Laboratory Diagnosis of Infective Endocarditis

Changes and advances in the field of infective endocarditis

Infective endocarditis is a rare but deadly disease, with a highly variable presentation. The clinical manifestations of the condition are often multisystemic, ranging from dermatological to ophthalmic, and cardiovascular to renal. Thus, patients with infective endocarditis may first present to the acute or general physician, who may have a variable knowledge of the condition. The diagnosis of infective endocarditis can be challenging, relying on clinical, imaging and microbiological features. Recent decades have seen a transformation in the epidemiology and microbiology of infective endocarditis and yet, despite advances in diagnostics and therapeutics, mortality rates remain high. This review outlines the emerging studies and guidelines on the assessment and management of infective endocarditis, focusing on the evolving epidemiology of the condition, the role of new imaging modalities, updated diagnostic criteria, the latest on antimicrobial and surgical management, and the role of a multidisciplinary approach in the management of patients with infective endocarditis.

Staphylococcus aureus β-Toxin Exerts Anti-angiogenic Effects by Inhibiting Re-endothelialization and Neovessel Formation

Staphylococcus aureus causes severe, life-threatening infections that often are complicated by severe local and systemic pathologies with non-healing lesions. A classic example is S. aureus infective endocarditis (IE), where the secreted hemolysin β-toxin potentiates the disease via its sphingomyelinase and biofilm ligase activities. Although these activities dysregulate human aortic endothelial cell activation, β-toxin effect on endothelial cell function in wound healing has not been addressed. With the use of the ex vivo rabbit aortic ring model, we provide evidence that β-toxin prevents branching microvessel formation, highlighting its ability to interfere with tissue re-vascularization and vascular repair. We show that β-toxin specifically targets both human aortic endothelial cell proliferation and cell migration and inhibits human umbilical vein endothelial cell rearrangement into capillary-like networks in vitro. Proteome arrays specific for angiogenesis-related molecules provided evidence that β-toxin promotes an inhibitory profile in endothelial cell monolayers, specifically targeting production of TIMP-1, TIMP-4, and IGFBP-3 to counter the effect of a pro-angiogenic environment. Dysregulation in the production of these molecules is known to result in sprouting defects (including deficient cell proliferation, migration, and survival), vessel instability and/or vascular regression. When endothelial cells are grown under re-endothelialization/wound healing conditions, β-toxin decreases the pro-angiogenic molecule MMP-8 and increases the anti-angiogenic molecule endostatin. Altogether, the data indicate that β-toxin is an anti-angiogenic virulence factor and highlight a mechanism where β-toxin exacerbates S. aureus invasive infections by interfering with tissue re-vascularization and vascular repair.

Mycotic abdominal aortic aneurysm caused by Borrelia afzelii: a case report

Background

Inflammatory aneurysms and mycotic aneurysms make up a minority of abdominal aortic aneurysms. Mainly autoimmune mechanisms are proposed in the pathogenesis of inflammatory aneurysms, and it is not routine to check for infectious agents as disease culprits.

Case presentation

A 58-year-old European male with complaints of abdominal and back pain for 8 weeks was admitted after a semi-urgent computed tomography scan revealed an 85 mm inflammatory abdominal aortic aneurysm. The patient had normal vital signs, slightly elevated inflammatory markers, and mild anemia on admission. Clinical examination revealed a tender pulsating mass in his abdomen. His clinical condition was interpreted as impending rupture and urgent repair of the aneurysm was deemed necessary. Due to the patient’s relatively young age and aneurysm neck morphology, open aortic repair was preferred. Preoperatively, the aneurysm appeared inflamed, with fibrous wall thickening and perianeurysmal adhesions. Aneurysm wall biopsies were sent to histopathological and microbiological diagnostics. Routine cultures were negative, but 16S rRNA gene real-time polymerase chain reaction was positive and Borrelia afzelii was identified by DNA sequencing of the polymerase chain reaction product. B. afzelii was also identified by sequencing the polymerase chain reaction product of a Borrelia-specific groEL target. Immunoglobulin G and M anti-Borrelia antibodies were present on serological analysis. Histopathological analysis displayed loss of normal aortic wall structure and diffuse infiltration of lymphocytes and plasma cells. The patient had an uneventful recovery and was discharged after 1 week to a regional rehabilitation facility. Though the patient fares clinically well and inflammatory markers had normalized, antimicrobial treatment with doxycycline continues at 3 months follow-up due to remaining radiologic signs of inflammation.

Conclusions

Borrelia infection in the setting of acute aortic pathology is a rare entity. To our knowledge, this is the first case report to demonstrate a mycotic abdominal aortic aneurysm as a rare manifestation of Lyme disease. Aortic wall biopsies and real-time polymerase chain reaction analysis of the specimen were essential for accurate diagnosis. This finding may contribute to the understanding of the etiology of inflammatory aneurysmal disease and abdominal aneurysms in general.

Fungal Endocarditis: A Case Report

Fungal endocarditis is a rare disease, and it is associated with severe complications and poor prognosis despite combined clinical and surgical treatment. Although Candida albicans (C. albicans) is the most common etiological agent of this severe form of endocarditis, Candida parapsilosis (C. parapsilosis) is the most common non-albicans causative species. It occurs mostly in patients with predisposing risk factors, and the rarity of this disease demands a high index of suspicion; the diagnosis must be vigilantly pursued by echocardiography and multiple blood cultures. The past few decades have witnessed a rise in the incidence of this disease, mainly due to improvements in the diagnostic approach. We report the case of a 63-year-old man with no previous medical history of cardiac disease and no risk factors who was diagnosed with fungal endocarditis due to C. parapsilosis without fungemia. This report illustrates a rare case of fungal endocarditis in a patient with no risk factors and highlights the challenges encountered in the diagnosis, along with complications and predictors of poor prognosis.

Enterococcus faecalis colonizes and forms persistent biofilm microcolonies on undamaged endothelial surfaces in a rabbit endovascular infection model

Infectious endocarditis (IE) is an uncommon disease with significant morbidity and mortality. The pathogenesis of IE has historically been described as a cascade of host-specific events beginning with endothelial damage and thrombus formation and followed by bacterial colonization of the nascent thrombus. Enterococcus faecalis is a Gram-positive commensal bacterial member of the gastrointestinal tract microbiota in most terrestrial animals and a leading cause of opportunistic biofilm-associated infections, including endocarditis. Here, we provide evidence that E. faecalis can colonize the endocardial surface without pre-existing damage and in the absence of thrombus formation in a rabbit endovascular infection model. Using previously described light and scanning electron microscopy techniques, we show that inoculation of a well-characterized E. faecalis lab strain in the marginal ear vein of New Zealand White rabbits resulted in rapid colonization of the endocardium throughout the heart within 4 days of administration. Unexpectedly, ultrastructural imaging revealed that the microcolonies were firmly attached directly to the endocardium in areas without morphological evidence of gross tissue damage. Further, the attached bacterial aggregates were not associated with significant cellular components of coagulation or host extracellular matrix damage repair (i.e. platelets). These results suggest that the canonical model of mechanical surface damage as a prerequisite for bacterial attachment to host sub-endothelial components is not required. Furthermore, these findings are consistent with a model of initial establishment of stable, endocarditis-associated E. faecalis biofilm microcolonies that may provide a reservoir for the eventual valvular infection characteristic of clinical endocarditis. The similarities between the E. faecalis colonization and biofilm morphologies seen in this rabbit endovascular infection model and our previously published murine gastrointestinal colonization model indicate that biofilm production and common host cell attachment factors are conserved in disparate mammalian hosts under both commensal and pathogenic contexts.

