Preliminary view of the global distribution and spread of the tet(X) family of tigecycline resistance genes

Unraveling the evolution and global transmission of high level tigecycline resistance gene tet(X)

An increasing number of tet(X) variants conferring tigecycline resistance have been reported, posing a threat to clinical treatment of multi-drug resistance bacteria as tigecycline serves as the last-resort antibiotic. In this study, a total of 721 tet(X)-like sequences were retrieved from public database and clinical isolates. All currently known tet(X) variants including newly identified variants tet(X49) to tet(X57) in our study were integrated into a database. tet(X) variants were detected in 17 countries and phylogenetically classified into 3 types: Type A, Type B and Type C, among which Type-C variants exhibited higher level tigecycline resistance. Most of Type-C variants were plasmid-mediated (65.31 %, 352/539), mainly carried by IncX1 (16.19 %, 57/352) and IncFIA/IncFIB/IncX1 (15.63 %, 55/352) plasmids. Type-C variants have achieved global spread by a two-stage expansion within 15 years. Bayesian analysis revealed that Type-C variants originated from Riemerella anatipestifer-carried Type-A variants, followed by a transfer to Escherichia and Acinetobacter strains, leading to a sharp rise of Type-C variants. Type-A variants were primarily borne in Riemerella anatipestifer and Bacteroides spp. tet(X) emerged in animal source, and gradually spread to humans and the environment. tet(X3), tet(X4) and tet(X6) were found co-occurred with more than ten antimicrobial resistance genes including blaNDM, blaOXA, floR, sul2, tet(M) and tet(Q). Temporal changes of transfer networks of tet(X) variants, IS elements and plasmids revealed that IS elements especially ISVsa3 facilitated the expansion of tet(X). Our findings highlight the substantial transmission risk of Type-C tet(X) variants. Persistent surveillance of the global transmission and evolutionary trend of tet(X) is essential.

Sequence-structure-function characterization of the emerging tetracycline destructase family of antibiotic resistance enzymes

Tetracycline destructases (TDases) are flavin monooxygenases which can confer resistance to all generations of tetracycline antibiotics. The recent increase in the number and diversity of reported TDase sequences enables a deep investigation of the TDase sequence-structure-function landscape. Here, we evaluate the sequence determinants of TDase function through two complementary approaches: (1) constructing profile hidden Markov models to predict new TDases, and (2) using multiple sequence alignments to identify conserved positions important to protein function. Using the HMM-based approach we screened 50 high-scoring candidate sequences in Escherichia coli, leading to the discovery of 13 new TDases. The X-ray crystal structures of two new enzymes from Legionella species were determined, and the ability of anhydrotetracycline to inhibit their tetracycline-inactivating activity was confirmed. Using the MSA-based approach we identified 31 amino acid positions 100% conserved across all known TDase sequences. The roles of these positions were analyzed by alanine-scanning mutagenesis in two TDases, to study the impact on cell and in vitro activity, structure, and stability. These results expand the diversity of TDase sequences and provide valuable insights into the roles of important residues in TDases, and flavin monooxygenases more broadly.

Mobile genetic elements affect the dissemination of antibiotic resistance genes (ARGs) of clinical importance in the environment

The prevalence of antibiotic resistance genes (ARGs) in the environment is a quintessential One Health issue that threats both human and ecosystem health; however, the source and transmission of ARGs, especially clinically important ARGs (CLIARGs), in the environment have not yet been well studied. In the present study, shotgun metagenomic approaches were used to characterize the microbiome, resistome, and mobilome composition in human feces and six different environment sample types in South China. Overall, the resistome harbored 157 CLIARGs, with specific ARG hotspots (e.g., human feces, wastewater treatment plants, livestock manure and wastewater) excreting significantly higher abundance of CLIARGs compared with the natural environment. A redundancy analysis (RDA) was performed and revealed that the bacterial community compositions and mobile genetic elements (MGEs) explained 55.08% and 34.68% of the variations in ARG abundance, respectively, indicating that both bacterial community and MGEs are key contributors to the maintenance and dissemination of CLIARGs in the environment. The network analysis revealed non-random co-occurrence patterns between 200 bacterial genera and 147 CLIARGs, as well as between 135 MGEs and 123 CLIARGs. In addition to numerous co-shared CLIARGs among different sample types, the source tracking program based on the FEAST probabilistic model was used to estimate the relative contributions of the CLIARGs from potential sources to the natural environment. The source tracking analysis results delineated that mobilome, more than microbiome, contributed CLIARG transmission from those ARG hotspots into natural environment, and the MGEs in WWTPs seem to play the most significant role in the spread of CLIARGs to the natural environment (average contribution 32.9%-46.4%). Overall, this study demonstrated the distribution and dissemination of CLIARGs in the environment, and aimed to better inform strategies to control the spread of CLIARGs into the natural environment.

