Gene expression analysis of children with acute hematogenous osteomyelitis caused by Methicillin-resistant Staphylococcus aureus: correlation with clinical severity of illness

The Modulation of Septic Shock: A Proteomic Approach

Sepsis poses a significant challenge due its lethality, involving multiple organ dysfunction and impaired immune responses. Among several factors affecting sepsis, monocytes play a crucial role; however, their phenotype, proteomic profile, and function in septic shock remain unclear. Our aim was to fully characterize the subpopulations and proteomic profiles of monocytes seen in septic shock cases and discuss their possible impact on the disease. Peripheral blood monocyte subpopulations were phenotype based on CD14/CD16 expression by flow cytometry, and proteins were extracted from the monocytes of individuals with septic shock and healthy controls to identify changes in the global protein expression in these cells. Analysis using 2D-nanoUPLC-UDMSE identified 67 differentially expressed proteins in shock patients compared to controls, in which 44 were upregulated and 23 downregulated. These proteins are involved in monocyte reprogramming, immune dysfunction, severe hypotension, hypo-responsiveness to vasoconstrictors, vasodilation, endothelial dysfunction, vascular injury, and blood clotting, elucidating the disease severity and therapeutic challenges of septic shock. This study identified critical biological targets in monocytes that could serve as potential biomarkers for the diagnosis, prognosis, and treatment of septic shock, providing new insights into the pathophysiology of the disease.

Staphylococcus aureus isolates from children with clinically differentiated osteomyelitis exhibit distinct transcriptomic signatures

There is substantial genomic heterogeneity among Staphylococcus aureus isolates of children with acute hematogenous osteomyelitis (AHO) but transcriptional behavior of clinically differentiated strains has not been previously described. This study evaluates transcriptional activity of S. aureus isolates of children with AHO that may regulate metabolism, biosynthesis, or virulence during bacterial growth and pathogenesis. In vitro growth kinetics were compared between three S. aureus clinical isolates from children with AHO who had mild, moderate, and severe illness. Total RNA sequencing was performed for each isolate at six separate time points throughout the logarithmic phase of growth. The NASA RNA-Sequencing Consensus Pipeline was used to identify differentially expressed genes allowing for 54 comparisons between the three isolates during growth. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment pathways were used to evaluate transcriptional variation in metabolism, biosynthesis pathways and virulence potential of the isolates. The S. aureus isolates demonstrated differing growth kinetics under standardized conditions with the mild isolate having higher optical densities with earlier and higher peak rates of growth than that of the other isolates (p<0.001). Enrichment pathway analysis established distinct transcriptional signatures according to both sampling time and clinical severity. Moderate and severe isolates demonstrated pathways of bacterial invasion, S. aureus infection, quorum sensing and two component systems. In comparison, the mild strain favored biosynthesis and metabolism. These findings suggest that transcriptional regulation during the growth of S. aureus may impact the pathogenetic mechanisms involved in the progression of severity of illness in childhood osteomyelitis. The clinical isolates studied demonstrated a tradeoff between growth and virulence. Further investigation is needed to evaluate these transcriptional pathways in an animal model or during active clinical infections of children with AHO.

Genomic characterization of Staphylococcus aureus isolates causing osteoarticular infections in otherwise healthy children

Background

Pediatric osteoarticular infections are commonly caused by Staphylococcus aureus. The contribution of S. aureus genomic variability to pathogenesis of these infections is poorly described.

Methods

We prospectively enrolled 47 children over 3 1/2 years from whom S. aureus was isolated on culture—12 uninfected with skin colonization, 16 with skin abscesses, 19 with osteoarticular infections (four with septic arthritis, three with acute osteomyelitis, six with acute osteomyelitis and septic arthritis and six with chronic osteomyelitis). Isolates underwent whole genome sequencing, with assessment for 254 virulence genes and any mutations as well as creation of a phylogenetic tree. Finally, isolates were compared for their ability to form static biofilms and compared to the genetic analysis.

Results

No sequence types predominated amongst osteoarticular infections. Only genes involved in evasion of host immune defenses were more frequently carried by isolates from osteoarticular infections than from skin colonization (p = .02). Virulence gene mutations were only noted in 14 genes (three regulating biofilm formation) when comparing isolates from subjects with osteoarticular infections and those with skin colonization. Biofilm results demonstrated large heterogeneity in the isolates’ capacity to form static biofilms, with healthy control isolates producing more robust biofilm formation.

Conclusions

S. aureus causing osteoarticular infections are genetically heterogeneous, and more frequently harbor genes involved in immune evasion than less invasive isolates. However, virulence gene carriage overall is similar with infrequent mutations, suggesting that pathogenesis of S. aureus osteoarticular infections may be primarily regulated at transcriptional and/or translational levels.

