life-threatening infections that may also complicate the treatment of the patients’ existing medical conditions. Staphylococcus aureus is one such bacterium, and it can cause several types of infection including pneumonia, blood infections and long-term infections of prosthetic devices.

It is thought that S. aureus is able to cause so many different types of infection because it is capable of colonizing distinct tissues and organs in various parts of the body. Understanding the biological processes that drive the different infections is crucial to improving how these infections are treated.

S. aureus lives either as an independent, free-swimming cell or as part of a community known as a biofilm. These different lifestyles dictate the type of infection the bacterium can cause, with free-swimming cells producing toxins that contribute to intense, usually short-lived, infections and biofilms promoting longer-term infections that are difficult to eradicate. However, it is not clear how a population of S. aureus cells chooses to adopt a particular lifestyle and whether there are any environmental signals that influence this decision.

Here, Garcia-Betancur et al. found that S. aureus populations contain small groups of cells that have already specialized into a particular lifestyle. These groups of cells collectively influence the choice made by other cells in the population. While both lifestyles will be represented in the population, environmental factors influence the numbers of cells that initially adopt each type of lifestyle, which ultimately affects the choice made by the rest of the population. For example, if the bacteria colonize a tissue or organ that contains high levels of magnesium ions, the population is more likely to form biofilms.

In the future, the findings of Garcia-Betancur et al. may help us to predict how an infection may develop in a particular patient, which may help to diagnose the infection more quickly and allow it to be treated more effectively.

A Formidable Foe Is Sabotaging Your Results: What You Should Know about Biofilms and Wound Healing

LEARNING OBJECTIVES

After reading this article, the participant should be able to: 1. Describe biofilm pathogenesis as it relates to problem wounds. 2. Understand the preclinical and clinical evidence implicating biofilm in problem wounds. 3. Explain the diagnostic and treatment challenges that biofilms create for problem wounds. 4. Demonstrate a basic understanding of emerging strategies aimed at counteracting these processes.

SUMMARY

Biofilm represents a protected mode of growth for bacteria, allowing them to evade standard diagnostic techniques and avoid eradication by standard therapies. Although only recently discovered, biofilm has existed for millennia and complicates nearly every aspect of medicine. Biofilm impacts wound healing by allowing bacteria to evade immune responses, prolonging inflammation and disabling skin barrier function. It is important to understand why problem wounds persist despite state-of-the-art treatment, why they are difficult to accurately diagnose, and why they recur. The aim of this article is to focus on current gaps in knowledge related to problem wounds, specifically, biofilm infection.

The Staphylococcal Biofilm: Adhesins, Regulation, and Host Response

The staphylococci comprise a diverse genus of Gram-positive, nonmotile commensal organisms that inhabit the skin and mucous membranes of humans and other mammals. In general, staphylococci are benign members of the natural flora, but many species have the capacity to be opportunistic pathogens, mainly infecting individuals who have medical device implants or are otherwise immunocompromised. Staphylococcus aureus and Staphylococcus epidermidis are major sources of hospital-acquired infections and are the most common causes of surgical site infections and medical device-associated bloodstream infections. The ability of staphylococci to form biofilms in vivo makes them highly resistant to chemotherapeutics and leads to chronic diseases. These biofilm infections include osteomyelitis, endocarditis, medical device infections, and persistence in the cystic fibrosis lung. Here, we provide a comprehensive analysis of our current understanding of staphylococcal biofilm formation, with an emphasis on adhesins and regulation, while also addressing how staphylococcal biofilms interact with the immune system. On the whole, this review will provide a thorough picture of biofilm formation of the staphylococcus genus and how this mode of growth impacts the host.

Candida-Bacteria Interactions: Their Impact on Human Disease

Candida species are the most common infectious fungal species in humans; out of the approximately 150 known species, Candida albicans is the leading pathogenic species, largely affecting immunocompromised individuals. Apart from its role as the primary etiology for various types of candidiasis, C. albicans is known to contribute to polymicrobial infections. Polymicrobial interactions, particularly between C. albicans and bacterial species, have gained recent interest in which polymicrobial biofilm virulence mechanisms have been studied including adhesion, invasion, quorum sensing, and development of antimicrobial resistance. These trans-kingdom interactions, either synergistic or antagonistic, may help modulate the virulence and pathogenicity of both Candida and bacteria while uniquely impacting the pathogen-host immune response. As antibiotic and antifungal resistance increases, there is a great need to explore the intermicrobial cross-talk with a focus on the treatment of Candida-associated polymicrobial infections. This article explores the current literature on the interactions between Candida and clinically important bacteria and evaluates these interactions in the context of pathogenesis, diagnosis, and disease management.

Blended Chitosan Paste for Infection Prevention: Preliminary and Preclinical Evaluations

BACKGROUND

Local drug delivery devices offer a promising method for delivering vancomycin and amikacin for musculoskeletal wounds. However, current local delivery devices such as beads and sponges do not necessarily allow for full coverage of a wound surface with eluted antibiotics and do not address the need for reducing the antibiotic diffusion distance to help prevent contamination by bacteria or other microorganisms. We blended chitosan/polyethylene glycol (PEG) pastes/sponges to increase biocompatibility and improve antibiotic coverage within the wound.

QUESTIONS/PURPOSES

(1) Are blended chitosan/PEG pastes biodegradable? (2) Are the blended pastes biocompatible? (3) How much force does paste require for placement by injection? (4) Will the pastes elute active antibiotics to inhibit bacteria in vitro? (5) Can the pastes prevent infection in a preclinical model with hardware?

METHODS

Our blended paste/sponge formulations (0.5% acidic, 1% acidic, and acidic/neutral) along with a control neutral 1% chitosan sponge were tested in vitro for degradability, cytocompatibility, injectability tested by determining the amount of force needed to inject the pastes, elution of antibiotics, and activity tested using zone of inhibition studies. Along with these studies, in vivo models for biocompatibility and infection prevention were tested using a rodent model and an infected mouse model with hardware, respectively. By evaluating these characteristics, an improved local drug delivery device can be determined.

