Bi-FoRe: an efficient bidirectional knockin strategy to generate pairwise conditional alleles with fluorescent indicators

Gene expression labeling and conditional manipulation of gene function are important for elaborate dissection of gene function. However, contemporary generation of pairwise dual-function knockin alleles to achieve both conditional and geno-tagging effects with a single donor has not been reported. Here we first developed a strategy based on a flipping donor named FoRe to generate conditional knockout alleles coupled with fluorescent allele-labeling through NHEJ-mediated unidirectional targeted insertion in zebrafish facilitated by the CRISPR/Cas system. We demonstrated the feasibility of this strategy at sox10 and isl1 loci, and successfully achieved Cre-induced conditional knockout of target gene function and simultaneous switch of the fluorescent reporter, allowing generation of genetic mosaics for lineage tracing. We then improved the donor design enabling efficient one-step bidirectional knockin to generate paired positive and negative conditional alleles, both tagged with two different fluorescent reporters. By introducing Cre recombinase, these alleles could be used to achieve both conditional knockout and conditional gene restoration in parallel; furthermore, differential fluorescent labeling of the positive and negative alleles enables simple, early and efficient real-time discrimination of individual live embryos bearing different genotypes prior to the emergence of morphologically visible phenotypes. We named our improved donor as Bi-FoRe and demonstrated its feasibility at the sox10 locus. Furthermore, we eliminated the undesirable bacterial backbone in the donor using minicircle DNA technology. Our system could easily be expanded for other applications or to other organisms, and coupling fluorescent labeling of gene expression and conditional manipulation of gene function will provide unique opportunities to fully reveal the power of emerging single-cell sequencing technologies.

Construction of transgenic mice with specific Cre recombinase expression in the zona fasciculata in adrenal cortex / 生理学报

The adrenal gland is an important endocrine organ of human body. CYP11B1 gene was specifically expressed in the zona fasciculata in adrenal cortex. In order to better study the function of genes specifically expressed in the zona fasciculata in adrenal cortex, the mice with Cre recombinase specifically expressed in the zona fasciculata in adrenal cortex were constructed. It was then confirmed that CYP11B1 was specifically expressed in adrenal glands. Then, using CRISPR/Cas9 technique, CYP11B1-2A-GfpCre recombinant vector was constructed and subsequently injected into the fertilized eggs of mice. It was confirmed that the Cre gene was mainly expressed in the zona fasciculata in adrenal cortex of CYP11B1Cre mice by using mTmG and LacZ staining. The CYP11B1Cre mice were then mated with cystathionine γ-lyase (CTH) mice, thereby generating CTH/CYP11B1Cre mice. It was also confirmed that CTH gene in the zona fasciculata in adrenal cortex was specifically knocked out in these mice. These results suggest that transgenic mice with specific Cre recombinase expression in the zona fasciculata in adrenal cortex were constructed successfully. This animal model can be a powerful tool for the study of the function of genes expressed in the zona fasciculata in adrenal cortex.

Enfermedad por VIH, Inhibidores de integrasa y el futuro de los controladores elite, revisión bibliográfica / VIH disease, Integrase Strand Transfer Inhibitors and the future of elite controllers: bibliographic review

La Guía Colombiana de práctica clínica para la atención de la infección por VIH / Sida en adolescentes y adultos incluye como primera línea de tratamiento el uso de Inhibidores de integrasa; sin embargo, no incluye recomendaciones que soporten la decisión de tratar a los pacientes controladores elite (CE). La definición de controladores elite es confusa pues varía de un estudio a otro y se desconoce si las recomendaciones de tratamiento, se pueden aplicar a los controladores de forma similar; tampoco existen mecanismos apropiados para el seguimiento sistemático de los controladores elite cuando se inicia en ellos una terapia antirretroviral. Este artículo es una revisión bibliográfica de la información disponible sobre la definición de los pacientes controladores, y los controladores elite, su evolución clinica e inmunológica, el tratamiento y las terapias disponibles en Colombia.

