Fig. 1
Post-antibiotic effect induced by peptide P4–9 in P. aeruginosa Ps4. Growth curves of cultures not previously exposed (solid circles) or preexposed to P4–9 (open circles) at twice the peptide MIC for 1 h. Time 0 corresponds to the beginning of growth monitoring immediately after peptide removal and cell resuspensión in fresh MH medium. a, conventional viable count based technique: the 10-fold increments in cell number used to calculate PAE (red arrow) are indicated with green arrows; b, turbidimetry-based system (Bioscreen C): the red arrow indicates the value of PAE, which corresponds to the delay undergone by the treated culture with respect to the untreated control in reaching an OD value half of the final OD (i.e. 1.9/2 = 0.95; note that final OD value after 15 h of incubation is not shown). Error bars overlap with symbols in most of the time-points of panel b. For a detailed explanation on PAE calculation, see the Methods section. Assays were repeated three times independently and each experiment was performed in triplicate. Data were analysed by Mann–Whitney’s U test and statistical differences in growth kinetics between the treated and untreated cultures were significant (∗; P = 0.002, both for panel a and b)