Characterization of a fosA3 Carrying IncC-IncN Plasmid From a Multidrug-Resistant ST17 Salmonella Indiana Isolate.

Li-Juan Zhang,Xi-Xi Gu,Hong-Xia Jiang,Yue-Wei Lu,Liang-Xing Fang,Ling Yang,Jie Zhang

doi:10.3389/fmicb.2020.01582

Abstract

The aim of this study was to investigate the characteristics of a fosA3 carrying IncC–IncN plasmid from a multidrug-resistant Salmonella isolate HNK130. HNK130 was isolated from a chicken and identified as ST17 Salmonella enterica serovar Indiana and exhibited resistance to 13 antibiotics including the cephalosporins and fosfomycin. S1 nuclease pulsed-field gel electrophoresis and Southern blot assays revealed that HNK130 harbored only one ∼180-kb plasmid carrying fosA3 and blaCTX–M–14, which was not transferable via conjugation. We further examined 107 Escherichia coli electro-transformants and identified 3 different plasmid variants, pT-HNK130-1 (69), pT-HNK130-2 (15), and pT-HNK130-3 (23), in which pT-HNK130-1 seemed to be the same as the plasmid harbored in HNK130. We completely sequenced an example of each of these variants, and all three variants were IncC–IncN multi-incompatible plasmid and showed a mosaic structure. The fosA3 gene was present in all three and bounded by IS26 elements in the same orientation (IS26-322bp-fosA3-1758bp-IS26) that could form a minicircle containing fosA3. The blaCTX–M–14 gene was located within an IS15DI-ΔIS15DI-iroN-IS903B-blaCTX–M–14-ΔISEcp1-IS26 structure separated from the fosA3 gene in pT-HNK130-1, but was adjacent to fosA3 in pT-HNK130-3 in an inverted orientation. Linear comparison of the three variants showed that pT-HNK130-2 and pT-HNK130-3 resulted from the sequence deletion and inversion of pT-HNK130-1. Stability tests demonstrated that pT-HNK130-1 and pT-HNK130-3 could be stably maintained in the transformants without antibiotic selection but pT-HNK130-2 was unstable. This is the first description of an IncC–IncN hybrid plasmid from an ST17 S. Indiana strain and indicates that this plasmid may further facilitate dissemination of fosfomycin and cephalosporin resistance in Salmonella.

Highlights

Fosfomycin is a natural broad-spectrum antibiotic with activity against both Gram-positive and Gram-negative bacteria and has a unique mechanism of action and can synergize with other antibiotics including β-lactams, aminoglycosides, and fluoroquinolones (Raz, 2015; He et al, 2017)
S1PFGE and hybridization revealed only one plasmid (∼180 kb) in the strain HNK130 and fosA3 and blaCTX−M−14 were present on this plasmid (Figure 1)
Multiple attempts to transfer the fosA3-bearing plasmid from the donor bacteria to E. coli J53 by conjugation were not successful, the fosfomycin resistance trait could be successfully transferred into E. coli DH5α via electrotransformation

Summary

Introduction

Fosfomycin is a natural broad-spectrum antibiotic with activity against both Gram-positive and Gram-negative bacteria and has a unique mechanism of action and can synergize with other antibiotics including β-lactams, aminoglycosides, and fluoroquinolones (Raz, 2015; He et al, 2017). The use of fosfomycin is prohibited in animals in China, a plasmid-mediated fosfomycin resistance gene fosA3 is often observed in Escherichia coli isolates from pets and food animals (Hou et al, 2012, 2013; He et al, 2013, 2017). FosA3 has been found in association with blaCTX−M, rmtB, floR, blaNDM, and other antibiotic resistance genes (ARGs) on disseminated plasmids, and this has promoted further spread of fosA3 (Hou et al, 2012, 2013; He et al, 2013, 2017; Villa et al, 2015; Hadziabdic et al, 2018). There are only a few reports that have identified fosA3 in Salmonella isolates (Lin and Chen, 2015; Villa et al, 2015; Wang et al, 2017; Hadziabdic et al, 2018; Fang et al, 2019)

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