Host-pathogen interactions of clinical S. aureus isolates to induce infective endocarditis.

To evaluate potential pathomechanisms in the induction of infective endocarditis (IE), 34 Staphylococcus aureus (S. aureus) isolates, collected from patients with S. aureus endocarditis and from healthy individuals were investigated both in vitro and in vivo. S. aureus isolates were tested in vitro for their cytotoxicity, invasion and the association with platelets. Virulence factor expression profiles and cellular response were additionally investigated and tested for correlation with the ability of S. aureus to induce vegetations on the aortic valves in vivo. In an animal model of IE valvular conspicuity was assessed by in vivo magnetic resonance imaging at 9.4 T, histology and enrichment gene expression analysis. All S. aureus isolates tested in vivo caused a reliable infection and inflammation of the aortic valves, but could not be differentiated and categorized according to the measured in vitro virulence profiles and cytotoxicity. Results from in vitro assays did not correlate with the severity of IE. However, the isolates differed substantially in the activation and inhibition of pathways connected to the extracellular matrix and inflammatory response. Thus, comprehensive approaches of host-pathogen interactions and corresponding immune pathways are needed for the evaluation of the pathogenic capacity of bacteria. An improved understanding of the interaction between virulence factors and immune response in S. aureus infective endocarditis would offer novel possibilities for the development of therapeutic strategies and specific diagnostic imaging markers.

Borrelia burgdorferi infection induces long-term memory-like responses in macrophages with tissue-wide consequences in the heart.

Lyme carditis is an extracutaneous manifestation of Lyme disease characterized by episodes of atrioventricular block of varying degrees and additional, less reported cardiomyopathies. The molecular changes associated with the response to Borrelia burgdorferi over the course of infection are poorly understood. Here, we identify broad transcriptomic and proteomic changes in the heart during infection that reveal a profound down-regulation of mitochondrial components. We also describe the long-term functional modulation of macrophages exposed to live bacteria, characterized by an augmented glycolytic output, increased spirochetal binding and internalization, and reduced inflammatory responses. In vitro, glycolysis inhibition reduces the production of tumor necrosis factor (TNF) by memory macrophages, whereas in vivo, it produces the reversion of the memory phenotype, the recovery of tissue mitochondrial components, and decreased inflammation and spirochetal burdens. These results show that B. burgdorferi induces long-term, memory-like responses in macrophages with tissue-wide consequences that are amenable to be manipulated in vivo.

IgM ANCA in healthy individuals and in patients with ANCA-associated vasculitis.

Low levels of IgM auto-antibodies have been reported in health and disease. IgM anti-neutrophil cytoplasmic antibodies (ANCA) have been reported in patients with ANCA-associated vasculitis (AAV). We sought to investigate if healthy individuals may have IgM ANCA in their sera. The first aim of the study was to determine whether IgM ANCA was present in healthy individuals and in patients with ANCA-associated vasculitis. The second aim was to determine what happens to IgM ANCA levels over time. The third aim was to determine whether bacterial infections affected IgM ANCA levels in non-AAV patients. Sera from healthy individuals and patients with AAV were tested for IgM ANCA by immunofluorescence on fixed neutrophils, immunoprecipitation, Western blot and ELISA. Peripheral blood mononuclear cells were isolated and tested by ELISpot for circulating IgM ANCA B cells. To determine whether infection affected IgM ANCA levels, we studied non-AAV patients with bacterial endocarditis or Staphylococcus aureus bacteraemia and measured IgM ANCA levels over time. IgM ANCA is detectable in both healthy individuals and patients with AAV and the titres decreased with increasing age. Circulating IgM ANCA B cells were identified by ELISpot. In the presence of infection, we could not find a significant change in IgM ANCA levels. We report the presence of low-level specific IgM ANCA in the sera of healthy individuals and in patients with ANCA-associated vasculitis. Bacterial infection did not affect the level of IgM ANCA in this small study.

Recognition of specific sialoglycan structures by oral streptococci impacts the severity of endocardial infection.

