What's New in the Treatment of Enterococcal Endocarditis?

Microbiologic diagnostics and pathogen spectrum in infective endocarditis of surgically treated patients: a five-year, retrospective, monocentric study

PURPOSE

The spectrum of causative organisms in infective endocarditis (IE) has changed significantly in the last decades. Reliable pathogen detection is crucial for appropriate antimicrobial therapy for IE. The aim of the study was to evaluate the diagnostic value of microbiological methods for detecting the causative microorganism of IE and to analyze the spectrum of pathogens.

METHODS

A total of 224 cases (211 unique patients, some with multiple surgeries) were included into this retrospective study. Patients were diagnosed with IE according to the modified Duke criteria from January 2016 to July 2021 and underwent heart valve surgery in a tertiary hospital. Pathogen detection was performed by blood culture, microbiological culture and 16S rDNA PCR of explanted heart valve material.

RESULTS

A causative pathogen of IE was detected in 95.5% (n = 214) of cases. Blood cultures were positive in 83.3%, while a pathogen in the examined heart valve samples was identified in 32.6% by culture and in 88.2% by 16S rDNA PCR. A microorganism was identified by 16S rDNA PCR in 61.1% of blood culture negative cases but only in 19.4% by heart valve culture. The most common pathogens were Staphylococcus aureus (27%), viridans group streptococci (20%), enterococci (19%) and coagulase-negative staphylococci (CoNS 8%). Cutibacterium acnes (7%) was detected in prosthetic valve IE cases only.

CONCLUSION

Blood culture as a comparatively non-invasive and straightforward technique remains an important and reliable method for initial detection of the causative organism in IE. Diagnostic stewardship programs should broadly emphasize proper collection of blood cultures, particularly sampling prior to any antibiotic treatment. Additionally, molecular testing using 16S rDNA tissue PCR can be used with culture techniques to increase the diagnostic yield, especially in the case of a negative blood culture.

Analysis of virulence genes, drug resistance detection, and pathogenicity in Enterococcus from farm animals

This study aimed to investigate the presence of eight virulence genes (ace, asa1, esp, efaA, gelE, cylA, agg, fsr) in Enterococcus from a variety of animals and to explore the drug resistance and pathogenicity. This could provide a theoretical basis for clinical treatment of Enterococcus infections. Anal swabs from pigs, chickens, cattle, and dogs in farms and pet hospitals were collected for Enterococcus isolation and identification. Eight virulence genes were detected (PCR method), and drug resistance was assessed (drug-sensitive paper method). The strains containing different virulence genes were then divided into EV1, EV2, and EV3 groups. The LD₅₀ and pathogenicity was examined by intra-peritoneal injection to infect mice. Differences were found in the detection rates of virulence genes in Enterococcus from the different animals. The highest overall detection rate was for the esp gene (78.0%), and the lowest for the cylA gene (15.5%). Eight genes were detected most frequently in Enterococcus from dogs and least frequently from cattle. Among the Enterococcus strains from four variety of animals, drug resistance was highest against sulfamethoxazole (100%), cefotaxime (>97%), and cefotaxitin (>93%). Drug resistance was lowest against vancomycin (0%), levofloxacin (<12%) and ciprofloxacin (<13%). The LD₅₀ for each of the three groups was EV1_LD50=8.71×10⁹CFU， EV2_LD50=2.34×10¹⁰CFU，and EV3_LD50=9.33×10¹⁰CFU. The Enterococcus12LD₅₀ dose group caused significant clinical symptoms in mice, with pathological effects on the heart, liver, lungs, and kidneys, and particularly on the urinary system. The abundance of Enterococcus virulence genes, drug resistance, and pathogenicity vary among different animal origins, and the pathology caused by Enterococcus requires effective treatment protocols based on species and regional characteristics.

Phage Cocktails with Daptomycin and Ampicillin Eradicates Biofilm-Embedded Multidrug-Resistant Enterococcus faecium with Preserved Phage Susceptibility

