Effects of local delivery of D-amino acids from biofilm-dispersive scaffolds on infection in contaminated rat segmental defects

Poly(d-amino acid) Nanoparticles Target Staphylococcal Growth and Biofilm Disassembly by Interfering with Peptidoglycan Synthesis

d-Amino acids are signals for biofilm disassembly. However, unexpected metabolic pathways severely attenuate the utilization of d-amino acids in biofilm disassembly, resulting in unsatisfactory efficiency. Herein, three-dimensional poly(d-amino acid) nanoparticles (NPs), which possess the ability to block intracellular metabolism, are constructed with the aim of disassembling the biofilms. The obtained poly(α-N-acryloyl-d-phenylalanine)-block-poly(β-N-acryloyl-d-aminoalanine NPs (denoted as FA NPs) present α-amino groups and α-carboxyl groups of d-aminoalanine on their surface, which guarantees that FA NPs can effectively insert into bacterial peptidoglycan (PG) via the mediation of PG binding protein 4 (PBP4). Subsequently, the FA NPs trigger the detachment of amyloid-like fibers that connect to the PG and reduce the number of polysaccharides and proteins in extracellular polymeric substances (EPS). Finally, FA NPs damage the structural stability of EPS and lead to the disassembly of the biofilm. Based on this feature, FA NPs significantly enhance the killing efficacy of encapsulated sitafloxacin sesquihydrate (Sita) by facilitating the penetration of Sita within the biofilm, achieving complete elimination of Staphylococcal biofilm in mice. Therefore, this study strongly demonstrates that FA NPs can effectively improve biofilm disassembly efficacy and provide great potential for bacterial biofilm infection treatment.

Choosing the right animal model for osteomyelitis research: Considerations and challenges

Osteomyelitis is a debilitating bone disorder characterized by an inflammatory process involving the bone marrow, bone cortex, periosteum, and surrounding soft tissue, which can ultimately result in bone destruction. The etiology of osteomyelitis can be infectious, caused by various microorganisms, or noninfectious, such as chronic nonbacterial osteomyelitis (CNO) and chronic recurrent multifocal osteomyelitis (CRMO). Researchers have turned to animal models to study the pathophysiology of osteomyelitis. However, selecting an appropriate animal model that accurately recapitulates the human pathology of osteomyelitis while controlling for multiple variables that influence different clinical presentations remains a significant challenge. In this review, we present an overview of various animal models used in osteomyelitis research, including rodent, rabbit, avian/chicken, porcine, minipig, canine, sheep, and goat models. We discuss the characteristics of each animal model and the corresponding clinical scenarios that can provide a basic rationale for experimental selection. This review highlights the importance of selecting an appropriate animal model for osteomyelitis research to improve the accuracy of the results and facilitate the development of novel treatment and management strategies.

Predictive factors and clinical efficacy of Chinese medicine Shengji ointment in the treatment of diabetic foot ulcers in the elderly: a prospective study

Objective: This study aims to investigate the predictive factors and efficacy of traditional Chinese medicine Shengji Ointment in the treatment of diabetic foot ulcers in the elderly population, with the intent of formulating an effective predictive model for deep diabetic foot ulcer healing. The importance of this research lies in its provision of new perspectives and tools for addressing the severe health impact of diabetic foot ulcers in the elderly population, considering the complexity and diversity of its treatment methods. Methods: The study includes 180 elderly patients with Wagner grade 3-4 diabetic foot ulcers that involve the tendon or fascia. The dependent variable is the initiation time of granulation tissue development. Independent variables encompass demographic information, a treatment strategy including Shengji Ointment, pre-treatment trauma assessment data, routine blood count, and biochemical index test results. Lasso regression is employed for variable selection, and Cox regression is utilized for the construction of a prediction model. A nomogram is generated to authenticate the model. Results: The Chinese Medicine treatment approach, ulcer location, creatinine levels, BMI, and haemoglobin levels are identified as independent predictors of granulation tissue development in diabetic foot ulcers. The combined treatment of Chinese herbal Shengji ointment and bromelain positively influenced granulation tissue development. The location of plantar ulcers, impaired renal functionality, obesity, and anaemia are established as independent risk factors that might influence the speed and probability of ulcer healing. The area under the time-dependent ROC curve fluctuates between 0.7 and 0.8, demonstrating substantial discrimination and calibration of the model. Conclusion: The study ascertains that a combined treatment strategy incorporating Shengji Ointment demonstrates greater effectiveness than the use of cleansing gel debridement alone in facilitating the healing of Wagner grade 3 or higher diabetic foot ulcers. Furthermore, the predictive model developed in this research serves as a valuable tool in evaluating the efficacy of Chinese Medicine treatments like Shengji Ointment for diabetic foot ulcers in the elderly. It aids clinicians in effectively assessing and adjusting treatment strategies, thereby proving its significant application value in clinical practice. Clinical Trial Registration: (https://www.chictr.org.cn/hvshowproject.html?id=73862&v=1.5&u_atoken=b403af53-d3b9-41ae-a7e2-db5498609b0c&u_asession=01tNh69p235bMUO4CmHIXcv8Hxirl5-557Duue9QB5lGfl3mf8IvPlcs2kN2zC30voX0KNBwm7Lovlpxjd_P_q4JsKWYrT3W_NKPr8w6oU7K_AyPrQhedMUWBMR2-ZDL_KO0uwDPR9XlF566xraDvT9mBkFo3NEHBv0PZUm6pbxQU&u_asig=05Kd_Q8fjv-24MVbZpOS9ef3xuCCN-tSVH5eUoJKgNLM7E0-n0zMpW6xLq9gh9aUhkKEEA15rdDoCydncF99APBwVSaTPgEG_V_B1iT4wimdCTxV_4ZVbTlDewxyQtE4YgU4-Oza7KPi94RJ64Utel0yZfqg3Tlm-bVxFNOY-zXFP9JS7q8ZD7Xtz2Ly-b0kmuyAKRFSVJkkdwVUnyHAIJzSYJ6SfhFl0WMTCCasZ7zV2I2qfyrp5m-SELPVeREKgX_6yRmLu26qT8kGfcS-Yaeu3h9VXwMyh6PgyDIVSG1W-7D_Sko5YQtpDbs3uvezYkZcUUY4o9-zDPaoYelmMDs8u7I4TPvtCXaPp44YUJcQ9bHr-_RmKA5V8nji3daArhmWspDxyAEEo4kbsryBKb9Q&u_aref=NNH1nHSUCE6pNvCilV%2F1MD0aERs%3D), identifier (ChiCTR2000039327).

Promising applications of D-amino acids in periprosthetic joint infection

Due to the rise in our aging population, a disproportionate demand for total joint arthroplasty (TJA) in the elderly is forecast. Periprosthetic joint infection (PJI) represents one of the most challenging complications that can occur following TJA, and as the number of primary and revision TJAs continues to rise, an increasing PJI burden is projected. Despite advances in operating room sterility, antiseptic protocols, and surgical techniques, approaches to prevent and treat PJI remain difficult, primarily due to the formation of microbial biofilms. This difficulty motivates researchers to continue searching for an effective antimicrobial strategy. The dextrorotatory-isoforms of amino acids (D-AAs) are essential components of peptidoglycan within the bacterial cell wall, providing strength and structural integrity in a diverse range of species. Among many tasks, D-AAs regulate cell morphology, spore germination, and bacterial survival, evasion, subversion, and adhesion in the host immune system. When administered exogenously, accumulating data have demonstrated that D-AAs play a pivotal role against bacterial adhesion to abiotic surfaces and subsequent biofilm formation; furthermore, D-AAs have substantial efficacy in promoting biofilm disassembly. This presents D-AAs as promising and novel targets for future therapeutic approaches. Despite their emerging antibacterial efficacy, their role in disrupting PJI biofilm formation, the disassembly of established TJA biofilm, and the host bone tissue response remains largely unexplored. This review aims to examine the role of D-AAs in the context of TJAs. Data to date suggest that D-AA bioengineering may serve as a promising future strategy in the prevention and treatment of PJI.

