Isolation, characterization, and proof of concept evaluation of serially adapted bacteriophages against multidrug-resistant Escherichia coli.

This study was conducted to test serially passaged bacteriophages for combating multidrug-resistant Escherichia coli strains and to address the urgent need for sustainable alternatives to antibiotics. Bacteriophages were isolated from diverse environmental sources against E. coli MTCC 1687. All bacteriophages were sequentially passaged for adaptation against three multidrug-resistant (MDR) strains, E. coli (R1, R2, and R4), with host efficiency expansion measured by efficiency of plating (EOP). Two phages (VR1 and VR4*) were selected based on their in vitro lytic, antibiofilm activity, and live-dead analysis. Both phages were characterized for adsorption kinetics, one-step growth parameters, pH tolerance, and thermal stability. A proof-of-concept in vivo study was conducted with a two-phage (VR1 and VR4*) cocktail. Phages were orally delivered in drinking water to one-week-old chickens 24 h after an intraperitoneal challenge with MDR E. coli R4. Bacteriophages exhibited significant lytic and antibiofilm activity in a dose-dependent manner. Short latent periods of 10 min (VR1) and 15 min (VR4*), stability > 50% at pH ≥ 4, when formulated in a stabilizing buffer, and thermal stability at room temperature were observed in the bacteriophages. In the proof-of-concept study of a controlled chicken infection model using a resistant E. coli strain, an orally administered two-phage cocktail (VR1 and VR4*) achieved 100% survival over a 7-day observation period. Lesion severity and histopathological outcomes were comparable to those of antibiotic treatment. This research established a proof-of-concept for host-adapted bacteriophages as adaptable and potent antimicrobial agents against field-isolated multidrug-resistant strains. The findings provide preliminary support for developing a phage platform to improve animal health, food safety, and, ultimately, human health.