Practice Variation in the Surgical Management of Children With Acute Hematogenous Osteomyelitis

INTRODUCTION

The surgical indications to manage children with acute hematogenous osteomyelitis (AHO) remain poorly defined. The purpose of this study was to identify if practice pattern variation exists in the surgical management of pediatric AHO among tertiary pediatric medical centers across the United States. A secondary purpose was to evaluate variables that may impact the rate of surgical intervention among these institutions.

METHODS

Children with AHO were retrospectively analyzed between January 1, 2010, and December 31, 2016, from 18 pediatric medical centers throughout the United States. The rates of surgery were identified. Admission vitals, labs, weight-bearing status, length of stay, and readmission rates were compared between those who did and did not undergo surgery. Multivariate regression and classification and regression tree analyses were performed to identify the variables that were associated with surgical intervention.

RESULTS

Of the 1003 children identified with AHO in this retrospective, multicenter database, 619/1003 (62%) were treated surgically. Multivariate analysis revealed institution, inability to ambulate, presence of multifocal infection, elevated admission C-reactive protein, increased admission platelet count, and location of the osteomyelitis were significant predictors of surgery (P<0.01). Patients who underwent surgery were more than twice as likely to have a recurrence or readmission and stayed a median of 2 days longer than those who did not have surgery. In the classification and regression tree analysis, 2 distinct patterns of surgical intervention were identified based on institution, with 12 institutions operating in most cases (72%), regardless of clinical factors. A second cohort of 6 institutions operated less routinely, with 47% receiving surgery overall. At these 6 institutions, patients without multifocal infection only received surgery 26% of the time, which increased to 74% with multifocal infection and admission erythrocyte sedimentation rate >37.5 mm/h.

CONCLUSIONS

This study is the first to objectively identify significant differences in the rates of surgical management of pediatric AHO across the United States. Variation in the surgical management of AHO appears to be driven primarily based on institutional practice. Twelve institutions operated on 72% of patients, regardless of the severity of disease, indicating that the institution custom or dogma may drive the surgical indications. Six institutions relied more on clinical judgment with significant variability in rates of surgical intervention (26% vs. 74%), depending on the severity of the disease. Surgical intervention is associated with increased recurrence, readmission, and hospital length of stay. As a result of these findings, it is essential to prospectively study the appropriate surgical indications and measure the outcomes in children with pediatric AHO.

LEVEL OF EVIDENCE

Level III.

Team Approach: Pediatric Musculoskeletal Infection

A team approach is optimal in the evaluation and treatment of musculoskeletal infection in pediatric patients given the complexity and uncertainty with which such infections manifest and progress, particularly among severely ill children. The team approach includes emergency medicine, pediatric intensive care, pediatric hospitalist medicine, infectious disease service, orthopaedic surgery, radiology, anesthesiology, pharmacology, and hematology. These services follow evidence-based clinical practice guidelines with integrated processes of care so that children and their families may benefit from data-driven continuous process improvement. Important principles based on our experience in the successful treatment of pediatric musculoskeletal infection include relevant information gathering, pattern recognition, determination of the severity of illness, institutional workflow management, closed-loop communication, patient and family-centered care, ongoing dialogue among key stakeholders within and outside the context of direct patient care, and periodic data review for programmatic improvement over time. Such principles may be useful in almost any setting, including rural communities and developing countries, with the understanding that the team composition, institutional capabilities or limitations, and specific approaches to treatment may differ substantially from one setting or team to another.

The inflammatory response to bone infection - a review based on animal models and human patients

Bone infections are difficult to diagnose and treat, especially when a prosthetic joint replacement or implant is involved. Bone loss is a major complication of osteomyelitis, but the mechanism behind has mainly been investigated in cell cultures and has not been confirmed in human settings. Inflammation is important in initiating an appropriate immune response to invading pathogens. However, many of the signaling molecules used by the immune system can also modulate bone remodeling and contribute to bone resorption during osteomyelitis. Our current knowledge of the inflammatory response relies heavily on animal models as research based on human samples is scarce. Staphylococcus aureus is one of the most common causes of bone infections and is the pathogen of choice in animal models. The regulation of inflammatory genes during prosthetic joint infections and implant-associated osteomyelitis has only been studied in rodent models. It is important to consider the validity of an animal model when results are extrapolated to humans, and both bone composition and the immune system of pigs has been shown to be more similar to humans, than to rodents. Here in vivo studies on the inflammatory response to prosthetic joint infections and implant-associated osteomyelitis are reviewed.

