Influence of aspirin on development and treatment of experimental Staphylococcus aureus endocarditis

Antithrombotic Therapy in Patients With Infective Endocarditis: A Systematic Review and Meta-Analysis

Background

Antithrombotic therapy (ATT) in patients with infective endocarditis (IE) is challenging.

Objectives

The authors evaluated the impact of anticoagulant and antiplatelet therapy on clinical endpoints in IE patients.

Methods

We performed a systematic review and meta-analysis comparing IE patients with prior and/or ongoing use of ATT vs those without any ATT during IE course. Primary outcome was reported in-hospital cerebrovascular events. Secondary outcomes were in-hospital mortality, intracranial hemorrhage (ICH), systemic thromboembolism (ST), and mortality within 6 months.

Results

Twelve studies, with a total of 12,151 patients, were included. The primary endpoint was not different comparing 10,115 IE patients with or without prior anticoagulation (OR: 1.10; 95% CI: 0.56-2.17; P = 0.77) or comparing 838 IE patients with or without prior antiplatelet (OR: 0.90; 95% CI: 0.61-1.33; P = 0.61). In-hospital mortality was lower in IE patients with prior anticoagulation compared to those without (OR: 0.74; 95% CI: 0.57-0.96; P = 0.03). There was no difference in reported ICH rates between patients with or without prior anticoagulation (OR: 0.54; 95% CI: 0.27-1.09; P = 0.09) or between patients with or without prior antiplatelet (OR: 0.35; 95% CI: 0.11-1.10; P = 0.07). The rate of ST was lower in IE patients with prior antiplatelet therapy compared to those without (OR: 0.53; 95% CI: 0.38-0.72; P < 0.01).

Conclusions

ATT in IE patients was not associated with higher frequency of cerebrovascular events or ICH. Moreover, we found that the use of anticoagulation was associated with decreased in-hospital mortality and the use of antiplatelets was associated with decreased ST. Due to the limitations of this study, these results should be interpreted cautiously showing the necessity of a randomized setup.

Salicylic acids and pathogenic bacteria: new perspectives on an old compound

Salicylic acids have been used in human and veterinary medicine for their anti-pyretic, anti-inflammatory, and analgesic properties for centuries. A key role of salicylic acid-immune modulation in response to microbial infection-was first recognized during studies of their botanical origin. The effects of salicylic acid on bacterial physiology are diverse. In many cases, they impose selective pressures leading to development of cross-resistance to antimicrobial compounds. Initial characterization of these interactions was in Escherichia coli, where salicylic acid activates the multiple antibiotic resistance (mar) operon, resulting in decreased antibiotic susceptibility. Studies suggest that stimulation of the mar phenotype presents similarly in closely related Enterobacteriaceae. Salicylic acids also affect virulence in many opportunistic pathogens by decreasing their ability to form biofilms and increasing persister cell populations. It is imperative to understand the effects of salicylic acid on bacteria of various origins to illuminate potential links between environmental microbes and their clinically relevant antimicrobial-resistant counterparts. This review provides an update on known effects of salicylic acid and key derivatives on a variety of bacterial pathogens, offers insights to possible potentiation of current treatment options, and highlights cellular regulatory networks that have been established during the study of this important class of medicines.

Diflunisal and Analogue Pharmacophores Mediating Suppression of Virulence Phenotypes in Staphylococcus aureus

Invasive methicillin-resistant Staphylococcus aureus (MRSA) infections are leading causes of morbidity and mortality that are complicated by increasing resistance to conventional antibiotics. Thus, minimizing virulence and enhancing antibiotic efficacy against MRSA is a public health imperative. We originally demonstrated that diflunisal (DIF; [2-hydroxy-5-(2,4-difluorophenyl) benzoic acid]) inhibits S. aureus virulence factor expression. To investigate pharmacophores that are active in this function, we evaluated a library of structural analogues for their efficacy to modulate virulence phenotypes in a panel of clinically relevant S. aureus isolates in vitro. Overall, the positions of the phenyl, hydroxyl, and carboxylic moieties and the presence or type of halogen (F vs. Cl) influenced the efficacy of compounds in suppressing hemolysis, proteolysis, and biofilm virulence phenotypes. Analogues lacking halogens inhibited proteolysis to an extent similar to DIF but were ineffective at reducing hemolysis or biofilm production. In contrast, most analogues lacking the hydroxyl or carboxylic acid groups did not suppress proteolysis but did mitigate hemolysis and biofilm production to an extent similar to DIF. Interestingly, chirality and the substitution of fluorine with chlorine resulted in a differential reduction in virulence phenotypes. Together, this pattern of data suggests virulence-suppressing pharmacophores of DIF and structural analogues integrate halogen, hydroxyl, and carboxylic acid moiety stereochemistry. The anti-virulence effects of DIF were achieved using concentrations that are safe in humans, do not impair platelet antimicrobial functions, do not affect S. aureus growth, and do not alter the efficacy of conventional antibiotics. These results offer proof of concept for using novel anti-virulence strategies as adjuvants to antibiotic therapy to address the challenge of MRSA infection.