Escalating incidence of infective endocarditis in Europe in the 21st century

AIM

To provide a contemporary analysis of incidence trends of infective endocarditis (IE) with its changing epidemiology over the past two decades in Europe.

METHODS

A systematic review was conducted at the Mayo Clinic, Rochester. Ovid EBM Reviews, Ovid Embase, Ovid Medline, Scopus and Web of Science were searched for studies published between 1 January 2000 and 30 November 2020. All studies were independently reviewed by four referees and those that included a population-based incidence of IE in patients, irrespective of age, in Europe were included. Least squares regression was used to estimate pooled temporal trends in IE incidence.

RESULTS

Of 9138 articles screened, 18 studies were included in the review. Elderly men predominated in all studies. IE incidence increased 4.1% per year (95% CI 1.8% to 6.4%) in the pooled regression analysis of eight studies that included comprehensive and consistent trends data. When trends data were weighted according to population size of individual countries, an increase in yearly incidence of 0.27 cases per 100 000 people was observed. Staphylococci and streptococci were the most common pathogens identified. The rate of surgical intervention ranged from 10.2% to 60.0%, and the rate of inpatient mortality ranged from 14.3% to 17.5%. In six studies that examined the rate of injection drug use, five of them reported a rate of less than 10%.

CONCLUSION

Based on findings from our systematic review, IE incidence in Europe has doubled over the past two decades in Europe. Multiple factors are likely responsible for this striking increase.

TRIAL REGISTERATION NUMBER

CRD42020191196.

Infective endocarditis in paediatric population

Infective endocarditis is very uncommon in children; however, when it does arise, it can lead to severe consequences. The biggest risk factor for paediatric infective endocarditis today is underlying congenital heart defects. The most common causative organisms are Staphylococcus aureus and the viridans group of streptococci. The spectrum of symptoms varies widely in children and this produces difficulty in the diagnosis of infective endocarditis. Infective endocarditis in children is reliant on the modified Duke criteria. The use of blood cultures remains the most effective microbiological test for pathogen identification. However, in blood culture-negative infective endocarditis, serology testing and IgG titres are more effective for diagnosis. Imaging techniques used include echocardiograms, computed tomography and positron emission tomography. Biomarkers utilised in diagnosis are C-reactive protein, with recent literature reviewing the use of interleukin-15 and C-C motif chemokine ligand for reliable risk prediction. The American Heart Association (AHA) and European Society of Cardiology (ESC) guidelines have been compared to describe the differences in the approach to infective endocarditis in children. Medical intervention involves the use of antimicrobial treatment and surgical interventions include the repair and replacement of cardiac valves. Quality of life is highly likely to improve from surgical intervention.Conclusion: Over the past decades, there have been great advancements in clinical practice to improve outcomes in patients with infective endocarditis. Nonetheless, further work is required to better investigative and manage such high risk cohort. What is Known: • The current diagnostic techniques including 'Duke's criteria' for paediatric infective endocarditis diagnosis • The current management guidelines utilised for paediatric infective endocarditis What is New: • The long-term outcomes of patients that underwent medical and surgical intervention • The quality of life of paediatric patients that underwent medical and surgical intervention.

Epidemiology and antibiotic susceptibility in anaerobic bacteraemia: a 15-year retrospective study in South-Eastern Hungary

INTRODUCTION

Bloodstream infections are considered as important factors of morbidity and represent a remarkable number of death, especially in developed countries.

METHODS

In a 15-year retrospective study in the South-Eastern region of Hungary, the microbiological results of anaerobic blood culture (BC) bottles were analysed. The incubation of BCs was performed in the automated incubation system, and the isolates were cultured in an anaerobic chamber. The identification of the isolates was based on their biochemical profile (2004-2012) and mass spectrometry analyses (2013-2018). Antibiotic susceptibility testing was performed with minimal inhibitory concentration gradient diffusion method.

RESULTS

The majority of the samples were submitted by the Department of Internal Medicine (37.7%), Intensive Care Unit (31.6%) and the Emergency Department (16.4%), and the number of strict anaerobic isolates per year showed an increasing tendency throughout the study. More than half of the isolates were Cutibacterium acnes (54.4%), but this bacterium was considered as a contaminant. The most frequent species upon Cutibacterium acnes were Bacteroides fragilis (9.2%), Clostridium perfringens (6.4%), other Clostridium species (4.8%), other Cutibacterium species (3.5%) and other Bacteroides species (2.5%). Penicillin, amoxicillin/clavulanic acid, imipenem, clindamycin, metronidazole and tigecyclin were very effective against Bacteroides fragilis, Clostridium perfringens, Fusobacterium nucleatum, Gemella morbillorum, Parvimonas micra and Eggerthella lenta strains.

CONCLUSION

We performed a 15-year period, retrospective investigation in South-Eastern Hungary with the participation of more than 1000 patients. The results of antibiotic susceptibility tests are in line with previous reports in the literature, and the results from the different geographical regions of the world suggest similar resistance mechanisms.

Diagnostic Value of 16S Ribosomal RNA Gene Polymerase Chain Reaction/Sanger Sequencing in Clinical Practice

BACKGROUND

Accurate microbiologic diagnosis is important for appropriate management of infectious diseases. Sequencing-based molecular diagnostics are increasingly used for precision diagnosis of infections. However, their clinical utility is unclear.

METHODS

We conducted a retrospective analysis of specimens that underwent 16S ribosomal RNA (rRNA) gene polymerase chain reaction (PCR) followed by Sanger sequencing at our institution from April 2017 through March 2019.

RESULTS

A total of 566 specimens obtained from 460 patients were studied. Patients were considered clinically infected or noninfected based on final diagnosis and management. In 17% of patients, 16S rRNA PCR/sequencing was positive and in 5% of patients, this test led to an impact on clinical care. In comparison, bacterial cultures were positive in 21% of patients. Specimens with a positive Gram stain had 12 times greater odds of having a positive molecular result than those with a negative Gram stain (95% confidence interval for odds ratio, 5.2-31.4). Overall, PCR positivity was higher in cardiovascular specimens (37%) obtained from clinically infected patients, with bacterial cultures being more likely to be positive for musculoskeletal specimens (P < .001). 16S rRNA PCR/sequencing identified a probable pathogen in 10% culture-negative specimens.

CONCLUSION

16S rRNA PCR/sequencing can play a role in the diagnostic evaluation of patients with culture-negative infections, especially those with cardiovascular infections.

