Enterococcal bacteraemia 'silent but deadly': a population-based cohort study

In vitro resensitization of multidrug-resistant clinical isolates of Enterococcus faecium and E. faecalis through phage-antibiotic synergy

Bacteriophages are an increasingly attractive option for the treatment of antibiotic-resistant infections, but their efficacy is difficult to discern due to the confounding effects of antibiotics. Phages are generally delivered in conjunction with antibiotics, and thus, when patients improve, it is unclear whether the phages, antibiotics, or both are responsible. This question is particularly relevant for enterococcus infections, as limited data suggest phages might restore antibiotic efficacy against resistant strains. Enterococci can develop high-level resistance to vancomycin, a primary treatment. We assessed clinical and laboratory isolates of Enterococcus faecium and Enterococcus faecalis to determine whether we could observe synergistic interactions between phages and antibiotics. We identified synergy between multiple phages and antibiotics including linezolid, ampicillin, and vancomycin. Notably, antibiotic susceptibility did not predict synergistic interactions with phages. Vancomycin-resistant isolates (n = 6) were eradicated by the vancomycin-phage combination as effectively as vancomycin-susceptible isolates (n = 2). Transcriptome analysis revealed significant gene expression changes under antibiotic-phage conditions, especially for linezolid and vancomycin, with upregulated genes involved in nucleotide and protein biosynthesis and downregulated stress response and prophage-related genes. While our results do not conclusively determine the mechanism of the observed synergistic interactions between antibiotics and phages, they do confirm and build upon previous research that observed these synergistic interactions. Our work highlights how using phages can restore the effectiveness of vancomycin against resistant isolates. This finding provides a promising, although unexpected, strategy for moving forward with phage treatments for vancomycin-resistant Enterococcus infections.

Trends in Enterococcus faecium Bacteremia: Exploring Risk Factors with Emphasis on Prior Antibiotic Exposure

Enterococcal bacteremia (EB) is on the rise both in Sweden and globally. While Enterococcus faecalis (E. faecalis) is susceptible to ampicillin and piperacillin/tazobactam (pip/taz), Enterococcus faecium (E. faecium) is not. Historically, most enterococcal infections have been caused by E. faecalis, but the epidemiology is changing with increasing recognition of enterococci as nosocomial pathogens and the emergence of resistance to commonly used antimicrobial agents. The use of pip/taz has increased dramatically in Sweden, but it is unknown if this has affected the relative incidence of E. faecalis/E. faecium bacteremia. Here, we investigate whether the number and proportion of E. faecium bacteremia (EfmB) cases have increased. Additionally, risk factors associated with EfmB with a focus on prior antibiotic exposure are analyzed. Medical journals of 360 patients with EB admitted to Sahlgrenska University Hospital are reviewed. The proportion of EfmB cases increased from 41% in 2015 to 51% in 2021. Hospital-acquired infection, previous exposure to pip/taz, and carbapenems are identified as independent risk factors for EfmB. There are considerable patient-related differences between the EfmB and EfsB groups, but there is no difference in mortality rates. In conclusion, the increasing proportion of EfmB cases is concerning and is seen parallel to the expanding use of pip/taz, one possible contributing factor. Our findings suggest that a cautious approach to antibiotic use is essential to prevent the spread of antibiotic-resistant bacteria.

Epidemiological and microbial trends of infective endocarditis in western Norway: a 7-year prospective observational study

BACKGROUND

In this prospective, observational study, we aimed to investigate epidemiologic and microbial trends of infective endocarditis in western Norway.

METHODS

Clinical and microbiological characteristics of 497 cases of infective endocarditis from 2016 through 2022 were investigated. Categorical data were analysed using Chi-squared tests. Survival data were analysed using multiple Cox regression and reported using hazard ratios.

RESULTS

The mean age was 67 years, and 74% were men. The annual incidence rates varied from 10.4 to 14.1 per 100,000 inhabitants per year. Infective endocarditis on native valves was observed in 257 (52%) of the cases, whereas infective endocarditis on prosthetic valves and/or cardiac implantable electronic devices was observed in 240 (48%) of the cases: infection on surgically implanted bioprostheses was observed in 124 (25%) of the patients, infection on transcatheter aortic valve implantation was observed in 47 (10%) patients, and infection on mechanical valves was observed in 34 (7%) cases. Infection related to cardiac implantable electronic devices was observed in a total of 50 (10%) cases. Staphylococcus aureus and viridans streptococci were the most common microbial causes, and isolated in 145 (29%) and 130 (26%) of the cases, respectively. Enterococcal endocarditis showed a rising trend during the study period and constituted 90 (18%) of our total cases of infective endocarditis, and 67%, 47%, and 26% of the cases associated with prosthetic material, transcatheter aortic valve implantation and cardiac implantable electronic devices, respectively. There was no significant difference in 90-day mortality rates between the native valve endocarditis group (12%) and the group with infective endocarditis on prosthetic valves or cardiac implants (14%), p = 0.522. In a model with gender, age, people who inject drugs, microbiology and type of valve affected, only advanced age was significantly associated with fatal outcome within 90 days.