Diflunisal Attenuates Virulence Factor Gene Regulation and Phenotypes in Staphylococcus aureus

Virulence factor expression is integral to pathogenicity of Staphylococcus aureus. We previously demonstrated that aspirin, through its major metabolite, salicylic acid (SAL), modulates S. aureus virulence phenotypes in vitro and in vivo. We compared salicylate metabolites and a structural analogue for their ability to modulate S. aureus virulence factor expression and phenotypes: (i) acetylsalicylic acid (ASA, aspirin); (ii) ASA metabolites, salicylic acid (SAL), gentisic acid (GTA) and salicyluric acid (SUA); or (iii) diflunisal (DIF), a SAL structural analogue. None of these compounds altered the growth rate of any strain tested. ASA and its metabolites SAL, GTA and SUA moderately impaired hemolysis and proteolysis phenotypes in multiple S. aureus strain backgrounds and their respective deletion mutants. Only DIF significantly inhibited these virulence phenotypes in all strains. The kinetic profiles of ASA, SAL or DIF on expression of hla (alpha hemolysin), sspA (V8 protease) and their regulators (sigB, sarA, agr (RNAIII)) were assessed in two prototypic strain backgrounds: SH1000 (methicillin-sensitive S. aureus; MSSA) and LAC-USA300 (methicillin-resistant S. aureus; MRSA). DIF induced sigB expression which is coincident with the significant inhibition of RNAIII expression in both strains and precedes significant reductions in hla and sspA expression. The inhibited expression of these genes within 2 h resulted in the durable suppression of hemolysis and proteolysis phenotypes. These results indicate that DIF modulates the expression of key virulence factors in S. aureus via a coordinated impact on their relevant regulons and target effector genes. This strategy may hold opportunities to develop novel antivirulence strategies to address the ongoing challenge of antibiotic-resistant S. aureus.

Low-Dose Aspirin for Venous Thromboembolism Prophylaxis is Associated With Lower Rates of Periprosthetic Joint Infection After Total Joint Arthroplasty

BACKGROUND

Aspirin as a venous thromboembolism (VTE) prophylactic agent has been shown to have antistaphylococcal and antibiofilm roles. Optimal acetylsalicylic acid (ASA) dosage would facilitate antimicrobial effects while avoiding over-aggressive inhibition of platelet antimicrobial function. Our purpose was to determine the periprosthetic joint infection (PJI) rate after total joint arthroplasty in patients receiving low-dose ASA (81 mg twice a day), in comparison to high-dose ASA (325 mg twice a day).

METHODS

We conducted a retrospective cohort study between 2008 and 2020. Eligible patients were older than 18 years, underwent primary total joint arthroplasty, both total knee arthroplasty and total hip arthroplasty, had a minimum 30-day follow-up, and received a full course ASA as VTE prophylaxis. Patients' records were reviewed for PJI, according to Musculoskeletal Infection Society criteria. Patients were excluded if they underwent revision arthroplasty, had a history of coagulopathy, or had an ASA regimen that was not completed. In total 15,825 patients were identified, 8,761 patients received low-dose ASA and 7,064 received high-dose ASA.

RESULTS

The high-dose cohort had a higher PJI rate (0.35 versus 0.10%, P = .001). This relationship was maintained when comparing subgroups comprising total knee arthroplasty (0.32 versus 0.06%, P = .019) or total hip arthroplasty (0.38 versus 0.14%, P = .035) and accounting for potentially confounding demographic and surgical variables (odds ratio = 2.59, 95% CI = 1.15-6.40, P = .028).

CONCLUSION

Comparing low-dose to high-dose ASA as a VTE prophylactic agent, low-dose ASA had a lower PJI rate. This may be attributable to a balance of anti-infective properties of ASA and antiplatelet effects.

Role of sodium salicylate in Staphylococcus aureus quorum sensing, virulence, biofilm formation and antimicrobial susceptibility

The widespread threat of antibiotic resistance requires new treatment options. Disrupting bacterial communication, quorum sensing (QS), has the potential to reduce pathogenesis by decreasing bacterial virulence. The aim of this study was to investigate the influence of sodium salicylate (NaSa) on Staphylococcus aureus QS, virulence production and biofilm formation. In S. aureus ATCC 25923 (agr III), with or without serum, NaSa (10 mM) downregulated the agr QS system and decreased the secretion levels of alpha-hemolysin, staphopain A and delta-hemolysin. Inhibition of agr expression caused a downregulation of delta-hemolysin, decreasing biofilm dispersal and increasing biofilm formation on polystyrene and titanium under static conditions. In contrast, NaSa did not increase biofilm biomass under flow but caused one log₁₀ reduction in biofilm viability on polystyrene pegs, resulting in biofilms being twice as susceptible to rifampicin. A concentration-dependent effect of NaSa was further observed, where high concentrations (10 mM) decreased agr expression, while low concentrations (≤0.1 mM) increased agr expression. In S. aureus 8325-4 (agr I), a high concentration of NaSa (10 mM) decreased hla expression, and a low concentration of NaSa (≤1 mM) increased rnaIII and hla expression. The activity of NaSa on biofilm formation was dependent on agr type and material surface. Eight clinical strains isolated from prosthetic joint infection (PJI) or wound infection belonging to each of the four agr types were evaluated. The four PJI S. aureus strains did not change their biofilm phenotype with NaSa on the clinically relevant titanium surface. Half of the wound strains (agr III and IV) did not change the biofilm phenotype in the 3D collagen wound model. In addition, compared to the control, ATCC 25923 biofilms formed with 10 mM NaSa in the collagen model were more susceptible to silver. It is concluded that NaSa can inhibit QS in S. aureus, decreasing the levels of toxin production with certain modulation of biofilm formation. The effect on biofilm formation was dependent on the strain and material surface. It is suggested that the observed NaSa inhibition of bacterial communication is a potential alternative or adjuvant to traditional antibiotics.