Multidrug-resistant (MDR) Enterococcus faecium is a challenging nosocomial pathogen known to colonize medical device surfaces and form biofilms. Bacterio (phages) may constitute an emerging anti-infective option for refractory, biofilm-mediated infections. This study evaluates eight MDR E. faecium strains for biofilm production and phage susceptibility against nine phages. Two E. faecium strains isolated from patients with bacteremia and identified to be biofilm producers, R497 (daptomycin (DAP)-resistant) and HOU503 (DAP-susceptible dose-dependent (SDD), in addition to four phages with the broadest host ranges (ATCC 113, NV-497, NV-503-01, NV-503-02) were selected for further experiments. Preliminary phage-antibiotic screening was performed with modified checkerboard minimum biofilm inhibitory concentration (MBIC) assays to efficiently screen for bacterial killing and phage-antibiotic synergy (PAS). Data were compared by one-way ANOVA and Tukey (HSD) tests. Time kill analyses (TKA) were performed against R497 and HOU503 with DAP at 0.5× MBIC, ampicillin (AMP) at free peak = 72 µg/mL, and phage at a multiplicity of infection (MOI) of 0.01. In 24 h TKA against R497, phage-antibiotic combinations (PAC) with DAP, AMP, or DAP + AMP combined with 3- or 4-phage cocktails demonstrated significant killing compared to the most effective double combination (ANOVA range of mean differences 2.998 to 3.102 log10 colony forming units (CFU)/mL; p = 0.011, 2.548 to 2.868 log10 colony forming units (CFU)/mL; p = 0.023, and 2.006 to 2.329 log10 colony forming units (CFU)/mL; p = 0.039, respectively), with preserved phage susceptibility identified in regimens with 3-phage cocktails containing NV-497 and the 4-phage cocktail. Against HOU503, AMP combined with any 3- or 4-phage cocktail and DAP + AMP combined with the 3-phage cocktail ATCC 113 + NV-497 + NV-503-01 demonstrated significant PAS and bactericidal activity (ANOVA range of mean differences 2.251 to 2.466 log10 colony forming units (CFU)/mL; p = 0.044 and 2.119 to 2.350 log10 colony forming units (CFU)/mL; p = 0.028, respectively), however, only PAC with DAP + AMP maintained phage susceptibility at the end of 24 h TKA. R497 and HOU503 exposure to DAP, AMP, or DAP + AMP in the presence of single phage or phage cocktail resulted in antibiotic resistance stabilization (i.e., no antibiotic MBIC elevation compared to baseline) without identified antibiotic MBIC reversion (i.e., lowering of antibiotic MBIC compared to baseline in DAP-resistant and DAP-SDD isolates) at the end of 24 h TKA. In conclusion, against DAP-resistant R497 and DAP-SDD HOU503 E. faecium clinical blood isolates, the use of DAP + AMP combined with 3- and 4-phage cocktails effectively eradicated biofilm-embedded MDR E. faecium without altering antibiotic MBIC or phage susceptibility compared to baseline.

Measuring Epidemiologic Effects of Enterococcal Bacteremia and Outcomes From a Nationwide Inpatient Sample Database

Introduction

Enterococcus is a gram-positive, non-sporing, facultative anaerobe. It is a common cause of nosocomial infections in the United States. Enterococcal bacteremia is primarily a nosocomial infection in the medical intensive care unit (ICU), with a preference for elderly patients with multiple comorbidities. 

Material and methods

This is a retrospective cohort study using the publicly accessible National (Nationwide) Inpatient Sample (NIS) database from October 2015 to December 2017. We examined data from 75,430 patients aged 18 years and older in the NIS who developed enterococcal bacteremia, as identified from the ICD-10 CM codes (B95), to discuss the epidemiologic effects and outcomes of enterococcal bacteremia. Patients were classified based on demographics, and comorbidities were identified. Three primary outcomes were studied: in-hospital mortality, length of stay, and healthcare cost. The secondary outcome was identifying any comorbidities associated with enterococcal bacteremia. Length of stay was defined as days from admission to discharge or death. Healthcare costs were estimated from the hospital perspective from hospital-level ratios of costs-to-charges. SAS 9.4 (2013; SAS Institute Inc., Cary, North Carolina, United States) was used for univariate and multivariate analyses. For data analysis, mortality was modeled using logistic regression. Length of stay and costs were modeled using linear regression, controlling for patient and hospital characteristics. Statistical analyses were performed using SAS. Statistical significance was defined as P<0.05.

Results

A total of 75,430 patients with enterococcal bacteremia were included in the study. Of this, 44,270 were males and 31,160 females. A total of 50,270 (68.67%) were Caucasians, 11,210 (15.31%) were African Americans, 6,445 (8.80%) were Hispanic and 2,025 (2.77%) were native Americans. Important comorbidities were congestive heart failure (25.91%), valvular disease (8.08%), neurological complications (11.87%), diabetes mellitus with complications (18.89%), renal failure (28.52%), and obesity (11.61%). In-hospital mortality was 11.07%, length of stay was 13.8 days, and a healthcare cost of 41,232.6 USD. 

Conclusions

Enterococcal bacteremia is a nosocomial infection with a preference for the elderly with renal failure, cardiac failure, cardiac valvular diseases, stroke, obesity, and diabetes with complications. Further studies are needed to see whether the mortality caused by enterococcal bacteremia is attributable to comorbidities or to the bacteremia. It is associated with a more extended hospital stay and higher healthcare expenditure. Implementing contact precautions to contain the spread of methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus(VRE) has also checked the spread of enterococci. Further prospective studies can be planned using chart-based data.

Infective Endocarditis in High-Income Countries

Infective endocarditis remains an illness that carries a significant burden to healthcare resources. In recent times, there has been a shift from Streptococcus sp. to Staphylococcus sp. as the primary organism of interest. This has significant consequences, given the virulence of Staphylococcus and its propensity to form a biofilm, rendering non-surgical therapy ineffective. In addition, antibiotic resistance has affected treatment of this organism. The cohorts at most risk for Staphylococcal endocarditis are elderly patients with multiple comorbidities. The innovation of transcatheter technologies alongside other cardiac interventions such as implantable devices has contributed to the increased risk attributable to this cohort. We examined the pathophysiology of infective endocarditis carefully. Inter alia, the determinants of Staphylococcus aureus virulence, interaction with host immunity, as well as the discovery and emergence of a potential vaccine, were investigated. Furthermore, the potential role of prophylactic antibiotics during dental procedures was also evaluated. As rates of transcatheter device implantation increase, endocarditis is expected to increase, especially in this high-risk group. A high level of suspicion is needed alongside early initiation of therapy and referral to the heart team to improve outcomes.