European Food Safety Authority (EFSA), European Centre for Disease Prevention and Control (ECDC). The European Union summary report on antimicrobial resistance in zoonotic and indicator bacteria from humans, animals and food in 2021-2022

This report by the European Food Safety Authority and the European Centre for Disease prevention and Control, provides an overview of the main findings of the 2021-2022 harmonised Antimicrobial Resistance (AMR) monitoring in Salmonella spp., Campylobacter jejuni and C. coli from humans and food-producing animals (broilers, laying hens and fattening turkeys, fattening pigs and cattle under one year of age) and relevant meat thereof. For animals and meat thereof, AMR data on indicator commensal Escherichia coli, presumptive extended-spectrum beta-lactamases (ESBL)-/AmpC beta-lactamases (AmpC)-/carbapenemase (CP)-producing E. coli, and the occurrence of methicillin-resistant Staphylococcus aureus (MRSA) are also analysed. Generally, resistance levels differed greatly between reporting countries and antimicrobials. Resistance to commonly used antimicrobials was frequently found in Salmonella and Campylobacter isolates from humans and animals. In humans, increasing trends in resistance to one of two critically antimicrobials (CIA) for treatment was observed in poultry-associated Salmonella serovars and Campylobacter, in at least half of the reporting countries. Combined resistance to CIA was however observed at low levels except in some Salmonella serovars and in C. coli from humans and animals in some countries. While CP-producing Salmonella isolates were not detected in animals in 2021-2022, nor in 2021 for human cases, in 2022 five human cases of CP-producing Salmonella were reported (four harbouring bla OXA-48 or bla OXA-48-like genes). The reporting of a number of CP-producing E. coli isolates (harbouring bla OXA-48, bla OXA-181, bla NDM-5 and bla VIM-1 genes) in fattening pigs, cattle under 1 year of age, poultry and meat thereof by a limited number of MSs (5) in 2021 and 2022, requires a thorough follow-up. The temporal trend analyses in both key outcome indicators (rate of complete susceptibility and prevalence of ESBL-/AmpC-producers in E. coli) showed an encouraging progress in reducing AMR in food-producing animals in several EU MSs over the last 7 years.

Emergence of plasmid-mediated high-level tigecycline resistance gene tet(X4) in Enterobacterales from retail aquatic products

The spread of antimicrobial-resistant microbes and genes in various foods poses a significant threat to public health. Of particular global concern is the plasmid-mediated tigecycline resistance gene tet(X4), which, while identified in various sources, has not hitherto been reported in aquatic products. This study aimed to investigate the occurrence and characterization of tigecycline-resistant strains from aquatic products. A total of 73 nonrepetitive seafood samples were purchased from 26 farmers' markets to detect tigecycline-resistant strains. Of these, nine Escherichia coli strains (comprising two ST58, one ST195, ST10, ST48, ST88, ST877, ST1244, ST14462) and one Citrobacter meridianamericanus, recovered from nine (12.33 %, 9/73) seafood samples (fish, n = 7; shrimp, clam and crab, n = 1 respectively), were positive for the tet(X4). Notably, phylogenetic analysis showed that E. coli ST195, a common ST carrying tet(X4), has a close phylogenetic relationship (23∼48 SNPs) with 32 tet(X4)-harboring E. coli ST195 isolates (isolated from pigs, animal foods, vegetable, and humans) deposited in NCBI database. Additionally, E. coli ST58 was closely (2 SNPs) related to one tet(X4)-positive E. coli strain from retail vegetables documented in the NCBI database. Whole genome sequencing and bioinformatic analysis revealed that tet(X4) genes were located on IncX1 (7 E. coli) or hybrid plasmid IncFIA(HI1)/IncHI1B(R27)/IncHI1A (2 E.coli and one C. meridianamericanus). These plasmids displayed high homology with those of plasmids from other sources deposited in GenBank database. These findings underscore the role of epidemic clones and plasmids in driving the dissemination of tet(X4) gene within Enterobacterales of aquatic products origin. To the best of our knowledge, this is the first report of tet(X4)-positive Enterobacterales from aquatic products. The pervasive propagation of tet(X4) gene facilitated by epidemic plasmids and clones across food animals, food products, humans, and the environment presents a serious threat to public health.