Staphylococcus aureus increases platelet reactivity in patients with infective endocarditis

Thromboembolism is frequent in infective endocarditis (IE). However, the optimal antithrombotic regimen in IE is unknown. Staphylococcus aureus (SA) is the leading cause of IE. First studies emphasize increased platelet reactivity by SA. In this pilot study, we hypothesized that platelet reactivity is increased in patients with SA− IE, which could be abrogated by antiplatelet medication. We conducted a prospective, observatory, single-center cohort study in 114 patients with IE, with four cohorts: (1) SA coagulase positive IE without aspirin (ASA) medication, (2) coagulase negative IE without ASA, (3) SA coagulase positive IE with ASA, (4) coagulase negative IE with ASA. Platelet function was measured by Multiplate electrode aggregometry, blood clotting by ROTEM thromboelastometry. Bleeding events were assessed according to TIMI classification. In ASA-naïve patients, aggregation with ADP was increased with coag. pos. IE (coagulase negative: 39.47 ± 4.13 AUC vs. coagulase positive: 59.46 ± 8.19 AUC, p = 0.0219). This was abrogated with ASA medication (coagulase negative: 42.4 ± 4.67 AUC vs. coagulase positive: 45.11 ± 6.063 AUC p = 0.7824). Aspirin did not increase bleeding in SA positive patients. However, in SA negative patients with aspirin, red blood cell transfusions were enhanced. SA coagulase positive IE is associated with increased platelet reactivity. This could be abrogated by aspirin without increased bleeding risk. The results of this pilot study suggest that ASA might be beneficial in SA coagulase positive IE. This needs to be confirmed in clinical trials.

Coagulation Disorders in Infective Endocarditis: Role of Pathogens, Biomarkers, Antithrombotic Therapy (Systematic Review)

The issue of antithrombotic therapy in patients with infective endocarditis has been studied for over 75 years. During that time studying of pathogenesis of the disease and its embolic complications, lead to the introduction of the concept of “immunothrombosis”. That mechanism allows infective agents (mostly bacteria) to be cloaked from the immune system and to multiply freely, leading to growth of vegetation, thus resulting in higher chance of fragmentation. Small-scale experimental and clinical studies on the correction of hemostatic disorders in infective endocarditis, that were performed in 20th century, didn’t show any significant results, that could affect clinical practice. However, reinterpretation of available data on coagulative system will allow to have elements of hemostasis as an application point in treating infective endocarditis. The article will discuss latest insights on the role of hemostasis system in pathophysisology of infective endocarditis, its effects on the development of the embolic complications, perspectives for diagnostics and treatment.

Aspirin and Infection: A Narrative Review

Acetylsalicylic acid (ASA) is one of the most commonly used drugs in the world. It derives from the extract of white willow bark, whose therapeutic potential was known in Egypt since 1534 BC. ASA’s pharmacological effects are historically considered secondary to its anti-inflammatory, platelet-inhibiting properties; however, human studies demonstrating a pro-inflammatory effect of ASA exist. It is likely that we are aware of only part of ASA’s mechanisms of action; moreover, the clinical effect is largely dependent on dosages. During the past few decades, evidence of the anti-infective properties of ASA has emerged. We performed a review of such research in order to provide a comprehensive overview of ASA and viral, bacterial, fungal and parasitic infections, as well as ASA’s antibiofilm properties.

A Retrospective Review of the Natural Progression of Cardiac Vegetation

Introduction: Infective endocarditis (IE) is a life-threatening condition with an annual mortality of up to 40%. Vegetations are the hallmark of IE, however, factors that affect the initial size and changes in size remain unclear. Our study aims to investigate the natural history of cardiac vegetation, including changes in size and/or resolution with adequate treatment, and to analyze factors that influence size and potential for persistence.

Material and methods: We conducted a retrospective review of 102 patients admitted with native-valve endocarditis at Henry Ford Health System from September 1, 2017, to June 30, 2019. We included patients treated with six weeks of intravenous antibiotics who had both a diagnostic and a follow-up echocardiogram after antibiotic completion.

The primary outcome was the change in vegetation size. Secondary measures included pathogen identification, valve involvement, number of complications, associated IV drug use, and co-infection with hepatitis B/C.

Results: Of the 102 patients reviewed, 30 patients matched the inclusion criteria. There was a significant decrease in vegetation size after adequate antibiotic treatment. However, complete resolution was not often seen. A statistically significant relationship was seen between vegetation size, IV drug use, and Staphylococcal species (including both methicillin-susceptible Staphylococcus aureus [MSSA] and methicillin-resistant S. aureus [MRSA]), whereas a history of hepatitis B or C was not significantly related to vegetation size.

Conclusion: Large vegetation may predict a higher risk of embolic complications and can be reduced with IV antibiotics, although complete resolution is not likely. IV drug use and Staphylococcal endocarditis influence vegetation size and embolic complications. We argue that these subgroups should be prioritized for early surgical intervention.

The role of antiaggregant agents and anticoagulants in the prevention of aortic valve endocarditis: A double-cohort retrospective study

Objective

Antiaggregants (Ag) could prevent infective endocarditis (IE) in preclinical studies. In this study we investigated whether Ag or anticoagulants (Ac) were also protective in humans.

Methods

In part I we determined the incidence of IE of bioprosthetic aortic valves (PVE) in 333 consecutive patients who underwent aortic valve replacement for noninfective aortic insufficiency between 2009 and 2019. In part II we retrospectively analyzed data of 137 patients who had developed IE of the native aortic valve (NVE) between 2007 and 2015. Multivariable Fine–Gray and logistic regression models were used to investigate associations between Ag and Ac therapy and IE.

Results

Sixteen of 333 (4.8%) aortic valve replacement recipients developed PVE after a median of 3.72 years. There was no association between Ag and PVE, whereas Ac was associated with a higher IE occurrence (no association for vitamin K antagonists but significant for fondaparinux or low molecular-weight heparins; hazard ratio, 4.61; 95% CI, 1.01-21.9). In contrast, among the 137 patients in part II, vitamin K antagonists (odds ratio [OR], 7.52; 95% CI, 2.51-22.6), double antiplatelet therapy (OR, 44.3; 95% CI, 4.83-407), novel oral Ac (OR, 4.17; 95% CI, 1.15-15.1), and fondaparinux or low molecular-weight heparins (OR, 9.87; 95% CI, 1.81-53.9), but not acetylsalicylic acid, were associated with NVE.