In-hospital Outcomes of Infective Endocarditis from 1978 to 2015: Analysis Through Machine-Learning Techniques

Background

Early identification of patients with infective endocarditis (IE) at higher risk for in-hospital mortality is essential to guide management and improve prognosis.

Methods

A retrospective analysis was conducted of a cohort of patients followed up from 1978 to 2015, classified according to the modified Duke criteria. Clinical parameters, echocardiographic data, and blood cultures were assessed. Techniques of machine learning, such as the classification tree, were used to explain the association between clinical characteristics and in-hospital mortality. Additionally, the log-linear model and graphical random forests (GRaFo) representation were used to assess the degree of dependence among in-hospital outcomes of IE.

Results

This study analyzed 653 patients: 449 (69.0%) with definite IE; 204 (31.0%) with possible IE; mean age, 41.3 ± 19.2 years; 420 (64%) men. Mode of IE acquisition: community-acquired (67.6%), nosocomial (17.0%), undetermined (15.4%). Complications occurred in 547 patients (83.7%), the most frequent being heart failure (47.0%), neurologic complications (30.7%), and dialysis-dependent renal failure (6.5%). In-hospital mortality was 36.0%. The classification tree analysis identified subgroups with higher in-hospital mortality: patients with community-acquired IE and peripheral stigmata on admission; and patients with nosocomial IE. The log-linear model showed that surgical treatment was related to higher in-hospital mortality in patients with neurologic complications.

Conclusions

The use of a machine-learning model allowed identification of subgroups of patients at higher risk for in-hospital mortality. Peripheral stigmata, nosocomial IE, absence of vegetation, and surgery in the presence of neurologic complications are predictors of fatal outcomes in machine learning–based analysis.

Change of the Pattern of the Demographic Characteristics of the Patients with Endocarditis: Clinical Case of Infectious Endocarditis in Man with Injectible Drug Dependence, Complicated with Pneumonia and Peripheral Necroses of Feet, Arms, Nose (Own Clinical Observations and Experience of Education in State and English Language)

Infectious endocarditis is multisystem disease, which is the result of the infection (usually bacterial) of endocardial heart surface. Despite of the latest medical achievements in diagnostics and treatment, infectious endocarditis is still a disease with high mortality rate and severe complications. During last decades in developed countries there are obvious changes of demographic characteristics of the patients with infectious endocarditis, namely increasing of aged patients with degenerative valvular diseases, of patients with anamnesis of invasive manipulations and procedures. Beside with well known risk factors (artificial valves and implanted heart devices), there are increasing roles of injectible drug-dependence, human immunodeficiency virus and wide contact with health protection system as predisposing factors for infectious endocarditis. The article contains literature data of the main populational risk groups of infectious endocarditis. Clinical case of severe (fatal) infectious endocarditis in patient with injectible drug dependence is submitted. Special features of the case are peripheral dry necroses of feet, arms, nose, which are very close to the description of symmetrical peripheral gangrene. This rare disorder was first described by Hutchinson in 1891 in 37-year old man, who had gangrene of fingers, hands and ears after shock. Symmetrical peripheral gangrene can be induced by different infection and non-inflection causes. The majority of these cases are connected to the treatment of cardiogenic shock with disseminated intravascular coagulation. Submitted description of the case of symmetrical peripheral gangrene in patient with infectious endocarditis will be useful for different medical care specialists as a reminder of the necessity of constant monitoring of the skin color of the distal parts of the limbs in severe sick patients.

Development of high level daptomycin resistance (HLDR) in Abiotrophia and Granulicatella spp isolates from patients with infective endocarditis (IE)

Abiotrophia and Granulicatella species are fastidious organisms, representing around 1%-3% of infective endocarditis (IE). Little is known about the optimal antibiotic treatment of these species, and daptomycin has been suggested as a therapeutic option. We describe the antimicrobial profile in Abiotrophia and Granulicatella IE isolates, investigate high-level daptomycin resistance (HLDR) development and evaluate daptomycin activity in combination therapy. In vitro studies with 16 IE strains (6 A. defectiva, 9 G. adiacens and 1 G. elegans) were performed using microdilution to determine minimal inhibitory concentration (MIC) and time-kill methodology to evaluate combination therapy. Daptomycin non-susceptibility (DNS; MIC≥ 2 mg/L) and HLDR (MIC≥256 mg/L) were based on existing Clinical and Laboratory Standards (CLSI) breakpoints for viridans streptococci. All isolates were susceptible to vancomycin: G. adiacens was more susceptible to penicillin and ampicillin than A. defectiva (22% vs. 0%, and 67% vs. 33%) but less susceptible to ceftriaxone and daptomycin (56% vs. 83%, and 11% vs. 50%). HLDR developed in both A. defectiva (33%) and G. adiacens (78%) after 24h exposure to daptomycin. Combination therapy did not prevent the development of daptomycin resistance with ampicillin (2/3 strains), gentamicin (2/3 strains), ceftriaxone (2/3 strains) or ceftaroline (2/3 strains). Once developed, HLDR was stable for a prolonged time (>3 weeks) in G. adiacens, whereas in A. defectiva the HLDR it reversed to baseline MIC at day 10. This study is first to demonstrate rapid HLDR development in Abiotrophia and Granulicatella species in vitro. Resistance was stable, and most combination therapies did not prevent it.

Ultrastructural mitral valve abnormalities in infective endocarditis

Aim. Using an original method based on backscattered scanning electron microscopy, to study the structural features of the mitral valve leaflets in infective endocarditis.

Material and methods. We examined 9 mitral valves extracted during surgical interventions due to structural malfunction in patients with infective endocarditis (IE). The samples were fixed in buffered paraformaldehyde with osmium tetraoxide postfixation. After dehydration by increasing alcohol concentration and acetone, the samples were placed in epoxy resin. After the resin has polymerized, the samples were ground and then polished to the desired depth. To increase the electronic contrast, the samples were treated with a uranyl acetate alcohol solution during dehydration and with Reynolds' lead citrate after polishing the epoxy blocks. The samples were visualized by backscattered scanning electron microscopy at an accelerating 15-kV voltage.

Results. Structural leaflet injuries caused by IE were most pronounced in the central part and the base. Necrotic areas were extensive electron-dense formations located in the central leaflet layers, or displaced towards the ventricular surface. The electron-dense material in the necrotic area was poorly structured and contained individual cells and bacteria. Bacteria were also present outside the necrotic area. Necrotic areas were surrounded by a layer of a modified extracellular matrix, usually covered with a fibrin layer. Among the extracellular matrix fibers, the macrophages, smooth myocytes and fibroblasts was noted. The fibrin layer, in addition to these cells, contained a large number of blood vessels and was often covered with endothelium.

Conclusion. Infection of the mitral valve leaflets causes a simultaneous inflammatory response and regeneration activation. Without adequate regulatory factors, the processes of inflammation and connective tissue creation lead to structural and functional leaflet failure. Specific causes may be overgrowth of necrotic and inflammatory areas, edema and fiber orientation disorder, as well as leaflet rupture.