CONCLUSIONS

The incidence of infective endocarditis, and particularly enterococcal endocarditis, increased during the study period. Enterococci appeared to have a particular affinity for prosthetic cardiac material. Advanced age was the only independent risk factor for death within 90 days.

The Impact of Enterococcus spp. in the Immunocompromised Host: A Comprehensive Review

The immunocompromised host is usually vulnerable to infectious diseases due to broad-spectrum treatments and immunological dysregulation. The Enterococcus genus consists of normal gut commensals, which acquire a leading role in infective processes among individuals with compromised immune systems. These microorganisms may express a potential virulence and resistance spectrum, enabling their function as severe pathogens. The Enterococcus spp. infections in immunocompromised hosts appear to be difficult to resolve due to the immunological response impairment and the possibility of facing antimicrobial-resistant strains. As regards the related risk factors, several data demonstrated that prior antibiotic exposure, medical device insertion, prolonged hospitalization and surgical interventions may lead to Enterococcus overgrowth, antibiotic resistance and spread among critical healthcare settings. Herein, we present a comprehensive review of Enterococcus spp. in the immunocompromised host, summarizing the available knowledge about virulence factors, antimicrobial-resistance mechanisms and host-pathogen interaction. The review ultimately yearns for more substantial support to further investigations about enterococcal infections and immunocompromised host response.

The Role of Platelets in Infective Endocarditis

Over the last decade, the incidence of infective endocarditis (IE) has increased, with a change in the frequency of causative bacteria. Early evidence has substantially demonstrated the crucial role of bacterial interaction with human platelets, with no clear mechanistic characterization in the pathogenesis of IE. The pathogenesis of endocarditis is so complex and atypical that it is still unclear how and why certain bacterial species will induce the formation of vegetation. In this review, we will analyze the key role of platelets in the physiopathology of endocarditis and in the formation of vegetation, depending on the bacterial species. We provide a comprehensive outline of the involvement of platelets in the host immune response, investigate the latest developments in platelet therapy, and discuss prospective research avenues for solving the mechanistic enigma of bacteria-platelet interaction for preventive and curative medicine.

Molecular and Clinical Data of Antimicrobial Resistance in Microorganisms Producing Bacteremia in a Multicentric Cohort of Patients with Cancer in a Latin American Country

Patients with cancer have a higher risk of severe bacterial infections. This study aims to determine the frequency, susceptibility profiles, and resistance genes of bacterial species involved in bacteremia, as well as risk factors associated with mortality in cancer patients in Colombia. In this prospective multicenter cohort study of adult patients with cancer and bacteremia, susceptibility testing was performed and selected resistance genes were identified. A multivariate regression analysis was carried out for the identification of risk factors for mortality. In 195 patients, 206 microorganisms were isolated. Gram-negative bacteria were more frequently found, in 142 cases (68.9%): 67 Escherichia coli (32.5%), 36 Klebsiella pneumoniae (17.4%), and 21 Pseudomonas aeruginosa (10.1%), and 18 other Gram-negative isolates (8.7%). Staphylococcus aureus represented 12.4% (n = 25). Among the isolates, resistance to at least one antibiotic was identified in 63% of them. Genes coding for extended-spectrum beta-lactamases and carbapenemases, blaCTX-M and blaKPC, respectively, were commonly found. Mortality rate was 25.6% and it was lower in those with adequate empirical antibiotic treatment (22.0% vs. 45.2%, OR: 0.26, 95% CI: 0.1-0.63, in the multivariate model). In Colombia, in patients with cancer and bacteremia, bacteria have a high resistance profile to beta-lactams, with a high incidence of extended-spectrum beta-lactamases and carbapenemases. Adequate empirical treatment diminishes mortality, and empirical selection of treatment in this environment of high resistance is of key importance.

Enterococcus faecalis bloodstream infection: does infectious disease specialist consultation make a difference?

PURPOSE

To evaluate the relationship between mortality or relapse of bloodstream infection (BSI) due to Enterococcus faecalis and infectious diseases specialist consultation (IDC) and other factors potentially associated with outcomes.

