Single point mutations in global regulatory genes restore cephalosporin resistance in a low-MIC Enterococcus faecium natural isolate
Sánchez-Osuna, Miquel (Universitat Autònoma de Barcelona. Institut de Biotecnologia i de Biomedicina "Vicent Villar Palasí")
Bierge, Paula (Universitat Autònoma de Barcelona. Institut de Biotecnologia i de Biomedicina "Vicent Villar Palasí")
Gómez Sánchez, Inmaculada (Parc Taulí Hospital Universitari. Institut d'Investigació i Innovació Parc Taulí (I3PT))
Guitart Matas, Judith (Universitat Autònoma de Barcelona. Institut de Biotecnologia i de Biomedicina "Vicent Villar Palasí")
Monsálvez, Víctor (Parc Taulí Hospital Universitari. Institut d'Investigació i Innovació Parc Taulí (I3PT))
Rabanal, Patricia (Universitat Autònoma de Barcelona. Institut de Biotecnologia i de Biomedicina "Vicent Villar Palasí")
Pereira, Ana P. (Universidade do Porto)
Freitas, Ana R. (Universidade do Porto)
Peixe, Luisa (Universidade do Porto)
Espasa, Mateu (Parc Taulí Hospital Universitari. Institut d'Investigació i Innovació Parc Taulí (I3PT))
Gasch Blasi, Oriol (Parc Taulí Hospital Universitari. Institut d'Investigació i Innovació Parc Taulí (I3PT))
Novais, Carla (Universidade do Porto)
Pich, Oscar Q. (Universitat Autònoma de Barcelona. Institut de Biotecnologia i de Biomedicina "Vicent Villar Palasí")

Date:	2026
Abstract:	Enterococcus faecium exhibits intrinsic resistance to cephalosporins (CPHs), yet the genetic determinants of this phenotype remain incompletely understood. To date, E. faecium strains with low minimum inhibitory concentrations (MICs) of CPH have only been described following genetic manipulation. At Parc Taulí University Hospital, we identified a clinical isolate of ampicillin-susceptible E. faecium (Efm5) that exhibited unusually low MICs to cefotaxime (1 mg/L), ceftriaxone (3 mg/L), and ceftaroline (0. 19 mg/L). Upon single exposure to ceftriaxone (100 mg/L), Efm5 rapidly yielded variants with markedly increased MICs of ceftriaxone (>256 mg/L) and cefotaxime (>32 mg/L), while MICs of ampicillin and ceftaroline were unaffected. Whole-genome sequencing revealed that the high-MIC variants carried single-nucleotide polymorphisms leading to non-synonymous mutations in croS, nusG, or rpoB genes. Phenotypic assays confirmed that these mutations were associated with ceftriaxone resistance, and immunoblots revealed increased expression of penicillin-binding protein 5 (PBP5) in all the high-MIC variants. Transcriptional profiling showed upregulation of the pbp5 operon, which includes ftsW, psr, and pbp5, in the croS variants. This study provides evidence that E. faecium isolates with low MICs to CPH can arise in clinical settings without laboratory manipulation, enabling further investigation of resistance pathways.
Grants:	Instituto de Salud Carlos III PI24/01294
Rights:	Aquest document està subjecte a una llicència d'ús Creative Commons. Es permet la reproducció total o parcial, la distribució, la comunicació pública de l'obra i la creació d'obres derivades, fins i tot amb finalitats comercials, sempre i quan es reconegui l'autoria de l'obra original.
Language:	Anglès
Document:	Article ; recerca ; Versió publicada
Subject:	Ampicillin-susceptible Enterococcus faecium ; Cephalosporin intrinsic resistance ; CroS ; NusG ; RpoB ; PBP5
Published in:	Antimicrobial Agents and Chemotherapy, Vol. 70, Num. 5 (May 2026) , art. e01948-25, ISSN 1098-6596

DOI: 10.1128/aac.01948-25

16 p, 5.7 MB

The record appears in these collections:
Research literature > UAB research groups literature > Research Centres and Groups (research output) > Health sciences and biosciences > Parc Taulí Research and Innovation Institute (I3PT
Research literature > UAB research groups literature > Research Centres and Groups (research output) > Health sciences and biosciences > Institut de Biotecnologia i de Biomedicina (IBB)
Articles > Research articles
Articles > Published articles