Development of uracil-DNA-glycosylase-supplemented loop-mediated isothermal amplification coupled with nanogold probe (UDG-LAMP-AuNP) for specific detection of Pseudomonas aeruginosa

A colorimetric loop-mediated isothermal amplification assay (c-LAMP) for rapid detection of Pythium insidiosum

Pythiosis, caused by Pythium insidiosum, is a severe infectious disease affecting humans and animals worldwide. There is an urgent need for a simple and rapid detection method for pythiosis, especially in remote areas where this disease is prevalent. To address this, a colorimetric loop-mediated isothermal amplification assay (c-LAMP) using hydroxynaphthol blue dye as a color indicator has been developed. This method utilized a one-step closed-tube system under a single temperature reaction to detect P. insidiosum, minimizing DNA carry-over contamination and eliminating the need for expensive tools. The test result can be easily read through the color change from violet (negative) to sky blue (positive). When tested with DNA samples from P. insidiosum (n = 51) and other fungi (n = 70), c-LAMP showed a detection sensitivity, specificity, and accuracy of 100.0 %, 95.7 %, and 97.5 %, respectively. The assay detection limit was 1 x 10-5 ng of DNA template, 10,000 times lower than the reference multiplex PCR assay (m-PCR). c-LAMP also showed a faster assay turnaround time, taking only 65 min, as opposed to the 180 min required for m-PCR. This newly established c-LAMP is rapid, cost-effective, and efficient, making it a promising tool for detecting P. insidiosum in resource-limited laboratories.

Rapid, sensitive, and user-friendly detection of Pseudomonas aeruginosa using the RPA/CRISPR/Cas12a system

BACKGROUND

Pseudomonas aeruginosa (P. aeruginosa) is a life-threatening bacterium known for its rapid development of antibiotic resistance, posing significant challenges in clinical treatment, biosecurity, food safety, and environmental monitoring. Early and accurate identification of P. aeruginosa is crucial for effective intervention.

METHODS

The lasB gene of P. aeruginosa was selected as the target for the detection. RPA primers for recombinase polymerase amplification (RPA) and crRNA for CRISPR/Cas12a detection were meticulously designed to target specific regions within the lasB gene. The specificity of the RPA/CRISPR/Cas12a detection platform was assessed using 15 strains. The detection limit of RPA/CRISPR/Cas12a detection platform was determined by utilizing a pseudo-dilution series of the P. aeruginosa DNA. The practical applicability of the RPA/CRISPR/Cas12a detection platform was validated by comparing it with qPCR on 150 samples (35 processed meat product samples, 55 cold seasoned vegetable dishes, 60 bottled water samples).

RESULTS

The RPA/CRISPR/Cas12a detection platform demonstrates high specificity, with no cross-reactivity with non-P. aeruginosa strains. This assay exhibits remarkable sensitivity, with a limit of detection (LOD) of 100 copies/µL for fluorescence assay and 101 copies/µL for the LFTS method. Furthermore, the performance of the RPA/CRISPR/Cas12a detection platform is comparable to that of the well-established qPCR method, while offering advantages such as shorter reaction time, simplified operation, and reduced equipment requirements.

CONCLUSIONS

The RPA/CRISPR/Cas12a detection platform presents a straightforward, accurate, and sensitive approach for early P. aeruginosa detection and holds great promise for diverse applications requiring rapid and reliable identification.

High Fidelity Machine-Learning-Assisted False Positive Discrimination in Loop-Mediated Isothermal Amplification Using Nanopore-Based Sizing and Counting

Loop-mediated isothermal amplification (LAMP) is a rapid, sensitive, and cost-effective method for developing point-of-care nucleic acid testing due to its isothermal nature. Yet, LAMP can suffer from the issue of false positives, which can compromise the specificity of the results. LAMP false positives typically arise due to contamination, nonspecific amplification, and nonspecific signal reporting (intercalating dyes, colorimetric, turbidity, etc.). While dye-labeled primers or probes have been introduced for multiplexed detection and enhanced specificity in LAMP assays, they carry the risk of reaction inhibition. This inhibition can result from the labeled primers with fluorophores or quenchers and probes that do not fully dissociate during reaction. This work demonstrated a nanopore-based system for probe-free LAMP readouts by employing amplicon sizing and counting, analogous to an electronic version of gel electrophoresis. We first developed a model to explore LAMP kinetics and verified distinct patterns between true and false positives via gel electrophoresis. Subsequently, we implemented nanopore sized counting and calibrated the event charge deficit (ECD) values and frequencies to ensure a fair analysis of amplicon profiles. This sized counting method, integrated with machine learning, achieved 91.67% accuracy for false positive discrimination, enhancing LAMP's reliability for nucleic acid detection.

Investigation and validation of labelling loop mediated isothermal amplification (LAMP) products with different nucleotide modifications for various downstream analysis

Loop mediated isothermal amplification (LAMP) is one of the best known and most popular isothermal amplification methods. It's simplicity and speed make the method particularly suitable for point-of-care diagnostics. Nevertheless, false positive results remain a major drawback. Many (downstream) applications are known for the detection of LAMP amplicons like colorimetric assays, in-situ LAMP or CRISPR-Cas systems. Often, modifications of the LAMP products are necessary for different detection applications such as lateral flow assays. This is usually achieved with pre-modified primer. The aim of this study is to evaluate amplicon labelling with different modified nucleotides such as Cy5-dUTP, biotin-dUTP and aminoallyl-dUTP as an alternative to pre-labelled primers. To realise this, the effects on amplification and labelling efficiency were studied as a function of molecule size and nucleotide amount as well as target concentration. This research shows that diverse labelling of LAMP amplicons can be achieved using different, modified nucleotides during LAMP and that these samples can be analysed by a wide range of downstream applications such as fluorescence spectroscopy, gel electrophoresis, microarrays and lateral flow systems. Furthermore, microarray-based detection and the ability to identify and distinguish false positives were demonstrated as proof of concept.

