Daptomycin Tolerance in the Staphylococcus aureus pitA6 Mutant Is Due to Upregulation of the dlt Operon

Antimicrob Agents Chemother. 2016 Apr 22;60(5):2684-91. doi: 10.1128/AAC.03022-15. Print 2016 May.


Understanding the mechanisms of how bacteria become tolerant toward antibiotics during clinical therapy is a very important object. In a previous study, we showed that increased daptomycin (DAP) tolerance of Staphylococcus aureus was due to a point mutation in pitA (inorganic phosphate transporter) that led to intracellular accumulation of both inorganic phosphate (Pi) and polyphosphate (polyP). DAP tolerance in the pitA6 mutant differs from classical resistance mechanisms since there is no increase in the MIC. In this follow-up study, we demonstrate that DAP tolerance in the pitA6 mutant is not triggered by the accumulation of polyP. Transcriptome analysis revealed that 234 genes were at least 2.0-fold differentially expressed in the mutant. Particularly, genes involved in protein biosynthesis, carbohydrate and lipid metabolism, and replication and maintenance of DNA were downregulated. However, the most important change was the upregulation of the dlt operon, which is induced by the accumulation of intracellular Pi The GraXRS system, known as an activator of the dlt operon (d-alanylation of teichoic acids) and of the mprF gene (multiple peptide resistance factor), is not involved in DAP tolerance of the pitA6 mutant. In conclusion, DAP tolerance of the pitA6 mutant is due to an upregulation of the dlt operon, triggered directly or indirectly by the accumulation of Pi.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Anti-Bacterial Agents / pharmacology
  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism*
  • Daptomycin / pharmacology*
  • Microbial Sensitivity Tests
  • Operon / genetics*
  • Point Mutation / genetics
  • Staphylococcus aureus / drug effects*
  • Staphylococcus aureus / genetics
  • Staphylococcus aureus / metabolism*
  • Teichoic Acids / metabolism
  • Transcriptome / genetics


  • Anti-Bacterial Agents
  • Bacterial Proteins
  • Teichoic Acids
  • Daptomycin

Grant support

The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.