Musculoskeletal Infection in Pediatrics: Assessment of the 2018 International Consensus Meeting on Musculoskeletal Infection

The Second International Consensus Meeting (ICM) on Musculoskeletal Infection was held in July 2018 in Philadelphia, Pennsylvania. This meeting involved contributions from an international multidisciplinary consortium of experts from orthopaedic surgery, infectious disease, pharmacology, rheumatology, microbiology, and others. Through strict delegate engagement in a comprehensive 13-step consensus process based on the Delphi technique, evidence-based consensus guidelines on musculoskeletal infection were developed. The 2018 ICM produced updates to recommendations from the inaugural ICM that was held in 2013, which primarily focused on periprosthetic infection of the hip and the knee, and added new guidelines with the expansion to encompass all subspecialties of orthopaedic surgery. The following proceedings from the pediatrics section are an overview of the ICM consensus recommendations on the prevention, diagnosis, and treatment of pediatric musculoskeletal infection.

Differentiation of Deep Venous Thrombosis Among Children With or Without Osteomyelitis

BACKGROUND

Children with osteomyelitis are at risk for deep venous thrombosis (DVT). This study evaluates the characteristics of DVT among children to differentiate between those with and without osteomyelitis.

METHODS

Children with DVT of any cause were studied between 2008 and 2016. Children with DVT and osteomyelitis were compared with those with DVT without osteomyelitis. Another comparison cohort included children with osteomyelitis but without DVT. Comorbidities, severity of illness (SOI), and clinical course were compared between cohorts.

RESULTS

DVT was identified in 224 children, a prevalence of 2.5 per 10,000 children. Among those with DVT, 28 (12.1%) had osteomyelitis. The DVT rate among 466 children with osteomyelitis was 6.0%. Children with osteomyelitis and DVT had greater SOI (9.1 vs. 2.7), bacteremia rate (82.1% vs. 38.4%), methicillin-resistant Staphylococcus aureus rate (89.3% vs. 21.2%), surgeries per child (2.1 vs. 0.7), and intensive care unit admission rate (67.9% vs. 5.9%) than that of children without DVT (P<0.00001). Of 196 children who had DVT without osteomyelitis, 166 (84.7%) had comorbidities including defined hypercoagulability (27 or 13.8%). Children with DVT due to osteomyelitis were without comorbidities or hypercoagulability (P<0.00001). The rate of pulmonary embolism was similar for children with DVT with or without osteomyelitis (3/28, or 10.7% vs. 18/196, or 9.2%).

CONCLUSIONS

Children with DVT and osteomyelitis differ substantially from other children with DVT by the absence of comorbidities or post-thrombotic syndrome. They also differ from children with osteomyelitis without DVT by higher SOI, methicillin-resistant S. aureus rate, and occurrence of intensive care. Awareness of for the characteristics of DVT among children with osteomyelitis will reduce delay to diagnostic ultrasound and improve anticoagulation management which must be carefully coordinated given the high rate of surgery of these children.

LEVEL OF EVIDENCE

Level II-prognostic, retrospective cohort comparison.

Comparison of gene expression profiles induced by fresh or ozone-oxidized black carbon particles in A549 cells

Epidemiological studies have showed an association between black carbon (BC) exposure and adverse health effects. This study intends to investigate the influence of oxidation processes in atmosphere on the initial cellular responses of BC. The changes of gene expressions induced by fresh BC (FBC) and ozone-oxidized BC (OBC) in human lung epithelial A549 cells were analyzed. And their toxic effects presented by viability, LDH release and DNA damage were compared. Totally 47, 000 genes in A549 cells were examined using Affymetrix Human U133 plus 2.0 chips. Some of the differentially expressed genes were verified by reverse transcription-quantitative polymerase chain reaction (RT-qPCR). The results showed that 1446 genes (including 756 up-regulated and 690 down-regulated) and 1594 genes (including 788 up-regulated and 806 down-regulated genes) were significantly changed by FBC and OBC respectively. Only 4 of 14 (FBC)/15 (OBC) oxidative stress related genes, up- or down-regulated by FBC and OBC, were identical; 13 of 29 (FBC)/31 (OBC) inflammation related genes, and 6 of 20 (FBC)/18 (OBC) autophagy related genes were identical. No obvious differences were observed between the toxic effects of FBC and OBC. The cytotoxicity of OBC and FBC in A549 cells is at least partially induced by oxidative stress and consequent inflammation or autophagy process. Previous studies indicated that OBC may be more toxic than FBC. However, our results suggested that FBC and OBC might lead to diverse toxic endpoints through activating different molecular pathways.

