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Updated: Jul 14, 2026

Testing the Role of Multicopy Plasmids in the Evolution of Antibiotic Resistance
09:00

Testing the Role of Multicopy Plasmids in the Evolution of Antibiotic Resistance

Published on: May 2, 2018

Evolutionary dynamics of the multidrug-resistant Salmonella Infantis harbouring the pESI megaplasmid across Europe

Patricia Alba1, Elena Lavinia Diaconu1, Virginia Carfora1

  • 1Department of General Diagnostics, National Reference Laboratory for Antimicrobial Resistance, Istituto Zooprofilattico Sperimentale del Lazio e della Toscana "M. Aleandri", Rome, Italy.

Microbial Genomics
|July 13, 2026
PubMed

Insights

A multidrug-resistant Salmonella Infantis clone carrying the pESI megaplasmid circulates globally. This study reveals two main pESI variants in Europe, differing in accessory genes and conferring antimicrobial resistance, impacting One Health surveillance.

Area of Science:

  • Microbiology
  • Genomics
  • Epidemiology

Background:

  • Multidrug-resistant *Salmonella enterica* subsp. *enterica* serovar Infantis* (S. Infantis) clone, associated with the pESI megaplasmid, emerged in Israel in 2014 and is now a global concern in poultry and humans.
  • This clone exhibits resistance to multiple antibiotics, including sulphonamides, tetracycline, streptomycin, and spectinomycin, with increasing detection of extended-spectrum beta-lactamase (ESBL) genes like *bla*CTX-M-1.

Purpose of the Study:

  • To investigate the genomic epidemiology of *S. Infantis* in Europe, analyzing samples from human, food, and animal sources.
  • To understand the evolutionary dynamics of pESI-like plasmids within Europe and compare them globally in a One Health context.

Main Methods:

  • Utilized a combination of short- and long-read sequencing approaches for comprehensive genomic analysis.
  • Collected and analyzed *S. Infantis* samples from nine European Public Health Institutions between 2011 and 2021.
  • Compared European pESI-like sequences with publicly available global sequences.

Main Results:

  • Identified the circulation of a *S. Infantis* clone in Europe carrying a mosaic pESI-like megaplasmid, associated with specific antimicrobial resistance genes (*sul*, *tet*, *aadA1*).
  • Detected two main types of pESI variants in Europe, differing in accessory gene content, including *bla*CTX-M variants, indicating stability across different regions and sources over a decade (2011-2021).
  • Observed that variations in pESI variants are linked to the acquisition of resistance, virulence, or fitness-enhancing genes.

Conclusions:

  • The study confirms the sustained circulation of a specific multidrug-resistant *S. Infantis* clone and its pESI-like megaplasmid variants in Europe.
  • The genomic diversity of pESI variants suggests ongoing evolution and adaptation, potentially conferring advantages to the *Salmonella* host.
  • Findings underscore the importance of integrated genomic surveillance across human, animal, and food sources for effective One Health antimicrobial resistance monitoring.
Keywords:
One HealthSalmonella Infantisextended-spectrum beta-lactamase (ESBL)multi-drug resistancepESI plasmidwhole-genome sequence

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