Effects of intra-articular D-amino acids combined with systemic vancomycin on an experimental Staphylococcus aureus-induced periprosthetic joint infection

BACKGROUND

The D-isoforms of amino acids (D-AAs) exhibit anti-biofilm potential against a diverse range of bacterial species in vitro, while its role in vivo remains unclear. The aim of this study was to investigate the effects of a combination of D-AAs and vancomycin on a PJI rat model.

METHODS

Eight-week-old male SD rats were randomized to the control group, sham group, vancomycin group, D-AAs-vancomycin group. After treatment for 6 weeks, we analysed the levels of inflammatory factors in serum, behavioural change, imaging manifestations. The anti-biofilm ability of D-AAs was detected by crystal violet staining and scanning electron microscope observation, and its ability to assist antibiotics in killing bacteria was assessed by culture of bacteria. Additionally, micro-CT and histological analysis were used to evaluate the impact of D-AAs combined with vancomycin on the bone remodelling around the prosthesis.

RESULTS

The group treated with a D-AAs-vancomycin combination sustained normal weight gain and exhibited reduced the serum levels of α2M, IL-1β, IL-6, IL-10, TNF-α and PGE2. Moreover, treated with D-AAs in combination with vancomycin improved the weight-bearing activity performance, increased the sizes and widths of distal femurs, and improved Rissing scale scoring. In particular, treatment using D-AAs enhanced the ability of vancomycin to eradicate Staphylococcus aureus, as demonstrated by the dispersion of existing biofilms and the inhibition of biofilm formation that occurred in a concentration-dependent manner. This treatment combination also resulted in a reduction in bacterial burden with in the soft tissues, bones, and implants. Furthermore, D-AAs-vancomycin combination treatment attenuated abnormal bone remodelling around the implant, as evidenced by an observed increase in BMD, BV/TV, and Tb.Th and the presence of reduced Trap⁺ osteoclasts and elevated osterix⁺ osteo-progenitors.

CONCLUSIONS

Combining D-AAs with vancomycin provides an effective therapeutic strategy for the treatment of PJI by promoting biofilm dispersion to enhance antimicrobial activity.

New insights into the inhibitory roles and mechanisms of D-amino acids in bacterial biofilms in medicine, industry, and agriculture

Biofilms are complex aggregates of microbes that are tightly protected by an extracellular matrix (ECM) and may attach to a surface or adhere together. A higher persistence of bacteria on biofilms makes them resistant not only to harsh conditions but also to various antibiotics which led to the emergence of problems in different applications. Recently, it has been discovered that many bacteria produce and release various D-amino acids (D-AAs) to inhibit biofilm formation, which made a great deal of interest in research into the control of bacterial biofilms in diverse fields, such as human health, industrial settings, and medical devices. D-AAs have various mechanisms to inhibit bacterial biofilms such as: (i) interfering with protein synthesis (ii) Inhibition of extracellular polymeric materials (EPS) productions (protein, eDNA, and polysaccharide) (iii) Inhibition of quorum sensing (autoinducers), and (iv) interfere with peptidoglycan synthesis, these various modes of action, enables these small molecules to inhibit both Gram-negative and Gram-positive bacterial biofilms. Since most biofilms are multi-species, D-AAs in combination with other antimicrobial agents are good choices to combat a variety of bacterial biofilms without displaying toxicity on human cells. This review article addressed the role of D-AAs in controlling several bacterial biofilms and described the possible or definite mechanisms involved in this process.

Role of Animal Models to Advance Research of Bacterial Osteomyelitis

Osteomyelitis is an inflammatory bone disease typically caused by infectious microorganisms, often bacteria, which causes progressive bone destruction and loss. The most common bacteria associated with chronic osteomyelitis is Staphylococcus aureus. The incidence of osteomyelitis in the United States is estimated to be upwards of 50,000 cases annually and places a significant burden upon the healthcare system. There are three general categories of osteomyelitis: hematogenous; secondary to spread from a contiguous focus of infection, often from trauma or implanted medical devices and materials; and secondary to vascular disease, often a result of diabetic foot ulcers. Independent of the route of infection, osteomyelitis is often challenging to diagnose and treat, and the effect on the patient's quality of life is significant. Therapy for osteomyelitis varies based on category and clinical variables in each case. Therapeutic strategies are typically reliant upon protracted antimicrobial therapy and surgical interventions. Therapy is most successful when intensive and initiated early, although infection may recur months to years later. Also, treatment is accompanied by risks such as systemic toxicity, selection for antimicrobial drug resistance from prolonged antimicrobial use, and loss of form or function of the affected area due to radical surgical debridement or implant removal. The challenges of diagnosis and successful treatment, as well as the negative impacts on patient's quality of life, exemplify the need for improved strategies to combat bacterial osteomyelitis. There are many in vitro and in vivo investigations aimed toward better understanding of the pathophysiology of bacterial osteomyelitis, as well as improved diagnostic and therapeutic strategies. Here, we review the role of animal models utilized for the study of bacterial osteomyelitis and their critically important role in understanding and improving the management of bacterial osteomyelitis.

On-Demand Multifunctional Electrostatic Complexation for Synergistic Eradication of MRSA Biofilms

Recently, methicillin-resistant Staphylococcus aureus (MRSA) severely threatened the public health, especially when the biofilms developed. Although the biofilm eradication capability of nanoparticles (NPs) has been proposed and confirmed, efficient biofilm penetration and retention are still a big challenge. To solve this problem, a multifunctional electrostatic complexation (denoted as TDZ-G4@CA) was constructed for biofilm combination therapy. TDZ-G4@CA was composed of a TDZ-grafted amino-ended poly(amidoamine) dendrimer (TDZ-PAMAM) as the inner core and cis-aconitic anhydride-modified d-tyrosine (CA-Tyr) wrapped outside via electrostatic interaction. In our design, TDZ-G4@CA could simultaneously reduce the particle size and reverse the surface charge under an acidic microenvironment, which was designed for efficient biofilm penetration and retention. Meanwhile, the on-demand two-step sequential delivery of biofilm dispersal and antibacterial agents was also obtained. The acid responsiveness of TDZ-G4@CA triggered the immediate release of d-Tyr to damage the matrix of the biofilm. Subsequently, TDZ-G4 could penetrate over the depth of the biofilm and bind tightly to MRSA, which could enhance the permeability of the bacterial membrane for TDZ internalization. Additionally, TDZ exhibited a sustained-release pattern as a response to lipase to maintain an effective bactericidal concentration for a long time. As expected, in vitro experiments demonstrated that surface charge/particle size-adaptive TDZ-G4@CA with a sequential delivery strategy exhibited intensive infiltration in the biofilm matrix and excellent biofilm eradication capabilities. Afterward, in vivo experimental results also confirmed the prolonged circulation time and comprehensive therapeutic efficacy of TDZ-G4@CA against MRSA-induced subcutaneous abscess without any systemic side effects. Based on the comprehensive evaluation of the therapeutic outcome, the electrostatic complexation (TDZ-G4@CA) can serve as a promising strategy for enhanced antibiotic therapy for combating biofilm-associated infections.

