Rapid and sensitive detection of lower respiratory tract infections by stuffer-free multiplex ligation-dependent probe amplification

Sensitive detection of viable salmonella bacteria based on tertiary cascade signal amplification via splintR ligase ligation-PCR amplification-CRISPR/Cas12a cleavage

Several viable Salmonella bacteria are capable of causing severe human diseases and huge economic losses. In this regard, viable Salmonella bacteria detection techniques that can identify small numbers of microbial cells are highly valuable. Here, we present a detection method (referred to as SPC) based on the amplification of tertiary signals using splintR ligase ligation, PCR amplification and CRISPR/Cas12a cleavage. The detection limit of the SPC assay was 6 copies (HilA RNA) and 10 CFU (cell). Based on Intracellular HilA RNA detection, this assay can be used to distinguish between viable and dead Salmonella. In addition, it is able to detect multiple serotypes of Salmonella and has been successfully used to detect Salmonella in milk or isolated from farms. Overall, this assay is a promising test for viable pathogens detection and biosafety control.

Advances of multiplex ligation-dependent probe amplification technology in molecular diagnostics

Multiplex ligation-dependent probe amplification (MLPA) is a multiplex copy number analysis tool which is routinely used to detect large mutations in genetic diseases. With continuous modifications, MLPA has been extended for the detection of DNA methylation variation, single nucleotide polymorphisms, chromosome abnormalities and other forms of genomic variation. The combination with other techniques has even enlarged the application of MLPA in molecular diagnostics of various human diseases. In this review, the principle of MLPA-based techniques as well as their main and latest applications in clinical detection are described. It is believed that with improved automation, increased multiplexing, lower cost and the combination with other technologies, MLPA will play an increasingly important role in molecular diagnosis of human disease.

Programmable Ligation-Transcription Circuit-Driven Cascade Amplification Machinery for Multiple Long Noncoding RNAs Detection in Lung Tissues

The measurement of long noncoding RNAs (lncRNAs) is essential to diagnosis and treatment of various diseases such as cancers. Herein, we develop a simple method to simultaneously detect multiple lncRNAs using programmable ligation-transcription circuit-driven cascade amplification and single-molecule counting. The presence of targets lncRNA HOTAIR and lncRNA MALAT1 activates the ligation-transcription circuits to produce two corresponding functional RNAs. The functional RNAs then cyclically initiate the digestion of signal probes by duplex-specific nuclease to liberate Cy5 and Cy3 molecules. After magnetic separation, the liberated Cy5 and Cy3 molecules are measured by single-molecule counting. In this assay, a single lncRNA can activate ligation-transcription circuit to generate abundant functional RNAs, endowing this assay with high sensitivity. Integration of single-molecule counting ensures the high sensitivity. This method shows extremely high sensitivity with a limit of detection (LOD) of 0.043 aM for HOX gene antisense intergenic RNA (lncRNA HOTAIR) and 0.126 aM for mammalian metastasis-related lung adenocarcinoma transcript 1 (lncRNA MALAT1). Importantly, this method enables simultaneous measurement of multiple endogenous lncRNAs at the single-cell level, and it may discriminate the expressions of various lncRNA in lung tumor tissues of nonsmall cell lung cancer (NSCLC) patients and their corresponding healthy adjacent tissues, offering a promising platform for clinical diagnosis and biomedical research.

Sensitive fluorescence detection of SARS-CoV-2 RNA in clinical samples via one-pot isothermal ligation and transcription

The control of viral outbreaks requires nucleic acid diagnostic tests that are sensitive, simple and fast. Here, we report a highly sensitive and specific one-pot assay for the fluorescence-based detection of RNA from pathogens. The assay, which can be performed within 30-50 min of incubation time and can reach a limit of detection of 0.1-attomolar RNA concentration, relies on a sustained isothermal reaction cascade producing an RNA aptamer that binds to a fluorogenic dye. The RNA aptamer is transcribed by the T7 RNA polymerase from the ligation product of a promoter DNA probe and a reporter DNA probe that hybridize with the target single-stranded RNA sequence via the SplintR ligase (a Chlorella virus DNA ligase). In 40 nasopharyngeal SARS-CoV-2 samples, the assay reached positive and negative predictive values of 95 and 100%, respectively. We also show that the assay can rapidly detect a range of viral and bacterial RNAs.