The Colombian Guide to Clinical Practice for HIV / AIDS Care in Adolescents and Adults, includes as first line of treatment the use of integrase inhibitors; however, there is no information to support the decision to treat elite control patients (EC). The definition of elite controller is confusing, because of the changes in definitions between studies, and it is unknown whether these recommendations apply to these patients in a similar way; and how should be systematic follow-up of elite controllers when antiretroviral therapy is initiated. Present paper is a bibliographic review of the available information on the definition of the controllers, and elite controllers its clinical and immunological evolution, the treatment and therapies available in Colombia.

Atypical Teratoid/Rhabdoid Tumor Presenting as a Cutaneous Lesion: A Case Report / 대한피부과학회지

An atypical teratoid/rhabdoid tumor (AT/RT) is a rare malignancy occurring in the first few years of life. This tumor shows rapid growth, a poor response to treatment, and poor prognosis. Cutaneous metastases presents as hamartomatous lesions mimicking skin tags. Immunohistochemical examination shows varied patterns of expression based on the sites of the body affected. Integrase interactor-1 (INI-1) gene sequencing and loss of expression of INI-1 observed with immunostaining can confirm AT/RT. In our patient, the skin lesion was identified at birth. Histopathological examination of the skin lesion could not establish an accurate diagnosis. Two months later, the patient presented with a brain tumor. Immunohistochemical examination of the brain lesion revealed complete loss of INI-1 expression in tumor cells, and the lesion was diagnosed as AT/RT. After that, we can detect the loss of INI-1 expression in the skin on the back. We report a rare case of AT/RT affecting the brain with cutaneous metastasis diagnosed with immunohistochemical staining.

Analysis of Integrons and Antimicrobial Resistances of Multidrug Resistant Escherichia coli Isolated in Korea

Antibacterial drugs are one of the most important therapeutic agents of bacterial infections but multidrug resistant Escherichia coli (MDREC) is an increasing problem worldwide. Major resistance mechanism of MDREC is horizontal gene transfer of R plasmids harboring integrons, which the integron integrase (IntI) catalyzes gene cassette insertion and excision through site specific recombination. In this study, resistance profiles of integron harboring E. coli isolated in Korea and the genetic environments of integron gene cassettes were analyzed by PCR and direct sequencing to clarify the mechanisms of spread of integron harboring E. coli. Resistance rates of integron harboring E. coli, including β-lactams, aminoglycosides, and fluoroquinolones and MDR frequencies were significantly higher than that of E. coli without integron (p < 0.01). Majority (80%) of integron harboring E. coli showed resistance transfer by conjugation. Most (80%) of E. coli had dfrA17-aadA5 cassette array and PcH1 hybrid promoter; 16.7% of E. coli had dfrA12-orfF-aadA2 cassette array and PcW promoter. The higher prevalence of weak Pc variants among most (96.7%) of integron harboring MDREC suggests that a flexible cassette array is more important than enhanced expression. All the integrons had LexA binding motif suggests that SOS responses control the expression of these integrons. In conclusion, the genetic bases of integrons were diverse, and the spread and the expression of prevalent gene cassette arrays may be deeply related with strengths of Pc promoters in integrons. These informations will provide important knowledge to control the increase of integron harboring MDREC.

An Intrarenal Adrenocortical Carcinoma Arising in an Adrenal Rest

We describe a case of a 61-year-old Korean man who was diagnosed with renal cell carcinoma that was discovered on abdominopelvic computed tomography obtained after the patient complained of back pain. A radical nephrectomy was performed, and the surgical specimen showed a relatively well-circumscribed and yellowish lobulated hard mass. Microscopically, the tumor showed sheets and nests of hypercellular pleomorphic cells with thick fibrous septation, frequent mitoses, and areas of adrenal cortical-like tissue. Immunohistochemical staining revealed that the tumor cells were positive for inhibin-α, vimentin, synaptophysin, and melan A. It also revealed that the tumor cells were negative for pan-cytokeratin, epithelial membrane antigen, paired box 8, α-methylacyl-coenzyme A racemase, CD10, cytokeratin 7, carbonic anhydrase 9, c-Kit, renal cell carcinoma, transcription factor E3, human melanoma black 45, desmin, smooth muscle actin, S-100, chromogranin A, CD34, anaplastic lymphoma kinase, and integrase interactor 1. Based on these histopathological and immunohistochemical findings, we diagnosed the tumor as intrarenal adrenocortical carcinoma arising in an adrenal rest. Several cases of intrarenal adrenocortical carcinoma have been reported, although they are very rare. Due to its poor prognosis and common recurrence or metastasis, clinicians and pathologists must be aware of this entity.