METHODS

In a tertiary-care center, consecutive adult patients with E. faecalis BSI between January 1, 2016 and January 31, 2019, were prospectively followed. The management of E. faecalis BSI was evaluated in terms of adherence to evidence-based quality-of-care indicators (QCIs). IDC and other factors potentially associated with 90-day-mortality or relapse of E. faecalis BSI were analyzed by multivariate logistic regression.

RESULTS

A total of 151 patients with a median age of 68 years were studied. IDC was performed in 38% of patients with E. faecalis BSI. 30 cases of endocarditis (20%) were diagnosed. All-cause in-hospital mortality was 23%, 90-day mortality was 37%, and 90-day relapsing E. faecalis BSI was 8%. IDC was significantly associated with better adherence to 5 QCIs. Factors significantly associated with 90-day mortality or relapsing EfB in multivariate analysis were severe sepsis or septic shock at onset (HR 4.32, CI 2.36e7.88) and deep-seated focus of infection (superficial focus HR 0.33, CI 0.14e0.76).

CONCLUSION

Enterococcus faecalis bacteremia is associated with a high mortality. IDC contributed to improved diagnostic and therapeutic management.

Enterococcus spp.: Is It a Bad Choice for a Good Use-A Conundrum to Solve?

Since antiquity, the ubiquitous lactic acid bacteria (LAB) Enterococci, which are just as predominant in both human and animal intestinal commensal flora, have been used (and still are) as probiotics in food and feed production. Their qualities encounter several hurdles, particularly in terms of the array of virulence determinants, reflecting a notorious reputation that nearly prevents their use as probiotics. Additionally, representatives of the Enterococcus spp. genus showed intrinsic resistance to several antimicrobial agents, and flexibility to acquire resistance determinants encoded on a broad array of conjugative plasmids, transposons, and bacteriophages. The presence of such pathogenic aspects among some species represents a critical barrier compromising their use as probiotics in food. Thus, the genus neither has Generally Recognized as Safe (GRAS) status nor has it been included in the Qualified Presumption of Safety (QPS) list implying drastic legislation towards these microorganisms. To date, the knowledge of the virulence factors and the genetic structure of foodborne enterococcal strains is rather limited. Although enterococcal infections originating from food have never been reported, the consumption of food carrying virulence enterococci seems to be a risky path of transfer, and hence, it renders them poor choices as probiotics. Auspiciously, enterococcal virulence factors seem to be strain specific suggesting that clinical isolates carry much more determinants that food isolates. The latter remain widely susceptible to clinically relevant antibiotics and subsequently, have a lower potential for pathogenicity. In terms of the ideal enterococcal candidate, selected strains deemed for use in foods should not possess any virulence genes and should be susceptible to clinically relevant antibiotics. Overall, implementation of an appropriate risk/benefit analysis, in addition to the case-by-case assessment, the establishment of a strain's innocuity, and consideration for relevant guidelines, legislation, and regulatory aspects surrounding functional food development seem to be the crucial elements for industries, health-staff and consumers to accept enterococci, like other LAB, as important candidates for useful and beneficial applications in food industry and food biotechnology. The present review aims at shedding light on the world of hurdles and limitations that hampers the Enterococcus spp. genus and its representatives from being used or proposed for use as probiotics. The future of enterococci use as probiotics and legislation in this field are also discussed.

Enterococcal Endocarditis: Hiding in Plain Sight

Enterococcus faecalis is a major opportunistic bacterial pathogen of increasing clinical relevance. A substantial body of experimental evidence suggests that early biofilm formation plays a critical role in these infections, as well as in colonization and persistence in the GI tract as a commensal member of the microbiome in most terrestrial animals. Animal models of experimental endocarditis generally involve inducing mechanical valve damage by cardiac catheterization prior to infection, and it has long been presumed that endocarditis vegetation formation resulting from bacterial attachment to the endocardial endothelium requires some pre-existing tissue damage. Here we review both historical and contemporary animal model studies demonstrating the robust ability of E. faecalis to directly attach and form stable microcolony biofilms encased within a bacterially-derived extracellular matrix on the undamaged endovascular endothelial surface. We also discuss the morphological similarities when these biofilms form on other host tissues, including when E. faecalis colonizes the GI epithelium as a commensal member of the normal vertebrate microbiome - hiding in plain sight where it can serve as a source for systemic infection via translocation. We propose that these phenotypes may allow the organism to persist as an undetected infection in asymptomatic individuals and thus provide an infectious reservoir for later clinical endocarditis.