Conclusions

Ac were associated with IE in both cohorts, whereas Ag were not associated with PVE. This might reflect differences in the studied populations, with Ag and Ac being prescribed for conditions associated with long-term IE risk in the NVE cohort. Therefore, determining the potential protective effect of Ag and Ac will necessitate further well–controlled studies.

Aspirin or Ticagrelor in Staphylococcus aureus Infective Endocarditis: Where Do We Stand?

Infective endocarditis is a challenging disease with a high mortality and morbidity rate. Antibiotic prophylaxis is currently recommended in high-risk infective endocarditis patients. However, the use of antibiotics faces the challenge of a low efficacy and contributes further to the emerging infection rate by antibiotic-resistant strains, emphasizing the need for new therapeutic strategies. Platelets are essential in the initial phase of infective endocarditis, acting as first-line immune responders. During the first phase of disease, bacteria can interact with platelets and counteract platelet antimicrobial activities. Mechanistic in vitro and animal studies on the effect of aspirin on bacteria-platelet interactions and the prevention of vegetation development showed promising results. However, data from clinical studies on the outcome of infective endocarditis patients who were receiving medically indicated aspirin therapy remain controversial. Therefore, the benefit of antiplatelet agents in infective endocarditis prevention has been questioned. Besides aspirin, it has been discovered that the platelet P2Y12 receptor antagonist ticagrelor has antibacterial properties in addition to its potent antiplatelet activity. Furthermore, a recent study in mice and a case report remarkably indicated the ability of this drug to eradicate Staphylococcus aureus bacteremia. This review will focus on current knowledge on antibacterial activity of ticagrelor, compared to aspirin, pointing out main unanswered questions. The goal is to provide food for thought as to whether a prior ticagrelor therapy might be beneficial for the prevention of infective endocarditis.

Aspirin Effect on Staphylococcus aureus-Platelet Interactions During Infectious Endocarditis

Infectious endocarditis (IE) is a rare disease associated with high mortality and morbidity rate. The platelet-bacterial interaction presents the cornerstone of the development of endocardial vegetation. The epidemiology of IE has undergone profound changes between the last and the new decade, with Staphylococcus aureus becoming the main incriminated species. Despite improvements in antibiotic and surgical therapies, embolic disorders remain highly associated with IE that can be fatal. Antiplatelet drugs have been widely proposed to overcome embolic events associated with IE. This proposal has been supported by numerous in vitro, experimental, and clinical studies. However, other studies have yielded conflicting results. In this review, we focus on the effect of aspirin on the genesis of S. aureus endocarditic vegetation, as well as on the management of embolic and hemorrhagic events related to it, starting by its influence on the platelet-bacteria interaction.

Meloxicam inhibits biofilm formation and enhances antimicrobial agents efficacy by Pseudomonas aeruginosa

Microbial biofilms are communities of surface‐adhered cells enclosed in a matrix of extracellular polymeric substances. Bacterial cells in biofilm are 10~1,000‐fold more resistant to antimicrobials than the planktonic cells. Burgeoning antibiotic resistance in Pseudomonas aeruginosa biofilm has necessitated the development of antimicrobial agents. Here, we have investigated the antibiofilm effect of meloxicam against P. aeruginosaPAO1 and its potential mechanisms. Further, we have explored whether meloxicam could enhance the susceptibility of bacterial biofilms to treatment with conventional antimicrobials. Here, we found that meloxicam could significantly inhibit PAO1 biofilm formation in a dose‐dependent manner at the concentration without influence on planktonic cell growth. Meloxicam could also significantly inhibit the motilities, production of extracellular matrix, and expression of quorum sensing‐related genes and virulence factors of PAO1. Furthermore, synergistic interaction was observed when meloxicam combined with tetracycline, gentamicin, tobramycin, ciprofloxacin, ceftriaxone, ofloxacin, norfloxacin, ceftazidime, and DNase at subminimal inhibitory concentrations against PAO1 bioiflm. Collectively, our study lays the foundation for further investigation of repurposing meloxicam as a topical antibiofilm agent to treat P. aeruginosa biofilm‐related infections.

Anti-thrombotic therapy in infective endocarditis

Despite advances in medical and surgical treatment, infective endocarditis (IE) still carries a high risk of morbidity and mortality. One of the determinants of an adverse outcome is the presence of systemic embolization and in particular, of CNS embolization. IE vegetations consist of bacteria, platelets and inflammatory cells in a fibrin mesh. The interactions between pathogens, platelets and the coagulation system are critical to vegetation initiation and growth. This understanding has led to the study of the effect of anti-thrombotic treatment on IE vegetation formation and embolization. Although it has been demonstrated that antiplatelet and anticoagulant strategies have an impact on in vitro and animal models of IE, results from the available clinical studies are conflicting. In this article, we provide an overview of the available experimental and clinical data on anti-thrombotic treatment in IE and summarize the current guidelines. An early diagnosis, prompt empiric antibiotic treatment and a careful selection of patients who benefit from early surgical intervention remain essential in the prevention of embolic complications. In patients who have other indications for antiplatelet or anticoagulant treatment, the continuation of this treatment is deemed safe in the absence of hemorrhagic complications.

Modifiers of symptomatic embolic risk in infective endocarditis

OBJECTIVE

To ascertain the impact of prior antiplatelet and statin therapy on symptomatic embolic events in [corrected] infective endocarditis (IE).

