Investigation of the introduction and dissemination of vanB Enterococcus faecium in the Capital Region of Denmark and development of a rapid and accurate clone-specific vanB E. faecium PCR

Development of a PCR assay for rapid and accurate detection of an emerging vanB Enterococcus faecium clone in the Capital Region of Denmark

Objectives

To develop and validate a real-time PCR assay detecting the sequence bridging Tn1549 and the Enterococcus faecium chromosome in the emerging vanB vancomycin-resistant E. faecium (VREfm) clone (ST80/CT2406).

Methods

The Tn1549 insertion site was determined on routinely sequenced VREfm isolates. The outer boundaries of Tn1549 and adjoining host bacterial sequences were determined using a BLAST search in the silent information regulator gene sir2. Next, the primers and probe were developed, targeting the sequence bridging Tn1549 and the E. faecium chromosome. Finally, the PCR assay was validated on well-characterized strains and prospectively performed on rectal screening samples submitted to our laboratory.

Results and conclusions

The PCR assay proved to be accurate and provide rapid diagnosis of the emerging vanB VREfm in rectal screening samples.

Rapid detection of vanB vancomycin-resistant enterococci by laboratory-developed PCR on enrichment broth

Diagnostic accuracy of laboratory-developed PCR after overnight enrichment for the detection of vanB vancomycin-resistant enterococci was evaluated on 537 rectal swabs. Defining Ct-values of 27-34 (40 samples, 7 % inconclusive), we found an excellent sensitivity of 98,3 % and specificity of 99,7 % for the remaining 497 samples.

Surveillance of vancomycin-resistant enterococci reveals shift in dominating clusters from vanA to vanB Enterococcus faecium clusters, Denmark, 2015 to 2022

BackgroundVancomycin-resistant enterococci (VRE) are increasing in Denmark and Europe. Linezolid and vancomycin-resistant enterococci (LVRE) are of concern, as treatment options are limited. Vancomycin-variable enterococci (VVE) harbour the vanA gene complex but are phenotypically vancomycin-susceptible.AimThe aim was to describe clonal shifts for VRE and VVE in Denmark between 2015 and 2022 and to investigate genotypic linezolid resistance among the VRE and VVE.MethodsFrom 2015 to 2022, 4,090 Danish clinical VRE and VVE isolates were whole genome sequenced. We extracted vancomycin resistance genes and sequence types (STs) from the sequencing data and performed core genome multilocus sequence typing (cgMLST) analysis for Enterococcus faecium. All isolates were tested for the presence of mutations or genes encoding linezolid resistance.ResultsIn total 99% of the VRE and VVE isolates were E. faecium. From 2015 through 2019, 91.1% of the VRE and VVE were vanA E. faecium. During 2020, to the number of vanB E. faecium increased to 254 of 509 VRE and VVE isolates. Between 2015 and 2022, seven E. faecium clusters dominated: ST80-CT14 vanA, ST117-CT24 vanA, ST203-CT859 vanA, ST1421-CT1134 vanA (VVE cluster), ST80-CT1064 vanA/vanB, ST117-CT36 vanB and ST80-CT2406 vanB. We detected 35 linezolid vancomycin-resistant E. faecium and eight linezolid-resistant VVEfm.ConclusionFrom 2015 to 2022, the numbers of VRE and VVE increased. The spread of the VVE cluster ST1421-CT1134 vanA E. faecium in Denmark is a concern, especially since VVE diagnostics are challenging. The finding of LVRE, although in small numbers, ia also a concern, as treatment options are limited.

Characterization of a Tigecycline-, Linezolid- and Vancomycin-Resistant Clinical Enteroccoccus faecium Isolate, Carrying vanA and vanB Genes

INTRODUCTION

Increasing incidence of Enterococcus faecium resistant to key antimicrobials used in therapy of hospitalized patients is a worrisome phenomenon observed worldwide. Our aim was to characterize a tigecycline-, linezolid- and vancomycin-resistant E. faecium isolate with the vanA and vanB genes, originating from a hematoma of a patient hospitalized in an intensive care unit in Poland.

METHODS

Antimicrobial susceptibility (a broad panel) was tested using gradient tests with predefined antibiotic concentrations. The complete genome sequence was obtained from a mixed assembly of Illumina MiSeq and Oxford Nanopore's MinION reads. The genome was analyzed with appropriate tools available at the Center for Genomic Epidemiology, PubMLST and GenBank. Transferability of oxazolidinone, tigecycline and vancomycin resistance genes was investigated by conjugation, followed by PCR screen of transconjugants for antimicrobial resistance genes and plasmid rep genes characteristic for the donor and genomic sequencing of selected transconjugants.

RESULTS

The isolate was resistant to most antimicrobials tested; susceptibility to daptomycin, erythromycin and chloramphenicol was significantly reduced, and only oritavancin retained the full activity. The isolate represented sequence type 18 (ST18) and carried vanA, vanB, poxtA, fexB, tet(L), tet(M), aac(6')-aph(2''), ant(6)-Ia and ant(6')-Ii. The vanA, poxtA and tet(M) genes located on ~ 40-kb plasmids were transferable by conjugation yielding transconjugants resistant to vancomycin, linezolid and tigecycline. The substitutions in LiaS, putative histidine kinase, SulP, putative sulfate transporter, RpoB and RpoC were potential determinants of an elevated daptomycin MIC. Comparative analyses of the studied isolate with E. faecium isolates from other countries revealed its similarity to ST18 isolates from Ireland and Uganda from human infections.