Prevalence of High Level Gentamicin Resistance among the Clinical Isolates of Enterococci Species

Enterococci infections, have drawn attention of clinicians due to rapid increase in high level aminoglycoside resistance (HLAR). This resistance predicts failure of β-lactam antibiotic and aminoglycoside combination, which is the current treatment of choice for serious enterococci infections. This led us to investigate about the prevalence of HLAR enterococci in our hospital setting in Shimoga, Karnataka. All the clinical samples received at Microbiology laboratory, McGan hospital, Shivamogga between June 2016 and December 2016 was considered for the study. Enterococci were identified and further speciated by following conventional method. Antibiotic susceptibility pattern of all the isolates was determined according to CLSI guidelines. High level gentamicin resistance was detected by disc diffusion method using 120µg gentamicin disc. A total of 64 Enterococci species were isolated from the clinical specimens. On speciation, Enterococcus faecalis (E. faecalis) accounted for 72% (46) of the total isolates, 24%(16) of the isolates were Enterococcus faecium (E. faecium)and 4% (2) isolates were Enterococcus durans (E. durans). High level gentamicin resistance was noted in 42% (27) among the total isolates. E. faecium was found to be more resistant compared to E. faecalis. E. durans was a sensitive strain. Our study reconfirms the high prevalence of HLAR in the clinical setting. The study stresses on the need for regular screening of HLAR in all Enterococci infections and revise the battery of drugs for its treatment according to the report.

Enterococcus innesii sp. nov., isolated from the wax moth Galleria mellonella

Four bacterial strains were isolated from two different colony sources of the wax moth Galleria mellonella. They were characterized by a polyphasic approach including 16S rRNA gene sequence analysis, core-genome analysis, average nucleotide identity (ANI) analysis, digital DNA-DNA hybridization (dDDH), determination of G+C content, screening of antibiotic resistance genes, and various phenotypic analyses. Initial analysis of 16S rRNA gene sequence identities indicated that strain GAL7^T was potentially very closely related to Enterococcus casseliflavus and Enterococcus gallinarum, having 99.5-99.9 % sequence similarity. However, further analysis of whole genome sequences revealed a genome size of 3.69 Mb, DNA G+C content of 42.35 mol%, and low dDDH and ANI values between the genomes of strain GAL7^T and closest phylogenetic relative E. casseliflavus NBRC 100478^T of 59.0 and 94.5 %, respectively, indicating identification of a putative new Enterococcus species. In addition, all novel strains encoded the atypical vancomycin-resistance gene vanC-4. Results of phylogenomic, physiological and phenotypic characterization confirmed that strain GAL7^T represented a novel species within the genus Enterococcus, for which the name Enterococcus innesii sp. nov. is proposed. The type strain is GAL7^T (=DSM 112306^T=NCTC 14608^T).

A sampling survey of enterococci within pasteurized, fermented dairy products and their virulence and antibiotic resistance properties

Globally, fermented foods (FFs), which may be traditional or industrially-produced, are major sources of nutrition. In the traditional practice, the fermentation process is driven by communities of virtually uncharacterized microflora indigenous to the food substrate. Some of these flora can have virulent or antibiotic resistance properties, posing risk to consumers. Others, such as Enterococcus faecalis and Enterococcus faecium, may also be found in such foods. Enterococci that harbor antibiotic resistance or virulence factors can cycle among animals, food, humans and the environment, thereby transferring these harmful properties at the gene level to harmless commensals in the food matrix, animals and humans. In this work, several microbial isolates obtained from different FF sources were analyzed for their identity and virulence and/or antibiotic resistance properties. For identification aiming at enterococci, isolates that were Gram-positive and catalase- and oxidase-negative were subjected to multiple tests including for growth in broth containing 6.5% NaCl, growth and hydrolytic activity on medium containing bile-esculin, hemolytic activity on blood agar, and growth at 45°C and survival after incubation at 60°C for 30 min. Furthermore, the isolates were tested for susceptibility/resistance to a select group of antibiotics. Finally, the isolates were molecularly-characterized with respect to species identity and presence of virulence-encoding genes by amplification of target genes. Most sources contained enterococci, in addition to most of them also containing Gram-negative flora. Most of these also harbored virulence factors. Several isolates were also antibiotic-resistant. These results strongly suggest attention should be given to better control presence of such potentially pathogenic species.

Infective Endocarditis: A Case Series

Infective endocarditis (IE) is an infection of the endocardial surface of the heart. The incidence of IE worldwide is approximately 3 to 10 per 100,000 people annually. Twenty percent of patients die during the hospital stay, and the mortality may reach 25 to 30% six months postinfection. We hereby present our experience of six patients, of whom five survived. The cause of one death was late presentation and lack of coverage for Burkholderia in the prescribed empirical antibiotic therapy. One of our patients, with culture-negative endocarditis, responded to doxycycline and did not require any surgery. Five out of six patients who underwent surgery had vegetations more than 10 mm in size, and one patient had an aortic valve abscess (caused by Staphylococcus haemolyticus). Both prosthetic endocarditis and native valve endocarditis can be treated successfully with antimicrobial agents and surgery (when indicated). A high index of suspicion is required to diagnose IE caused by fungus and atypical bacteria.

