A novel point mutation promotes growth phase-dependent daptomycin tolerance in Staphylococcus aureus

Area of Science:

• Microbiology
• Molecular Biology
• Drug Discovery

Background:

• Bacterial drug tolerance, distinct from resistance, allows survival during antibiotic treatment.
• This phenomenon is crucial in chronic infections caused by pathogens like Staphylococcus aureus.
• Understanding tolerance mechanisms is vital for developing effective antimicrobial strategies.

Purpose of the Study:

• To investigate the in vitro evolution of Staphylococcus aureus towards daptomycin nonsusceptibility.
• To elucidate the genetic basis and cellular mechanisms underlying this acquired drug tolerance.
• To explore the implications of this tolerance phenotype for intracellular bacterial survival and therapeutic interventions.

Main Methods:

• In vitro evolution of S. aureus through cyclic exposure to daptomycin.
• Phenotypic characterization of drug tolerance and distinction from resistance.
• Genetic analysis to identify mutations, specifically in the pitA gene.
• Assessment of intracellular inorganic phosphate (Pi) and polyphosphate levels.
• Evaluation of bacterial survival within human endothelial cells.

Main Results:

• An S. aureus strain evolved significant daptomycin nonsusceptibility, attributed to stationary phase-dependent drug tolerance.
• A point mutation in the pitA gene (pitA6) was identified as the genetic cause, dependent on the upstream gene pitR.
• Elevated intracellular Pi and polyphosphate concentrations correlated with tolerance to daptomycin, ADEP4, and other drugs.
• The evolved strain showed enhanced survival within human endothelial cells, linking drug tolerance to intracellular persistence.

Conclusions:

• Adaptive mutations in pitA can confer significant drug tolerance in S. aureus.
• Elevated intracellular polyphosphate may play a role in reversible interference with cellular functions, leading to drug tolerance.
• This study provides insights into bacterial drug tolerance mechanisms and identifies potential targets for novel antipersister therapies.