Targeting STEC-induced edema disease in weaned piglets: prophylactic oral phage P-GXEC-L2P5 attenuates bacterial colonization, toxin production, and endothelial damage

Edema disease (ED), a fatal disease in weaned piglets, is caused by Shiga toxin-producing Escherichia coli (STEC). The increasing emergence of antibiotic-resistant E. coli strains has necessitated the exploration of alternatives such as bacteriophage therapy. Using a porcine model, this study evaluated the prophylactic effect of bacteriophage P-GXEC-L2P5 administered by oral gavage against ED. The novel phage P-GXEC-L2P5 was isolated using a multidrug-resistant (MDR) STEC strain GXEC-STL2 as the host. P-GXEC-L2P5 was identified as a member of Caudoviricetes, Dhillonvirus, with an 88,607 base pair (bp) genome, and it possessed a short latent period (10 min), moderate pH stability (5-10), and appropriate thermal tolerance (4-60 ℃). Piglets pretreated with P-GXEC-L2P5 showed no apparent clinical signs (e.g., eyelid edema or neurological symptoms) after challenge with GXEC-STL2. B-scan ultrasound revealed no significant hydronephrosis. Necropsy showed only mild intestinal congestion, with no other gross pathological lesions noted. Histopathology demonstrated no significant differences in features compared with noninfected controls. Phage treatment significantly reduced fecal STEC shedding (P < 0.05) and significantly decreased Stx2e concentrations in serum, cerebral cortex, kidney, and small intestine (P < 0.01). The messenger RNA (mRNA) expression of Gb4 (Stx2e receptor) was significantly lower in these tissues (P < 0.05). Concurrently, vascular endothelial cells exhibited increased FITC-labeled wheat germ agglutinin (FITC-WGA) fluorescence intensity and increased mRNA expression of endothelial integrity factors (connexin43, vinculin, and zonula occludens-1; P < 0.05). In addition, phage treatment preserved jejunal microbiota diversity and abundance. In conclusion, P-GXEC-L2P5 effectively prevented STEC-induced ED by reducing STEC load and Stx2e levels, while mitigating increased vascular permeability.