121. Cardiac Implantable Electronic Device-Related Infective Endocarditis (CIED-IE): Clinical Features and Outcomes of Patients with Definite IE Who Fulfill Both Major Duke Criteria

Background

Cardiac implantable electronic device-related infective endocarditis (CIED-IE) comprises 10–57% of total CIED infections. Patients with definite CIED-IE who fulfill both major modified Duke criteria have not been well characterized.

Methods

Data from the Multicenter Electrophysiologic Device Infection Cohort, a prospective, multinational study of CIED infections were used to describe a subset of patients with CIED-IE who met both major Duke criteria for definite IE (bloodstream infection and intracardiac vegetations [VEG]).

Results

Of 433 patients with CIED infection, 144 (33.3%) had definite CIED-IE. The median age was 68 years and 77.1% were male. Twelve (8.3%) had past CIED infection. Seventy-seven patients (53.5%) had permanent pacemakers, 38 (26.4%) had implantable cardioverter defibrillators, and 29 (20.1%) had combination devices. The median time following the last device procedure was 550 days. CIED-IE was early in 60 patients (41.7%) and late in 84 (58.3%). Most patients presented with fever (77.8%) and sepsis (44.4%) with a median symptom duration of 7 days. On echocardiography, lead VEG was noted in 125 patients (86.8%) and valvular VEG in 54 patients (37.5%) with the tricuspid valve involved in 56.5%. On the basis of VEG location, there were 90 patients (62.5%) with isolated lead-associated IE (LAE), 19 patients (13.2%) with isolated valve-associated IE (VAE), and 35 patients (24.3%) with both (LVAE). All patients had positive blood cultures and 63/119 (52.9%) had positive lead cultures. The predominant organism in blood was Staphylococcus aureus (42.4%), followed by coagulase-negative staphylococci (20.1%). CIED removal occurred in 131 patients (91%). There were 25 deaths during the index hospitalization and 34 total deaths (24.3%) by 6 months. Mortality correlated with age >75 (P = 0.023) and sepsis on presentation (P = 0.052). Infecting organism, site of VEG, and device removal did not impact the risk of death.

Conclusion

Definite CIED-IE is relatively common. The majority of patients tend to have late-onset infection and often present with sepsis. S. aureus is the dominant organism causing definite CIED-IE. Isolated LAE occurs in 63% of patients. Older age and sepsis on admission are associated with higher mortality.

Disclosures

All authors: No reported disclosures.

Role of Phenol-Soluble Modulins in Staphylococcus epidermidis Biofilm Formation and Infection of Indwelling Medical Devices

Phenol-soluble modulins (PSMs) are amphipathic, alpha-helical peptides that are secreted by staphylococci in high amounts in a quorum-sensing-controlled fashion. Studies performed predominantly in Staphylococcus aureus showed that PSMs structure biofilms, which results in reduced biofilm mass, while it has also been reported that S. aureus PSMs stabilize biofilms due to amyloid formation. We here analyzed the roles of PSMs in in vitro and in vivo biofilms of Staphylococcus epidermidis, the leading cause of indwelling device-associated biofilm infection. We produced isogenic deletion mutants for every S. epidermidis psm locus and a sequential deletion mutant in which production of all PSMs was abolished. In vitro analysis substantiated the role of all PSMs in biofilm structuring. PSM-dependent biofilm expansion was not observed, in accordance with our finding that no S. epidermidis PSM produced amyloids. In a mouse model of indwelling device-associated infection, the total psm deletion mutant had a significant defect in dissemination. Notably, the total psm mutant produced a significantly more substantial biofilm on the implanted catheter than the wild-type strain. Our study, which for the first time directly quantified the impact of PSMs on biofilm expansion on an implanted device, shows that the in vivo biofilm infection phenotype in S. epidermidis is in accordance with the PSM biofilm structuring and detachment model, which has important implications for the potential therapeutic application of quorum-sensing blockers.