RESULTS

All three of the paste formulations evaluated were almost fully degraded and with 6 days of degradation, the percent remaining being was less than that of the control sponge (percent remaining: control 99.251% ± 1.0%; 0.5% acidic 1.6% ± 2.1%, p = 0.002; 1% acidic 1.7% ± 1.6%, p = 0.002; acidic/neutral 2.3% ± 1.7%, p = 0.010). There was good biocompatibility because cell viability in vitro was high (control 100.0 ± 14.3; 0.5% acidic formulation at 79.4 ± 12.6, p < 0.001; 1% acidic formulation at 98.6 ± 6.1, p = 0.993; acidic/neutral formulation at 106.7 ± 12.8, p = 0.543), and in vivo inflammation was moderate (control 2.1 ± 1.2; 0.5% acidic 3.3 ± 0.2, p = 0.530; 1% acidic 2.5 ± 0.9, p = 0.657; acidic/neutral 2.9 ± 1.1, p = 0.784). Force required to inject the 0.5% acidic and 1% acidic pastes was less than the acidic/neutral paste used as a control (control 167.7 ± 85.6; 0.5% acidic 41.3 ± 10.7, p = 0.070; 1% acidic 28.0 ± 7.0, p = 0.940). At 72 hours, all paste formulations exhibited in vitro activity against Staphylococcus aureus (control 2.6 ± 0.8; 0.5% acidic 98.1 ± 33.5, p = 0.002; 1% acidic 87.3 ± 17.2, p = 0.006; acidic/neutral 83.5 ± 14.3, p = 0.010) and Pseudomonas aeruginosa (control 163.0 ± 1.7; 0.5% acidic 85.7 ± 83.6, p = 0.373; 1% acidic 38.0 ± 45.1, p = 0.896; acidic/neutral 129.7 ± 78.0, p = 0.896). Also, the paste formulations were able to prevent the infection with 100% clearance on the implanted hardware and surrounding tissue with the control being a 0.5% acidic paste group without antibiotics (control 4 × 10⁴ ± 4.8 × 10⁴; 0.5% acidic 0.0 ± 0.0, p value: 0.050; 1% acidic 0.0 ± 0.0, p = 0.050; acidic/neutral 0.0 ± 0.0, p = 0.050).

CONCLUSIONS

The preliminary studies demonstrated promising results for the blended chitosan/PEG pastes with antibiotics provided degradability, biocompatibility, injectability, and infection prevention for musculoskeletal-type wounds.

CLINICAL RELEVANCE

The preliminary studies with the chitosan paste delivered antibiotics to a contaminated musculoskeletal wound with hardware and prevented infection. More studies in a complex musculoskeletal wound and dosage studies are needed for continued development.

Influence of the Microstructure and Silver Content on Degradation, Cytocompatibility, and Antibacterial Properties of Magnesium-Silver Alloys In Vitro

Implantation is a frequent procedure in orthopedic surgery, particularly in the aging population. However, it possesses the risk of infection and biofilm formation at the surgical site. This can cause unnecessary suffering to patients and burden on the healthcare system. Pure Mg, as a promising metal for biodegradable orthopedic implants, exhibits some antibacterial effects due to the alkaline pH produced during degradation. However, this antibacterial effect may not be sufficient in a dynamic environment, for example, the human body. The aim of this study was to increase the antibacterial properties under harsh and dynamic conditions by alloying silver metal with pure Mg as much as possible. Meanwhile, the Mg-Ag alloys should not show obvious cytotoxicity to human primary osteoblasts. Therefore, we studied the influence of the microstructure and the silver content on the degradation behavior, cytocompatibility, and antibacterial properties of Mg-Ag alloys in vitro. The results indicated that a higher silver content can increase the degradation rate of Mg-Ag alloys. However, the degradation rate could be reduced by eliminating the precipitates in the Mg-Ag alloys via T4 treatment. By controlling the microstructure and increasing the silver content, Mg-Ag alloys obtained good antibacterial properties in harsh and dynamic conditions but had almost equivalent cytocompatibility to human primary osteoblasts as pure Mg.

Epigenetic Modification Mediates the Increase of LAG-3+ T Cells in Chronic Osteomyelitis

Immune suppression plays critical roles in the development of chronic osteomyelitis, and the mechanisms underlying the development of immune suppression in chronic osteomyelitis have attracted much attention. LAG-3 is an important suppressor of T cell activation, but the role of LAG-3 in the immune regulation of chronic osteomyelitis is currently unknown. We sought to demonstrate if LAG-3 plays crucial roles in chronic osteomyelitis progression and has effects on immune suppression and exhausting of T cells, and what is the mechanism underlying LAG-3 deregulation in chronic osteomyelitis. We examined the expression of LAG-3 in the T cells of peripheral blood of 50 healthy controls and 50 patients with chronic osteomyelitis by flow cytometry. Clinical data were analyzed to determine the correlation between inflammation index and LAG-3 expression. Moreover, we isolated the CD4⁺ T cells from healthy controls and chronic osteomyelitis patients to compare cell proliferation and IFN-γ production. Chromatin immunoprecipitation assays were utilized to analyze the epigenetic modification on LAG-3 expression in T cells. We found that LAG-3 was significantly increased in the T cells of peripheral blood from chronic osteomyelitis patients. Subsequently, clinical data analysis suggested that the higher expression of LAG-3 was associated with severer inflammation situation. Consistently, LAG-3⁺CD4⁺ T cells exhibited impaired cell proliferation and IFN-γ secretion. Deregulation of histone methylation mediated the increase of LAG-3⁺ T cells during chronic osteomyelitis. Taken together, our study demonstrates the increase of LAG-3⁺ T cells and its immune regulatory roles in chronic osteomyelitis progression, suggesting new mechanisms and potential therapeutic targets for chronic osteomyelitis.

Evidence of Staphylococcus Aureus Deformation, Proliferation, and Migration in Canaliculi of Live Cortical Bone in Murine Models of Osteomyelitis

Although Staphylococcus aureus osteomyelitis is considered to be incurable, the major bacterial reservoir in live cortical bone has remained unknown. In addition to biofilm bacteria on necrotic tissue and implants, studies have implicated intracellular infection of osteoblasts and osteocytes as a mechanism of chronic osteomyelitis. Thus, we performed the first systematic transmission electron microscopy (TEM) studies to formally define major reservoirs of S. aureus in chronically infected mouse (Balb/c J) long bone tissue. Although rare, evidence of colonized osteoblasts was found. In contrast, we readily observed S. aureus within canaliculi of live cortical bone, which existed as chains of individual cocci and submicron rod-shaped bacteria leading to biofilm formation in osteocyte lacunae. As these observations do not conform to the expectations of S. aureus as non-motile cocci 1.0 to 1.5 μm in diameter, we also performed immunoelectron microscopy (IEM) following in vivo BrdU labeling to assess the role of bacterial proliferation in canalicular invasion. The results suggest that the deformed bacteria: (1) enter canaliculi via asymmetric binary fission; and (2) migrate toward osteocyte lacunae via proliferation at the leading edge. Additional in vitro studies confirmed S. aureus migration through a 0.5-μm porous membrane. Collectively, these findings define a novel mechanism of bone infection, and provide possible new insight as to why S. aureus implant-related infections of bone tissue are so challenging to treat. © 2016 American Society for Bone and Mineral Research.