PATIENTS AND METHODS

We studied a retrospective cohort of adult patients with a diagnosis of IE who presented to Mayo Clinic (Rochester, MN) from January 1, 2003, to December 31, 2006. Patients were grouped into those who received treatment before infection or controls who did not receive treatment for both antiplatelet therapy and, separately, statin therapy. Because of the retrospective study design and thus the nonrandomized treatment groups, a propensity score approach was used to account for the confounding factors that may have influenced treatment allocation. Antiplatelet therapy included aspirin, dipyridamole, clopidogrel, ticlopidine or any combination of these agents. Statin therapy included atorvastatin, simvastatin, pravastatin, lovastatin, rosuvastatin, or fluvastatin. The primary end point was a symptomatic embolic event that occurred before or during hospitalization. Multivariable logistic regression was used to assess the propensity-adjusted effects of continuous daily therapy with antiplatelet and statin agents on risk of symptomatic emboli. Likewise, Cox proportional hazards regression was used to test for an independent association with 6-month mortality for each of the treatments.

RESULTS

The study cohort comprised 283 patients with [corrected] IE. Twenty-eight patients (24.1%) who received prior continuous antiplatelet therapy developed a symptomatic embolic event compared with 66 (39.5%) who did not receive such treatment. After adjusting for propensity to treat, the effect of antiplatelet therapy on embolic risk was not statistically significant (odds ratio, 0.71; 95% confidence interval [CI], 0.37-1.36; P=.30). Only 14 patients (18.2%) who received prior continuous statin therapy developed a symptomatic embolic event compared with 80 (39.4%) of the 203 patients who did not. After adjusting for propensity to treat with statin therapy, the benefit attributable to statins was significant (odds ratio, 0.30; 95% CI, 0.14-0.62; P=.001). The 6-month mortality rate of the entire cohort was 28% (95% CI, 23%-34%). No significant difference was found in the propensity-adjusted rate of 6-month mortality between patients who had and had not undergone prior antiplatelet therapy (P=.91) or those who had and had not undergone prior statin therapy (P=.87).

CONCLUSION

The rate of symptomatic emboli associated with IE was reduced in patients who received continuous daily statin therapy before onset of IE. Despite fewer embolic events observed in patients who received antiplatelet agents, a significant association was not found after adjusting for propensity factors. A continued evaluation of these drugs and their potential impact on subsequent embolism among IE patients is warranted.

Is there a role for antiplatelet therapy in infective endocarditis? A review of current scientific evidence

Recently, interest has emerged regarding adjuvant antiplatelet therapy in infective endocarditis (IE) and its impact on clinical outcomes. Despite ongoing research, the role of antiplatelet therapy in this setting remains unclear. Generally, investigations of IE are limited by the low incidence of the disease, practical issues related to diagnosis, and the highly variable latency period between symptom onset and definitive diagnosis. This article reviews the rationale for using antiplatelet therapy in the setting of IE and the contemporary literature that investigates its use.

Influence of ticlopidine on the development of experimental Staphylococcus aureus endocarditis

Previously, we have shown that aspirin administration reduces the bacterial density and weight of aortic vegetations in a rabbit model of Staphylococcus aureus endocarditis. In the present paper, we sought to determine if ticlopidine, another potent inhibitor of platelet aggregation, also influences the development of endocarditis. Animals received either no ticlopidine (control), or oral doses of 10, 50, and 100 mg/kg daily. The 10 and 100 mg/kg treated groups had a statistically significant reduction of the vegetative weight as compared with the untreated controls. Although the 50 mg/kg dose did not result in a statistically significant difference (P = 0.058) in weight when compared with control, this dose also produced a substantial reduction in aortic value vegetation weights. None of the ticlopidine doses tested significantly altered the bacterial density relative to untreated controls. These findings suggest that ticlopidine alters the development of cardiac vegetations and may be useful agent for the prevention and/or treatment of infective endocarditis.

Impact of Prior Antiplatelet Therapy on Risk of Embolism in Infective Endocarditis

BACKGROUND

Embolism is a dreaded complication of infective endocarditis (IE). Currently, antimicrobial therapy is the only medical intervention proven to decrease the risk of embolism associated with IE. We hypothesized that, because platelet aggregation is operative in the pathogenesis of vegetation formation, embolism associated with IE should occur less frequently among patients who have received prior, continuous daily antiplatelet therapy for noninfectious reasons.

METHODS

We studied a retrospective cohort of adult patients with a diagnosis of IE who presented to the Mayo Clinic (Rochester, MN) during 1980-1998. The cohort was divided into 2 groups on the basis of whether they had received continuous daily antiplatelet therapy for at least 6 months prior to the time of hospitalization for IE. Antiplatelet therapy included aspirin, dipyridamole, clopidogrel, ticlopidine, or any of combination of these agents. The primary end point was a symptomatic embolic event that occurred prior to or during hospitalization. Multivariable logistic regression was used to assess the impact of continuous daily antiplatelet therapy on risk of symptomatic emboli associated with IE.

RESULTS

One hundred forty-seven (24.5%) of 600 patients experienced a symptomatic embolic event; the most common embolic manifestation was stroke (in 48.2% of patients). Embolic events occurred significantly less often among those who had received prior, continuous daily antiplatelet therapy (12.0% of patients who had received therapy vs. 27.8% patients who had not receive therapy; P<.001). After adjustment for several covariates known to influence both risk of embolism and propensity for antiplatelet use, the adjusted odds ratio for a symptomatic embolic event was 0.36 (95% confidence interval, 0.19-0.68; P=.002) for patients receiving continuous daily antiplatelet therapy.

CONCLUSIONS

The risk of symptomatic emboli associated with IE was reduced in patients who received continuous daily antiplatelet therapy before onset of IE.

