Specific and sensitive, ready-to-use universal fungi detection by visual color using ITS1 loop-mediated isothermal amplification combined hydroxynaphthol blue

Rapid detection of Shiga-toxin-producing Escherichia coli O157:H7 based on a colorimetric loop-mediated isothermal amplification (cLAMP) assay using a molecular beacon paired with HRPzyme

Contamination by Escherichia coli O157:H7 is considered a threat in the livestock and food industries. Therefore, it is necessary to develop methods for the convenient and rapid detection of Shiga-toxin-producing E. coli O157:H7. This study aimed to develop a colorimetric loop-mediated isothermal amplification (cLAMP) assay using a molecular beacon to rapidly detect E. coli O157:H7. Primers and a molecular beacon were designed for targeting the Shiga-toxin-producing virulence genes (stx1 and stx2) as molecular markers. Additionally, Bst polymerase concentration and amplification conditions for bacterial detection were optimized. The sensitivity and specificity of the assay were also investigated and validated on artificially tainted (100-104 CFU/g) Korean beef samples. The cLAMP assay could detect 1 × 101 CFU/g at 65 °C for both genes, and the assay was confirmed to be specific for E. coli O157:H7. The cLAMP takes about an hour and does not require expensive devices (e.g., thermal cycler and detector). Hence, the cLAMP assay proposed herein can be used in the meat industry as a fast and simple way to detect E. coli O157:H7.

Development and clinical application of a rapid, visually interpretable polymerase spiral reaction for tcdB gene of Clostridioides difficile in fecal cultures

In the surveillance of outbreaks of Clostridioides difficile infection, the rapid detection and diagnosis of C. difficile remain a major challenge. Polymerase spiral reaction (PSR) is a nucleic acid amplification technique that uses mixed primers and the strand displacement activity of Bst DNA polymerase to achieve a pair of primers and a single enzyme in an isothermal environment. The primer design is simple, the reaction is efficient, and a color indicator can be used to visualize the result. In this study, we developed a rapid and visually interpretable PSR to detect C. difficile by analyzing artificially contaminated feces samples and clinical isolates from patient feces samples. We designed two pairs of primers for a PSR that specifically targeted the conserved tcdB gene of C. difficile. The amplification results were visualized with the chromogenic dye hydroxynaphthol blue. The entire process was accomplished in 50 min at 64°C, with high specificity. The limit of detection of C. difficile with PSR was 150 fg/μl genomic DNA or 2 × 10 CFU/ml in artificially contaminated feces samples. With this method, we analyzed four clinical isolates and also compared the PSR with an isolation-and-culture detection method, polymerase chain reaction, and the Sanger sequencing. The four clinical isolates were found positive for tcdB, which confirmed the high specificity of the primers. The positive rates of tcdB in toxigenic C. difficile detected with PSR, PCR, and Sanger sequencing were 100%. The proportions of toxin types in these clinical C. difficile strains were 50% tcdA+tcdB+CDT- and 50% tcdA+tcdB+CDT+. The assay described should extend our understanding of the incidence of C. difficile. This may allow the rapid diagnosis and screening of C. difficile-related disease outbreaks in the field.

Multiplex recombinase polymerase amplification for high-risk and low-risk type HPV detection, as potential local use in single tube

High rates of new cervical cancer cases and deaths occur in low- and middle-income countries yearly, and one reason was found related to limitation of regular cervical cancer screening in local and low-resource settings. HPV has over 150 types, yet certain 14-20 high-risk and 13-14 low-risk types are common, and, thus, most conventional HPV nucleic acid assays, for examples, Cobas 4800 HPV test (Roche Diagnostics, New Jersey, USA) and REBA HPV-ID (Molecules and Diagnostics, Wonju, Republic of Korea) were developed to cover these types. We thereby utilized bioinformatics combined with recent isothermal amplification technique at 35-42 °C to firstly describe multiplex recombinase polymerase amplification assay that is specific to these common 20 high-risk and 14 low-risk types, and also L1 and E6/E7 genes that target different stages of cervical cancer development. Multiplex primer concentrations and reaction incubation conditions were optimized to allow simultaneous two gene detections at limit of detection of 1000 copies (equivalent to 2.01 fg) for L1 and 100 copies (0.0125 fg) for E6/E7, respectively. The assay was validated against urogenital and other pathogens, normal flora, and human control. In 130 real clinical sample tests, the assay demonstrated 100% specificity, 78% diagnostic accuracy, and 75% sensitivity compared with REBA HPV-ID test, and is much more rapid (15-40 min), less expensive (~ 3-4 USD/reaction) and does not require instrumentation (35-42 °C reaction condition so hand holding or tropical temperature is possible). Hence, the developed novel assay provides alternative screening tool for potential local screening. Furthermore, as this assay uses safe chemical reagents, it is safe for users.