Persistence and potential risks of tetracyclines and their transformation products in two typical different animal manure composting treatments

Abundant residues of tetracyclines in animal manures and manure-derived organic fertilizers can pose a substantial risk to environments. However, our knowledge on the residual levels and potential risk of tetracyclines and their transformation products (TPs) in manure and manure-derived organic fertilizers produced by different composting treatments is still limited. Herein, the occurrence and distribution of four veterinary tetracyclines (tetracycline, oxytetracycline, chlortetracycline, and doxycycline) and ten of their TPs were investigated in paired samples of fresh manure and manure-derived organic fertilizers. Tetracyclines and TPs were frequently detected in manure and manure-derived organic fertilizer samples in ranging from 130 to 118,137 μg·kg-1 and 54.6 to 104,891 μg·kg-1, respectively. Notably, the TPs concentrations of tetracycline and chlortetracycline were comparable to those of the parent compounds, with 4-epimers being always dominant and retained antibacterial potency. Based on paired-sampling strategy, the removal efficiency of tetracyclines and TPs in thermophilic composting was higher than that in manure storage. Toxicological data in the soil environment and the data derived from equilibrium partitioning method, indicated that tetracyclines and some TPs like 4-epitetracycline, 4-epichlortetracycline and isochlortetracycline could pose median to high ecological risk to terrestrial organisms. Total concentrations of TPs in manure-derived organic fertilizers were significantly correlated with the absolute abundance of tet(X) family genes, which provide evidence to evaluate the effects of TPs on the levels of antibiotic resistance in the environment. Among them, the 4-epitetracycline could pose ecological risk and retain antibacterial potency. Our findings emphasize the importance of monitoring and controlling the prevalence of tetracyclines and their TPs in livestock-related environments.

European Food Safety Authority (EFSA), European Centre for Disease Prevention and Control (ECDC). The European Union Summary Report on Antimicrobial Resistance in zoonotic and indicator bacteria from humans, animals and food in 2020/2021

Antimicrobial resistance (AMR) data on zoonotic and indicator bacteria from humans, animals and food are collected annually by the EU Member States (MSs) and reporting countries, jointly analysed by EFSA and ECDC and presented in a yearly EU Summary Report. This report provides an overview of the main findings of the 2020-2021 harmonised AMR monitoring in Salmonella spp., Campylobacter jejuni and C. coli in humans and food-producing animals (broilers, laying hens and turkeys, fattening pigs and bovines under 1 year of age) and relevant meat thereof. For animals and meat thereof, indicator E. coli data on the occurrence of AMR and presumptive Extended spectrum β-lactamases (ESBL)-/AmpC β-lactamases (AmpC)-/carbapenemases (CP)-producers, as well as the occurrence of methicillin-resistant Staphylococcus aureus are also analysed. In 2021, MSs submitted for the first time AMR data on E. coli isolates from meat sampled at border control posts. Where available, monitoring data from humans, food-producing animals and meat thereof were combined and compared at the EU level, with emphasis on multidrug resistance, complete susceptibility and combined resistance patterns to selected and critically important antimicrobials, as well as Salmonella and E. coli isolates exhibiting ESBL-/AmpC-/carbapenemase phenotypes. Resistance was frequently found to commonly used antimicrobials in Salmonella spp. and Campylobacter isolates from humans and animals. Combined resistance to critically important antimicrobials was mainly observed at low levels except in some Salmonella serotypes and in C. coli in some countries. The reporting of a number of CP-producing E. coli isolates (harbouring bla OXA-48, bla OXA-181, and bla NDM-5 genes) in pigs, bovines and meat thereof by a limited number of MSs (4) in 2021, requests a thorough follow-up. The temporal trend analyses in both key outcome indicators (rate of complete susceptibility and prevalence of ESBL-/AmpC- producers) showed that encouraging progress have been registered in reducing AMR in food-producing animals in several EU MSs over the last years.

Metagenomic Insight into Microbiome and Antibiotic Resistance Genes of High Clinical Concern in Urban and Rural Hospital Wastewater of Northern India Origin: a Major Reservoir of Antimicrobial Resistance

India is one of the largest consumers and producers of antibiotics and a hot spot for the emergence and proliferation of antimicrobial resistance genes (ARGs). Indian hospital wastewater (HWW) accumulates ARGs from source hospitals and often merges with urban wastewater, with the potential for environmental and human contamination. Despite its putative clinical importance, there is a lack of high-resolution resistome profiling of Indian hospital wastewater, with most studies either relying on conventional PCR-biased techniques or being limited to one city. In this study, we comprehensively analyzed antibiotic resistomes of wastewater from six Indian hospitals distributed in rural and urban areas of northern India through shotgun metagenomics. Our study revealed the predominance of ARGs against aminoglycoside, macrolide, carbapenem, trimethoprim, and sulfonamide antibiotics in all the samples through both read-based analysis and assembly-based analysis. We detected the mobile colistin resistance gene mcr-5.1 for the first time in Indian hospital sewage. blaNDM-1 was present in 4 out of 6 samples and was carried by Pseudomonas aeruginosa in HWW-2, Klebsiella pneumoniae in HWW-4 and HWW-6, and Acinetobacter baumanii in HWW-5. Most ARGs were plasmid-mediated and hosted by Proteobacteria. We identified virulence factors and transposable elements flanking the ARGs, highlighting the role of horizontal gene transmission of ARGs. IMPORTANCE There is a paucity of research on detailed antibiotic resistome and microbiome diversity of Indian hospital wastewater. This study reports the predominance of clinically concerning ARGs such as the beta-lactamases blaNDM and blaOXA and the colistin resistance gene mcr and their association with the microbiome in six different Indian hospital wastewaters of both urban and rural origin. The abundance of plasmid-mediated ARGs and virulence factors calls for urgent AMR crisis management. The lack of proper wastewater management strategies meeting international standards and open drainage systems further complicates the problem of containing the ARGs at these hospitals. This metagenomic study presents the current AMR profile propagating in hospital settings in India and can be used as a reference for future surveillance and risk management of ARGs in Indian hospitals.

