Linezolid-resistant Enterococcus faecalis isolated from a cord blood transplant recipient

Empiric use of linezolid in febrile hematology and hematopoietic stem cell transplantation patients colonized with vancomycin-resistant Enterococcus spp

OBJECTIVES

We conducted a retrospective study on the impact of the empiric use of linezolid on mortality in vancomycin-resistant Enterococcus spp (VRE)-colonized hematology and hematopoietic stem cell transplantation (HSCT) patients.

METHODS

VRE-colonized inpatients for whom complete data were available (n=100) were divided into two groups: those who received empiric linezolid in the course of fever refractory to broad-spectrum antibiotics, replacing the glycopeptide utilized for the previous 48 h, and those who did not (control group). All patients were followed until hospital discharge or death. The impact of linezolid and risk factors for all-cause mortality were evaluated; variables with p<0.10 were analyzed in a multivariate model. A Kaplan-Meier survival analysis was done to compare survival among febrile patients colonized by VRE who received empiric linezolid with patients who did not receive linezolid.

RESULTS

Patients empirically prescribed linezolid were generally younger (median age 33 vs. 44 years; p=0.008) and more likely to be recipients of an allogeneic HSCT (24 (68.6%) vs. 24 (36.9%); p=0.009) than patients who did not receive the drug. Fourteen (21.5%) VRE bloodstream infections were diagnosed, all in patients who did not receive empiric linezolid (p=0.002). In-hospital mortality was comparable in empiric linezolid and non-linezolid users (19 (54.3%) vs. 27 (41.5%), respectively; p=0.293). The Kaplan-Meier survival analysis showed no significant difference in survival comparing the group that received linezolid to the group that did not (p=0.72). Graft-versus-host disease (GVHD; odds ratio (OR) 5.90, 95% confidence interval (CI) 1.46-23.79; p=0.012) and persistence of neutropenia (OR 6.93, 95% CI 1.72-27.94; p=0.0065) were independent predictors of all-cause in-hospital death in HSCT patients, and persistence of neutropenia in non-HSCT patients (OR 8.12, 95% CI 1.22-53.8; p=0.030).

CONCLUSIONS

The empiric use of linezolid in VRE-colonized hematology patients had no impact on mortality, which appeared rather to be associated with the persistence of neutropenia in general and GVHD in the HSCT group.

Relative incidences and outcomes of Clostridium difficile infection following transplantation of unrelated cord blood, unrelated bone marrow, and related peripheral blood in adult patients: a single institute study

BACKGROUND

Clostridium difficile is a major cause of nosocomial diarrhea. The incidence and prognosis of C. difficile-associated diarrhea (CDAD) has not yet been assessed in adult patients after unrelated cord blood transplantation (uCBT).

METHODS

The medical records of 135 adult unrelated cord blood transplant recipients were reviewed retrospectively to investigate the clinical features of CDAD after uCBT. These data were compared to medical records of 39 unrelated bone marrow transplant recipients and 27 related peripheral blood stem cell transplant recipients as controls.

RESULTS

A total of 17 recipients developed CDAD, with onset occurring at a median of 22 days (range, 0-56 days) after transplantation. Among the unrelated cord blood transplant recipients, 11 (9%) developed CDAD. These results were comparable with those of CDAD after unrelated bone marrow transplantation (uBMT) (2/39, 6%) and related peripheral blood stem cell transplantation (rPBSCT) (4/27, 16%) (P=0.37). Fifteen of the infected recipients were successfully treated with oral metronidazole, vancomycin, or cessation of antibiotics. The remaining 2 recipients who developed CDAD after uCBT died of other causes. The development of CDAD did not negatively affect overall survival after uCBT.

CONCLUSIONS

These data indicate that the incidence and prognosis of CDAD after uCBT are comparable with those after uBMT and rPBSCT.