Step-by-step dual stimuli-responsive nanoparticles for efficient bacterial biofilm eradication

Biofilm-related bacterial infections are extremely resistant to antibiotics, mainly due to the impermeability of the intensive matrices, which allow the bacteria to survive antibiotic treatment. Herein, step-by-step dual stimuli-responsive azithromycin-loaded nanoparticles (CM/AZM@Tyr) was constructed for efficient biofilm eradication. CM/AZM@Tyr was prepared by the self-assembly of poly(ε-caprolactone)-polyethylene glycol-polyethylenimine (PCL-PEG-PEI) into cationic micelles and simultaneously encapsulated AZM into the hydrophobic core, which is further bound with cis-aconityl-D-tyrosine (CA-Tyr) through electrostatic interaction. Upon initial penetration, CM/AZM@Tyr could show step-by-step dual-response to the microenvironment of biofilms. Firstly, the CA-Tyr shell rapidly responded to the acidic microenvironment and released D-Tyr to disassemble the biofilm mass. Then, the exposed cationic CM/AZM micelles could bind firmly to the negatively-charged bacteria cell membrane. With the enzymolysis of the PCL core, the rapidly releasing AZM could kill the bacteria over the depth of biofilms. Massive accumulation was observed in the infected lungs of biofilms-associated lung infection mice after the i.v. injection of CM/Cy5.5@Tyr under the 3D mode of the in vivo Imaging System. Reduced bacterial burden and alleviated fibrosis in the infected lungs were also obtained after treatment with CM/AZM@Tyr mainly due to its intensive penetration in the biofilm and the orderly release of the biofilm dispersant and antimicrobial agents. In summary, this research developed an effective strategy for the treatment of blood-accessible biofilm-induced infections.

Antimicrobial d-Peptide Hydrogels

Biofilms are widely involved in human lives, such as in medical infection, environmental remediation, and industrial processes. However, the control of the biofilm has still been a challenge because of its strong drug resistance. Here, we designed and synthesized an amphipathic antimicrobial peptide (Ac-^DK^DH^DH^DQ^DK^DL^DV^DF^DF^DA^DK-NH₂ (KKd-11)) that was composed of d-amino acids (DAAs). KKd-11 was found to self-assemble into a hydrogel with an improved long-term antimicrobial ability and a better antiprotease activity as compared to the hydrogel formed by Ac-^LK^LH^LH^LQ^LK^LL^LV^LF^LF^LA^LK-NH₂ (KK-11). Our results indicated that KKd-11 was not only able to inhibit the formation of biofilms but also could effectively damage preformed mature biofilms and kill the bacteria within the biofilms. Besides, cell viability assays indicated that the KKd-11 peptide had very good biocompatibility. We think d-peptide hydrogels may have great potential in the treatment of biofilm-induced infections.

Innovations in osteomyelitis research: A review of animal models

Infection of bone tissue, or osteomyelitis, has become a growing concern in modern healthcare due in no small part to a rise in antibiotic resistance among bacteria, notably Staphylococcus aureus. The current standard of care involves aggressive, prolonged antibiotic therapy combined with surgical debridement of infected tissues. While this treatment may be sufficient for resolving a portion of cases, recurrences of the infection and associated risks including toxicity with long-term antibiotic usage have been reported. Therefore, there exists a need to produce safer, more efficacious options of treatment for osteomyelitis. In order to test treatment regimens, animal models that closely mimic the clinical condition and allow for accurate evaluation of therapeutics are necessary. Establishing a model that replicates features of osteomyelitis in humans continues to be a challenge to scientists, as there are many variables involved, including choosing an appropriate species and method to establish infection. This review addresses the refinement of animal models of osteomyelitis to reflect the clinical disease and test prospective therapeutics. The aim of this review is to explore studies regarding the use of animals for osteomyelitis therapeutics research and encourage further development of such animal models for the translation of results from the animal experiment to human medicine.

Therapeutics and delivery vehicles for local treatment of osteomyelitis

Osteomyelitis, or the infection of the bone, presents a major complication in orthopedics and may lead to prolonged hospital visits, implant failure, and in more extreme cases, amputation of affected limbs. Typical treatment for this disease involves surgical debridement followed by long-term, systemic antibiotic administration, which contributes to the development of antibiotic-resistant bacteria and has limited ability to eradicate challenging biofilm-forming pathogens including Staphylococcus aureus-the most common cause of osteomyelitis. Local delivery of high doses of antibiotics via traditional bone cement can reduce systemic side effects of an antibiotic. Nonetheless, growing concerns over burst release (then subtherapeutic dose) of antibiotics, along with microbial colonization of the nondegradable cement biomaterial, further exacerbate antibiotic resistance and highlight the need to engineer alternative antimicrobial therapeutics and local delivery vehicles with increased efficacy against, in particular, biofilm-forming, antibiotic-resistant bacteria. Furthermore, limited guidance exists regarding both standardized formulation protocols and validated assays to predict efficacy of a therapeutic against multiple strains of bacteria. Ideally, antimicrobial strategies would be highly specific while exhibiting a broad spectrum of bactericidal activity. With a focus on S. aureus infection, this review addresses the efficacy of novel therapeutics and local delivery vehicles, as alternatives to the traditional antibiotic regimens. The aim of this review is to discuss these components with regards to long bone osteomyelitis and to encourage positive directions for future research efforts.

Controlled Block Polypeptide Composed of d-Type Amino Acids: A Therapeutics Delivery Platform to Inhibit Biofilm Formation of Drug-Resistant Bacteria

Antibiotic resistance of bacteria has been widely developed due to biofilm protection and separating the bacteria from antibiotics. The phenomenon of biofilm inhibition or disassembly by d-amino acids (DAAs) has been reported recently, while it was also challenged by some other scientists. Presuming DAAs work for biofilms on the surface of bacteria, delivery of the DAAs to disease sites is important while small DAAs are easily removed by kidney. To resolve the above issues, it is urgent to develop a biofilm inhibitor. To achieve this goal, we synthesized d-type polypeptides via NCA ring-opening polymerization with the initiator of HMDS to generate poly(CBZ-l-lysine)₃₃-block-poly(d-phenylalanine)₁₄. After deprotection, the resultant polypeptides were converted into amphiphilic poly(l-lysine)₃₃-block-poly(d-phenylalanine)₁₄, which can be self-assembled into well-defined homogeneous nanoparticles capable of capsulizing penicillin G. For the molecular weight of polypeptides resulting in various bioeffects, we prepared similar-sized polypeptides of an l-type equivalent polypeptide as control. The data from microbial experiments indicated that poly(l-lysine)₃₃-block-poly(d-phenylalanine)₁₄ can inhibit biofilm formation of Bacillus subtilis at a low final concentration (24 μg/mL), much stronger than poly(l-lysine)₄₀-block-poly(l-phenylalanine)₁₉ at the same concentration. This is the first report in that synthetic d-type polypeptides can inhibit biofilms of bacteria. Poly(l-lysine)₃₃-block-poly(d-phenylalanine)₁₄ can be assembled into well-defined, biostable homogeneous nanoparticles. This research provides a potential solution to overcome bacteria antibiotic resistance from small molecules to material sciences and gives a unique angle to understand the current dispute if DAAs can disassemble the biofilms. Additionally, these nanoparticles have great potential in the development of nanomedicines with a longer circulation time in blood and this discovery has implications in developing antimicrobial nanodevices for therapy and basic scientific interest.

