Isobologram representation of MIC values of LysMK34 in combination with colistin in MH broth (A) or in 50% human serum (B) against A. baumannii MK34 (blue filled diamond; colistin MIC values of 2 μg/ml in both MH broth and serum), RUH134 (red open square; colistin MIC values of 2 and 4 μg/ml in MH broth and serum, respectively), Greek46 (black cross; colistin MIC values of 8 and 32 μg/ml in MH broth and serum, respectively), and Greek47 (green filled circle; colistin MIC value of 32 and 64 μg/ml in MH broth and serum, respectively) and P. aeruginosa Br667 (yellow cross; colistin MIC values of 2 and 4 μg/ml in MH broth and serum, respectively) and PA14 (purple filled triangle; colistin MIC values of 1 and 2 μg/ml in MH broth and serum, respectively). In panel B, the curves of RUH134 and Br667 completely overlap. The plots represent inhibitory combinations of LysMK34 (expressed in μg/ml) and colistin (expressed in reduced MIC fold, with 1× MIC corresponding to the above-mentioned values). Values represent the means of three independent replicates.