Integrase Strand Transfer Inhibitor Resistance Mutations in Antiretroviral Treatment-naïve Patients in Korea: a Prospective, Observational Study

The present study investigated prevalence of integrase strand transfer inhibitors (INSTI) resistance mutations in HIV-1-infected antiretroviral therapy (ART)-naïve patients in Korea. From 106 plasma samples, amplification and sequencing of integrase genes was performed, and major or minor mutations were calculated by the Stanford HIV drug resistance mutation interpretation algorithm. No major INSTI resistance mutations were found, and 14 minor mutations were detected in 13 (12.3%) patients. The present data support the recommendation that routine testing for INSTI resistance mutations before starting ART is not necessary.

O papel do dolutegravir na terapia antiretroviral / The role of dolutegravir in antiretroviral therapy

os inibidores da integrase são a mais nova classe de antirretroviral aprovada, que agem impedindo a incorporação do DNA do HIV no genoma do linfócito T CD4+ (LTCD4+) do hospedeiro, limitando a propagação do vírus. o Dolutegravir e o inibidor da integrase mais moderno e como os demais inibidores apresenta de alta performance, boa tolerância; alta barreira genética para mutações de resistência, além de apresentar eficácia em pacientes já submetidos a tratamento antirretroviral anterior. Neste contexto o presente estudo trata-se de um estudo de revisão bibliográfica realizada de janeiro a junho de 2018, de artigos científicos de artigos científicos que abordam aspectos exclusivos do dolutegravir na terapia antirretroviral em comparação com outros esquemas terapêuticos. Concluindo que o tratamento com dolutegravir apresenta como principais vantagens à rápida supressão virológica; boa tolerância e alta barreira genética para mutações de resistência.

Integrase inhibitors are the newest class of approved antiretroviral drugs that act by preventing the incorporation of HIV DNA into the CD4 + T lymphocyte (LTCD4 +) genome of the host, limiting the spread of the virus. Dolutegravir and the most modern integrase inhibitor and like the other inhibitors presents high performance, good tolerance; high genetic barrier for resistance mutations, in addition to being effective in patients already submitted to previous antiretroviral treatment. In this context, the present study is a bibliographical review study conducted from January to June, 2018, of scientific papers on scientific articles dealing with exclusive aspects of dolutegravir in antiretroviral therapy compared to other therapeutic regimens. Concluding that dolutegravir treatment has the main advantages of rapid virological suppression; good tolerance and high genetic barrier for resistance mutations

Astroblastoma in a Young Female Patient: A Case Report and Literature Review of Clinicopathological, Radiological and Prognostic Characteristics and Current Treatment Strategies

Astroblastoma is an uncommon glial tumor with predominant manifestation in the young age. Herein, we report a case of 18-year-old astroblastoma female patient who presented with history of two months headache. Magnetic resonance imaging (MRI) of the brain demonstrated well circumscribed, intra-axial abnormal signal intensity lesion (size=5×4 cm²) in the right parieto-occipital region of the brain. The patient underwent complete surgical resection of the gross tumor, as confirmed by an early post-surgical MRI (i.e., within 24 hours of surgery). Histopathological examination revealed neoplastic lesion exhibiting perivascular pseudo-rosettes with centrally hyalinized blood vessel and focal nuclear pleomorphism. Immunohistochemistry staining illustrated reactivity for glial fibrillary acidic protein and integrase interactor 1 (INI-1). These features rendered the diagnosis of astroblastoma. A comprehensive review of the current literature to summarize the clinicopathological and radiological characteristics, prognostic factors and current treatment strategies of astroblastomas is also presented. Our study would expand the pool of this uncommon tumor towards its better understanding and optimal treatment.