Mobile tigecycline resistance gene tet(X4) persists with different animal manure composting treatments and fertilizer receiving soils

The emergence of plasmid-mediated tigecycline-resistant genes [tet(X3)to tet(X6)] in animals and humans has raised serious concerns over their possible cross-environmental dissemination. However, behavior of these emerging mobile tet(X)-variant genes in manure treatment processes, particularly for different composting treatments, has not yet been studied. Here, we explored the environmental behavior of mobile tet(X)-variant genes in two typical manure composting treatments and amended soils based on a large-scale molecular investigation across eight provinces in China. Results showed that tet(X4) was the predominant mobile tet(X)-variant gene in fresh manure, natural and thermophilic composting products with both the highest detection frequency (82.5% ± 14.7%), and absolute abundance of tet(X4)[4.26 ± 0.09) × 10¹⁰] copies/g dry weight, followed by tet(X3), tet(X6), and tet(X5). The occurrence of all mobile tet(X)-variant genes, particularly tet(X4), in receiving soil following composting fertilizer application indicated their transmission from manure to soil. Paired-sampling strategy revealed no significant reduction in mobile tet(X)-variant genes by natural composting, while thermophilic composting exhibited clear efficacy in removing tet(X)-variant genes. After thermophilic composting, tet(X4) exhibited the lowest reduction (94.1%) compared with other mobile tet(X)-variant genes (96.9%-99.9%), which may be attributable to its significant correlation with ISCR2 (P < 0.05) facilitating its transfer to various hosts including persisted thermotolerant bacteria. Thus, tet(X4) showed better persistence in livestock-related environments. Collectively, this study highlights the importance of controlling the environmental dissemination of clinically relevant mobile tet(X)-variant genes by establishing a sound process and operational strategy.

Dissemination and prevalence of plasmid-mediated high-level tigecycline resistance gene tet (X4)

With the large-scale use of antibiotics, antibiotic resistant bacteria (ARB) continue to rise, and antibiotic resistance genes (ARGs) are regarded as emerging environmental pollutants. The new tetracycline-class antibiotic, tigecycline is the last resort for treating multidrug-resistant (MDR) bacteria. Plasmid-mediated horizontal transfer enables the sharing of genetic information among different bacteria. The tigecycline resistance gene tet(X) threatens the efficacy of tigecycline, and the adjacent ISCR2 or IS26 are often detected upstream and downstream of the tet(X) gene, which may play a crucial driving role in the transmission of the tet(X) gene. Since the first discovery of the plasmid-mediated high-level tigecycline resistance gene tet(X4) in China in 2019, the tet(X) genes, especially tet(X4), have been reported within various reservoirs worldwide, such as ducks, geese, migratory birds, chickens, pigs, cattle, aquatic animals, agricultural field, meat, and humans. Further, our current researches also mentioned viruses as novel environmental reservoirs of antibiotic resistance, which will probably become a focus of studying the transmission of ARGs. Overall, this article mainly aims to discuss the current status of plasmid-mediated transmission of different tet(X) genes, in particular tet(X4), as environmental pollutants, which will risk to public health for the "One Health" concept.

Metagenomic insights into the antibiotic resistomes of typical Chinese dairy farm environments

Antibiotic resistance genes (ARGs) in the environment pose a threat to human and animal health. Dairy cows are important livestock in China; however, a comprehensive understanding of antibiotic resistance in their production environment has not been well clarified. In this study, we used metagenomic methods to analyze the resistomes, microbiomes, and potential ARG bacterial hosts in typical dairy farm environments (including feces, wastewater, and soil). The ARGs resistant to tetracyclines, MLS, β-lactams, aminoglycoside, and multidrug was dominant in the dairy farm ecosystem. The abundance and diversity of total ARGs in dairy feces and wastewater were significantly higher than in soil (P < 0.05). The same environmental samples from different dairy have similar resistomes and microbiomes. A high detection rate of tet(X) in wastewater and feces (100% and 71.4%, respectively), high abundance (range from 5.74 to 68.99 copies/Gb), and the finding of tet(X5) challenged the clinical application of the last antibiotics resort of tigecycline. Network analysis identified Bacteroides as the dominant genus in feces and wastewater, which harbored the greatest abundance of their respective total ARG coverage and shared ARGs. These results improved our understanding of ARG profiles and their bacterial hosts in dairy farm environments and provided a basis for further surveillance.

