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Objectives To elucidate the mechanism of tigecycline resistance in Escherichia coli that is mediated by the tet (A) variant gene. Methods E. coli strain 573 carried a plasmid-borne tet (A) variant gene, tentatively designated tet (A)TIG, that conferred decreased tigecycline susceptibility (MIC 0.5 mg/L). When exposed to increasing concentrations of tigecycline (0.25–8 mg/L), mutants growing at 2, 4 and 8 mg/L were obtained and sequenced. Copies of plasmid and tet (A)TIG relative to the chromosomal DNA in the mutants were determined by WGS and quantitative PCR (qPCR). Expression of tet (A)TIG in the mutants was evaluated by RT–qPCR. The tet (A)TIG-carrying plasmids were visualized by S1-PFGE and Southern blot hybridization. PCR served for the detection of a tet (A)TIG-carrying unconventional circularizable structure (UCS). Results Tigecycline resistance with maximum MICs of 16 mg/L was seen in E. coli mutants selected in the presence of tigecycline. Compared with the parental strain, the relative copy number and transcription level of tet (A)TIG in the mutants increased significantly in the presence of 2, 4 and 8 mg/L tigecycline, respectively. With increasing tigecycline selection pressure, the tet (A)TIG-carrying plasmids in the mutants increased in size, correlating with the number of tandem amplificates of a ΔTn As1 -flanked UCS harbouring tet (A)TIG. These tandem amplificates were not stable in the absence of tigecycline. Conclusions Tigecycline resistance is due to the tandem amplification of a ΔTn As1 -flanked tet (A)TIG-carrying plasmid-borne segment in E. coli. The gain/loss of the tandem amplificates in the presence/absence of tigecycline represents an economic way for the bacteria to survive in the presence of tigecycline. [ABSTRACT FROM AUTHOR]

To investigate the prevalence of a tet (A) gene variant and its role in developing high-level tigecycline resistance among carbapenem-resistant Klebsiella pneumoniae (CRKP) clinical isolates. The mechanism of high-level tigecycline resistance in CRKP mediated by a tet (A) variant was explored by induction experiments, antimicrobial susceptibility testing, whole-genome sequencing and bioinformatics analysis. The amplification and overexpression of the tet (A) variant were measured by the determination of sequencing depth, gene copy numbers, and qRT-PCR. A high rate (62.1%, 998/1607) of tet (A) variant carriage was observed among 1607 CRKP clinical isolates from Henan Province, China. High-level tigecycline resistance could rapidly develop by the amplification of the tet (A) variant in these isolates. The analysis of the raw sequencing data and the plasmid mapping depth revealed that the Δ tnpA homologous sequence of Tn 1721 supports the amplification of the region that harbours the tet (A) variant by forming a large number of repeat arrays through translocatable units (TUs). Moreover, the epidemiological analysis of tet (A) variant-carrying structures among 1607 clinical CRKPs showed that the TU structure is widely present. The presence of a tigecycline resistance-mediating tet (A) variant in CRKP clinical isolates represents a greater health concern than initially thought and should be monitored consistently. [ABSTRACT FROM AUTHOR]

Objectives: To identify the genetic context and the transferability of the multiresistance gene lsa(E) in Listeria monocytogenes.Methods: MICs were determined by broth microdilution. Transferability of lsa(E) was investigated by conjugation, electrotransformation and natural transformation. The lsa(E)-carrying plasmid was sequenced using the Illumina MiSeq and PacBio RSII platforms. The presence of translocatable units (TUs) was examined by PCR.Results: The 85 555 bp non-conjugative multiresistance plasmid pNH1 from L. monocytogenes harboured nine antimicrobial resistance genes including a multiresistance gene cluster, consisting of the genes aphA3, erm(B), aadE, spw, lsa(E) and lnu(B), and in addition the genes dfrG, tet(S) and catA8 were also located on plasmid pNH1 The multiresistance gene cluster, and each of the genes tet(S), catA8 and cadA were flanked by IS1216 elements. PCR identified four types of TUs, consisting of either the multiresistance gene cluster and one copy of IS1216, the catA8 gene and one copy of IS1216, or both, but also the tet(S) gene and one copy of IS1216, respectively. Natural transformation into Streptococcus mutans UA159 yielded transformants that harboured a novel 13 208 bp transposon, designated Tn6659. This transposon consisted of the multiresistance gene cluster bounded by IS1216 copies. All transformants displayed elevated MICs of the respective antimicrobial agents. At the integration site in the transformants, 8 bp direct target duplications (5'-ATTCAAAC-3') were found immediately up- and downstream of Tn6659.Conclusions: To the best of our knowledge, this is the first report of this novel multiresistance gene cluster and the gene catA8, flanked by IS1216 elements located on a plasmid of L. monocytogenes. Moreover, a novel functionally active multiresistance transposon was identified. [ABSTRACT FROM AUTHOR]

Biomass‐based hydrogel is a promising flame‐retardant material and has a high potential for applications in transportation, aerospace, building and electrical engineering, and electronics. However, rapid vat photopolymerization (VP) 3D printing of biomass‐based hydrogels, especially that of all‐natural ones, is still rare. Herein, a new class of VP 3D‐printed hydrogels with strong covalent networks, fabricating using fully biomass materials and a commercial liquid crystal display (LCD) printer assembled with low‐intensity visible light is presented. Encouragingly, the highly ordered layer‐by‐layer packing structures provided by VP 3D printing technology endow these hydrogels with remarkable flame retardancy, exceptional temperature resistance, advantageous combustion behaviors, and favorable mechanical strength, in particular, giving them a better limit oxygen index (83.5%) than various biomass‐based hydrogels. The proposed approach enables the green design as well as the precise and efficient preparation for flame‐retardant materials, paving the way for the future flame‐retardant materials toward attaining green sustainability. [ABSTRACT FROM AUTHOR]

Lincomycin is widely used in respiratory and gastrointestinal infection in veterinary medicine and food animal production. Campylobacter members are vital foodborne pathogens causing campylobacteriosis, and the resistance to lincosamides is seldom reported. To date, only the rRNA methyltransferase Erm(B) has been confirmed to be associated with lincosamides resistance in Campylobacter. In this study, we identified a lnu (C) variant conferring lincomycin resistance in this pathogen of chicken origin. The Lnu(C) encoded by this gene variant showed substitution at position 8 (Asn8Lys), 11 (Phe11Leu) and 112 (Leu112Phe), when compared with the firstly reported Lnu(C) from Streptococcus agalactiae. Cloning of the lnu (C) variant into lincosamide-susceptible Campylobacter jejuni NCTC 11168 confirmed its function in conferring resistance to lincomycin with the 32-fold increased MICs. Sequencing analysis showed that the lnu (C) variant was located within a MTn Sag1 -like transposon together with insLNU , which is inserted between panB and cj0299 genes on the chromosome. lnu (C) gene was distributed among C. coli globally, and various STs were involved in the dissemination of lnu (C). Although transposition mediated by MTn Sag1 -like transposon failed to occur, the horizontal transfer mediated by natural transformation and reservoir for resistance genes may facilitate their adaptation to the antimicrobial selection pressure in chickens, which should not be ignored. • A lnu (C) variant was identified in Campylobacter coli from chicken origin. • The lnu (C) variant could confer lincomycin resistance. • lnu (C) was distributed among C. coli globally and various STs were involved. • Homologous recombination is the major mechanism for lnu (C) transformation. [ABSTRACT FROM AUTHOR]