AUTHOR=Shao Li , Wu Changbu , Li Chengjuan , He Ruowen , Chen Guanping , Sun Dandan , Yang Yanxian , Feng Yu , Zhang Guili , Yan Bin , Dai Min , Tian Guo-Bao , Zhong Lan-Lan 

TITLE=Genomic characterization revealing the high rate of tet(X4)-positive Escherichia coli in animals associated with successful genetic elements

JOURNAL=Frontiers in Microbiology

VOLUME=15

YEAR=2024

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2024.1423352

DOI=10.3389/fmicb.2024.1423352

ISSN=1664-302X

ABSTRACT=<sec><title>Introduction</title><p>The rapid spread of plasmid-mediated <italic>tet(X4)</italic> conferring high tigecycline resistance poses a significant threat to public health. <italic>Escherichia coli</italic> as the most common pathogen which carries <italic>tet(X4)</italic> has been widely disseminated in China. Thus, comprehensive investigations are required to understand the mechanism of transmission of <italic>tet(X4)</italic>-positive <italic>E. coli</italic>.</p></sec><sec><title>Methods</title><p>In this study, a total of 775 nonduplicate samples were collected in Guangdong, China from 2019 to 2020. We screened for <italic>tet(X4)</italic>-positive <italic>E. coli</italic> by PCR amplification and species identification. Furthermore, we analyzed the phylogenetics and genetic context of <italic>tet(X4)</italic>-positive <italic>E. coli</italic> through whole-genome sequencing and long-reads sequencing.</p></sec><sec><title>Results</title><p>Overall, 146 (18.84%) <italic>tet(X4)</italic>-positive <italic>E. coli</italic> were isolated, comprising 2 isolates from humans and 144 isolates from pigs. The majority of <italic>tet(X4)</italic>-positive E. coli exhibited resistance to multiple antibiotics but all of them were susceptible to amikacin and colistin. Phylogenetic analysis showed that ST877, ST871, and ST195 emerged as the predominant sequence types in <italic>tet(X4)</italic>-positive <italic>E. coli</italic>. Further analysis revealed various genetic environments associated with the horizontal transfer of <italic>tet(X4)</italic>. Notably, a 100-kbp large fragment insertion was discovered downstream of <italic>tet(X4)</italic>, containing a replicon and a 40-kbp gene cluster for the bacterial type IV secretion system.</p></sec><sec><title>Discussion</title><p>The high colonization rate of <italic>tet(X4)</italic>-positive <italic>E. coli</italic> in animals suggests that colonization as a key factor in its dissemination to humans. Diverse genetic context may contribute to the transfer of <italic>tet(X4)</italic>. Our findings underline the urgent need for controlling the spread of plasmid-mediated tigecycline resistance.</p></sec>