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ArticleEuropean journal of clinical microbiology & infectious diseases : official publication of the European Society of Clinical Microbiology2026

Heteroresistance in vancomycin-variable Enterococcus faecium ST80 isolate.

Serena Simoni, Alessandra Di Gregorio, Sara Caucci, Andrea Brenciani, Eleonora Giovanetti, Carla Vignaroli

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Article in European journal of clinical microbiology & infectious diseases : official publication of the European Society of Clinical Microbiology, 2026. The graph could read no effect estimate from its abstract, so it casts no vote on the map. Not yet cited in PubMed.

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5 · Who and what money

Authors and funding

6 authors.

Serena SimoniDepartment of Life and Environmental Sciences (DiSVA), Polytechnic University of Marche, Via Brecce Bianche, 60131, Ancona, Italy.
Alessandra Di GregorioDepartment of Life and Environmental Sciences (DiSVA), Polytechnic University of Marche, Via Brecce Bianche, 60131, Ancona, Italy.
Sara CaucciDepartment of Biomedical Sciences and Public Health, Polytechnic University of Marche, Ancona, Italy.
Andrea BrencianiDepartment of Biomedical Sciences and Public Health, Polytechnic University of Marche, Ancona, Italy.
Eleonora GiovanettiDepartment of Life and Environmental Sciences (DiSVA), Polytechnic University of Marche, Via Brecce Bianche, 60131, Ancona, Italy.
Carla VignaroliDepartment of Life and Environmental Sciences (DiSVA), Polytechnic University of Marche, Via Brecce Bianche, 60131, Ancona, Italy. c.vignaroli@staff.univpm.it.ORCID http://orcid.org/0000-0002-0993-5967

Funding

No grant is acknowledged in the PubMed record.

6 · The paper itself

Abstract

purposeTo investigate the gradual genetic changes occurred in heteroresistant vancomycin-variable (VVE) Enterococcus faecium ST80 isolate - belonging to the vanA ST80 nosocomial clone although recovered from marine environment - contributing to its reversion to a resistant phenotype after exposure to increasing concentrations of vancomycin.

methodsWGS of the parental strain and three revertants obtained by exposure to vancomycin was performed. vanA copy number and difference in vanA expression between VVE and revertants were evaluated by RT-qPCR. Heteroresistance was demonstrated by vancomycin E-test and population analysis profiling.

resultsThe E. faecium JSEG15 isolate, susceptible to vancomycin although carrying a Tn1546-like transposon on 36-kb plasmid, gave rise to three different resistant mutants following gradual passages on increasing vancomycin concentrations. Revertants showed increased vancomycin MICs, with the highest resistance in JSEG15-rev3 (MIC = 128 mg/L). All revertants presented a deleted Tn1546-like on a 34-kb plasmid and JSEG15-rev2 and JSEG15-rev3 also showed an additional chromosomal copy of the vanRS and vanHAX clusters, and higher vanA gene copies and expression. A mutation in the chromosomal D-Ala-D-Ala ligase gene was identified in JSEG15-rev3 which also transferred the vanA carrying plasmid by in vitro conjugation. The parental strain and all revertants exhibited heteroresistance, with higher frequency of resistant subpopulations in the revertants.

conclusionThese findings emphasize the dynamic genetical changes enabling VVE to regain full resistance, underscoring the need for vigilant treatment strategies to address enterococcal infections and for monitoring the spread of clinically relevant strains in the environment for public health protection.

Indexed as

Anti-Bacterial AgentsEnterococcus faeciumVancomycinVancomycin ResistanceBacterial ProteinsCarbon-Oxygen LigasesDNA Transposable ElementsGram-Positive Bacterial InfectionsHumansMicrobial Sensitivity TestsMutationPlasmidsWhole Genome SequencingAnti-Bacterial AgentsBacterial ProteinsCarbon-Oxygen LigasesDNA Transposable ElementsVanA ligase, BacteriaVancomycinConjugative plasmidsEnterococcus faeciumHeteroresistancevanAVancomycin-variable enterococci

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Read under generation 80e0d062 · epoch 390. Bibliography from PubMed, PubMed Central and OpenAlex; grants from NIH RePORTER; trial links from ClinicalTrials.gov; estimates, votes and beliefs from the OpenQuestion graph.