AUTHOR=Yang Yanxian , He Ruowen , Wu Yiping , Qin Mingyang , Chen Jieyun , Feng Yu , Zhao Runping , Xu Lei , Guo Xilong , Tian Guo-Bao , Dai Min , Yan Bin , Qin Li-Na 

TITLE=Characterization of two multidrug-resistant Klebsiella pneumoniae harboring tigecycline-resistant gene tet(X4) in China

JOURNAL=Frontiers in Microbiology

VOLUME=14

YEAR=2023

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2023.1130708

DOI=10.3389/fmicb.2023.1130708

ISSN=1664-302X

ABSTRACT=<sec><title>Objectives</title><p>Tigecycline is recognized as one of the last-line antibiotics to treat serious bacterial infection caused by carbapenem-resistant <italic>Klebsiella pneumoniae</italic> (CRKP). The plasmid-borne gene <italic>tet</italic>(X4) mediates high resistance to tigecycline. However, the prevalence and genetic context of <italic>tet</italic>(X4) in <italic>K. pneumoniae</italic> from various sources are not fully understood. Here, we investigated the prevalence of <italic>tet</italic>(X4)-positive <italic>K. pneumoniae</italic> and characterized the genetic context of <italic>tet</italic>(X4)-bearing plasmids in <italic>K. pneumoniae</italic> isolates.</p></sec><sec><title>Methods</title><p>Polymerase chain reaction (PCR) was used to detect the <italic>tet</italic>(X4) gene. The transferability of the <italic>tet</italic>(X4)-carrying plasmids was tested by conjugation assays. The <italic>Galleria mellonella</italic> infection model was used to test virulence of <italic>tet</italic>(X4)-positive strains. Whole-genome sequencing and genome-wide analysis were performed to identify the antimicrobial resistance and the virulence genes, and to clarify the genetic characteristics of the <italic>tet</italic>(X4)-positive isolates.</p></sec><sec><title>Results</title><p>Among 921 samples, we identified two <italic>tet</italic>(X4)-positive <italic>K. pneumoniae</italic> strains collected from nasal swabs of two pigs (0.22%, 2/921). The two <italic>tet</italic>(X4)-positive isolates exhibited high minimum inhibitory concentrations to tigecycline (32–256 mg/L) and tetracycline (256 mg/L). The plasmids carrying the <italic>tet</italic>(X4) gene can transfer from the donor strain <italic>K. pneumoniae</italic> to the recipient strain <italic>Escherichia coli</italic> J53. Genetic analysis of the complete sequence of two <italic>tet</italic>(X4)-carrying plasmids pTKPN_3-186k-tetX4 and pTKPN_8-216k-tetX4 disclosed that the <italic>tet</italic>(X4) gene was flanked by delta IS<italic>CR2</italic> and IS<italic>1R</italic>, which may mediate the transmission of the <italic>tet</italic>(X4) gene.</p></sec><sec><title>Conclusion</title><p>The prevalence of <italic>tet</italic>(X4)-positive <italic>K. pneumoniae</italic> among different sources was low. IS<italic>CR2</italic> and IS<italic>1R</italic> may contribute to the horizontal transfer of <italic>tet</italic>(X4) gene. Effective measures should be taken to prevent the transmission of <italic>tet</italic>(X4)-producing <italic>K. pneumoniae</italic> in humans or animals.</p></sec>