Electrocatalytic Oxygen Reduction Activity of E. coli O157:H7 under H₂O₂ Stress for Biosensing Application

The electrocatalytic activity of environmental stressed bacteria is closely related to their cellular activity. In this study, the electrocatalytic activity toward oxygen reduction of E. coli O157:H7 under physical, chemical, and biological environmental stress was explored through cyclic voltammetry (CV). Interestingly, when E. coli O157:H7 was stimulated under 5 mM H₂O₂ stress for 30 min, a distinct reduction peak and a reduction current at the mA level could be observed, indicating that the electrocatalytic oxygen reduction ability of E. coli O157:H7 was significantly enhanced. Then, the electrocatalytic mechanism of the E. coli O157:H7 under H₂O₂ stress was systematically analyzed from the growth dynamics, microscopic morphology, oxidative stress response, and metabolomics, and the electron transfer mechanism of its respiratory chain was clarified. Furthermore, metabolic pathway enrichment analysis showed that tricarboxylic acid (TCA) cycle and respiratory chain promoted NADH and ATP synthesis. The L-fucose synthesis indicated that ubiquinone (UQ, the core electron carrier of biocatalytic reaction) pathway was upregulated, enhancing bacterial cell catalytic activity and electron transport efficiency. Moreover, an electrochemical sensor utilizing H₂O₂ stress was developed for E. coli O157:H7 detection. The sensor demonstrated exceptional performance, displaying a maximum variation of 9.34 times in the ECL signal under H₂O₂ stress and achieving a remarkably low detection limit of 10 CFU E. coli O157:H7 in 1 mL sample volume. This study provides a new solution for the sensitive screening of electrochemically active bacteria, with broad application prospects.