# Large-genome phage vB_Eco_ZCEC15 targets gastrointestinal MDR E. coli: evidence from in vitro and Caco-2 cell models

## TL;DR

This study explores a large-genome phage that effectively targets drug-resistant E. coli in lab and cell models, showing promise as a safe alternative to antibiotics.

## Contribution

The study introduces a novel phage with a large genome and demonstrates its efficacy and safety against MDR E. coli in gastrointestinal conditions.

## Key findings

- ΦZCEC15 has a large genome of 170,313 bp with 272 ORFs and shows stability under acidic conditions.
- The phage effectively reduces MDR E. coli without harming Caco-2 cells, even at low MOI.
- Untreated E. coli infections caused cytotoxic effects in Caco-2 cells, highlighting the phage's safety advantage.

## Abstract

Bacterial resistance to traditional antibiotics is spreading at an alarming rate, threatening public health and various industrial applications. Phage therapy has emerged as a promising alternative for combating multidrug-resistant (MDR) bacterial infections. However, most studies have focused on in vitro interactions, often overlooking phage dynamics within human cell environments.

In this study, we characterized MDR stool-derived Escherichia coli isolates and assessed their antibiotic resistance profiles. We then isolated, characterized and evaluated the efficacy of bacteriophage vB_Eco_ZCEC15 (ΦZCEC15) against selected strains under optimized culture conditions (pH 7.3) and acidic conditions mimicking the human gastrointestinal tract. To assess host safety, we tested the impact of ΦZCEC15 on Caco-2 colon carcinoma cells. Furthermore, we explored the effect of bacterial lysis by ΦZCEC15 on Caco-2 cell viability to optimize its therapeutic applications.

Whole-genome sequencing revealed a large ΦZCEC15 genome (170,313 bp) encoding 272 annotated ORFs, eight tRNAs, and multiple accessory genes. The phage exhibited remarkable stability under diverse physical stressors, including pH 3. Notably, ΦZCEC15 achieved optimal antibacterial activity at a low multiplicity of infection (MOI 0.1), efficiently reducing bacterial titers without compromising eukaryotic host cell viability. In contrast, untreated bacterial infections induced cytotoxic effects in Caco-2 cells.

These findings highlight the potential of ΦZCEC15 as a safe and effective therapeutic agent against MDR E. coli and encourage the importance of addressing resistance mechanisms to optimize clinical outcomes.

The online version contains supplementary material available at 10.1186/s12866-026-04737-x.