A Mixture of D-Amino Acids Enhances the Biocidal Efficacy of CMIT/MIT Against Corrosive Vibrio harveyi Biofilm

Biocides are widely used for the mitigation of microbial contamination, especially in the field of the aviation fuel industry. However, the long-term use of biocide has raised the concerns regarding the environmental contamination and microbial drug resistance. In this study, the effect of a mixture of D-amino acids (D-tyrosine and D-methionine) on the enhancement of the bactericidal effect of 5-Chloro-2-Methyl-4-isothiazolin-3-one/2-Methyl-2H-isothiazole-3-one (CMIT/MIT) against corrosive Vibrio harveyi biofilm was evaluated. The results revealed that D-Tyr and D-Met alone can enhance the biocidal efficacy of CMIT/MIT, while the treatment of 5 ppm CMIT/MIT, 1 ppm D-Tyr and 100 ppm D-Met showed the best efficacy comparable to that of 25 ppm CMIT/MIT alone. The triple combination treatment successfully prevented the establishment of the corrosive V. harveyi biofilm and effectively removed the mature V. harveyi biofilm. These conclusions were confirmed by the results of sessile cell counts, images obtained by scanning electron microscope and confocal laser scanning microscope, and the ATP test kit.

Targeting Biofilms Therapy: Current Research Strategies and Development Hurdles

Biofilms are aggregate of microorganisms in which cells are frequently embedded within a self-produced matrix of extracellular polymeric substance (EPS) and adhere to each other and/or to a surface. The development of biofilm affords pathogens significantly increased tolerances to antibiotics and antimicrobials. Up to 80% of human bacterial infections are biofilm-associated. Dispersal of biofilms can turn microbial cells into their more vulnerable planktonic phenotype and improve the therapeutic effect of antimicrobials. In this review, we focus on multiple therapeutic strategies that are currently being developed to target important structural and functional characteristics and drug resistance mechanisms of biofilms. We thoroughly discuss the current biofilm targeting strategies from four major aspects—targeting EPS, dispersal molecules, targeting quorum sensing, and targeting dormant cells. We explain each aspect with examples and discuss the main hurdles in the development of biofilm dispersal agents in order to provide a rationale for multi-targeted therapy strategies that target the complicated biofilms. Biofilm dispersal is a promising research direction to treat biofilm-associated infections in the future, and more in vivo experiments should be performed to ensure the efficacy of these therapeutic agents before being used in clinic.

Concurrent Local Delivery of Diflunisal Limits Bone Destruction but Fails To Improve Systemic Vancomycin Efficacy during Staphylococcus aureus Osteomyelitis

Staphylococcus aureus osteomyelitis is a debilitating infection of bone. Treatment of osteomyelitis is impaired by the propensity of invading bacteria to induce pathological bone remodeling that may limit antibiotic penetration to the infectious focus. The nonsteroidal anti-inflammatory drug diflunisal was previously identified as an osteoprotective adjunctive therapy for osteomyelitis, based on the ability of this compound to inhibit S. aureus quorum sensing and subsequent quorum-dependent toxin production. When delivered locally during experimental osteomyelitis, diflunisal significantly limits bone destruction without affecting bacterial burdens. However, because diflunisal's "quorum-quenching" activity could theoretically increase antibiotic recalcitrance, it is critically important to evaluate this adjunctive therapy in the context of standard-of-care antibiotics. The objective of this study is to evaluate the efficacy of vancomycin to treat osteomyelitis during local diflunisal treatment. We first determined that systemic vancomycin effectively reduces bacterial burdens in a murine model of osteomyelitis and identified a dosing regimen that decreases bacterial burdens without eradicating infection. Using this dosing scheme, we found that vancomycin activity is unaffected by the presence of diflunisal in vitro and in vivo Similarly, locally delivered diflunisal still potently inhibits osteoblast cytotoxicity in vitro and bone destruction in vivo in the presence of subtherapeutic vancomycin. However, we also found that the resorbable polyester urethane (PUR) foams used to deliver diflunisal serve as a nidus for infection. Taken together, these data demonstrate that diflunisal does not significantly impact standard-of-care antibiotic therapy for S. aureus osteomyelitis, but they also highlight potential pitfalls encountered with local drug delivery.

Lysostaphin and BMP-2 co-delivery reduces S. aureus infection and regenerates critical-sized segmental bone defects

Staphylococcus aureus is the most common pathogen associated with bacterial infections in orthopedic procedures. Infections often lead to implant failure and subsequent removal, motivating the development of bifunctional materials that both promote repair and prevent failure due to infection. Lysostaphin is an anti-staphylococcal enzyme resulting in bacterial lysis and biofilm reduction. Lysostaphin use is limited by the lack of effective delivery methods to provide sustained, high doses of enzyme to infection sites. We engineered a BMP-2-loaded lysostaphin-delivering hydrogel that simultaneously prevents S. aureus infection and repairs nonhealing segmental bone defects in the murine radius. Lysostaphin-delivering hydrogels eradicated S. aureus infection and resulted in mechanically competent bone. Cytokine and immune cell profiling demonstrated that lysostaphin-delivering hydrogels restored the local inflammatory environment to that of a sterile injury. These results show that BMP-2-loaded lysostaphin-delivering hydrogel therapy effectively eliminates S. aureus infection while simultaneously regenerating functional bone resulting in defect healing.

Bacterial biofilm destruction by size/surface charge-adaptive micelles

Biofilms formed by pathogenic bacteria are one of the most important reasons for multidrug resistance. One of the major limitations in the biofilm treatment is the existence of intensive matrices, which greatly block the diffusion of antimicrobial agents. In the current study, we designed poly(aspartamide)-derived micelles self-assembled from cationic copolymers with azithromycin-conjugated and pH-sensitive copolymers, followed by loading cis-aconityl-d-tyrosine (CA-Tyr) via electrostatic interactions. In response to the acidic microenvironment of the biofilm matrix, the hydrophilic transition of the pH-sensitive copolymers and the removal of CA-Tyr led to a sharp decrease in micelle size from 107 nm to 54 nm and a rapid shift in their zeta potential from -11.7 mV to +26.4 mV, which facilitated the penetration of the micelles into biofilms. The acid-labile release of d-tyrosine disintegrated the biofilm matrix, and the lipase-triggered release of azithromycin eradicated the bacteria in the biofilms. An in vitro test was performed on pre-established P. aeruginosa biofilms in microwells, while biofilms grown on catheters were surgically implanted in rats for in vivo evaluation. The results demonstrated the capabilities of the size/surface charge-adaptive micelles in the intensive infiltration in the biofilm matrix and spatiotemporal release of biofilm dispersion and antibacterial agents for the comprehensive treatment of biofilm-relevant infections.

Malnutrition and Fracture Healing: Are Specific Deficiencies in Amino Acids Important in Nonunion Development?

With the increasing incidence of fractures now, and in the future, the absolute number of bone-healing complications such as nonunion development will also increase. Next to fracture-dependent factors such as large bone loss volumes and inadequate stabilization, the nutritional state of these patients is a major influential factor for the fracture repair process. In this review, we will focus on the influence of protein/amino acid malnutrition and its influence on fracture healing. Mainly, the arginine-citrulline-nitric oxide metabolism is of importance since it can affect fracture healing via several precursors of collagen formation, and through nitric oxide synthases it has influences on the bio-molecular inflammatory responses and the local capillary growth and circulation.

