title: In Vitro Tolerance of Drug-Naive Staphylococcus aureus Strain FDA209P to Vancomycin.
abstract: The mechanisms underlying bacterial tolerance to antibiotics are unclear. A possible adaptation strategy was explored by exposure of drug-naive methicillin-susceptible Staphylococcus aureus strain FDA209P to vancomycin in vitro Strains surviving vancomycin treatment (vancomycin survivor strains), which appeared after 96 h of exposure, were slow-growing derivatives of the parent strain. Although the vancomycin MICs for the survivor strains were within the susceptible range, the cytokilling effects of vancomycin at 20-fold the MIC were significantly lower for the survivor strains than for the parent strain. Whole-genome sequencing demonstrated that ileS, encoding isoleucyl-tRNA synthetase (IleRS), was mutated in two of the three vancomycin survivor strains. The IleRS Y723H mutation is located close to the isoleucyl-tRNA contact site and potentially affects the affinity of IleRS binding to isoleucyl-tRNA, thereby inhibiting protein synthesis and leading to vancomycin tolerance. Introduction of the mutation encoding IleRS Y723H into FDA209P by allelic replacement successfully transferred the vancomycin tolerance phenotype. We have identified mutation of ileS to be one of the bona fide genetic events leading to the acquisition of vancomycin tolerance in S. aureus, potentially acting via inhibition of the function of IleRS.
authors.affiliation: Department of Microbiology, Faculty of Medicine, Juntendo University, Tokyo, Japan.
authors.forename: Madhuri
authors.initials: M
authors.lastname: Singh
authors.affiliation: Department of Microbiology, Faculty of Medicine, Juntendo University, Tokyo, Japan mmatsuo@juntendo.ac.jp.
authors.forename: Miki
authors.initials: M
authors.lastname: Matsuo
authors.affiliation: Department of Microbiology, Faculty of Medicine, Juntendo University, Tokyo, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Sasaki
authors.affiliation: Department of Microbiology, Faculty of Medicine, Juntendo University, Tokyo, Japan.
authors.forename: Yuh
authors.initials: Y
authors.lastname: Morimoto
authors.affiliation: Department of Microbiology, Faculty of Medicine, Juntendo University, Tokyo, Japan.
authors.forename: Tomomi
authors.initials: T
authors.lastname: Hishinuma
authors.affiliation: Department of Microbiology, Faculty of Medicine, Juntendo University, Tokyo, Japan.
authors.forename: Keiichi
authors.initials: K
authors.lastname: Hiramatsu
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D007533:Isoleucine-tRNA Ligase / Q000037:antagonists & inhibitors / Q000235:genetics; D008826:Microbial Sensitivity Tests; D016712:Mupirocin / Q000494:pharmacology; D009154:Mutation; D020641:Polymorphism, Single Nucleotide; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000235:genetics*; D014640:Vancomycin / Q000494:pharmacology*; D020713:Vancomycin Resistance / Q000235:genetics
chemical_list: D000900:Anti-Bacterial Agents; D014640:Vancomycin; D016712:Mupirocin; D007533:Isoleucine-tRNA Ligase
keywords: MSSA; ileS; killing rate; resistance; tolerance; vancomycin