AUTHOR=Xiao Xia , Liu Ziyi , Chen Xiaojun , Peng Kai , Li Ruichao , Liu Yuan , Wang Zhiqiang 

TITLE=Persistence of plasmid and tet(X4) in an Escherichia coli isolate coharboring blaNDM-5 and mcr-1 after acquiring an IncFII tet(X4)-positive plasmid

JOURNAL=Frontiers in Microbiology

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2022.1010387

DOI=10.3389/fmicb.2022.1010387

ISSN=1664-302X

ABSTRACT=<p>The prevalence of plasmid-mediated tigecycline resistance gene <italic>tet</italic>(X4) is presenting an increasing trend. Once <italic>tet</italic>(X4)-bearing plasmids are captured by multidrug-resistant bacteria, such as <italic>bla</italic><sub>NDM</sub> and <italic>mcr</italic>-coharboring bacteria, it will promote bacteria to develop an ultra-broad resistance spectrum, limiting clinical treatment options. However, little is known about the destiny of such bacteria or how they will evolve in the future. Herein, we constructed a multidrug-resistant bacteria coharboring <italic>tet</italic>(X4), <italic>bla</italic><sub>NDM-5</sub>, and <italic>mcr-1</italic> by introducing a <italic>tet</italic>(X4)-bearing plasmid into a <italic>bla</italic><sub>NDM-5</sub> and <italic>mcr-1</italic> positive <italic>E. coli</italic> strain. Subsequently, the stability of <italic>tet</italic>(X4) and the plasmid was measured after being evolved under tigecycline or antibiotic-free circumstance. Interestingly, we observed both <italic>tet</italic>(X4)-bearing plasmids in tigecycline treated strains and non-tigecycline treated strains were stable, which might be jointly affected by the increased conjugation frequency and the structural alterations of the <italic>tet</italic>(X4)-positive plasmid. However, the stability of <italic>tet</italic>(X4) gene showed different scenarios in the two types of evolved strains. The <italic>tet</italic>(X4) gene in non-tigecycline treated strains was stable whereas the <italic>tet</italic>(X4) gene was discarded rapidly in tigecycline treated strains. Accordingly, we found the expression levels of <italic>tet</italic>(X4) gene in tigecycline-treated strains were several times higher than in non-tigecycline treated strains and ancestral strains, which might in turn impose a stronger burden on the host bacteria. SNPs analysis revealed that a myriad of mutations occurred in genes involving in conjugation transfer, and the missense mutation of <italic>marR</italic> gene in chromosome of tigecycline treated strains might account for the completely different stability of <italic>tet</italic>(X4)-bearing plasmid and <italic>tet</italic>(X4) gene. Collectively, these findings shed a light on the possibility of the emergence of multidrug resistant bacteria due to the transmission of <italic>tet</italic>(X4)-bearing plasmid, and highlighted that the antibiotic residues may be critical to the development of such bacteria.</p>