Isolation and characterization of antimicrobial-resistant Escherichia coli from national horse racetracks and private horse-riding courses in Korea

Limited information is available regarding horse-associated antimicrobial resistant (AR) Escherichia (E.) coli. This study was designed to evaluate the frequency and characterize the pattern of AR E. coli from healthy horse-associated samples. A total of 143 E. coli (4.6%) were isolated from 3,078 samples collected from three national racetracks and 14 private horse-riding courses in Korea. Thirty of the E. coli isolates (21%) showed antimicrobial resistance to at least one antimicrobial agent, and four of the AR E. coli (13.3%) were defined as multi-drug resistance. Most of the AR E. coli harbored AR genes corresponding to their antimicrobial resistance phenotypes. Four of the AR E. coli carried class 1 integrase gene (intI1), a gene associated with multi-drug resistance. Pulsed-field gel electrophoretic analysis showed no genetic relatedness among AR E. coli isolated from different facilities; however, cross-transmissions between horses or horses and environments were detected in two facilities. Although cross-transmission of AR E. coli in horses and their environments was generally low, our study suggests a risk of transmission of AR bacteria between horses and humans. Further studies are needed to evaluate the risk of possible transmission of horse-associated AR bacteria to human communities through horse riders and horse-care workers.

In Silico Structural and Functional Annotation of Hypothetical Proteins of Vibrio cholerae O139

In developing countries threat of cholera is a significant health concern whenever water purification and sewage disposal systems are inadequate. Vibrio cholerae is one of the responsible bacteria involved in cholera disease. The complete genome sequence of V. cholerae deciphers the presence of various genes and hypothetical proteins whose function are not yet understood. Hence analyzing and annotating the structure and function of hypothetical proteins is important for understanding the V. cholerae. V. cholerae O139 is the most common and pathogenic bacterial strain among various V. cholerae strains. In this study sequence of six hypothetical proteins of V. cholerae O139 has been annotated from NCBI. Various computational tools and databases have been used to determine domain family, protein-protein interaction, solubility of protein, ligand binding sites etc. The three dimensional structure of two proteins were modeled and their ligand binding sites were identified. We have found domains and families of only one protein. The analysis revealed that these proteins might have antibiotic resistance activity, DNA breaking-rejoining activity, integrase enzyme activity, restriction endonuclease, etc. Structural prediction of these proteins and detection of binding sites from this study would indicate a potential target aiding docking studies for therapeutic designing against cholera.

Comparison of Antiretroviral Regimens: Adverse Effects and Tolerability Failure that Cause Regimen Switching

BACKGROUND: The efficacy of antiretroviral therapy (ART) has improved, and the adverse effects of antiretroviral drugs have been reduced. However, these adverse effects still significantly influence patient compliance, increasing the risk of tolerability failure. Therefore, we investigated the adverse effects and tolerability failure causing changes in the first ART regimen, and identified the regimens that were most vulnerable to switching. MATERIALS AND METHODS: We enrolled patients with human immunodeficiency virus (HIV) who commenced their first ART between January 1, 2011 and July 30, 2014. Patients who started their first ART regimen at the Kyungpook National University Hospital were included in the study if they were aged > or =18 years and were followed-up for > or =12 weeks. The primary dependent variable was the duration of treatment on the same ART regimen. We analyzed the maintenance rate of the first ART regimen based on the treatment duration between these groups using survival analysis and log rank test. The frequency of the adverse effects of ART regimens was analyzed by multiple response data analysis. RESULTS: During the investigation period, 137 patients were enrolled. Eighty-one patients were maintained on the initial treatment regimen (59.1%). In protease inhibitor (PI)-based regimen group, 54 patients were maintained on the initial treatment regimen (54/98, 55.1%). In non-nucleoside reverse transcriptase inhibitor (NNRTI)-and integrase inhibitor (II)-based regimen group, 15 (15/26, 57.7%) and 12 (12/13, 92.3%) patients were maintained on the initial treatment regimen, respectively. Adverse effects that induced ART switching included rash (16/35, 45.7%), gastrointestinal discomfort or pain (7/35, 20%), diarrhea (7/35, 20%), hyperbilirubinemia (6/35, 17.1%), headache or dizziness (3/35, 8.5%). Among the treatment regimens, the group receiving an II-based regimen showed the least switching. The group receiving PI-and NRTI-based regimens were most likely to switch due to adverse effects during the early treatment period. However, after about 18 months, switching was rarely observed in these groups. Among the PI drugs, darunavir/ritonavir showed fewer drug changes than atazanavir/ritonavir (P = 0.004, log rank test) and lopinavir/ritonavir (P = 0.010). Among the NNRTI drugs, rilpivirne produced less switching than efavirenz (P = 0.045). CONCLUSION: Adverse effects to ART resulted in about a quarter of patients switching drugs during the early treatment period. II-based regimens were advantageous because they were less likely to induce switching within 18 months of treatment commencement. These findings indicated the importance of considering and monitoring the adverse effects of ART in order to improve adherence.

