Response to emerging infection leading to outbreak of linezolid-resistant enterococci

Risk factors and outcome associated with the acquisition of MDR linezolid-resistant Enterococcus faecium: a report from tertiary care centre

OBJECTIVE

The aim of the study was to determine the resistance profile of linezolid-resistant Enterococcus faecium (LREfm) and to investigate risk factors and outcomes associated with LREfm infections.

MATERIAL AND METHODS

A prospective case-control study was undertaken (2019 to 2022) and included 202 patients with LREfm infections (cases) and 200 controls with LSEfm infections. Clinical data was prospectively collected and analysed for risk factors and outcomes. Antimicrobial susceptibility was performed, and resistance profile was studied using WHOnet.

RESULTS

Risk factors associated with LREfm infection were site of infection UTI (OR 5.87, 95% CI 2.59-13.29, p ≤ 0.001), prior use of carbapenem (OR 2.85 95% CI 1.62-5.02, p ≤ 0.001) and linezolid (OR 10.13, 95% CI 4.13-24.82, p ≤ 0.001), use of central line (OR 5.54, 95% CI 2.35-13.09, p ≤ 0.001), urinary catheter (OR 0.29, 95% CI 0.12-0.70, p ≤ 0.001) and ventilation (OR 14.87, 95% CI 7.86-28.11, p ≤ 0.007). The hospital stay 8-14 days (< 0.001) prior to infection and the mortality rate (p = 0.003) were also significantly high among patients with LREfm infections. Linezolid and vancomycin resistance coexisted; further, MDR, XDR and PDR phenotypes were significantly higher among LREfm.

CONCLUSION

This study provided insight into epidemiology of MDR LREfm in a setting where linezolid use is high. The main drivers of infections with LREfm are multiple, including use of carbapenems and linezolid. Invasive procedures and increased hospital stay facilitate spread through breach in infection control practises. As therapeutic options are limited, ongoing surveillance of LREfm and VRE is critical to guide appropriate use of linezolid and infection control policies.

Linezolid Resistance in Enterococcus faecalis Associated With Urinary Tract Infections of Patients in a Tertiary Hospitals in China: Resistance Mechanisms, Virulence, and Risk Factors

Background:Enterococcus faecalis has been commonly considered as one of the major pathogens of the urinary tract infection (UTI) in human host worldwide, whereas the molecular characteristics of E. faecalis clinical isolates from the patients with UTI in China remains seldomly reported. This study aimed to investigate the resistance mechanism, molecular characteristics and risk factors of E. faecalis clinical isolates from patients with UTI in China.

Methods: A total of 115 non-duplicated E. faecalis clinical isolates from patients with UTI were retrospectively collected in a tertiary hospital in China and their clinical data was further analyzed. The linezolid and tedizolid susceptibility were determined by agar dilution. The resistance genes, including erm(A), erm(B), erm(C), tet(M), optrA, cfr, cfr(B), poxtA, and MLST-based housekeeping genes were investigated by PCR.

Results: In 115 non-duplicated E. faecalis clinical isolates from the patients with UTI in this hospital setting, the frequency of linezolid or tedizolid-resistant/intermediate isolates were 22.61 and 13.04%, respectively, and the frequency of linezolid-resistant/intermediate E. faecalis clinical isolates carrying with erm(A) were 86%. Among the five linezolid-resistant E. faecalis strains found in this study, three optrA-positive isolates and the other two linezolid-resistant strains were G2576U genetic mutations in the V domain of the 23S rRNA genes. The ST clonality analysis indicated that 31.42% (11/35) of ST16 E. faecalis UTI isolates were not susceptible to linezolid. Moreover, the univariable analysis indicated that the high risk factors of linezolid-resistant/intermediate E. faecalis infections involved the indwelling catheter, trachea cannula catheter and the carriage of erm(A) or optrA. Furthermore, the indwelling catheter and trachea cannula catheter were demonstrated as the independent predictors of linezolid-resistant/intermediate E. faecalis strains in patients with UTI by multivariable analysis.

Conclusion: Linezolid-resistant/intermediate E. faecalis associated with urinary tract infections of patients in this hospital setting from China might be explained by the high carriage frequency of optrA genes and moreover, indwelling catheter and trachea cannula should be considered as the independent predictors of linezolid-resistant/intermediate E. faecalis infections. The transmission mechanism of linezolid-resistant/intermediate E. faecalis in this hospital setting should be further studied.

Analysis of bacteriological pollution and the detection of antibiotic resistance genes of prevailing bacteria emanating from pig farm seepage

Management and disposal of pig farm seepage constitute a serious environmental challenge, and seepage discharge from agricultural waste‐water is considered to be one of the greatest contributors of organic substances, bacterial pathogens, and antibiotic resistance genes into the environment. The objectives of this study were to assess the level of bacteriological pollution and to identify the resident antibiotic‐resistant genes of culturable bacteria from a studied pig farm seepage. Enumeration of the viable bacterial cell of plated bacteria suspensions (10⁻¹ to 10⁻⁸ cfu/mL) was performed; also, identification of pure bacterial colonies was done using an API 20E bacterial identification kit. CLSI guidelines for antimicrobial susceptibility testing were adopted to determine the antibiotic susceptibility/resistance of the cultured bacterial isolates. Identification of resident‐resistant genes was done using molecular biology procedures. The results on viable cells in seepage samples ranged from 4.30 × 10² to 1.29 × 10⁹ cfu/mL. Pseudomonas luteola, Enterococcus vulneris, Salmonella choleraesuis spp arizonae, Escherichia coli, Enterobacter cloacae, Proteus mirabillis etc. were isolated from the pig farm soil samples. Almost all of the cultured isolates were resistant to Penicillin G, Vancomycin, Oxytetracycline, Spectinomycin, and Lincomycin. The most frequent resistant genes detected in the isolates were Van A, Van B, InuA, aph (3”)‐llla, bla_TEM, Otr A, and Otr B. It was inferred from the study that Pig farm seepage has the ability to cause bacterial pollution that may negatively impact the natural environment, by introducing bacteria pathogens that harbor antibiotic‐resistant genes.

