Fig. 3

Exploitation of PAEP by sub-MIC concentrations of antibiotics of different classes. Experiments were performed with Ps4 exactly as indicated in Fig. 2b using fosfomycin (a), erythromycin (b), or ceftazidime (c) instead of novobiocin. Fosfomycin, erythromycin and ceftazidime were added at 1/8, 1/8 and 1/4 x MIC, respectively. As control, a P4–9 treated culture was left unexposed to the corresponding antibiotic (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 revealed that S-PAEPs induced by fosfomycin and erythromycin were lower than that caused by an equivalent dose of novobiocin (p < 0.05; *). For the sake of clarity, error bars are not shown in the figure, although they barely surpass symbol length in most of the cases. For a detailed explanation on PAEP and S-PAEP calculation, see the Methods section