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

Mobile tigecycline resistance (MTR) threatens the clinical efficacy of the salvage antibiotic, tigecycline (TIG) used in treating deadly infections in humans caused by superbugs (multidrug-, extensively drug-, and pandrug-resistant bacteria), including carbapenem- and colistin-resistant bacteria. Currently, non-mobile tet(X) and mobile plasmid-mediated transmissible tet(X) and resistance-nodulation-division (RND) efflux pump tmexCD-toprJ genes, conferring high-level TIG (HLT) resistance have been detected in humans, animals, and environmental ecosystems. Given the increasing rate of development and spread of plasmid-mediated resistance against the two last-resort antibiotics, colistin (COL) and TIG, there is a need to alert the global community on the emergence and spread of plasmid-mediated HLT resistance and the need for nations, especially developing countries, to increase their antimicrobial stewardship. Justifiably, MTR spread projects One Health ramifications and portends a monumental threat to global public and animal health, which could lead to outrageous health and economic impact due to limited options for therapy. To delve more into this very important subject matter, this current work will discuss why MTR is an emerging health catastrophe requiring urgent One Health global intervention, which has been constructed as follows: (a) antimicrobial activity of TIG; (b) mechanism of TIG resistance; (c) distribution, reservoirs, and traits of MTR gene-harboring isolates; (d) causes of MTR development; (e) possible MTR gene transfer mode and One Health implication; and (f) MTR spread and mitigating strategies.

Structural diversity of the ISCR2-mediated rolling-cycle transferable unit carrying tet(X4)

BACKGROUND

Mobile tigecycline-resistance gene tet(X) variants have emerged as diverse pathogens from animal, human as well as their associated environments, which could potentially threaten public health. The insertion sequence, ISCR2, carries tet(X4) for horizontal transfer by rolling-cycle (RC) transposition. However, the diversity of ISCR2 and tet(X4) isolated from different sources is largely unknown.

METHODS

The tet(X4)-carrying isolates were collected from human and livestock in several multiple regions of China. The whole genomic sequences of these isolates were either obtained from NCBI GenBank or determined by Illumina Hiseq 2500 and the MinION platform. The intact transposon region, ISCR2-tet(X4)-ISCR2, observed in a small number of isolates as the reference sequence to construct the transposon phylogeny. The diversity of the genetic environments of all ISCR2-tet(X4) elements were analyzed.

RESULTS

A 2760-bp element encompassing the tet(X4)-hydrolase-encoding gene, catD, located between two ISCR2 elements was highly conserved in all isolates and could form an RC transposable unit (RC-TU). ISCR2 could also capture more resistance genes and formed a larger RC-TU base on RC transposition. However, the ISCR2-mediated RC-TUs were constantly truncated and inserted by other IS elements, indicating frequent recombination events. Of these elements, IS26 disrupted both the upstream and downstream ISCR2-mediated RC-TUs, indicating that IS26 captured tet(X4), thus leading to a wider spread of tet(X4).

CONCLUSIONS

These results confirmed the critical role of ISCR2 for dissemination and co-transmission of tet(X4) and other resistance genes. More effort is needed to monitor the variation tendencies of tet(X4)-carrying mobile elements and determine the driving factors for disseminating transferable tigecycline resistance.

In Vitro Antibacterial Activity of Imipenem/Relebactam against Clinical Isolates in Japan

