ERIC-PCR was applied using the ERIC-1 and ERIC-2 primers for colistin-resistant E. coli and K. pneumoniae isolates (Table 1).27 (link) The ERIC-PCR conditions were regulated based on the published report by Smith et al28 (link). Analyses of the DNA fingerprints were performed by using GelCompar II; version 6.5 (Applied Maths, NV, Keistraat, Belgium). A cutoff value of 80% similarity was applied to define the clusters. The similarity between the profiles was evaluated with the band matching Dice coefficient, and dendrograms for each species were produced by the unweighted pair group method with arithmetic averages (UPGMA). Based on the UPGMA dendrograms, identical strains were defined as isolates with >97% similarity, closely related isolates with ≥95% similarity and isolates with <95% similarity as unrelated strains.