title: Increased uptake and improved intracellular survival of a teicoplanin-resistant mutant of methicillin-resistant Staphylococcus aureus in non-professional phagocytes.
abstract: OBJECTIVE
  Endogenous development of glycopeptide-intermediate resistance is linked to multiple genetic and phenotypic changes in clinical and laboratory isolates of Staphylococcus aureus. This study evaluated endocytic uptake and intracellular survival of a teicoplanin-resistant derivative of S. aureus in a human epithelial cell line, and compared these to the isogenic teicoplanin-susceptible parent or a spontaneously derived, susceptible revertant.
  
  
  METHODS
  Endocytic uptake of teicoplanin-resistant and teicoplanin-susceptible strains by human embryonic kidney 293 cells was estimated by a lysostaphin protection assay. Differential intracellular survival of all S. aureus strains from 2 to 24 h was evaluated by colony-forming unit counts of Triton X-100-lysed 293 cells, following lysostaphin inactivation.
  
  
  RESULTS
  Endocytic uptake of the teicoplanin-resistant strain increased by approximately 4-fold over its teicoplanin-susceptible counterparts. Furthermore, the teicoplanin-resistant strain showed an 11-fold increase in intracellular colony-forming unit counts from 2 to 24 h, compared to its teicoplanin-susceptible counterparts that showed marginal (<2-fold) changes during the same time period. Infected host cells showed no significant viability loss at 24 h, as assessed by Trypan blue dye exclusion.
  
  
  CONCLUSIONS
  Intracellular location might confer a significant fitness benefit to glycopeptide-intermediate isolates of methicillin-resistant S. aureus and further protect them from cell wall-active antibiotics whose intracellular activity is limited.
authors.affiliation: Service of Infectious Diseases, Geneva University Hospital, Geneva, Switzerland.
authors.forename: Adriana
authors.initials: A
authors.lastname: Renzoni
authors.forename: Elzbieta
authors.initials: E
authors.lastname: Huggler
authors.forename: William L
authors.initials: WL
authors.lastname: Kelley
authors.forename: Daniel
authors.initials: D
authors.lastname: Lew
authors.forename: Pierre
authors.initials: P
authors.lastname: Vaudaux
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002460:Cell Line; D024881:Drug Resistance, Bacterial; D006801:Humans; D008248:Lysostaphin / Q000378:metabolism; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification; D008826:Microbial Sensitivity Tests; D009154:Mutation; D010586:Phagocytes / Q000382:microbiology*; D017334:Teicoplanin / Q000494:pharmacology*; D013997:Time Factors
chemical_list: D000900:Anti-Bacterial Agents; D017334:Teicoplanin; D008248:Lysostaphin