Daptomycin-resistant Enteroccoccus faecium in a patient with no prior exposure to daptomycin

A mutation in the glycosyltransferase gene lafB causes daptomycin hypersusceptibility in Enterococcus faecium

OBJECTIVES

To verify dissemination of daptomycin-non-susceptible Enterococcus faecium in a hospital where daptomycin was not in use and to understand the evolutionary pathways connecting daptomycin hypersusceptibility to non-susceptibility.

METHODS

Clonality of 26 E. faecium was assessed by PFGE and the STs of these isolates were determined. The most daptomycin-susceptible isolate was evolved in vitro by stepwise daptomycin selection, generating isolates for genome comparisons.

RESULTS

The spread of a high-risk daptomycin-non-susceptible VRE clone was detected, as was the occurrence of an unusual daptomycin-hypersusceptible strain (HBSJRP18). To determine the basis for daptomycin hypersusceptibility, we evolved HBSJRP18 in vitro and identified candidate genetic alterations potentially related to daptomycin susceptibility. Both lafB, encoding glycosyltransferase, which is putatively involved in lipoteichoic acid (LTA) biosynthesis, and dak, encoding a dihydroxyacetone kinase likely involved in fatty acid metabolism, were mutated in multiple independent experiments. Trans-complementation showed that the lafB polymorphism naturally occurring in HBSJRP18 caused its daptomycin hypersusceptibility. Fourier-transform infrared spectroscopy identified differences between the extracted LTA spectra from the hypersusceptible isolate and its revertant, as well as other non-susceptible variants, supporting a role for LafB in E. faecium LTA biosynthesis. Zeta potential difference was detected in one evolved dak mutant derivative. While much more susceptible to daptomycin, HBSJRP18 showed enhanced growth in the presence of piperacillin, suggesting that this, or another cell wall-targeting antibiotic, may have selected for the daptomycin-hypersusceptible phenotype.

CONCLUSIONS

Our findings provide new information on the basis for daptomycin susceptibility in E. faecium, with implications for limiting the development and spread of daptomycin resistance.

Emergence and Transmission of Daptomycin and Vancomycin-Resistant Enterococci Between Patients and Hospital Rooms

BACKGROUND

Vancomycin-resistant enterococci (VRE) are a major cause of morbidity and mortality in immunocompromised patients. Tracking the dissemination of VRE strains is crucial to understand the dynamics of emergence and spread of VRE in the hospital setting.

METHODS

Whole genome sequencing (WGS) and phylogenetic analyses were performed to identify dominant VRE strains and potential transmission networks between 35 patients with VRE-positive rectal swabs and their rooms (main rooms and bathrooms) on the leukemia (LKM) and the hematopoietic cell transplant (HCT) floors. Sequence types (STs), drug resistance genes, and patients' outcomes were also determined.

RESULTS

A total of 89 VRE strains grouped into 10 different STs, of which newly described STs were isolated from both floors (ST736, ST494, ST772, and ST1516). We observed highly genetically related strains transmitted between rooms, floors, and time periods in an average period of 39 days (ranging from 3 to 90 days). Of 5 VRE bacteremia events, 3 strains were lacking the pili operon fms14-17-13 (ST203) and the remaining 2 were resistant to daptomycin (DAP; ST736, ST664). Of 10 patients harboring DAP-resistant strains, only 2 were exposed to DAP within 4 months before strain recovery.

CONCLUSION

Our comparisons of VRE strains derived from the environment and immunocompromised patients confirmed horizontal transfer of highly related genetic lineages of multidrug-resistant (particularly to DAP) VRE strains between HCT and LKM patients and their room environment. Implementing WGS can be useful in distinguishing VRE reservoirs where interventions can be targeted to prevent and control the spread of highly resistant organisms.

Comparison of risk factors and outcomes of daptomycin-susceptible and -nonsusceptible vancomycin-resistant Enterococcus faecium infections in liver transplant recipients

BACKGROUND

Vancomycin-resistant Enterococcus faecium (VRE) infections are common in liver transplant recipients (LTRs). Daptomycin (DAP) is an important treatment for such infections; however, DAP-nonsusceptible VRE (DNS-VRE) are increasingly frequent. The purpose of this study was to compare clinical characteristics and outcomes of LTRs with infections due to DNS-VRE and DAP-susceptible VRE (DS-VRE).

