Bacterial toxins in musculoskeletal infections

Mechanobiology of bacterial biofilms: Implications for orthopedic infection

Postoperative bacterial infections are prevalent complications in both human and veterinary orthopedic surgery, particularly when a biofilm develops. These infections often result in delayed healing, early revision, permanent functional loss, and, in severe cases, amputation. The diagnosis and treatment pose significant challenges, and bacterial biofilm further amplifies the therapeutic difficulty as it confers protection against the host immune system and against antibiotics which are usually administered as a first-line therapeutic option. However, the inappropriate use of antibiotics has led to the emergence of numerous multidrug-resistant organisms, which largely compromise the already imperfect treatment efficiency. In this context, the study of bacterial biofilm formation allows to better target antibiotic use and to evaluate alternative therapeutic strategies. Exploration of the roles played by mechanical factors on biofilm development is of particular interest, especially because cartilage and bone tissues are reactive environments that are subjected to mechanical load. This review delves into the current landscape of biofilm mechanobiology, exploring the role of mechanical factors on biofilm development through a multiscale prism starting from bacterial microscopic scale to reach biofilm mesoscopic size and finally the macroscopic scale of the fracture site or bone-implant interface.

Beyond the acute phase: a comprehensive literature review of long-term sequelae resulting from infectious diseases

Infectious diseases have consistently served as pivotal influences on numerous civilizations, inducing morbidity, mortality, and consequently redirecting the course of history. Their impact extends far beyond the acute phase, characterized by the majority of symptom presentations, to a multitude of adverse events and sequelae that follow viral, parasitic, fungal, or bacterial infections. In this context, myriad sequelae related to various infectious diseases have been identified, spanning short to long-term durations. Although these sequelae are known to affect thousands of individuals individually, a comprehensive evaluation of all potential long-term effects of infectious diseases has yet to be undertaken. We present a comprehensive literature review delineating the primary sequelae attributable to major infectious diseases, categorized by systems, symptoms, and duration. This compilation serves as a crucial resource, illuminating the long-term ramifications of infectious diseases for healthcare professionals worldwide. Moreover, this review highlights the substantial burden that these sequelae impose on global health and economies, a facet often overshadowed by the predominant focus on the acute phase. Patients are frequently discharged following the resolution of the acute phase, with minimal long-term follow-up to comprehend and address potential sequelae. This emphasizes the pressing need for sustained vigilance, thorough patient monitoring, strategic health management, and rigorous research to understand and mitigate the lasting economic and health impacts of infectious diseases more fully.

Osteoarthritis Can Also Start in the Gut: The Gut-Joint Axis

Background

Osteoarthritis is a common cause of pain and disability with an increasing prevalence among the global population (Hunter and Bierma-Zeinstra in Lancet 393(10182):1745-1759, 2019; Zhang and Jordan in Clinics in Geriatric Medicine 26(3):355-369, 2010). Altered immune responses and low-grade systemic inflammation driven by gut dysbiosis are being increasingly recognized as contributing factors to the pathophysiology of OA (Tan et al. in International Journal of Rheumatic Diseases. https://doi.org/10.1111/1756-185X.14123, 2021; Binvignat et al. in Joint, Bone, Spine 88(5):105203, 2021; Ramasamy et al. in Nutrients 13(4):1272, 2021), which increased the interest in the so-called "gut-joint axis". The various microbiota in the gastrointestinal tract is commonly referred to as the gut microbiome. The gut microbiome is affected by age, sex, and immune system activity as well as medications, environment, and diet (Arumugam in Nature. https://doi.org/10.1038/nature09944, 2011). The microbiome is pivotal to maintain host health and contributes to nutrition, host defense, and immune development (Nishida et al. in Clinical Journal of Gastroenterology 11:1-10, 2018). Alterations in this microbiome can induce dysbiosis, which is associated with many human disease states including allergies, autoimmune disease, diabetes, and cancer (Lin and Zhang in BMC Immunology 18(1):2, 2017). A gut-joint axis is proposed as a link involving the gastrointestinal microbiome, the immune response that it induces, and joint health.

Results

Emerging evidence has shown that there are specific changes in the microbiome that are associated with osteoarthritis, including increased Firmicutes/Bacteroides ratio, Streptococcus spp. prevalence, and local inflammation (Collins in Osteoarthritis and Cartilage. https://doi.org/10.1016/j.joca.2015.03.014, 2015; Rios in Science and Reports. https://doi.org/10.1038/s41598-019-40601-x, 2019; Schott in JCI insight. https://doi.org/10.1172/jci.insight.95997, 2018; Boer et al. in Nature Communications 10:4881, 2019). Both the innate and adaptive immune systems are affected by the gut microbiome and can become dysregulated in dysbiosis which ultimately triggers events associated with joint OA.

Conclusions

The gut is an intriguing and novel target for OA therapy. Dietary modification or supplementation with fiber, probiotics, or prebiotics could provide a positive impact on the gut joint axis.

