Molecular Basis for Different Levels of tet(M) Expression in Streptococcus Pneumoniae Clinical Isolates

Antimicrob Agents Chemother. 2012 Oct;56(10):5040-5. doi: 10.1128/AAC.00939-12. Epub 2012 Jul 16.


Seventy-four unrelated clinical isolates of Streptococcus pneumoniae harboring the tet(M) gene were studied. Seven strains with low tetracycline (Tc) MICs (0.25 to 0.5 μg/ml) were found to harbor truncated tet(M) alleles that were inactivated by different frameshift mutations. In contrast, five strains bore deletions in the tet(M) promoter region, among which four displayed increased Tc MICs (16 to 64 μg/ml). The same promoter mutations were detected in Tc-resistant mutants selected in vitro from various susceptible strains. Sequence analysis revealed that these deletions might impede the formation of the transcriptional attenuator located immediately upstream of tet(M). Expression in Enterococcus faecalis of a tet(M) reporter gene transcribed from these promoter mutants conferred a level of Tc resistance similar to that observed in the parental S. pneumoniae strains. These results show that different levels of Tc susceptibility found in clinical isolates of S. pneumoniae can be explained by frameshift mutations within tet(M) and by alterations of the upstream transcriptional attenuator.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acinetobacter / drug effects
  • Acinetobacter / metabolism
  • Acinetobacter / ultrastructure
  • Alginates / chemistry
  • Anti-Bacterial Agents / pharmacology*
  • Bacterial Proteins / metabolism
  • Biofilms / drug effects
  • Burkholderia / drug effects
  • Burkholderia / metabolism
  • Burkholderia / ultrastructure
  • Glucuronic Acid / chemistry
  • Hexuronic Acids / chemistry
  • Microscopy, Atomic Force
  • Microscopy, Confocal
  • Oligosaccharides / chemical synthesis
  • Oligosaccharides / chemistry
  • Oligosaccharides / pharmacology*
  • Pseudomonas / drug effects
  • Pseudomonas / metabolism
  • Pseudomonas / ultrastructure
  • Streptococcus pneumoniae / drug effects*
  • Streptococcus pneumoniae / metabolism
  • Streptococcus pneumoniae / ultrastructure
  • Tetracycline Resistance


  • Alginates
  • Anti-Bacterial Agents
  • Bacterial Proteins
  • Hexuronic Acids
  • Oligosaccharides
  • Glucuronic Acid