Objective In vitro anti-bacterial and in vivo anti-inflammatory effects of herbal combination of Schisandra chinensis and fructus mume on drug-resistant Clostridium welchii strains were analyzed.

Methods The drug-resistant Type A and Type D caprine strains of C. welchii previously isolated from 70 diarrheic dairy goats in Kunming area with their toxin types and antimicrobial resistance phenotypes determined were used to test the in vitro antibacterial activity as well as the in vivo anti-inflammatory effects of S. chinensis and fructus mume (Prunus mume (Sieb.) Sieb. et Zucc). Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of the herbal combination on Type A and Type D C. welchii were determined using the broth microdilution method, while K⁺ concentration and alkaline phosphatase (AKP) activity in bacterial culture supernatants measured using the bacterial potassium ion colorimetric and bacterial alkaline phosphatase assay kits and effects of the treatment on bacterial structural integrity analyzed. RT q-PCR was used to assess the regulation of key biofilm-related genes and inflammatory cytokines in mouse blood with a mouse diarrhea model established for therapeutic efficacy evaluation of the treatment.

Results MIC and MBC of S. chinensis–fructus mume treatment were 1.95mg·mL⁻¹ and 3.91mg·mL⁻¹, respectively, on Type A strain, and 0.98mg·mL⁻¹ and 1.95mg·mL⁻¹, respectively, on Type D strain. The herbal combination concentration-dependently increased K⁺ content and AKP activity in the bacterial culture supernatants and caused disruptions on the bacterial cell membranes and cell walls. It also significantly downregulated the transcriptional expressions of key biofilm-related genes in both strains. In animal experiments, the herbs alleviated diarrhea, intestinal congestion and mucosal pathological injury, and transcription of pro-inflammatory cytokines in mice. The inhibitory effect on TNF-α upregulation induced by Type A strain was more pronounced, whereas Type D strain exerted stronger regulation effect on the excessive IL-1β expression.

Conclusion S. chinensis–fructus mume combination displayed significant in vitro antibacterial activity against Type A and Type D C. welchii. In vivo, it disrupted the bacterial membrane, downregulated the biofilm-related gene expressions, suppressed the inflammatory cytokines, and mitigated diarrhea and intestinal injury in mice. There appeared to be promising potential for the herbal combination be applied as a natural agent to treat the drug-resistant C. welchii infections on goats.