(A) Population analysis profiles of three colistin-heteroresistant Klebsiella pneumoniae blood isolates and Escherichia coli ATCC 25922. LOQ, limit of quantification. The three isolates—S1703-35, S1703-109, and S1703-112—grew in the presence of colistin at concentrations of 4–10 mg/L. (B) The results of disk diffusion test or E-test. Resistant subpopulations (each two in three isolates) analyzed further are indicated; 35-RP, 109-RP, and 112-RP indicate the resistant subpopulations of S1703-35, S1703-109, and S1703-112, respectively. For S1703-35, no resistant colonies were detected in the E-test; thus, we selected resistant colonies in independent disk diffusion tests.