A series of human and animal diseases that are caused by Salmonella infections pose a serious threat to human health and huge economic losses to the livestock industry. We found antibiotic resistance (AR) genes in the genome of 133 strains of S. Indiana from a poultry production site in Shandong Province, China. Salmonella enterica subsp. enterica serovar Indiana strain MHYL had multidrug-resistance (MDR) genes on its genome. Southern blot analysis was used to locate genes on the genomic DNA. High-throughput sequencing technology was used to determine the gene sequence of the MHYL genome. Areas containing MDR genes were mapped based on the results of gene annotation. The AR genes bla_TEM, strA, tetA, and aac(6′)-Ib-cr were found on the MHYL genome. The resistance genes were located in two separate MDR regions, RR1 and RR2, containing type I integrons, and Tn7 transposons and multiple IS26 complex transposons with transposable functions. Portions of the MDR regions were determined to be highly homologous to the structure of plasmid pAKU_1 in S. enterica serovar Paratyphi A (accession number: AM412236), SGI11 in S. enterica serovar Typhimurium (accession number: KM023773), and plasmid pS414 in S. Indiana (accession No.: KC237285).

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.