Acute Hematogenous Osteomyelitis in Children: Pathogenesis, Diagnosis, and Treatment

Acute hematogenous osteomyelitis (AHO) in children is an ideal condition to study due to its representation of a wide spectrum of disorders that comprise pediatric musculoskeletal infection. Proper care for children with AHO is multidisciplinary and collaborative. AHO continues to present a significant clinical challenge due to evolving epidemiology and complex pathogenesis. A guideline-driven, multidisciplinary approach has been introduced and shown to effectively reduce hospital stay, improve the timing and selection of empirical antibiotic administration, reduce delay to initial MRI, reduce the rate of readmission, and shorten antibiotic duration.

Bone and Joint Infections in Children: Acute Hematogenous Osteomyelitis

Acute hematogenous osteomyelitis (AHO) is one of the commonest bone infection in childhood. Staphylococcus aureus is the commonest organism causing AHO. With use of advanced diagnostic methods, fastidious Kingella kingae is increasingly becoming an important organism in etiology of osteoarticular infections in children under the age of 3 y. The diagnosis of AHO is primarily clinical. The main clinical symptom and sign in AHO is pain and tenderness over the affected bone especially in the metaphyseal region. However, in a neonate the clinical presentation may be subtle and misleading. Laboratory and radiological investigations supplement the clinical findings. The acute phase reactants such as C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) are frequently elevated. Ultrasonography and MRI are key imaging modalities for early detection of AHO. Determination of infecting organism in AHO is the key to the correct antibiotic choice, treatment duration and overall management and therefore, organism isolation using blood cultures and site aspiration should be attempted. Several effective antibiotics regimes are available for managing AHO in children. The choice of antibiotic and its duration and mode of delivery requires individualization depending upon severity of infection, causative organism, regional sensitivity patterns, time elapsed between onset of symptoms and child's presentation and the clinical and laboratory response to the treatment. If pus has been evidenced in the soft tissues or bone region, surgical decompression of abscess is mandatory.

Genomic Heterogeneity of Methicillin Resistant Staphylococcus aureus Associated with Variation in Severity of Illness among Children with Acute Hematogenous Osteomyelitis

Introduction

The association between severity of illness of children with osteomyelitis caused by Methicillin-resistant Staphylococcus aureus (MRSA) and genomic variation of the causative organism has not been previously investigated. The purpose of this study is to assess genomic heterogeneity among MRSA isolates from children with osteomyelitis who have diverse severity of illness.

Materials and Methods

Children with osteomyelitis were prospectively studied between 2010 and 2011. Severity of illness of the affected children was determined from clinical and laboratory parameters. MRSA isolates were analyzed with next generation sequencing (NGS) and optical mapping. Sequence data was used for multi-locus sequence typing (MLST), phylogenetic analysis by maximum likelihood (PAML), and identification of virulence genes and single nucleotide polymorphisms (SNP) relative to reference strains.

Results

The twelve children studied demonstrated severity of illness scores ranging from 0 (mild) to 9 (severe). All isolates were USA300, ST 8, SCC mec IVa MRSA by MLST. The isolates differed from reference strains by 2 insertions (40 Kb each) and 2 deletions (10 and 25 Kb) but had no rearrangements or copy number variations. There was a higher occurrence of virulence genes among study isolates when compared to the reference strains (p = 0.0124). There were an average of 11 nonsynonymous SNPs per strain. PAML demonstrated heterogeneity of study isolates from each other and from the reference strains.

Discussion

Genomic heterogeneity exists among MRSA isolates causing osteomyelitis among children in a single community. These variations may play a role in the pathogenesis of variation in clinical severity among these children.

Assessment of immune status using blood transcriptomics and potential implications for global health

The immune system plays a key role in health maintenance and pathogenesis of a wide range of diseases. Leukocytes that are present in the blood convey valuable information about the status of the immune system. Blood transcriptomics, which consists in profiling blood transcript abundance on genome-wide scales, has gained in popularity over the past several years. Indeed, practicality and simplicity largely makes up for what this approach may lack in terms of cell population-level resolution. An extensive survey of the literature reveals increasingly widespread use across virtually all fields of medicine as well as across a number of different animal species, including model organisms but also animals of economical importance. Dissemination across such a wide range of disciplines holds the promise of adding a new perspective, breadth or context, to the considerable depth afforded by whole genome profiling of blood transcript abundance. Indeed, it is only through such contextualization that a truly global perspective will be gained from the use of systems approaches. Also discussed are opportunities that may arise for the fields of immunology and medicine from using blood transcriptomics as a common denominator for developing interactions and cooperation across fields of research that have traditionally been and largely remain compartmentalized. Finally, an argument is made for building immunology research capacity using blood transcriptomics platforms in low-resource and high-disease burden settings.