Fig. 3.

Selection for resistance. (A and B) A culture of P. aeruginosa in log phase growth in TSB media was treated with serial dilutions of four conventional antibiotics (A) and four antimicrobial peptides (B). The bacteria that grew in the highest concentration of antibiotic were cultured overnight in the absence of antibiotic and then treated similarly the next day. This was continued for 10 passages to select for stable resistance mutants. MICs for each passage are shown in A and B. The highest concentrations tested were 350 μM for conventional antibiotics and 67.5 μM for AMPs. (C and D) Cross-resistance was measured by testing the zeroth passage (unselected) and the 10th passages of P. aeruginosa selected in the presence of either ceftazidime (C) or D-CONGA (D) against the whole panel of four conventional and four peptide antibiotics.