AUTHOR=Wang Jing , Wang Zhen-Yu , Wang Yan , Sun Fan , Li Wei , Wu Han , Shen Peng-Cheng , Pan Zhi-Ming , Jiao Xinan 

TITLE=Emergence of 16S rRNA Methylase Gene rmtB in Salmonella Enterica Serovar London and Evolution of RmtB-Producing Plasmid Mediated by IS26

JOURNAL=Frontiers in Microbiology

VOLUME=11

YEAR=2021

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2020.604278

DOI=10.3389/fmicb.2020.604278

ISSN=1664-302X

ABSTRACT=<p>This study aimed to characterize 16S rRNA methylase genes among <italic>Salmonella</italic> and to elucidate the structure and evolution of <italic>rmtB</italic>-carrying plasmids. One hundred fifty-eight <italic>Salmonella</italic> isolates from one pig slaughterhouse were detected as containing 16S rRNA methylase genes; two (1.27%) <italic>Salmonella</italic> London isolates from slaughtered pigs were identified to carry <italic>rmtB</italic>. They were resistant to gentamicin, amikacin, streptomycin, ampicillin, tetracycline, florfenicol, ciprofloxacin, and sulfamethoxazole/trimethoprim. The complete sequences of RmtB-producing isolates were obtained by PacBio single-molecule real-time sequencing. The isolate HA1-SP5 harbored plasmids pYUHAP5-1 and pYUHAP5-2. pYUHAP5-1 belonged to the IncFIB<sub>K</sub> plasmid and showed high similarity to multiple IncFIB<sub>K</sub> plasmids from <italic>Salmonella</italic> London in China. The <italic>rmtB</italic>-carrying plasmid pYUHAP5-2 contained a typical IncN-type backbone; the variable region comprising several resistance genes and an IncX1 plasmid segment was inserted in the resolvase gene <italic>resP</italic> and bounded by IS<italic>26</italic>. The sole plasmid in HA3-IN1 designated as pYUHAP1 was a cointegrate of plasmids from pYUHAP5-1-like and pYUHAP5-2-like, possibly mediated by IS<italic>26</italic> via homologous recombination or conservative transposition. The structure differences between pYUHAP1 and its corresponding part of pYUHAP5-1 and pYUHAP5-2 may result from insertion, deletion, or recombination events mediated by mobile elements (IS<italic>26</italic>, IS<italic>CR1</italic>, and IS<italic>Kpn43</italic>). This is the first report of <italic>rmtB</italic> in <italic>Salmonella</italic> London. IncN plasmids are efficient vectors for <italic>rmtB</italic> distribution and are capable of evolving by reorganization and cointegration. Our results further highlight the important role of mobile elements, particularly IS<italic>26</italic>, in the dissemination of resistance genes and plasmid evolution.</p>