AUTHOR=Yang Chen , Chen Kaichao , Chan Edward Wai-Chi , Yao Wen , Chen Sheng 

TITLE=Transmission of Chromosomal MDR DNA Fragment Encoding Ciprofloxacin Resistance by a Conjugative Helper Plasmid in Salmonella

JOURNAL=Frontiers in Microbiology

VOLUME=11

YEAR=2020

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2020.556227

DOI=10.3389/fmicb.2020.556227

ISSN=1664-302X

ABSTRACT=<p>Resistance to ciprofloxacin, a treatment choice for <italic>Salmonella</italic> infections, has increased dramatically in recent years in particular in serotype <italic>Salmonella</italic> Derby with most of strains carrying chromosome-encoded multiple plasmid-mediated quinolone resistance (PMQR) genes. In this work, we discovered a conjugative plasmid, pSa64-96kb, in a <italic>Salmonella</italic> Derby isolate, namely Sa64, which could extract and fuse to a multiple drug resistance (MDR) DNA fragment containing two PMQR genes, <italic>aac(6’)-Ib-cr</italic>, and <italic>qnrS2</italic> located on the chromosome of the <italic>Salmonella</italic> strain. This process led to the formation of a new 188 kb fusion plasmid, which could be then subsequently transmitted to recipient strain Escherichia <italic>coli</italic> J53. The chromosomal MDR DNA fragment was shown to be flanked by one copy of IS<italic>26</italic> element at each end and could be excised from the chromosome to form circular intermediate, which was then fused to pSa64-96kb and form a single plasmid through IS<italic>26</italic> mediated homologous recombination. The role of IS<italic>26</italic> on enhancing the efficacy of fusion and transmission of this chromosomal MDR DNA fragment was further proven in other <italic>Salmonella</italic> strains. These findings showed that dynamic interaction between specific chromosomal fragment and plasmids may significantly enhance resistance development and transferability of mobile resistance-encoding elements among bacterial pathogens.</p>