Streptococcus gordonii and Streptococcus sanguinis are primary colonizers of the tooth surface. Although generally non-pathogenic in the oral environment, they are a frequent cause of infective endocarditis. Both streptococcal species express a serine-rich repeat surface adhesin that mediates attachment to sialylated glycans on mucin-like glycoproteins, but the specific sialoglycan structures recognized can vary from strain to strain. Previous studies have shown that sialoglycan binding is clearly important for aortic valve infections caused by some S. gordonii, but this process did not contribute to the virulence of a strain of S. sanguinis. However, these streptococci can bind to different subsets of sialoglycan structures. Here we generated isogenic strains of S. gordonii that differ only in the type and range of sialoglycan structures to which they adhere and examined whether this rendered them more or less virulent in a rat model of endocarditis. The findings indicate that the recognition of specific sialoglycans can either enhance or diminish pathogenicity. Binding to sialyllactosamine reduces the initial colonization of mechanically-damaged aortic valves, whereas binding to the closely-related trisaccharide sialyl T-antigen promotes higher bacterial densities in valve tissue 72 hours later. A surprising finding was that the initial attachment of streptococci to aortic valves was inversely proportional to the affinity of each strain for platelets, suggesting that binding to platelets circulating in the blood may divert bacteria away from the endocardial surface. Importantly, we found that human and rat platelet GPIbα (the major receptor for S. gordonii and S. sanguinis on platelets) display similar O-glycan structures, comprised mainly of a di-sialylated core 2 hexasaccharide, although the rat GPIbα has a more heterogenous composition of modified sialic acids. The combined results suggest that streptococcal interaction with a minor O-glycan on GPIbα may be more important than the over-all affinity for GPIbα for pathogenic effects.

Beyond Penicillin: Rapid Desensitization for Specific Flucloxacillin Hypersensitivity.

Beta-lactam therapy for severe staphylococcal infections is associated with superior outcomes, compared to non-beta-lactam therapy. For patients with immediate hypersensitivity to beta-lactams, desensitization has been widely employed to allow beta-lactam therapy, but published protocols for antistaphylococcal beta-lactams such as flucloxacillin are lacking. Here, we report a case and describe the desensitization protocol successfully used for a patient with isolated flucloxacillin immediate hypersensitivity, for whom a penicillin desensitization protocol would likely have resulted in an adverse drug reaction.

Surveillance for Q Fever Endocarditis in the United States, 1999-2015.

BACKGROUND: Q fever is a worldwide zoonosis caused by Coxiella burnetii. In some persons, particularly those with cardiac valve disease, infection with C. burnetii can cause a life-threatening infective endocarditis. There are few descriptive analyses of Q fever endocarditis in the United States. METHODS: Q fever case report forms submitted during 1999-2015 were reviewed to identify reports describing endocarditis. Cases were categorized as confirmed or probable using criteria defined by the Council for State and Territorial Epidemiologists (CSTE). Demographic, laboratory, and clinical data were analyzed. RESULTS: Of 140 case report forms reporting endocarditis, 49 met the confirmed definition and 36 met the probable definition. Eighty-two percent were male and the median age was 57 years (range, 16-87 years). Sixty-seven patients (78.8%) were hospitalized, and 5 deaths (5.9%) were reported. Forty-five patients (52.9%) had a preexisting valvulopathy. Eight patients with endocarditis had phase I immunoglobulin G antibody titers >800 but did not meet the CSTE case definition for Q fever endocarditis. CONCLUSIONS: These data summarize a limited set of clinical and epidemiological features of Q fever endocarditis collected through passive surveillance in the United States. Some cases of apparent Q fever endocarditis could not be classified by CSTE laboratory criteria, suggesting that comparison of phase I and phase II titers could be reexamined as a surveillance criterion. Prospective analyses of culture-negative endocarditis are needed to better assess the clinical spectrum and magnitude of Q fever endocarditis in the United States.

Physiopathological approach to infective endocarditis in chronic hemodialysis patients: left heart versus right heart involvement.

