Chen, S., Larsson, M., Robinson, R.C. et al. Direct and convenient measurement of plasmid stability in lab and clinical isolates of E. coli. Sci Rep 7, 4788 (2017). https://doi.org/10.1038/s41598-017-05219-x
Plasmids are important mobile elements in bacteria, contributing to evolution, virulence, and antibiotic resistance. Natural plasmids are generally large and maintained at low copy number and thus prone to be lost. Therefore, dedicated plasmid maintenance systems have evolved, leading to plasmid loss rates as low as 1 per 107 divisions. These low rates complicate studies of plasmid loss, as traditional techniques for measuring plasmid loss are laborious and not quantitative. To overcome these limitations, we leveraged a stringent negative selection system to develop a method for performing direct, quantitative measurements of plasmid loss in E. coli. We applied our method to gain mechanistic insights into a heterologously reconstituted segregation system in lab strains and clinical isolates of E. coli. We also performed direct stability studies of a currently circulating resistance plasmid in a clinical isolate, strain EC958, which is a member of the rapidly expanding global ST131 E. coli clone. Our results establish the foundational assays required to screen for small molecules targeting plasmid stability, which could complement current strategies for reducing the spread of antibiotic resistance, complementing other strategies for treating antibiotic resistant bacteria.
We thank Mark Schembri for providing the original EC958 clone. We thank Majid Eshaghi, William Burkholder, Kimberly Kline, other members of the Chen lab, and the Singapore Bacterial Ultra Group for helpful discussions, feedback, and comments on the manuscript. This work was funded by the National Research Foundation, Prime Minister’s Office, Singapore under its NRF Research Fellowship Scheme (NRF-RF2010-10 to S.L.C.) and the National Medical Research Council, Ministry of Health, Singapore (NMRC/CIRG/1357/2013 to S.L.C.). Additional facilities support and synthesis of the pSLC-295 plasmid were provided by the Genome Institute of Singapore (GIS) and the Institute of Molecular and Cell Biology (IMCB)/Agency for Science, Technology and Research (A*STAR).