Hyperbaric Oxygen Therapy is Ineffective as an Adjuvant to Daptomycin with Rifampicin Treatment in a Murine Model of Staphylococcus aureus in Implant-Associated Osteomyelitis

Implant-associated infections caused by bacterial biofilms are difficult to treat. Surgical intervention is often necessary to cure the patient, as the antibiotic recalcitrance of biofilms renders them untreatable with conventional antibiotics. Intermittent hyperbaric oxygen treatment (HBOT) has been proposed as an adjuvant to conventional antibiotic treatment and it has been speculated that combining HBOT with antibiotics could improve treatment outcomes for biofilm infections. In this study we addressed whether HBOT could improve treatment outcomes of daptomycin and rifampicin combination therapy. The effect of HBOT on the treatment outcomes of daptomycin and rifampicin against implant-associated osteomyelitis was quantified in a murine model. In total, 80 mice were randomized into two groups receiving antibiotics, either alone or in combination with daily intermittent HBOT (304 kPa for 60 min) following injection of antibiotics. Treatment was initiated 11 days after animals were infected with Staphylococcus aureus and treatment duration was 14 days. We found that HBOT did not improve the cure rate and did not reduce the bacterial load on the implant surface or in the surrounding tissue. Cure rates of daptomycin + rifampicin were 40% in infected tibias and 75% for implants while cure rates for HBOT-daptomycin + rifampicin were 50% and 85%, respectively, which were not significantly higher (Fisher’s exact test). While it is encouraging that the combination of daptomycin and rifampicin is very effective, our study demonstrates that this efficacy cannot be improved by adjuvant HBOT.

Biofilms and host response - helpful or harmful

Biofilm infections are one of the modern medical world's greatest challenges. Probably, all non-obligate intracellular bacteria and fungi can establish biofilms. In addition, there are numerous biofilm-related infections, both foreign body-related and non-foreign body-related. Although biofilm infections can present in numerous ways, one common feature is involvement of the host response with significant impact on the course. A special characteristic is the synergy of the innate and the acquired immune responses for the induced pathology. Here, we review the impact of the host response for the course of biofilm infections, with special focus on cystic fibrosis, chronic wounds and infective endocarditis.

Spinal Implants Can Be Inserted in Patients With Deep Spine Infection: Results From a Large Cohort Study

STUDY DESIGN

A retrospective, cohort study of 84 patients with deep spine infection managed at a major tertiary hospital over 14 years with a minimum follow up of 2 years.

OBJECTIVE

To determine the role of instrumentation in spines with deep infection.

SUMMARY OF BACKGROUND DATA

It is often believed that implants should not be inserted in patients with deep spine infection because of the risk of persistent or recurrent infection. However, there are often concerns about spinal stability and a paucity of evidence to guide clinical practice in this field.

METHODS

We compared the mortality, reoperation, and reinfection rates in patients with spine infection treated with antibiotics alone, antibiotics with debridement, and antibiotics with debridement and instrumentation. Significant outcome predictors were determined using multivariable logistic regression model.

RESULTS

Forty-nine males and 35 females with a mean age was 62.0 years had spine infection affecting the lumbar spine predominantly. The most common form of infection was osteomyelitis and spondylodiscitis (69.4%). Staphylococcus aureus was the most common causative organism (61.2%).There was no difference in terms of reoperation or relapse for patients treated with antibiotics alone, antibiotics with debridement, or antibiotics with debridement and instrumentation. However, compared with antibiotics alone, the crude inhospital mortality was lower for patients treated with instrumentation (odds ratio, OR, 0.82; P = 0.01), and antibiotics with debridement (OR 0.80; P = 0.02).

CONCLUSION

Spinal instrumentation in an infected spine is safe and not associated with higher reoperation or relapse rates. Mortality is lower for patients treated with instrumentation.

LEVEL OF EVIDENCE

3.

Surgical site infections following oral cavity cancer resection and reconstruction is a risk factor for plate exposure

Background

Plate-related complications following head and neck cancer ablation and reconstruction remains a challenging problem often requiring further management and reconstructive surgeries. We aim to identify an association between surgical site infections (SSI) and plate exposure.

Methods

A retrospective study between 1997 and 2014 was performed to study the association between postoperative SSI and plate exposures. Eligible patients included those with a history of oral squamous cell carcinoma who underwent surgical resection, neck dissection, and free tissue reconstruction. Demographic and treatment related information was collected. SSI were classified based on CDC definition and previously published literature. Univariable analysis on demographic factors, smoking history, diabetes, radiation, surgical and hardware related factors; while multivariable analysis on SSI, plate height, segmental mandibulectomy defects and radiation were conducted such as using cox proportional hazard models.

Results

Three hundred sixty-five patients were identified and included in our study. The mean age of the study group was 59.2 (+/−13.8), with a predominance of male patients (61.9%). 10.7% of our patient cohort had diabetes, and another 63.8% had post-operative radiation therapy. Patients with SSI were more likely to have plate exposure (25 vs. 6.4%, p <0.001). Post-operative SSI, mandibulectomy defects, and plate profile/thickness were associated with plate exposure on univariable analysis (OR = 5.72, p < 0.001; OR = 2.56, p = 0.014; OR = 1.44, p = 0.003 respectively) and multivariable analysis (OR = 5.13, p < 0.001; OR = 1.36, p = 0.017; OR = 2.58, p = 0.02 respectively).

Conclusion

Surgical site infections are associated with higher rates of plate exposure. Plate exposure may require multiple procedures to manage and occasionally free flap reconstruction.

Quantification of Peri-Implant Bacterial Load and in Vivo Biofilm Formation in an Innovative, Clinically Representative Mouse Model of Periprosthetic Joint Infection

BACKGROUND

Periprosthetic joint infection (PJI) is a devastating complication following total joint arthroplasty. Current animal models of PJI are limited because of a lack of quantitative methods and failure to effectively recreate the periprosthetic space. We therefore developed a murine PJI model involving a 3-dimensionally printed Ti-6Al-4V implant capable of bearing weight and permitting quantitative analysis of periprosthetic bacterial load and evaluation of biofilm.

METHODS

Twenty-five 12-week-old C57BL/6 mice received a unilateral proximal tibial implant and intra-articular injection of either 3 × 10 colony forming units (CFUs) of Staphylococcus aureus Xen 36 or saline solution. Postoperatively, mice underwent gait analysis, knee radiographs, and serum inflammatory marker measurements. Following euthanasia at 2 or 6 weeks, bone and soft tissues were homogenized to quantify bacteria within periprosthetic tissues. Implants were either sonicated to quantify adherent bacteria or examined under scanning electron microscopy (SEM) to characterize biofilm.

