Distribution and spread of tigecycline resistance gene tet(X4) in Escherichia coli from different sources

Background Visualisation of genome comparisons is invaluable for helping to determine genotypic differences between closely related prokaryotes. New visualisation and abstraction methods are required in order to improve the validation, interpretation and communication of genome sequence information; especially with the increasing amount of data arising from next-generation sequencing projects. Visualising a prokaryote genome as a circular image has become a powerful means of displaying informative comparisons of one genome to a number of others. Several programs, imaging libraries and internet resources already exist for this purpose, however, most are either limited in the number of comparisons they can show, are unable to adequately utilise draft genome sequence data, or require a knowledge of command-line scripting for implementation. Currently, there is no freely available desktop application that enables users to rapidly visualise comparisons between hundreds of draft or complete genomes in a single image. Results BLAST Ring Image Generator (BRIG) can generate images that show multiple prokaryote genome comparisons, without an arbitrary limit on the number of genomes compared. The output image shows similarity between a central reference sequence and other sequences as a set of concentric rings, where BLAST matches are coloured on a sliding scale indicating a defined percentage identity. Images can also include draft genome assembly information to show read coverage, assembly breakpoints and collapsed repeats. In addition, BRIG supports the mapping of unassembled sequencing reads against one or more central reference sequences. Many types of custom data and annotations can be shown using BRIG, making it a versatile approach for visualising a range of genomic comparison data. BRIG is readily accessible to any user, as it assumes no specialist computational knowledge and will perform all required file parsing and BLAST comparisons automatically. Conclusions There is a clear need for a user-friendly program that can produce genome comparisons for a large number of prokaryote genomes with an emphasis on rapidly utilising unfinished or unassembled genome data. Here we present BRIG, a cross-platform application that enables the interactive generation of comparative genomic images via a simple graphical-user interface. BRIG is freely available for all operating systems at http://sourceforge.net/projects/brig/.

Tigecycline is a last-resort antibiotic that is used to treat severe infections caused by extensively drug-resistant bacteria. tet(X) has been shown to encode a flavin-dependent monooxygenase that modifies tigecycline1,2. Here, we report two unique mobile tigecycline-resistance genes, tet(X3) and tet(X4), in numerous Enterobacteriaceae and Acinetobacter that were isolated from animals, meat for consumption and humans. Tet(X3) and Tet(X4) inactivate all tetracyclines, including tigecycline and the newly FDA-approved eravacycline and omadacycline. Both tet(X3) and tet(X4) increase (by 64-128-fold) the tigecycline minimal inhibitory concentration values for Escherichia coli, Klebsiella pneumoniae and Acinetobacter baumannii. In addition, both Tet(X3) (A. baumannii) and Tet(X4) (E. coli) significantly compromise tigecycline in in vivo infection models. Both tet(X3) and tet(X4) are adjacent to insertion sequence ISVsa3 on their respective conjugative plasmids and confer a mild fitness cost (relative fitness of >0.704). Database mining and retrospective screening analyses confirm that tet(X3) and tet(X4) are globally present in clinical bacteria-even in the same bacteria as blaNDM-1, resulting in resistance to both tigecycline and carbapenems. Our findings suggest that both the surveillance of tet(X) variants in clinical and animal sectors and the use of tetracyclines in food production require urgent global attention.

Tigecycline is one of the last-resort antibiotics to treat complicated infections caused by both multidrug-resistant (MDR) Gram-negative and Gram-positive bacteria1. 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.