Management of enterococcal central line-associated bloodstream infections in patients with cancer

OBJECTIVE

Enterococcus species are the third most common organisms causing central line-associated bloodstream infections (CLABSIs). The management of enterococcal CLABSI, including the need for and timing of catheter removal, is not well defined. We therefore conducted this study to determine the optimal management of enterococcal CLABSI in cancer patients.

METHODS

We reviewed data for 542 patients diagnosed with Enterococcus bacteremia between September 2011 to December 2018. After excluding patients without an indwelling central venous catheter (CVC), polymicrobial bacteremia or with CVC placement less than 48 h from bacteremia onset we classified the remaining 397 patients into 3 groups: Group 1 (G1) consisted of patients with CLABSI with mucosal barrier injury (MBI), Group 2 (G2) included patients with either catheter-related bloodstream infection (CRBSI) as defined in 2009 Clinical Practice Guidelines for the Diagnosis and Management of Intravascular Catheter-Related Infection by the Infectious Diseases Society of America (IDSA) or CLABSI without MBI, and Group 3 (G3) consisted of patients who did not meet the CDC criteria for CLABSI. The impact of early (< 3 days after bacteremia onset) and late (3-7 days) CVC removal was compared. The composite primary outcome included absence of microbiologic recurrence, 90-day infection-related mortality, and 90-day infection-related complications.

RESULTS

Among patients in G2, CVC removal within 3 days of bacteremia onset was associated with a trend towards a better overall outcome than those whose CVCs were removed later between days 3 to 7 (success rate 88% vs 63%). However, those who had CVCs retained beyond 7 days had a similar successful outcome than those who had CVC removal < 3 days (92% vs. 88%). In G1, catheter retention (removal > 7 days) was associated with a better success rates than catheter removal between 3 and 7 days (93% vs. 67%, p = 0.003). In non-CLABSI cases (G3), CVC retention (withdrawal > 7 days) was significantly associated with a higher success rates compared to early CVC removal (< 3 days) (90% vs. 64%, p = 0.006).

CONCLUSION

Catheter management in patients with enterococcal bacteremia is challenging. When CVC removal is clinically indicated in patients with enterococcal CLABSI, earlier removal in less than 3 days may be associated with better outcomes. Based on our data, we cannot make firm conclusions about whether earlier removal (< 3 days) could be associated with better outcomes in patients with Enterococcal CLABSI whose CVC withdrawal is clinically indicated. In contrast, it seemed that catheter retention was associated to higher success outcome rates. Therefore, future studies are needed to clearly assess this aspect.

Urinary tract infection caused by Enterococcus spp.: Risk factors and mortality. An observational study

BACKGROUND AND OBJECTIVE

Urinary tract infections (UTIs) are frequently caused by Enterococcus spp. This work aims to define the risk factors associated with UTIs caused by Enterococci and to determine its overall mortality and predictive risk factors.

MATERIALS AND METHODS

A retrospective study was conducted on bacteremic UTIs caused by Enterococcus spp. among inpatients. We compared 106 inpatients with bacteremic UTIs caused by Enterococcus spp. vs. a random sample of 100 inpatients with bacteremic UTIs caused by other enterobacteria.

RESULTS

A total of 106 inpatients with UTIs caused by Enterococcus spp. were analyzed, 51 of whom had concomitant positive blood cultures. Distribution by species was 83% E. faecalis and 17% E. faecium. The mean Charlson Comorbidity Index score was 5.9±2.9. Upon comparing bacteremic UTIs caused by Enterococcus spp. vs. bacteremic UTIs caused by others enterobacteria, we found the following independent predictors of bacteremic UTI by Enterococcus: male sex, obstructive uropathy, nosocomial infection, cancers of the urinary system, and previous antimicrobial treatment. Overall, inpatient mortality was 16.5% and was associated with a higher Sequential Organ Failure Assessment (SOFA) score (>4); severe comorbidities such as immunosuppression, malignant hemopathy, and nephrostomy; and Enterococcus faecium species and its pattern of resistance to ampicillin or vancomycin (p<0.05). Appropriate empiric antibiotic therapy was not associated with a better prognosis (p>0.05).

CONCLUSIONS

Enterococcus spp. is a frequent cause of complicated UTI in patients with risk factors. High mortality secondary to a severe clinical condition and high comorbidity may be sufficient for justifying the implementation of empiric treatment of at-risk patients.