The Incidence and Clinical Characteristics of Acute Serum Creatinine Elevation more than 1.5 mg/dL among the Patients Treated with Tenofovir/Emtricitabine-containing HAART Regimens

BACKGROUND: The combination of tenofovir disoproxil fumarate (TDF) and emtricitabine (FTC) has been the first choice nucleoside reverse transcriptase inhibitor (NRTI) according to many reliable antiretroviral treatment (ART) guidelines because of its high efficacy. However, TDF-related renal toxicity reported in Western countries is a challenging issue regarding clinical use. We conducted this study to evaluate the incidence and characteristics of an acute increase in serum creatinine (Cr) level > 1.5 mg/dL among TDF/FTC-based highly active antiretroviral treatment (HAART)-treated patients. MATERIALS AND METHODS: We retrospectively reviewed the medical records of 205 HIV-infected patients treated with TDF/FTC-containing regimens between 1 February 2010 and 30 April 2014. Three groups of TDF/FTC + ritonavir-boosted protease inhibitor (PI/r), TDF/FTC + non-nucleoside reverse transcriptase inhibitor (NNRTI), and TDF/FTC + integrase strand transfer inhibitor (INSTI), and three PI/r subgroups of TDF/FTC + lopinavir (LPV)/r, TDF/FTC + atazanavir (ATV)/r, TDF/FTC + darunavir (DRV)/r were evaluated. RESULTS: A total 136 patients (91 in the TDF/FTC + PI/r group, 20 in the TDF/FTC + NNRTI group and 25 in the TDF/FTC + INSTI group) were included in the statistical analysis. Four cases (4.9%; all in the TDF/FTC + PI/r group) among 136 patients showed an acute increase in serum Cr more than 1.5 mg/dL, so the overall incidence was 2.8 cases per 100 patient-years. One case was a patient treated with TDF/FTC + LPV/r, and the others were treated with TDF/FTC + ATV/r. No case of an acute increase in serum Cr was observed in the TDF/FTC + DRV/r group. The incidence of serum Cr increase more than 1.5 mg/dL in TDF/FTC + PI/r group was 4.0 cases per 100 patient-years. CONCLUSION: Although only a small number of patients were evaluated retrospectively from a single center, the TDF/FTC + PI/r regimen may have been related with relatively higher tendency of increment of serum Cr level. These findings reinforce the importance of close follow-ups of HIV-infected patients treated with the TDF/FTC + PI/r regimens.

