Methods to Determine Mutational Trajectories After Experimental Evolution of Antibiotic Resistance.

The evolution of bacterial resistance to antibiotics by mutation within the genome (as distinct from horizontal gene transfer of new material into a genome) could occur in a single step but is usually a multistep process. Resistance evolution can be studied in laboratory environments by serial passage of bacteria in liquid culture or on agar, with selection at constant, or varying, concentrations of drug. Whole genome sequencing can be used to make an initial analysis of the evolved mutants. The trajectory of evolution can be determined by sequence analysis of strains from intermediate steps in the evolution, complemented by phenotypic analysis of genetically reconstructed isogenic strains that recapitulate the intermediate steps in the evolution.