Title |
Soft sweep development of resistance in Escherichia coli under fluoroquinolone stress |
Author |
Xianxing Xie1, Ruichen Lv1,2, Chao Yang1, Yajun Song1, Yanfeng Yan1, Yujun Cui1, and Ruifu Yang1* |
Address |
1State Key Laboratory of Pathogen and Biosecurity, Beijing Institute of Microbiology and Epidemiology, Beijing, P. R. China, 2Huadong Research Institute for Medicine and Biotechnics, Nanjing, P. R. China |
Bibliography |
Journal of Microbiology, 57(12),1056-1064, 2019,
|
DOI |
10.1007/s12275-019-9177-5
|
Key Words |
soft sweeps, stepwise selection, Escherichia coli,
ciprofloxacin, fitness cost |
Abstract |
We employed a stepwise selection model for investigating the
dynamics of antibiotic-resistant variants in Escherichia coli
K-12 treated with increasing concentrations of ciprofloxacin
(CIP). Firstly, we used Sanger sequencing to screen the variations
in the fluoquinolone target genes, then, employed Illumina
NGS sequencing for amplicons targeted regions with
variations. The results demonstrated that variations G81C in
gyrA and K276N and K277L in parC are standing resistance
variations (SRVs), while S83A and S83L in gyrA and G78C
in parC were emerging resistance variations (ERVs). The variants
containing SRVs and/or ERVs were selected successively
based on their sensitivities to CIP. Variant strain 1, containing
substitution G81C in gyrA, was immediately selected
following ciprofloxacin exposure, with obvious increases in
the parC SRV, and parC and gyrA ERV allele frequencies.
Variant strain 2, containing the SRVs, then dominated the
population following a 20× increase in ciprofloxacin concentration,
with other associated allele frequencies also elevated.
Variant strains 3 and 4, containing ERVs in gyrA and parC,
respectively, were then selected at 40× and 160× antibiotic
concentrations. Two variants, strains 5 and 6, generated in
the selection procedure, were lost because of higher fitness
costs or a lower level of resistance compared with variants 3
and 4. For the second induction, all variations/indels were
already present as SRVs and selected out step by step at different
passages. Whatever the first induction or second induction,
our results confirmed the soft selective sweep hypothesis
and provided critical information for guiding clinical
treatment of pathogens containing SRVs. |