Fig. 2

Identification of Post-antibiotic Effect associated Permeabilization (PAEP). Growth curves of Ps4 cultures not previously exposed (solid circles) or preexposed to peptide P4–9 at twice the peptide MIC for 1 h and then treated with a sub-MIC concentration of novobiocin. Time 0 corresponds to the beginning of growth monitoring immediately after peptide removal and cell resuspension in fresh MH medium. At times 0, 1 and 2 h after growth resumption, independent cultures pre-treated with the peptide were exposed to novobiocin at 1/8 x MIC and growth kinetics was monitored by viable counts (a) or by using the Bioscreen C system (b). Table in panel c shows the delay in hours (S-PAEP) caused by each treatment as indicated graphically by red arrows. As control, a P4–9 treated culture was left unexposed to novobiocin (open circles). PAEP was calculated as the average of two independent experiments performed in triplicate. Data were analysed by Kruskal–Wallis test followed by Mann–Whitney’s U test and statistical differences in growth kinetics between cultures exposed to novobiocin at different times (i.e. 0 h vs. 1 h; 0 h vs. 2 h; 1 h vs. 2 h) were significant (∗; P = 0.002). Error bars overlap with symbols in most of the plots. For a detailed explanation on PAEP and S-PAEP calculation, see the Methods section