A transferable IncC-IncX3 hybrid plasmid co-carrying blaNDM-4, tet(X4), and tmexCD3-toprJ3 confers resistance to carbapenem and tigecycline

Tigecycline is a last-resort antimicrobial that exhibits promising activity against carbapenemase-producing Enterobacterales (CPE). However, mobile tigecycline resistance genes, tet(X) and tmexCD-toprJ, have emerged in China and have spread possibly worldwide. Tet(X) family proteins, Tet(X3) to Tet(X14), function as tigecycline-inactivating enzymes, and TMexCD-TOprJ complexes function as efflux pumps for tigecycline. Here, we report a CPE isolate co-harboring both emerging tigecycline resistance factors for the first time. A carbapenem- and tigecycline-resistant Klebsiella aerogenes NUITM-VK5 was isolated from an urban drainage in Vietnam in 2021 and a plasmid pNUITM-VK5_mdr co-carrying tet(X4) and tmexCD3-toprJ3 along with the carbapenemase gene blaNDM-4 was identified in NUITM-VK5. pNUITM-VK5_mdr was transferred to Escherichia coli by conjugation and simultaneously conferred high-level resistance against multiple antimicrobials, including carbapenems and tigecycline. An efflux pump inhibitor canceled TMexCD3-TOprJ3-mediated tigecycline resistance, suggesting that both tigecycline resistance factors independently and additively contribute to the high-level resistance. The plasmid had the IncX3 and IncC replicons and was estimated to be a hybrid of plasmids with different origins. Unlike IncX3 plasmids, IncC plasmids are stably maintained in an extremely broad range of bacterial hosts in humans, animals, and environment. Thus, future global spread of multidrug-resistance plasmids such as pNUITM-VK5_mdr poses a public health crisis.