The widespread of tigecycline resistance gene tet(X4) has a serious impact on the clinical efficacy of tigecycline. The development of effective antibiotic adjuvants to combat the looming tigecycline resistance is needed. The synergistic activity between the natural compound β-thujaplicin and tigecycline in vitro was determined by the checkerboard broth microdilution assay and time-dependent killing curve. The mechanism underlining the synergistic effect between β-thujaplicin and tigecycline against tet(X4)-positive Escherichia coli was investigated by determining cell membrane permeability, bacterial intracellular reactive oxygen species (ROS) content, iron content, and tigecycline content. β-thujaplicin exhibited potentiation effect on tigecycline against tet(X4)-positive E. coli in vitro, and presented no significant hemolysis and cytotoxicity within the range of antibacterial concentrations. Mechanistic studies demonstrated that β-thujaplicin significantly increased the permeability of bacterial cell membranes, chelated bacterial intracellular iron, disrupted the iron homeostasis and significantly increased intracellular ROS level. The synergistic effect of β-thujaplicin and tigecycline was identified to be related to interfere with bacterial iron metabolism and facilitate bacterial cell membrane permeability. Our studies provided theoretical and practical data for the application of combined β-thujaplicin with tigecycline in the treatment of tet(X4)-positive E. coli infection.
Humans ; Tigecycline/pharmacology* ; Escherichia coli/metabolism* ; Reactive Oxygen Species/therapeutic use* ; Plasmids ; Anti-Bacterial Agents/metabolism* ; Escherichia coli Infections/microbiology* ; Bacteria/genetics* ; Microbial Sensitivity Tests

Manipulation of genes, including knock-out or knock-in, replacement of gene elements (such as promoters), fusion with a fluorescent protein gene, and construction of in situ gene reporter, is required in most of the biotechnological laboratories. The widely used gene manipulating methods based on two-step allelic exchange are cumbersome in terms of constructing plasmids, transforming and screening. In addition, the efficiency of using this method for long fragment knockout is low. To simplify the process of gene manipulation, we constructed a minimized integrative vector pln2. When a gene needs to be inactivated, an internal fragment of the target gene (non-frameshift) is cloned into the pln2 plasmid. Once the single-crossover recombination between genome and the constructed plasmid occurs, the endogenous gene is segmented by the plasmid backbone and thus inactivated. We developed a toolbox based on pln2 that can be used for different genomic operation mentioned above. With the help of this toolbox, we successfully knocked out large fragments of 20-270 kb.
Genetic Vectors/genetics* ; Pseudomonas aeruginosa/genetics* ; Plasmids/genetics* ; Promoter Regions, Genetic ; Genome

The antigen gene expression level of a DNA vaccine is the key factor influencing the efficacy of the DNA vaccine. Accordingly, one of the ways to improve the antigen gene expression level of a DNA vaccine is to utilize a plasmid vector that is replicable in eukaryotic cells. A replicative DNA vaccine vector pCMVori was constructed based on the non-replicative pcDNA3.1 and the replicon of porcine circovirus 2 (PCV2) in this study. An EGFP gene was cloned into pCMVori and the control plasmid pcDNA3.1. The two recombinant vectors were transfected into PK-15 cell, and the plasmid DNA and RNA were extracted from the transfected cells. Real-time PCR was used to determine the plasmid replication efficiency of the two plasmids using plasmid before and after Bcl Ⅰ digestion as templates, and the transcription level of the Rep gene in PCV2 replicon was detected by RT-PCR. The average fluorescence intensity of cells transfected with the two plasmids was analyzed with software Image J, and the transcription level of EGFP was determined by means of real-time RT-PCR. The results showed that the replication efficiency of pCMVori in PK-15 cells incubated for 48 h was 136%, and the transcriptions of Rep and Rep' were verified by RT-PCR. The average fluorescence intensity of the cells transfected with pCMVori-EGFP was 39.14% higher than that of pcDNA3.1-EGFP, and the transcription level of EGFP in the former was also 40% higher than that in the latter. In conclusion, the DNA vaccine vector pCMVori constructed in this study can independently replicate in eukaryotic cells. As a result, the expression level of cloned target gene was elevated, providing a basis for developing the pCMVori-based DNA vaccine.
Animals ; Swine ; Circovirus/genetics* ; Vaccines, DNA/genetics* ; Replicon/genetics* ; Genetic Vectors/genetics* ; Plasmids/genetics*

