Fig. 3
ampC copy number for different strains carrying an ampC amplification. The ampC copy number was determined with qPCR, using untreated wild-type E. coli as a reference. With exception of wild-type (which only acquired resistance to amoxicillin), all strains carried a previous resistance to enrofloxacin (ENROR), kanamycin (KANR), or tetracycline (TETR), resulting in a secondary resistance to amoxicillin The number displayed under the strain indicates the concentration amoxicillin used for resistance development. Bars indicate the average copy number from 25 colonies