Identification and architecture of a putative secretion tube across mycobacterial outer envelope

Tuberculosis-causing mycobacteria have thick cell-wall and capsule layers that are formed from complex structures. Protein secretion across these barriers depends on a specialized protein secretion system, but none has been reported. We show that Mycobacterium tuberculosis Rv3705c and its homologous MSMEG_6251 in Mycobacterium smegmatis are tube-forming proteins in the mycobacterial envelope (TiME). Crystallographic and cryo-EM structures of these two proteins show that both proteins form rotationally symmetric rings. Two layers of TiME rings pack together in a tail-to-tail manner into a ring-shaped complex, which, in turn, stacks together to form tubes. M. smegmatis TiME was detected mainly in the cell wall and capsule. Knocking out the TiME gene markedly decreased the amount of secreted protein in the M. smegmatis culture medium, and expression of this gene in knocked-out strain partially restored the level of secreted protein. Our structure and functional data thus suggest that TiME forms a protein transport tube across the mycobacterial outer envelope.

Large-Scale, In-House Production of Viral Transport Media To Support SARS-CoV-2 PCR Testing in a Multihospital Health Care Network during the COVID-19 Pandemic

ABSTRACT The COVID-19 pandemic has severely disrupted worldwide supplies of viral transport media (VTM) due to widespread demand for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) reverse transcription-PCR (RT-PCR) testing. In response to this ongoing shortage, we began production of VTM in-house in support of diagnostic testing in our hospital network. As our diagnostic laboratory was not equipped for reagent production, we took advantage of space and personnel that became available due to closure of the research division of our medical center. We utilized a formulation of VTM described by the CDC that was simple to produce, did not require filtration for sterilization, and used reagents that were available from commercial suppliers. Performance of VTM was evaluated by several quality assurance measures. Based on cycle threshold (CT) values of spiking experiments, we found that our VTM supported highly consistent amplification of the SARS-CoV-2 target (coefficient of variation = 2.95%) using the Abbott RealTime SARS-CoV-2 Emergency Use Authorization (EUA) assay on the Abbott m2000 platform. VTM was also found to be compatible with multiple swab types and, based on accelerated stability studies, able to maintain functionality for at least 4 months at room temperature. We further discuss how we met logistical challenges associated with large-scale VTM production in a crisis setting, including use of a staged assembly line for VTM transport tube production.

Large-scale, in-house production of viral transport media to support SARS-CoV-2 PCR testing in a multi-hospital healthcare network during the COVID-19 pandemic

The COVID-19 pandemic has severely disrupted worldwide supplies of viral transport media (VTM) due to widespread demand for SARS-CoV-2 RT-PCR testing. In response to this ongoing shortage, we began production of VTM in-house in support of diagnostic testing in our hospital network. As our diagnostic laboratory was not equipped for reagent production, we took advantage of space and personnel that became available due to closure of the research division of our medical center. We utilized a formulation of VTM described by the CDC that was simple to produce, did not require filtration for sterilization, and used reagents that were available from commercial suppliers. Performance of VTM was evaluated by several quality assurance measures. Based on Ct values of spiking experiments, we found that our VTM supported highly consistent amplification of the SARS-CoV-2 target (coefficient of variation = 2.95%) using the Abbott RealTime SARS-CoV-2 EUA assay on the Abbott m2000 platform. VTM was also found to be compatible with multiple swab types and, based on accelerated stability studies, able to maintain functionality for at least four months at room temperature. We further discuss how we met logistical challenges associated with large-scale VTM production in a crisis setting including use of staged, assembly line for VTM transport tube production.

Performance evaluation of three rapid antigen tests for the diagnosis of group AStreptococci

ObjectiveTo compare the diagnostic performance of three rapid antigen detection tests (RADTs) for group AStreptococcus(GAS).DesignA hospital-based, cross-sectional, retrospective study.SettingA comparative study of rapid diagnostic tests for GAS using clinical specimens in a single institute.Participants225 children in the outpatient clinics ofKorea University Guro Hospitalwith suspicious symptoms were subjected to throat swab sampling. A dual-swab applicator was used. Samples were stored at below −70°C in a 10 mL transport tube containing 1 mL liquid Stuart’s transport medium.Outcome measuresAll tests were performed in the laboratory by trained clinical laboratory scientists. Sensitivity, specificity, accuracy and kappa index of three RADTs were compared with the reference PCR test and culture results.ResultsOf the 225 patients suspected of having GAS, 67 and 90 were positive for GAS in the culture and PCR tests, respectively. Compared with the reference culture, the sensitivity for GAS was 92.5% (CI 83.4 to 97.5), 71.6% (CI 59.3 to 81.9) and 74.63% (CI 62.5 to 84.4) for careUS Strep A Plus, SD Bioline and BD Veritor, respectively, and the specificity was 97.0% (CI 93.1 to 99.0), 94.6% (CI 90.1 to 97.5) and 92.9% (CI 87.8 to 96.2) for careUS Strep A Plus, SD Bioline and BD Veritor, respectively. Compared with the reference GAS real-time PCR, the sensitivity was 73.3% (CI 62.9 to 82.1), 63.3% (CI 52.5 to 73.2) and 67.8% (CI 57.1 to 77.2) for careUS Strep A Plus, SD Bioline and BD Veritor, respectively, and the specificity was 99.3% (CI 95.9 to 99.9), 100.0% (CI 97.3 to 100.0) and 99.3% (CI 95.9 to 99.9) for careUS Strep A Plus, SD Bioline and BD Veritor, respectively.ConclusionsThe careUS Strep A Plus is a useful test that showed highly comparable results with those of the culture test and superior performances among the three RADTs. The use of RADTs should be encouraged to provide acceptable and fast results using simple equipment.

A Novel Analytical Modeling of a Loop Heat Pipe Employing the Thin-Film Theory: Part I—Modeling and Simulation

In this study, steady-state analytical modeling of a loop heat pipe (LHP) equipped with a flat evaporator is presented to predict the temperatures and pressures at each important part of the LHP—evaporator, liquid reservoir (compensation chamber), vapor-transport tube, liquid-transport tube, and condenser. Additionally, this study primarily focuses on analysis of the evaporator—the only LHP component comprising a capillary structure. The liquid thin-film theory is considered to determine pressure and temperature values concerning the region adjacent to the liquid-vapor interface within the evaporator. The condensation-interface temperature is subsequently evaluated using the modified kinetic theory of gases. The present study introduces a novel method to estimate the liquid temperature at the condensation interface. Existence of relative freedom is assumed with regard to the condenser configuration, which is characterized by a simplified liquid–vapor interface. The results obtained in this study demonstrate the effectiveness of the proposed steady-state analytical model with regard to the effect of design variables on LHP heat-transfer performance. To this end, the condenser length, porosity of its capillary structure, and drop in vapor temperature therein are considered as design variables. Overall, the LHP thermal performance is observed to be reasonably responsive to changes in design parameters.