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Conjugal mobilization of the mega element carrying mef(E) from Streptococcus salivarius to Streptococcus pneumoniae

Maria Santagati1, Agnese Lupo, Marina Scillato

  • 1Department of Microbiological Science, University of Catania, Catania, Italy.

FEMS Microbiology Letters
|November 26, 2008
PubMed

Insights

This study identifies a unique Streptococcus salivarius strain (3C30) with dual antibiotic resistance. The mega element, conferring macrolide resistance, was transferable to Streptococcus pneumoniae.

Area of Science:

  • Microbiology
  • Molecular Biology
  • Genetics

Background:

  • Antimicrobial resistance is a growing global health concern.
  • Streptococcus salivarius is a common oral bacterium that can cause opportunistic infections.
  • Understanding the genetic basis of antibiotic resistance in bacteria is crucial for developing effective treatments.

Purpose of the Study:

  • To isolate and characterize a novel strain of Streptococcus salivarius exhibiting multiple antibiotic resistance.
  • To investigate the genetic elements responsible for macrolide-lincosamide-streptogramin B (MLSB) and tetracycline resistance in the identified strain.
  • To determine the transferability and genetic behavior of these resistance elements.

Main Methods:

  • Isolation and phenotypic characterization of Streptococcus salivarius strain 3C30.
  • Long PCR and DNA sequencing to identify and analyze resistance genes (mef(E), erm(B), tet(M)) and associated genetic elements (mega, Tn3872-like).
  • Conjugation experiments to assess the transferability of resistance elements to Streptococcus pneumoniae.
  • Real-time PCR to detect circular DNA structures of the mega element.

Main Results:

  • Strain 3C30 displayed both MLSB and tetracycline resistance phenotypes.
  • The strain harbored the mef(E) gene within the mega element and erm(B) and tet(M) genes on a Tn3872-like element.
  • The mega element, with a unique deletion, was transferable to Streptococcus pneumoniae but not subsequently transferable from transconjugants.
  • Mega element formed circular structures exclusively in the original S. salivarius 3C30 strain.

Conclusions:

  • A clinical isolate of Streptococcus salivarius (3C30) possesses both mega and Tn3872-like genetic elements conferring antibiotic resistance.
  • The mega element is transferable to Streptococcus pneumoniae, suggesting potential horizontal gene transfer mechanisms.
  • The inability to re-transfer mega from transconjugants points to possible mobilization by the core-resident Tn3872-like transposon, highlighting complex genetic interactions in antibiotic resistance dissemination.

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