METHODS

A single center, retrospective review of patients who underwent liver transplantation between January 1, 2010 and December 31, 2015 and developed infections due to DS-VRE or DNS-VRE post transplant was performed. Patients with DNS-VRE and DS-VRE infections were compared using univariate and logistic regression analysis.

RESULTS

Fourteen LTRs developed DNS-VRE and 20 LTRs developed DS-VRE infection post-transplantation. No significant differences were observed in demographics, model for end-stage liver disease (MELD) scores, causes of end-stage liver disease, or rate of pre-transplant perirectal VRE colonization between groups. Bleeding complications and renal replacement therapy were more common in the DNS-VRE group than in the DS-VRE group. The duration of transplant hospitalization and post-transplant intensive care unit (ICU) admission was longer in the DNS-VRE group than in the DS-VRE group. The 30-day and 6-month mortality rate associated with DNS-VRE infection was similar to that associated with DS-VRE infection.

CONCLUSIONS

Liver transplant recipients who develop DNS-VRE infection have higher bleeding complications and longer, more complex hospitalizations compared to those who develop DS-VRE infection post transplantation; however, mortality at 30 days and 6 months is not significantly worse. Further study is needed to determine optimal strategies for the prevention and treatment of DNS-VRE infections in LTRs.

Vancomycin-Resistant Enterococci: Therapeutic Challenges in the 21st Century

Vancomycin-resistant enterococci are serious health threats due in part to their ability to persist in rugged environments and their propensity to acquire antibiotic resistance determinants. Enterococci have now established a home in our hospitals and possess mechanisms to defeat most currently available antimicrobials. This article reviews the history of the struggle with this pathogen, what is known about the traits associated with its rise in the modern medical environment, and the current understanding of therapeutic approaches in severe infections caused by these microorganisms. As the 21st century progresses, vancomycin-resistant enterococci continue to pose a daunting clinical challenge.

Daptomycin nonsusceptible vancomycin resistant Enterococcus bloodstream infections in patients with hematological malignancies: risk factors and outcomes

Daptomycin is typically the treatment of choice for vancomycin resistant Enterococcus (VRE) bloodstream infections (BSI) in patients with hematological malignancies, but increasingly daptomycin nonsusceptible VRE are being reported. We reviewed our experience with daptomycin nonsusceptible VRE BSI among patients with hematological malignancies. We compared risk factors and outcomes of 20 patients with daptomycin nonsusceptible VRE BSI (case patients) with 40 matched control patients with daptomycin susceptible VRE BSI. Case patients had more complications (6/20 vs. 2/40, p = .013); all-cause mortality was similar in both groups. By multivariable analysis, only prior daptomycin exposure within 90 days was significantly associated with daptomycin nonsusceptible VRE BSI (odds ratio 26.71; p < .0001). In 25% of case patients, all of whose VRE isolates had an initial minimum inhibitory concentration (MIC) of 4 μg/mL, nonsusceptibility developed during treatment, raising the question of whether higher doses of daptomycin should be used for VRE BSI in hematology patients.

Vancomycin-resistant enterococci with reduced daptomycin susceptibility in Singapore: prevalence and associated factors

Prevalence of vancomycin-resistant enterococci (VRE) and use of daptomycin are increasing in Asia. To determine the prevalence of daptomycin non-susceptible enterococci (DNSE) and understand factors associated with reduced daptomycin susceptibility in VRE, we conducted a case-control study in a 1600-bed adult tertiary hospital in Singapore. All VRE isolates from inpatients in 2012 were tested for daptomycin susceptibility. Patients with VRE isolates of daptomycin minimum inhibitory concentration (MIC) ⩾3 µg/ml were classified as daptomycin-reduced susceptible VRE (DRS-VRE) and those with daptomycin MIC 4 µg/ml (DNSE). About half (135, 55%) had reduced susceptibility to daptomycin (MIC 3-4 µg/ml). None in the DS-VRE group had prior exposure to daptomycin. After adjusting for age, gender, comorbidity, hospitalization duration, surgical history, indwelling device use, and duration of antibiotic exposure in the prior 3 months, >1 movement between wards [odds ratio (OR) 0·35, 95% confidence interval (CI) 0·16-0·74, P = 0·006] and minocycline resistance (OR 0·45, 95% CI 0·25-0·84, P = 0·011) were independently associated with DRS-VRE. Our study suggests that daptomycin exposure, >1 movement between wards, and resistance to minocycline, were associated with reduced daptomycin susceptibility in VRE.

