Phenotypic switching of antibiotic resistance circumvents permanent costs in Staphylococcus aureus

Curr Biol. 2001 Nov 13;11(22):1810-4. doi: 10.1016/s0960-9822(01)00507-3.


Bacterial antibiotic resistance is often associated with a fitness cost in the absence of the antibiotic [1,2]. We have examined a resistance mechanism in Staphylococcus aureus that negates these costs. Exposure to gentamicin both in vitro and in vivo has been reported to result in the emergence of a gentamicin-resistant small colony variant (SCV)[3-8]. We show that the emergence of SCVs following exposure to gentamicin results from a rapid switch and that bacteria exposed to cycles of gentamicin followed by antibiotic-free medium repeatedly switched between a resistant SCV and a sensitive parental phenotype (revertants). The fitness of revertants relative to S. aureus with stable gentamicin resistance was greater in drug-free media, which suggests that S. aureus has evolved an inducible and reversible resistance mechanism that circumvents a permanent cost to fitness.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptation, Physiological / drug effects*
  • Anti-Bacterial Agents / pharmacology*
  • Drug Resistance, Bacterial
  • Gentamicins / pharmacology*
  • Humans
  • Phenotype
  • Spectinomycin / pharmacology
  • Staphylococcal Infections / microbiology
  • Staphylococcus aureus / drug effects*
  • Staphylococcus aureus / growth & development
  • Staphylococcus aureus / isolation & purification
  • Staphylococcus aureus / physiology
  • Streptomycin / pharmacology


  • Anti-Bacterial Agents
  • Gentamicins
  • Spectinomycin
  • Streptomycin