Risk Factors and Outcomes Associated With Acquisition of Daptomycin and Linezolid-Nonsusceptible Vancomycin-Resistant Enterococcus

Background

Vancomycin-resistant enterococcus (VRE) causes substantial health care–associated infection with increasing reports of resistance to daptomycin or linezolid. We conducted a case–control study reporting 81 cases of daptomycin and linezolid–nonsusceptible VRE (DLVRE), a resistance pattern not previously reported.

Methods

We reviewed VRE isolates from June 2010 through June 2015 for nonsusceptibility to both daptomycin (minimum inhibitory concentration [MIC] > 4) and linezolid (MIC ≥ 4). We matched cases by year to control patients with VRE susceptible to both daptomycin and linezolid and performed retrospective chart review to gather risk factor and outcome data.

Results

We identified 81 DLVRE cases. Resistance to both daptomycin and linezolid was more common than resistance to either agent individually. Compared with susceptible VRE, DLVRE was more likely to present as bacteremia without focus (P < 0.01), with DLVRE patients more likely to be immune suppressed (P = .04), to be neutropenic (P = .03), or to have had an invasive procedure in the prior 30 days (P = .04). Any antibiotic exposure over the prior 30 days conferred a 4-fold increased risk for DLVRE (odds ratio [OR], 4.25; 95% confidence interval [CI], 1.43−12.63; P = .01); multivariate analysis implicated daptomycin days of therapy (DOT) over the past year as a specific risk factor (OR, 1.10; 95% CI, 1.01−1.19; P = .03). DLVRE cases had longer hospitalizations (P = .04) but no increased risk for in-hospital death.

Conclusions

DLVRE is an emerging multidrug-resistant pathogen associated with immune suppression, neutropenia, and recent invasive procedure. Prior antibiotic exposure, specifically daptomycin exposure, confers risk for acquisition of DLVRE.

Prolonged linezolid use is associated with the development of linezolid-resistant Enterococcus faecium

We assessed risk factors for and outcomes of linezolid-resistant vancomycin-resistant Enterococcus faecium (LRVREF) bacteremia over 7 years. Thirty-four LRVREF cases were matched to 68 linezolid-susceptible VREF controls. The odds of bacteremia with LRVREF increased by 7% for each additional day of prior linezolid exposure.

Evaluation antibacterial and antibiofilm activity of the antimicrobial peptide P34 against Staphylococcus aureus and Enterococcus faecalis

The adhesion ability of bacteria to abiotic surfaces has important implications in food industries, because these organisms can survive for long periods through the biofilm formation. They can be transferred from one place to another in the industry causing contamination of the food processing environment. In this study, the antibacterial and antibiofilm activities of the antimicrobial peptide P34, characterized as a bacteriocin-like substance (BLS P34) were tested against planktonic and sessile cells of Staphylococcus aureus and Enterococcus faecalis isolated from foods. The BLS P34 showed inhibitory effect against all planktonic cells of E. faecalis. The inhibition of biofilm formation and the eradication of pre-formed biofilm were evaluated with the crystal violet assay and with the reduction of 3-bromide [4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium. The BLS P34 promoted a reduction of percentage of adhered microbial cells on the surface, not being able to perform the complete elimination of biofilm formation. The metabolic activity of S. aureus biofilms decreased considerably between 41-95%. However, E. faecalis cells showed up metabolically stimulated. The BLS P34 has the potential antibiofilm for the species S. aureus. Studies suggest more detailed approaches to a better understanding of the interactions between the antimicrobial and bacterial cells within the biofilm structure.

Characteristics of and Virulence Factors Associated with Biofilm Formation in Clinical Enterococcus faecalis Isolates in China

Enterococcus faecalis biofilm traits and distribution characteristics in China have not been clarified. This study aimed to determine the prevalence and characteristics of E. faecalis biofilm formation in a sample of clinical isolates and to explore the virulence factors associated with biofilm formation in those isolates. A total of 265 E. faecalis isolates were collected from patients in Shenzhen, China. Virulence genes were detected within the genomes of the microbes by polymerase chain reaction. The isolates were subjected to multilocus sequence typing (MLST) based on housekeeping genes. Biofilms were detected by crystal violet staining. The expression levels of the clinical E. faecalis isolates’ genes were determined by quantitative real-time polymerase chain reaction. The prevalence of biofilm formation among E. faecalis clinical isolates was 47.2%. MLST yielded 44 different sequence types (STs). The main STs were ST16 and ST179; the ST16 isolates were more likely to form strong or medium biofilm than the ST179 isolates (p < 0.001). Strong or medium biofilm formation was more common in linezolid-resistant isolates than in linezolid-sensitive isolates (p = 0.001). Biofilm formation was more frequently detected in enterococcal surface protein (esp+), surface aggregating protein (asa1+), cytolysin A (cylA+), or aggregation substance (agg+) positive isolates than in isolates that were negative (-) for these virulence factors. Multivariate regression analysis indicated that cylA [odds ratio (OR) 4.083, p < 0.001] was a risk factor for weak biofilm formation, and that esp (OR 8.207, p < 0.001) was a risk factor for strong or medium biofilm formation. The expression of cylA was raised (4.02 to 6.00-fold) in weak biofilm isolates compared to the biofilm-negative isolates, and the expression of esp was greatly elevated (11.39 to 134.08-fold) in strong biofilm isolates compared to biofilm-negative isolates. In conclusion, the ST16 classification and linezolid resistance were positively associated with strong/medium biofilm formation in clinical E. faecalis isolates. cylA was associated with weak biofilm formation, and esp was only associated with strong or medium biofilm formation of the clinical E. faecalis isolates.

