Allicin E enhances the antibacterial activity of enrofloxacin against Aeromonas hydrophila in Carassius auratus gibelio

Abstract

Aeromonas spp. are major pathogens severely affecting the Carassius auratus gibelio farming industry. The prolonged use of enrofloxacin (Enr) has led to reduced therapeutic efficacy, drug residues, and the emergence of antibiotic resistance. Simply increasing antibiotic dosage is unsustainable, and the core challenge lies in potentiating antibiotic efficacy without dose escalation. Here, we employed combination therapy using allicin E (ALE) as a potentiator of Enr and investigated its synergistic antibacterial activity, underlying mechanisms, and protective effects against A. hydrophila in C. auratus gibelio. In vitro, the combination of Enr and ALE exhibited broad-spectrum synergistic or additive activity against multiple aquatic pathogens, rapidly eradicating A. hydrophila without regrowth during the observation period. Mechanistically, the combination triggered a burst of bacterial reactive oxygen species (1.67-fold vs. control), leading to irreversible membrane damage and leakage of intracellular contents, and significantly inhibited biofilm formation and disrupted mature biofilms. In vivo, oral administration of the combination in C. auratus gibelio challenged with A. hydrophila significantly improved survival (66.6% vs. 26.6% in model), reduced bacterial loads in liver, spleen and kidney (by 70.9%, 81.3% and 72.9%, respectively, vs. model group), and mitigated oxidative damage by restored antioxidant enzymes (T-SOD, CAT) activity, decrease MDA, as well as attenuated inflammatory infiltration and hemorrhage in spleen and kidney tissues. This is the first report of ALE potentiating Enr against A. hydrophila via a synergistic ROS-mediated membrane damage, validated in C. auratus gibelio, with approximately 50% Enr reduction potential.