Blood culture negative endocarditis in the modern era of 16S rRNA sequencing

Blood culture negative endocarditis (BCNE) accounts for up to 20% of infective endocarditis. While the most common cause of BCNE remains the initiation of antibiotics prior to culture, intracellular organisms such as Coxiella and Bartonella spp account for a significant proportion of cases. Identifying the infecting organism remains important to ensure optimal antimicrobial treatment. However, these organisms can be difficult to diagnose. We outline a systematic approach to BCNE. Over half of patients with infective endocarditis now undergo early surgery and 16S ribosomal ribonucleic acid (rRNA) polymerase chain reaction (PCR) of excised tissue can be vitally important to secure a diagnosis. Molecular testing is likely to become a key tool in improving outcomes from BCNE and contribute to an improved understanding of the aetiology. We advocate modifying the Duke criteria to incorporate organisms identified on molecular testing, including 16S rRNA PCR, in particular from explanted tissue.

Evaluation of Laboratory Predictors for In-Hospital Mortality in Infective Endocarditis and Negative Blood Culture Pattern Characteristics

Objective: This study aimed to identify possible differences between blood culture-negative and blood culture-positive groups of infective endocarditis (IE), and explore the associations between biological parameters and in-hospital mortality. Methods: This was a retrospective study of patients hospitalized for IE between 2007 and 2017. Epidemiological, clinical and paraclinical characteristics, by blood culture-negative and positive groups, were collected. The best predictors of in-hospital mortality based on the receiver-operating characteristic (ROC) analysis and AUC (area under the curve) results were identified. Results: A total of 126 IE patients were included, 54% with negative blood cultures at admission. Overall, the in-hospital mortality was 28.6%, higher in the blood culture-negative than positive group (17.5% vs. 11.1%, p = 0.207). A significant increase in the Model for End-Stage Liver Disease Excluding International Normalized Ratio (MELD-XI) score was observed in the blood culture-negative group (p = 0.004), but no baseline characteristics differed between the groups. The best laboratory predictors of in-hospital death in the total study group were the neutrophil count (AUC = 0.824), white blood cell count (AUC = 0.724) and MELD-XI score (AUC = 0.700). Conclusion: Classic laboratory parameters, such as the white blood cell count and neutrophil count, were associated with in-hospital mortality in infective endocarditis. In addition, MELD-XI was a good predictor of in-hospital death.

Use of Plasma Metagenomic Next-generation Sequencing for Pathogen Identification in Pediatric Endocarditis

Pediatric infective endocarditis incurs significant morbidity and generally occurs among children with underlying heart disease. Identification of a pathogen is critical in determining appropriate therapy. However, standard diagnostic testing has limited sensitivity. We describe a case series of children with infective endocarditis in whom plasma next-generation sequencing (Karius, Redwood, CA) identified an organism in 8 of 10 cases.

Blood culture negative infective endocarditis in adult congenital heart disease patients with prosthetic grafts: a case series

Background

Blood culture negative infective endocarditis (BCNIE) is often a diagnostic challenge in adult congenital heart disease patients leading to misdiagnosis, treatment delay and associated high mortality. Studies of BCNIE in adult congenital heart disease patients repaired with prosthetic cardiovascular grafts are limited.

Case summary

We report two cases of BCNIE where serology testing, multiple polymerase chain reaction testing of explanted valve material and multi-modality imaging including ¹⁸F-fluorodeoxyglucose positron emission tomography/computed tomography (¹⁸F-FDG PET/CT) were utilized not only to confirm the diagnosis but also to guide management strategy and inform prognosis. Both patients were treated successfully with cardiac surgery and prolonged anti-microbial therapy.

Discussion

Clinical presentation of BCNIE in repaired CHD patients is highly variable. The symptoms are often non-specific with subacute or chronic presentation. This may mislead initial diagnosis and subsequent management. Multi-modality imaging including PET/CT should be considered to support the diagnosis, define the extent of infection, decide the management strategy and inform prognosis in patients. A thorough history of animal exposure, and consideration of serology and multiple molecular testing to identify the causative organism, is critical in the management of BCNIE.

Practical aspects of infective endocarditis prevention

The review is devoted to the practical aspects of infective endocarditis (IE) prevention, the issues of which, as before, remain the subject of lengthy discussions. Despite repeatedly updated national and international guidelines on this topic, medical practitioners are not always fully aware of antibiotic prophylaxis of IE. After a brief consideration of the etiological, pathogenetic features and risk factors of the disease, the main provisions of 2015 European Society of Cardiology guidelines on IE prevention, which were approved by the Russian Society of Cardiology, are presented. The categories of patients with the highest risk of IE, procedures associated with an increased risk of IE (dental and other invasive procedures) are described in detail. The main practical approaches to the identification of risk groups and performing invasive procedures that influence the decision to prescribe antibiotic prophylaxis are described. Particular attention is paid to the characteristics of both first-line antibiotic drugs and alternative agents for penicillin allergy or in cases of β-lactamase secreting pathogens.

Modern trends in identification of causative agents in infective endocarditis

Advances in the diagnosis and treatment of patients with infectious endocarditis are limited by the high frequency of cases with an unknown etiology and imperfection of microbiological (cultural) methods. To overcome these problems new approaches to the identification of infectious endocarditis pathogens were introduced, which allowed achieving certain positive results. However, it should be noted that despite the wide variety of diagnostic tools currently used, there is no ideal method for etiological laboratory diagnosis of infectious endocarditis. The article discusses the features and place of immunochemical, molecular biological (MALDI-TOF MS, real-time PCR, sequencing, in situ fluorescence hybridization, metagenomic methods, etc.), immunohistochemical methods, and their advantages and limitations.

Lawsonella clevelandensis: an emerging cause of vascular graft infection

Lawsonella clevelandensis, an emerging pathogen, was first described in 2016, and has been implicated in abdominal, breast and spinal abscesses in a limited number of cases. Being a fastidious organism, it is primarily identified with molecular methods. With the incorporation of broad-range PCR testing in clinical diagnostics, L. clevelandensis has been increasingly reported in the literature. We describe a case of a 65-year-old man who presented with bilateral psoas abscesses secondary to aorto-bi-iliac vascular graft infection with L. clevelandensis identified using 16S rRNA/PCR sequencing. The patient underwent surgical resection and replacement of infected graft, followed by 6 weeks of intravenous antibiotic therapy and then chronic suppression with doxycycline and cefadroxil. He was infection-free at last follow-up.

