Lytic activity of novel bacteriophages recovered from pig farm sewage against multidrug-resistant Escherichia coli

Abstract

Antimicrobial resistance (AMR) presents a critical challenge to both human and animal health, with multidrug-resistant (MDR) Escherichia coli (E. coli) posing serious risks in livestock systems, particularly in pig farming. This study aimed to isolate and characterize bacteriophages (phages) from pig farm sewage and evaluate their lytic efficacy against MDR E. coli recovered from diarrheal pig feces. Forty E. coli isolates (n = 40) from pigs at different production stages exhibited high resistance to amoxicillin (100%) and oxytetracycline (95%), while maintaining susceptibility to enrofloxacin (98%) and gentamicin (85%). Thirteen phages (ECVL1–ECVL13) were isolated from pig farm sewage samples, among which ECVL1, ECVL2, and ECVL6 showed strong lytic activity, lysing over 90% of the tested isolates. A phage cocktail composed of these three phages was tested against representative E. coli isolates at various multiplicity of infections (MOIs). At MOI 105, bacterial reductions of up to 71% were observed within 6 h, particularly for isolate VL19, indicating a dose-dependent and time-sensitive response. The findings support the feasibility of using highly lytic phage cocktails to reduce MDR E. coli in pig production environments. These results highlight phage therapy as a viable biocontrol strategy for AMR mitigation, especially in agricultural systems burdened by high antibiotic use.