RESULTS

All mice survived surgery and were not systemically septic. The control mice immediately tolerated weight-bearing and had normal inflammatory markers and radiographic signs of osseointegration. Infected mice had difficulty walking over time, exhibited radiographic findings of septic implant loosening, and had significantly elevated inflammatory markers. Periprosthetic tissues of the infected animals displayed a mean of 4.46 × 10 CFUs of S. aureus at 2 weeks and 2.53 × 10 CFUs at 6 weeks. Viable S. aureus was quantified on retrieved implant surfaces. SEM demonstrated S. aureus cocci in clusters encased within biofilm.

CONCLUSIONS

This animal model is, to our knowledge, the most clinically representative PJI replication to date. It is the first that we know of to produce infection through the same method hypothesized to occur clinically, utilize a weight-bearing implant that can osseointegrate, and provide quantitative data on 8 aspects of PJI, including radiographic features, inflammatory markers, and bacterial loads.

CLINICAL RELEVANCE

This novel animal model is, to our knowledge, the first to provide a load-bearing translational representation of clinical PJI that effectively recreates the periprosthetic space.

Evaluation of a chitosan-polyethylene glycol paste as a local antibiotic delivery device

AIM

To investigate the efficacy of a chitosan/polyethylene glycol blended paste as a local antibiotic delivery device, particularly in musculoskeletal wounds.

METHODS

Acidic (A) chitosan sponges and neutralized (N) chitosan/polyethylene glycol (PEG) blended sponges were combined in ratios of 3A:2N, 1A:1N, and 2A:3N; then hydrated with phosphate buffered saline to form a chitosan/PEG paste (CPP). Both in vitro and in vivo studies were conducted to determine the potential CPP has as a local antibiotic delivery device. In vitro biocompatibility was assessed by the cytotoxic response of fibroblast cells exposed to the experimental groups. Degradation rate was measured as the change in dry mass due to lysozyme based degradation over a 10-d period. The antibiotic elution profiles and eluate activity of CPP were evaluated over a 72-h period. To assess the in vivo antimicrobial efficacy of the CPP, antibiotic-loaded paste samples were exposed to subcutaneously implanted murine catheters inoculated with Staphylococcus aureus. Material properties of the experimental paste groups were evaluated by testing the ejection force from a syringe, as well as the adhesion to representative musculoskeletal tissue samples.

RESULTS

The highly acidic CPP group, 3A:2N, displayed significantly lower cell viability than the control sponge group. The equally distributed group, 1A:1N, and the highly neutral group, 2A:3N, displayed similar cell viability to the control sponge group and are deemed biocompatible. The degradation studies revealed CPP is more readily degradable than the chitosan sponge control group. The antibiotic activity studies indicated the CPP groups released antibiotics at a constant rate and remained above the minimum inhibitory concentrations of the respective test bacteria for a longer time period than the control chitosan sponges, as well as displaying a minimized burst release. The in vivo functional model resulted in complete bacterial infection prevention in all catheters treated with the antibiotic loaded CPP samples. All experimental paste groups exhibited injectability and adhesive qualities that could be advantageous material properties for drug delivery to musculoskeletal injuries.

CONCLUSION

CPP is an injectable, bioadhesive, biodegradable, and biocompatible material with potential to allow variable antibiotic loading and active, local antibiotic release to prevent bacterial contamination.

Syringa oblata Lindl. Aqueous Extract Is a Potential Biofilm Inhibitor in S. suis

Streptococcus suis (S. suis) is a zoonotic pathogen that causes severe disease symptoms in pigs and humans. Syringa oblata Lindl. distributed in the middle latitudes of Eurasia and North America were proved as the most development potential of Chinese Medicine. In this study, biofilm formation by S. suis decreased after growth with 1/2 MIC, 1/4 MIC, or 1/8 MIC of Syringa oblata Lindl. aqueous extract and rutin. Scanning electron microscopy analysis revealed the potential effect of Syringa oblata Lindl. aqueous extract and rutin against biofilm formation by S. suis. Using iTRAQ technology, comparative proteomic analyses was performed at two conditions: 1/2 MIC of Syringa oblata Lindl. aqueous extract treated and non-treated cells. The results revealed the existence of 28 proteins of varying amounts. We found that the majority of the proteins were related to cell growth and metabolism. We also found that Syringa oblata Lindl. Aqueous extract affected the synthesis enzymes. In summary, Syringa oblata Lindl. aqueous extract might be used to inhibit the biofilm formation effectively by S. suis, and the active ingredients of the Syringa oblate Lindl. aqueous extract is rutin. The content of rutin is 9.9 ± 0.089 mg/g dry weight.

Pathogenic properties of a Corynebacterium diphtheriae strain isolated from a case of osteomyelitis

Corynebacterium diphtheriae is typically recognized as a colonizer of the upper respiratory tract (respiratory diphtheria) and the skin (cutaneous diphtheria). However, different strains of Corynebacteriumdiphtheriae can also cause invasive infections. In this study, the characterization of a non-toxigenic Corynebacteriumdiphtheriae strain (designated BR-INCA5015) isolated from osteomyelitis in the frontal bone of a patient with adenoid cystic carcinoma was performed. Pathogenic properties of the strain BR-INCA5015 were tested in a Caenorhabditis elegans survival assay showing strong colonization and killing by this strain. Survival rates of 3.8±2.7 %, 33.6±7.3 % and 0 % were observed for strains ATCC 27010T, ATCC 27012 and BR-INCA5015, respectively, at day 7. BR-INCA5015 was able to colonize epithelial cells, showing elevated capacity to adhere to and survive within HeLa cells compared to other Corynebacteriumdiphtheriae isolates. Intracellular survival in macrophages (THP-1 and RAW 264.7) was significantly higher compared to control strains ATCC 27010T (non-toxigenic) and ATCC 27012 (toxigenic). Furthermore, the ability of BR-INCA5015 to induce osteomyelitis was confirmed by in vivo assay using Swiss Webster mice.

