RESUMO
BackgroundThe SARS-CoV-2 outbreak urgently requires sensitive and convenient COVID-19 diagnostics for the containment and timely treatment of patients. We aimed to develop and validate a novel reverse transcription loop-mediated isothermal amplification (RT-LAMP) assay to detect SARS-CoV-2 in qualified laboratories and point-of-care settings. MethodsPatients with suspected COVID-19 and close contacts were recruited from two hospitals between Jan 26 and April 8, 2020. Respiratory samples were collected and tested using the RT-LAMP assays, and the results were compared with those obtained by RT-qPCR. Samples yielding inconsistent results between these two methods were subjected to next-generation sequencing for confirmation. The RT-LAMP assay was also tested on an asymptomatic COVID-19 carrier and patients with other respiratory viral infections. ResultsSamples were collected from a cohort of 129 cases (329 nasopharyngeal swabs) and an independent cohort of 76 patients (152 nasopharyngeal swabs and sputum samples). The RT-LAMP assay was validated to be accurate (overall sensitivity and specificity: 88.89% and 99.00%; positive and negative predictive values: 94.74% and 97.78%, respectively) and diagnostically useful (positive and negative likelihood ratios: 88.89 and 0.11, respectively). RT-LAMP showed an increased sensitivity (88.89% vs 81.48%) and high consistency (kappa 0.92) compared with RT-qPCR for SARS-CoV-2 screening while requiring only constant temperature heating and visual inspection. The time required for RT-LAMP was less than 1 h from sample preparation to result. In addition, RT-LAMP was feasible for use with asymptomatic patients and did not cross-react with other respiratory pathogens. ConclusionThe developed RT-LAMP assay offers rapid, sensitive and straightforward detection of SARS-CoV-2 infection and could aid the expansion of COVID-19 testing in the public domain and hospitals.
RESUMO
Objective To evaluate the regulatory role of azithromycin-induced persistent Chlamydia trachomatis (Ct) infection in the apoptosis of Hela229 cells.Methods Hela229 cells were firstly co-cultured with Ct for 22 hours,and then cultured with Dulbecco's modified Eagle's medium (DMEM) containing 0.08 mg/L azithromycin for 26 hours to establish a cell model of persistent Ct infection (persistent infection group).These infected Hela229 cells cultured with azithromycin-free DMEM served as a cell model of acute Ct infection (acute infection group).After 48-hour infection with Ct,azithromycin was removed,and infected Hela229 cells in the above 2 groups were successively cultured with DMEM for the resurgence of Ct.Immunofluorescence assay and electron microscopy were performed to verify the persistent Ct infection model.The Hela229 cells in the persistent infection group and acute infection group as well as uninfected Hela229 cells (control group) were treated with staurosporine (STS) for 4 hours to induce the apoptosis,and then cell apoptosis was detected by Hoechst 33258 staining,annexin V/propidium iodide staining and flow cytometry.Results After the treatment with azithromycin,atypical inclusions with aberrant reticulate bodies appeared in the Ct-infected cells.After removing azithromycin,cells were cultured until 96 hours after infection,and infectious elementary bodies reappeared in the Ct inclusions.After the treatment with STS,Hoechst staining showed that there was loose chromatin in the persistently infected cells,while chromatin condensation was observed in the uninfected cells.After 24-hour infection with Ct and 4-hour induction with STS,the apoptosis rate was significantly higher in the persistent infection group (45.567％ ± 2.631％) than in the acute infection group (38.567％ ± 1.701％,t =2.686,P =0.028),but significantly lower in the persistent infection group than in the uninfected group (69.800％ ± 2.835％,t =8.187,P ＜ 0.001).After 48-hour infection with Ct and 4-hour induction with STS,there was a significant difference in the apoptosis rate between the persistent infection group (46.700％ ± 5.257％) and acute infection group (61.767％ ± 1.815％,t =5.781,P ＜ 0.001),as well as between the persistent infection group and the uninfected group (68.667％ ± 3.156％,t =7.421,P ＜ 0.001).Conclusion This study showed that azithromycin-induced persistent Ct infection regulated the apoptosis of host cells,and this effect lasted 48 hours.