In vitro activity of ampicillin and ceftriaxone against ampicillin-susceptible Enterococcus faecium

OBJECTIVES

To assess activity of the combination of ceftriaxone and ampicillin against clinical isolates of ampicillin-susceptible Enterococcus faecium.

METHODS

Ampicillin-susceptible E. faecium (n = 29) and Enterococcus faecalis (n = 10) collected from locations in the USA and France were used for this analysis. Susceptibility testing was performed by gradient diffusion strip (GDS) and broth microdilution (BMD). Synergy with the combination of ceftriaxone and ampicillin was assessed in all isolates using GDS crossing and double disc diffusion methods. Selected isolates (nine E. faecium and three E. faecalis) were assessed for synergy in time-kill studies using ampicillin alone and in combination with ceftriaxone.

RESULTS

In isolates of E. faecium, the median (range) ampicillin MIC by BMD was 0.5 (0.25-4) mg/L and by GDS it was 2 (1-8)  mg/L. In E. faecalis, the median (range) ampicillin MIC by BMD was 0.5 (0.5-1) mg/L and by GDS it was 2 (0.75-3) mg/L. A total of 24/29 (82.8%) isolates of E. faecium displayed synergy by GDS and 22/29 (75.9%) by double disc diffusion. Seven of 10 (70%) isolates of E. faecalis displayed synergy by GDS and 4/10 (40%) by double disc diffusion. Time-kill studies found synergy in 3/9 (33.3%) E. faecium and 3/3 (100%) E. faecalis.

CONCLUSIONS

In contrast to the demonstrated synergy in time-kill models of ceftriaxone and ampicillin for E. faecalis, this combination does not appear to provide uniform synergy in E. faecium. Antagonism was not observed. Clinical correlation is necessary and caution should be used when considering ampicillin and ceftriaxone for the treatment of infections caused by ampicillin-susceptible E. faecium.

In vivo synergism of ampicillin, gentamicin, ceftaroline and ceftriaxone against Enterococcus faecalis assessed in the Galleria mellonella infection model

BACKGROUND

The unfavourable safety profile of aminoglycosides and the synergistic effects observed in vitro have prompted the development of novel dual β-lactam therapies, e.g. ampicillin/ceftriaxone or ampicillin/ceftaroline, for the treatment of Enterococcus faecalis endocarditis.

OBJECTIVES

For comparison with in vitro chequerboard assay results, a partial chequerboard setup of ampicillin/gentamicin, ampicillin/ceftriaxone and ampicillin/ceftaroline against E. faecalis was established in the Galleria mellonella larval infection model.

METHODS

Discrimination of synergistic and additive interactions was based on the evaluation of larval survival, bacterial quantity in the haemolymph and a pathology score index (internal to the workgroup). Single and multiple dosing schemes based on the half-life of ampicillin were applied. Pharmacokinetic data of the antibiotics in the larvae were determined via agar plate diffusion assays.

RESULTS

Ampicillin and ceftriaxone exhibited strain-specific synergistic interactions in the larvae under both dosing regimens, while the other two combinations showed additive effects. Ampicillin/ceftaroline was inferior to ampicillin/ ceftriaxone. Not all synergistic effects observed in vitro could be replicated in the larvae.

CONCLUSIONS

Our results suggest superior efficacy of ampicillin/ceftriaxone for the treatment of high-inoculum enterococcal infections, for at least some strains, but question the benefit of the current standard of adding the nephrotoxic gentamicin compared with the safer ceftriaxone. This is the first study to develop a scheme for differentiation between additive and synergistic effects in larvae and apply a multiple-antibiotic dosing scheme based on the pharmacokinetics of ampicillin. The model allows the analysis of synergistic effects of antimicrobials in an in vivo setting, but the clinical correlation warrants further study.

Tedizolid as Step-Down Therapy following Daptomycin versus Continuation of Daptomycin against Enterococci and Methicillin- and Vancomycin-Resistant Staphylococcus aureus in a Rat Endocarditis Model

Tedizolid (TZD) and daptomycin (DAP) were assessed in a rat endocarditis model against Enterococcus faecalis, Enterococcus faecium (resistant to vancomycin and ampicillin), and Staphylococcus aureus As a monotherapy, TZD for 5 days was not effective in a comparison with no-treatment controls, while DAP for 5 days was significantly effective against these bacteria. Step-down therapy (DAP for 3 days followed by TZD for 2 days) was as effective as DAP for 5 days and was comparable to 3 days of DAP plus ceftriaxone against all bacteria and to 3 days of DAP plus gentamicin against E. faecalis OG1RF.

Should High-dose Daptomycin be an Alternative Treatment Regimen for Enterococcal Endocarditis?

INTRODUCTION

Previous series on the use of daptomycin in enterococcal infective endocarditis (EIE) have shown various outcomes, including higher mortality rates. We analyzed the effectiveness of high-dose daptomycin for the treatment of EIE.

METHODS

We performed a prospective study from 2010 to 2018 in a referral center in patients with native (NVE) and prosthetic valve endocarditis (PVE) due to Enterococcus spp. The standard high-dose daptomycin at our institution is 10-12 mg/kg/day (CLCr > 30 ml/min). We compared the efficacy of a daptomycin-based regimen (DBR) versus daptomycin-sparing regimen (DSR) and daptomycin monotherapy versus combination therapy. Primary endpoints of the study were evaluation of risk factors associated with 30-day mortality and failure at end of therapy.

