Emergence of 16S rRNA Methylase Gene in London and Evolution of RmtB-Producing Plasmid Mediated by IS.

This study aimed to characterize 16S rRNA methylase genes among and to elucidate the structure and evolution of -carrying plasmids. One hundred fifty-eight isolates from one pig slaughterhouse were detected as containing 16S rRNA methylase genes; two (1.27%) London isolates from slaughtered pigs were identified to carry . 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 plasmid and showed high similarity to multiple IncFIB plasmids from London in China. The -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 and bounded by IS. 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 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, IS, and IS). This is the first report of in London. IncN plasmids are efficient vectors for distribution and are capable of evolving by reorganization and cointegration. Our results further highlight the important role of mobile elements, particularly IS, in the dissemination of resistance genes and plasmid evolution.