The emerging problem of linezolid-resistant enterococci

Enterococcus is a significant pathogen in numerous infections, particularly in nosocomial infections, and is thus a great challenge to clinicians. Linezolid (LNZ), an oxazolidinone antibiotic, is an important therapeutic option for infections caused by Gram-positive bacterial pathogens, especially vancomycin-resistant enterococci. A systematic review was performed of the available literature on LNZ-resistant enterococci (LRE) to characterise these infections with respect to epidemiological, microbiological and clinical features. The results validated the potency of LNZ against enterococcal infections, with a sustained susceptibility rate of 99.8% in ZAAPS and 99.2% in LEADER surveillance programmes. Patients with LRE had been predominantly exposed to LNZ prior to isolation of LRE, with a mean treatment duration of 29.8±48.8days for Enterococcus faecalis and 23.1±21.4days for Enterococcus faecium. Paradoxically, LRE could also develop in patients without prior LNZ exposure. LNZ resistance was attributed to 23S rRNA (G2576T) mutations (51.2% of E. faecalis and 80.5% of E. faecium) as well as presence of the cfr gene (4.7% and 4.8%, respectively), which could transfer horizontally among the strains. In addition to the cfr gene, 32 cases of optrA-positive LRE were identified. Further study is required to determine the prevalence of novel resistance genes. The emergence of LRE thus hampers the treatment of such infections, which warrants worldwide surveillance.

First outbreak of colonization by linezolid- and glycopeptide-resistant Enterococcus faecium harbouring the cfr gene in a UK nephrology unit

AIM

To describe an outbreak of colonization by linezolid- and glycopeptide-resistant Enterococcus faecium harbouring the cfr gene in a UK nephrology unit.

METHODS

Isolates of linezolid-resistant E. faecium were typed by pulsed-field gel electrophoresis (PFGE), and examined by polymerase chain reaction (PCR) and sequencing for the transmissible cfr gene that confers resistance to linezolid. Enhanced environmental cleaning, initial and weekly screening of all patients, and monitoring of adherence to standard infection control precautions were implemented.

FINDINGS

Five patients with pre-existing renal disease were found to have rectal colonization with linezolid-resistant E. faecium over a two-week period. The index case was a 57-year-old male from India who had travelled to the UK. One patient also had a linezolid-resistant E. faecium of a different PFGE profile isolated from a heel wound. All isolates were confirmed to harbour the cfr gene by PCR and Sanger sequencing, and all were resistant to glycopeptides (VanA phenotype).

CONCLUSIONS

This article describes the first UK outbreak with a single strain of linezolid- and glycopeptide-resistant E. faecium harbouring the cfr gene, affecting five patients in a nephrology unit. Following the implementation of aggressive infection control measures, no further cases were detected beyond a two-week period.

Convergence of Minds: For Better Patient Outcome in Intensive Care Unit Infections

BACKGROUND

There is emergence of resistance to the last-line antibiotics such as carbapenems in Intensive Care Units (ICUs), leaving little effective therapeutic options. Since there are no more newer antibiotics in the armamentarium in the near future, it has become imperative that we harness the interdisciplinary knowledge for the best clinical outcome of the patient.

AIMS

The aim of the conference was to utilize the synergies between the clinical microbiologists and critical care specialists for better patient care and clinical outcome.

MATERIALS AND METHODS

A combined continuing medical education program (CME) under the aegis of the Indian Association of Medical Microbiologists - Delhi Chapter and the Indian Society of Critical Care Medicine, Delhi and national capital region was organized to share their expertise on the various topics covering epidemiology, diagnosis, management, and prevention of hospital-acquired infections in ICUs.

RESULTS

It was agreed that synergy between the clinical microbiologists and critical care medicine is required in understanding the scope of laboratory tests, investigative pathway testing, hospital epidemiology, and optimum use of antibiotics. A consensus on the use of rapid diagnostics such as point-of-care tests, matrix-assisted laser desorption ionization-time of flight mass spectrometry, and molecular tests for the early diagnosis of infectious disease was made. It was agreed that stewardship activities along with hospital infection control practices should be further strengthened for better utilization of the antibiotics. Through this CME, we identified the barriers and actionables for appropriate antimicrobial usage in Indian ICUs.

CONCLUSIONS

A close coordination between clinical microbiology and critical care medicine opens up avenues to improve antimicrobial prescription practices.

