title: A novel point mutation promotes growth phase-dependent daptomycin tolerance in Staphylococcus aureus.
abstract: Recalcitrance of genetically susceptible bacteria to antibiotic killing is a hallmark of bacterial drug tolerance. This phenomenon is prevalent in biofilms, persisters, and also planktonic cells and is associated with chronic or relapsing infections with pathogens such as Staphylococcus aureus. Here we report the in vitro evolution of an S. aureus strain that exhibits a high degree of nonsusceptibility to daptomycin as a result of cyclic challenges with bactericidal concentrations of the drug. This phenotype was attributed to stationary growth phase-dependent drug tolerance and was clearly distinguished from resistance. The underlying genetic basis was revealed to be an adaptive point mutation in the putative inorganic phosphate (Pi) transporter gene pitA. Drug tolerance caused by this allele, termed pitA6, was abrogated when the upstream gene pitR was inactivated. Enhanced tolerance toward daptomycin, as well as the acyldepsipeptide antibiotic ADEP4 and various combinations of other drugs, was accompanied by elevated intracellular concentrations of Pi and polyphosphate, which may reversibly interfere with critical cellular functions. The evolved strain displayed increased rates of survival within human endothelial cells, demonstrating the correlation of intracellular persistence and drug tolerance. These findings will be useful for further investigations of S. aureus drug tolerance, toward the development of additional antipersister compounds and strategies.
authors.affiliation: Department of Microbial Genetics, Faculty of Science, Interfaculty Institute of Microbiology and Infection Medicine Tübingen, University of Tübingen, Tübingen, Germany.
authors.forename: Lukas
authors.initials: L
authors.lastname: Mechler
authors.affiliation: Department of Archaeological Sciences, University of Tübingen, Tübingen, Germany Center for Bioinformatics, University of Tübingen, Tübingen, Germany.
authors.forename: Alexander
authors.initials: A
authors.lastname: Herbig
authors.affiliation: Department of Microbiology, University of Würzburg, Würzburg, Germany.
authors.forename: Kerstin
authors.initials: K
authors.lastname: Paprotka
authors.affiliation: Department of Microbiology, University of Würzburg, Würzburg, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Fraunholz
authors.affiliation: Center for Bioinformatics, University of Tübingen, Tübingen, Germany.
authors.forename: Kay
authors.initials: K
authors.lastname: Nieselt
authors.affiliation: Department of Microbial Genetics, Faculty of Science, Interfaculty Institute of Microbiology and Infection Medicine Tübingen, University of Tübingen, Tübingen, Germany ralph.bertram@pmu.ac.at.
authors.forename: Ralph
authors.initials: R
authors.lastname: Bertram
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D017576:Daptomycin / Q000494:pharmacology*; D024881:Drug Resistance, Bacterial / Q000235:genetics; D006801:Humans; D008826:Microbial Sensitivity Tests; D017354:Point Mutation / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000235:genetics*
chemical_list: D000900:Anti-Bacterial Agents; D017576:Daptomycin