Phylogenetic grouping and pathotypic comparison of urine and fecal Escherichia coli isolates from children with urinary tract infection

The aim of this study was to investigate the phylogenetic background and to assess hlyD (involved in the secretion of haemolysin A) and intll (encoding a class 1 integrase) in Escherichia coli isolates derived from urinary and fecal specimens. A total of 200 E. coli isolates was collected from patients presenting with urinary tract infection (UTI) during September 2009 to September 2010 and screened for hlyD and intll genes by polymerase chain reaction (PCR). Phylogenetic analysis showed that E. coli is composed of four main phylogenetic groups (A, B1, B2 and D) and that uropathogenic E. coli (UPEC) isolates mainly belong to groups B2 (54%) and D (34%) whereas group A (44%) and D (26%) are predominant among commensal E. coli isolates. In this study, hlyD was present in 26% of UPEC and 2% of commensal E. coli isolates. However, hemolytic activity was detected for 42% of UPEC and 6% of commensal E. coli isolates (p < 0.05). intll gene was more frequently expressed in UPEC (24%) in comparison with commensal E. coli isolates (12%). Resistance to aztreonam, co-trimoxazole and cefpodoxime were frequently found among UPEC isolates whereas commensal E. coli isolates were commonly resistant to co-trimoxazole, nalidixic acid and cefotaxime. Concluding, a considerable difference between UPEC and commensal E. coli isolates was observed regarding their phylogenetic groups, presence of class 1 integron and hlyD gene, hemolysin activity and resistance pattern. The detection of class 1 integrons and hlyD gene was higher among UPEC compared with commensal E. coli isolates. These findings may contribute for a better understanding of the factors involved in the pathogenesis of UPEC.

Commonly used cre transgenic mice and their applications in hematopoietic system / 中国实验血液学杂志

Cre-lox recombination system consists of two elements: Cre recombinase enzyme and lox sites. Cre recombinase can recombine the lox site sequences by specifically detecting and cutting them. The direction and position of lox sites determine the functional effects of Cre enzyme such as deletion, inversion or chromosomal translocation. The hematopoietic system of mouse consists of multi-lineages and various developmental stage hematopoietic cells that are differentiated from hematopoietic stem cells (hematopoietic stem cells, HSC). The hematopoietic stem cells are maintained in the bone marrow microenvironment (niche). Currently, a variety of floxed conditional-knockout mice, recognized by Cre-lox recombination system, are used for the study of the hematopoietic system. This review summarizes the commonly used Cre transgenic mice and their applications in the study of hematopoietic system.

Loop-mediated isothermal amplification assays for screening of bacterial integrons

BACKGROUND: The occurrence and prevalence of integrons in clinical microorganisms and their role played in antimicrobial resistance have been well studied recently. As screening and detection of integrons are concerned, current diagnostic methodologies are restricted by significant drawbacks and novel methods are required for integrons detection. RESULTS: In this study, three loop-mediated isothermal amplification (LAMP) assays targeting on class 1, 2 and 3 integrons were implemented and evaluated. Optimization of these detection assays were performed, including studing on the reaction temperature, volume, time, sensitivity and specificity (both primers and targets). Application of the established LAMP assays were further verified on a total of 1082 isolates (previously identified to be 397 integron-positive and 685 integron-negative strains). According to the results, the indispensability of each primer had been confirmed and the optimal reaction temperature, volume and time were found to be 65°C, 45 min and 25 µL, respectively. As application was concerned, 361, 28 and 8 isolates carrying intI1, intI2 and intI3 yielded positive amplicons, respectively. Other 685 integron-negative bacteria were negative for the integron-screening LAMP assays, totaling the detection rate and specificity to be 100%. CONCLUSIONS: The intI1-, intI2- and intI3-LAMP assays established in this study were demonstrated to be the valid and rapid detection methodologies for the screening of bacterial integrons.

Antimicrobial Resistance Patterns and Integron Carriage of Escherichia coli Isolates Causing Community-Acquired Infections in Turkey