The first linezolid-resistant Enterococcus faecium in India: High level resistance in a patient with no previous antibiotic exposure

Linezolid provides high rates of the clinical cure and microbiological success in complicated infections due to Enterococcus spp., including vancomycin-resistant Enterococcus faecium. However, the emergence of resistance during linezolid treatment has been reported for clinical strains of Enterococcus, which is alarming given the fact that, this leaves the clinician with very few treatment options. We report the first case of linezolid resistant Enterococcus faecium from India, which was isolated from the blood culture of a hypoglycemic encephalopathy patient. There have been previous reports of linezolid resistant enterococci from different parts of the world, with minimum inhibitory concentration (MIC) ranging from 16 to 64 μg/mL and most of them were associated with vancomycin resistance but the isolate reported over here had an MIC of 1024 μg/mL and interestingly was sensitive to vancomycin.

Treatment considerations in vancomycin-resistant enterococcal bacteremia: daptomycin or linezolid? A review

BACKGROUND

Vancomycin resistant enterococcal bloodstream infections are an important cause of morbidity and mortality in hospitalized patients.

AIM OF THE REVIEW

A search of the literature was undertaken to determine the optimal antimicrobial therapy for the management of vancomycin resistant enterococcal bloodstream infections.

METHOD

MEDLINE, EMBASE, and the Cochrane Library (unrestricted to time or language) were searched for studies of vancomycin resistant enterococcal bloodstream infections in adults reporting outcomes of direct comparisons of linezolid versus daptomycin on November 26, 2012. Studies of basic science, reviews, commentaries, pharmacologic, epidemiologic, or pediatric studies, and those studies examining conditions other than enterococcal bacteremia, a single antimicrobial agent or other antimicrobials were excluded.

RESULTS

226 studies were screened for eligibility and yielded eight studies evaluating a total of 807 patients. Inter-rater agreement was 100 %. Qualitative evaluation of the studies was performed using the Newcastle-Ottawa scale. No randomized controlled trials were identified. All studies were retrospective cohorts and non-randomized. 458 (57 %) patients treated with linezolid and 349 (43 %) with daptomycin were analyzed. Variable comorbidities and severity of illness were described in the included studies and reported here for comparison.

CONCLUSION

The optimal treatment of vancomycin resistant enterococcal bloodstream infections is yet to be determined. Well-designed prospective studies are needed to lend more convincing evidence regarding choice of antimicrobial therapy for this important multidrug resistant organism.

Pharmacological issues of linezolid: an updated critical review

Linezolid is the first oxazolidinone agent introduced into clinical practice for use against Gram-positive bacteria that are resistant to beta-lactams and glycopeptides, including methicillin (meticillin)-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE). An optimal antibacterial effect is achieved when plasma drug concentrations are above the minimum inhibitory concentration (MIC) [T>MIC] for the entire length of treatment and the ratio between the area under the plasma concentration-time curve (AUC) and the MIC (AUC/MIC) is greater than 100, as is most commonly obtained with administration of the standard dosage of linezolid 600 mg twice daily. A wide tissue distribution, including the CNS and respiratory tract, nearly linear pharmacokinetics and good tolerability are additional characteristics of linezolid. However, variability in the drug pharmacokinetics associated with clinical conditions (e.g. sepsis, burn injuries, end-stage renal disease, cystic fibrosis), haemodialysis and/or young age may lower the T>MIC and the AUC/MIC ratio, thus impairing both antibacterial activity and prevention of mutants. In most cases, changes in the dosage or in the schedule of administration (e.g. an additional [third] daily dose) may improve the effectiveness of linezolid. It is worth noting that linezolid could affect its own metabolism as a result of protein synthesis inhibition in mitochondria, and this could lead to high plasma concentrations and an increased risk of non-negligible toxicities. The latter may be reported during long-term administration of linezolid or in the presence of some pathological conditions (e.g. renal disease or kidney transplantation) associated with high plasma drug concentrations. Therefore, treatment optimization should be considered a requirement for more effective and tolerable use of the drug, particularly in special populations.