Linezolid-resistant enterococci in Polish hospitals: species, clonality and determinants of linezolid resistance

The significant increase of the linezolid-resistant enterococci (LRE) has been observed in Polish hospitals since 2012 and our study aimed at elucidating the possible reasons for this phenomenon. Polish LRE isolates were analysed by multilocus-sequence typing (MLST) and multiple locus variable-number tandem repeat (VNTR) analysis (MLVA), polymerase chain reaction (PCR) and PCR-restriction fragment length polymorphism (PCR-RFLP) to establish clonal relatedness and mechanism of linezolid resistance, respectively. Fifty analysed LRE (2008–2015) included mostly Enterococcus faecium (82%) and Enterococcus faecalis (16%). Enterococcus faecium belonged to the hospital-adapted lineages 17/18 and 78, while E. faecalis isolates represented ST6, a hospital-associated type, and ST116, found in both humans and food-production animals. The G2576T 23S rRNA mutation was the most frequent (94%) mechanism of linezolid/tedizolid resistance of LRE. None of the isolates carried the plasmid-associated gene of Cfr methyltransferase, whereas optrA, encoding the ABC-type drug transporter, was identified in two E. faecalis isolates. In these isolates, optrA was located on a plasmid, transferable to both E. faecium and E. faecalis, whose partial (36.3 kb) sequence was 100% identical to the pE394 plasmid, identified previously in China in both clinical and farm animal isolates. The optrA–E. faecium transconjugant displayed a significant growth deficiency, in contrast to the optrA–E. faecalis. Our study indicates the role of mutation acquisition by hospital-adapted clones of enterococci as a major driver of increasing resistance to linezolid and tedizolid. Transferability and apparent lack of a biological cost of resistance suggest that E. faecalis may be a natural reservoir of optrA, an emerging mechanism of oxazolidinone resistance.

Linezolid: a promising option in the treatment of Gram-positives

Linezolid, an oxazolidinone antimicrobial agent that acts by inhibiting protein synthesis in a unique fashion, is used in the treatment of community-acquired pneumonia, skin and soft-tissue infections and other infections caused by Gram-positive bacteria including VRE and methicillin-resistant staphylococci. Currently, linezolid resistance among these pathogens remains low, commonly <1.0%, although the prevalence of antibiotic resistance is increasing in many countries. Therefore, the development of resistance by clinical isolates should prompt increased attention of clinical laboratories to routinely perform linezolid susceptibility testing for this important agent and should be taken into account when considering its therapeutic use. Considering the importance of linezolid in the treatment of infections caused by Gram-positive bacteria, this review was undertaken to optimize the clinical use of this antibiotic.

Characterization of methicillin-resistant Staphylococcus aureus isolates from fitness centers in the Memphis metropolitan area, Tennessee

Indoor skin-contact surfaces of public fitness centers may serve as reservoirs of potential human transmission of methicillin-resistant Staphylococcus aureus (MRSA). We found a high prevalence of multidrug-resistant (MDR) MRSA of clonal complex 59 lineage harboring a variety of extracellular toxin genes from surface swab samples collected from inanimate surfaces of fitness centers in the Memphis metropolitan area, Tennessee. Our findings underscore the role of inanimate surfaces as potential sources of transmission of MDR MRSA strains with considerable genetic diversity.

Emergence of linezolid- and vancomycin-resistant Enterococcus faecium in a department for hematologic stem cell transplantation

Background

Prevalence of vancomycin-resistant enterococci has increased in Germany. Here, we report the cluster of linezolid- and vancomycin-resistant Enterococcus faecium (LVRE) in a German department for hematologic stem cell transplantation (HSCT).

Methods

In this retrospective analysis we included all patients with LVRE in a university-based department for HSCT in 2014 and 2015. Patients chart reviews were used to investigate the epidemiology and clinical outcome. Available LVRE isolates underwent detailed microbiological characterization and genotyping by pulsed-field gel electrophoresis (PFGE).

Results

In total, 20 patients with LVRE were identified within the observed time period. All except two patients underwent allogeneic HSCT. Surveillance culture results from incoming patients and chart review revealed that 10 of 20 patients were colonized at hospital admission. Eight of 10 patients with in-hospital acquired LVRE had previous linezolid treatment. Analysis of spatio-temporal patterns showed no evidence for LVRE patient-to-patient or environment-to-patient transmission within the HSCT department. In five cases (25 %) LVRE bloodstream infection occurred. Nine LVRE isolates could be saved for characterization. Eight isolates carried vanA, one isolate vanB. PFGE analysis showed that four different LVRE clones were responsible for the cluster. One single genotype was present in six LVRE isolates whereupon the corresponding patients were all referred from the same hospital to the HSCT department.

Conclusions

This is the first report demonstrating the emergence of LVRE in a German HSCT department. (L)VRE screening at patients’ admission and appropriate infection control strategies were sufficient to prevent any transmission. Further studies in this predisposed patient collective are warranted.

Virulence and resistance pattern of a novel sequence type of linezolid-resistant Enterococcus faecium identified by whole-genome sequencing

