Phenotypic Characterization of Escherichia coli DP51 Reveals Strong Epithelial Adhesion and Chemical Stress Tolerance

Escherichia coli comprises a diverse group of bacteria that includes both harmless commensals and pathogenic strains capable of causing extraintestinal infections. Here, we report an integrated phenotypic characterization of E. coli strain DP51, a human-derived isolate previously identified through whole-genome sequencing as a presumptive extraintestinal pathogenic E. coli (ExPEC). Biofilm formation was evaluated using a microtiter plate assay, epithelial adhesion was assessed using Caco-2 human intestinal epithelial cells, and stress tolerance was analyzed using Biolog Phenotype MicroArray plates PM11–PM20, covering 240 antimicrobial compounds, metabolic inhibitors, and metal-containing stressors. DP51 formed weak biofilm compared with the hyper-biofilm-forming control strain E. coli O157:H7 43894OR yet adhered to Caco-2 cells at a level comparable to the reference strain E. coli O157:H7, indicating strong host–cell interaction capability. DP51 tolerated most chemical stressors, with tolerant well fractions of 64.6% to 84.4% across the ten panels; however, 2,2′-dipyridyl, sodium metavanadate, sodium orthovanadate, and polymyxin B produced sensitivity at every concentration tested. Principal component analysis indicated that the chemical stress response of DP51 was largely panel- and compound-specific rather than governed by a small number of shared defense mechanisms. These findings indicate that DP51 combines broad but mechanistically selective stress tolerance with strong epithelial adhesion, and identify candidate compounds for further investigation as intervention targets.