Linezolid for patients with neutropenia: are bacteriostatic agents appropriate?

A long-held doctrine is that bactericidal antibiotics are required for infections in neutropenic patients. We evaluated the available published evidence regarding the role of linezolid, a bacteriostatic antibiotic, in neutropenic patients with Gram-positive infection. We retrieved two prospective comparative studies (one of them a double-blind, randomized, controlled trial), a prospective cohort study, two retrospective studies and eight case reports that focused on the use of linezolid for Gram-positive bacterial infections in neutropenic patients. Linezolid was administered to 438 neutropenic patients, mainly on a compassionate-use basis, as other antibiotics failed to cure the infection or were associated with significant adverse events. The clinical cure rate ranged between 57 and 87.3% in the intention-to-treat population of the prospective studies. In total, 56 out of 438 (12.7%) neutropenic patients that received linezolid died during therapy. In the only randomized controlled trial that compared linezolid with vancomycin in the treatment of Gram-positive infections in neutropenic patients, mortality was 5.6 versus 7.6%, respectively (p = 0.4). In conclusion, the available evidence suggests that linezolid may be successful in a significant proportion of neutropenic patients with infection, despite the fact that it is a bacteriostatic agent. Such data seem to justify further studies regarding the role of linezolid in this patient population.

In vivo efficacy of a novel oxazolidinone compound in two mouse models of infection

A novel oxazolidinone, AM 7359, was evaluated in two mouse models of Staphylococcus aureus infection. AM 7359 and linezolid were equally efficacious in a methicillin-susceptible S. aureus organ burden model and a methicillin-resistant S. aureus localized infection model. However, AM 7359 was eightfold more efficacious than linezolid against a linezolid- and methicillin-resistant S. aureus strain in this localized (thigh) infection model.

Role of linezolid in the treatment of orthopedic infections

Gram-positive organisms, particularly staphylococci and streptococci, are responsible for the majority of bone and joint infections. The rising incidence of antimicrobial resistance among Staphylococcus aureus, coagulase-negative staphylococci and enterococci means that novel antibiotics with unique mechanisms of antimicrobial activity are needed, especially in orthopedic infections. Linezolid is the first of the oxazolidinones, a new class of antibacterial agents particularly effective against Gram-positive infections including methicillin- and vancomycin-resistant strains. With an excellent oral bioavailability and acceptable safety profile, linezolid offers a valuable alternative to more traditional therapies, such as glycopeptides. No large randomized trials have been published on its use in patients with orthopedic infections, but early results are encouraging. Reported adverse events, especially bone marrow suppression and optic neuropathy seen with prolonged administration, mean that treatment of such patients must be undertaken with careful follow-up of laboratory tests. Until now, little resistance has been reported.

Central venous catheter colonization by linezolid-resistant, vancomycin-susceptible Enterococcus faecalis

Resistance to linezolid is rare in clinical isolates of Enterococcus faecalis. A strain resistant to this antimicrobial but susceptible to vancomycin was found to cause central venous catheter colonization in a patient who never received linezolid.

Comparison of testing methods for detection of decreased linezolid susceptibility due to G2576T mutation of the 23S rRNA gene in Enterococcus faecium and Enterococcus faecalis

E-test, Vitek 2, MicroScan, agar dilution, and disk diffusion were compared for detection of decreased linezolid susceptibility due to 23S rRNA gene G2576T mutation among 32 clinical Enterococcus strains initially reported as intermediate or resistant by E-test alone or Vitek 2 confirmed by E-test. Agar and broth dilution methods were in concordance with PCR detection of the mutation, and disk diffusion was somewhat less sensitive but equally specific.