RESULTS

We collected 43 EIE cases; 29 were NVE (67.4%). Overall, 16 (37.2%) were treated with DBR, mainly with combination regimens (11, 68.7%), in the majority of cases in association with ß-lactam (7, 43.7%). The mean administered dose of daptomycin was 10.125 mg/kg/day (range 8-12 mg/kg/day). Overall, patients treated with DBR compared with patients treated with DSR had no higher mortality rates and/or failure at end of therapy (6.2% vs. 22. 2%; P 0.41 and MICs 0.25-2 mg/l, 6.2% vs. 3.7%; P 1.0). In the sub-group of patients with NVE and PVE treated with DBR and DSR, no difference was found regarding the primary endpoints on the single or combined use of daptomycin.

CONCLUSION

Our findings suggest that high-dose daptomycin might be used as an alternative treatment regimen in EIE.

Enterococcus faecalis Endocarditis After Endoscopic Mucosal Resection of a Large Sessile Colonic Polyp

A 71-year-old man with mitral regurgitation and apical cardiomyopathy underwent endoscopic mucosal resection of a 22-mm transverse colon tubulovillous adenoma with high-grade dysplasia. Six weeks later, he presented with fever, valvular vegetations, and positive blood cultures for Enterococcus faecalis. To our knowledge, this is the first reported case of endocarditis involving native heart valves after endoscopic mucosal resection.

In search of novel protein drug targets for treatment of Enterococcus faecalis infections

Enterococcus faecalis (Ef) is one of the major pathogens involved in hospital-acquired infections. It can cause nosocomial bacteremia, surgical wound infection, and urinary tract infection. It is important to mention here that Ef is developing resistance against many commonly occurring antibiotics. The occurrence of multidrug resistance (MDR) and extensive-drug resistance (XDR) is now posing a major challenge to the medical community. In this regard, to combat the infections caused by Ef, we have to look for an alternative. Rational structure-based drug design exploits the three-dimensional structure of the target protein, which can be unraveled by various techniques such as X-ray crystallography or nuclear magnetic resonance (NMR) spectroscopy. In this review, we have discussed the complete picture of Ef infections, the possible treatment available at present, and the alternative treatment options to be explored. This study will help in better understanding of novel biological targets against Ef and the compounds, which are likely to bind with these targets. Using these detailed structural informations, rational structure-based drug design is achievable and tight inhibitors against Ef can be prepared.

Anti-Ace monoclonal antibody reduces Enterococcus faecalis aortic valve infection in a rat infective endocarditis model

Ace (Adhesin to collagen from Enterococcus faecalis) is a cell-wall anchored protein that is expressed conditionally and is important for virulence in a rat infective endocarditis (IE) model. Previously, we showed that rats immunized with the collagen binding domain of Ace (domain A), or administered anti-Ace domain A polyclonal antibody, were less susceptible to E. faecalis endocarditis than sham-immunized controls. In this work, we demonstrated that a sub nanomolar monoclonal antibody (mAb), anti-Ace mAb70, significantly diminished E. faecalis binding to ECM collagen IV in in vitro adherence assays and that, in the endocarditis model, anti-Ace mAb70 pre-treatment significantly reduced E. faecalis infection of aortic valves. The effectiveness of anti-Ace mAb against IE in the rat model suggests it might serve as a beneficial agent for passive protection against E. faecalis infections.

Non-Antimicrobial Drugs: Etodolac as a Possible Antimicrobial or Adjuvant Agent Against ESKAPE Pathogens

Introduction:

Multiple-drug resistant bacteria are emerging exponentially in healthcare units, threatening public health and requiring novel therapeutic approaches. In 2017, World Health Organization published a list that frames antimicrobial resistant bacteria into priority levels for research of novel drugs to fight them.

Methods & Materials:

Antimicrobial resistant ESKAPE (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, Enterobacter sp.) and Enterococcus faecalis and Escherichia coli pathogens are present in this list. Representative isolates of each species were used to test the Antibacterial and anti-biofilm formation activities of Etodolac (a Non-Steroidal Anti-Inflammatory Drug, NSAID) at 10 and 1 mM using a broth microdilution technique.

Results & Discussion:

Statistically significant (p< 0,05) results were observed against all tested gram-positives, particularly anti-biofilm activity against E. faecium. Etodolac had an almost null influence on tested gram-negatives, with the exception of one A. baumannii clinical isolate regarding biofilm formation inhibition. Observed differences deserve further analysis and prospection of the involved mechanisms, to unravel possible novel bacterial targets for drug development. Similar work with other NSAID’s may also be worth exploring to ascertain novel therapeutic applications for these drugs, particularly regarding biofilm formation inhibition, per si or as adjuvants of current antibiotherapy, mainly against gram-positives, as suggested by present work.

Conclusion:

Already approved drugs in terms of pharmacokinetics and safety may deploy faster solutions for antimicrobial therapy against priority pathogens. Current work intends to bring attention to that possibility, particularly regarding NSAIDs, anti-biofilm formation and top priority pathogens.