Objective: To investigate the antimicrobial resistance of food-borne diarrheagenic Escherichia coli (DEC) and the prevalence of mcr genes that mediates mobile colistin resistance in parts of China, 2020. Methods: For 91 DEC isolates recovered from food sources collected from Fujian province, Hebei province, Inner Mongolia Autonomous Region and Shanghai city in 2020, Vitek2 Compact biochemical identification and antimicrobial susceptibility testing platform was used for the detection of antimicrobial susceptibility testing (AST) against to 18 kinds of antimicrobial compounds belonging to 9 categories, and multi-polymerase chain reaction (mPCR) was used to detect the mcr-1-mcr-9 genes, then a further AST, whole genome sequencing (WGS) and bioinformatics analysis were platformed for these DEC isolates which were PCR positive for mcr genes. Results: Seventy in 91 isolates showed different antimicrobial resistance levels to the drugs tested with a resistance rate of 76.92%. The isolates showed the highest antimicrobial resistance rates to ampicillin (69.23%, 63/91) and trimethoprim-sulfamethoxazole (59.34%, 54/91), respectively. The multiple drug-resistant rate was 47.25% (43/91). Two mcr-1 gene and ESBL (extended-spectrum beta-lactamase) positive EAEC (enteroaggregative Escherichia coli) strains were detected. One of them was identified as serotype of O11:H6, which showed a resistance profile to 25 tested drugs referring to 10 classes, and 38 drug resistance genes were predicted by genome analysis. The other one was O16:H48 serotype, which was resistant to 21 tested drugs belonging to 7 classes and carried a new variant of mcr-1 gene (mcr-1.35). Conclusion: An overall high-level antimicrobial resistance was found among foodborne DEC isolates recovered from parts of China in 2020, and so was the MDR (multi-drug resistance) condition. MDR strains carrying multiple resistance genes such as mcr-1 gene were detected, and a new variant of mcr-1 gene was also found. It is necessary to continue with a dynamic monitoring on DEC contamination and an ongoing research into antimicrobial resistance mechanisms.
Humans ; Colistin/pharmacology* ; Anti-Bacterial Agents/pharmacology* ; Escherichia coli Infections/epidemiology* ; Escherichia coli Proteins/genetics* ; Drug Resistance, Bacterial/genetics* ; China/epidemiology* ; Escherichia coli ; Plasmids/genetics* ; Microbial Sensitivity Tests

Antimicrobial resistance has become a major public health issue of global concern. Conjugation is an important way for fast spreading drug-resistant plasmids, during which the type Ⅳ pili plays an important role. Type Ⅳ pili can adhere on the surfaces of host cell and other medium, facilitating formation of bacterial biofilms, bacterial aggregations and microcolonies, and is also a critical factor in liquid conjugation. PilV is an adhesin-type protein found on the tip of type Ⅳ pili encoded by plasmid R64, and can recognize the lipopolysaccharid (LPS) molecules that locate on bacterial membrane. The shufflon is a clustered inversion region that diversifies the PilV protein, which consequently affects the recipient recognition and conjugation frequency in liquid mating. The shufflon was firstly discovered on an IncI1 plasmid R64 and has been identified subsequently in plasmids IncI2, IncK and IncZ, as well as the pathogenicity island of Salmonella typhi. The shufflon consists of four segments including A, B, C, and D, and a specific recombination site named sfx. The shufflon is regulated by its downstream-located recombinase-encoding gene rci, and different rearrangements of the shufflon region in different plasmids were observed. Mobile colistin resistance gene mcr-1, which has attracted substantial attentions recently, is mainly located in IncI2 plasmid. The shufflon may be one of the contributors to fast spread of mcr-1. Herein, we reviewed the discovery, structure, function and prevalence of plasmid mediated shufflon, aiming to provide a theoretical basis on transmission mechanism and control strategy of drug-resistant plasmids.
Plasmids/genetics* ; Proteins/genetics* ; Bacteria/genetics* ; Recombinases ; Genes, Bacterial ; Anti-Bacterial Agents