Infectious endocarditis (IE), a complication that is both cardiac and infectious, occurs frequently and is associated with a heavy burden of morbidity and mortality in chronic hemodialysis patients (CHD). About 2-6% of chronic hemodialysis patients develop IE and the incidence is 50-60 times higher among CHD patients than in the general population. The left heart is the most frequent location of IE in CHD and the different published series report a prevalence of left valve involvement varying from 80% to 100%. Valvular and perivalvular abnormalities, alteration of the immune system, and bacteremia associated with repeated manipulation of the vascular access, particularly central venous catheters, comprise the main factors explaining the left heart IE in CHD patients. While left-sided IE develops in altered valves in a high-pressure system, right-sided IE on the contrary, generally develops in healthy valves in a low-pressure system. Right-sided IE is rare, with its incidence varying from 0% to 26% depending on the study, and the tricuspid valve is the main location. Might the massive influx of pathogenic and virulent germs via the central venous catheter to the right heart, with the tricuspid being the first contact valve, have a role in the physiopathology of IE in CHD, thus facilitating bacterial adhesion? While the physiopathology of left-sided IE entails multiple and convincing mechanisms, it is not the case for right-sided IE, for which the physiopathological mechanism is only partially understood and remains shrouded in mystery.

A 1-Year-Old with Mycobacterium tuberculosis Endocarditis with Mass Spectrometry Analysis of Cardiac Vegetation Composition.

In this study, we report the first case of Mycobacterium tuberculosis endocarditis in an immunocompetent child born in the United States. Mass spectrometry of the vegetation identified coagulation, humoral immune proteins, neutrophil granule proteins, and histones. Few neutrophils on histopathology suggest that neutrophil extracellular traps may contribute to tuberculous endocardiac mass formation.

Antiphospholipid Antibody Syndrome With Valvular Vegetations in Acute Q Fever.

BACKGROUND: Coxiella burnetii endocarditis is considered to be a late complication of Q fever in patients with preexisting valvular heart disease (VHD). We observed a large transient aortic vegetation in a patient with acute Q fever and high levels of IgG anticardiolipin antibodies (IgG aCL). Therefore, we sought to determine how commonly acute Q fever could cause valvular vegetations associated with antiphospholipid antibody syndrome, which would be a new clinical entity. METHODS: We performed a consecutive case series between January 2007 and April 2014 at the French National Referral Center for Q fever. Age, sex, history of VHD, immunosuppression, and IgG aCL assessed by enzyme-linked immunosorbent assay were tested as potential predictors. RESULTS: Of the 759 patients with acute Q fever and available echocardiographic results, 9 (1.2%) were considered to have acute Q fever endocarditis, none of whom had a previously known VHD. After multiple adjustment, very high IgG aCL levels (>100 immunoglobulin G-type phospholipid units; relative risk [RR], 24.9 [95% confidence interval {CI}, 4.5-140.2]; P = .002) and immunosuppression (RR, 10.1 [95% CI, 3.0-32.4]; P = .002) were independently associated with acute Q fever endocarditis. CONCLUSIONS: Antiphospholipid antibody syndrome with valvular vegetations in acute Q fever is a new clinical entity. This would suggest the value of systematically testing for C. burnetii in antiphospholipid-associated cardiac valve disease, and performing early echocardiography and antiphospholipid dosages in patients with acute Q fever.

Moraxella osloensis, an emerging pathogen of endocarditis in immunocompromised patients?

We report two cases of endocarditis due to Moraxella osloensis. Only one previous case of such infection has been described. These infections occurred in immunocompromised patients (B-cell chronic lymphocytic leukaemia and kidney graft associated with Hodgkin's disease) and both patients had a favourable outcome with a complete cure of their infectious endocarditis. This bacterium could be an emerging pathogen revealed by MALDI-TOF. Indeed, its characterisation within the Moraxella group by use of biochemistry-based methods is difficult. Moreover, this strain could be particularly involved in immunocompromised patients.