Saponins increase susceptibility of vancomycin-resistant enterococci to antibiotic compounds

The resistance of commensal bacteria to first and second line antibiotics has reached an alarming level in many parts of the world and endangers the effective treatment of infectious diseases. In this study, the influence of the plant-derived natural saponins glycyrrhizic acid, β-aescin, α-hederin, hederacoside C, and primulic acid 1 on the susceptibility of vancomycin-resistant enterococci (VRE) against antibiotics of clinical relevance was investigated in 20 clinical isolates. Furthermore, the antibacterial properties of saponins under study against VRE were determined in vitro. Results reveal that the susceptibility of VRE against gentamicin, teicoplanin, and daptomycin was enhanced in the presence of the saponin glycyrrhizic acid. Most importantly, glycyrrhizic acid (1 mg/ml) diminished the minimal inhibitory concentration (MIC) of gentamicin in gentamicin low-level intrinsic resistant VRE from 2 - >8 mg/l to ≤ 0.125-1 mg/l. The adding of β-aescin, α-hederin, hederacoside C, and primulic acid 1 to the antibiotics under study showed, compared to glycyrrhizic acid, less influence on the antibiotic potency. Only glycyrrhizic acid (1 mg/ml) and α‑hederin (0.2 mg/ml) showed weak antibacterial properties against the clinical isolates. Our study points towards a therapeutic potential of saponins in the coapplication with antibiotics for bacterial infections.

Whole-genome analysis of a daptomycin-susceptible enterococcus faecium strain and its daptomycin-resistant variant arising during therapy

Development of daptomycin (DAP) resistance in Enterococcus faecalis has recently been associated with mutations in genes encoding proteins with two main functions: (i) control of the cell envelope stress response to antibiotics and antimicrobial peptides (LiaFSR system) and (ii) cell membrane phospholipid metabolism (glycerophosphoryl diester phosphodiesterase and cardiolipin synthase [cls]). However, the genetic bases for DAP resistance in Enterococcus faecium are unclear. We performed whole-genome comparative analysis of a clinical strain pair, DAP-susceptible E. faecium S447 and its DAP-resistant derivative R446, which was recovered from a single patient during DAP therapy. By comparative whole-genome sequencing, DAP resistance in R446 was associated with changes in 8 genes. Two of these genes encoded proteins involved in phospholipid metabolism: (i) an R218Q substitution in Cls and (ii) an A292G reversion in a putative cyclopropane fatty acid synthase enzyme. The DAP-resistant derivative R446 also exhibited an S333L substitution in the putative histidine kinase YycG, a member of the YycFG system, which, similar to LiaFSR, has been involved in cell envelope homeostasis and DAP resistance in other Gram-positive cocci. Additional changes identified in E. faecium R446 (DAP resistant) included two putative proteins involved in transport (one for carbohydrate and one for sulfate) and three enzymes predicted to play a role in general metabolism. Exchange of the "susceptible" cls allele from S447 for the "resistant" one belonging to R446 did not affect DAP susceptibility. Our results suggest that, apart from the LiaFSR system, the essential YycFG system is likely to be an important mediator of DAP resistance in some E. faecium strains.

De novo daptomycin-nonsusceptible enterococcal infections

Potential emergence of enterococcal daptomycin nonsusceptibility among patients with no prior exposure to daptomycin poses clinical and public health challenges. We found that development of infections with daptomycin-nonsusceptible enterococci in these patients could be associated with sporadic emergence and clonal spread.

Daptomycin exposure precedes infection and/or colonization with daptomycin non-susceptible enterococcus

Background

Daptomycin non-susceptible enterococci (DNSE) are emerging as an important cause of healthcare-associated infection, however little is known about the epidemiology of DNSE. At the University of Iowa Hospitals and Clinics (UIHC) an increase in the frequency of patients infected and/or colonized with DNSE has occurred. The goals of this study were to evaluate potential factors associated with the development of DNSE colonization and/or infection and to compare the characteristics of patients with prior daptomycin exposure to those without prior daptomycin exposure.

