Background

The rise of antimicrobial resistance (AMR) is a serious threat to global health in the 21st century. Life-threatening multi-drug resistant microbes have emerged and thus new approaches are needed to maximize the "shelf-life" of antimicrobials by reducing the risk of the emergence and spread of resistance.

Objective

Recent studies have shown how different strains belonging to the same bacterial species possess a different propensity to develop AMR ("evolvability"). The genetic determinants of differences in evolvability have however not been determined in E. coli; our aim is to discover them using large-scale laboratory evolution.

Methods

We have so far exposed 380 E. coli strains to 3 antimicrobials and 6 biological replicates: Amikacin, Ceftriaxone, and Ciprofloxacin, using a serial passaging protocol with daily doublings in concentration, from 1/8th of the Minimum Inhibitory Concentration (MIC) until 64X MIC. We have preserved one evolved population for each biological replicate for genome sequencing and further characterization.

Results

Using the passage at which we last observe growth as a measure of evolvability, we observed substantial variability in the ability of each strain to become resistant, which varies by genetic background and drug class, with Ceftriaxone showing the largest variance. At the genome level, we observed differences in the mutations acquired during the experiment, further underscoring the influence of E. coli"s genetic background on evolution. We will show data on more strains and antimicrobials, as well as patterns of cross-sensitivity in the evolved isolates, which have important implications in designing combination therapies.