Immune Evasion Mechanisms of Staphylococcus epidermidis Biofilm Infection

The primary virulence factor of the skin commensal and opportunistic pathogen, Staphylococcus epidermidis, is the ability to form biofilms on surfaces of implanted materials. Much of this microorganism’s pathogenic success has been attributed to its ability to evade the innate immune system. The primary defense against S. epidermidis biofilm infection consists of complement activation, recruitment and subsequent killing of the pathogen by effector cells. Among pathogen-derived factors, the biofilm exopolysaccharide polysaccharide intercellular adhesion (PIA), as well as the accumulation-associated protein (Aap), and the extracellular matrix binding protein (Embp) have been shown to modulate effector cell-mediated killing of S. epidermidis. Phenol-soluble modulins (PSMs) constitute the only class of secreted toxins by S. epidermidis, at least one type of which (PSMδ) possesses strong cytolytic properties toward leukocytes. However, through selective production of non-cytolytic subtypes of PSMs, S. epidermidis is able to maintain a low inflammatory infection profile and avoid eradication by the host immune system. Taken together, our emerging understanding of the mechanisms behind immune modulation by S. epidermidis elucidates the microorganism’s success in the initial colonization of device surfaces as well as the maintenance of a chronic and indolent course of biofilm infection.

Detection and analysis of methicillin-resistant human-adapted sequence type 398 allows insight into community-associated methicillin-resistant Staphylococcus aureus evolution

Background

Severe infections with highly virulent community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) are a global problem. However, the molecular events defining the evolution of CA-MRSA are still poorly understood. MRSA of sequence type (ST) 398 is known to frequently infect livestock, while ST398 isolates infecting humans are commonly methicillin-susceptible or represent MRSA originating from livestock-associated (LA)-MRSA.

Methods

We used whole genome sequencing of newly detected CA-MRSA ST398 isolates, in comparison to geographically matched LA-MRSA and methicillin-sensitive ST398, to determine their evolutionary history. Furthermore, we used phenotypic analyses including animal infection models to gain insight into the evolution of virulence in these CA-MRSA isolates. Finally, we determined methicillin resistance and expression of the methicillin resistance-conferring gene mecA and its penicillin-binding protein product, PBP2a, in a large series of CA-MRSA strains of divergent STs.

Results

We report several cases of severe and fatal infections due to ST398 CA-MRSA. The responsible isolates showed the typical genetic characteristics reported for human-adapted methicillin-sensitive ST398. Whole genome sequencing demonstrated that they evolved from human-adapted, methicillin-susceptible clones on several different occasions. Importantly, the isolates had not undergone consistent genetic alterations or changes in virulence as compared to their methicillin-susceptible predecessors. Finally, we observed dramatically and consistently lower methicillin resistance and expression of the resistance gene mecA, as compared to hospital-associated MRSA strains, in a diverse selection of CA-MRSA strains.

Conclusions

Our study presents evidence for the development of highly virulent human-adapted ST398 CA-MRSA isolates from methicillin-susceptible predecessors. Notably, our investigation indicates that, in contrast to widespread notions, the development of CA-MRSA is not necessarily associated with the acquisition of specific virulence genes or other virulence-increasing changes. Rather, our findings emphasize the importance of the CA-MRSA-characteristic staphylococcal cassette chromosome mec types, which provide only low-level methicillin resistance, for that process. Our findings are of particular importance for the diagnosis of CA-MRSA, inasmuch as they indicate that the presence of specific virulence genes cannot generally be used for that purpose.

Electronic supplementary material

The online version of this article (doi:10.1186/s13073-018-0514-9) contains supplementary material, which is available to authorized users.

Do amyloid structures formed by Staphylococcus aureus phenol-soluble modulins have a biological function?

Phenol-soluble modulins (PSMs) are alpha-helical, amphipathic peptides that have multiple functions in staphylococcal physiology and virulence. Recent research has suggested that PSMs form amyloid fibrils and amyloids are involved in PSM-mediated phenotypes such as cytolysis and biofilm stability. While we observed PSM amyloid formation using electron microscopy and dye assays, there were no apparent differences in the production of extracellular fibrous material between a PSM-deficient strain and the isogenic wild-type strain. Furthermore, we detected no correlation between cytolytic or pro-inflammatory activities with the propensity of PSM derivatives to form amyloids. In addition, we propose a model based on our finding of non-specific attachment of PSMs to DNA, which we here report results in resistance to DNase digestion, explaining previous findings on PSM-mediated biofilm stability without the necessity to assume amyloid involvement. Collectively, our results indicate that PSM amyloid formation may not be of major relevance for known key biological functions of PSMs. Intriguingly, however, we found that amyloid-forming capacity of PSMalpha3 allows almost no amino acid exchanges, suggesting importance of amyloid formation in possibly yet unknown functions of PSMs.