Magnetic Glycol Chitin-Based Hydrogel Nanocomposite for Combined Thermal and d-Amino-Acid-Assisted Biofilm Disruption

Bacterial biofilms are highly antibiotic resistant microbial cell associations that lead to chronic infections. Unlike free-floating planktonic bacterial cells, the biofilms are encapsulated in a hardly penetrable extracellular polymeric matrix and, thus, demand innovative approaches for treatment. Recent advancements on the development of gel-nanocomposite systems with tailored therapeutic properties provide promising routes to develop novel antimicrobial agents that can be designed to disrupt and completely eradicate preformed biofilms. In our study, we developed a unique thermoresponsive magnetic glycol chitin-based nanocomposite containing d-amino acids and iron oxide nanoparticles, which can be delivered and undergoes transformation from a solution to a gel state at physiological temperature for sustained release of d-amino acids and magnetic field actuated thermal treatment of targeted infection sites. The d-amino acids in the hydrogel nanocomposite have been previously reported to inhibit biofilm formation and also disrupt existing biofilms. In addition, loading the hydrogel nanocomposite with magnetic nanoparticles allows for combination thermal treatment following magnetic field (magnetic hyperthermia) stimulation. Using this novel two-step approach to utilize an externally actuated gel-nanocomposite system for thermal treatment, following initial disruption with d-amino acids, we were able to demonstrate in vitro the total eradication of Staphylococcus aureus biofilms, which were resistant to conventional antibiotics and were not completely eradicated by separate d-amino acid or magnetic hyperthermia treatments.

Staphylococcus aureus biofilm removal by targeting biofilm-associated extracellular proteins

Background & objectives:

Among cell surface proteins, biofilm-associated protein (Bap) promotes biofilm development in Staphylococcus aureus strains. The aim of this study was to investigate proteinase-mediated biofilm dispersion in different isolates of S. aureus.

Methods:

Biofilm assay was done in 96-well microtitre plate to evaluate the effect of proteinase K on biofilms of bovine mastitis S. Aureus isolates. Extracellular polymeric substances were extracted and evaluated for their composition (protein, polysaccharides and extracellular DNA), before and after the proteinase K treatment.

Results:

Biofilm assay showed that 2 µg/ml proteinase K significantly inhibited biofilm development in bap-positive S. aureus V329 as well as other S. aureus isolates (SA7, SA10, SA33, SA352), but not in bap-mutant M556 and SA392 (a weak biofilm-producing strain). Proteinase K treatment on S. aureus planktonic cells showed that there was no inhibition of planktonic growth up to 32 µg/ml of proteinase K. Proteinase K treatment on 24 h old preformed biofilms showed an enhanced dispersion of bap-positive V329 and SA7, SA10, SA33 and SA352 biofilms; however, proteinase K did not affect the bap-mutant S. aureus M556 and SA392 biofilms. Biofilm compositions study before and after proteinase K treatment indicated that Bap might also be involved in eDNA retention in the biofilm matrix that aids in biofilm stability. When proteinase K was used in combination with antibiotics, a synergistic effect in antibiotic efficacy was observed against all biofilm-forming S. aureus isolates.

Interpretation & conclusions:

Proteinase K inhibited biofilms growth in S. aureus bovine mastitis isolates but did not affect their planktonic growth. An enhanced dispersion of preformed S. aureus biofilms was observed on proteinase K treatment. Proteinase K treatment with antibiotics showed a synergistic effect against S. aureus biofilms. The study suggests that dispersing S. aureus by protease can be of use while devising strategies against S. aureus biofilms.

Effects of d-valine on periodontal or peri-implant pathogens: Porphyromonas gingivalis biofilm

BACKGROUND

When presented with a surface or an interface, bacteria often grow as biofilms in which cells are held together by an extracellular matrix. Biofilm formation on implants is an initiating factor for their failure. Porphyromonas gingivalis is the primary etiologic bacteria of initiation and progression of periodontal disease. This microorganism is also the risk factor of many systemic diseases, such as cardiovascular disease, diabetes, and pulmonary infection. To date, no medication that can remove such biofilm has been accepted for clinical use. D-valine (D-val) can reportedly inhibit the formation of biofilm and/or trigger the scattering of mature biofilm. Accordingly, this study investigated the effects of d-val on single-species P. gingivalis biofilms in vitro.

METHODS

P. gingivalis grown in brain heart infusion culture with or without d-val was inoculated in 24- or 96-well plates. After incubation for 72 hours, biomass via crystal violet staining, extracellular polysaccharide production by biofilms, and scanning electron microscopy (SEM) were used to determine the d-val concentration that can effectively prevent P. gingivalis biofilm formation.

RESULTS

Experimental results showed that d-val effectively inhibited biofilm formation at concentrations ≥50 mM (mMol/L), and that d-val inhibition increased with increased concentration. Moreover, at high concentrations, the bacterial form changed from the normal baseball form into a rodlike shape. d-val also notably affected extracellular polysaccharide production by P. gingivalis.

CONCLUSIONS

d-val can inhibit P. gingivalis biofilm formation, and high concentrations can affect bacterial morphology.

Micro and nanotechnologies for bone regeneration: Recent advances and emerging designs

Treatment of critical-size bone defects is a major medical challenge since neither the bone tissue can regenerate nor current regenerative approaches are effective. Emerging progresses in the field of nanotechnology have resulted in the development of new materials, scaffolds and drug delivery strategies to improve or restore the damaged tissues. The current article reviews promising nanomaterials and emerging micro/nano fabrication techniques for targeted delivery of biomolecules for bone tissue regeneration. In addition, recent advances in fabrication of bone graft substitutes with similar properties to normal tissue along with a brief summary of current commercialized bone grafts have been discussed.

Application of D-Amino Acids as Biofilm Dispersing Agent in Dental Unit Waterlines

Aim and Purpose

Biofilms in dental unit waterlines (DUWLs) are extremely difficult to eliminate. Aim of this study is to evaluate the efficacy of a mixture of four D-amino acids on biofilm dispersion in DUWLs.

Materials and Methods

A mixture of four D-amino acids (D-methionine, D-tryptophan, D-leucine, and D-tyrosine, 10 mM each), distilled water (control), and 0.1 M hydrochloric acid (HCl) was used in the experiment. In laboratory, pieces of DUWLs covered with biofilms were submerged in different solutions for 5 days, flushed, and measured OD⁶⁰⁰ of the dispersed biofilms. Remnants of biofilms on the DUWLs were evaluated by SEM. In clinic, fifteen DCUs were incubated with test and control solutions, flushed, and measured OD⁶⁰⁰ of the dispersed biofilms. Microbial count of DUWL output water was enumerated twice a week for four weeks.

Results

There was a slight, but not significant, increase in OD⁶⁰⁰ of flushing water in D-amino acids group. D-amino acids effectively reduced bacterial plaque as demonstrated by SEM. Incubation with D-amino acids significantly reduced biofilms especially after the first day of flushing. Bacterial count in DUWL output water was significantly reduced after treatment with D-amino acids.

Conclusion

D-amino acids are applicable as biofilm dispersing agents in DUWLs.

Inhibition of fracture healing in the presence of contamination by Staphylococcus aureus: Effects of growth state and immune response

Extremity injuries comprise a significant portion of trauma, affecting quality of life, financial burden, and return to duty. Bacterial contamination is commonly associated with failure to heal, despite antibiotic treatment, suggesting that additional therapies must be developed to combat these complications. Treatment failure is likely due to the presence of resistant microbial communities known as biofilms. Biofilm bacteria are able to elicit a direct inhibition of healing through a multitude of known factors. However, they likely also inhibit healing through alteration of the inflammatory response. As inflammation is a critical step in fracture healing, how the presence of biofilm bacteria shifts this response to one that is suboptimal for healing is an important consideration that is currently understudied. The profile of inflammatory factors in response to biofilm bacteria is unique and distinct from those induced during normal healing or by planktonic bacteria alone. This review will examine the presence of inflammatory factors during normal healing and those induced by contaminating bacteria, and will discuss how these differences may ultimately lead to nonunion. Specifically, this review will focus on the Th1/Th2/Th17 type inflammatory responses and how shifts in the balance of these responses during infection can lead to both ineffective clearance and disruption of fracture healing. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1845-1854, 2017.