The Active Component of Aspirin, Salicylic Acid, Promotes Staphylococcus aureus Biofilm Formation in a PIA-dependent Manner

Aspirin has provided clear benefits to human health. But salicylic acid (SAL) -the main aspirin biometabolite- exerts several effects on eukaryote and prokaryote cells. SAL can affect, for instance, the expression of Staphylococcus aureus virulence factors. SAL can also form complexes with iron cations and it has been shown that different iron chelating molecules diminished the formation of S. aureus biofilm. The aim of this study was to elucidate whether the iron content limitation caused by SAL can modify the S. aureus metabolism and/or metabolic regulators thus changing the expression of the main polysaccharides involved in biofilm formation. The exposure of biofilm to 2 mM SAL induced a 27% reduction in the intracellular free Fe²⁺ concentration compared with the controls. In addition, SAL depleted 23% of the available free Fe²⁺ cation in culture media. These moderate iron-limited conditions promoted an intensification of biofilms formed by strain Newman and by S. aureus clinical isolates related to the USA300 and USA100 clones. The slight decrease in iron bioavailability generated by SAL was enough to induce the increase of PIA expression in biofilms formed by methicillin-resistant as well as methicillin-sensitive S. aureus strains. S. aureus did not produce capsular polysaccharide (CP) when it was forming biofilms under any of the experimental conditions tested. Furthermore, SAL diminished aconitase activity and stimulated the lactic fermentation pathway in bacteria forming biofilms. The polysaccharide composition of S. aureus biofilms was examined and FTIR spectroscopic analysis revealed a clear impact of SAL in a codY-dependent manner. Moreover, SAL negatively affected codY transcription in mature biofilms thus relieving the CodY repression of the ica operon. Treatment of mice with SAL induced a significant increase of S aureus colonization. It is suggested that the elevated PIA expression induced by SAL might be responsible for the high nasal colonization observed in mice. SAL-induced biofilms may contribute to S. aureus infection persistence in vegetarian individuals as well as in patients that frequently consume aspirin.

Biodegradable nitric oxide precursor-loaded micro- and nanoparticles for the treatment of Staphylococcus aureus biofilms

Bacteria in biofilms are more difficult to eradicate than planktonic bacteria and result in treatment challenges for many chronic infectious diseases. Nitric oxide (NO) is an endogenous molecule that offers potential as an alternative to conventional antibiotics; however its sustained topical delivery to biofilms is not readily achieved. With this in mind, we report the development of biodegradable poly(lactide-co-glycolide) (PLGA) based microparticles (MP) and nanoparticles (NP) for encapsulation of the NO precursor isosorbide mononitrate (ISMN) and the controlled delivery to Staphylococcus aureus (S. aureus) biofilms. Firstly, water-in-oil-in-water (w/o/w) emulsification/solvent evaporation methods for PLGA NP and MP syntheses were experimentally optimised with respect to particle size and ISMN loading/encapsulation efficiency. The influence of various experiment parameters, such as the volume of inner aqueous phase, concentration of surfactants, mixing time on the particle size, drug loading and encapsulation efficiency were investigated systematically. Both PLGA MP and NP formulations enabled sustained ISMN release in physiological media over 3 to 5 days. PLGA MP with diameters of ∼3 μm and ISMN loading of 2.2% (w/w) were identified as the optimum delivery system and demonstrated significant antibacterial activity in S. aureus biofilms. This behaviour is considered to be due to targeted biofilm delivery through a combination of effective penetration and sustained release of ISMN.

Bad to the Bone: On In Vitro and Ex Vivo Microbial Biofilm Ability to Directly Destroy Colonized Bone Surfaces without Participation of Host Immunity or Osteoclastogenesis

Bone infections are a significant public health burden associated with morbidity and mortality in patients. Microbial biofilm pathogens are the causative agents in chronic osteomyelitis. Research on the pathogenesis of osteomyelitis has focused on indirect bone destruction by host immune cells and cytokines secondary to microbial insult. Direct bone resorption by biofilm pathogens has not yet been seriously considered. In this study, common osteomyelitis pathogens (Staphylococcus aureus, Pseudomonas aeruginosa, Candida albicans, and Streptococcus mutans) were grown as biofilms in multiple in vitro and ex vivo experiments to analyze quantitative and qualitative aspects of bone destruction during infection. Pathogens were grown as single or mixed species biofilms on the following substrates: hydroxyapatite, rat jawbone, or polystyrene wells, and in various media. Biofilm growth was evaluated by scanning electron microscopy and pH levels were monitored over time. Histomorphologic and quantitative effects of biofilms on tested substrates were analyzed by microcomputed tomography and quantitative cultures. All tested biofilms demonstrated significant damage to bone. Scanning electron microscopy indicated that all strains formed mature biofilms within 7 days on all substrate surfaces regardless of media. Experimental conditions impacted pH levels, although this had no impact on biofilm growth or bone destruction. Presence of biofilm led to bone dissolution with a decrease of total volume by 20.17±2.93% upon microcomputed tomography analysis, which was statistically significant as compared to controls (p <0.05, ANOVA). Quantitative cultures indicated that media and substrate did not impact biofilm formation (Kruskall-Wallis test, post-hoc Dunne's test; p <0.05). Overall, these results indicate that biofilms associated with osteomyelitis have the ability to directly resorb bone. These findings should lead to a more complete understanding of the etiopathogenesis of osteomyelitis, where direct bone resorption by biofilm is considered in addition to the well-known osteoclastic and host cell destruction of bone.

Phage therapy of staphylococcal chronic osteomyelitis in experimental animal model

Background & objectives:

Methicillin resistant Staphylococcus aureus (MRSA) are the commonest cause of osteomyelitis. The aim of this study was to evaluate the role of an alternative therapy i.e. application of S. aureus specific bacteriophages in cases of osteomyelitis caused by MRSA in animal model.

Methods:

Twenty two rabbits were included in this study. The first two rabbits were used to test the safety of phage cocktail while the remaining 20 rabbits were divided into three groups; group A (n=4) to assess the establishment of osteomyelitis; group B (n=4) osteomyelitis developed but therapy started only after six weeks; and group C (n=12) osteomyelitis developed and therapy started after three weeks. Groups B and C rabbits were treated with four doses of cocktail of seven virulent bacteriophages at the interval of 48 h. Comparison between three groups was made on the basis of observation of clinical, radiological, microbiological, and histopathological examinations.

Results:

Experimental group rabbits recovered from the illness in the subsequent two weeks of the therapy. Appetite and activity of the rabbits improved, local oedema, erythema and induration subsided. There were minimal changes associated with osteomyelitis in X-ray and histopathology also showed no signs of infection with new bone formation. Control B group rabbits also recovered well from the infection.

Interpretation & conclusions:

The present study shows a potential of phage therapy to treat difficult infections caused by multidrug resistant bacteria.

Ceramic Biocomposites as Biodegradable Antibiotic Carriers in the Treatment of Bone Infections

Local release of antibiotic has advantages in the treatment of chronic osteomyelitis and infected fractures. The adequacy of surgical debridement is still key to successful clearance of infection but local antibiotic carriers seem to afford greater success rates by targeting the residual organisms present after debridement and delivering much higher local antibiotic concentrations compared with systemic antibiotics alone. Biodegradable ceramic carriers can be used to fill osseous defects, which reduces the dead space and provides the potential for subsequent repair of the osseous defect as they dissolve away. A dissolving ceramic antibiotic carrier also raises the possibility of single stage surgery with definitive closure and avoids the need for subsequent surgery for spacer removal.

