AUTHOR=Mei Li , Song Yang , Liu Dongxin , Li Yixiao , Liu Li , Yu Keyi , Jiang Mengnan , Wang Duochun , Wei Qiang 

TITLE=Characterization of a mobilizable megaplasmid carrying multiple resistance genes from a clinical isolate of Pseudomonas aeruginosa

JOURNAL=Frontiers in Microbiology

VOLUME=14

YEAR=2023

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2023.1293443

DOI=10.3389/fmicb.2023.1293443

ISSN=1664-302X

ABSTRACT=<sec><title>Introduction</title><p>The horizontal transfer of antibiotic resistance genes mediated by plasmids seriously hinders the effectiveness of modern medical treatment, and thus has attracted widespread attention. Additionally, the co-selection mechanism of antibiotic resistance genes (ARGs) and heavy metal resistance genes (MRGs) on mobile elements may further exacerbate the horizontal transfer of resistance genes.</p></sec><sec><title>Methods</title><p>In this study, a multidrug-resistant <italic>Pseudomonas aeruginosa</italic> strain, termed BJ86 (CHPC/NPRC1.4142), was isolated from a patient's sputum specimen. <italic>In vitro</italic> tests for antimicrobial susceptibility, conjugation, whole-genome sequencing, and bioinformatics analysis were used to explore the potential mechanisms of resistance and its spread.</p></sec><sec><title>Results and discussion</title><p>Sequencing analysis indicates that <italic>P. aeruginosa</italic> BJ86 carries an amazing 522.5 kb-length megaplasmid, pBJ86, which contained a 93.5 kb-length multiple resistance region (MRR); 18 kinds of genes were identified as ARGs in this region, including <italic>tmexCD-oprJ</italic>, <italic>bla</italic><sub>DIM−1</sub>, <italic>qnrVC6</italic> that mediate resistance to multiple antibiotics and the operons <italic>mer</italic> that mediates heavy metal mercury resistance. In addition, there is also an 80 kb variable region (VR) on the plasmid pBJ86, and the genes encoding relaxase and type IV coupling protein (T4CP) were determined in this region, both of which are related to the conjugation and transfer ability of the plasmid. Bioinformatics analysis shows that many functional genes have insertion sequences and transposases on their flanks, which may have accumulated in the plasmid pBJ86 after multiple acquisition events. Conjugated transfer and <italic>in vitro</italic> tests for antimicrobial susceptibility verified the mobility and plasmid pBJ86-mediated resistance. To our knowledge, we are the first to report a mobilizable megaplasmid that simultaneously carried <italic>tmexCD-oprJ</italic>, <italic>bla</italic><sub>DIM−1</sub>, <italic>qnrVC6</italic>, and the operons <italic>mer</italic> and can be transferred with frequencies of 6.24 × 10<sup>−7</sup> transconjugants per donor cell.</p></sec>