Fermented Navy Bean-Derived Agents Restore Antibiotic Susceptibility in Escherichia coli Persisting on Fresh Produce after Washing through Transcriptional Modulation of Genes Associated with an rpoS-Centered Regulatory Network.

Mechanical washing is an essential practice for reducing microbial contamination on fresh produce, yet the physiological adaptation of bacteria that persist after washing remains poorly understood. Here, we investigated the adaptive responses of lettuce-associated Escherichia coli ATCC25922 that remained attached after mechanical washing and evaluated the effects of fermented navy bean extract (FBE) and a PCC13-62-derived synthetic peptide (MFP-1). Saline washing detached only 25.1±3.9% of the attached bacterial population as the wash-removed population (WRP), while the majority of cells remained as a surface-retained population (SRP). Compared with the WRP, the SRP exhibited markedly higher survival following ampicillin treatment, accompanied by coordinated upregulation of stress-response genes (rpoS, dnaK, and dps), adhesion (csgD), and multidrug efflux (marA, acrA, acrB, and tolC) genes. In contrast, washing with FBE or MFP-1 at 200 μg/mL significantly increased recovery of the WRP to 80.8±5.4% without affecting bacterial viability, while suppressing expression of these stress-response, adhesion, and multidrug efflux genes in the ampicillin-resistant SRP (AMPR-SRP), restoring ampicillin susceptibility, and thereby reducing AMPR-SRP survival following ampicillin treatment to 2.4-2.8 log CFU/mL. These findings indicate that bacteria remaining attached after washing is associated with enhanced antibiotic resistance and concerted transcriptional activation of a proposed rpoS-centered regulatory network. FBE and MFP-1 effectively restored antibiotic susceptibility associated with transcriptional suppression of genes involved in this adaptive response, highlighting their potential as functional washing additives for improving the microbial safety of fresh produce.