Antimicrobial peptides versus invasive infections

It has been estimated that there are more microorganisms within and upon the human body than there are human cells. By necessity, every accessible niche must be defended by innate mechanisms to prevent invasive infection, and ideally that precludes the need for robust inflammatory responses. Yet the potential for pathogens to transcend the integument actively or passively and access the bloodstream emphasizes the need for rapid and potent antimicrobial defense mechanisms within the vascular compartment. Antimicrobial peptides from leukocytes have long been contemplated as being integral to defense against these infections. Recently, platelets are increasingly recognized for their likely multiple roles in antimicrobial host defense. Platelets and leukocytes share many structural and functional archetypes. Once activated, both cell types respond in specific ways that emphasize key roles for their antimicrobial peptides in host defense efficacy: (a) targeted accumulation at sites of tissue injury or infection; (b) direct interaction with pathogens; and (c) deployment of intracellular (leukocyte phagosomes) or extracellular (platelet secretion) antimicrobial peptides. Antimicrobial peptides from these cells exert rapid, potent, and direct antimicrobial effects against organisms that commonly access the bloodstream. Experimental models in vitro and in vivo show that antimicrobial peptides from these cells significantly contribute to prevent or limit infection. Moreover, certain platelet antimicrobial proteins are multifunctional kinocidins (microbicidal chemokines) that recruit leukocytes to sites of infection, and potentiate the antimicrobial mechanisms of these cells. In turn, pathogens pre-decorated by kinocidins may be more efficiently phagocytosed and killed by leukocytes and their antimicrobial peptide arsenal. Hence, multiple and relevant interactions between platelets and leukocytes have immunologic functions yet to be fully understood. A clearer definition of these interactions, and the antimicrobial peptide effectors contributing to these functions, will significantly advance our understanding of antimicrobial host defense against invasive infection. In addition, this knowledge may accelerate development of novel anti-infective agents and strategies against pathogens that have become refractory to conventional antimicrobials.

Aspirin treatment for neonatal infectious endocarditis

We describe a term female neonate with Serratia marcescens endocarditis. Despite adequate antibiotic therapy for 8 days, the bacteremia persisted and there was an increase in vegetation size. Treatment with aspirin was initiated, with resolution of the bacteremia and a gradual decrease in vegetation size. We conclude that in neonatal endocarditis, aspirin may be beneficial additional treatment.

Influence of acetylsalicylic acid (aspirin) on biofilm production by Candida species

Candida spp. are important causative agents of infections associated with biofilm formation. Management of biofilm-related infections is extremely difficult and therefore new therapeutic solutions are needed. This study for the first time explored the possible effect of aspirin on Candida spp. Biofilm-producing capacity. Two strains of C. guilliermondii, and one strain per species of C. kefyr, C. glabrata, C. albicans, and C. parapsilosis were included in the study. The antifungal property of aspirin was tested by the broth microdilution method, while effect of aspirin on biofilm formation was determined by the microtiter-plate test. The minimal inhibitory concentrations of aspirin obtained ranged from 2.17 to 8.67 mM and minimal fungicidal concentrations were from 4.33 to 8.67 mM. The concentrations of aspirin which induced statistically significant decrease in biofilm formation ranged from 0.43 mM to 1.73 mM of aspirin, depending on the tested yeast strain. Therefore, the significant effects of aspirin on growth and biofilm formation of Candida spp. were achieved only with suprapharmacological concentrations of the drug. The influence of the inoculum size on the effect of aspirin on biofilm formation was determined for C. albicans only and a significant decrease was observed also at suprapharmacological concentrations of aspirin, irrespective of the inoculum size. The results obtained in the present study show aspirin to be a drug with the potential to affect and suppress biofilm formation by Candida spp., and provide support for further investigation.

Fluid Shear Regulates the Kinetics and Receptor Specificity ofStaphylococcus aureusBinding to Activated Platelets

The interaction between surface components on the invading pathogen and host cells such as platelets plays a key role in the regulation of endovascular infections. However, the mechanisms mediating Staphylococcus aureus binding to platelets under shear remain largely unknown. This study was designed to investigate the kinetics and molecular requirements of platelet-S. aureus interactions in bulk suspensions subjected to a uniform shear field. Hydrodynamic shear-induced collisions augment platelet-S. aureus binding, which is further potentiated by platelet activation with stromal derived factor-1beta. Peak adhesion efficiency occurs at low shear (100 s(-1)) and decreases with increasing shear. The molecular interaction of platelet alpha(IIb)beta(3) with bacterial clumping factor A through fibrinogen bridging is necessary for stable bacterial binding to activated platelets under shear. Although this pathway is sufficient at low shear (</=400 s(-1)), the involvement of platelet gpIb and staphylococcal protein A through von Willebrand factor bridging is essential for optimal recruitment of S. aureus cells by platelets in the high shear regime. IgG plays an inhibitory role in the adhesion process, presumably by interfering with the binding of von Willebrand factor to staphylococcal protein A. This study demonstrates that platelet activation and a fluid-mechanical environment representative of the vasculature affect platelet-S. aureus cell-adhesive interactions pertinent to the process of S. aureus-induced bloodstream infections.

Soluble fibrin is the main mediator of Staphylococcus aureus adhesion to platelets

BACKGROUND

Infective endocarditis (IE) caused by Staphylococcus aureus is associated with significant morbidity and mortality rates. Platelets play a dual role as adhesive cells forming associates with bacteria as well as specialized inflammatory cells. The specific role of the various factors involved in bacteria-platelet association has not yet been fully elucidated.

METHODS AND RESULTS

We observed a dramatic increase in the capability to bind S aureus when platelets were activated with thrombin (from 5% to 30%, P<0.001). To pinpoint platelet-binding sites involved in the interaction, platelets from knockout mice and from patients with selective inherited deficiency of membrane proteins or of granules were used. CD36, GPIIb/IIIa, and P-selectin were excluded as receptors for S aureus. Platelets from patients with alpha-delta-storage pool disease and Gray platelet syndrome indicate the requirement of alpha-granule contents. Platelet activation by ADP did not promote platelet-S aureus associate formation, although these platelets were covered with bound fibrinogen. Only small numbers of associates between fibrinogen-covered bacteria and ADP-activated platelets were observed. Formation of fibrin alone was also not sufficient to induce association. Only when fibrin formation and platelet activation occurred together were large numbers of associates formed (P<0.001). A potential receptor for fibrin on S aureus is clumping factor A. Addition of thrombospondin-1 to control platelets increased the number of associates (P=0.02).