Relebactam is a novel β-lactamase inhibitor of Ambler class A and C β-lactamases that has been developed in combination with imipenem/cilastatin for the treatment of carbapenem-resistant bacterial infections. In this study, we evaluated the in vitro antibacterial activity of imipenem/relebactam (IMR) against imipenem-nonsusceptible Enterobacterales and Pseudomonas aeruginosa isolates from Japan. Two sets of antibacterial susceptibility tests were conducted according to the susceptibility testing standard of the Clinical and Laboratory Standards Institute. In the first set, antibacterial susceptibility as measured by the MIC_50/90 (MIC range) of IMR was assessed for the following 61 imipenem-nonsusceptible strains: 2 Enterobacter cloacae complex (not determined [0.25 μg/mL]), 33 Klebsiella aerogenes (0.5/1 μg/mL [0.5 to 1 μg/mL]), 2 Serratia marcescens (not determined [1 to 2 μg/mL]), and 24 P. aeruginosa (2/128 μg/mL [0.25 to >128 μg/mL]). In the second set, antibacterial susceptibility was assessed for the following 8 imipenem-nonsusceptible strains: 4 Escherichia coli, 1 E. cloacae complex and 3 Klebsiella pneumoniae. The MIC ranges of IMR for these strains were 0.25 to 0.5 μg/mL, 0.5 μg/mL, and 0.5 to 16 μg/mL, respectively. The antibacterial activity of IMR was similar to or lower than that of amikacin and comparable to or greater than those of other reference drugs. In conclusion, IMR has shown antibacterial activity against clinical isolates from Japan and, therefore, is expected to become a new therapeutic option for carbapenem-resistant infections in Japan. IMPORTANCE Carbapenem-resistant Enterobacterales and carbapenem-resistant Pseudomonas aeruginosa strains pose a global threat. Antibacterial activity of imipenem/relebactam (IMR) against clinical isolates of these bacteria from several global regions has been shown; however, as yet there are no reports on Japanese isolates. In this study, we evaluated the in vitro antibacterial activity of IMR against imipenem-nonsusceptible Enterobacterales and Pseudomonas aeruginosa isolates from Japan. The antibacterial activity of IMR against imipenem-nonsusceptible Enterobacterales was generally comparable to that of amikacin (AMK) and comparable to or higher than those of other reference drugs tested. The antibacterial activity of IMR against imipenem-nonsusceptible P. aeruginosa isolates was lower than that of AMK but comparable to or higher than those of other drugs. These results support the use of IMR as a new treatment option for infections due to Enterobacterales and P. aeruginosa strains that are resistant to existing β-lactams and other antibacterial agents.

Source Tracking and Global Distribution of the Tigecycline Non-Susceptible tet(X)

The emergence of tet(X) genes has compromised the clinical use of the last-line antibiotic tigecycline. We identified 322 (1.21%) tet(X) positive samples from 12,829 human microbiome samples distributed in four continents (Asia, Europe, North America, and South America) using retrospective data from worldwide. These tet(X) genes were dominated by tet(X2)-like orthologs but we also identified 12 samples carrying novel tet(X) genes, designed tet(X45), tet(X46), and tet(X47), were resistant to tigecycline. The metagenomic analysis indicated these tet(X) genes distributed in anaerobes dominated by Bacteroidaceae (78.89%) of human-gut origin. Two mobile elements ISBf11 and IS4351 were most likely to promote the transmission of these tet(X2)-like orthologs between Bacteroidaceae and Riemerella anatipestifer. tet(X2)-like orthologs was also developed during transmission by mutation to high-level tigecycline resistant genes tet(X45), tet(X46), and tet(X47). Further tracing these tet(X) in single bacterial isolate from public repository indicated tet(X) genes were present as early as 1960s in R. anatipestifer that was the primary tet(X) carrier at early stage (before 2000). The tet(X2) and non-tet(X2) orthologs were primarily distributed in humans and food animals respectively, and non-tet(X2) were dominated by tet(X3) and tet(X4). Genomic comparison indicated these tet(X) genes were likely to be generated during tet(X) transmission between Flavobacteriaceae and E. coli/Acinetobacter spp., and ISCR2 played a key role in the transmission. These results suggest R. anatipestifer was the potential ancestral source of tet(X). In addition, Bacteroidaceae of human-gut origin was an important hidden reservoir and mutational incubator for the mobile tet(X) genes that enabled spread to facultative anaerobes and aerobes. IMPORTANCE The emergence of the tigecycline resistance gene tet(X) has posed a severe threat to public health. However, reports of its origin and distribution in human remain rare. Here, we explore the origin and distribution of tet(X) from large-scale metagenomic data of human-gut origin and public repository. This study revealed the emergency of tet(X) gene in 1960s, which has refreshed a previous standpoint that the earliest presence of tet(X) was in 1980s. The metagenomic analysis from data mining covered the unculturable bacteria, which has overcome the traditional bacteria isolating and purificating technologies, and the analysis indicated that the Bacteroidaceae of human-gut origin was an important hidden reservoir for tet(X) that enabled spread to facultative anaerobes and aerobes. The continuous monitoring of mobile tigecycline resistance determinants from both culturable and unculturable microorganisms is imperative for understanding and tackling the dissemination of tet(X) genes in both the health care and agricultural sectors.