Empirical use of linezolid has been advocated in neutropenic febrile patients colonised by vancomycin-resistant enterococci (VRE) because of the risk of bloodstream infection (BSI). This study aimed to genetically describe a vancomycin-resistant Enterococcus faecium (VREfm) BSI isolate resistant to linezolid (VRLRE) in a patient previously colonised by VREfm and to determine the incidence of colonisation and infection by VREfm in a bone marrow transplant unit over a 10-year period. Data for VREfm colonisation and infection were evaluated. PCR for the vanA and vanB genes, pulsed-field gel electrophoresis (PFGE) and microdilution antimicrobial susceptibility testing (vancomycin, teicoplanin, linezolid and aminoglycosides) were performed. Three isolates, including the VRLRE, were selected for whole-genome sequencing by Ion Torrent™, with E. faecium CP006620-Aus0085 used as a reference. Eighty-seven VREfm were analysed; all were linezolid-susceptible and harboured vanA, except for one blood isolate from a febrile neutropenic patient colonised by VREfm who received linezolid for 12 days and developed a BSI by VRLRE (linezolid MIC≥8μg/mL). Linezolid resistance was associated with a G2576T mutation in the 23SrRNA gene. PFGE analysis demonstrated that the 87 isolates belonged to four major clusters; however, the VRLRE presented only 50% similarity. Three sequence types (STs) were identified: ST412 (the predominant clone, which was more virulent compared with the other isolates); ST478 (linezolid-susceptible VREfm); and a novel ST named ST987 (VRLRE). SNP analysis showed a higher similarity between linezolid-susceptible VREfm and the predominant clone compared with VRLRE. VRLRE presented a G2576T mutation and belonged to a novel ST (ST987).

Infective Endocarditis in Adults: Diagnosis, Antimicrobial Therapy, and Management of Complications: A Scientific Statement for Healthcare Professionals From the American Heart Association

BACKGROUND

Infective endocarditis is a potentially lethal disease that has undergone major changes in both host and pathogen. The epidemiology of infective endocarditis has become more complex with today's myriad healthcare-associated factors that predispose to infection. Moreover, changes in pathogen prevalence, in particular a more common staphylococcal origin, have affected outcomes, which have not improved despite medical and surgical advances.

METHODS AND RESULTS

This statement updates the 2005 iteration, both of which were developed by the American Heart Association under the auspices of the Committee on Rheumatic Fever, Endocarditis, and Kawasaki Disease, Council on Cardiovascular Disease of the Young. It includes an evidence-based system for diagnostic and treatment recommendations used by the American College of Cardiology and the American Heart Association for treatment recommendations.

CONCLUSIONS

Infective endocarditis is a complex disease, and patients with this disease generally require management by a team of physicians and allied health providers with a variety of areas of expertise. The recommendations provided in this document are intended to assist in the management of this uncommon but potentially deadly infection. The clinical variability and complexity in infective endocarditis, however, dictate that these recommendations be used to support and not supplant decisions in individual patient management.

Guía de consenso para el abordaje de la neumonía adquirida en la comunidad en el paciente anciano

La incidencia de la neumonía adquirida en la comunidad se incrementa con la edad y se asocia a una elevada morbimortalidad debido a los cambios fisiológicos asociados al envejecimiento y a una mayor presencia de enfermedades crónicas. Debido a la importancia que tiene desde un punto de epidemiológico y pronóstico, y a la enorme heterogeneidad descrita en el manejo clínico, creemos que existía la necesidad de realizar un documento de consenso específico para este perfil de paciente. El propósito de este fue realizar una revisión de las evidencias en relación con los factores de riesgo para la etiología, la presentación clínica, el manejo y el tratamiento de la neumonía adquirida en la comunidad en los ancianos con el fin de elaborar una serie de recomendaciones específicas basadas en el análisis crítico de la literatura. Este documento es fruto de la colaboración de diferentes especialistas en representación de la Sociedad Española de Medicina de Urgencias y Emergencias (SEMES), Sociedad Española de Geriatría y Gerontología (SEGG), Sociedad Española de Quimioterapia (SEQ), Sociedad Española de Medicina Interna (SEMI), Sociedad Española de Neumología y Cirugía Torácica (SEPAR), Sociedad Española de Hospitalización a Domicilio (SEHAD) y Sociedad Española de Enfermedades Infecciosas y Microbiología Clínica (SEIMC).

Decolonization of gastrointestinal carriage of vancomycin-resistant Enterococcus faecium: case series and review of literature

Background

Prolonged asymptomatic carriage of vancomycin-resistant enterococci (VRE) in the gastrointestinal tract and the lack of effective decolonization regimen perpetuate the endemicity of VRE in the healthcare settings.

Case presentation

We report a regimen for decolonization of gastrointestinal carriage of VRE by a combination of environmental disinfection, patient isolation, bowel preparation to wash-out the fecal bacterial population using polyethylene glycol, a five-day course of oral absorbable linezolid and non-absorbable daptomycin to suppress any remaining VRE, and subsequent oral Lactobacillus rhamnosus GG to maintain the colonization resistance in four patients, including two patients with end-stage liver cirrhosis, one patient with complication post liver transplant, and one patient with complicated infective endocarditis. All patients had clearance of VRE immediately after decolonization, and 3 of them remained VRE-free for 23 to 137 days of hospitalization, despite subsequent use of intravenous broad-spectrum antibiotics without anti-VRE activity.

Conclusion

This strategy should be further studied in settings of low VRE endemicity with limited isolation facilities.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2334-14-514) contains supplementary material, which is available to authorized users.

Bugs, hosts and ICU environment: countering pan-resistance in nosocomial microbiota and treating bacterial infections in the critical care setting

ICUs are areas where resistance problems are the largest, and these constitute a major problem for the intensivist's clinical practice. Main resistance phenotypes among nosocomial microbiota are (i) vancomycin-resistance/heteroresistance and tolerance in grampositives (MRSA, enterococci) and (ii) efflux pumps/enzymatic resistance mechanisms (ESBLs, AmpC, metallo-betalactamases) in gramnegatives. These phenotypes are found at different rates in pathogens causing respiratory (nosocomial pneumonia/ventilator-associated pneumonia), bloodstream (primary bacteremia/catheter-associated bacteremia), urinary, intraabdominal and surgical wound infections and endocarditis in the ICU. New antibiotics are available to overcome non-susceptibility in grampositives; however, accumulation of resistance traits in gramnegatives has led to multidrug resistance, a worrisome problem nowadays. This article reviews microorganism/infection risk factors for multidrug resistance, suggesting adequate empirical treatments. Drugs, patient and environmental factors all play a role in the decision to prescribe/recommend antibiotic regimens in the specific ICU patient, implying that intensivists should be familiar with available drugs, environmental epidemiology and patient factors.

