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Abstract. The objective of this study is to characterize the relationship between the persistent profile and the ability to produce iron-binding compounds of intestinal isolates of E. coli and K. pneumoniae with the genetic determinants iucBC and clbBN, both at the phenotypic and genetic levels. The use of designed primers and a developed unified multiplex-PCR algorithm permitted the establishment of a wide frequency of occurrence (44.0–80.0%) among opportunistic strains of E. coli and K. pneumoniae cultures with genetic determinants clbBN and iucBC, which encode the synthesis of aerobactin and colibactin. The presence of the clbBN/iucBC genes in the genetic apparatus of enterobacteria was found to result in a pronounced ability to produce iron-binding compounds and a wide range of persistent characteristics (antilysozyme, anticarnosine, antipeptide activity with respect to TNFα, antiimmunoglobulin activity with respect to IgM/IgG and biofilm formation). A comparison of the genomes of sequenced clbBN⁺iucBC⁺ strains with those of clbBN^-iucBC^- strains revealed the presence of genes essential for the biosynthesis and transport of aerobactin, a comprehensive list of pks island genes, and the existence of known homologues of the lysozyme inhibitor determinants Ivy and MliC, EspP (E. coli M-17) and PliC, LprI (K. pneumoniae ICIS-278_PBV and K. pneumoniae ICIS-277_SVA) were identified. Therefore, strains of E. coli and K. pneumoniae that possess the genetic determinants of iron chelators, namely clbBN and iucBC, exhibit both genotypic and phenotypic indications of siderophore production and protease activity against host antimicrobial factors. This allows for the use of these strains as markers of the pathogenic and persistent potential of opportunistic enterobacteria.