Identification of Leptotrichia goodfellowii infective endocarditis by next-generation sequencing of 16S rDNA amplicons

The oral aerotolerant anaerobe Leptotrichia goodfellowii is an unusual cause of endocarditis and is amenable to treatment with β-lactam antibiotics. Because this organism is difficult to identify by conventional methods, molecular detection is a key diagnostic modality. Broad-range 16S rDNA PCR followed by Sanger sequencing constitute the first-line molecular approach, yet poor DNA quality, contaminating DNA, or low template quantity make identification challenging. Here we report a case of culture-negative, aortic and mitral valve endocarditis in a 66-yr-old woman with a history of cardiomyopathy, atrial fibrillation with intracardiac pacer, poor dentition, and recent tooth infection. In this case, 16S rDNA amplicon Sanger sequencing was not sufficient for pathogen identification because of interfering DNA, but deconvolution of the clinical sample using reflexive next-generation amplicon sequencing enabled confident identification of a single pathogenic organism, L. goodfellowii. The patient developed a sigmoid colon perforation and died despite additional surgical treatment. Most Leptotrichia endocarditis cases have been subacute and have been successfully treated with antibiotics, with or without valve replacement. This case highlights both an unusual etiologic agent of endocarditis, as well as the rational utilization of advanced molecular diagnostics tools for characterizing serious infections.

[Infective Endocarditis with Unknown Etiology: Possibilities of Conquering and Role of Microbiologistics]

Current infectious endocarditis (IE) is characterized by changes in its etiological and epidemiological profiles associated with increased incidence of IE of undetermined etiology. This requires a search for ways to enhance the effectivity of diagnosis. Microbiologistics along with high-tech methods becomes decisively important for identifying the pathogen by studying cultures of blood and tissues from the affected heart valve. This determines timely diagnosis and treatment to be introduced to medical practice as a component of personalized medicine. The article focuses on the validity and features of microbiological (cultural), immunochemical, and molecular biological [MALDI-TOF MS (matrix-activated laser desorption/ionization with time-of-flight mass spectrometry), polymerase chain reaction, sequencing] studies.

A rare cause of culture negative bioprosthetic valve endocarditis: a case report of Aggregatibacter aphrophilus infection

Background

The prevalence of culture negative infective endocarditis (IEC) is reported as 2–7% though this figure may be as high as 70% in developing countries.¹ This higher rate will, at least in part, be due to reduced diagnostic facilities though some data suggests higher rates even when appropriate cultures were taken. The frequency is significantly elevated in patients who have already been exposed to antibiotics prior to blood cultures.^1,2 A rare cause of culture negative IEC is the HACEK group of organisms that are normal habitants of the oropharyngeal flora and account for 1–3% of native valve endocarditis.³Aggregatibacter aphrophilus (A. aphrophilus) is a member of the HACEK group of organisms.

Case summary

A 32-year-old gentleman with a previous bioprosthetic aortic valve presented with a 1-week history of diarrhoea, vomiting, malaise, and weight loss. He was awaiting redo surgery for stenosis of the bioprosthesis, which had been inserted aged 17 for aortic stenosis secondary to a bicuspid valve. The initial blood tests revealed liver and renal impairment with anaemia. A transoesophageal echocardiogram demonstrated a complex cavitating aortic root abscess, complicated by perforation into the right ventricle. He underwent emergency redo surgery requiring debridement of the aortic abscess, insertion of a mechanical aortic prosthesis (St Jude Medical, USA), annular reconstruction and graft replacement of the ascending aorta. Despite antibiotic therapy, he remained septic with negative blood and tissue cultures. Bacterial 16S rRNA gene sequencing confirmed A. aphrophilus infection, for which intravenous ceftriaxone was initiated. This was subsequently changed to ciprofloxacin due to neutropenia. The patient self-discharged from the hospital during the third week of antibiotic therapy. One week later, he was re-admitted with fever, night sweats, and dyspnoea. Transthoracic echocardiogram revealed a large recurrent aortic abscess cavity around the aortic annulus fistulating into the right heart chambers; this was confirmed by a computed tomography scan. There was dehiscence of the patch repair. Emergency redo aortic root replacement (25 mm mechanical valve conduit, ATS Medical, USA) and annular reconstruction was performed with venoarterial extracorporeal membrane oxygenation (VA-ECMO) support. VA-ECMO was weaned after 3 days. The patient completed a full course of intravenous meropenem and ciprofloxacin and made a good recovery.

Discussion

IEC with oropharyngeal HACEK organisms is rare and difficult to diagnose, due to negative blood culture results. The broad-range polymerase chain reaction and gene sequencing with comparison to the DNA database is useful in these circumstances. This case demonstrates the importance of the 16S rRNA gene sequencing for HACEK infection diagnosis and appropriate antibiotic treatment.

Molecular Approach to Diagnosis of Cardiovascular Implantable Electronic Device Infection

BACKGROUND

Sonicate fluid (SF), a solution derived from vortexing and sonication of explanted cardiovascular implantable electronic devices (CIEDs), is a higher-yield specimen compared with swabs or tissues for culture-based detection of microorganisms associated with CIED infection. Despite this, SF culture fails to identify a causative organism in ~50% of cases. We aimed to evaluate the diagnostic performance of 16S ribosomal RNA gene (rRNA) polymerase chain reaction (PCR)/sequencing of SF and compare it with that of SF culture.

METHODS

We identified 322 SF specimens from extracted CIEDs and reviewed clinical data for each patient. Subjects were classified as having or not having CIED infection. Cases were subcategorized as culture negative if no significant growth was reported from SF cultures and as culture positive if an organism was detected above predefined thresholds. 16S rRNA PCR/sequencing was performed, with the organisms identified reported according to Clinical and Laboratory Standards Institute guidelines for sequence data interpretation.

RESULTS

A total of 278 SF samples corresponded to infected cases, of which 160 were culture positive and 118 culture negative. The remaining 44 were from noninfected cases, of which 2 were culture positive. Compared with SF culture, the sensitivity of 16S rRNA PCR/sequencing was higher (64% vs 57.5%, P = .003). 16S rRNA PCR/sequencing detected a potential pathogen in 28 of 118 culture-negative cases, identifying staphylococci in the majority (18/28).

CONCLUSIONS

16S rRNA PCR/sequencing has higher sensitivity to detect bacteria in SF from extracted CIEDs than does SF culture.

Redo aortic valve replacement for prosthesis endocarditis in patients previously classified as high or prohibitive risk: a narrative review

Transcatheter aortic valve implantation (TAVI) and sutureless aortic valve replacement (Su-AVR) enabled in the last years many patients at high or prohibitive risk to be treated for their severe symptomatic aortic valve stenosis. As often happens in medicine, new techniques bring not only new hopes, but also new problems. In recent years, alongside the lengthening of the life of these patients treated with TAVI or Su-AVR, cardiologists and cardiac surgeons have had to face the long-term complications associated with the implantation of these devices, such as the prosthetic infective endocarditis. The correct management of prosthesis valve endocarditis after TAVI or Su-AVR in high risk patients, and the possible role of surgery are a matter of debate because pushing the limits of the modern medicine and becoming a new challenge for cardiac surgeons of 21^st century. In this review, we summarized the incidence, characteristics and evidences for this new and controversial problem of the cardiovascular community. Moreover, we investigated the outcomes reported in literature of the conservative and the surgical strategy. Although the reported mortality rate of surgical treatment is high, seems not prohibitive, mostly if compared to conservative medical therapy. The collaborative exchange between cardiologist, cardiac surgeons, clinical microbiologists and expert of imaging is mandatory to face this challenge.

