Targeting STEC-Induced Edema Disease in Weaned Piglets: Prophylactic Oral Phage P-GXEC-L2P5 Mitigates Vascular Endothelial Injury

Edema disease (ED), a frequently fatal disease in weaned piglets, is caused by Shiga toxin-producing Escherichia coli (STEC). With the increasing emergence of antibiotic-resistant E. coli strains, bacteriophage therapy has been considered a promising alternative to prevent and control bacterial diseases in swine farms. Using a porcine infection model, the present study evaluated the prophylactic effect of bacteriophage P-GXEC-L2P5 administered by oral gavage against ED. A novel phage named P-GXEC-L2P5 was isolated using a multidrug-resistant (MDR) STEC named GXEC-STL2 as host strain. Phage P-GXEC-L2P5 was identified as a member of Dhillonvirus, Caudoviricetes with an 88,607 bp genome and possessed a short latent period (10 min), moderate pH stability (5–10), and appropriate thermal tolerance (4–60°C). Piglets pretreated with phage P-GXEC-L2P5 showed no apparent clinical signs such as eyelid edema or neurological symptoms after GXEC-STL2 challenge. B-scan ultrasonographic examination revealed no significant hydronephrosis. Necropsy findings indicated only mild intestinal congestion with no other gross pathological lesions observed. Histopathological examination demonstrated no significant differences compared to non-infected controls. Phage P-GXEC-L2P5 significantly reduced fecal shedding of STEC (P<0.05) in piglets, with a concurrent marked decrease (P<0.01) in Stx2e concentrations detected in serum, cerebral cortex, kidney, and small intestine. The cerebral cortex, kidney, and small intestine displayed significantly lower mRNA expression of Gb4 (Stx2e receptor) (P<0.05), while vascular endothelia exhibited a significant increase (P<0.05) in both FITC-WGA fluorescence intensity and mRNA expression of endothelial integrity-associated factors (connexin43, vinculin, zonula occludens-1). Furthermore, gut microbiota analysis found that phage treatment preserved the diversity and abundance of jejunal microbiota. In conclusion, phage P-GXEC-L2P5 effectively prevented STEC-induced ED by reducing STEC load and Stx2e levels, while mitigating vascular permeability.