Identification of multiple transfer units and novel subtypes of tmexCD-toprJ gene clusters in clinical carbapenem-resistant Enterobacter cloacae and Klebsiella oxytoca

OBJECTIVES

Tigecycline is a last-resort antibiotic used to treat lethal infections caused by carbapenem-resistant Enterobacterales; however, plasmid-borne tigecycline resistance tmexCD-toprJ gene clusters can confer tigecycline resistance. The aim of the study was to identify novel subtypes and the spread of tmexCD-toprJ.

METHODS

Five non-duplicate isolates of different species, carrying tmexCD-toprJ gene clusters or novel subtypes, were isolated from patients across China between November 2018 and June 2019. WGS was performed using Illumina and Nanopore platforms. A phylogenetic tree was constructed using a dataset of 77 sequences carrying the tmexCD-toprJ gene clusters, 72 of which were downloaded from NCBI with a blastn identity cut-off of 95%.

RESULTS

We detected six different transfer units and two novel subtypes (tmexC1D1.2-toprJ1 and tmexC2D2.2-toprJ2) of the tmexCD-toprJ gene clusters. Among the six transfer units, three were mediated by IS26, while the rest were presumably mediated by Tn5393, hypothetical integrases (xerD-hp clusters-umuC-integrases-tnfxB2-tmexC2D2-toprJ2-umuC) and hypothetical units (hp-hp-hp-tnfxB2-tmexC2D2.2-toprJ2-ΔTn5393-Tn6292). Moreover, two tmexCD-toprJ-like gene clusters co-located on the same plasmid with blaNDM in five isolates. Phylogenetic analysis revealed that tmexCD-toprJ gene clusters may have originated in Pseudomonas spp., being mainly distributed in Pseudomonas spp. and Klebsiella spp. (64/77). Most tmexCD-toprJ gene clusters in Enterobacterales were located on plasmids, indicating that the gene clusters have a high inter-species transfer risk after transfer to Enterobacterales.

CONCLUSIONS

In summary, to the best of our knowledge, this is the first report of tmexCD-toprJ gene clusters being isolated from Enterobacter cloacae and Klebsiella oxytoca, revealing that these multiple transfer units should be further studied because of their clinical significance.

Whole-genome epidemiology and characterisation of mcr-1-encoding Escherichia coli in aquatic bird farms from the Pearl River Delta, China, 2019-2020

Due to their unique breeding pattern, aquatic bird farms are increasingly considered as hotspots in the development and spread of antimicrobial resistance. However, comprehensive studies addressing the whole-genomic features of colistin-resistant bacteria in aquatic bird farms are scarce. Over a 2-year period, we conducted surveillance to determine the whole-genome epidemiology and characterisation of mcr-1-positive Escherichia coli in aquatic bird farms in southeastern coastal China. A total of 100 mcr-1-producing isolates among 654 E. coli strains were recovered from 781 samples collected in 11 aquatic bird farms and 1 veterinary clinic in the Pearl River Delta area. Higher resistance phenotypes to 17 antibiotics were found in mcr-1-positive isolates compared with other isolates. Subsequently, 20 mcr-1-carrying isolates were sequenced to analyse the whole-genomic features. Molecular typing as well as antimicrobial resistance gene and virulence factor profiles of the isolates showed considerable diversity. Three types of genetic backbones of mcr-1 in the isolates were assembled and were identified in diverse broad-host-range plasmids and bacterial species. Pangenome analyses revealed a large genetic pool composed of the isolates. Furthermore, phylogenetic trees both of the isolates in this study and a global data set were built, indicating the spread of the three mcr-1 backbones and the mcr-1-positive isolates among different habitats, farms and even countries. This study highlights that aquatic bird farms may act as an important reservoir for mcr-1-producing E. coli, from which colistin resistance may be spread to diverse habitats, different geographical locations and even across bacterial species.

Distribution and genomic characterization of tigecycline-resistant tet(X4)-positive Escherichia coli of swine farm origin

Abstract

The emergence of plasmid-mediated tigecycline-resistant strains is posing a serious threat to food safety and human health, which has attracted worldwide attention. The tigecycline resistance gene tet (X4) has been found in diverse sources, but the distribution of tet (X4) and its genetic background in the animal farming environment is not fully understood. Thirty-two tet (X)-positive Escherichia coli strains isolated from 159 samples collected from swine farms showed resistance to tigecycline. The tet (X)-positive strains were characterized by antimicrobial susceptibility testing, conjugation assay, PCR, Illumina and long-read Nanopore sequencing, and bioinformatics analysis. A total of 11 different sequence types (STs) were identified and most of them belonged to phylogroup A, except ST641. In total, 196 possible prophage sequences were identified and some of the prophage regions were found to carry resistance genes, including tet (X4). Furthermore, our results showed possible correlations between CRISPR spacer sequences and serotypes or STs. The co-existence of tigecycline-resistant tet (A) variants and tet (X4) complicates the evolution of vital resistance genes in farming environments. Further, four reorganization plasmids carrying tet (X4) were observed, and the formation mechanism mainly involved homologous recombination. These findings contribute significantly to a better understanding of the diversity and complexity of tet (X4)-bearing plasmids, an emerging novel public health concern.

