Effective treatment of multidrug-resistant Riemerella anatipestifer infection in ducks using a compound Chinese herbal medicine in drinking water.

Riemerella anatipestifer (R. anatipestifer), a pathogenic bacterium, causes systemic infection in poultry. Although antibiotics can alleviate R. anatipestifer infection, their irrational use has worsened antibiotic resistance, rendering existing drugs less effective against the growing number of multidrug-resistant strains. Treatment with compound Chinese herbal medicines (CCHMs), which show the ability to eliminate pathogens and reduce inflammation in the body, offers a promising alternative for the treatment of bacterial infections. Herein, we characterized a multidrug-resistant R. anatipestifer strain isolated from a duck farm in northern Henan Province. On the basis of the pathological characteristics of the infected ducks, a novel CCHM was developed, and its therapeutic efficacy against R. anatipestifer infection was evaluated alongside a preliminary assessment of the therapeutic mechanism. The results showed that the isolated R. anatipestifer belonged to serotype 1 and was multidrug-resistant. The median lethal dose (LD50) of the strain was approximately 1.89 × 109 CFU/mL. In vitro antibacterial assay revealed that the MIC and MBC of the CCHM against the pathogen were both 0.97 mg/mL. The CCHM killed the bacteria rapidly within hours by disrupting bacterial cell structure and integrity. In vivo therapeutic experiments demonstrated that CCHM treatment cleared the bacteria, ameliorated pathological damage, and increased the survival rate by 30 %. Integrated network pharmacology prediction and experimental validation further showed that CCHM treatment significantly downregulated the expression of the pro-inflammatory cytokines interleukin (IL)-1β, IL-8, IL-17A, IL-17F, IL-22, interferon (IFN)-γ, and signal transducer and activator of transcription 3 (STAT3; P < 0.05). These results confirm that CCHM treatment effectively reduced mortality from R. anatipestifer infection through multiple pathways in ducks, providing an important basis for the development of CCHM as an effective alternative for controlling multidrug-resistant R. anatipestifer infections.