In Vivo and In Vitro Effects of a ClpP-Activating Antibiotic against Vancomycin-Resistant Enterococci

Antibiotics with novel bactericidal mechanisms of action are urgently needed. The antibiotic acyldepsipeptide 4 (ADEP4) activates the ClpP protease and causes cells to self-digest. The effects of ADEP4 and ClpP activation have not been characterized sufficiently for the enterococci, which are important pathogens known for high levels of acquired and intrinsic antibiotic resistance. In the present study, ADEP4 was found to be potently active against both Enterococcus faecalis and Enterococcus faecium, with MIC₉₀s of 0.016 μg/ml and 0.031 μg/ml, respectively. ClpP purified from E. faecium was found to bind ADEP4 in a surface plasmon resonance analysis, and ClpP activation by ADEP4 was demonstrated biochemically with a β-casein digestion assay. In addition, E. faecium ClpP was crystallized in the presence of ADEP4, revealing ADEP4 binding to ClpP in the activated state. These results confirm that the anti-enterococcal activity of ADEP4 occurs through ClpP activation. In killing curve assays, ADEP4 was found to be bactericidal against stationary-phase vancomycin-resistant E. faecalis (VRE) strain V583, and resistance development was prevented when ADEP4 was combined with multiple classes of approved antibiotics. ADEP4 in combination with partnering antibiotics also eradicated mature VRE biofilms within 72 h of treatment. Biofilm killing with ADEP4 antibiotic combinations was superior to that with the clinically used combinations ampicillin-gentamicin and ampicillin-daptomycin. In a murine peritoneal septicemia model, ADEP4 alone was as effective as ampicillin. ADEP4 coadministered with ampicillin was significantly more effective than either drug alone. These data suggest that ClpP-activating antibiotics may be useful for treating enterococcal infections.

Infectious endocarditis: An update for emergency clinicians

INTRODUCTION

Infectious endocarditis (IE) is a potentially deadly disease without therapy and can cause a wide number of findings and symptoms, often resembling a flu-like illness, which makes diagnosis difficult.

OBJECTIVE

This narrative review evaluates the presentation, evaluation, and management of infective endocarditis in the emergency department, based on the most current literature.

DISCUSSION

IE is due to infection of the endocardial surface, most commonly cardiac valves. Major risk factors include prior endocarditis (the most common risk factor), structural heart damage, IV drug use (IVDU), poor immune function (vasculitis, HIV, diabetes, malignancy), nosocomial (surgical hardware placement, poor surgical technique, hematoma development), and poor oral hygiene, and a wide variety of organisms can cause IE. Patients typically present with flu-like illness. Though fever and murmur occur in the majority of cases, they may not be present at the time of initial presentation. Other findings such as Roth spots, Janeway lesions, Osler nodes, etc. are not common. An important component is consideration of risk factors. A patient with IVDU (past or current use) and fever should trigger consideration of IE. Other keys are multiple sites of infection, poor dentition, and abnormal culture results with atypical organisms. If endocarditis is likely based on history and examination, admission for further evaluation is recommended. Blood cultures and echocardiogram are key diagnostic tests.

CONCLUSIONS

Emergency physicians should consider IE in the patient with flu-like symptoms and risk factors. Appropriate evaluation and management can significantly reduce disease morbidity and mortality.

Epidemiological trends of infective endocarditis in a single center in Italy between 2003-2015

OBJECTIVE

Changes in the incidence, clinical features and microbiology of infective endocarditis (IE) observed in a single center in Italy were compared between the period 2003-2010 and 2011-2015.

METHODS

All cases of IE, defined as definite or possible according to the modified Duke criteria, observed at the 'L. Sacco' Hospital in Milan, Italy between 2003 and 2015 were retrospectively reviewed.

RESULTS

366 episodes of IE were identified in 325 patients. The mean number of incident IE over the period 2003-2015 was 1.43 (range: 0.6-2.1) cases per 1000 admissions, with a significantly increasing trend from a mean of 1.28-1.72 cases per 1000 admissions/year in 2003-2010 and 2011-2015, respectively (+34%; p = .04). Staphylococci remain the leading pathogens causing IE (29%) with a relative increase of methicillin-resistant Staphylococcus aureus between the two periods. Streptococci and enterococci account for 26% and 18% of IE, respectively. We found an increase in the proportion of cases due to enterococci (from 14% in 2003-2010 to 22% in 2011-2015). The rate of in-hospital mortality was 19%, similar in the two periods studied.

CONCLUSION

The incidence of IE continuously increased in our cohort over the past decade and, along with the aging of the population, a raise in the incidence of health care-associated infections and a change in the distribution of prevalent pathogens were observed. Surgery was independently associated with higher in-hospital survival (AOR, 95% CI: 0.38, 0.19-0.74; p = .005). A constant surveillance is required to guide the optimal management of the changing epidemiology of IE.