Lysis is a common functional module in synthetic biology and is widely used in genetic circuit design. Lysis could be achieved by inducing expression of lysis cassettes originated from phages. However, detailed characterization of lysis cassettes hasn't been reported yet. Here, we first adopted arabinose- and rhamnose-inducible systems to develop inducible expression of five lysis cassettes (S₁₀₅, A52G, C51S S76C, LKD, LUZ) in Escherichia coli Top10. By measuring OD₆₀₀, we characterized the lysis behavior of strains harboring different lysis cassettes. These strains were harvested at different growth stages, induced with different concentrations of chemical inducers, or contained plasmids with different copy numbers. We found that although all five lysis cassettes could induce bacterial lysis in Top10, lysis behaviors differed a lot at various conditions. We further found that due to the difference in background expression levels between strain Top10 and Pseudomonas aeruginosa PAO1, it was hard to construct inducible lysis systems in strain PAO1. The lysis cassette controlled by rhamnose-inducible system was finally inserted into the chromosome of strain PAO1 to construct lysis strains after careful screen. The results indicated that LUZ and LKD were more effective in strain PAO1 than S₁₀₅, A52G and C51S S76C. At last, we constructed an engineered bacteria Q16 using an optogenetic module BphS and the lysis cassette LUZ. The engineered strain was capable of adhering to target surface and achieving light-induced lysis by tuning the strength of ribosome binding sites (RBSs), showing great potential in surface modification.
Rhamnose/pharmacology* ; Plasmids/genetics* ; Pseudomonas aeruginosa ; Escherichia coli/metabolism*

The construction of efficient and stable Lactobacillus expression vector is critical for strain improvement and development of customized strains. In this study, four endogenous plasmids were isolated from Lacticaseibacillus paracasei ZY-1 and subjected to functional analysis. The Escherichia coli-Lactobacillus shuttle vectors pLPZ3N and pLPZ4N were constructed by combining the replicon rep from pLPZ3 or pLPZ4, the chloramphenicol acetyltransferase gene cat from pNZ5319 and the replicon ori from pUC19. Moreover, the expression vectors pLPZ3E and pLPZ4E with the promoter P_ldh3 of lactic acid dehydrogenase and the mCherry red fluorescent protein as a reporter gene were obtained. The size of pLPZ3 and pLPZ4 were 6 289 bp and 5 087 bp, respectively, and its GC content, 40.94% and 39.51%, were similar. Both shuttle vectors were successfully transformed into Lacticaseibacillus, and the transformation efficiency of pLPZ4N (5.23×10²-8.93×10² CFU/μg) was slightly higher than that of pLPZ3N. Furthermore, the mCherry fluorescent protein was successfully expressed after transforming the expression plasmids pLPZ3E and pLPZ4E into L. paracasei S-NB. The β-galactosidase activity of the recombinant strain obtained from the plasmid pLPZ4E-lacG constructed with P_ldh3 as promoter was higher than that of the wild-type strain. The construction of shuttle vectors and expression vectors provide novel molecular tools for the genetic engineering of Lacticaseibacillus strains.
Lacticaseibacillus ; Lacticaseibacillus paracasei ; Plasmids/genetics* ; Genetic Vectors/genetics* ; Lactobacillus/genetics* ; Escherichia coli/genetics*