Methods

The study is a retrospective case-series involving all patients with DNSE infection and/or colonization at UIHC, a 734-bed academic referral center, from June 1, 2005 to June 1, 2011.

Results

The majority of patients with DNSE colonization and/or infection had prior daptomycin exposure (15 of 25; 60%), a concomitant gastrointestinal process (19 of 25; 76%), or were immunosuppressed (21 of 25; 84%). DNSE infection was confirmed in 17 of 25 (68%) patients, including 9 patients with bacteremia. Twelve of 17 (71%) patients with DNSE infection had prior daptomycin exposure, including 7 of 9 (78%) patients with bacteremia. Compared to patients without prior daptomycin exposure, patients with prior daptomycin exposure were less likely to harbor E. faecalis (0% vs. 33%; p = 0.019). A high proportion of patients (10 of 25; 40%) died during their hospitalizations. Most enterococcal isolates were E. faecium (86%), and were vancomycin-resistant (72%). Molecular typing revealed a diverse population of DNSE.

Conclusions

Prior daptomycin exposure, immunosuppression, and/or a concomitant gastrointestinal process, may be associated with the development of DNSE. PFGE revealed a diverse population of DNSE, which along with both increasing numbers of DNSE detected yearly and increasing annual rates of daptomycin usage, suggests the emergence of DNSE under antimicrobial pressure.

Emergence of daptomycin-resistant VRE: experience of a single institution

Recent surveillance from US hospitals shows that more than 99.5% of vancomycin-resistant enterococci (VRE) isolates remain susceptible to daptomycin. This report describes emergence of daptomycin-resistant VRE at a major cancer center. The percentage of patients with daptomycin-resistant VRE bacteremia increased from 3.4% in 2007 to 15.2% in 2009 ([Formula: see text]). Without susceptibility data, empiric daptomycin therapy for VRE infections should be used with caution.

Vancomycin-resistant enterococcal urinary tract infections

Enterococci are a common cause of urinary tract infections (UTIs) among hospitalized patients. The rising prevalence of vancomycin-resistant enterococci (VRE) is of particular concern within many institutions because of its association with increased mortality and health care costs, as well as limited treatment options. Clinicians need to differentiate between VRE-associated urinary colonization, asymptomatic bacteriuria, and UTIs in order to determine the need for treatment, optimal therapeutic options, and length of therapy. Unnecessary use of antibiotics in patients simply colonized and not infected with VRE in the urine has become a large problem in both hospitals and long-term care facilities. A PubMed-MEDLINE search was conducted to identify all English-language literature published between January 1975 and March 2010 in order to summarize diagnostic criteria and treatment options for VRE UTIs. Several antimicrobials are discussed, with the specific focus on those with the potential to treat VRE UTIs and susceptibility patterns of VRE from urinary sources: ampicillin, amoxicillin, daptomycin, doxycycline, fosfomycin, imipenem-cilastatin, linezolid, nitrofurantoin, penicillin, piperacillin, quinupristin-dalfopristin, tetracycline, and tigecycline. Recommendations for empiric treatment of enterococcal UTIs and definitive treatment of VRE UTIs, including an evidence-based treatment algorithm, are proposed. Ampicillin generally is considered the drug of choice for ampicillin-susceptible enterococcal UTIs, including VRE. Nitrofurantoin, fosfomycin, and doxycycline have intrinsic activity against enterococci, including VRE, and are possible oral options for VRE cystitis. Linezolid and daptomycin should be reserved for confirmed or suspected upper and/or bacteremic VRE UTIs among ampicillin-resistant strains. Use of other antimicrobials, such as quinupristin-dalfopristin and tigecycline, should be evaluated on a case-by-case basis due to concerns of toxicity, resistance, and insufficient supportive data. Additional clinical data are needed to determine the optimal management and duration of therapy for VRE UTIs.

