Search

The emergence and spread of carbapenemase genes, colistin resistance genes mcr-1, and tigecycline resistance gene tet(X) represent a significant threat to clinical therapy and public health. In this study, we investigated the presence of carbapenemase genes, mcr-1, and tet(X) in 298 Escherichia coli strains obtained from a teaching hospital in China. In total, eight (2.68%), six (2.01%), and one (0.34%) E. coli isolates carried blaNDM, mcr-1, and tet(X4), respectively. The blaNDM gene was located on IncX3 (n = 4), F2:A-:B- (n = 3), and F2:A1:B1 (n = 1) plasmids, with high similarity to multiple plasmids belonging to the same incompatibility type from Enterobacteriaceae. Six MCR-producing strains contained mcr-1-carrying IncI2 plasmids, organized similarly to other mcr-1-bearing IncI2 plasmids from animals in China. The blaCTX−M−55/64/132/199 gene located within a typical transposition unit (ISEcp1-blaCTX−M-orf477Δ) was inserted near dnaJ to generate 5-bp direct repeats in four mcr-1-positive plasmids. The tet(X) and another four resistance genes [aadA2, tet(A), floR, and Δlnu(F)] were co-located on an IncX1 plasmid, highly similar to other tet(X4)-carrying IncX1 plasmids from Escherichia and Klebsiella of animal or food origin, except that the conjugative transfer region of IncX1 plasmids was absent in our plasmid. Although a low prevalence of blaNDM, mcr-1, and tet(X) was observed in E. coli from patients in this study, their dissemination associated with some successful pandemic plasmids is of great concern. The continued surveillance of these crucial resistance genes in patients should be strengthened.

This study aimed to investigate the prevalence and characterization of tet(X4) in Escherichia coli isolates from a pig farm in Shanghai, China, and to elucidate tet(X4) dissemination mechanism in this swine farm. Forty-nine (80.33%) E. coli strains were isolated from 61 samples from a pig farm and were screened for the presence of tet(X). Among them, six (12.24%) strains were positive for tet(X4) and exhibited resistance to tigecycline (MIC ≥ 16 mg/L). They were further sequenced by Illumina Hiseq. Six tet(X4)-positive strains belonged to ST761 with identical resistance genes, resistance profiles, plasmid replicons, and cgMLST type except that additional ColE10 plasmid was present in isolate SH21PTE35. Isolate SH21PTE31, as a representative ST761 E. coli strain, was further sequenced using Nanopore MinION. The tet(X4) in SH21PTE31 was located on IncFIA18/IncFIB(K)/IncX1 hybrid plasmid pYUSHP31-1, highly similar to other tet(X4)-carrying IncFIA18/IncFIB(K)/IncX1 plasmids from ST761 E. coli and other E. coli lineages in China. These IncFIA18/IncFIB(K)/IncX1 plasmids shared closely related multidrug resistance regions, and could reorganize, acquire or lose resistance modules mediated by mobile elements such as ISCR2 and IS26. Phylogenetic analysis were performed including all tet(X4)-positive isolates obtained in this pig farm combined with 43 tet(X4)-positive E. coli from pigs, cow, pork, wastewater, and patients with the same ST from NCBI. The 50 tet(X4)-carrying E. coli ST761 isolates from different areas in China shared a close phylogenetic relationship (0-49 SNPs). In conclusion, clonal transmission of tet(X4)-positive E. coli ST761 has occurred in this swine farm. E. coli ST761 has the potential to become a high-risk clone for tet(X4) dissemination in China.

This study aimed to investigate the prevalence of fosfomycin fosA7 in Salmonella enterica isolates from food animals and retail meat products in China and the impact of fosA7 on bacterial fitness. A total of 360 Salmonella isolates collected from 11 provinces and cities in China were detected for fosA7. All fosA7-positive Salmonella isolates were determined minimum inhibitory concentrations (MICs) and sequenced by Illumina Hiseq. The fosA7 gene of S. Derby isolate HA2-WA5 was knocked out. The full length of fosA7 was cloned into vector pBR322 and then transformed into various hosts. MICs of fosfomycin, growth curves, stability, and fitness of fosA7 were evaluated. The fosA7 gene was identified in S. Derby (ST40, n = 30) and S. Reading (ST1628, n = 5). MICs to fosfomycin of 35 fosA7-positive isolates were 1 to 32 mg/L. All fosA7 were located on chromosomes of Salmonella. The deletion of fosA7 in HA2-WA5 decreased fosfomycin MIC by 16-fold and slightly affected its fitness. The acquisition of plasmid-borne fosA7 enhanced MICs of fosfomycin in Salmonella (1,024-fold) and Escherichia coli (16-fold). The recombinant plasmid pBR322-fosA7 was stable in Salmonella Typhimurium, S. Pullorum, S. Derby, and E. coli, except for Salmonella Enteritidis, and barely affected on the growth of them but significantly increased biological fitness in Salmonella. The spread of specific Salmonella serovars such as S. Derby ST40 will facilitate the dissemination of fosA7. fosA7 can confer high-level fosfomycin resistance and enhance bacterial fitness in Salmonella if transferred on plasmids; thus, it has the potential to be a reservoir of the mobilized fosfomycin resistance gene.

