Structure-based virtual screening identifies dicoumarol as a potent InhA inhibitor against Nocardia seriolae infection in largemouth bass (Micropterus salmoides)

This is the authors' abstract. We don't add key points for this paper.

Nocardiosis, caused by Nocardia seriolae , represents a critical bottleneck in the intensive aquaculture of largemouth bass ( Micropterus salmoides ), complicated by the pathogen's unique mycolic acid barrier and emerging multidrug resistance. To overcome the inefficiencies of traditional random screening, this study adopted a structure-based drug discovery strategy targeting InhA, the enoyl-acyl carrier protein reductase of the type II fatty acid synthase (FAS-II) pathway. Using AlphaFold 3-based structural modeling and high-throughput virtual screening, we identified dicoumarol (DIC) as a lead candidate. Biophysical assays, including isothermal titration calorimetry and fluorescence quenching, demonstrated high-affinity binding of DIC to the hydrophobic substrate-binding pocket of N. seriolae InhA (nsInhA). In vitro , DIC showed potent bactericidal activity and reduced intracellular bacterial loads in EPC cells. In vivo , dietary administration of DIC significantly improved survival and ameliorated granulomatous pathology in infected fish. Transcriptional analysis further showed reduced expression of the pro-inflammatory cytokines il1b and il6 in treated fish, consistent with an attenuated inflammatory burden during infection. Together, these findings support nsInhA as a druggable target and identify DIC as a promising therapeutic lead for the control of fish nocardiosis.