In this article we provide an overview of the properties of various biodegradable ceramics, including calcium sulphate, the calcium orthophosphate ceramics, calcium phosphate cement and polyphasic carriers. We summarise the antibiotic elution properties as investigated in previous animal studies as well as the clinical outcomes from clinical research investigating their use in the surgical management of chronic osteomyelitis.

Calcium sulphate pellets have been shown to be effective in treating local infection, although newer polyphasic carriers may support greater osseous repair and reduce the risk of further fracture or the need for secondary reconstructive surgery. The use of ceramic biocomposites to deliver antibiotics together with BMPs, bisphosphonates, growth factors or living cells is under investigation and merits further study.

We propose a treatment protocol, based on the Cierny-Mader classification, to help guide the appropriate selection of a suitable ceramic antibiotic carrier in the surgical treatment of chronic osteomyelitis.

In vitro characterization of biofilms formed by Kingella kingae

The Gram-negative bacterium Kingella kingae is part of the normal oropharyngeal mucosal flora of children <4 years old. K. kingae can enter the submucosa and cause infections of the skeletal system in children, including septic arthritis and osteomyelitis. The organism is also associated with infective endocarditis in children and adults. Although biofilm formation has been coupled with pharyngeal colonization, osteoarticular infections, and infective endocarditis, no studies have investigated biofilm formation in K. kingae. In this study we measured biofilm formation by 79 K. kingae clinical isolates using a 96-well microtiter plate crystal violet binding assay. We found that 37 of 79 strains (47%) formed biofilms. All strains that formed biofilms produced corroding colonies on agar. Biofilm formation was inhibited by proteinase K and DNase I. DNase I also caused the detachment of pre-formed K. kingae biofilm colonies. A mutant strain carrying a deletion of the pilus gene cluster pilA1pilA2fimB did not produce corroding colonies on agar, autoaggregate in broth, or form biofilms. Biofilm forming strains have higher levels of pilA1 expression. The extracellular components of biofilms contained 490 μg cm^-2 of protein, 0.68 μg cm^-2 of DNA, and 0.4 μg cm^-2 of total carbohydrates. We concluded that biofilm formation is common among K. kingae clinical isolates, and that biofilm formation is dependent on the production of proteinaceous pili and extracellular DNA. Biofilm development may have relevance to the colonization, transmission, and pathogenesis of this bacterium. Extracellular DNA production by K. kingae may facilitate horizontal gene transfer within the oral microbial community.

The antifungal caspofungin increases fluoroquinolone activity against Staphylococcus aureus biofilms by inhibiting N-acetylglucosamine transferase

Biofilms play a major role in Staphylococcus aureus pathogenicity but respond poorly to antibiotics. Here, we show that the antifungal caspofungin improves the activity of fluoroquinolones (moxifloxacin, delafloxacin) against S. aureus biofilms grown in vitro (96-well plates or catheters) and in vivo (murine model of implanted catheters). The degree of synergy among different clinical isolates is inversely proportional to the expression level of ica operon, the products of which synthesize poly-N-acetyl-glucosamine polymers, a major constituent of biofilm matrix. In vitro, caspofungin inhibits the activity of IcaA, which shares homology with β-1-3-glucan synthase (caspofungin's pharmacological target in fungi). This inhibition destructures the matrix, reduces the concentration and polymerization of exopolysaccharides in biofilms, and increases fluoroquinolone penetration inside biofilms. Our study identifies a bacterial target for caspofungin and indicates that IcaA inhibitors could potentially be useful in the treatment of biofilm-related infections.

Biofilms formed by Staphylococcus aureus are poorly responsive to antibiotics. Here, Siala et al. show that an antifungal drug (caspofungin) enhances the activity of fluoroquinolone antibiotics against S. aureus biofilms by inhibiting an enzyme involved in synthesis of the biofilm matrix.

Evaluation of Silver Ion-Releasing Scaffolds in a 3D Coculture System of MRSA and Human Adipose-Derived Stem Cells for Their Potential Use in Treatment or Prevention of Osteomyelitis

Bone infection, also called osteomyelitis, can result when bacteria invade a bone. Treatment of osteomyelitis usually requires surgical debridement and prolonged antimicrobial therapy. The rising incidence of infection with multidrug-resistant bacteria, in particular methicillin-resistant staphylococcus aureus (MRSA), however, limits the antimicrobial treatment options available. Silver is well known for its antimicrobial properties and is highly toxic to a wide range of microorganisms. We previously reported our development of biocompatible, biodegradable, nanofibrous scaffolds that released silver ions in a controlled manner. The objective of this study was to determine the efficacy of these scaffolds in treating or preventing osteomyelitis. To achieve this objective, antimicrobial efficacy was determined using a 3D coculture system of human adipose-derived stem cells (hASC) and MRSA. Human ASC were seeded on the scaffolds and induced to undergo osteogenic differentiation in both the absence and presence of MRSA. Our results indicated that the silver ion-releasing scaffolds not only inhibited biofilm formation, but also supported osteogenesis of hASC. Our findings suggest that these biocompatible, degradable, silver ion-releasing scaffolds can be used at an infection site to treat osteomyelitis and/or to coat bone implants as a preventative measure against infection postsurgery.

Biofilm formation and antimicrobial susceptibility of staphylococci and enterococci from osteomyelitis associated with percutaneous orthopaedic implants

Staphylococci and enterococci account for most deep infections associated with bone-anchored percutaneous implants for amputation treatment. Implant-associated infections are difficult to treat; therefore, it is important to investigate if these infections have a biofilm origin and to determine the biofilm antimicrobial susceptibility to improve treatment strategies. The aims were: (i) to test a novel combination of the Calgary biofilm device and a custom-made susceptibility MIC plate (Sensititre^® ), (ii) to determine the biofilm formation and antimicrobial resistance in clinical isolates causing implant-associated osteomyelitis, and (iii) to describe the associated clinical outcome. Enterococci and staphylococci were characterized by microtitre plate assay, Congo Red Agar plate test, and PCR. Biofilm susceptibility to 10 antimicrobials and its relationship to treatment outcomes were determined. The majority of the strains produced biofilm in vitro showing inter- and intraspecies differences. Biofilms showed a significantly increased antimicrobial resistance compared with their planktonic counterparts. Slime-producing strains tolerated significantly higher antimicrobial concentrations compared with non-producers. All seven staphylococcal strains carried ica genes, but two did not produce slime. The degree of biofilm formation and up-regulated antibiotic resistance may translate into a variable risk of treatment failure. This new method set-up allows for the reproducible determination of minimum biofilm eradication concentration of antimicrobial agents, which may guide future antimicrobial treatment decisions in orthopaedic implant-associated infection. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 2630-2640, 2017.

