Vancomycin-resistant Enterococcus faecium carrying Tn1546-plasmid rep17 found in Algerian maternity wards

Two hospitalised patients in obstetrics and gynaecology departments in northeastern Algeria, recovering from post-operative wound infections, turned out to be carrying something far more alarming than routine surgical site infections. Twenty days apart, clinicians isolated two strains of Enterococcus faecium from their wounds, and when researchers sequenced the entire genomes of those isolates, they found nearly identical bacteria carrying a complete vancomycin-resistance package on a mobile plasmid. The findings, published in Molecular Genetics and Genomics by a team led by Chahinez Boutefnouchet of the Université Badji Mokhtar-Annaba and the Aix-Marseille University-affiliated IHU Méditerranée Infection, provide a detailed genomic portrait of one of the world’s most troublesome hospital pathogens circulating in a North African healthcare setting.

Enterococcus faecium is not an exotic microbe. It lives quietly in the human gut, but in hospitals it has become a leading cause of bloodstream infections, wound infections and endocarditis, particularly in patients weakened by surgery, broad-spectrum antibiotics or invasive devices. What makes E. faecium a global public health threat is its extraordinary capacity to acquire resistance. The emergence of vancomycin-resistant E. faecium, known as VREfm, has drastically narrowed treatment options, because vancomycin has long been one of the few reliable drugs against enterococcal infections. The World Health Organization has flagged vancomycin-resistant enterococci as high-priority targets for new antibiotic development, and genomic surveillance has become the sharpest available tool for tracking how these bacteria spread and evolve inside hospitals.

In the new study, the two clinical isolates, designated EF_35 and EF_38, were recovered from surgical site infections in two different hospitalised patients treated in obstetrics and gynaecology departments. Both patients had developed post-operative wound infections, a well-known complication of caesarean sections and other surgical procedures. The research team performed antibiotic susceptibility testing, whole-genome sequencing and a battery of bioinformatic analyses designed to answer three key questions: what resistance genes did the bacteria carry, on what mobile elements were those genes located, and how closely related were the two isolates to each other and to E. faecium genomes reported elsewhere in the world.

The answer to the relatedness question was striking. Multilocus sequence typing placed both isolates in sequence type 80, or ST80, a lineage belonging to clonal complex CC17, the group of hospital-adapted E. faecium strains that has spread through healthcare systems worldwide since it first emerged as a nosocomial clone. Even more telling, whole-genome single nucleotide polymorphism analysis revealed that the two isolates differed by only eight genomic SNPs. In practical terms, bacteria from different patients that differ by only a handful of SNPs are considered closely related, strongly suggesting a common source or direct transmission within the hospital environment. An interval of twenty days between the two isolations fits the classic pattern of a nascent hospital outbreak, in which a single strain moves between patients, surfaces or healthcare workers before being detected.

Genetically, the isolates were textbook multidrug-resistant VREfm. Phenotypic testing confirmed resistance to vancomycin, and the genomes harboured genes conferring resistance to aminoglycosides and macrolides as well. This stacking of resistance determinants is what makes CC17 lineages so successful in hospitals: a patient colonised by such a strain who then develops an infection has very few oral or intravenous options, and clinicians are pushed toward last-line agents such as linezolid or daptomycin, drugs that are expensive, toxic and themselves threatened by emerging resistance.

The centrepiece of the genomic analysis was the vanA operon, the genetic machinery that renders enterococci resistant to vancomycin and teicoplanin. Vancomycin normally works by binding the D-Ala-D-Ala termini of peptidoglycan precursors, blocking cell-wall synthesis. The vanA system rewires that target: it enzymatically remodels cell-wall precursors to end in D-Ala-D-Lac instead, an terminus to which vancomycin binds with drastically reduced affinity, while simultaneously degrading the normal precursors. In both Algerian isolates, the researchers found the vanA operon embedded within a Tn1546 transposon-like element, the mobile genetic unit first characterised in the 1990s in the French reference strain E. faecium BM4147 and since then responsible for disseminating glycopeptide resistance around the globe.

Crucially, that Tn1546 element was not sitting on the chromosome. It was located on a rep17-type plasmid, a replicon family related to the well-known pRUM plasmids that circulate among hospital E. faecium strains. Plasmids are circular, self-replicating DNA molecules that can transfer horizontally between bacteria, sometimes across species boundaries, and they are widely regarded as the primary vehicles by which resistance genes move through hospital microbial communities. Recent work has shown that plasmids were central to the recent emergence of E. faecium as a major nosocomial pathogen, so pinpointing which plasmid carries a resistance cassette in a given region provides both an evolutionary and an epidemiological clue.

One detail of the plasmid’s cargo raised the stakes considerably. Alongside the vanA-Tn1546 cassette, the rep17 plasmid also carried a specific resistance locus, designated locus 3, composed of the genes ant(6), sat(4) and aph(3′). This exact gene combination has drawn attention because it has been found in vancomycin-resistant Staphylococcus aureus, the feared VRSA isolates in which the vanA operon has jumped from enterococci into staphylococcal genomes, including cases in which the entire vanA locus integrated into the S. aureus chromosome. The presence of the same Tn1546-associated aminoglycoside locus on an E. faecium plasmid in Algeria raises, as the authors note, the possibility that such a plasmid could transfer the vanA operon into a staphylococcal genome. Although VRSA remains rare worldwide, each documented case has followed precisely this route of plasmid-mediated gene transfer from enterococci to staphylococci, so plasmids of this architecture are watched as potential launching pads for that dangerous jump.

For Algeria specifically, the study fills in an important piece of a growing picture. Earlier reports documented the first vancomycin-resistant enterococcal cases in the country in 2008, the emergence of glycopeptide-resistant E. faecium in subsequent years, molecular characterisation of related vanA E. faecium healthcare-associated infections, and a 2021 survey showing high frequency and diversity of VRE in Algerian healthcare settings, followed by the detection of vanA-positive E. faecium CC17 even in hospital wastewater. The new genomic data demonstrate that the epidemic VREfm ST80 clone is not merely present but actively evolving within Algerian hospitals, carrying the same mobile resistance elements described on other continents. Genomic surveillance of this kind, the authors argue, is essential for detecting clonal transmission early enough to interrupt it with infection-control measures, from hand hygiene and environmental disinfection to active screening and isolation of colonised patients.

The technical approach also illustrates how modern clinical microbiology increasingly relies on whole-genome sequencing as a routine investigative tool. By combining sequencing with tools for plasmid detection and typing, transposon annotation, resistome identification and SNP-based phylogenetic comparison, the team could reconstruct, from two wound isolates, a narrative of clonal spread, plasmid-borne resistance and cross-genus transmission risk that older methods such as pulsed-field gel electrophoresis could only hint at. The genomes of both isolates have been deposited in GenBank under accession numbers JBAIVL000000000 and JBAIVM000000000, making them available for future comparative studies across the Mediterranean region and beyond.

The broader message is sobering but not hopeless. VREfm ST80 is now documented on multiple continents, and the genetic elements that give it its armour are inherently mobile. Yet the same mobility that makes the threat means surveillance works: identifying a rep17 plasmid carrying Tn1546-vanA in a specific hospital department tells infection-control teams exactly what to look for and where to intervene. For obstetric and gynaecology patients, who undergo some of the most common surgeries in medicine, keeping this clone from gaining a foothold is a matter of routine vigilance, genomic alertness and the unglamorous but decisive practice of infection prevention.