Characterization of Three Porcine Acinetobacter towneri Strains Co-Harboring tet(X3) and blaOXA-58

Abstract

Tigecycline is the antibiotic of last resort for the treatment of extensively drug-resistant bacterial infections, mainly those of multidrug-resistant Gram-negative bacteria. The plasmid-mediated tet(X3) gene has recently been described in various pathogens that are resistant to tigecycline. We report three tigecycline-resistant Acinetobacter towneri strains isolated from porcine faeces in China, which all contained the tet(X3)-harboring plasmids. A broth microdilution method was used to examine the antimicrobial susceptibility of the isolates, and S1-Nuclease digestion pulsed-field gel electrophoresis (S1-PFGE) was used to characterize their plasmid profiles. The whole-genome sequences of the isolates were determined with the Nanopore PromethION platform. The sequence analysis indicated that the strains were A. towneri. They showed resistance to multiple antibiotics, and all the resistance genes were located on plasmids. The three tet(X3)-harboring plasmids had a similar backbone structure, and all contained blaOXA-58 with various insertion elements (IS). ISCR2 is considered an important factor in tet(X3) mobilization. In addition to ISCR2, we demonstrate that IS26 generates a circular intermediate containing the tet(X3) gene, which could increase the dissemination risk. To our knowledge, this is the first report of tet(X3)- and blaOXA-58-harboring plasmids in A. towneri. Because the IS26 is frequently found in front of tet(X3), research should be directed toward the action of IS26 in the spread of tet(X3).

Occurrence and Molecular Characterization of Abundant tet(X) Variants Among Diverse Bacterial Species of Chicken Origin in Jiangsu, China

“…Hence, the emergence of tet(X4)-positive common plasmids with high mobility might cause an increasing prevalence of tet(X4). In addition, we found that all tet(X)-positive plasmids in Acinetobacter in the chicken farm had no ability of horizontal transfer, which is consistent with the previous reports (Cui et al, 2020;Ma et al, 2020;Wang et al, 2020). Genetic structure analysis found that those tet(X) genes in plasmids harbored by Acinetobacter were adjacent to ISCR2, indicating that ISCR2-mediated mobilization of tet(X) also deserved concerns among bacteria of different genus.…”

“…What is noteworthy is that a carbapenemase gene bla OXA−58 was found in the tet(X6)-bearing plasmid. Although many plasmids co-harboring tet(X3) and bla OXA−58 have been reported in other species of Acinetobacter (Cui et al, 2020;Ma et al, 2020), tet(X6)-and bla OXA−58bearing plasmid was rarely reported (Zheng et al, 2020). As a clinically critical opportunistic pathogen, the emergence of carbapenem-and tigecycline-resistant A. baumannii poses a great threat to public health.…”

Mobile Tigecycline Resistance: An Emerging Health Catastrophe Requiring Urgent One Health Global Intervention

“…Ecological niches in which plasmid-encoded TIG resistance tet (X) genes have been detected are shown in Table 1 . Clearly, there is increasing evidence of plasmid-encoded TIG resistance tet (X) genes reported in countries across Europe, Asia, United States, South America, and Africa involving humans, food animals, including chickens, pigs, ducks, pigeons, geese, and cattle, as well as companion animals, food animal products (meats), aquaculture and environment such as soil, livestock-farm water, wastewaters, sewages, and wildlife as reservoirs of MTR ( Bai et al, 2019 ; Chen et al, 2019a , b , 2020 , 2021 ; He et al, 2019 ; Sun C. et al, 2019 , 2020 ; Sun J. et al, 2019 ; Cao et al, 2020 ; Cui et al, 2020 , 2021b ; Ding et al, 2020 ; Du et al, 2020 ; He T. et al, 2020 ; Li et al, 2020 , 2021f ; Ma et al, 2020 ; Pan et al, 2020 ; Ruan et al, 2020 ; Song et al, 2020 ; Wang et al, 2020a , b ; Zhang et al, 2020b , 2021 ; Zheng et al, 2020 ; Cheng et al, 2021a , b ; Feng et al, 2021 ; Hirabayashi et al, 2021a , b ; Hsieh et al, 2021 ; Li et al, 2021e , f ; Lu et al, 2021 ; Marathe et al, 2021 ; Martelli et al, 2021 ; Mohsin et al, 2021 ; Soliman et al, 2021 ; Sun et al, 2021a , b ; Tang et al, 2021 ; Wang et al, 2021f , g ; Xu et al, 2021 ; Yu Y. et al, 2021 ; Wu et al, 2022 ; Zhai et al, 2022 ). We further demonstrate this, through the specific reservoirs in which plasmid-borne transmissible tet (X) and tmexCD-toprJ genes have been detected as shown in Table 2 .…”

Genome-based taxonomic reclassification of Acinetobacter species using type and reference strains

“…Acinetobacter towneri, belonging to the genus Acinetobacter whose members are gram-negative aerobic coccobacilli, is often isolated from water environments worldwide (1). This species has become increasingly important in recent years as a natural reservoir of antimicrobial resistance (AMR) genes (2)(3)(4)(5)(6). Acinetobacter baumannii, a cause of opportunistic infections in humans, has acquired resistance mechanisms to various antimicrobials, including clinically important carbapenems, making antimicrobial therapy di cult (7).…”

“…AMR genes, such as those for carbapenem-hydrolyzing enzymes (carbapenemases), have spread among environmental and clinical Acinetobacter species via mobile gene elements such as plasmids (2)(3)(4). Tigecycline is a last-resort antimicrobial with promising activity against carbapenemaseproducing gram-negative bacteria, including Acinetobacter species; however, mobile genes for tigecyclineinactivating enzymes, tet(X), have also emerged in A. towneri (5,6) and A. baumannii (8)(9)(10). Accumulation of such clinically relevant AMR genes in environmental bacteria such as A. towneri and their transmission to human pathogenic bacteria such as A. baumannii poses a global public health threat.…”