Evaluation of Antibiotics Active against Methicillin-Resistant Staphylococcus aureus Based on Activity in an Established Biofilm

We used in vitro and in vivo models of catheter-associated biofilm formation to compare the relative activity of antibiotics effective against methicillin-resistant Staphylococcus aureus (MRSA) in the specific context of an established biofilm. The results demonstrated that, under in vitro conditions, daptomycin and ceftaroline exhibited comparable activity relative to each other and greater activity than vancomycin, telavancin, oritavancin, dalbavancin, or tigecycline. This was true when assessed using established biofilms formed by the USA300 methicillin-resistant strain LAC and the USA200 methicillin-sensitive strain UAMS-1. Oxacillin exhibited greater activity against UAMS-1 than LAC, as would be expected, since LAC is an MRSA strain. However, the activity of oxacillin was less than that of daptomycin and ceftaroline even against UAMS-1. Among the lipoglycopeptides, telavancin exhibited the greatest overall activity. Specifically, telavancin exhibited greater activity than oritavancin or dalbavancin when tested against biofilms formed by LAC and was the only lipoglycopeptide capable of reducing the number of viable bacteria below the limit of detection. With biofilms formed by UAMS-1, telavancin and dalbavancin exhibited comparable activity relative to each other and greater activity than oritavancin. Importantly, ceftaroline was the only antibiotic that exhibited greater activity than vancomycin when tested in vivo in a murine model of catheter-associated biofilm formation. These results emphasize the need to consider antibiotics other than vancomycin, most notably, ceftaroline, for the treatment of biofilm-associated S. aureus infections, including by the matrix-based antibiotic delivery methods often employed for local antibiotic delivery in the treatment of these infections.

Streptokinase Treatment Reverses Biofilm-Associated Antibiotic Resistance in Staphylococcus aureus

Biofilms formed by Staphylococcus aureus is a serious complication to the use of medical implants. A central part of the pathogenesis relies on S. aureus’ ability to adhere to host extracellular matrix proteins, which adsorb to medical implants and stimulate biofilm formation. Being coagulase positive, S. aureus furthermore induces formation of fibrin fibers from fibrinogen in the blood. Consequently, we hypothesized that fibrin is a key component of the extracellular matrix of S. aureus biofilms under in vivo conditions, and that the recalcitrance of biofilm infections can be overcome by combining antibiotic treatment with a fibrinolytic drug. We quantified S. aureus USA300 biofilms grown on peg-lids in brain heart infusion (BHI) broth with 0%–50% human plasma. Young (2 h) and mature (24 h) biofilms were then treated with streptokinase to determine if this lead to dispersal. Then, the minimal biofilm eradication concentration (MBEC) of 24 h old biofilms was measured for vancomycin and daptomycin alone or in combination with 10 µg/mL rifampicin in the presence or absence of streptokinase in the antibiotic treatment step. Finally, biofilms were visualized by confocal laser scanning microscopy. Addition of human plasma stimulated biofilm formation in BHI in a dose-dependent manner, and biofilms could be partially dispersed by streptokinase. The biofilms could be eradicated with physiologically relevant concentrations of streptokinase in combination with rifampicin and vancomycin or daptomycin, which are commonly used antibiotics for treatment of S. aureus infections. Fibronolytic drugs have been used to treat thromboembolic events for decades, and our findings suggest that their use against biofilm infections has the potential to improve the efficacy of antibiotics in treatment of S. aureus biofilm infections.

Combining in vitro protein detection and in vivo antibody detection identifies potential vaccine targets against Staphylococcus aureus during osteomyelitis

Currently, little is known about the in vivo human immune response against Staphylococcus aureus during a biofilm-associated infection, such as osteomyelitis, and how this relates to protein production in biofilms in vitro. Therefore, we characterized IgG responses in 10 patients with chronic osteomyelitis against 50 proteins of S. aureus, analyzed the presence of these proteins in biofilms of the infecting isolates on polystyrene (PS) and human bone in vitro, and explored the relation between in vivo and in vitro data. IgG levels against 15 different proteins were significantly increased in patients compared to healthy controls. Using a novel competitive Luminex-based assay, eight of these proteins [alpha toxin, Staphylococcus aureus formyl peptide receptor-like 1 inhibitor (FlipR), glucosaminidase, iron-responsive surface determinants A and H, the putative ABC transporter SACOL0688, staphylococcal complement inhibitor (SCIN), and serine-aspartate repeat-containing protein E (SdrE)] were also detected in a majority of the infecting isolates during biofilm formation in vitro. However, 4 other proteins were detected in only a minority of isolates in vitro while, vice versa, 7 proteins were detected in multiple isolates in vitro but not associated with significantly increased IgG levels in patients. Detection of proteins was largely confirmed using a transcriptomic approach. Our data provide further insights into potential therapeutic targets, such as for vaccination, to reduce S. aureus virulence and biofilm formation. At the same time, our data suggest that either in vitro or immunological in vivo data alone should be interpreted cautiously and that combined studies are necessary to identify potential targets.

Antibiotic-loaded phosphatidylcholine inhibits staphylococcal bone infection

AIM: To test antibiotic-loaded coating for efficacy in reducing bacterial biofilm and development of osteomyelitis in an orthopaedic model of implant infection.

METHODS: Phosphatidylcholine coatings loaded with 25% vancomycin were applied to washed and sterilized titanium wires 20 mm in length. A 10 mm segment was removed from rabbit radius (total = 9; 5 coated, 4 uncoated), and the segment was injected with 1 × 10⁶ colony forming units (CFUs) of Staphylococcus aureus (UAMS-1 strain). Titanium wires were inserted through the intramedullary canal of the removed segment and into the proximal radial segment and the segment was placed back into the defect. After 7 d, limbs were removed, X-rayed, swabbed for tissue contamination. Wires were removed and processed to determine attached CFUs. Tissue was swabbed and streaked on agar plates to determine bacteriological score.

RESULTS: Antibiotic-loaded coatings resulted in significantly reduced biofilm formation (4.7 fold reduction in CFUs; P < 0.001) on titanium wires and reduced bacteriological score in surrounding tissue (4.0 ± 0 for uncoated, 1.25 ± 0.5 for coated; P = 0.01). Swelling and pus formation was evident in uncoated controls at the 7 d time point both visually and radiographically, but not in antibiotic-loaded coatings.

CONCLUSION: Active antibiotic was released from coated implants and significantly reduced signs of osteomyelitic symptoms. Implant coatings were well tolerated in bone. Further studies with additional control groups and longer time periods are warranted. Antibiotic-loaded phosphatidylcholine coatings applied at the point of care could prevent implant-associated infection in orthopaedic defects.