Development of Loop-Mediated Isothermal Amplification Rapid Diagnostic Assays for the Detection of Klebsiella pneumoniae and Carbapenemase Genes in Clinical Samples

Klebsiella pneumoniae is an important pathogenic bacterium commonly associated with human healthcare and community-acquired infections. In recent years, K. pneumoniae has become a significant threat to global public and veterinary health, because of its high rates of antimicrobial resistance (AMR). Early diagnosis of K. pneumoniae infection and detection of any associated AMR would help to accelerate directed therapy and reduce the risk of the emergence of multidrug-resistant isolates. In this study, we identified three target genes (yhaI, epsL, and xcpW) common to K. pneumoniae isolates from both China and Europe and designed loop-mediated isothermal amplification (LAMP) assays for the detection of K. pneumoniae in clinical samples. We also designed LAMP assays for the detection of five AMR genes commonly associated with K. pneumoniae. The LAMP assays were validated on a total of 319 type reference strains and clinical isolates of diverse genetic backgrounds, in addition to 40 clinical human sputum samples, and were shown to be reliable, highly specific, and sensitive. For the K. pneumoniae-specific LAMP assay, the calculated sensitivity, specificity, and positive and negative predictive values (comparison with culture and matrix-assisted laser desorption/ionization-time of flight mass spectrometry) were all 100% on clinical isolates and, respectively, of 100%, 91%, and 90%, and 100% when tested on clinical sputum samples, while being significantly faster than the reference methods. For the bla KPC and other carbapenemases' LAMP assays, the concordance between the LAMP results and the references methods (susceptibility tests) was 100%, on both pure cultures (n = 125) and clinical samples (n = 18). In conclusion, we developed highly sensitive and specific LAMP assays for the clinical identification of K. pneumoniae and detection of carbapenem resistance.

Characteristics of Isolates of Pseudomonas aeruginosa and Serratia marcescens Associated With Post-harvest Fuzi (Aconitum carmichaelii) Rot and Their Novel Loop-Mediated Isothermal Amplification Detection Methods

Fuzi (the lateral root of Aconitum carmichaelii Debx.) is a traditional Chinese medicine that is cultivated in more than eight provinces in China. However, it can be easily devastated by post-harvest rot, causing huge losses. Therefore, it is extremely important that the primary causal pathogens of post-harvest Fuzi rot are identified and appropriate detection methods for them are developed to prevent and control losses. In this study, two bacterial strains (X1 and X2) were isolated from rotten post-harvest Fuzi. Based on their morphological, physiological, and biochemical characteristics, housekeeping gene homologies, and matrix-assisted laser desorption ionization/time-of-flight mass spectrometry (MALDI-TOF MS) results, these isolates were identified as Pseudomonas aeruginosa and Serratia marcescens. The pathogenicities of these isolates were confirmed by fulfilling Koch's postulates demonstrating that they were post-harvest Fuzi rot pathogens. Two loop-mediated isothermal amplification (LAMP) methods targeting the gyrase B subunit (gyrB) gene of P. aeruginosa and the phosphatidylinositol glycan C (pigC) gene of S. marcescens were successfully developed, and it was found that the target genes were highly specific to the two pathogens. These LAMP methods were used to detect P. aeruginosa and S. marcescens in 46 naturally occurring Fuzi and their associated rhizosphere soil samples of unknown etiology. The two bacterial assays were positive in some healthy and rotten samples and could be accomplished within 1 h at 65°C without the need for complicated, expensive instruments. To our knowledge, this is the first report of P. aeruginosa and S. marcescens causing post-harvest Fuzi rot. The newly developed methods are expected to have applications in point-of-care testing for the two pathogens under different Fuzi planting procedures and will significantly contribute to the control and prevention of Fuzi rot.

Simple, Rapid and Sensitive Detection of Pseudomonas aeruginesa by Colorimetric Multiple Cross Displacement Amplification

Pseudomonas aeruginosa (P. aeruginosa) is a major opportunistic pathogen in hospital-acquired infections. Thus, early diagnosis is the best strategy for fighting against these infections. In this report, we incorporated multiple cross displacement amplification (MCDA) combined with the malachite green (MG) for rapid, sensitive, specific and visual detection of P. aeruginosa by targeting the oprl gene. The MCDA-MG assay was conducted at 67°C for only 40 min during the amplification stage, and then products were directly detected by using colorimetric indicators (MG), eliminating the use of an electrophoresis instrument or amplicon analysis equipment. The entire process, including specimen processing (35 min), amplification (40 min) and detection (5 min), can be finished within 80 min. All 30 non-P. aeruginosa strains tested negative, indicating the high specificity of the MCDA primers. The analytical sensitivity of the MCDA-MG assay was 100 fg of genomic templates per reaction in pure culture, which was in complete accordance with MCDA by gel electrophoresis and real-time turbidity. The assay was also successfully applied to detecting P. aeruginosa in stool samples. Therefore, the rapidity, simplicity, and nearly equipment-free platform of the MCDA-MG technique make it possible for clinical diagnosis, and more.