We aimed to observe antimicrobial resistance patterns and integron carriage of Escherichia coli isolates causing community-acquired infections. Two hundred sixty-eight E. coli strains were obtained from outpatients with various infections at different polyclinics at the 82nd Year of State Hospital in Rize, Turkey. Susceptibility to antimicrobials was tested using a disk diffusion method. The presence of integrons was examined using PCR with specific primers. Positive PCR results were confirmed by sequencing. A broth mating method was used for conjugation assays. Extragenic palindromic-PCR was performed using the oligonucleotide primer BOXA1R. Resistance frequency for ampicillin, trimethoprim/sulfamethoxazole, and tetracycline was determined as 50.6%, 33.5%, and 36.8% respectively. No strains were resistant to amikacin. Seventy isolates were positive for the intI1 gene, of which 49 carried gene cassettes. Eleven isolates were positive for the intI2 gene, eight of which carried gene cassettes. Seven gene cassettes (dfrA1, dfrA5, dfrA7, dfrA17, aadA1, aadA5, and sat2) were predominantly harbored in integrons. We detected conjugative plasmids harboring integrons in two E. coli strains. Four strain clusters were yielded by BOX-PCR fingerprints showing that they were clonally related. No apparent relationship occurred among class 1 and 2 integron-carrying strains. We conclude that integrons are widespread in genetically variable E. coli strains and will continue to mediate dissemination of resistance genes in the community.

Optimizing the host bacteria to make a large naive phage antibody library in the recombination system / 药学学报

To prepare large naive phage antibody library, the host bacteria with high transformation efficiency is used in the Cre-LoxP recombination system. The variable regions of immunoglobulin light and heavy genes were amplified from lymphocytes collected from adult peripheral blood and newborn cord blood. The genes were spliced to form the single-chain variable fragments (scFv) by overlap PCR, cloned into pDAN5a vector and then transformed into XL2-blue MRF' with the Hte gene. Compared with XL1-blue strain, the size of the primary library was increased by 3.9 times. The primary library infected Cre recombinase-expressing bacteria, and the genes between phagemids created many new VH/VL combinations. The library was calculated to have a diversity of 1.7 x 10(11) and validated by the selection of antibodies against six different protein antigens. This library provides the basis for further selection of antibody-based drugs. It is the first time to report that XL2-blue MRF' can be used to improve the diversity of the library in the recombination system.

Cloning, expression, and in vitro functional activity assay of phiC31 integrase cDNA in Escherichia coli

The aim of present study was cloning and expression of phiC31 integrase cDNA in a bacterial expression vector. Thus, an intra molecular assay vector was applied to show in vitro activity of recombinant protein. In this experimental study, phiC31 cDNA was subcloned into a prokaryotic expression vector and transformed into E.coli Bl21 [DE3]. Recombinant phiC31 integrase was purified form the bacterial cell lysates and its activity was verified by an in vitro functional assessment. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis [SDS-PAGE] of the purified phiC31 integrase confirmed the size of protein [70 kDa]. Finally, the functionality of purified phiC31 integrase was verified. The results of this study indicated that the purified integrase has a great potential application for in vitro site-specific integration

Molecular Epidemiology of Integron-Associated Antimicrobial Gene Cassettes in the Clinical Isolates of Acinetobacter baumannii from Northern Taiwan

BACKGROUND: The aims of this study were to understand the molecular epidemiology of integron-associated gene cassettes in Acinetobacter baumannii across four hospitals in northern Taiwan and to clarify the relationship between the presence of integrons and antibiotic-resistant phenotypes. METHODS: Sixty-five A. baumannii isolates, collected from the patients of four regional hospitals in northern Taiwan in 2009, were tested for the presence of integrons and their associated gene cassettes. The susceptibility difference between integron-positive and integron-negative A. baumannii strains was analyzed. Antibiotic-resistant phenotypes among A. baumannii with different types of gene cassette array combinations were also compared. RESULTS: Around 72% of the A. baumannii isolates carried class 1 integrase genes. Despite this, only three gene cassette arrays were found in the integrons. Integron-positive strains were significantly more resistant to all the tested antibiotics than the integrase-negative strains. All the four types of A. baumannii with different gene cassette array combinations were multidrug-resistant in nature. Gene cassette array aacA4-catB8-aadA1 existed in all the integron-positive A. baumannii isolates. Repetitive-sequence-based PCR (rep-PCR) results revealed the prevalence of one major cluster of imipenem-resistant A. baumannii strains (84%) in the four regional hospitals. CONCLUSIONS: The presence of integrons with associated antimicrobial resistance gene cassettes can be used as a representative marker of multidrug resistance in A. baumannii. Some prevalent gene cassette arrays may exist among epidemiologically unrelated A. baumannii strains.