Immune Response to Persistent Staphyloccocus Aureus Periprosthetic Joint Infection in a Mouse Tibial Implant Model

Staphyloccocus aureus is one of the major pathogens in orthopedic periprosthetic joint infection (PJI), a devastating complication of total joint arthroplasty that often results in chronic and persistent infections that are refractory to antibiotics and require surgical interventions. Biofilm formation has been extensively investigated as a reason for persistent infection. The cellular composition, activation status, cytokine profile, and role of the immune response during persistent S. aureus PJI are incompletely understood. In this study, we used histology, multiparametric flow cytometry, and gene expression analysis to characterize the immune response in a clinically relevant orthopedic PJI model. We tested the hypothesis that persistent S. aureus infection induces feedback mechanisms that suppress immune cell activation, thereby affecting the course of infection. Surprisingly, persistent infection was characterized by strikingly high cytokine gene expression indicative of robust activation of multiple components of innate and adaptive immunity, along with ongoing severe neutrophil-dominated inflammation, in infected joint and bone tissues. Activation and expansion of draining lymph nodes and a bone marrow stress granulopoiesis reaction were also maintained during late phase infection. In parallel, feedback mechanisms involving T-cell inhibitory receptors and exhaustion markers, suppressive cytokines, and regulatory T cells were activated and associated with decreased T-cell proliferation and tissue infiltration during the persistent phase of infection. These results identify the cellular and molecular components of the mouse immune response to persistent S. aureus PJI and indicate that neutrophil infiltration, inflammatory cytokine responses, and ongoing lymph node and bone marrow reactions are insufficient to clear infection and that immune effector mechanisms are suppressed by feedback inhibitory pathways. These immune-suppressive mechanisms are associated with diminished T-cell proliferation and tissue infiltration and can be targeted as part of adjuvant immunotherapeutic strategies in combination with debridement of biofilm, antibiotics, and other therapeutic modalities to promote eradication of infection. © 2021 American Society for Bone and Mineral Research (ASBMR).

The relation between the gut microbiome and osteoarthritis: A systematic review of literature

Background

Along with mechanical and genetic factors, emerging evidence suggests that the presence of low-grade inflammation has a role in the pathogenesis of osteoarthritis (OA) and seems to be related to the microbiome composition of the gut.

Purpose

To provide evidence whether there is clinical or preclinical evidence of gut-joint axis in the pathogenesis and symptoms of OA.

Methods

An extensive review of the current literature was performed using three different databases. Human, as well as animal studies, were included. The risk of bias was identified using ROBINS and SYRCLE tools, while the quality of evidence was assessed using GRADE and CAMADARES criteria.

Results

A total of nineteen articles were included. Multiple animal studies demonstrated that both obesity, and high-fat and high-sugar diets resulted in a gut dysbiosis status characterized by increased Firmicutes/Bacteroidetes (F/B) phyla ratio and increased permeability. These changes were associated with increased lipopolysaccharide serum levels, which consequently resulted in synovitis and OA severity. The administration of pre-and probiotics partially reversed this bacterial composition. In addition, in human studies, a decreased amount of gut Bacteroidetes, subsequent increased F/B ratio, have also been observed in OA patients.

Conclusions

Our review confirms preliminary yet sound evidence supporting a gut-joint axis in OA in primarily preclinical models, by showing an association between diet, gut dysbiosis and OA radiological severity and self-reported symptoms. Clinical studies are needed to confirm these findings, and to investigate whether interventions targeting the composition of the microbiome will have a beneficial clinical effect.

Antibacterial and Anti-Biofilm Activity of Omega-3 Polyunsaturated Fatty Acids against Periprosthetic Joint Infections-Isolated Multi-Drug Resistant Strains

Background: Implantable medical devices, such as prosthetics, catheters, and several other devices, have revolutionized medicine, but they increase the infection risk. In previous decades, commercially available antibiotics lost their activity against coagulase-negative Staphylococci (CoNS) and several other microorganisms. Docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) are the two major omega-3 polyunsaturated fatty acids (ω-3 PUFAs) with antimicrobial properties. Materials and Methods: In this study, we tested the EPA and the DHA for its antibacterial and anti-biofilm activity in vitro against Staphylococcus epidermidis, Staphylococcus aureus, and different CoNS as reference strains and isolated from patients undergoing orthopedic treatment for implant infections. The tests were carried out with the strains in planktonic and biofilm form. Cytotoxicity assay was carried out with EPA and DHA using human gingival fibroblasts HGF-1. Results: The highest concentration of EPA and DHA promoted the complete killing of S. epidermidis 1457 and S. aureus ATCC 25923 in planktonic form. The fatty acids showed low activity against P. aeruginosa. EPA and DHA completely killed or significantly reduced the count of planktonic bacteria of the patient isolated strains. When incubated with media enriched with EPA and DHA, the biofilm formation was significantly reduced on S. epidermidis 1457 and not present on S. aureus ATCC 25923. The reduction or complete killing were also observed with the clinical isolates. The pre-formed biofilms showed reduction of the cell counting after treatment with EPA and DHA. Conclusion: In this study, the ω-3 PUFAs EPA and DHA showed antimicrobial and anti-biofilm activity in vitro against S. aureus, S. epidermidis, and P. aeruginosa, as well as against multi-drug resistant S. aureus and CoNS strains isolated from patients undergoing periprosthetic joint infections (PJI) treatment. Higher concentrations of the fatty acids showed killing activity on planktonic cells and inhibitory activity of biofilm formation. Although both substances showed antimicrobial activity, EPA showed better results in comparison with DHA. In addition, when applied on human gingival fibroblasts in vitro, EPA and DHA showed a possible protective effect on cells cultured in medium enriched with ethanol. Further studies are required to confirm the antimicrobial activity of EPA and DHA against multi-drug resistant strains and pan-drug resistant strains.

Precision Medicine in the Diagnosis and Management of Orthopedic Biofilm Infections

Orthopedic biofilm infections are difficult to treat and require a multidisciplinary approach to diagnostics and management. Recent advances in the field include methods to disrupt biofilm, sequencing tools, and antibiotic susceptibility tests for bacteria residing in biofilm. The observation of interclonal differences in biofilm properties of the causative microorganisms, together with considerations of comorbidities and polypharmacy in a growing aging population, calls for a personalized approach to treat these infections. In this article, we highlight aspects of precision medicine that may open new perspectives in the diagnosis and management of orthopedic biofilm infections.