Novel mechanism of resistance to oxazolidinones, macrolides, and chloramphenicol in ribosomal protein L4 of the pneumococcus

Two clinical Streptococcus pneumoniae isolates, identified as resistant to macrolides and chloramphenicol and nonsusceptible to linezolid, were found to contain 6-bp deletions in the gene encoding riboprotein L4. The gene transformed susceptible strain R6 so that it exhibited such resistance, with the transformants also showing a fitness cost. We demonstrate a novel bacterial mechanism of resistance to chloramphenicol and nonsusceptibility to linezolid.

New agents for the prevention of opportunistic infections in haematopoietic stem cell transplant recipients

Over the past three decades, autologous and allogeneic haematopoietic stem cell transplants (HSCTs) have become effective treatments for a variety of malignant and nonmalignant conditions. Patients who undergo HSCT receive high doses of chemotherapy and/or radiation that induce a prolonged period of profound immunodeficiency, placing them at high risk for infection from a panoply of opportunistic organisms. Although supportive treatment for these patients has markedly improved, 10-20% of allogeneic HSCT recipients will ultimately succumb to infection. Joint guidelines to prevent opportunistic infection were released in 2000 by the Centers for Disease Control, the Infectious Diseases Society of America, and the American Society of Blood and Marrow Transplantation; however, treatment decisions for these patients are often based on limited studies or depend on institution-specific transplant protocols and antibiotic resistance patterns. This paper will discuss new agents for preventing bacterial, fungal and viral infections in HSCT recipients.

Comparison of Mortality Associated with Vancomycin-Resistant and Vancomycin-Susceptible Enterococcal Bloodstream Infections: A Meta-analysis

BACKGROUND

Whether vancomycin resistance is independently associated with mortality among patients with enterococcal bloodstream infection (BSI) is controversial. To address this issue, we performed a systematic literature review with meta-analysis.

METHODS

Data sources were studies identified using the MEDLINE database (for articles from 1988 through March 2003), the Cochrane Library (for articles published up to March 2003), and bibliographies of identified articles. Inclusion criteria were that the study assessed mortality after enterococcal BSI, compared mortality after vancomycin-resistant enterococci (VRE) BSI with that after vancomycin-susceptible enterococci (VSE) BSI, and adjusted for severity of illness. Study exclusion criteria were as follows: no report of the adjusted measure of effect (adjusted odds ratio [OR], adjusted hazard ratio, or adjusted relative risk) of vancomycin resistance on mortality available and/or its adjusted 95% confidence interval (95% CI). Data in the tables, figures, or text were independently extracted by 2 of the authors. Individual weights were calculated using the 95% CI of the adjusted measures of effect performing both fixed-effect and random-effects models.

RESULTS

Nine studies were eligible (11 studies met the inclusion criteria, and 2 were excluded), with a total of 1614 enterococcal BSI episodes (683 VRE episodes and 931 VSE episodes). Patients with bacteremia caused by VRE were more likely to die than were those with VSE bacteremia (summary OR, 2.52; 95% CI, 1.9-3.4).

CONCLUSIONS

Vancomycin resistance is independently associated with increased mortality among patients with enterococcal bloodstream infection.

Treatment and prevention of enterococcal infections--alternative and experimental approaches

Enterococci are one of the leading types of organisms isolated from infections of hospitalised patients and the third most common cause of nosocomial bloodstream infections. They contribute significantly to patient mortality and morbidity, as well as healthcare costs. The emergence of resistance against virtually all clinically available antibiotics and the ability to transfer these resistance determinants to other pathogens demonstrates the urgency for an improved understanding of enterococcal virulence mechanisms, and the development of alternative treatment and prevention options. This article reviews new antimicrobials, vaccine targets, bacteriophage therapy, as well as treatments targeting virulence factors and biofilm, for their potential to treat and/or prevent enterococcal infections. Although clinical isolates often cause serious infections, so-called 'non-pathogenic' strains are used as therapeutics in the form of probiotics. Understanding the differences between true pathogens and beneficial commensals may help to evaluate future treatment and prophylactic options.