Extracellular superoxide produced by Enterococcus faecalis reduces endometrial receptivity via inflammatory injury

PROBLEM

Chronic endometritis (CE) can cause infertility. Enterococcus faecalis is an opportunistic pathogen that is often found in the endometrium of CE patients. However, the mechanisms by which E. faecalis affects endometrial health are still unclear. In this study, we investigated the mechanism how extracellular superoxide produced by E. faecalis affected the endometrial receptivity.

METHOD OF STUDY

Superoxide production was blocked by deleting menB gene in E. faecalis OG1RF. Endometrial epithelial cells were infected by superoxide-producing E. faecalis OG1RF and superoxide-deficient strain WY84. Inflammatory cytokines, apoptosis, and biomarkers for the endometrial receptivity were analyzed.

RESULTS

Infection of endometrial epithelial cells with superoxide-producing E. faecalis OG1RF induced expression of inflammatory cytokines, promoted apoptosis, and down-regulated expression of receptivity biomarkers compared to uninfected control. In contrast, superoxide-deficient E. faecalis WY84 had little effect on inflammatory cytokine production, apoptosis, and endometrial receptivity biomarkers.

CONCLUSIONS

Extracellular superoxide produced by E. faecalis is an important virulence factor for E. faecalis-induced endometritis leading to reduced receptivity of endometrial epithelial cells.

Pathogen influence on epidemiology, diagnostic evaluation and management of infective endocarditis

Infective endocarditis (IE) is uncommon and has, in the past, been most often caused by viridans group streptococci (VGS). Due to the indolent nature of these organisms, the phrase 'subacute bacterial endocarditis', so-called 'SBE', was routinely used as it characterised the clinical course of most patients that extended for weeks to months. However, in more recent years, there has been a significant shift in the microbiology of IE with the emergence of staphylococci as the most frequent pathogens, and for IE due to Staphylococcus aureus, the clinical course is acute and can be associated with sepsis. Moreover, increases in IE due to enterococci have occurred and have been characterised by treatment-related complications and worse outcomes. These changes in pathogen distribution have been attributed to a diversification in the target population at risk of IE. While prosthetic valve endocarditis and history of IE remain at highest risk of IE, the rise in prevalence of injection drug use, intracardiac device implantations and other healthcare exposures have heavily contributed to the existing pool of at-risk patients. This review focuses on common IE pathogens and their impact on the clinical profile of IE.

Risks associated with enterococci as probiotics

Probiotics are naturally occurring microorganisms that confer health benefits by altering host commensal microbiota, modulating immunity, enhancing intestinal barrier function, or altering pain perception. Enterococci are human and animal intestinal commensals that are used as probiotics and in food production. These microorganisms, however, express many virulence traits including cytolysin, proteases, aggregation substance, capsular polysaccharide, enterococcal surface protein, biofilm formation, extracellular superoxide, intestinal translocation, and resistance to innate immunity that can lead to serious hospital-acquired infections. In addition, enterococci are facile in acquiring antibiotic resistance genes to many clinically important antibiotics encoded on a wide variety of conjugative plasmids, transposons, and bacteriophages. The pathogenicity and disease burden caused by enterococci render them poor choices as probiotics. No large, randomized, placebo-controlled clinical trials have demonstrated the safety and efficacy of any enterococcal probiotic. As a result, no enterococcal probiotic has been approved by the United States Food and Drug Administration for the treatment, cure, or amelioration of human disease. In 2007, the European Food Safety Authority concluded that enterococci do not meet the standard for "Qualified Presumption of Safety". Enterococcal strains used or proposed for use as probiotics should be carefully screened for efficacy and safety.

Eradication of Vancomycin-Resistant Enterococci by Combining Phage and Vancomycin

Currently, effective options are needed to fight vancomycin-resistant Enterococcus faecalis (VRE). The present study shows that combinations of phage and vancomycin are highly efficient against VRE, despite being resistant to the antibiotic. Vancomycin-phage EFLK1 (anti-E. faecalis phage) synergy was assessed against VRE planktonic and biofilm cultures. The effect of the combined treatment on VRE biofilms was determined by evaluating the viable counts and biomass and then visualized using scanning electron microscopy (SEM). The cell wall peptidoglycan was stained after phage treatment, visualized by confocal microscopy and quantified by fluorescence activated cell sorting (FACS) analysis. The combined treatment was synergistically effective compared to treatment with phage or antibiotic alone, both in planktonic and biofilm cultures. Confocal microscopy and FACS analysis showed that fluorescence intensity of phage-treated bacteria increased eight-fold, suggesting a change in the peptidoglycan of the cell wall. Our results indicate that with combined treatment, VRE strains are not more problematic than sensitive strains and thus give hope in the continuous struggle against the current emergence of multidrug resistant pathogens.