CONCLUSIONS

Soluble fibrin but not fibrinogen is the main mediator of platelet-S aureus association. In addition, platelet activation and the release of alpha-granule contents, particularly thrombospondin-1, is a requirement for platelet-S aureus association.

Recent trends in infective endocarditis: influence of case definitions

PURPOSE OF REVIEW

Infective endocarditis continues to pose major challenges in diagnosis and management despite advances in understanding the epidemiology, microbiology, and pathology of the disease. The purpose of this article is to provide a review of diagnosis, microbiology, and treatment of infective endocarditis, particularly as they are influenced by case definitions.

RECENT FINDINGS

Case definitions have a critical effect on the interpretation of trends in infective endocarditis, and recent studies have proposed more specific criteria. Studies have also addressed the appropriate use of echocardiography to assist in the diagnosis and management of infective endocarditis. Staphylococcus aureus has become an increasingly common cause of infective endocarditis, and the microbiology of nosocomial infective endocarditis is changing. Newer techniques are being used to aid in the identification of causal agents in blood culture-negative infective endocarditis. Antimicrobial guidelines for the treatment of infective endocarditis are readily available, including a proposal to avoid premature discharge of patients on outpatient antibiotic therapy. Additional studies have been conducted on combination antibiotic therapy, duration of treatment, dosing of aminoglycosides, alternative agents for gram-positive organisms, aspirin therapy, and surgical interventions.

SUMMARY

Recent trends in diagnosis, microbiology, and treatment of infective endocarditis are described, and case definitions play a critical role in their interpretation.

A randomized trial of aspirin on the risk of embolic events in patients with infective endocarditis

OBJECTIVES

This study examined the effect of aspirin on the risk of embolic events in infective endocarditis (IE).

BACKGROUND

Embolism is a major complication of IE, and studies in animal models have shown that platelet inhibition with aspirin can lead to more rapid vegetation resolution and a lower rate of embolic events.

METHODS

We conducted a randomized, double-blinded, placebo-controlled trial of aspirin treatment (325 mg/day) for four weeks in patients with IE to test the hypothesis that the addition of aspirin would reduce the incidence of clinical systemic embolic events. Patients with perivalvular abscess were excluded. Serial cerebral computed tomograms and transesophageal echocardiograms were obtained in a subset of patients.

RESULTS

During the four-year study period, 115 patients were enrolled: 60 assigned to aspirin and 55 assigned to placebo. Embolic events occurred in 17 patients (28.3%) on aspirin and 11 patients (20.0%) on placebo, with an odds ratio (OR) of 1.62 (95% confidence interval [CI] 0.68 to 3.86, p = 0.29). There was a trend toward a higher incidence of bleeding in the patients taking aspirin versus placebo (OR 1.92, 95% CI 0.76 to 4.86, p = 0.075). Development of new intracranial lesions was similar in both groups. Aspirin had no effect on vegetation resolution and valvular dysfunction.

CONCLUSIONS

In endocarditis patients already receiving antibiotic treatment, the addition of aspirin does not appear to reduce the risk of embolic events and is likely associated with an increased risk of bleeding. Aspirin is not indicated in the early management of patients with IE.

Risk factors for "major" embolic events in hospitalized patients with infective endocarditis

BACKGROUND

Infective endocarditis often is complicated by embolic events after hospital admission. Identifying patients at higher risk may improve the disease outcome. This study was aimed at identifying predictors of embolic risk among the clinical and laboratory data obtained on hospital admission in patients diagnosed as having definite infective endocarditis according to the Duke criteria.

METHODS

Ninety-four patients were enrolled in a prospective study. The results of hematologic, echocardiographic, and microbiological investigations were analyzed, using statistical methods as appropriate. Multivariate analysis was applied to variables significantly associated with embolism in univariate analysis.

RESULTS

Forty-six percent of patients had a major embolic complication after admission. No association was found between embolism and sex, site of infection, or microorganism involved. Patients with embolism were significantly younger, had larger vegetation, and showed a significantly higher level of serum C-reactive protein and lower albumin concentrations than those without embolism. Young age, larger vegetation size, and high levels of C-reactive protein were the independent variables associated with an increased incidence of embolic events in the multivariate logistic regression analysis.

CONCLUSIONS

Our data indicate that patients with infective endocarditis with young age and/or with large vegetation and/or with high serum levels of C-reactive protein are at increased risk of major embolic complications during the in-hospital course of the disease.

Platelets and Platelet Inhibitors in Infective Endocarditis

The pathogenesis of infective endocarditis depends on complex interactions between the causative pathogen, plasma proteins, platelets, and vascular endothelial cells. In addition to being the main target of bacteria in the initial stage of bacterial adherence to the endocardium, platelets now appear to play an important role in antimicrobial host defense against endocarditis through the secretion of so-called platelet microbicidal proteins. In animal models of endocarditis, low-dose aspirin was shown to significantly reduce the vegetation weight, the bacterial density of vegetation, the hematogenous bacterial dissemination, and the frequency of embolic events. However, these facts cannot be extrapolated to clinical care in humans, since to date, there is no definitive proof of the adjunctive benefit of aspirin in human infective endocarditis.