Corynebacterium jeikeium native valve infective endocarditis case report: a confirmed microbiological and pathological diagnosis from heart valvular tissue

Background

The Modified Duke criteria is an important structured schematic for the diagnosis of infective endocarditis (IE). Corynebacterium jeikeium is a rare cause of IE that is often resistant to standard IE anti-microbials. We present a case of C. jeikeium IE, fulfilling the Modified Duke pathological criteria.

Case summary

A 50-year-old male presented with left leg peripheral vascular disease with septic changes requiring amputation. Routine echocardiography post-amputation demonstrated severe aortic valve regurgitation with vegetations that required valve replacement. Two initial blood cultures from a single venepuncture showed Streptococcus mitis which was treated with penicillin G prior to surgery. Subsequent aortic valve tissue cultured C. jeikeium with suggestive IE histological valvular changes and was successfully treated on a prolonged course of vancomycin.

Discussion

This is the first C. jeikeium IE case diagnosed on heart valvular tissue culture and highlights the importance for the fulfilment of the Modified Duke criteria in diagnosing left-sided IE. Mixed infection IE is rare, and this case possibly represents an unmasking of resistant C. jeikeium IE following initial treatment of penicillin G.

Esculin and ferric citrate-incorporated sturgeon skin gelatine as an antioxidant film for food packaging to prevent Enterococcus faecalis contamination

Herein, a sturgeon skin gelatine film combined with esculin and ferric citrate was developed as an edible food packaging material to prevent Enterococcus faecalis (E. faecalis) contamination. E. faecalis is able to hydrolyse esculin in the film, and then the hydrolysed product, esculetin, combines with ferric citrate to form a brown-black phenol iron complex. This phenomenon can be observed easily after 48 h of contamination under visible light, and it can be determined under 365 nm ultraviolet light with high sensitivity. With the addition of esculin and ferric citrate, the film showed better mechanical properties and water vapour permeability than those of the unmodified gelatine. When an increased amount of esculin was added, an increase in thermal stability, antioxidant activity, and antioxidant stability of the film was observed. These physicochemical characteristics are beneficial for developing a packaging material for food storage that mitigates foodborne illness caused by E. faecalis.

The role of endocarditis in sudden cardiac death: highlighting the value of the autopsy, pathological features and cardiac complications

OBJECTIVE

Endocarditis is increasing in incidence due to growing numbers of cardiac interventions, valve replacements and immunosuppressants. It can be difficult to diagnose clinically, has high mortality and can present as sudden cardiac death (SCD) with few/subtle preceding symptoms. True incidence of SCD related to endocarditis is unknown.

METHODS

Retrospective analysis of UK national database of 6000 cases of SCD, 1994-2020, for "endocarditis" as cause of death.

RESULTS

Of 30 cases (0.50%), 19(63%) were male and mean age was 36.2 ± 20.1 years. Postmortem examination showed the aortic valve was solely affected in 13 (43%), mitral in 9 (30%), tricuspid in 2(6.7%) and pulmonary in 1 (3.3%). Three cases (10%) had more than one valve affected and 2 (6.7%) were nonvalvular affecting the ascending aorta. Vegetations ranged from small easily missed irregularities to large fungating masses. Ten (33%) patients developed aortic abscesses, 2 of which had aneurysms, 13 (43%) had coronary artery septic emboli with micro-abscesses and myocardial microinfarction, and 2 (6.7%) were healed endocarditis with perforation and regurgitation with ventricular remodeling. Thirteen (43%) had an identifiable underlying valve abnormality or replacement, most common being a bicuspid aortic valve (7; 54%).

CONCLUSIONS

This study highlights that although rare, endocarditis is an important cause of SCD in those with normal valves, valvular disease and valve replacement surgery. Absence of a premortem diagnosis in 70% of our cohort highlights the need for detailed analysis of the heart and cardiac valves at autopsy. Gross appearance of vegetations varies widely and can be missed. Awareness of associated cardiac complications is required for elucidation of the cause of death and will provide valuable lessons for clinicians.

Case report: A fatal case of aortic and mitral valve endocarditis caused by Streptobacillus moniliformis

Background

Infective endocarditis (IE) secondary to rat-bite fever (RBF) is rare but potentially lethal. Rapid diagnosis is of utmost prognostic importance. However, the diagnosis of RBF is challenging because Streptobacillus moniliformis does not grow under conventional culture conditions.

Case summary

A 65-year-old male without previous cardiac history presented with sudden onset of balance problems and facial palsy. For 2 weeks, he had experienced intermittent fever and myalgia. Transoesophageal echocardiography (TOE) revealed severe mitral and aortic valve IE with aortic root abscess. The patient underwent a double biological valve replacement. Blood cultures remained negative after 9 days of incubation. However, sub-cultivation on solid media demonstrated the growth of pleomorphic Gram-negative rods, identified as S. moniliformis. After 4 weeks of antibiotic therapy, he was discharged. One month later, control TOE showed valve excrescences and aortic annular aneurysm. Despite comprehensive surgery, antibiotic treatment, and intensive care, the patient died 1 week after reoperation.

Discussion

A fatal outcome of S. moniliformis IE is rare. The majority of previous cases describe underlying valvular abnormalities or death due to insufficient antimicrobial therapy. Here, the patient had no prehistory of valvular heart disease and despite appropriate antibiotics, the outcome was fatal. Rapid diagnosis of RBF IE has prognostic implications. Identification of S. moniliformis is, however, difficult, because the bacterium is fastidious and does not grow under standard laboratory conditions. Therefore, diagnosis often relies on clinical symptoms or a history of rodent exposure. Close attention to this disease by clinicians, in addition to, dialogue with clinical microbiologists is essential.

Analysis of microbial changes in the tonsillar formalin-fixed paraffin-embedded tissue of Chinese patients with IgA nephropathy

BACKGROUND

Immunoglobulin A nephropathy (IgAN) is a prevalent chronic glomerular disease contribution to end-stage renal failure (ESRD). The tonsillar microbiota is closely associated with IgAN diseases based on the mucosal immune response. However, the composition and function of in tonsillar microbiota in participant patients with IgAN remains unknown. In this study, we detected the tonsillar microbiota changes of IgAN patients in Heilongjiang province located in northeast China.

MATERIAL AND METHODS

We collected from 21 patients with IgAN and 16 patients with chronic tonsillitis (CT) who had undergone tonsillectomy previously. Histological review of all samples from formalin-fixed paraffin-embedded (FFPE) tissue were performed. Extracted DNA from FFPE tissue blocks, after that V4 regions of 16S ribosomal RNA (rRNA) sequencing and comparative analyses of tonsillar flora between two groups were performed. The statistical analysis used the SPSS version of 21.