Multiplex identification of sepsis-causing Gram-negative pathogens from the plasma of infected blood

Early and accurate detection of bacterial pathogens in the blood is the most crucial step for sepsis management. Gram-negative bacteria are the most common organisms causing severe sepsis and responsible for high morbidity and mortality. We aimed to develop a method for rapid multiplex identification of clinically important Gram-negative pathogens and also validated whether our system can identify Gram-negative pathogens with the cell-free plasm DNA from infected blood. We designed five MLPA probe sets targeting the genes specific to major Gram-negative pathogens (uidA and lacY for E. coli, ompA for A. baumannii, phoE for K. pneumoniae, and ecfX for P. aeruginosa) and one set targeting the CTX-M group 1 to identify the ESBL producing Gram-negative pathogens. All six target-specific peaks were clearly separated without any non-specific peaks in a multiplex reaction condition. The minimum detection limit was 100 fg of pathogen DNA. When we tested 28 Gram-negative clinical isolates, all of them were successfully identified without any non-specific peaks. To evaluate the clinical applicability, we tested seven blood samples from febrile patients. Three blood culture positive cases showed E. coli specific peaks, while no peak was detected in the other four culture negative samples. This technology can be useful for detection of major sepsis-causing, drug-resistant Gram-negative pathogens and also the major ESBL producing Gram-negatives from the blood of sepsis patients in a clinical setting. This system can help early initiation of effective antimicrobial treatment against Gram-negative pathogens for sepsis patients, which is very crucial for better treatment outcomes.

Multiplex identification of drug-resistant Gram-positive pathogens using stuffer-free MLPA system

Early detection of pathogens from blood and identification of their drug resistance are essential for sepsis management. However, conventional culture-based methods require relatively longer time to identify drug-resistant pathogens, which delays therapeutic decisions. For precise multiplex detection of drug-resistant Gram-positive pathogens, we developed a method by using stuffer-free multiplex ligation-dependent probe amplification (MLPA) coupled with high-resolution CE single-strand conformation polymorphisms (CE-SSCP) system. We designed three probe sets for genes specific to Gram-positive species (Staphylococcus aureus: nuc, Enterococcus faecium: sodA, and Streptococcus pneumoniae: lytA) and two sets for genes associated with drug resistance (mecA and vanA) to discriminate major Gram-positive pathogens with the resistance. A total of 94 different strains (34 reference strains and 60 clinical isolates) were used to validate this method and strain-specific peaks were successfully observed for all the strains. To improve sensitivity of the method, a target-specific preamplification step was introduced and, consequently, the sensitivity increased from 10 pg to 100 fg. We also reduced a total assay time to 8 h by optimizing hybridization time without compromising test sensitivity. Taken together, our multiplex detection system can improve detection of drug-resistant Gram-positive pathogens from sepsis patients' blood.

Capillary electrophoresis applied to DNA: determining and harnessing sequence and structure to advance bioanalyses (2009-2014)

This review of capillary electrophoresis methods for DNA analyses covers critical advances from 2009 to 2014, referencing 184 citations. Separation mechanisms based on free-zone capillary electrophoresis, Ogston sieving, and reptation are described. Two prevalent gel matrices for gel-facilitated sieving, which are linear polyacrylamide and polydimethylacrylamide, are compared in terms of performance, cost, viscosity, and passivation of electroosmotic flow. The role of capillary electrophoresis in the discovery, design, and characterization of DNA aptamers for molecular recognition is discussed. Expanding and emerging techniques in the field are also highlighted.