Virulence of vancomycin-resistant Enterococcus faecium according to linezolid resistance and clinical outbreak status

Assessing clinical virulence differences between vancomycin-resistant Enterococcus faecium (VREF) strains resistant to linezolid (LRVRE) and linezolid-susceptible VRE (LSVRE) strains is difficult due to confounding patient variables. Galleria mellonella is a validated host interaction model allowing straightforward organism virulence assessment. The objective of this study was to assess the virulence of VREF in G. mellonella according to linezolid resistance and clinical outbreak status. A genetically related pair of VREF strains with and without genotypically confirmed linezolid resistance was selected for analysis. Additionally, six strains of LSVRE and two strains of LRVRE were selected according to epidemiologic outbreak status. Mortality of G. mellonella was assessed daily over a 5-day period and analyzed using Kaplan-Meier survival curves and log rank tests. Linezolid resistance did not have a significant effect on G. mellonella mortality in the genetically related pair (P = 0.93). There was no significant difference in mortality over time between strains (non-outbreak [i.e., no patient transmissions were recorded] [n = 2] versus outbreak [i.e., transmission occurred between 3 or more patients in a period of 30 days] [n = 6], P = 0.84; extensive transmission [i.e., the isolate was transmitted between at least 80 patients] [n = 2] versus limited transmission [i.e., the isolate was transmitted between fewer than 10 patients] [n = 4], P = 0.78). These results suggest that patients infected with LRVRE or outbreak strains of VREF are at no greater risk of poor outcomes mediated by organism virulence than those infected with LSVRE or non-outbreak strains.

Risk factors associated with linezolid-nonsusceptible enterococcal infections

Linezolid is one of few treatment options available for vancomycin-resistant enterococci. The present study investigated risk factors for linezolid-nonsusceptible enterococci using a case-control study of 15 cases and 60 control patients. Previous hospitalization, admission to a medical service, comorbidity, and linezolid and sulfonamide therapy were identified as risk factors.

Resistance patterns and occurrence of virulence determinants among GRE strains in southwestern Poland

PURPOSE

The aim of this study was to determine the antimicrobial resistance and the occurrence of virulence determinants among glycopeptide-resistant enterococci (GRE) isolated in 2007-2009 from patients hospitalized in southwestern Poland.

MATERIAL AND METHODS

The minimal inhibitory concentrations (MICs) of antibiotics were determined by agar dilution method or by E-test®. The presence of vanA - vanG resistance and virulence genes (agg, esp, gelE and cylA, cylB, cylM) was investigated using PCR. The ability to form biofilm and the activity of gelatinase, hemolysins, lipase and DNase were tested.

RESULTS

All the GRE strains were susceptible to linezolid, daptomycin, and tigecycline and resistant to norfloxacin. In the Enterococcus faecium group, 17 strains carried the vanA gene and 20 the vanB gene. In the Enterococcu faecalis group, 4 strains carried the vanA gene and 1 the vanB gene. There were differences in tetracycline susceptibility between the VanA (70%) and the VanB (55%) phenotypes. Only linezolid had high activity against both the VanA and the VanB phenotypes. The esp gene was present in most of the GRE strains, but only 3 E. faecalis strains produced biofilm. Lipase was produced by 10/42 examined strains, gelatinase by 4/42 and hemolysin by 3/42 isolates.

CONCLUSIONS

Linezolid seems to be the optimal option in empirical therapy of infections caused by GRE strains because of the relationship between its activity (MIC value) and susceptibility breakpoint. There was no correlation between the prevalence of different virulence genes and resistance to the antibiotics tested.

Glycopeptide resistance in gram-positive cocci: a review

Vancomycin-resistant enterococci (VRE) have emerged as important nosocomial pathogens in the past two decades all over the world and have seriously limited the choices available to clinicians for treating infections caused by these agents. Methicillin-resistant Staphylococcus aureus, perhaps the most notorious among the nosocomial pathogens, was till recently susceptible to vancomycin and the other glycopeptides. Emergence of vancomycin nonsusceptible strains of S. aureus has led to a worrisome scenario where the options available for treating serious infections due to these organisms are very limited and not well evaluated. Vancomycin resistance in clinically significant isolates of coagulase-negative staphylococci is also on the rise in many setups. This paper aims to highlight the genetic basis of vancomycin resistance in Enterococcus species and S. aureus. It also focuses on important considerations in detection of vancomycin resistance in these gram-positive bacteria. The problem of glycopeptide resistance in clinical isolates of coagulase-negative staphylococci and the phenomenon of vancomycin tolerance seen in some strains of Streptococcus pneumoniae has also been discussed. Finally, therapeutic options available and being developed against these pathogens have also found a mention.