Quorum-sensing regulation in staphylococci-an overview

Staphylococci are frequent human commensals and some species can cause disease. Staphylococcus aureus in particular is a dangerous human pathogen. In staphylococci, the ability to sense the bacterial cell density, or quorum, and to respond with genetic adaptations is due to one main system, which is called accessory gene regulator (Agr). The extracellular signal of Agr is a post-translationally modified peptide containing a thiolactone structure. Under conditions of high cell density, Agr is responsible for the increased expression of many toxins and degradative exoenzymes, and decreased expression of several colonization factors. This regulation is important for the timing of virulence factor expression during infection and the development of acute disease, while low activity of Agr is associated with chronic staphylococcal infections, such as those involving biofilm formation. Accordingly, drugs inhibiting Agr are being evaluated for their capacity to control acute forms of S. aureus infection.

Molecular determinants of staphylococcal biofilm dispersal and structuring

Staphylococci are frequently implicated in human infections, and continue to pose a therapeutic dilemma due to their ability to form deeply seated microbial communities, known as biofilms, on the surfaces of implanted medical devices and host tissues. Biofilm development has been proposed to occur in three stages: (1) attachment, (2) proliferation/structuring, and (3) detachment/dispersal. Although research within the last several decades has implicated multiple molecules in the roles as effectors of staphylococcal biofilm proliferation/structuring and detachment/dispersal, to date, only phenol soluble modulins (PSMs) have been consistently demonstrated to serve in this role under both in vitro and in vivo settings. PSMs are regulated directly through a density-dependent manner by the accessory gene regulator (Agr) system. They disrupt the non-covalent forces holding the biofilm extracellular matrix together, which is necessary for the formation of channels, a process essential for the delivery of nutrients to deeper biofilm layers, and for dispersal/dissemination of clusters of biofilm to distal organs in acute infection. Given their relevance in both acute and chronic biofilm-associated infections, the Agr system and the psm genes hold promise as potential therapeutic targets.

Variability in clinical features of early versus late cardiovascular implantable electronic device pocket infections

BACKGROUND

Cardiovascular implantable electronic device (CIED) pocket infections are often related to recent CIED placement or manipulation, but these infections are not well characterized. The clinical presentation of CIED pocket infection, based on temporal onset related to last CIED procedure, deserves further study.

METHODS

The MEDIC (Multicenter Electrophysiologic Device Infection Cohort) prospectively enrolled subjects with CIED infection. Subjects were stratified into those whose infection occurred <12 months (early) or ≥ 12 months (late) since their last CIED-related procedure.

RESULTS

There were 132 subjects in the early group and 106 in the late group. There were more females (P = 0.009) and anticoagulation use (P = 0.039) in the early group. Subjects with early infections were more likely to have had a generator change or lead addition as their last procedure (P = 0.03) and had more prior CIED procedures (P = 0.023). Early infections were more likely to present with pocket erythema (P < 0.001), swelling (P < 0.001), and pain (P = 0.007). Late infections were more likely to have pocket erosion (P = 0.005) and valvular vegetations (P = 0.009). In bacteremic subjects, early infections were more likely healthcare-associated (P < 0.001). In-hospital and 6-month mortality were equivalent.

CONCLUSION

A total of 45% of patients with CIED pocket infection presented >12 months following their last CIED-related procedure. Patients with early infection were more likely to be female, on anticoagulation, and present with localized inflammation, whereas those with late infection were more likely to have CIED erosion or valvular endocarditis.

Clinical presentation and outcomes of cardiovascular implantable electronic device infections in hemodialysis patients

BACKGROUND

Infection is a serious complication of cardiovascular implantable electronic device (CIED) implantation. Kidney failure is as an independent risk factor for CIED infection and associated mortality. The presence of multiple comorbid conditions may contribute to varied clinical presentations and poor outcomes in hemodialysis (HD)-dependent patients with cardiac device infection.

STUDY DESIGN

Case series.

SETTING & PARTICIPANTS

CIED infections in HD patients (n=17) and non-HD patients (n=398) at Mayo Clinic in Rochester, MN, between 1991 and 2008.

OUTCOMES

Surgical management and death.

MEASUREMENTS

Clinical presentations, microbial organisms.

RESULTS

Of 415 patients admitted with CIED infection, 17 (4%) were receiving maintenance HD therapy. Among those on HD therapy, mean age was 72±15 (SD) years, 59% were women, and 53% had a central venous catheter for dialysis access. All 17 patients receiving HD therapy presented with CIED-associated bloodstream infection and 41% of these had infected vegetations on CIED leads or cardiac valves. A majority (82%) were managed with complete device removal and almost half (43%) received a replacement device when bloodstream infection cleared. Device infection was associated with significant short-term mortality in HD patients and 90-day survival was only 76% in this group of patients.