First report of mobile tigecycline resistance gene tet(X4)-harbouring multidrug-resistant Escherichia coli from wastewater in Norway

OBJECTIVES

The mobile tigecycline resistance gene tet(X4), conferring resistance to all tetracyclines, is largely reported from China, however the global spread of such a novel resistance mechanism is a concern for preserving the efficacy of these last-resort antibiotics. The aim of our study was to determine the genetic basis of resistance in a tigecycline-resistant Escherichia coli strain (2-326) isolated from sewage in Bergen, Norway, using whole-genome sequencing (WGS).

METHODS

WGS was carried out using Illumina MiSeq-based sequencing. In vitro conjugation assays were performed to determine the potential of isolate 2-326 to transfer tigecycline resistance to other strains.

RESULTS

Escherichia coli isolate 2-326 belongs to pathogenic sequence type 167 (ST167) and carries several clinically important antibiotic resistance genes including tet(X4), bla_CTX-M-14, dfrA12, sul2, qnrS1 as well as several aminoglycoside resistance genes. Tigecycline resistance along with resistance to tetracycline, sulfamethoxazole, chloramphenicol and azithromycin was transferred to green fluorescent protein (GFP)-encoding E. coli strain CV601-GFP by conjugation.

CONCLUSION

To the best of our knowledge, this is the first report of E. coli carrying mobile tet(X4) gene from Norway. Our study demonstrates the ongoing spread of new mechanisms of resistance against last-resort antibiotics and the need for surveillance of such resistance factors in the population in order to mitigate their spread.

Multidrug-resistant Klebsiella pneumoniae: mechanisms of resistance including updated data for novel β-lactam-β-lactamase inhibitor combinations

Introduction: Multi-drug-resistant Klebsiella pneumoniae is currently one of the most pressing emerging issues in bacterial resistance. Treatment of K.pneumoniae infections is often problematic due to the lack of available therapeutic options, with a relevant impact in terms of morbidity, mortality and healthcare-associated costs. Soon after the launch of Ceftazidime-Avibactam, one of the approved new β-lactam/β-lactamase inhibitor combinations, reports of ceftazidime-avibactam-resistant strains developing resistance during treatment were published. Being a hospital-associated pathogen, K.pneumoniae is continuously exposed to multiple antibiotics resulting in constant selective pressure, which in turn leads to additional mutations that are positively selected.Areas covered: Herein the authors present the K.pneumoniae mechanisms of resistance to different antimicrobials, including updated data for ceftazidime-avibactam.Expert opinion: K.pneumoniae is a nosocomial pathogen commonly implicated in hospital outbreaks with a propensity for antimicrobial resistance toward mainstay β-lactam antibiotics and multiple other antibiotic classes. Following the development of drug resistance and understanding the mechanisms involved, we can improve the efficacy of current antimicrobials, by applying careful stewardship and rational use to preserve their potential utility. The knowledge on antibiotic resistance mechanisms should be used to inform the design of novel therapeutic agents that might not be subject to, or can circumvent, mechanisms of resistance.

Abundance of tigecycline resistance genes and association with antibiotic residues in Chinese livestock farms

The discovery of plasmid-mediated tet(X) variants and efflux pump gene tmexCD1-toprJ1 conferring bacteria resistance to tigecycline has compromised glycylcycline as the last line of defense against infection, which poses serious threat to public health. Herein, real-time quantitative PCR was used to detect the abundance of seven tigecycline resistance genes (TRGs), including six tet(X) variants and tmexCD1-toprJ1, and insertion sequences ISCR2 and IS26. Then, the concentrations of nine antibiotics were quantified in fecal samples collected from 157 livestock farms in four Chinese provinces. TRGs, especially tet(X4), tmexCD1-toprJ1, and insertion sequences ISCR2 and IS26, were more abundant in chicken feces than in pig and cattle feces, suggesting the greater risk for the propagation of TRGs in chicken feces. Positive correlations (ρ = 0.3741-0.8275, P < 0.0001) between ISCR2/IS26 and TRGs (except tet(X1)) further demonstrated that ISCR2 mediates the transfer of tet(X3), tet(X4), and tet(X5) and that IS26 plays a certain role for the mobilization of tet(X4) and tmexCD1-toprJ1. Tetracyclines had no positive correlation with the abundance of TRGs (except tet(X1)), meanwhile florfenicol and tiamulin were positively correlated with TRGs. However, further research is needed to confirm whether or not florfenicol and tiamulin are potential driving factors of TRG accumulation.