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Curr Biol. 2001 Nov 13;11(22):1810-4.

Phenotypic switching of antibiotic resistance circumvents permanent costs in Staphylococcus aureus.

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Nuffield Department of Clinical Laboratory Sciences, University of Oxford, John Radcliffe Hospital, Oxford OX3 9DU, United Kingdom.


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.

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