LIMITATIONS

Smaller sample size, majority white cohort, observational study.

CONCLUSIONS

CIED infection in patients receiving HD usually is associated with bloodstream infection and frequently is complicated with device-related endocarditis. Despite complete device removal in the majority of HD patients with infection, mortality remains high.

Predictors of mortality in patients with cardiovascular implantable electronic device infections

Infection reduces survival in cardiovascular implantable electronic device (CIED) recipients. However, the clinical predictors of short- and long-term mortality in patients with CIED infection are not well understood. We retrospectively reviewed all patients with CIED infection who were admitted to Mayo Clinic from January 1991 to December 2008. Survival data were obtained from the medical records and the United Sates Social Security Index. The purported risk factors for short-term (30-day) and long-term (>30-day) mortality were analyzed using univariate and multivariate models. Overall, 415 cases of CIED infection were identified during the study period. The mean follow-up duration for the 243 patients who were alive at the last follow-up visit was 6.9 years. In a multivariate model, heart failure (odds ratio 9.31, 95% confidence interval 2.08 to 41.67), corticosteroid therapy (odds ratio 4.04, 95% confidence interval 1.40 to 11.60), and presentation with CIED-related infective endocarditis (odds ratio 5.60, 95% confidence interval 2.25 to 13.92) were associated with increased short-term mortality. The factors associated with long-term mortality in the multivariate model included patient age (hazard ratio 1.20, 95% confidence interval 1.06 to 1.36), heart failure (hazard ratio 2.01, 95% confidence interval 1.42 to 2.86), metastatic malignancy (hazard ratio 5.99, 95% confidence interval 1.67 to 21.53), corticosteroid therapy (hazard ratio 1.97, 95% confidence interval 1.22 to 3.18), renal failure (hazard ratio 1.94, 95% confidence interval 1.37 to 2.74), and CIED-related infective endocarditis (hazard ratio 1.68, 95% confidence interval 1.17 to 2.41). In conclusion, these data suggest that the development of CIED-related infective endocarditis and the presence of co-morbid conditions are associated with increased short- and long-term mortality in patients with CIED infection.

Clinical features and outcomes of cardiovascular implantable electronic device infections due to staphylococcal species

Staphylococci account for the bulk of cardiovascular implantable electronic device (CIED) infections. However, a detailed analysis of clinical features and outcomes of CIED infections due to staphylococcal species has not been published. We retrospectively reviewed all cases of CIED infection seen at the Mayo Clinic from 1991 through 2008. Differences in device and host factors, clinical features, and patient outcomes were compared between cases of early and late Staphylococcus aureus and coagulase-negative staphylococci (CoNS) CIED infections. Of 280 cases of staphylococcal CIED infections, 43.9% were due to S. aureus and 56.0% were due to CoNS. Staphylococcus aureus CIED infection cases more frequently involved initially implanted devices. Late S. aureus CIED infection cases compared to late CoNS cases were associated with corticosteroid therapy, hemodialysis, implanted catheters, prosthetic valves, and remote sources of bacteremia. Cases of S. aureus endovascular infections had longer duration of bacteremia (56.0% vs 20.3% ≥3 days), longer hospitalization (37.4% vs 15.2% >20 days), and increased mortality (25.2% vs 9.5%) compared to cases of CoNS endovascular infections (p <0.001 for all comparisons). Overall, CoNS CIED infections compared to S. aureus were associated with a history of multiple device revisions and a higher number of total and abandoned leads at presentation (p <0.001 for all comparisons). In conclusion, CIED infections due to S. aureus and CoNS have distinct clinical features and outcomes.

Risk factors associated with early- versus late-onset implantable cardioverter-defibrillator infections

AIMS

The infection rates of implantable cardioverter-defibrillators systems (ICDs) are higher than that of permanent pacemaker. Risk factors associated with ICD infection have not been characterized and are the subject of the current investigation.

METHODS

All patients who had an ICD implanted at Mayo Clinic Rochester between 1991 and 2008 were retrospectively reviewed. Each case of ICD infection was matched with two non-infected controls. Cases of ICD infection were further stratified by early- (≤ 6 months) versus late-onset (>6 months) infection. Multivariable analysis was performed to identify significant risk factors for ICD infection.