Leclercia adecarboxylata is a Gram-negative bacterium belonging to the Enterobacteriaceae family. To our knowledge, this is the first report of a carbapenem-resistant L. adecarboxylata strain isolated from a healthy newborn. The L. adecarboxylata strain isolated in this study carried four plasmids that may serve as reservoirs for antibiotic resistance genes. Plasmids 2 and 4 did not harbor any antimicrobial resistance genes. Plasmid 3 is a novel plasmid containing three resistance genes. The bla _IMP gene harbored in the strain was most similar to bla _IMP-79 at the nucleotide level, with a similarity of 99.4% (737/741). This case highlights the importance of considering L. adecarboxylata as a potential cause of infections in children.
Infant, Newborn ; Child ; Humans ; Female ; Enterobacteriaceae Infections/microbiology* ; Enterobacteriaceae/genetics* ; Anti-Bacterial Agents/therapeutic use* ; Plasmids

This study aimed to explore the expression changes of VASA gene in sheep testis development and to construct VASA gene knock-in vector to prepare for the study on the differentiation of sheep germ cells in vitro. The testicular tissues of 3-month-old (3M) and 9-month-old (9M) sheep which represent immature and mature stages, respectively, were collected. The differential expression of VASA gene was analyzed by quantitative real-time PCR (qPCR) and Western blotting, and the location of VASA gene was detected by immunohistochemistry. The sgRNA targeting the VASA gene was designed and homologous recombination vectors were constructed by PCR. Subsequently, plasmids were transferred into sheep ear fibroblasts. The VASA gene was activated in combination with CRISPR/dCas9 technology to further verify the efficiency of the vector. The results showed that the expression level of VASA gene increased significantly with the development of sheep testis (P < 0.01), and was mainly located in spermatocytes and round spermatids. The knock-in vector of VASA gene was constructed by CRISPR/Cas9 system, and the Cas9-gRNA vector and pEGFP-PGK puro-VASA vector were transfected into ear fibroblasts. After CRISPR/dCas9 system was activated, ear fibroblasts successfully expressed VASA gene. The results suggest that VASA gene plays a potential function in sheep testicular development and spermatogenesis, and the VASA gene knock-in vector can be constructed in vitro through the CRISPR/Cas9 system. Our results provided effective research tools for further research of germ cell development and differentiation.
Male ; Animals ; Sheep/genetics* ; CRISPR-Cas Systems/genetics* ; Gene Knock-In Techniques ; RNA, Guide, CRISPR-Cas Systems ; Plasmids ; Germ Cells

Plasmids are the most commonly used gene carriers in the field of gene synthesis and sequencing. However, the main problems faced by traditional plasmid DNA extraction technology are low extraction throughput and high production cost, so they cannot meet the growing demand. In this study, a double-magnetic-bead method (DMBM) for plasmid extraction was developed based on the principle of plasmid extraction. The effects of the input of magnetic beads, the size of plasmid DNA fragments, and the volume of bacterial on plasmid DNA extraction were explored. In addition, the quality, throughput, and cost of plasmid DNA extraction were also compared between this technique and the commercial plasmid DNA extraction kits. The results showed that the DMBM can meet the needs of extracting plasmid DNA with different cell densities and fragment lengths. Moreover, the sensitivity and quality of plasmid extraction by the DMBM method were both superior to those of the centrifugal adsorption column method. In addition, this technique could be applied on a 96-channel automated nucleic acid extractor, resulting in higher purity of the extracted plasmid DNA, 80% reduction in extraction time, and 57.1% reduction in cost. It also reduces manual operations, achieving high-throughput and low-cost plasmid DNA extraction, thus may facilitate gene synthesis and sequencing.
Plasmids/genetics* ; DNA/genetics* ; Nucleic Acids ; Genetic Techniques ; Magnetic Phenomena