CONCLUSIONS

We provide the detailed characteristics of the genomic determinants of antimicrobial resistance of a clinical E. faecium demonstrating the concomitant presence of both vanA and vanB and resistance to vancomycin, linezolid, tigecycline and several other compounds and decreased daptomycin susceptibility. This isolate is a striking example of an accumulation of resistance determinants involving various mechanisms by a single hospital strain.

Emergence of linezolid-resistant Enterococcus faecium in a tertiary hospital in Copenhagen

Linezolid is used as first-line treatment of infections caused by vancomycin-resistant Enterococcus faecium. However, resistance to linezolid is increasingly detected. The aim of the present study was to elucidate the causes and mechanisms for the increase in linezolid-resistant E. faecium at Copenhagen University Hospital - Rigshospitalet. We therefore combined patient information on linezolid treatment with whole-genome sequencing data for vancomycin- or linezolid-resistant E. faecium isolates that had been systematically collected since 2014 (n=458). Whole-genome sequencing was performed for multilocus sequence typing (MLST), identification of linezolid resistance-conferring genes/mutations and determination of phylogenetically closely related strains. The collection of E. faecium isolates belonged to prevalent vancomycin-resistant MLST types. Among these, we identified clusters of closely related linezolid-resistant strains compatible with nosocomial transmission. We also identified linezolid-resistant enterococcus isolates not genetically closely related to other isolates compatible with de novo generation of linezolid resistance. Patients with the latter isolates were significantly more frequently exposed to linezolid treatment than patients with related linezolid-resistant enterococcus isolates. We also identified six patients who initially carried a vancomycin-resistant, linezolid-sensitive enterococcus, but from whom vancomycin-resistant, linezolid-resistant enterococci (LVRE) closely related to their initial isolate were recovered after linezolid treatment. Our data illustrate that linezolid resistance may develop in the individual patient subsequent to linezolid exposure and can be transmitted between patients in a hospital setting.

The use of core genome multilocus sequence typing to determine the duration of vancomycin-resistant Enterococcus faecium outbreaks

The prevalence of vancomycin-resistant Enterococcus faecium has increased rapidly, and in Denmark, we are facing an endemic outbreak situation in hospitals. The aim of this study was to use whole-genome sequencing (WGS) and core genome multilocus sequencing typing (cgMLST) to determine the duration of VREfm outbreaks and thereby evaluate the effect of our infection control strategies. We included all VREfm isolates from six hospitals in the Capital Region of Denmark that were sequenced between 2012 and 2020. Ward data were collected from our laboratory information system. A ward outbreak was defined as two patient samples from the same ward within a period of 30 days belonging to the same cgMLST cluster. cgMLST complex types were determined using Ridom SeqSphere v7.2.3, where a maximum of 20 allelic differences between isolates defines a cluster. We included 1690 patient isolates between 2012 and 2020. Our collection consisted of 45 unique clusters and 227 ward outbreaks. The median duration of outbreaks was 20 days. We reported a median outbreak duration of VREfm outbreaks based on WGS data to be 20 days, and thus concluded that our infection control precautions are adequate.

Genomic analysis of 600 vancomycin-resistant Enterococcus faecium reveals a high prevalence of ST80 and spread of similar vanA regions via IS1216E and plasmid transfer in diverse genetic lineages in Ireland

BACKGROUND

Vancomycin-resistant Enterococcus faecium (VREfm) cause a wide range of hospital infections. Ireland has had one of the highest invasive VREfm infection rates in Europe over the last decade, yet little is known about Irish VREfm.

OBJECTIVES

To investigate the population structure of Irish VREfm, explore diversity by analysing the vanA transposon region and compare Irish, Danish and global isolates.

METHODS

E. faecium (n = 648) from five Irish hospitals were investigated, including VREfm [547 rectal screening and 53 bloodstream infection (BSI)] isolates and 48 vancomycin-susceptible (VSEfm) BSI isolates recovered between June 2017 and December 2019. WGS and core-genome MLST (cgMLST) were used to assess population structure. Genetic environments surrounding vanA were resolved by hybrid assembly of short-read (Illumina) and long-read (Oxford Nanopore Technologies) sequences.

RESULTS

All isolates belonged to hospital-adapted clade A1 and the majority (435/648) belonged to MLST ST80. The population structure was highly polyclonal; cgMLST segregated 603/648 isolates into 51 clusters containing mixtures of screening and BSI isolates, isolates from different hospitals, and VREfm and VSEfm. Isolates within clusters were closely related (mean average ≤16 allelic differences). The majority (96.5%) of VREfm harboured highly similar vanA regions located on circular or linear plasmids with multiple IS1216E insertions, variable organization of vanA operon genes and 78.6% harboured a truncated tnpA transposase. Comparison of 648 Irish isolates with 846 global E. faecium from 30 countries using cgMLST revealed little overlap.

CONCLUSIONS

Irish VREfm are polyclonal, yet harbour a characteristic plasmid-located vanA region with multiple IS1216E insertions that may facilitate spread.