title: Phenotypic switching of antibiotic resistance circumvents permanent costs in Staphylococcus aureus.
abstract: 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.
authors.affiliation: Nuffield Department of Clinical Laboratory Sciences, University of Oxford, John Radcliffe Hospital, Oxford OX3 9DU, United Kingdom. ruth.massey@ndcls.ox.ac.uk
authors.forename: R C
authors.initials: RC
authors.lastname: Massey
authors.forename: A
authors.initials: A
authors.lastname: Buckling
authors.forename: S J
authors.initials: SJ
authors.lastname: Peacock
mesh_terms: D000222:Adaptation, Physiological / Q000187:drug effects*; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D024881:Drug Resistance, Bacterial; D005839:Gentamicins / Q000494:pharmacology*; D006801:Humans; D010641:Phenotype; D000198:Spectinomycin / Q000494:pharmacology; D013203:Staphylococcal Infections / Q000382:microbiology; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000254:growth & development / Q000302:isolation & purification / Q000502:physiology; D013307:Streptomycin / Q000494:pharmacology
chemical_list: D000900:Anti-Bacterial Agents; D005839:Gentamicins; D000198:Spectinomycin; D013307:Streptomycin