Advances in the local and targeted delivery of anti-infective agents for management of osteomyelitis

INTRODUCTION

Osteomyelitis, a common and debilitating invasive infection of bone, is a frequent complication following orthopedic surgery and causes pathologic destruction of skeletal tissues. Bone destruction during osteomyelitis results in necrotic tissue, which is poorly penetrated by antibiotics and can serve as a nidus for relapsing infection. Osteomyelitis therefore frequently necessitates surgical debridement procedures, which provide a unique opportunity for targeted delivery of antimicrobial and adjunctive therapies. Areas covered: Following surgical debridement, tissue voids require implanted materials to facilitate the healing process. Antibiotic-loaded, non-biodegradable implants have been the standard of care. However, a new generation of biodegradable, osteoconductive materials are being developed. Additionally, in the face of widespread antimicrobial resistance, alternative therapies to traditional antibiotic regimens are being investigated, including bone targeting compounds, antimicrobial surface modifications of orthopedic implants, and anti-virulence strategies. Expert commentary: Recent advances in biodegradable drug delivery scaffolds make this technology an attractive alternative to traditional techniques for orthopedic infection that require secondary operations for removal. Advances in novel treatment methods are expanding the arsenal of viable antimicrobial treatment strategies in the face of widespread drug resistance. Despite a need for large scale clinical investigations, these strategies offer hope for future treatment of this difficult invasive disease.

Anti-biofilm effects of anthranilate on a broad range of bacteria

Anthranilate, one of tryptophan degradation products has been reported to interfere with biofilm formation by Pseudomonas aeruginosa. Here, we investigated the effects of anthranilate on biofilm formation by various bacteria and the mechanisms responsible. Anthranilate commonly inhibited biofilm formation by P. aeruginosa, Vibrio vulnificus, Bacillus subtilis, Salmonella enterica serovar Typhimurium, and Staphylococcus aureus, and disrupted biofilms preformed by these bacteria. Because anthranilate reduced intracellular c-di-GMP and enhanced swimming and swarming motilities in P. aeruginosa, V. vulnificus, B. subtilis, and S. enterica, it is likely that anthranilate disrupts biofilms by inducing the dispersion of these bacteria. On the other hand, in S. aureus, a non-flagellate bacterium that has no c-di-GMP signaling, anthranilate probably inhibits biofilm formation by reducing slime production. These results suggest that anthranilate has multiple ways for biofilm inhibition. Furthermore, because of its good biofilm inhibitory effects and lack of cytotoxicity to human cells even at high concentration, anthranilate appears to be a promising agent for inhibiting biofilm formation by a broad range of bacteria.

Functional Silver Nanocomposites as Broad-Spectrum Antimicrobial and Biofilm-Disrupting Agents

Biofilms' tolerance has become a serious clinical concern due to their formidable resistance to conventional antibiotics and prevalent virulence. Therefore, there is an urgent need to develop alternative antimicrobial agents to eradicate biofilms but avoid using antibiotics. Herein, we successfully developed polymer functional silver nanocomposites by reduction of silver nitrate in the presence of a biocompatible carbohydrate polymer and a membrane-disrupting cationic polymer. The nanocomposites presented effective antimicrobial activity against Gram-negative bacteria (Pseudomonas aeruginosa, Escherichia coli) and Gram-positive bacteria (Staphylococcus aureus and Bacillus amyloliquefaciens). Confocal laser scanning macroscopy imaging demonstrated that the nanocomposites could efficiently disperse and eradicate the mature biofilms formed by the above four bacterial strains. The introduction of carbohydrate polymers onto nanocomposites effectively improved the biocompatibility, and these nanocomposites induced no significant red blood cell hemolysis and cytotoxicity toward mammalian cells. More importantly, the nanocomposites were able to well eradicate the bacterial biofilms formed on the silicone implants in vivo. In conclusion, the nanocomposites as the broad-spectrum biofilm-disrupting agent are significant in the design of new strategies to eradicate biofilms on indwelling medical devices.

Advances in the treatment of problematic industrial biofilms

In nature, microorganisms tend to form biofilms that consist of extracellular polymeric substances with embedded sessile cells. Biofilms, especially mixed-culture synergistic biofilm consortia, are notoriously difficult to treat. They employ various defense mechanisms against attacks from antimicrobial agents. Problematic industrial biofilms cause biofouling as well as biocorrosion, also known as microbiologically influenced corrosion. Biocides are often used to treat biofilms together with scrubbing or pigging. Unfortunately, chemical treatments suppress vulnerable microbial species while allowing resistant species to take over. Repeated treatment cycles are typically needed in biofilm mitigation. This leads to biocide dosage escalation, causing environmental problems, higher costs and sometimes operational problems such as scale formation. New treatment methods are being developed such as enhanced biocide treatment and bacteriophage treatment. Special materials such as antibacterial stainless steels are also being created to combat biofilms. This review discussed some of the advances made in the fight against problematic industrial biofilms.

Eradication of Enterococcus faecalis Biofilms on Human Dentin

Objectives: This work assesses different methods to interfere with Enterococcus faecalis biofilms formed on human dentin slabs.

Methods: First, methods are presented that select for small molecule inhibitors of biofilm targets using multi-well polystyrene biofilm plates. Next, we establish methodologies to study and interfere with biofilm formation on a medically relevant model, whereby biofilms are grown on human root dentin slabs.

Results: Non-conventional D-amino acid (D-Leucine) can efficiently disperse biofilms formed on dentin slabs without disturbing planktonic growth. Cation chelators interfere with biofilm formation on dentin slabs and polystyrene surfaces, and modestly impact planktonic growth. Strikingly, sodium hypochlorite, the treatment conventionally used to decontaminate infected root canal systems, was extremely toxic to planktonic bacteria, but did not eradicate biofilm cells. Instead, it induced a viable but non-culturable state in biofilm cells when grown on dentin slabs.

Conclusion: Sodium hypochlorite may contribute to bacterial persistence. A combination of the methods described here can greatly contribute to the development of biofilm inhibitors and therapies to treat Enterococcus faecalis infections formed in the root canal system.

D-amino acids do not inhibit Pseudomonas aeruginosa biofilm formation

Objective

Pseudomonas aeruginosa, a known biofilm‐forming organism, is an opportunistic pathogen that plays an important role in chronic otitis media, tracheitis, cholesteatoma, chronic wounds, and implant infections. Eradication of biofilm infections has been a challenge because the biofilm phenotype provides bacteria with a protective environment from the immune system and antibiotics; thus, there has been great interest in adjunctive molecules that may inhibit biofilm formation or cause biofilm dispersal. There are reports that D‐amino acids may inhibit biofilms. In this study, we test the ability of various D‐amino acids to inhibit P. aeruginosa biofilm formation in vitro.

Study Design

We evaluated the effect of D‐alanine (10 mM), D‐leucine (10 mM), D‐methionine (10 mM), D‐tryptophan (10 mM), and D‐tyrosine (10 uM and 1 mM) on biofilm formation in two commonly studied laboratory strains of P. aeruginosa: PAO1 and PA14.

Methods

Biofilms were grown in 24‐well and 96‐well tissue culture plates, documented photographically and stained with 0.1% crystal violet and solubilized in 33% glacial acetic acid for quantification.