A retrospective clinical comparison of daptomycin vs daptomycin and a beta-lactam antibiotic for treating vancomycin-resistant Enterococcus faecium bloodstream infections

There is limited clinical evidence to support the combination of daptomycin and beta-lactam antibiotics (DAP + BLA) for treatment of vancomycin-resistant enterococci (VRE) bloodstream infections (BSI). We conducted a prospective observational cohort study of VRE-BSI during 2010-2015. The primary endpoint was mortality at the end of treatment. We included 114 patients who received DAP for VRE-BSI. Of these 87 (76.3%) received DAP + BLA. There were no significant differences in mortality between the DAP and DAP + BLA groups on univariable analysis (10/27 vs. 34/87, P = 0.85). A subgroup analysis of patients with enterococcal DAP minimum inhibitory concentrations (MICs) ≤2 mg/L, revealed that those treated with DAP + BLA had a lower mortality (adjusted hazard ratio [aHR], 0.23; 95% confidence interval [CI], 0.06-0.93; P = 0.04) after adjustment for other significant predictors of mortality, including the DAP dose. In addition, patients receiving high-dose (≥9 mg/kg) DAP + BLA independently had a better survival than those receiving low-dose DAP alone (aHR = 5.16), low-dose DAP + BLA (aHR = 5.39), and high-dose DAP alone (aHR = 19.01) (P < 0.05 for all comparisons). For patients with VRE-BSIs, the DAP MIC of the isolate and the DAP dose influence the effect of DAP + BLA on outcome. A high-dose DAP + BLA might improve survival. These findings support the use of high-dose DAP + BLA for treatment of VRE-BSI.

Enterococci and Their Interactions with the Intestinal Microbiome

The Enterococcus genus comprises over 50 species that live as commensal bacteria in the gastrointestinal (GI) tracts of insects, birds, reptiles, and mammals. Named "entero" to emphasize their intestinal habitat, Enterococcus faecalis and Enterococcus faecium were first isolated in the early 1900s and are the most abundant species of this genus found in the human fecal microbiota. In the past 3 decades, enterococci have developed increased resistance to several classes of antibiotics and emerged as a prevalent causative agent of health care-related infections. In U.S. hospitals, antibiotic use has increased the transmission of multidrug-resistant enterococci. Antibiotic treatment depletes broad communities of commensal microbes from the GI tract, allowing resistant enterococci to densely colonize the gut. The reestablishment of a diverse intestinal microbiota is an emerging approach to combat infections caused by antibiotic-resistant bacteria in the GI tract. Because enterococci exist as commensals, modifying the intestinal microbiome to eliminate enterococcal clinical pathogens poses a challenge. To better understand how enterococci exist as both commensals and pathogens, in this article we discuss their clinical importance, antibiotic resistance, diversity in genomic composition and habitats, and interaction with the intestinal microbiome that may be used to prevent clinical infection.

Efficacy of Telavancin Alone and in Combination with Ampicillin in a Rat Model of Enterococcus faecalis Endocarditis

We first assessed telavancin (TLV) pharmacokinetics in rats after a single subcutaneous dose of 35 mg/kg of body weight. The pharmacokinetic data were used to predict a TLV dose that simulates human exposure, and the efficacy of TLV was then evaluated using a TLV dose of 21 mg/kg every 12 h against Enterococcus faecalis OG1RF (TLV MIC of 0.06 μg/ml) in a rat endocarditis model with an indwelling catheter. Therapy was given for 3 days with TLV, daptomycin (DAP), or ampicillin (AMP) monotherapy and with combinations of TLV plus AMP, AMP plus gentamicin (GEN), and AMP plus ceftriaxone (CRO); rats were sacrificed 24 h after the last dose. Antibiotics were given to simulate clinically relevant concentrations or as used in other studies. TLV treatment resulted in a significant decrease in bacterial burden (CFU per gram) in vegetations from 6.0 log₁₀ at time 0 to 3.1 log₁₀ after 3 days of therapy. Bacterial burdens in vegetations were also significantly lower in the TLV-treated rats than in the AMP (P = 0.0009)- and AMP-plus-GEN (P = 0.035)-treated rats but were not significantly different from that of the AMP-plus-CRO-treated rats. Bacterial burdens from vegetations in TLV monotherapy and TLV-plus-AMP-and-DAP groups were similar to each other (P ≥ 0.05). Our data suggest that further study of TLV as a therapeutic alternative for deep-seated infections caused by vancomycin-susceptible E. faecalis is warranted.

Pharmacodynamics of Ceftaroline plus Ampicillin against Enterococcus faecalis in an In Vitro Pharmacokinetic/Pharmacodynamic Model of Simulated Endocardial Vegetations

The combination of ampicillin plus ceftaroline has been suggested to be more reliably synergistic against Enterococcus faecalis than ampicillin plus ceftriaxone using time-kill methods. The purpose of this study was to determine if this trend persists in a two-compartment model of simulated endocardial vegetations (SEV) using clinically relevant pharmacokinetic exposures of these antimicrobials. Three clinically derived E. faecalis strains were included in the study. The MICs of study antimicrobials were determined by broth microdilution. Simulations of ampicillin (2 g every 4 h [q4h]; maximum concentration of drug in serum [Cmax], 72.4 mg/liter; half-life [t1/2], 1.9 h), ceftaroline-fosamil (600 mg q8h; Cmax, 21.3 mg/liter; t1/2, 2.66 h), ceftriaxone (Cmax, 257 mg/liter; t1/2, 8 h), and ampicillin plus ceftaroline and ampicillin plus ceftriaxone were evaluated against 3 strains of E. faecalis isolated from patients with endocarditis in an in vitro PK/PD SEV model over 72 h, with a starting inoculum of ∼9 log10 CFU/g. All strains were susceptible to ampicillin (MIC, ≤2 mg/liter). Ceftaroline MICs varied from 2 to 16 mg/liter. All strains had ceftriaxone MICs of 256 mg/liter. W04 and W151 exhibited high-level aminoglycoside resistance but W07 did not. Ampicillin plus ceftaroline resulted in significantly greater reductions in CFU per gram by 72 h than ampicillin for all strains (P ≤ 0.025) than ampicillin plus ceftriaxone for W04 (P = 0.019) but not W07 or W151 (P ≥ 0.15). A 4-fold increase in ampicillin MIC was observed for W07 at 72 h, but this was prevented by the addition of ceftaroline or ceftriaxone. The combination of ampicillin plus ceftaroline appears to be at least as efficacious as ampicillin plus ceftriaxone and may lead to improved activity against some strains of E. faecalis, but these differences may be small and the clinical significance should not be overestimated.

