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ICESag08: A new composite integrative and conjugative element from Streptococcus agalactiae mediating resistance to

Yong-Hui Liu1

  • 1College of Applied Engineering, Henan University of Science and Technology, Sanmenxia, Henan, China; Sanmenxia-City Authentic Medicinal Materials Processing Engineering, Technology Research Center, Sanmenxia, Henan, China.

Journal of Global Antimicrobial Resistance
|February 18, 2026
PubMed
Abstract

Insights

A novel composite integrative and conjugative element (ICE), ICESag08, facilitates the spread of multidrug resistance in Streptococcus agalactiae. This element transfers efficiently between bacteria, though it imposes a fitness cost on the host.

Area of Science:

  • Microbiology
  • Genetics
  • Molecular Biology

Background:

  • Emerging antibiotic resistance in Streptococcus agalactiae, particularly to chloramphenicol, presents significant clinical challenges.
  • The catQ-mef(I) IQ module is a conserved mechanism mediating this resistance.
  • Previous studies identified several IQ module-carrying elements in different Streptococcus species.

Purpose of the Study:

  • To characterize a novel composite integrative and conjugative element (ICE) carrying an IQ module in chloramphenicol-resistant Streptococcus agalactiae.
  • To assess the transferability, fitness costs, and stability of this novel ICE.

Main Methods:

  • Bioinformatics analysis of sequenced Streptococcus agalactiae isolates.
  • Conjugation assays to confirm transferability.
  • Growth and competition assays to evaluate fitness costs.
  • Serial passage experiments to assess stability.

Main Results:

  • A novel 133-kb composite ICE, designated ICESag08, was identified, integrating four distinct elements.
  • ICESag08 carries the catQ-mef(I) locus conferring chloramphenicol resistance and erm(TR) conferring macrolide resistance.
  • ICESag08 was transferable to recipient strains with a frequency of 1.05 × 10⁻⁹.
  • Transconjugants showed impaired growth and reduced competitive ability, but the ICE remained stable and conferred resistance.

Conclusions:

  • Composite ICEs play a crucial role in the horizontal transfer of multidrug resistance, including chloramphenicol and macrolides.
  • The interplay between different ICEs contributes to the dissemination and evolution of antimicrobial resistance.
  • Understanding these mechanisms is vital for developing strategies to combat the spread of antibiotic resistance.
Keywords:
Antimicrobial resistanceChloramphenicolIntegrative and conjugative elementsStreptococcus agalactiae

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