Emergence of mosaic plasmids harboring Tn1546-ermB element in Staphylococcus aureus isolates

Antimicrobial resistance in Staphylococcus aureus is a major problem and the acquisition of resistance genes may occur by horizontal gene transfer (HGT). The transposon, an important means of HGT, is recognized as a mobile genetic element that can integrate in plasmids, replicate and transfer to other strains. We have previously reported a novel structure of the Enterococcus faecium -originated Tn 1546 - ermB element in S. aureus . The emergence of the Tn 1546 -like element is an emerging problem that requires continuous monitoring. In the present study, we expand the examination of Tn 1546 - ermB element to ermB -positive methicillin-susceptible S. aureus (MSSA) (n = 116) and ermB -positive methicillin-resistant S. aureus (MRSA) (n = 253) during a 16-year period, from 2000 to 2015. PCR mapping showed that 10 MSSA and 10 MRSA carried the Tn 1546 - ermB element. The 10 MSSA belonged to three sequence types (ST), ST7 (n = 6), ST5 (n = 3), and ST59 (n = 1), and the 10 MRSA belonged to two STs, ST188 (n = 8) and ST965 (n = 2). Since only clonal complex 5 (including ST5, ST85, ST231, and ST371) MRSA, ST8 MRSA and ST5 MSSA have been previously reported to carry Tn 1546 plasmids, this is the first report describing the presence of the Tn 1546 - ermB element in ST7/5/59 MSSA and ST188/965 MRSA. Plasmid sequencing revealed that the Tn 1546 - ermB element was harbored by five different mosaic plasmids. In addition to resistance genes, some plasmids also harbored toxin genes.