Results

In strains PAO1 and PA14, the addition of D‐amino acids did not result in an inhibitory effect on biofilm growth in 24‐well plates. Repeating the study in 96‐well plates confirmed our findings that D‐amino acids do not inhibit biofilm formation of P. aeruginosa.

Conclusion

We conclude that D‐amino acids only slow the production of biofilms rather than completely prevent biofilm formation; therefore, D‐amino acids represent a poor option for potential clinically therapeutic interventions.

Level of Evidence

N/A.

Assessment of antivirulence activity of several d-amino acids against Acinetobacter baumannii and Pseudomonas aeruginosa

OBJECTIVES

Biofilm formation and bacterial adherence are important requirements for persistence, multidrug resistance and infection. The d-amino acids play a role as modulators of bacterial growth and persistence, though their ability to inhibit biofilms is much debated. In this study, we analysed the effects of 18 different d-amino acids on the pathogens Acinetobacter baumannii and Pseudomonas aeruginosa.

METHODS

In vitro assays were carried out to analyse the effect of d-amino acids on bacterial growth, biofilm formation/disassembly, capacity to attach to eukaryotic cells and cellular death. In addition, in vivo assays were performed in mice, using experimental models of sepsis and pneumonia.

RESULTS

Biofilm formation was inhibited in A. baumannii by d-His, d-Cys and d-Trp (35%-86%) at 2 mM and in P. aeruginosa by d-Cys, d-Trp and d-Tyr (10%-30%) at 4 mM. Attachment to the A549 human alveolar cells was reduced in A. baumannii by d-Cys, d-His, d-Met, d-Val and d-Ser, and in P. aeruginosa by d-Arg and d-Trp. Growth was inhibited in A. baumannii by d-Cys and d-Trp, and in P. aeruginosa by d-Trp. In virulence assays, incubation of alveolar cells infected with P. aeruginosa with d-Cys, d-Trp and d-Arg reduced cell death (56%-45%). However, no significant effect of d-amino acids was observed in vivo.

CONCLUSIONS

Some d-amino acids can inhibit bacterial growth, biofilm formation and adherence to eukaryotic cells in A. baumannii and P. aeruginosa, and showed a protective effect against infection of alveolar cells with P. aeruginosa. Despite the fact that some considerable protection was observed in mice, survival differences between treated and control groups were not statistically significant.

Effects of norspermidine on Pseudomonas aeruginosa biofilm formation and eradication

Biofilms are defined as aggregation of single cell microorganisms and associated with over 80% of all the microbial infections. Pseudomonas aeruginosa is a Gram-negative opportunistic pathogen capable of leading to various infections in immunocompromised people. Recent studies showed that norspermidine, a kind of polyamine, prevented and disrupted biofilm formation by some Gram-negative bacterium. In this study, the effects of norspermidine on P. aeruginosa biofilm formation and eradication were tested. Microtiter plate combined with crystal violet staining was used to study the effects of norspermidine on P. aeruginosa initial attachment, then we employed SEM (scanning electron microscope), qRT-PCR, and QS-related virulence factor assays to investigate how norspermidine prevent biofilm formation by P. aeruginosa. We reported that high-dose norspermidine had bactericide effect on P. aeruginosa, and norspermidine began to inhibit biofilm formation and eradicate 24-h mature biofilm at concentration of 0.1 and 1 mmol/L, respectively, probably by preventing cell-surface attachment, inhibiting swimming motility, and downregulating QS-related genes expression. To investigate the potential utility of norspermidine in preventing device-related infections, we found that catheters immersed with norspermidine were effective in eradicating mature biofilm. These results suggest that norspermidine could be a potent antibiofilm agent for formulating strategies against P. aeruginosa biofilm.

Modeling Staphylococcus epidermidis-Induced Non-Unions: Subclinical and Clinical Evidence in Rats

S. epidermidis is one of the leading causes of orthopaedic infections associated with biofilm formation on implant devices. Open fractures are at risk of S. epidermidis transcutaneous contamination leading to higher non-union development compared to closed fractures. Although the role of infection in delaying fracture healing is well recognized, no in vivo models investigated the impact of subclinical low-grade infections on bone repair and non-union. We hypothesized that the non-union rate is directly related to the load of this commonly retrieved pathogen and that a low-grade contamination delays the fracture healing without clinically detectable infection. Rat femurs were osteotomized and stabilized with plates. Fractures were infected with a characterized clinical-derived methicillin-resistant S. epidermidis (10³, 10⁵, 10⁸ colony forming units) and compared to uninfected controls. After 56 days, bone healing and osteomyelitis were clinically assessed and further evaluated by micro-CT, microbiological and histological analyses. The biofilm formation was visualized by scanning electron microscopy. The control group showed no signs of infection and a complete bone healing. The 10³ group displayed variable response to infection with a 67% of altered bone healing and positive bacterial cultures, despite no clinical signs of infection present. The 10⁵ and 10⁸ groups showed severe signs of osteomyelitis and a non-union rate of 83–100%, respectively. The cortical bone reaction related to the periosteal elevation in the control group and the metal scattering detected by micro-CT represented limitations of this study. Our model showed that an intra-operative low-grade S. epidermidis contamination might prevent the bone healing, even in the absence of infectious signs. Our findings also pointed out a dose-dependent effect between the S. epidermidis inoculum and non-union rate. This pilot study identifies a relevant preclinical model to assess the role of subclinical infections in orthopaedic and trauma surgery and to test specifically designed diagnostic, prevention and therapeutic strategies.

Animal Models of Implant-Related Low-Grade Infections. A Twenty-Year Review

The demand for joint replacement and surgical treatment is continuously increasing, thus representing a clinical burden and a cost for the healthcare system. Among several pathogens involved in implant-related infections, staphylococci account for the two-thirds of clinically isolated bacteria. Despite most of them are highly virulent microorganisms (Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa), low virulent bacteria (Staphylococcus epidermidis, Propionibacterium acnes) are responsible for delayed, low-grade infections without specific clinical signs and hardly distinguishable from aseptic prosthetic failure. Therefore, there is a real need to study the pathogenesis of orthopedic infections through in vivo animal models. The present review of the literature provides a 20-year overview of animal models of acute, subclinical or chronic orthopedic infections according to the pathogen virulence and inocula. Through this analysis, a great variety of conditions in terms of bacterial strains and inocula emerged, thus encouraging the development of more reproducible in vivo studies to provide relevant information for a translational approach to humans.

D-amino acid inhibits biofilm but not new bone formation in an ovine model

BACKGROUND

Infectious complications of musculoskeletal trauma are an important factor contributing to patient morbidity. Biofilm-dispersive bone grafts augmented with D-amino acids (D-AAs) prevent biofilm formation in vitro and in vivo, but the effects of D-AAs on osteocompatibility and new bone formation have not been investigated.

QUESTIONS/PURPOSES

We asked: (1) Do D-AAs hinder osteoblast and osteoclast differentiation in vitro? (2) Does local delivery of D-AAs from low-viscosity bone grafts inhibit new bone formation in a large-animal model?

