Abstract
To characterize the formation mechanism and characteristics of two cointegrate plasmids in Salmonella enterica serotype Enteritidis strain S13, plasmids from strain S13 and three corresponding transconjugants were subjected to whole genome sequencing and analyzed using bioinformatics tools. The traits of two fusion plasmids in transconjugants were characterized by stability and conjugation experiments. Sequence analysis indicated that strain S13 contained four plasmids, including mcr-1-bearing pS13-1, blaCTX–M–55-carrying pS13-2, tet(M)-bearing pS13-3, and floR-carrying pS13-4. IncN1-F33:A–:B– plasmid pS13-2, respectively, fused with IncFI:A–:B– plasmid pS13-3 and IncX1 plasmid pS13-4, which generated two cointegrate plasmids, designated pS13D and pS13F, which involved in two intermolecular replicative mechanisms mediated by IS26 and the novel transposon Tn6952 (ΔTnAS3-IS26-ΔISEcp1-ramA-ΔIS26-ΔTnAS1), respectively. This is the first report of the fusion of the IncN1-F33:A–:B– plasmid and IncFI:A–:B– plasmid mediated by IS26, and with IncX1 plasmid mediated by Tn6952. The formation and evolution of cointegrate plasmids could expand the resistance and host spectrum of fusion plasmids.
Highlights
Salmonella is an important zoonotic intestinal pathogen and a leading cause of microbial food poisoning (Scallan et al, 2011)
The genes tet(M), mcr-1, blaCTX−M−55, and floR, and the genetic environment of tet(M) in strain S13 were characterized by polymerase chain reaction (PCR) analysis with the use of the primers listed in Supplementary Table 1
The S. enterica stain S13 carrying blaCTX−M−55, tet(M), floR, and mcr-1 genes was resistant to amoxicillin, ceftiofur, cefquinome, tetracycline, oxytetracycline, florfenicol, colistin, and sulfamethoxazole-trimethoprim (Supplementary Table 2)
Summary
Salmonella is an important zoonotic intestinal pathogen and a leading cause of microbial food poisoning (Scallan et al, 2011). The acquisition of genetic material, such as integron gene cassettes, transposons, and resistance plasmids, is the main reason for the rapid development of multidrug resistance (MDR) in Salmonella (Hsu et al, 2006; Wright, 2007; Hu and Li, 2009). Conjugative plasmids can capture MDR non-conjugative plasmids through replicative transposition of insertion sequences, such as IS1, IS26, and ISkpn, thereby expanding the host range of the plasmids (Ohtsubo et al, 1981; He et al, 2015; Chen et al, 2017; Xie et al, 2018; Li et al, 2020). The conjugative CTX-M-producing IncN1-F33:A–:B– plasmid was captured by two non-conjugative plasmids in Salmonella, resulting in the rapid transmission
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