Interleukin 1alpha increases the susceptibility of rabbits to experimental viridans streptococcal endocarditis

Efficacy of Antibiotic Prophylactic Regimens for the Prevention of Bacterial Endocarditis of Oral Origin

Despite the controversy about the risk of individuals developing bacterial endocarditis of oral origin, numerous Expert Committees in different countries continue to publish prophylactic regimens for the prevention of bacterial endocarditis secondary to dental procedures. In this paper, we analyze the efficacy of antibiotic prophylaxis in the prevention of bacteremia following dental manipulations and in the prevention of bacterial endocarditis (in both animal models and human studies). Antibiotic prophylaxis guidelines remain consensus-based, and there is scientific evidence of the efficacy of amoxicillin in the prevention of bacteremia following dental procedures, although the results reported do not confirm the efficacy of other recommended antibiotics. The majority of studies on experimental models of bacterial endocarditis have verified the efficacy of antibiotics administered after the induction of bacteremia, confirming the efficacy of antibiotic prophylaxis in later stages in the development of bacterial endocarditis. There is no scientific evidence that prophylaxis with penicillin is effective in reducing bacterial endocarditis secondary to dental procedures in patients considered to be "at risk". It has been suggested that there is a high risk of severe allergic reactions secondary to prophylactically administered penicillins, but, in reality, very few cases have been reported in the literature. It has been demonstrated that antibiotic prophylaxis could contribute to the development of bacterial resistance, but only after the administration of several consecutive doses. Future research on bacterial endocarditis prophylactic protocols should involve the re-evaluation of the time and route of administration of antibiotic prophylaxis, and a search for alternative antimicrobials.

Genetic variants in genes of the inflammatory response in association with infective endocarditis

Aims

Inflammation in infective endocarditis (IE) is a complex network including interactions of inflammatory cytokines and other components of host response. Certainly, any variation in this network could influence susceptibility or disease progression of IE. In this study, 14 single nucleotide variants (SNVs) in genes coding for interleukin-1β, interleukin-6, interleukin-10, toll–like receptor-4, tumor necrosis factor-α, selectin E and intercellular adhesion molecule-1 were analyzed for an association with susceptibility to IE and correlated with disease-related laboratory parameters. Furthermore, the occurrence of SNVs was examined to elucidate pathogen-dependent associations.

Methods and Results

The distribution of SNVs was determined in IE-patients and healthy blood donors by RFLP analysis. White blood cells (WBC) were counted using flow cytometry, concentration of C-reactive protein and procalcitonin was measured immunologically. Interleukin-6 c.471+870G>A genotypes differed significantly between IE patients and controls. The frequency of the heterozygote genotype GA was considerably higher in the patient group (68.9% vs. 43.8%, P_c<0.0003). Interleukin-6 c.-237 minor allele frequency was increased in patients, although not statistically significant. Additionally, we detected a potential relation between interleukin-1β c.315C>T and IE. Pathogen-dependent analysis showed no significantly associated subgroup in relation to IE susceptibility, but gave hints towards alterations regarding Enterococcus-caused IE cases. Patients with genotype selectin-E c.-19 GT tend to have higher preoperative WBC counts than patients with genotype GG. We further showed an association between two interleukin-1β SNVs and laboratory biomarkers.

Conclusion

This study shows genetic predispositions for the establishment of IE. Furthermore, correlation of SNVs with disease-related biomarkers suggests a role of genetic variants regarding the inflammatory response in IE.

Glycoprotein Ibα and FcγRIIa play key roles in platelet activation by the colonizing bacterium, Streptococcus oralis

BACKGROUND

Infective endocarditis (IE) is characterized by thrombus formation on a cardiac valve. The oral bacterium, Streptococcus oralis, is recognized for its ability to colonize damaged heart valves and is frequently isolated from patients with IE. Platelet interaction with S. oralis leads to the development of a thrombotic vegetation on heart valves, which results in valvular incompetence and congestive heart failure.

OBJECTIVE

To investigate the mechanism through which platelets become activated upon binding S. oralis.

PATIENTS AND METHODS

Platelet interactions with immobilized bacteria under shear conditions were assessed using a parallel flow chamber. S. oralis-inducible platelet reactivity was determined using light transmission aggregometry. Dense granule secretion was measured by luminometry using a luciferin/luciferase assay.

RESULTS

Using shear rates that mimic physiological conditions, we demonstrated that S. oralis was able to support platelet adhesion under venous (50-200 s(-1) ) and arterial shear conditions (800 s(-1) ). Platelets rolled along immobilized S. oralis through an interaction with GPIbα. Following rolling, platelet microaggregate formation was observed on immobilized S. oralis. Aggregate formation was dependent on S. oralis binding IgG, which cross-links to platelet FcγRIIa. This interaction led to phosphorylation of the ITAM domain on FcγRIIa, resulting in dense granule secretion, amplification through the ADP receptor and activation of RAP1, culminating in platelet microaggregate formation.