Speciation and frequency of virulence genes of Enterococcus spp. isolated from rainwater tank samples in Southeast Queensland, Australia

In this study, 212 Enterococcus isolates from 23 rainwater tank samples in Southeast Queensland (SEQ), Australia were identified to the species level. The isolates were also tested for the presence of 6 virulence genes associated with Enterococcus related infections. Among the 23 rainwater tank samples, 20 (90%), 10 (44%), 7 (30%), 5 (22%), 4 (17%), 2 (9%), and 1 (4%) samples yielded E. faecalis, E. mundtii, E. casseliflavus, E. faecium, E. hirae, E. avium, and E. durans, respectively. Among the 6 virulence genes tested, gelE and efaA were most prevalent, detected in 19 (83%) and 18 (78%) of 23 rainwater tank samples, respectively. Virulence gene ace was also detected in 14 (61%) rainwater tank samples followed by AS, esp (E. faecalis variant), and cylA genes which were detected in 3 (13%), 2 (9%), and 1 (4%) samples, respectively. In all, 120 (57%) Enterococcus isolates from 20 rainwater tank samples harbored virulence genes. Among these tank water samples, Enterococcus spp. from 5 (25%) samples harbored a single virulence gene and 15 (75%) samples were harboring two or more virulence genes. The significance of these strains in terms of health implications remains to be assessed. The potential sources of these strains need to be identified for the improved management of captured rainwater quality. Finally, it is recommended that Enterococcus spp. should be used as an additional fecal indicator bacterium in conjunction with E. coli for the microbiological assessment of rainwater tanks.

LEADER Program results for 2009: an activity and spectrum analysis of linezolid using 6,414 clinical isolates from 56 medical centers in the United States

The LEADER Program monitors the in vitro activity of linezolid in sampled U.S. medical centers using reference broth microdilution methods with supporting molecular investigations in a central laboratory design. This report summarizes data obtained in 2009, the 6th consecutive year of this longitudinal study. A total of 6,414 isolates from 56 medical centers in all nine Census regions across the United States participated in 2009. For the six leading species/groups, the following linezolid MIC(90) values were observed: Staphylococcus aureus, 2 μg/ml; coagulase-negative staphylococci (CoNS), 1 μg/ml; Enterococcus spp., 2 μg/ml; Streptococcus pneumoniae, 1 μg/ml; viridans group streptococci, 1 μg/ml; and beta-hemolytic streptococci, 1 μg/ml. Linezolid resistance was only 0.34% overall, with no evidence of significant increase in the LEADER Program since 2006. The predominant linezolid resistant mechanism found was a G2576T mutation in the 23S rRNA. L3/L4 riboprotein mutations were also found. The mobile multidrug-resistant cfr gene was found in four strains (two S. aureus strains and one strain each of S. epidermidis and S. capitis) from four different states, suggesting persistence but a lack of dissemination. Linezolid continues to exhibit excellent activity and spectrum, and this study documents the need for continued monitoring of emerging mechanisms of resistance over a wide geographic area.

Telavancin Activity against gram-positive bacteria isolated from patients with skin and skin-structure infections

Telavancin is approved in the United States and Canada for the treatment of complicated skin and skin structure infections (cSSSI) in adults caused by susceptible Gram-positive organisms. The antimicrobial activity of telavancin and comparators was evaluated against 5,027 (2007-2008) Gram-positive bacteria responsible for SSSI in medical centers in Asia-Pacific, European, Latin American, and North American regions. Telavancin was active against Staphylococcus aureus (MIC₅₀(/)₉₀, 0.12/0.25 mg/l; 100.0% susceptible) and coagulase-negative staphylococci (MIC₅₀(/)₉₀, 0.12/0.25 mg/l). telavancin inhibited all Enterococcus faecalis, including four strains displaying a VanB phenotype, at ≤ 1 mg/L (MIC₅₀(/)₉₀, 0.25/0.5 mg/l), except for two isolates with a VanA phenotype (MIC, >2 mg/l). Vancomycin-susceptible and VanB vancomycin-resistant E. faecium were inhibited by telavancin at ≤ 0.25 mg/L, while this drug exhibited elevated MIC values (≥ 0.5 mg/l) against E. faecium of VanA phenotype (MIC₅₀(/)₉₀, 2/>2 mg/l). Telavancin was potent against β-haemolytic streptococci (MIC₅₀(/)₉₀, 0.03/0.12 mg/l; 100.0% susceptible) and viridans group streptococci (MIC₅₀(/)₉₀, 0.03/0.06 mg/l; 100.0% susceptible). These in vitro data document the activity of telavancin against contemporary Gram-positive isolates and support its clinical use for the treatment of cSSSI caused by the indicated pathogens.

Differences in clinical outcomes in patients with vancomycin-resistant enterococci according to linezolid susceptibility

STUDY OBJECTIVE

To evaluate the differences in clinical outcomes in patients with linezolid-intermediate or -resistant vancomycin-resistant enterococci (LIRVRE) isolates, as defined by the presence of the G2576T mutation, compared with patients who had linezolid-susceptible VRE (LSVRE) isolates in order to further discern the clinical relevance of linezolid resistance associated with this mutation.

DESIGN

Retrospective cohort study.

SETTING

Large tertiary care academic medical center.

PATIENTS

Eighteen adults (mean age 55.4 yrs) with LIRVRE (case patients) who were frequency matched to 54 adults (mean age 58.1 yrs) with LSVRE (control patients) in a 1:3 ratio based on site of culture and VRE species.