RESULTS

Sixty-eight patients with ICD infection and 136 matched controls met the inclusion criteria. Thirty-five cases presented with early-onset infection and 33 had late-onset device infection. Staphylococcal species were the most common pathogens in both groups of patients. Patients with early-onset infection were more likely to present with generator pocket infection (p = 0.02). Patients with multiple comorbid conditions (high Charlson index) tended to have longer hospital stay during implantation admission (p = 0.009). In a multivariable logistic regression model, the presence of epicardial leads (odds ratio (OR) = 9.7, p = 0.03) and postoperative complications at the generator pocket (OR = 27.2, p < 0.001) were significant risk factors for early-onset ICD infection, whereas longer duration of hospitalization at the time of implantation (2 days versus 1 day: OR = 33.1, p < 0.001; ≥ 3 days versus 1 day: OR = 49.0, p < 0.001) and chronic obstructive pulmonary disease (OR = 9.8, p = 0.02) were associated with late-onset infections.

CONCLUSIONS

Our study findings suggest that risk factors associated with early- and late-onset ICD infection are different. While circumstances that may increase the chances of pocket contamination in the perioperative period are more likely to be associated with early-onset ICD infection, overall poor health of the host may increase the likelihood of late-onset ICD infection. These factors should be considered when developing strategies to minimize risk of device infection.

The association between physical activity and subclinical atherosclerosis: the Multi-Ethnic Study of Atherosclerosis

Prior reports regarding the association between physical activity and subclinical cardiovascular disease have not been consistent. The authors assessed physical activity and walking pace via questionnaire among 6,482 US adults aged 45-84 years without prior clinical cardiovascular disease participating in the Multi-Ethnic Study of Atherosclerosis from 2000 to 2002. Ankle-brachial index (ABI), coronary artery calcification, and internal and common carotid intima-media thickness (IMT) were measured. Metabolic equivalent-hours/week of physical activity were calculated. These data were analyzed by using multivariable linear or relative prevalence regression in gender-specific strata. After adjustment for age, race/ethnicity, clinic site, education, income, and smoking (model 1), increasing total, moderate + vigorous, and intentional-exercise physical activity were not associated with IMT or coronary artery calcification in either gender. These factors were associated with increased ABI (P<0.05) in women only. Walking pace was associated favorably with common carotid IMT, ABI, and coronary artery calcification in men and with common carotid IMT and ABI in women (all P<0.05) after adjustment for model 1 variables. These associations were attenuated and, for common carotid IMT, no longer significant when lipids, hypertension, diabetes, and body mass index were added to the model. These data suggest that walking pace is associated with less subclinical atherosclerosis; these associations may be mediated by cardiovascular disease risk factors.

Association of physical activity and body composition with insulin sensitivity in a community sample of adolescents

OBJECTIVE

To examine how body composition and physical activity are related to insulin sensitivity and secretion in adolescents.

DESIGN

Cross-sectional.

SETTING

Baltimore, Maryland.

PARTICIPANTS

Fifty-six healthy adolescents (34 boys and 22 girls; mean [SD] age, 13.3 [1.3] years; 95% were African American) who had been recruited at infancy from a health care clinic serving a low-income, urban community. Main Exposures Physical activity was measured for 5 to 7 days by a uniaxial accelerometer placed on the right ankle. Proportion of time spent in play-equivalent physical activity (PEPA) was defined as 1800 or more counts per minute. Body mass index (BMI) (calculated as weight in kilograms divided by height in meters squared) was converted to an age- and sex-specific z score.

MAIN OUTCOME MEASURES

Insulin sensitivity, insulin secretion, and disposition index calculated from a fasting oral glucose tolerance test.

RESULTS

Thirty-nine percent of the adolescents had a BMI in the 85th percentile or higher; half of those were overweight (BMI > or = 95th percentile). Play-equivalent physical activity and BMI z score were not correlated. In multivariate analyses, BMI z score and time spent in PEPA together explained 21% of the variance in insulin sensitivity and 18% in insulin secretion. Independent of each other, high BMI z score and low proportion of PEPA were significantly associated with low insulin sensitivity (partial r(2) = 0.14 and 0.10, respectively) and high insulin secretion (partial r(2) = 0.10 and 0.10, respectively), but not with disposition index.

CONCLUSIONS

In a cohort of urban, predominantly African American adolescents, both body composition and physical activity were independently associated with insulin sensitivity. At this point, insulin secretion is appropriately regulated.