Detection of Plasmid-Mediated Tigecycline Resistance Gene tet(X4) in a Salmonella enterica Serovar Llandoff Isolate

The emergence and spread of plasmid-mediated tigecycline resistance genes have attracted extensive attention worldwide.We investigated the distribution of mobile tigecycline resistance genes in Salmonella genomes generated by both our laboratory and public bacterial genomes downloaded from the NCBI GenBank.The tet(X4)-positive strains were subjected to susceptibility testing and conjugation assays.The genetic features of the tet(X4)-bearing plasmid sequence were analyzed.Here,we report the identification of the plasmid-mediated tigecycline resistance gene tet(X4)in a conjugative plasmid of the Salmonella enterica serovar Llandoff strain SH16G3606,isolated from a man in China in 2016,the first reported serovar Llandoff in China as a novel sequence type ST8300.The tet(X4)-mediated resistance phenotype was successfully transferred from the Salmonella Llandoff strain into Escherichia coli J53,resulting in a 32-fold increase in the minimal inhibitory concentration of tigecycline.The tet(X4)gene was located between two copies of ISCR2 in the plasmid pSal21GXH-tetX4.To our knowledge,this is the first report of the plasmid-mediated tigecycline resistance gene tet(X4)in a Salmonella Llandoff strain isolated from a human stool sample in China.In addition,our findings demonstrated that a total of 171 isolates are carrying tet(X)-like genes distributed in 21 countries or areas across 6 continents,posing a serious threat to humans and public health.Overall,our timely discovery of the recent emergence of the tet(X4)gene in Salmonella isolates and other Enterobacteriaceae bacteria species supports the need for rapid surveillance to prevent the tet(X)-like gene from spreading.

The effect of long-term application of nitrogen-rich fertilizers on soil resistome:A study of conventional and organic cropping systems

Metagenomic studies of various soil environments have previously revealed the widespread distribution of antibiotic resistance genes(ARGs)around the globe.In this study,we applied shotgun metagenomics to investigate differences in microbial communities and resistomes in Chernozem soils that have been under long-term organic and conventional cropping practices.The organic cropping system was seeded with Triticum spelta without any fertilizer.The conventional cropping system was seeded with Tríticum durum Desf and used mineral fertilizer(NPK),that resulted in an increased amount of total and available carbon and nitrogen in soils.Across all samples,we identified a total of 21 ARG classes,among which the dominant were vancomycin,tetracycline and multidrug.Profiling of soil microbial communities revealed differences between the studied fields in the relative abundances of 14 and 53 genera in topsoil and subsoil,respectively.Correlation analysis showed significant correlations(positive and negative)among 18 genera and 6 ARGs,as well as between these ARGs and some chemical properties of soils.The analysis of metagenome-assembled genomes revealed that Nitrospirota,Thermoproteota,Actinobacteriota and Binatota phyla of archaea and bacteria serve as hosts for glycopeptide and fluoroquinolone/tetracycline ARGs.Collectively,the data obtained enrich knowledge about the consequences of human agricultural activities in terms of soil microbiome modification and highlight the role of nitrogen cycling taxa,including uncultivated genera,in the formation of soil resistome.