METHODS

Methicillin-sensitive Staphylococcus aureus and methicillin-resistant S aureus clinical isolates, mouse bone marrow stromal cells, and osteoclast precursor cells were treated with an equal mass (1:1:1) mixture of D-Pro:D-Met:D-Phe. The effects of the D-AA dose on biofilm inhibition (n = 4), biofilm dispersion (n = 4), and bone marrow stromal cell proliferation (n = 3) were quantitatively measured by crystal violet staining. Osteoblast differentiation was quantitatively assessed by alkaline phosphatase staining, von Kossa staining, and quantitative reverse transcription for the osteogenic factors a1Col1 and Ocn (n = 3). Osteoclast differentiation was quantitatively measured by tartrate-resistant acid phosphatase staining (n = 3). Bone grafts augmented with 0 or 200 mmol/L D-AAs were injected in ovine femoral condyle defects in four sheep. New bone formation was evaluated by μCT and histology 4 months later. An a priori power analysis indicated that a sample size of four would detect a 7.5% difference of bone volume/total volume between groups assuming a mean and SD of 30% and 5%, respectively, with a power of 80% and an alpha level of 0.05 using a two-tailed t-test between the means of two independent samples.

RESULTS

Bone marrow stromal cell proliferation, osteoblast differentiation, and osteoclast differentiation were inhibited at D-AAs concentrations of 27 mmol/L or greater in a dose-responsive manner in vitro (p < 0.05). In methicillin-sensitive and methicillin-resistant S aureus clinical isolates, D-AAs inhibited biofilm formation at concentrations of 13.5 mmol/L or greater in vitro (p < 0.05). Local delivery of D-AAs from low-viscosity grafts did not inhibit new bone formation in a large-animal model pilot study (0 mmol/L D-AAs: bone volume/total volume = 26.9% ± 4.1%; 200 mmol/L D-AAs: bone volume/total volume = 28.3% ± 15.4%; mean difference with 95% CI = -1.4; p = 0.13).

CONCLUSIONS

D-AAs inhibit biofilm formation, bone marrow stromal cell proliferation, osteoblast differentiation, and osteoclast differentiation in vitro in a dose-responsive manner. Local delivery of D-AAs from bone grafts did not inhibit new bone formation in vivo at clinically relevant doses.

CLINICAL RELEVANCE

Local delivery of D-AAs is an effective antibiofilm strategy that does not appear to inhibit bone repair. Longitudinal studies investigating bacterial burden, bone formation, and bone remodeling in contaminated defects as a function of D-AA dose are required to further support the use of D-AAs in the clinical management of infected open fractures.

Disturbance of the bacterial cell wall specifically interferes with biofilm formation

In nature, bacteria communicate via chemical cues and establish complex communities referred to as biofilms, wherein cells are held together by an extracellular matrix. Much research is focusing on small molecules that manipulate and prevent biofilm assembly by modifying cellular signalling pathways. However, the bacterial cell envelope, presenting the interface between bacterial cells and their surroundings, is largely overlooked. In our study, we identified specific targets within the biosynthesis pathways of the different cell wall components (peptidoglycan, wall teichoic acids and teichuronic acids) hampering biofilm formation and the anchoring of the extracellular matrix with a minimal effect on planktonic growth. In addition, we provide convincing evidence that biofilm hampering by transglycosylation inhibitors and D-Leucine triggers a highly specific response without changing the overall protein levels within the biofilm cells or the overall levels of the extracellular matrix components. The presented results emphasize the central role of the Gram-positive cell wall in biofilm development, resistance and sustainment.

Inhibition of Pseudomonas aeruginosa biofilm formation on wound dressings

Chronic nonhealing skin wounds often contain bacterial biofilms that prevent normal wound healing and closure and present challenges to the use of conventional wound dressings. We investigated inhibition of Pseudomonas aeruginosa biofilm formation, a common pathogen of chronic skin wounds, on a commercially available biological wound dressing. Building on prior reports, we examined whether the amino acid tryptophan would inhibit P. aeruginosa biofilm formation on the three-dimensional surface of the biological dressing. Bacterial biomass and biofilm polysaccharides were quantified using crystal violet staining or an enzyme linked lectin, respectively. Bacterial cells and biofilm matrix adherent to the wound dressing were visualized through scanning electron microscopy. D-/L-tryptophan inhibited P. aeruginosa biofilm formation on the wound dressing in a dose dependent manner and was not directly cytotoxic to immortalized human keratinocytes although there was some reduction in cellular metabolism or enzymatic activity. More importantly, D-/L-tryptophan did not impair wound healing in a splinted skin wound murine model. Furthermore, wound closure was improved when D-/L-tryptophan treated wound dressing with P. aeruginosa biofilms were compared with untreated dressings. These findings indicate that tryptophan may prove useful for integration into wound dressings to inhibit biofilm formation and promote wound healing.

Development of a hematogenous implant-related infection in a rat model

Background

Implant-related osteomyelitis is a major complication that requires immediate treatment, often involving removal of the implant, prolonging patient recovery and inflating expenses. Current research involving interventions to diminish the prevalence of such measures include investigating prophylactic and therapeutic remedies. A proper and accurate animal model is needed to thoroughly investigate such treatments. The scope of this project was to develop an animal model in which a consistent and measurable infection can be formed on an orthopedic implant when bacteria is introduced via a hematogenous source.

Methods

Titanium Kirschner-wires were implanted into the intramedullary canals of both femurs. Staphylococcus aureus, ranging from10⁴ to 10⁹ colony forming units, was injected into a tail vessel. After a designated time (3, 7, 14, or 42 days) the femurs were harvested and bacterial numbers determined for both the femur and the implanted K-wire. In addition, histology and micro-computed tomography were used as subjective tools to further characterize the infection.

Results

Consistent infection, that is infection of ≥75 % of the femurs, wasn’t achieved until 10⁷ CFU S. aureus was injected. At 10⁷ CFU, the femurs contained 4.6x10⁶ CFU/g bone tissue at day 3 and 4.8×10⁸ CFU/g bone tissue by day 14. The wire showed comparable contamination with 4.8×10⁴ CFU/mm² at day 3 and 3.7×10⁵/mm² by day 14. After 42 days, the bacteria number decreased but was still occupying at 1.9×10⁵ CFU/g bone tissue. There were morphological changes to the bone as well. At day 42, there were signs of osteonecrosis and active bone formation when compared to control animals that received a K-wire but were inoculated with saline.

Conclusions

A model for hematogenous osteomyelitis, a common complication associated with implants, has been introduced. A reproducible, preclinical model is essential to evaluate future methods used to mitigate blood-borne bacteria hardware and bone infections.

Infected animal models for tissue engineering

Infection is one of the most common complications associated with medical interventions and implants. As tissue engineering strategies to replace missing or damaged tissue advance, the focus on prevention and treatment of concomitant infection has also begun to emerge as an important area of research. Because the in vivo environment is a complex interaction between host tissue, implanted materials, and native immune system that cannot be replicated in vitro, animal models of infection are integral in evaluating the safety and efficacy of experimental treatments for infection. In this review, considerations for selecting an animal model, established models of infection, and areas that require further model development are discussed with regard to cutaneous, fascial, and orthopedic infections.

Staphylococcus aureus biofilms: recent developments in biofilm dispersal

Staphylococcus aureus is a major cause of nosocomial and community-acquired infections and represents a significant burden on the healthcare system. S. aureus attachment to medical implants and host tissue, and the establishment of a mature biofilm, play an important role in the persistence of chronic infections. The formation of a biofilm, and encasement of cells in a polymer-based matrix, decreases the susceptibility to antimicrobials and immune defenses, making these infections difficult to eradicate. During infection, dispersal of cells from the biofilm can result in spread to secondary sites and worsening of the infection. In this review, we discuss the current understanding of the pathways behind biofilm dispersal in S. aureus, with a focus on enzymatic and newly described broad-spectrum dispersal mechanisms. Additionally, we explore potential applications of dispersal in the treatment of biofilm-mediated infections.