Pathogenesis of streptococcal and staphylococcal endocarditis

Although streptococcal and S. aureus IE share the same primary site of infection, their pathogenesis and clinical evolution present several major differences. Streptococci adhere to cardiac valves with pre-existing endothelial lesions. In contrast, S. aureus can colonize either damaged endothelium or invade physically intact endothelial cells. These interactions are mediated by multiple surface adhesins, some of which have been only partially characterized. Streptococci produce surface glucans (gtf and ftf), ECM adhesins (e.g., fibronectin-binding proteins, FimA), and platelet aggregating factors (phase I and phase II antigens, pblA, pblB, and pblT), all of which have been.

Challenges associated with the evaluation of veterinary product bioequivalence: an AAVPT perspective

The Generic Animal Drug Patent Term Restoration Act (GADPTRA) enacted in 1988 provided the same benefits to animal drug products that were granted to human generic products. It has been over 13 years since the GADPTRA was enacted, and veterinary drug sponsors and regulators have gained enormous insight and experience into some of the unique challenges associated with the determination of product bioequivalence for veterinary dosage forms. Moreover, advances in information and technology have opened both new issues that must be addressed and new mechanisms for demonstrating product bioequivalence. While many aspects of the existing Center for Veterinary Medicine Bioequivalence Guidance continue to provide invaluable guidance to the animal drug industry, there are also aspects of this guidance that are being called into question. Therefore, during the 2001 annual meeting of the American Academy of Veterinary Pharmacology and Therapeutics, participants were asked to address issues and concerns associated with the evaluation of veterinary product bioequivalence. This manuscript provides a summary of the concerns and discussions that transpired.

The effects of salicylate on bacteria

Salicylate and related compounds, such as aspirin, have a variety of effects in eucaryotic systems and are well known for their medicinal properties. Salicylate also has numerous effects on bacteria, yet only a handful of individuals within the scientific community appreciate these findings. From a bacterial viewpoint, growth in the presence of salicylate can be both beneficial and detrimental. On one hand, growth of certain bacteria in the presence of salicylate can induce an intrinsic multiple antibiotic resistance phenotype. On the other hand, growth in the presence of salicylate can reduce the resistance to some antibiotics and affect virulence factor production in some bacteria. This review provides an overview of the effects salicylate has on various bacterial species.

Acetylsalicylic acid reduces vegetation bacterial density, hematogenous bacterial dissemination, and frequency of embolic events in experimental Staphylococcus aureus endocarditis through antiplatelet and antibacterial effects

BACKGROUND

Platelets are integral to cardiac vegetations that evolve in infectious endocarditis. It has been postulated that the antiplatelet aggregation effect of aspirin (ASA) might diminish vegetation evolution and embolic rates.

METHODS AND RESULTS

Rabbits with Staphylococcus aureus endocarditis were given either no ASA (controls) or ASA at 4, 8, or 12 mg. kg-1. d-1 IV for 3 days beginning 1 day after infection. Vegetation weights and serial echocardiographic vegetation size, vegetation and kidney bacterial densities, and extent of renal embolization were evaluated. In addition, the effect of ASA on early S aureus adherence to sterile vegetations was assessed. In vitro, bacterial adherence to platelets, fibrin matrices, or fibrin-platelet matrices was quantified with either platelets exposed to ASA or S aureus preexposed to salicylic acid (SAL). ASA at 8 mg. kg-1. d-1 (but not at 4 or 12 mg. kg-1. d-1) was associated with substantial decreases in vegetation weight (P<0.05), echocardiographic vegetation growth (P<0.001), vegetation (P<0.05) and renal bacterial densities and renal embolic lesions (P<0.05) versus controls. Diminished aggregation resulted when platelets were preexposed to ASA or when S aureus was preexposed to SAL (P<0.05). S aureus adherence to sterile vegetations (P<0.05) or to platelets in suspension (P<0.05), fibrin matrices (P<0.05), or fibrin-platelet matrices (P<0.05) was significantly reduced when bacteria were preexposed to SAL.

CONCLUSIONS

ASA reduces several principal indicators of severity and metastatic events in experimental S aureus endocarditis. These benefits involve ASA effects on both the platelet and the microbe.

Beneficial effect of combination antiplatelet therapy on the development of experimental Staphylococcus aureus endocarditis

Previous studies in our laboratory have shown that antiplatelet agents, aspirin and ticlopidine, in clinically relevant concentrations influence the development and treatment of experimental endocarditis. To study the influence of combination antiplatelet treatment on the development of aortic vegetations, infected animals received either aspirin alone, ticlopidine alone, aspirin plus ticlopidine or no antiplatelet therapy. The combination antiplatelet treated group had a statistically significant (P = 0.043) reduction of the vegetative weight as compared with the untreated controls. While both the single antiplatelet agent groups showed a reduction in the size of the vegetation, neither achieved statistical significance. None of the treatment groups significantly altered the bacterial density relative to untreated controls. These findings reveal that the combination of aspirin and ticlopidine, two potent inhibitors of platelet aggregation with different mechanisms of action, act synergistically to optimally reduce the weight of aortic valve vegetations.

Influence of adjunctive ticlopidine on the treatment of experimental Staphylococcus aureus endocarditis

Antiplatelet therapy has been shown to reduce the size of aortic vegetations in a rabbit model of Staphylococcus aureus endocarditis. In addition, adjunctive aspirin improved the sterilization rate as compared with antibiotic treatment alone. To study the influence of ticlopidine, another potent inhibitor of platelet aggregation, infected animals received either vancomycin (Vm) alone or in combination with ticlopidine. When ticlopidine was given prior to and during antimicrobial therapy, a reduction in vegetation weight was observed. Ticlopidine administered with antimicrobial therapy, not only caused a reduction in vegetation weight, but also improved the rate of sterilization. This study provides additional data regarding the potential clinical role of antiplatelet agents in the treatment of endocarditis.