Abstract
This study aimed to characterize 16S rRNA methylase genes among Salmonella and to elucidate the structure and evolution of rmtB-carrying plasmids. One hundred fifty-eight Salmonella isolates from one pig slaughterhouse were detected as containing 16S rRNA methylase genes; two (1.27%) Salmonella London isolates from slaughtered pigs were identified to carry rmtB. 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 IncFIBK plasmid and showed high similarity to multiple IncFIBK plasmids from Salmonella London in China. The rmtB-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 resP and bounded by IS26. 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 IS26 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 (IS26, ISCR1, and ISKpn43). This is the first report of rmtB in Salmonella London. IncN plasmids are efficient vectors for rmtB distribution and are capable of evolving by reorganization and cointegration. Our results further highlight the important role of mobile elements, particularly IS26, in the dissemination of resistance genes and plasmid evolution.
Highlights
Aminoglycosides such as gentamicin and amikacin have been widely used to treat infections caused by Gram-negative bacteria in clinical settings, and they used for growth promotion in animal husbandry
We aimed to investigate the prevalence of 16S rRNA methylase genes among Salmonella isolates from one pig slaughterhouse in Jiangsu province, China, and to elucidate the structure and evolution of rmtB-carrying plasmids
2011; Bonardi et al, 2016; Jurado-Tarifa et al, 2016; Trimoulinard et al, 2017; Chen et al, 2019b). This is the first report of 16S rRNA methylase genes in Salmonella London
Summary
Aminoglycosides such as gentamicin and amikacin have been widely used to treat infections caused by Gram-negative bacteria in clinical settings (human and animal), and they used for growth promotion in animal husbandry. 16S rRNA methylases are of great concern for conferring high-level resistance to all aminoglycosides used to treat systemic infections. Since the identification of armA in 2003, 10 16S rRNA methylase genes (armA, rmtA, rmtB, rmtC, rmtD, rmtE, rmtF, rmtG, rmtH, and npmA) have been identified and globally disseminated in Enterobacteriaceae (Galimand et al, 2003; Doi et al, 2016). 16S rRNA methylase genes, especially armA and rmtB, are widely disseminated in Escherichia coli isolates from various sources, low prevalence is observed in Salmonella (Folster et al, 2009; Doi et al, 2016; Fang et al, 2019). The dramatic increase of antibiotic resistance in Salmonella has been a global health concern
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