Adaptive walks to antibiotic resistance

The mutational steps for the 10 most probable trajectories from wild-type susceptibility to the antibiotic cefotaxime to maximal resistance. Each circle represents an allele whose identity is denoted by a string of five + or – symbols corresponding (left to right) to the presence or absence of mutations g4205a, A42G, E104K, M182T, and G238S, respectively. Numbers indicate degree of cefotaxime resistance in micrograms per milliliter. The relative probability of each beneficial mutation is represented by the color and width of arrows: green—wide, highest; blue—medium, moderate; purple—narrow, low; and orange—very narrow, lowest.

[Data from D. Weinreich et al., Science 312, 2006, 111–114.]