Whole-genome sequencing, virulence, and drug resistance of a bovine-derived strain of Salmonella enterica subsp. enterica serovar Dublin

Abstract:

[Background] The virulence and drug resistance of Salmonella spp. as a major zoonotic pathogen have attracted widespread attention. [Objective] To investigate the virulence and drug resistance of Salmonella enterica subsp. enterica serovar Dublin isolated from a dead calf in Tongliao City. [Methods] Bacterial isolation and 16S rRNA gene sequencing were performed with the lung of a dead calf, and the pathogen was identified as Salmonella. Animal tests, drug sensitivity tests, and PCR were employed to examine the virulence gene, drug resistance, virulence, and drug resistance genes of the isolate, and the whole genome was sequenced. [Results] The isolate had strong virulence, with the median lethal dose of 2.8×10⁶ CFU/mL to mice. It was multidrug-resistant, sensitive to only polymyxin B and cephalothin, and moderately sensitive to doxycycline and enrofloxacin. The detection rate of 13 virulence genes was 92.3%. The whole genome of the isolate had the length of 4 965 370 bp and the GC content of 52.12%, and it carried two plasmids with the lengths of 79 524 bp (pTLS-1) and 45 301 bp (pTLS-2), respectively. The isolate carried 996 virulence genes and 24 pathogenicity islands. A total of 42 drug-resistant genes were detected, among which 4 were horizontal transferable genes. In addition, there were 9 mobile genetic elements in the genome, including insertion sequences, transposons, etc. [Conclusion] The Salmonella Dublin strain isolated from a calf was virulent and multidrug-resistant, carrying a large number of virulence genes and drug-resistant genes.