Fig. 4

mcr-1 increases bacterial resistance to colicin antimicrobial peptides. A Growth competition between E. coli mcr-1⁺ and E. coli mcr-1^- in the presence of E. coli C600 strains producing colicin A, D, E1, or E2. After 16 h of coculture in LB medium, serial dilutions were spread on blood sheep agar plates, and E. coli mcr-1⁺ and E. coli mcr-1^- colonies were counted. Data are expressed as the number of colony-forming units (CFUs). Data are means ± SEMs of four replicates and are representative of three independent experiments. B E. coli mcr-1⁺ or E. coli mcr-1^- were spread on MH agar, and 10 μl bacterial pellets of colicin-producing E. coli were spotted. Representative pictures are presented. The white arrow indicates the growth inhibition zone