The fibronectin-binding protein EfbA contributes to pathogenesis and protects against infective endocarditis caused by Enterococcus faecalis.

EfbA is a PavA-like fibronectin adhesin of Enterococcus faecalis previously shown to be important in experimental urinary tract infection. Here, we expressed and purified the E. faecalis OG1RF EfbA and confirmed that this protein binds with high affinity to immobilized fibronectin, collagen I, and collagen V. We constructed an efbA deletion mutant and demonstrated that its virulence was significantly attenuated (P < 0.0006) versus the wild type in a mixed inoculum rat endocarditis model. Furthermore, efbA deletion resulted in diminished ability to bind fibronectin (P < 0.0001) and reduced biofilm (P < 0.001). Reintroduction of efbA into the original chromosomal location restored virulence, adherence to fibronectin, and biofilm formation to wild-type levels. Finally, vaccination of rats with purified recombinant EfbA protein protected against OG1RF endocarditis (P = 0.008 versus control). Taken together, our results demonstrate that EfbA is an important factor involved in E. faecalis endocarditis and that rEfbA immunization is effective in preventing such infection, likely by interfering with bacterial adherence.

Imbalance of circulating lymphoid cells in Q fever endocarditis.

Q fever endocarditis is characterized by a defective cell-mediated immune response, which may be associated with the dysregulation of circulating subsets of immune cells. In this study, we found that naïve CD8(+) T lymphocytes and CD56dim natural killer cells were decreased patients whereas central memory CD8(+) T lymphocytes were increased. It is likely that these different subsets of immune cells play a role in the immunosuppression accompanying Q fever endocarditis.

Imbalance of circulating monocyte subsets and PD-1 dysregulation in Q fever endocarditis: the role of IL-10 in PD-1 modulation.

Q fever endocarditis, a severe complication of Q fever, is associated with a defective immune response, the mechanisms of which are poorly understood. We hypothesized that Q fever immune deficiency is related to altered distribution and activation of circulating monocyte subsets. Monocyte subsets were analyzed by flow cytometry in peripheral blood mononuclear cells from patients with Q fever endocarditis and controls. The proportion of classical monocytes (CD14(+)CD16(-) monocytes) was similar in patients and controls. In contrast, the patients with Q fever endocarditis exhibited a decrease in the non-classical and intermediate subsets of monocytes (CD16(+) monocytes). The altered distribution of monocyte subsets in Q fever endocarditis was associated with changes in their activation profile. Indeed, the expression of HLA-DR, a canonical activation molecule, and PD-1, a co-inhibitory molecule, was increased in intermediate monocytes. This profile was not restricted to CD16(+) monocytes because CD4(+) T cells also overexpressed PD-1. The mechanism leading to the overexpression of PD-1 did not require the LPS from C. burnetii but involved interleukin-10, an immunosuppressive cytokine. Indeed, the incubation of control monocytes with interleukin-10 led to a higher expression of PD-1 and neutralizing interleukin-10 prevented C. burnetii-stimulated PD-1 expression. Taken together, these results show that the immune suppression of Q fever endocarditis involves a cross-talk between monocytes and CD4(+) T cells expressing PD-1. The expression of PD-1 may be useful to assess chronic immune alterations in Q fever endocarditis.

Nontyphoidal cardiac salmonellosis: two case reports and a review of the literature.

Nontyphoidal Salmonella, especially Salmonella enterica, is a rare cause of endocarditis and pericarditis that carries a high mortality rate. Proposed predisposing conditions include immunodeficiency states, congenital heart defects, and cardiac valve diseases. We present 2 cases of cardiovascular salmonellosis. The first case is that of a 73-year-old woman with mechanical mitral and bioprosthetic aortic valves who died from sequelae of nontyphoidal Salmonella mitral valve vegetation, aortic valve abscess, and sepsis. The second case is that of a 62-year-old man with a recent systemic lupus erythematosus exacerbation treated with oral steroids, who presented with obstructive features of tamponade and sepsis secondary to a large S. enteritidis purulent pericardial cyst. He recovered after emergent pericardial drainage and antibiotic therapy. Identifying patients at risk of cardiovascular salmonellosis is important for early diagnosis and treatment to minimize sequelae and death. We reviewed the literature to identify the predisposing risk factors of nontyphoidal Salmonella cardiac infection.