RESULTS

Visualization of microorganisms by Gram and Warthin-Starry (WS) silver stains, preliminarily observed the morphological characteristics of microbiome in FFPE tissue cases, such as bacteria or fungi. Tonsillar FFPE samples from the IgAN patients and CT controls showed significant differences in tonsillar microbial certain compositions and functions. We found that there were eight dominant genera that can be available to distinguish IgAN patients from CT controls. Compared with CT controls, at genus level, the relative abundances of Methylocaldum and unclassified_f_Prevotellaceae were significantly higher, while the abundances of Anaerosphaera, Halomonas, Trichococcus, Peptostreptococcus, norank_f_Synergistaceae and unclassified_k_norank_d_Bacteria were significantly lower in IgAN patients. Principal co-ordinates analysis (PCOA) distinguished IgAN patients from CT controls, and receiver operating characteristic (ROC) curves analysis confirmed that the diagnosis of disease has certain diagnostic significance. In addition, Functional analysis revealed that partly Enzymes and KOs were increased in the IgAN patients.

CONCLUSIONS

Histological screening results were very helpful for further gene sequencing, not only to supplement the observation of bacterial morphology and structure, but also to prepare for subsequent gene sequencing and bioinformatics analysis. We elucidated subtle relevance between changes in tonsillar microbiota and IgAN patients, which can be utilized to predict the incidence of IgAN disease. In addition, we predicted that some enzymes, and KOs were closely related to IgAN.

Microbiome Diagnostics

BACKGROUND

During the past decade, breakthroughs in sequencing technology and computational biology have provided the basis for studies of the myriad ways in which microbial communities ("microbiota") in and on the human body influence human health and disease. In almost every medical specialty, there is now a growing interest in accurate and replicable profiling of the microbiota for use in diagnostic and therapeutic application.

CONTENT

This review provides an overview of approaches, challenges, and considerations for diagnostic applications borrowing from other areas of molecular diagnostics, including clinical metagenomics. Methodological considerations and evolving approaches for microbiota profiling from mitochondrially encoded 16S rRNA-based amplicon sequencing to metagenomics and metatranscriptomics are discussed. To improve replicability, at least the most vulnerable steps in testing workflows will need to be standardized and continuous efforts needed to define QC standards. Challenges such as purity of reagents and consumables, improvement of reference databases, and availability of diagnostic-grade data analysis solutions will require joint efforts across disciplines and with manufacturers.

SUMMARY

The body of literature supporting important links between the microbiota at different anatomic sites with human health and disease is expanding rapidly and therapeutic manipulation of the intestinal microbiota is becoming routine. The next decade will likely see implementation of microbiome diagnostics in diagnostic laboratories to fully capitalize on technological and scientific advances and apply them in routine medical practice.

Brucella prosthetic valve endocarditis with septic and cardiogenic shock

A young man with aortic prosthetic valve replacement, presented with prolonged fever and diagnosed with brucella endocarditis based on positive transthoracic echo findings with high titer positive brucellacapt serology. He was started on medical treatment with doxycycline and rifampin to which gentamicin and ceftriaxone were added and he was planned for surgical intervention. Unfortunately, the patient developed cardiogenic with septic shock before performing surgery and died within 24 h soon after admission.

Clinical outcomes for congenital heart disease patients presenting with infective endocarditis

INTRODUCTION

Infective endocarditis (IE) is a life-threatening adverse event for patients with congenital heart disease (CHD). Its incidence has changed little over time despite progress in techniques for diagnosis and treatment, and guidelines for prophylaxis.

AREAS COVERED

The review sought for key-words: 'congenital heart disease,' 'infective endocarditis,' 'microbial diagnosis,' 'imaging diagnosis,' 'surgical techniques,' 'prognosis,' 'prophylaxis.' Objectives were to investigate epidemiology, novel techniques for imaging and microbial diagnosis, therapeutic management and prognosis, and guidelines for prophylaxis in patients with CHD. The incidence of IE is increasing in adults with CHD. Morbidity caused by a broad clinical spectrum of cardiac and extracardiac episode-related complications is high. Surgical management is increasingly required in the early phase of the disease. Despite new techniques for diagnosis and microbiological therapy, mortality rate is still up to 10-20%.

EXPERT OPINION

IE has increased in the growing cohort of adults with complex heart disease, living with residual cardiac lesions and prosthetic materials. Diagnosis is challenging for complex heart defects. Pet-scan technique can provide beneficial information to locate intracardiac lesions and embolic foci. Identification of the microbiological agents is improving. Innovative surgical techniques aim to avoid prosthetic material. Guidelines for prophylaxis currently emphasize oral and skin daily hygiene.

The diagnostic benefit of 16S rDNA PCR examination of infective endocarditis heart valves: a cohort study of 146 surgical cases confirmed by histopathology

Aims

Upon suspicion of infective endocarditis, the causative microorganism must be identified to optimize treatment. Blood cultures and culturing of removed valves are the mainstay of this diagnosis and should be complemented by growth-independent methods. We assessed the diagnostic benefit of examining removed endocarditis valves by broad-range bacterial PCR to detect causative bacteria in cases where culturing was not available, negative, or inconclusive because a skin commensal was detected, in patients from our clinical routine practice.

Methods and results

Patients from Heidelberg University Hospital with suspicion of endocarditis, followed by valve replacement and analysis by 16S rDNA PCR, between 2015 and 2018, were evaluated. 146 patients with definite infective endocarditis, confirmed by the valve macroscopics and/or histology, were included. Valve PCRs were compared to corresponding blood and valve culture results. Overall, valve PCR yielded an additional diagnostic benefit in 34 of 146 cases (23%) and was found to be more sensitive than valve culture. In 19 of 38 patients with both negative blood and valve cultures, valve PCR was the only method rendering a pathogen. In 23 patients with positive blood cultures detecting skin commensals, 4 patients showed discordant valve PCR results, detecting a more plausible pathogen, and in 11 of 23 cases, valve PCR confirmed commensals in blood culture as true pathogens. Only the remaining 8 patients had negative valve PCRs.

Conclusion

Valve PCR was found to be a valuable diagnostic tool in surgical endocarditis cases with negative blood cultures or positive blood cultures of unknown significance.

Trial registration

S-440/2017 on 28.08.2017 retrospectively registered.

Graphic abstract

Subdividing of all infective endocarditis patients in this study, showing that valve PCR yields valuable information for patients with skin commensals in blood cultures, which were either confirmed by the same detection in valve PCR or refuted by the detection of a different and typical pathogen in valve PCR. Additionally, benefit was determined in patients with negative or not available blood cultures and only positive detection in valve PCR. +: Positive; −: negative; n/a: not available results

Electronic supplementary material

The online version of this article (10.1007/s00392-020-01678-x) contains supplementary material, which is available to authorized users.

New approach to managing infective endocarditis

Despite significant diagnostic and therapeutic improvements, infective endocarditis (IE) still carries high morbidity and mortality. In the last three decades, significant variations in epidemiological and clinical profile of IE have been observed. The diagnosis of IE requires an adequate clinical suspicion, given its pleomorphic presentation. Microbiological and imaging techniques, which are pivotal in confirming the diagnosis, need constant refinement because of suboptimal accuracy. A clinically integrated multidisciplinary approach is recommended. Guidelines provide useful support despite being based mainly on the opinion of experts rather than on randomized trials, with some inconsistencies among different recommendations. This review encounters the current state of knowledge, gaps in evidence, and future research direction in the field of IE.