This study aimed to characterize 16S rRNA methylase genes among Salmonella and to elucidate the structure and evolution of rmtB-carrying plasmids. One hundred fifty-eight Salmonella isolates from one pig slaughterhouse were detected as containing 16S rRNA methylase genes; two (1.27%) Salmonella London isolates from slaughtered pigs were identified to carry rmtB. They were resistant to gentamicin, amikacin, streptomycin, ampicillin, tetracycline, florfenicol, ciprofloxacin, and sulfamethoxazole/trimethoprim. The complete sequences of RmtB-producing isolates were obtained by PacBio single-molecule real-time sequencing. The isolate HA1-SP5 harbored plasmids pYUHAP5-1 and pYUHAP5-2. pYUHAP5-1 belonged to the IncFIBK plasmid and showed high similarity to multiple IncFIBK plasmids from Salmonella London in China. The rmtB-carrying plasmid pYUHAP5-2 contained a typical IncN-type backbone; the variable region comprising several resistance genes and an IncX1 plasmid segment was inserted in the resolvase gene resP and bounded by IS26. The sole plasmid in HA3-IN1 designated as pYUHAP1 was a cointegrate of plasmids from pYUHAP5-1-like and pYUHAP5-2-like, possibly mediated by IS26 via homologous recombination or conservative transposition. The structure differences between pYUHAP1 and its corresponding part of pYUHAP5-1 and pYUHAP5-2 may result from insertion, deletion, or recombination events mediated by mobile elements (IS26, ISCR1, and ISKpn43). This is the first report of rmtB in Salmonella London. IncN plasmids are efficient vectors for rmtB distribution and are capable of evolving by reorganization and cointegration. Our results further highlight the important role of mobile elements, particularly IS26, in the dissemination of resistance genes and plasmid evolution.

The purpose of this study was to characterize the complete sequence of a novel plasmid carrying tigecycline resistance gene tet(X) and carbapenemase gene blaOXA-58 from a swine Acinetobacter sp. strain SH19PTT10. Minimal inhibitory concentration (MIC) was performed using microbroth dilution method. The isolate SH19PTT10 was highly resistant (16 mg/L) to tigecycline, and also exhibited resistance to ampicillin, streptomycin, tetracycline, chloramphenicol, florfenicol, ciprofloxacin, and sulfamethoxazole/trimethoprim. Although SH19PTT10 harbored blaOXA-58, it was susceptible to cefotaxime and meropenem. The genome sequence of SH19PTT10 was determined using PacBio single-molecule real-time sequencing. Plasmid pYUSHP10-1 had a size of 174,032 bp and showed partial homology to several plasmids found in Acinetobacter isolates. It contained two repA genes, putative toxin-antitoxin systems (HipA/HipB, RelE/RelB, and BrnT/BrnA), partitioning genes (parA and parB), and heavy metal resistance-associated genes (copA/copB, nrp, and czcA/czcD) but the transfer region or proteins was not found. pYUSHP10-1 carried 16 resistance genes, mainly clustered in two mosaic multiresistance regions (MRRs). The first MRR contained sul3, qacI-aadA1-clmA1-aadA2-blaCARB-2-dfrA16 cassette, aac(3)-IId, and blaOXA-58. The blaOXA-58 gene was associated with ISAba3, as previously described. The second MRR is the tet(X) region (ISAcsp12-aph(3')-Ia-IS26-ΔxerD-tet(X)-res-ISCR2-sul2) related to the corresponding region in other tet(X)-bearing plasmids. The pdif sites, as well as mobile elements, play an important role in mobilization of DNA modules and plasmid evolution. Coexistence of numerous resistance genes on a single plasmid may contribute to the dissemination of these genes under pressure posed by different agents, which may explain the presence of clinically crucial resistance genes tet(X) and blaOXA-58 in livestock. Thus, rational drug use and continued surveillance of tet(X) and blaOXA-58 in livestock are warranted.