Tigecycline is one of the last-resort antibiotics to treat complicated infections caused by both multidrug-resistant (MDR) Gram-negative and Gram-positive bacteria 1 . Tigecycline resistance has sporadically occurred in recent years, primarily due to chromosome-encoding mechanisms, such as overexpression of efflux pumps and ribosome protection 2 , 3 . Here we report the emergence of plasmid-mediated mobile tigecycline resistance mechanism Tet(X4) in Escherichia coli isolates from China, which is capable of degrading all tetracyclines, including tigecycline and the FDA newly approved eravacycline. The tet (X4)-harboring IncQ1 plasmid is highly transferable, and can be successfully mobilized and stabilized in recipient clinical and laboratory strains of Enterobacteriaceae bacteria. It is noteworthy that tet (X4)-positive E. coli strains, including isolates co-harboring mcr-1 , have been widely detected in pigs, chickens, soil, and dust samples in China. In vivo murine models demonstrated that the presence of Tet(X4) led to tigecycline treatment failure. Consequently, the emergence of plasmid-mediated Tet(X4) challenges the clinical efficacy of the entire family of tetracycline antibiotics. Importantly, our study raises concern that the plasmid-mediated tigecycline resistance may further spread into a variety of ecological niches and into clinical high-risk pathogens. Collective efforts are in urgent need to preserve the potency of these essential antibiotics.
Background The recent emergence and dissemination of high-level mobile tigecycline resistance Tet(X) challenge the clinical effectiveness of tigecycline, one of the last-resort therapeutic options for complicated infections caused by multidrug-resistant Gram-negative and Gram-positive pathogens. Although tet(X) has been found in various bacterial species, less is known about phylogeographic distribution and phenotypic variance of different genetic variants. Methods Herein, we conducted a multiregional whole-genome sequencing study of tet(X)-positive Acinetobacter isolates from human, animal, and their surrounding environmental sources in China. The molecular and enzymatic features of tet(X) variants were characterized by clonal expression, microbial degradation, reverse transcription, and gene transfer experiments, while the tet(X) genetic diversity and molecular evolution were explored by comparative genomic and Bayesian evolutionary analyses. Results We identified 193 tet(X)-positive isolates from 3846 samples, with the prevalence ranging from 2.3 to 25.3% in nine provinces in China. The tet(X) was broadly distributed in 12 Acinetobacter species, including six novel species firstly described here. Besides tet(X3) (n = 188) and tet(X4) (n = 5), two tet(X5) variants, tet(X5.2) (n = 36) and tet(X5.3) (n = 4), were also found together with tet(X3) or tet(X4) but without additive effects on tetracyclines. These tet(X)-positive Acinetobacter spp. isolates exhibited 100% resistance rates to tigecycline and tetracycline, as well as high minimum inhibitory concentrations to eravacycline (2–8 μg/mL) and omadacycline (8–16 μg/mL). Genetic analysis revealed that different tet(X) variants shared an analogous ISCR2-mediated transposon structure. The molecular evolutionary analysis indicated that Tet(X) variants likely shared the same common ancestor with the chromosomal monooxygenases that are found in environmental Flavobacteriaceae bacteria, but sequence divergence suggested separation ~ 9900 years ago (7887 BC), presumably associated with the mobilization of tet(X)-like genes through horizontal transfer. Conclusions Four tet(X) variants were identified in this study, and they were widely distributed in multiple Acinetobacter spp. strains from various ecological niches across China. Our research also highlighted the crucial role of ISCR2 in mobilizing tet(X)-like genes between different Acinetobacter species and explored the evolutionary history of Tet(X)-like monooxygenases. Further studies are needed to evaluate the clinical impact of these mobile tigecycline resistance genes.
Plasmid-mediated antimicrobial resistance has emerged as one of the principal global issues, posing significant threats to public health. Herein, we reported a mobile tigecycline resistance mechanism Tet(X4) on both plasmid and chromosome in Escherichia coli strains from migratory birds in China. Besides tigecycline, these tet (X4)-positive strains also exhibited elevated MICs to the FDA newly approved tetracycline antibiotics, eravacycline (4 µg/ml) and omadacycline (8 µg/ml). Worrisomely, the tet (X4)-carrying plasmids and chromosome also shared high homology with the plasmids from human. Taken together, Tet(X4) represents another emerging antimicrobial threat and collective efforts from different sectors are needed to control its further spread.
Objectives The emergence and spread of plasmid-encoded tet(X3/X4) genes that confer high-level tigecycline and eravacycline resistance in Escherichia coli and Acinetobacter spp. pose serious threats to human and animal health. We developed a rapid and robust assay to detect Tet(X3/X4) in Gram-negative bacteria based on eravacycline degradation by the presence of the Tet(X) enzyme in the test strain. Methods This tetracycline inactivation method (TIM) is based on the degradation of eravacycline by the Tet(X3/X4)-producing strain, which results in reduced eravacycline activity against an acid-producing thermophile Bacillus stearothermophilus indicator strain. For Tet(X)-negative strains, eravacycline retains its antimicrobial activity. Coupled with a pH-sensitive dye (bromocresol purple), the reduced colorimetric inhibition zone can be measured to determine the production of Tet(X3/X4). One hundred and eighteen isolates, including 30 tet(X4)-positive E. coli, 30 tet(X3)-positive Acinetobacter spp. and 58 tet(X)-negative E. coli and Acinetobacter spp., were examined to evaluate the performance of this TIM. Results The sensitivity and specificity for E. coli carrying tet(X4) was 96.7% and 100%, respectively, and for Acinetobacter spp. carrying tet(X3) both were 100%. The TIM assay can be completed within 6.5 h. Conclusions The TIM is a simple, rapid and cost-effective method for the detection of plasmid-mediated high-level tigecycline resistance in E. coli and Acinetobacter spp.
Aims The aim of this study was to determine the effects of unsaturated fatty acids on clinical plasmids. Methods and Results Two unsaturated fatty acids, linoleic acid (LA) and α‐linolenic acid (ALA) at final concentration 0, 0·03, 0·3 and 3 mmol l−1, respectively, were used to assess the effects on conjugative transfer of a mcr‐1‐harbouring plasmid pCSZ4 (IncX4) in conjugation experiment. The inhibitory mechanisms were analysed by molecular docking and the gene expression of virB11 was quantitated by qRT‐PCR. Target plasmid diversity was carried out by TrwD/VirB11 homology protein sequence prediction analysis. Our results showed that LA and ALA inhibit plasmid pCSZ4 transfer by binding to the amino acid residues (Phe124 and Thr125) of VirB11 with dose‐dependent effects. The expression levels of virB11 gene were also significantly inhibited by LA and ALA treatment. Protein homology analysis revealed a wide distribution of TrwD/VirB11‐like genes among over 37 classes of plasmids originated from both Gram‐negative and Gram‐positive bacteria. Conclusions This study demonstrates representing a diversity of plasmids that may be potentially inhibited by unsaturated fatty acids. Significance and Impact of the Study Our work reported here provides additional support for application of curbing the spread of multiple plasmids by unsaturated fatty acids.
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