When Zoonotic Organisms Cross Over-Trueperella pyogenes Endocarditis Presenting as a Septic Embolic Stroke

Infective endocarditis (IE) remains a significant cause of morbidity and mortality worldwide, with numerous pathogens as culprits. We present a case of IE that evolved to a septic embolic stroke caused by an extremely rare bacteria Trueperella (T.) pyogenes that primarily infects non-humans. In contrast to most cases occurring outside the United States (US), this is the second case of T. pyogenes-associated endocarditis and the first to present as a stroke in the US. T. pyogenes has undergone numerous taxonomic revisions over the years since first being reported and characterized as Bacillus pyogenes in the 1800s. T. pyogenes is a zoonotic infection, and despite advancements in chemotaxonomic detection methods, Trueperella is often misidentified and under-diagnosed. Although epidemiological data is scarce, T. pyogenes infections have the propensity to cause endocarditis, and we aim to summarize all isolated reports of T. pyogenes infections that have been reported in the literature thus far.

The Versatility of Opportunistic Infections Caused by Gemella Isolates Is Supported by the Carriage of Virulence Factors From Multiple Origins

The molecular basis of the pathogenesis of the opportunistic invasive infections caused by isolates of the Gemella genus remains largely unknown. Moreover, inconsistencies in the current species assignation were detected after genome-level comparison of 16 public Gemella isolates. A literature search detected that, between the two most pathogenic species, Gemella morbillorum causes about twice the number of cases compared to Gemella haemolysans. These two species shared their mean diseases - sepsis and endocarditis - but differed in causing other syndromes. A number of well-known virulence factors were harbored by all species, such as a manganese transport/adhesin sharing 83% identity from oral endocarditis-causing streptococci. Likewise, all Gemellae carried the genes required for incorporating phosphorylcholine into their cell walls and encoded some choline-binding proteins. In contrast, other proteins were species-specific, which may justify the known epidemiological differences. G. haemolysans, but not G. morbillorum, harbor a gene cluster potentially encoding a polysaccharidic capsule. Species-specific surface determinants also included Rib and MucBP repeats, hemoglobin-binding NEAT domains, peptidases of C5a complement factor and domains that recognize extracellular matrix molecules exposed in damaged heart valves, such as collagen and fibronectin. Surface virulence determinants were associated with several taxonomically dispersed opportunistic genera of the oral microbiota, such as Granulicatella, Parvimonas, and Streptococcus, suggesting the existence of a horizontally transferrable gene reservoir in the oral environment, likely facilitated by close proximity in biofilms and ultimately linked to endocarditis. The identification of the Gemella virulence pool should be implemented in whole genome-based protocols to rationally predict the pathogenic potential in ongoing clinical infections caused by these poorly known bacterial pathogens.

Microbial biofilm correlates with an increased antibiotic tolerance and poor therapeutic outcome in infective endocarditis

Background

Infective endocarditis (IE) is associated with high rates of mortality. Prolonged treatments with high-dose intravenous antibiotics often fail to eradicate the infection, frequently leading to high-risk surgical intervention. By providing a mechanism of antibiotic tolerance, which escapes conventional antibiotic susceptibility profiling, microbial biofilm represents a key diagnostic and therapeutic challenge for clinicians. This study aims at assessing a rapid biofilm identification assay and a targeted antimicrobial susceptibility profile of biofilm-growing bacteria in patients with IE, which were unresponsive to antibiotic therapy.

Results

Staphylococcus aureus was the most common isolate (50%), followed by Enterococcus faecalis (25%) and Streptococcus gallolyticus (25%). All microbial isolates were found to be capable of producing large, structured biofilms in vitro. As expected, antibiotic treatment either administered on the basis of antibiogram or chosen empirically among those considered first-line antibiotics for IE, including ceftriaxone, daptomycin, tigecycline and vancomycin, was not effective at eradicating biofilm-growing bacteria. Conversely, antimicrobial susceptibility profile of biofilm-growing bacteria indicated that teicoplanin, oxacillin and fusidic acid were most effective against S. aureus biofilm, while ampicillin was the most active against S. gallolyticus and E. faecalis biofilm, respectively.

Conclusions

This study indicates that biofilm-producing bacteria, from surgically treated IE, display a high tolerance to antibiotics, which is undetected by conventional antibiograms. The rapid identification and antimicrobial tolerance profiling of biofilm-growing bacteria in IE can provide key information for both antimicrobial therapy and prevention strategies.

Utility of Histologic and Histochemical Screening for 16S Ribosomal RNA Gene Sequencing of Formalin-Fixed, Paraffin-Embedded Tissue for Bacterial Endocarditis

OBJECTIVES

16S ribosomal RNA (rRNA) sequencing is a powerful but expensive tool for the identification of bacteria in culture-negative endocarditis. Histologic criteria to screen formalin-fixed, paraffin-embedded (FFPE) specimens for testing are evaluated.

METHODS

Sixty-eight cases of infective endocarditis and controls were histologically reviewed and analyzed by 16S rRNA gene sequencing.

RESULTS

Sequencing identified a specific pathogenic organism in 33 (49%) of 68 cases with acute inflammation and in 0 of 10 controls (P = .004). Visualization of organisms by Gram or Grocott methenamine silver stains had the strongest association with positive sequencing, while antibiotic treatment effect and acid decalcification decreased sensitivity. Molecular identifications were concordant with blood culture results in 90% of the cases, and a positive sequencing result was obtained in approximately half of the cases with negative valve cultures.

CONCLUSIONS

Histologic screening criteria are extremely helpful for identifying cases likely to be positive by molecular testing and can provide significant cost savings in filtering out low-yield specimens.

Native Valve Infective Endocarditis with Osteomyelitis and Brain Abscess Caused by Granulicatella adiacens with Literature Review

Granulicatella adiacens is a type of NVS (nutritionally variant streptococci) rarely causing infective endocarditis (IE). NVS are fastidious and unable to sustain growth on routine culture media due to lack of specific nutrients. Endocarditis caused by NVS due to their virulence is associated with higher treatment failures and mortality rates. New antimicrobial susceptibility patterns are indicative of a significant rise in penicillin resistance and susceptibility differences between NVS subspecies. Initial empirical therapy is essential as a delay in using the appropriate agent leads to poor results. We present a case of an immunocompetent young female with recent intravenous drug abuse resulting in native mitral valve endocarditis with ruptured chordae tendineae and septic embolization, causing brain abscess and lumbar spine osteomyelitis. She was transferred to a tertiary center where she underwent mitral valve replacement successfully and treated with six weeks of intravenous vancomycin and ertapenem. To our knowledge, ours is the first case report of G. adiacens endocarditis in an adult with brain abscess and osteomyelitis with an excellent response to antibiotic therapy. Based on our case report, literature review, and new antimicrobial susceptibility patterns, updates to treatment guidelines are suggested to improve the therapeutic outcomes.