Figure 1. Experimental evolution of resistance to ciprofloxacin (CIP) in liquid-grown and biofilm-grown bacteria.

To understand how bacterial lifestyle influences the evolution antimicrobial resistance, strains of the bacterium A.baumannii were experimentally evolved either in liquid culture (A) or as biolfims on plastic beads (B). Santos-Lopez et al. found that liquid-grown and biofilm-grown strains of A.baumannii evolved resistance to the antimicrobial CIP in different ways: liquid-grown bacteria evolved a single resistant lineage that dominated the population (C), whereas biofilm-grown bacteria evolved multiple resistant lineages that co-exist within the population (D). Other important characteristics of the two evolved strains (such as resistance to CIP) are discussed in the main text.