Fig. 1: Collateral sensitivity measured with growth inhibition and killing efficacy may not overlap.

This schematic figure represents the growth inhibition-based standard broth dilution assay for defining the minimal inhibitory concentration (left part) of an antibiotic resistant (orange) and sensitive (grey) bacterial strain and their survival rate (right part). Bacterial survival is measured at a high, clinically relevant dose of the antibiotics after a predetermined amount of treatment time. In the presence of the green antibiotic, the effect on the resistant strain’s growth is not different compared to its sensitive counterpart (marked by the decrease of intensity in the orange and grey circles, respectively). However, the similar results in growth inhibition still leave two possibilities open: collateral sensitivity, when the resistant population (orange) is cleared orders of magnitude more efficiently than its sensitive counterpart (grey) or no interaction where both variants are equally affected.