Genomic Characterization of Multidrug-Resistant Escherichia coli from Bovine Mastitis and Therapeutic Evaluation of Thanatin Combined with Gallium Nitrate

Bovine mastitis caused by multidrug-resistant (MDR) Escherichia coli remains a major challenge in the dairy industry due to recurrent infection, excessive lipopolysaccharide (LPS) release, and persistent mammary inflammation. Whole-genome sequencing (WGS) revealed that the clinical isolate was resistant to seven classes of antibiotics and exhibited a marked enrichment of iron uptake systems, which accounted for 27.14% of the 140 virulence genes identified. Upon this, we developed a targeted combination therapy using the iron mimetic gallium nitrate and the antimicrobial peptide thanatin (Tn). A rat model of mastitis was established to evaluate the in vivo therapeutic efficacy of the Tn-gallium nitrate combination. Our results demonstrated that the combination of gallium nitrate and Tn exerted a potent enhanced therapeutic effect in the rat mastitis model. This regimen significantly inhibited bacterial proliferation, neutralized endotoxin activity, and downregulated the expression of pro-inflammatory cytokines. Histopathological evaluation confirmed that the combination therapy effectively protected the alveolar structure and alleviated tissue damage, with a protective effect superior to that of ceftiofur (CEF), the first-line clinical drug. Collectively, our findings demonstrate the therapeutic potential of the combination of thanatin and gallium nitrate in a rat model of mastitis and provide experimental evidence supporting the development of a novel non-antibiotic therapeutic strategy for bovine mastitis caused by multidrug-resistant E. coli.