Fig 9. Cell viability and persister formation after AMP priming.

The number of persister cells was determined after treating with priming doses of melittin and pexiganan. After priming for 30 minutes, the treatment was removed by centrifuging and washing cells twice with 2 ml of fresh MHB. Ciprofloxacin was added to a final concentration of 2 μg/ml and survival was determined by plating in MHB agar after 4 hours’ incubation (panel A). Before the addition of ciprofloxacin, the intracellular ATP concentration was also measured (panel B). The pre-treatment with melittin or pexiganan did not change the MIC of E. coli to melittin, pexiganan or ciprofloxacin (S1 Table).