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Open Access Highly Accessed Research article

The cost of antibiotic resistance depends on evolutionary history in Escherichia coli

Daniel C Angst123 and Alex R Hall123*

Author Affiliations

1 Institute of Integrative Biology, ETH Zürich, Zürich, CH-8092, Switzerland

2 Institute of Biogeochemistry and Pollutant Dynamics, ETH Zürich, Zürich, Switzerland

3 Department of Environmental Microbiology, Eawag, Dübendorf, Switzerland

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BMC Evolutionary Biology 2013, 13:163  doi:10.1186/1471-2148-13-163

Published: 2 August 2013

Abstract

Background

The persistence of antibiotic resistance depends on the fitness effects of resistance elements in the absence of antibiotics. Recent work shows that the fitness effect of a given resistance mutation is influenced by other resistance mutations on the same genome. However, resistant bacteria acquire additional beneficial mutations during evolution in the absence of antibiotics that do not alter resistance directly but may modify the fitness effects of new resistance mutations.

Results

We experimentally evolved rifampicin-resistant and sensitive Escherichia coli in a drug-free environment, before measuring the effects of new resistance elements on fitness in antibiotic-free conditions. Streptomycin-resistance mutations had small fitness effects in rifampicin-resistant genotypes that had adapted to antibiotic-free growth medium, compared to the same genotypes without adaptation. We observed a similar effect when resistance was encoded by a different mechanism and carried on a plasmid. Antibiotic-sensitive bacteria that adapted to the same conditions showed the same pattern for some resistance elements but not others.

Conclusions

Epistatic variation of costs of resistance can result from evolution in the absence of antibiotics, as well as the presence of other resistance mutations.

Keywords:
Antibiotic resistance; Epistasis; Experimental evolution; Escherichia coli