A central role for carbon-overflow pathways in the modulation of bacterial cell death.

Similar to developmental programs in eukaryotes, the death of a subpopulation of cells is thought to benefit bacterial biofilm development. However mechanisms that mediate a tight control over cell death are not clearly understood at the population level. Here we reveal that CidR dependent pyruvate oxidase (CidC) and α-acetolactate synthase/decarboxylase (AlsSD) overflow metabolic pathways, which are active during staphylococcal biofilm development, modulate cell death to achieve optimal biofilm biomass. Whereas acetate derived from CidC activity potentiates cell death in cells by a mechanism dependent on intracellular acidification and respiratory inhibition, AlsSD activity effectively counters CidC action by diverting carbon flux towards neutral rather than acidic byproducts and consuming intracellular protons in the process. Furthermore, the physiological features that accompany metabolic activation of cell death bears remarkable similarities to hallmarks of eukaryotic programmed cell death, including the generation of reactive oxygen species and DNA damage. Finally, we demonstrate that the metabolic modulation of cell death not only affects biofilm development but also biofilm-dependent disease outcomes. Given the ubiquity of such carbon overflow pathways in diverse bacterial species, we propose that the metabolic control of cell death may be a fundamental feature of prokaryotic development.

Targeting pili in enterococcal pathogenesis.

Passive protection, the administration of antibodies to prevent infection, has garnered significant interest in recent years as a potential prophylactic countermeasure to decrease the prevalence of hospital-acquired infections. Pili, polymerized protein structures covalently anchored to the peptidoglycan wall of many Gram-positive pathogens, are ideal targets for antibody intervention, given their importance in establishing infection and their accessibility to antibody interactions. In this work, we demonstrated that a monoclonal antibody to the major component of Enterococcus faecalis pili, EbpC, labels polymerized pilus structures, diminishes biofilm formation, and significantly prevents the establishment of a rat endocarditis infection. The effectiveness of this anti-EbpC monoclonal provides strong evidence in support of its potential as a preventative. In addition, after radiolabeling, this monoclonal identified the site of enterococcal infection, providing a rare example of molecularly specific imaging of an established bacterial infection and demonstrating the versatility of this agent for use in future diagnostic and therapeutic applications.

Vaccination against Staphylococcus aureus pneumonia.

BACKGROUND: Staphylococcus aureus causes serious infections in both hospital and community settings. Attempts have been made to prevent human infection through vaccination against bacterial cell-surface antigens; thus far all have failed. Here we show that superantigens and cytolysins, when used in vaccine cocktails, provide protection from S. aureus USA100-USA400 intrapulmonary challenge. METHODS: Rabbits were actively vaccinated (wild-type toxins or toxoids) or passively immunized (hyperimmune serum) against combinations of superantigens (toxic shock syndrome toxin 1, enterotoxins B and C, and enterotoxin-like X) and cytolysins (α-, ß-, and γ-toxins) and challenged intrapulmonarily with multiple strains of S. aureus, both methicillin-sensitive and methicillin-resistant. RESULTS: Active vaccination against a cocktail containing bacterial cell-surface antigens enhanced disease severity as tested by infective endocarditis. Active vaccination against secreted superantigens and cytolysins resulted in protection of 86 of 88 rabbits when challenged intrapulmonarily with 9 different S. aureus strains, compared to only 1 of 88 nonvaccinated animals. Passive immunization studies demonstrated that production of neutralizing antibodies was an important mechanism of protection. CONCLUSIONS: The data suggest that vaccination against bacterial cell-surface antigens increases disease severity, but vaccination against secreted virulence factors provides protection against S. aureus. These results advance our understanding of S. aureus pathogenesis and have important implications in disease prevention.