Daptomycin nonsusceptible enterococci: an emerging challenge for clinicians

Daptomycin is the only antibiotic with in vitro bactericidal activity against vancomycin-resistant Enterococcus (VRE) that is approved by the Food and Drug Administration (FDA). Data on the potential emergence of daptomycin nonsusceptibility among enterococci remain limited. We systematically reviewed the published literature for reports of isolates of enterococci that were daptomycin nonsusceptible and assessed the clinical significance and outcome of therapy. Based on susceptibility breakpoints approved by the Clinical Laboratory Standards Institute (CLSI), daptomycin has in vitro activity against >90% of enterococcal isolates. Less than 2% of enterococcal isolates were daptomycin nonsusceptible, with minimum inhibitory concentrations (MICs) >4 μg/mL. The prevalence of nonsusceptibility of VRE isolates to daptomycin may be overestimated due to the spread of clonally related isolates in health care settings. Clinicians should be aware of the possibility of the emergence of daptomycin nonsusceptibility and should closely monitor daptomycin MICs of enterococci isolated during treatment.

A potential role for daptomycin in enterococcal infections: what is the evidence?

Nosocomial infections caused by enterococci present a challenge for clinicians because treatment options are often limited due to the widespread occurrence of strains resistant to multiple antibiotics, including vancomycin. Daptomycin is a first-in-class cyclic lipopeptide that has proven efficacy for the treatment of Gram-positive infections. Although methicillin-resistant Staphylococcus aureus has been the most prominent target in the clinical development of daptomycin, this agent has demonstrated potent bactericidal activity in enterococcal infection models and has been used for the treatment of enterococcal infections in humans. In recent years, large-scale susceptibility studies have shown that daptomycin is active against >98% of enterococci tested, irrespective of their susceptibility to other antibacterial agents. This lack of cross-resistance reflects the fact that daptomycin has a mode of action distinct from those of other antibiotics, including glycopeptides. While there are limited data available from randomized controlled trials, extensive clinical experience with daptomycin in enterococcal infections (including bacteraemia, endocarditis, skin and soft tissue infections, bone and joint infections and urinary tract infections) has been reported. This growing body of evidence provides useful insights regarding the efficacy of daptomycin against enterococci in clinical settings.

Daptomycin in endocarditis and bacteraemia: a British perspective

Assessment of the place of daptomycin in the treatment of endocarditis and bacteraemia requires assimilation of data from one open-label randomized comparative clinical trial sized for equivalence, from registry data and from case reports. Selected relevant animal models and in vitro data are also considered in an effort to produce an integrated assessment of the current place of daptomycin in treatment. The evidence for the use of daptomycin is best in Staphylococcus aureus bacteraemia and endocarditis, but also includes some data on infections due to Enterococcus spp., especially if vancomycin-resistant. The emergence of resistance in a minority of patients on current dose regimens may mean that trials have to be repeated with higher doses, or the drug used in a combined therapy where rifampicin may be the best choice. In general, equivalence to comparator antibiotic regimens and a correlation for in vitro and in vivo findings have been demonstrated, but there are important gaps in the clinical data including a comparative equivalence trial in streptococcal and enterococcal endocarditis. Clinical benefit might be anticipated, but has not been proved, over aminoglycoside-containing regimens, and economic assessments are critical in the decision as to when and how daptomycin is deployed.

Vancomycin: understanding its past and preserving its future

The increase in vancomycin use in the 1980s to treat antibiotic-associated colitis and methicillin-resistant Staphylococcus aureus (MRSA) is largely responsible for the appearance of vancomycin-resistant enterococcus, which in turn spawned isolated cases of vancomycin-resistant S. aureus. Perhaps most worrisome to clinicians are strains of MRSA that are heteroresistant to vancomycin; these isolates are difficult to detect. Appropriate use of vancomycin coupled with awareness of infection control measures is paramount to abrogating the emergence of new vancomycin-resistant MRSA organisms and preserving its future efficacy. The continued reliance on vancomycin for the treatment of MRSA infections will depend on whether vancomycin resistance can be minimized. Newer antibacterial agents, particularly those with activity toward MRSA and vancomycin-resistant enterococcus, such as linezolid, quinupristin/dalfopristin, daptomycin, and tigecycline, may take a more prominent clinical role when gram-positive bacteria resistance to vancomycin further escalate.