The 2010 Garrod Lecture: the dimensions of evolution in antibiotic resistance: ex unibus plurum et ex pluribus unum.

Antibiotic resistance is not only the result of antibiotic-driven selection, as has been frequently considered, but rather the consequence of extremely complex evolutionary processes. These processes act on bacterial populations, but also on populations of subcellular (as plasmids) or supracellular (species, communities) units of evolution. The consideration of the effects of drift and selection provides a first intuition about the dimensions shaping the evolutionary field. We distinguish two alternative, orthogonal dimensions, respectively pushing evolutionary units towards diversification (ex unibus plurum) or towards unification (ex pluribus unum). Evolution in each one of these dimensions requires alternative evolutionary functional configurations in the evolving unit. These configurations are reached under the influence of evolutionary attractors for diversification or unification, presumably with an oscillatory dynamics. This view illustrates the complexity of possible outcomes in the emergence and evolution of antibiotic-resistant units, and indicates both the absolute need for multilevel epidemiological surveillance of antibiotic resistance, and the necessity of applying new evolutionary synthesis approaches to understand and predict human-driven changes in the microbial world.