Genome-wide Screening Identifies Phosphotransferase System Permease BepA to Be Involved in Enterococcus faecium Endocarditis and Biofilm Formation

Enterococcus faecium is a common cause of nosocomial infections, of which infective endocarditis is associated with substantial mortality. In this study, we used a microarray-based transposon mapping (M-TraM) approach to evaluate a rat endocarditis model and identified a gene, originally annotated as "fruA" and renamed "bepA," putatively encoding a carbohydrate phosphotransferase system (PTS) permease (biofilm and endocarditis-associated permease A [BepA]), as important in infective endocarditis. This gene is highly enriched in E. faecium clinical isolates and absent in commensal isolates that are not associated with infection. Confirmation of the phenotype was established in a competition experiment of wild-type and a markerless bepA mutant in a rat endocarditis model. In addition, deletion of bepA impaired biofilm formation in vitro in the presence of 100% human serum and metabolism of β-methyl-D-glucoside. β-glucoside metabolism has been linked to the metabolism of glycosaminoglycans that are exposed on injured heart valves, where bacteria attach and form vegetations. Therefore, we propose that the PTS permease BepA is directly implicated in E. faecium pathogenesis.

Infective endocarditis

Infective endocarditis occurs worldwide, and is defined by infection of a native or prosthetic heart valve, the endocardial surface, or an indwelling cardiac device. The causes and epidemiology of the disease have evolved in recent decades with a doubling of the average patient age and an increased prevalence in patients with indwelling cardiac devices. The microbiology of the disease has also changed, and staphylococci, most often associated with health-care contact and invasive procedures, have overtaken streptococci as the most common cause of the disease. Although novel diagnostic and therapeutic strategies have emerged, 1 year mortality has not improved and remains at 30%, which is worse than for many cancers. Logistical barriers and an absence of randomised trials hinder clinical management, and longstanding controversies such as use of antibiotic prophylaxis remain unresolved. In this Seminar, we discuss clinical practice, controversies, and strategies needed to target this potentially devastating disease.

The fibronectin-binding protein Fnm contributes to adherence to extracellular matrix components and virulence of Enterococcus faecium

The interaction between bacteria and fibronectin is believed to play an important role in the pathogenicity of clinically important Gram-positive cocci. In the present study, we identified a gene encoding a predicted fibronectin-binding protein of Enterococcus faecium (fnm), a homologue of Streptococcus pneumoniae pavA, in the genomes of E. faecium strain TX82 and all other sequenced E. faecium isolates. Full-length recombinant Fnm from strain TX82 bound to immobilized fibronectin in a concentration-dependent manner and also appeared to bind collagen type V and laminin, but not other proteins, such as transferrin, heparin, bovine serum albumin, mucin, or collagen IV. We demonstrated that the N-terminal fragment of Fnm is required for full fibronectin binding, since truncation of this region caused a 2.4-fold decrease (P < 0.05) in the adhesion of E. faecium TX82 to fibronectin. Deletion of fnm resulted in a significant reduction (P < 0.001) in the ability of the mutant, TX6128, to bind fibronectin relative to that of the wild-type strain; in situ reconstitution of fnm in the deletion mutant strain restored adherence. In addition, the Δfnm mutant was highly attenuated relative to TX82 (P ≤ 0.0001) in a mixed-inoculum rat endocarditis model. Taken together, these results demonstrate that Fnm affects the adherence of E. faecium to fibronectin and is important in the pathogenesis of experimental endocarditis.

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.

Enterococci and Their Interactions with the Intestinal Microbiome

The Enterococcus genus comprises over 50 species that live as commensal bacteria in the gastrointestinal (GI) tracts of insects, birds, reptiles, and mammals. Named "entero" to emphasize their intestinal habitat, Enterococcus faecalis and Enterococcus faecium were first isolated in the early 1900s and are the most abundant species of this genus found in the human fecal microbiota. In the past 3 decades, enterococci have developed increased resistance to several classes of antibiotics and emerged as a prevalent causative agent of health care-related infections. In U.S. hospitals, antibiotic use has increased the transmission of multidrug-resistant enterococci. Antibiotic treatment depletes broad communities of commensal microbes from the GI tract, allowing resistant enterococci to densely colonize the gut. The reestablishment of a diverse intestinal microbiota is an emerging approach to combat infections caused by antibiotic-resistant bacteria in the GI tract. Because enterococci exist as commensals, modifying the intestinal microbiome to eliminate enterococcal clinical pathogens poses a challenge. To better understand how enterococci exist as both commensals and pathogens, in this article we discuss their clinical importance, antibiotic resistance, diversity in genomic composition and habitats, and interaction with the intestinal microbiome that may be used to prevent clinical infection.