Classification and molecular characteristics of tet(X)-carrying plasmids in Acinetobacter species

Abstract

The rapid dissemination of plasmid-mediated tet(X) genes in Acinetobacter species has compromised the clinical effectiveness of tigecycline, one of the last-resort antibiotics. However, the classification strategy and homology group of tet(X)-positive Acinetobacter spp. plasmids remain largely unknown. In this study, we classified them by genome-based replicon typing, followed by analyses of structural characteristics, transferability and in vivo effect. A total of 34 plasmids distributed in at least nine Acinetobacter species were collected, including three tet(X3)-positive plasmids and one tet(X6)-positive plasmid from our genome sequencing results. Among them, there were 28 plasmids carrying Rep_3 superfamily replicase genes and classified into six homology groups, consisting of GR31 (82.1%), GR26 (3.6%), GR41 (3.6%), GR59 (3.6%), and novel groups GR60 (3.6%) and GR61 (3.6%). Our tet(X3)-positive plasmids pYH16040-1, pYH16056-1, and pYH12068-1 belonged to the dominant GR31 group, whereas the tet(X6)-positive plasmid pYH12068-2 was unclassified. Structurally, all tet(X)-positive GR31 plasmids shared similar plasmid replication (repB), stability (parA and parB) and accessory modules [tet(X) and sul2], and 97.6% of plasmid-mediated tet(X) genes in Acinetobacter species were adjacent to ISCR2. Conjugation and susceptibility testing revealed pYH16040-1, pYH16056-1, and pYH12068-2, carrying plasmid transfer modules, were able to mediate the mobilization of multiple antibiotic resistance. Under the treatment of tigecycline, the mortality rate of Galleria mellonella infected by pYH16040-1-mediated tet(X3)-positive Acinetobacter spp. isolate significantly increased when compared with its plasmid-cured strain (p < 0.0001). The spread of such plasmids is of great clinical concern, more effects are needed and will facilitate the future analysis of tet(X)-positive Acinetobacter spp. plasmids.

Epidemiological investigation and drug resistance characteristics of Riemerella anatipestifer strains from large-scale duck farms in Shandong Province, China from March 2020 to March 2022

“…The current extensive use of tetracycline antibiotics has led to the widespread presence of tetracycline resistance genes in gram-negative bacteria, which poses a serious threat to human and animal health ( Zheng et al, 2022 ). The tet X resistance gene family is thought to degrade tetracyclines, and notably this resistance gene family degrades tigecycline, an antibiotic used in recent years to treat MDR bacterial infections in humans and animals ( Chen et al, 2022 ). Recently, Cui et al (2020) reported that tet X resistance genes can be transmitted through plasmids in air and water ( Cui et al, 2020 ), and R. anatipestifer can carry a plasmid pRCAD0416RA1 that mediates tet X resistance genes ( Zhu et al, 2022 ), this suggests that tetracycline resistance in R. anatipestifers may also be mediated by plasmids and this resistance can be transmitted not only among livestock and poultry, but also to humans through a variety of transmission routes, posing a threat to human health.…”

Microbial evolution through horizontal gene transfer by mobile genetic elements

“…GR1 to GR19 are classified based on polymerase chain reaction (PCR) typing for the gene encoding RIPs (Bertini et al., 2010 ). Additionally, GR20 to GR61 have been proposed according to the above typing scheme, with at least 80% nucleotide coverage and at least 75% nucleotide identity of RIP genes in the same group (Castro‐Jaimes et al., 2022 ; Chen et al., 2022 ; Li et al., 2022 ). Notably, the genetic content encompassing RIPs and their adjacent DNA sequences within plasmids of Acinetobacter are similar, implying that some of the plasmids are within the same incompatibility group (Salgado‐Camargo et al., 2020 ).…”

“…Total DNA is directly extracted from the target environment and used as a template for PCR, allowing the detection of the presence or absence of plasmids based on amplification. Several primer sequences enabling multiplex PCR have been used to detect plasmids that are particularly important in the spread of ARGs (Carattoli, 2009 ; Carattoli et al., 2005 , 2014 ; Carloni et al., 2017 ; Castro‐Jaimes et al., 2022 ; Chen et al., 2022 ; Clewell, 2007 ; Li et al., 2022 ; Lozano et al., 2012 ). PCR‐Southern blot and quantitative PCR analyses using primers or probes specific to plasmid sequences have been used to detect the abundance of specific plasmids and their temporal changes in various environmental samples (Blau et al., 2020 ).…”