CONCLUSIONS

These results suggest a model of interaction between S. oralis and platelets that leads to the formation of a stable septic vegetation on damaged heart valves.

Use of a human-like low-grade bacteremia model of experimental endocarditis to study the role of Staphylococcus aureus adhesins and platelet aggregation in early endocarditis

Animal models of infective endocarditis (IE) induced by high-grade bacteremia revealed the pathogenic roles of Staphylococcus aureus surface adhesins and platelet aggregation in the infection process. In humans, however, S. aureus IE possibly occurs through repeated bouts of low-grade bacteremia from a colonized site or intravenous device. Here we used a rat model of IE induced by continuous low-grade bacteremia to explore further the contributions of S. aureus virulence factors to the initiation of IE. Rats with aortic vegetations were inoculated by continuous intravenous infusion (0.0017 ml/min over 10 h) with 10(6) CFU of Lactococcus lactis pIL253 or a recombinant L. lactis strain expressing an individual S. aureus surface protein (ClfA, FnbpA, BCD, or SdrE) conferring a particular adhesive or platelet aggregation property. Vegetation infection was assessed 24 h later. Plasma was collected at 0, 2, and 6 h postinoculation to quantify the expression of tumor necrosis factor (TNF), interleukin 1α (IL-1α), IL-1β, IL-6, and IL-10. The percentage of vegetation infection relative to that with strain pIL253 (11%) increased when binding to fibrinogen was conferred on L. lactis (ClfA strain) (52%; P = 0.007) and increased further with adhesion to fibronectin (FnbpA strain) (75%; P < 0.001). Expression of fibronectin binding alone was not sufficient to induce IE (BCD strain) (10% of infection). Platelet aggregation increased the risk of vegetation infection (SdrE strain) (30%). Conferring adhesion to fibrinogen and fibronectin favored IL-1β and IL-6 production. Our results, with a model of IE induced by low-grade bacteremia, resembling human disease, extend the essential role of fibrinogen binding in the initiation of S. aureus IE. Triggering of platelet aggregation or an inflammatory response may contribute to or promote the development of IE.

Prophylaxis of Infective Endocarditis: Prevention of the Perfect Storm

Despite the availability of endocarditis prophylaxis guidelines for more than five decades, no prospective, randomised trial has ever been conducted to evaluate the efficacy and safety of this practice. This fact, in combination with mixed results from case-control investigations and other factors, has prompted a re-evaluation of the appropriateness of the guidelines. The update provided herein highlights recent revisions in guidelines promulgated by different countries.

Rapid tissue factor induction by oral streptococci and monocyte-IL-1beta

The ability of pro-inflammatory cytokines to promote coagulation prompted the hypothesis that pro-inflammatory cytokines induced by oral streptococci might play a role in the pathogenesis of viridans endocarditis. We used supernatant fluids from peripheral blood mononuclear monocyte (PBMC) cultures, stimulated for just 4-6 hrs with representative streptococcal isolates, to study cytokines that promoted endothelial tissue factor (TF) activity. Neutralizing antibodies demonstrated that interleukin-1beta (IL-1beta) was a major early endothelial TF inducer, and that recombinant IL-1beta was comparable with the supernatant fluid in activity. IL-1beta-rich supernatant fluids from oral streptococci-stimulated or lipopolysaccharide-stimulated PBMC cultures up-regulated the expression of endothelial ICAM-1 and E-selectin. These molecules could help trap TF-producing monocytes or dendritic cells bearing streptococci at the site. Thus, the rapid IL-1beta-inducing capacity of oral streptococci could facilitate the early deposition of bacteria in fibrin clots and promote endocarditis.

New concepts in the pathophysiology of infective endocarditis

Endocarditis pathogens colonize valves with pre-existing sterile vegetations or valves with minimal endothelial lesions. Inflamed endothelia produce cytokines, integrins, and tissue factor, which in turn attract fibronectin, monocytes, and platelets. Bacteria attaching to such structures further activate the cascade, becoming embedded and protected from host defenses. Staphylococcus aureus also actively invade the endothelium, causing apoptosis and endothelial damage. Knowledge of this interplay identifies host factors as potential therapeutic targets. Blocking infection by modulating host factors might be opportune because host factors are conserved. In contrast, interfering with bacterial virulence factors might be more complicated because they vary among different bacteria.