(68)Ga-labeled phage-display selected peptides as tracers for positron emission tomography imaging of Staphylococcus aureus biofilm-associated infections: Selection, radiolabelling and preliminary biological evaluation

INTRODUCTION

Staphylococcus aureus is a major cause of skin and deep-sited infections, often associated with the formation of biofilms. Early diagnosis and initiated therapy is essential to prevent disease progression and to reduce complications that can be serious. Imaging techniques are helpful combining anatomical with functional data in order to describe and characterize site, extent and activity of the disease. The purpose of the study was to identify and (68)Ga-label peptides with affinity for S. aureus biofilm and evaluate their potential as bacteria-specific positron emission tomography (PET) imaging agents.

METHODS

Phage-displayed dodecapeptides were selected using an in vitro grown S. aureus biofilm as target. One cyclic (A8) and two linear (A9, A11) dodecapeptides were custom synthesized with 1,4,7,10-tetraazacyclododecane-N,N',N″,N‴-tetraacetic acid (DOTA) conjugated via a lysine linker (K), and for A11 also a glycine-serine-glycine spacer (GSG). The (68)Ga-labeling of A8-K-DOTA, A9-K-DOTA, and A11-GSGK-DOTA were optimized and in vitro bacterial binding was evaluated for (68)Ga-A9-K-DOTA and (68)Ga-A11-GSGK-DOTA. Stability of (68)Ga-A9-K-DOTA was studied in vitro in human serum, while the in vivo plasma stability was analyzed in mice and pigs. Additionally, the whole-body distribution kinetics of (68)Ga-A9-K-DOTA was measured in vivo by PET imaging of pigs and ex vivo in excised mice tissues.

RESULTS

The (68)Ga-A9-K-DOTA and (68)Ga-A11-GSGK-DOTA remained stable in product formulation, whereas (68)Ga-A8-K-DOTA was unstable. The S. aureus binding of (68)Ga-A11-GSGK-DOTA and (68)Ga-A9-K-DOTA was observed in vitro, though blocking of the binding was not possible by excess of cold peptide. The (68)Ga-A9-K-DOTA was degraded slowly in vitro, while the combined in vivo evaluation in pigs and mice showed a rapid blood clearance and renal excretion of the (68)Ga-A9-K-DOTA.

CONCLUSION

The preliminary in vitro and in vivo studies of the phage-display S. aureus biofilm-selected (68)Ga-A9-K-DOTA showed desirable features for a novel bacteria-specific imaging agent, despite of relative fast blood degradation in vivo.

Potent antimicrobial and antibiofilm activities of bacteriogenically synthesized gold–silver nanoparticles against pathogenic bacteria and their physiochemical characterizations

The objective of this study was to develop a bimetallic nanoparticle with enhanced antibacterial activity that would improve the therapeutic efficacy against bacterial biofilms. Bimetallic gold–silver nanoparticles were bacteriogenically synthesized using γ-proteobacterium, Shewanella oneidensis MR-1. The antibacterial activities of gold–silver nanoparticles were assessed on the planktonic and biofilm phases of individual and mixed multi-cultures of pathogenic Gram negative ( Escherichia coli and Pseudomonas aeruginosa) and Gram positive bacteria ( Enterococcus faecalis and Staphylococcus aureus), respectively. The minimum inhibitory concentration of gold–silver nanoparticles was 30–50 µM than that of other nanoparticles (>100 µM) for the tested bacteria. Interestingly, gold–silver nanoparticles were more effective in inhibiting bacterial biofilm formation at 10 µM concentration. Both scanning and transmission electron microscopy results further accounted the impact of gold–silver nanoparticles on biocompatibility and bactericidal effect that the small size and bio-organic materials covering on gold–silver nanoparticles improves the internalization and thus caused bacterial inactivation. Thus, bacteriogenically synthesized gold–silver nanoparticles appear to be a promising nanoantibiotic for overcoming the bacterial resistance in the established bacterial biofilms.

Hyaluronan Modulation Impacts Staphylococcus aureus Biofilm Infection

Staphylococcus aureus is a leading cause of chronic biofilm infections. Hyaluronic acid (HA) is a large glycosaminoglycan abundant in mammalian tissues that has been shown to enhance biofilm formation in multiple Gram-positive pathogens. We observed that HA accumulated in an S. aureus biofilm infection using a murine implant-associated infection model and that HA levels increased in a mutant strain lacking hyaluronidase (HysA). S. aureus secretes HysA in order to cleave HA during infection. Through in vitro biofilm studies with HA, the hysA mutant was found to accumulate increased biofilm biomass compared to the wild type, and confocal microscopy showed that HA is incorporated into the biofilm matrix. Exogenous addition of purified HysA enzyme dispersed HA-containing biofilms, while catalytically inactive enzyme had no impact. Additionally, induction of hysA expression prevented biofilm formation and also dispersed an established biofilm in the presence of HA. These observations were corroborated in the implant model, where there was decreased dissemination from an hysA mutant biofilm infection compared to the S. aureus wild type. Histopathology demonstrated that infection with an hysA mutant caused significantly reduced distribution of tissue inflammation compared to wild-type infection. To extend these studies, the impact of HA and S. aureus HysA on biofilm-like aggregates found in joint infections was examined. We found that HA contributes to the formation of synovial fluid aggregates, and HysA can disrupt aggregate formation. Taken together, these studies demonstrate that HA is a relevant component of the S. aureus biofilm matrix and HysA is important for dissemination from a biofilm infection.

Rifampicin-containing combinations are superior to combinations of vancomycin, linezolid and daptomycin against Staphylococcus aureus biofilm infection in vivo and in vitro

Susceptibility to antibiotics is dramatically reduced when bacteria form biofilms. In clinical settings this has a profound impact on treatment of implant-associated infections, as these are characterized by biofilm formation. Current routine susceptibility testing of microorganisms from infected implants does not reflect the actual susceptibility, and the optimal antibiotic strategy for treating implant-associated infections is not established. In this study of biofilm formation in implant-associated osteomyelitis, we compared thein vitroandin vivoefficacy of selected antibiotics alone and in combination againstStaphylococcus aureus.We tested vancomycin, linezolid, daptomycin and tigecycline alone and in combination with rifampicin, vancomycin, linezolid and daptomycin againstS. aureusIn vitro, biofilm formation dramatically reduced susceptibility by a factor of 500-2000.In vivo, antibiotic combinations were tested in a murine model of implant-associated osteomyelitis. Mice were infected by inserting implants colonized withS. aureustrough their tibia. After 11 days, the animals were divided into different groups (five animals/group) and given 14 days of antibiotic therapy. All antibiotics resulted in a reduced bacterial load in the infected bone surrounding the implant. Overall, the most effective antibiotic combinations contained rifampicin. Combinations containing two non-rifampicin antibiotics were not more active than single drugs.