MEASUREMENTS AND MAIN RESULTS

Linezolid resistance was determined by phenotype and genotype (G2576T mutation by polymerase chain reaction). Patients with LIRVRE received more linezolid before isolation of the organism than did those with LSVRE (mean 8.6 vs 0.2 days, p<0.001). No difference in mortality was found; however, compared with controls, patients with LIRVRE were more likely to be transferred to the intensive care unit (56% vs 28%, p=0.032), had more surgical procedures for VRE (39% vs 15%, p=0.029), and had more echocardiograms performed (44% vs 19%, p=0.028) as a result of their VRE. Multivariate analysis revealed that surviving case patients had an increased duration of culture positivity of approximately 1.5 days (p=0.049) and a near statistically significant increase of postculture length of stay of approximately 2 days (p=0.053).

CONCLUSION

The clinical relevance of the G2576T mutation among enterococci remains unclear; however, the increased morbidity and resource utilization among patients with LIRVRE is a finding of concern. Careful monitoring of genotypically confirmed LIRVRE emergence and ongoing epidemiologic studies will be critical to better characterize the clinical relevance of linezolid resistance.

Differential PilA pilus assembly by a hospital-acquired and a community-derived Enterococcus faecium isolate

Pili are hair-like structures protruding from the cell envelope of bacterial cells. Here, we describe the conditional and differential display of PilA-type pili, and PilE and PilF proteins, encoded from pilin gene cluster 1 at the surface of a hospital-acquired Enterococcus faecium bloodstream isolate (E1165) and a community-derived stool isolate (E1039), at two different temperatures. Both strains have virtually identical pilA gene clusters, as determined by sequencing. Western blotting and transmission immunoelectron microscopy revealed that PilA and PilF assembled into high-molecular-mass pilus-like structures at 37 degrees C in the E1165 strain, whereas PilE was not produced at either of the temperatures used; at 21 degrees C, PilA and PilF were cell-wall-anchored proteins. In contrast, in strain E1039, PilA, PilE and PilF pilin proteins were found to be displayed as cell-wall-anchored proteins at 37 degrees C only, and they were not associated with pilus-like structures. The discrepancy in pilus assembly between E1039 and E1165 cannot be explained by differences in expression of the genes encoding the predicted sortases in the pilA gene cluster, as these had similar expression levels in both strains at 21 and 37 degrees C. Double-labelling electron microscopy revealed that PilA formed the pilus backbone in E1165, and PilF the minor subunit which was distributed along the PilA pilus shaft and positioned at the tip; however, it was deposited as a cell-wall-anchored protein in a pilA isogenic mutant. The differential deposition of surface proteins from pilin gene cluster 1 and differences in pilus assembly in the two strains suggest a complex post-transcriptional regulatory mechanism of pilus biogenesis in E. faecium.

Linezolid surveillance program results for 2008 (LEADER Program for 2008)

The LEADER Program was initiated in 2004 and monitors emerging linezolid resistance in sampled US medical centers. This report summarizes the data obtained in 2008, the 5th consecutive year. A total of 57 institutions participated in 2008 representing all 9 US census regions with 100 target organisms per site (6113 isolates, 101.9% compliance to protocol design). The organisms tested by reference broth microdilution methods were Staphylococcus aureus (3156), coagulase-negative staphylococci (CoNS; 856), enterococci (901), Streptococcus pneumoniae (619), and viridans group (223) or beta-hemolytic streptococci (358); also, D-test was used to determine inducible clindamycin resistance in Staphylococcus aureus. Linezolid remained very potent against all sampled species with MIC(90) results ranging from 1 microg/mL (streptococci and CoNS) to 2 microg/mL (Staphylococcus aureus and enterococci). Only 0.36% of sampled strains were nonsusceptible to linezolid, a slight decrease from 0.45% and 0.44% in 2006 and 2007, respectively. The nonsusceptible strains (22) were Staphylococcus aureus (3), CoNS (14), and Enterococcus faecium (5) each with defined target mutations (G2576T in 19 strains; T2504A in 1 strain), mobile cfr element (1 strain Staphylococcus epidermidis with an identical pulsed-field gel electrophoresis pattern to a cfr-positive Staphylococcus epidermidis isolated from the same center in LEADER 2007), or an unknown (1 strain) mechanism. The mobile cfr resistance found in a Staphylococcus aureus strain in 2007 was not observed in 2008. In conclusion, linezolid activity sampled by the 5th year of this LEADER Program showed sustained potency and spectrum (99.64% susceptibility levels). The nonsusceptible strain isolation rates remained stable and the plasmid-mediated ribosomal-based resistance mechanism that emerged in Staphylococcus aureus and Staphylococcus epidermidis strains in 2007 showed no evidence of dissemination or increased prevalence. However, there was evidence of cfr persistence with the S. epidermidis strain. The LEADER Program continues to be an effective and sensitive surveillance tool to detect and monitor novel oxazolidinone resistance phenotypes and genotypes.

Review of virulence factors of enterococcus: an emerging nosocomial pathogen

Enterococcus, considered a normal commensal of intestinal tract, is fast emerging as a pathogen causing serious and life threatening hospital borne infections. This is attributed to acquisition of multi drug resistance and virulence factors of the organisms. The sequencing of Enterococcus faecalis has given a lot of insight into its genetic makeup. The E. faecalis strain V583, which has been sequenced, contains a total of 3182 open reading frames (ORFs) with 1760 of these showing similarity to known proteins and 221 of unknown functions. Strikingly unique to this genome is the fact that over 25% of the genome is made up of mobile and exogenously acquired DNA which includes a number of conjugative and composite transposons, a pathogenicity island, integrated plasmid genes and phage regions, and a high number of insertion sequence (IS) elements. This review addresses the genomic arrangement and the study of virulence factors that have occurred since the sequencing of the genome.