DNA-induced resistance of biofilms requires both cultivation and challenge under cation-limiting conditions.

aBiofilms were cultivated and challenged in BM2 defined medium containing different Mg2+ concentrations with or without DNA, as indicated.
bThe minimum biofilm eradication concentration (MBEC) is defined as the lowest concentration of antibiotic required for complete killing of the surface-adhered biofilm. The MBEC values shown are the median values from four replicate experiments.
The minimum inhibitory concentration (MIC) is defined as the lowest concentration of antibiotic required to inhibit the growth of planktonic cells that were shed from the peg.
PxnB  =  polymyxin B; Coln  =  colistin.