Rapid detection and identification of fungi in grain crops using colloidal Au nanoparticles based on surface-enhanced Raman scattering and multivariate statistical analysis

Grain crops are easily contaminated by fungi due to the existence of various microorganisms in the storage process, especially in humid and warm storage conditions. Compared with conventional methods, surface-enhanced Raman scattering (SERS) has paved the way for the detection of fungi in grain crops as it is a rapid, nondestructive, and sensitive analytical method. In this work, Aspergillus niger, Saccharomyces cerevisiae, Fusarium moniliforme and Trichoderma viride in grain crops were detected using colloidal Au nanoparticles and SERS. The results indicated that different fungi showed different Raman phenotypes, which could be easily characterized by SERS. Combined with multivariate statistical analysis, identification of a variety of fungi could be accomplished rapidly and accurately. This research can be applied for the rapid detection of fungi in the food and biomedical industries.

Rapid visual Candidatus Liberibacter asiaticus detection (citrus greening disease) using simple alkaline heat DNA lysis followed by loop-mediated isothermal amplification coupled hydroxynaphthol blue (AL-LAMP-HNB) for potential local use

An outbreak of citrus greening or Huanglongbing disease bacteria occurs in many areas. We sampled and identified an ongoing ~year 2020 orange tree endemic in northern Thailand as Candidatus Liberibacter asiaticus. We thereby developed a plant greening disease (C. Liberibacter asiaticus) detection assay using simple alkaline heat DNA lysis and loop-mediated isothermal amplification coupled hydroxynaphthol blue (AL-LAMP-HNB), and evaluated the developed assay for its feasibility as point-of-care detection on 65 plant leaf samples with 100–1×10⁴ copies of C. Liberibacter asiaticus or mocked injection compared with commercial DNA lysis kit and PCR-GE. Our assay is sensitive to 5–8.9 copies of omp (equaling 0.0056–0.01 fg) compatible with PCR-GE limit of detection. This ultra sensitive limit of detection could allow the disease detection before clinical apparent state of disease when C. Liberibacter asiaticus infection number is few, i.e. fewer than 100 copies of C. Liberibacter asiaticus. The assay is also specific with 6 degenerate primers targeting every strain of C. Liberibacter asiaticus omp from GenBank database, rapid (40 min total assay time), inexpensive (~2–3 USD/reaction), does not require sophisticated instrumentation, and has comparable assay accuracy (93.85–100% accuracy, 100% specificity, and 89.74–100% sensitivity) to bacterial DNA extraction by a commercial kit followed by PCR and gel electrophoresis (92.31% accuracy, 100% specificity, and 87.18% sensitivity) based on the real sample tests. Hence, the technique could be used in local or laboratory resource-restricted settings. The test result could be read by naked eyes through the color change from violet (negative) to sky blue (positive) for a C. Liberibacter asiaticus-infected specimen. Furthermore, this assay uses safe chemical reagents and, thus, is safe for the users.

Diagnosis of Neisseria Gonorrhoeae by Loop-Mediated Isothermal Amplification: Systematic Review and Meta-Analysis

Neisseria gonorrhoeae (gonococci) is the pathogen of gonorrhea. At present, there is no robust statistical analysis targeting the detection accuracy for N.gonorrhoeae of loop-mediated isothermal amplification (LAMP). We performed a full search of five databases for studies using the LAMP method to detect N.gonorrhoeae in this study. Nine datasets derived from eight studies satisfying the inclusion requirement were collected for this study. The pooled sensitivity rate and specificity were calculated as 98.53 and 99.49%. The pooled positive likelihood ratio (PLR), negative likelihood ratio (NLR) and diagnostic odds ratio (DOR) were 66.0, 0.04 and 1863.8. After plotting the summary receiver operating characteristic (sROC), the area under the curve (AUC) and Q* index was calculated as 0.99 and 0.9774. Subgroup analyses based on the type of samples, location, and gold standard did not find sources of significant heterogeneity. In conclusion, the LAMP method could be an effective and convenient method with high accuracy for the clinical detection of N.gonorrhoeae. Moreover, the confirmation of this finding needs more high-quality studies with regional data and large samples.

Development and Clinical Application of a Rapid and Visual Loop-Mediated Isothermal Amplification Test for tetM gene in Clostridioides difficile Strains Cultured from Feces

OBJECTIVES

To develop a rapid and visual loop-mediated isothermal amplification (LAMP) assay targeting the tetM gene in Clostridioides difficile (C. difficile) strains cultured from feces.

METHODS

Primers were designed to recognize the tetM gene in C. difficile by LAMP, using turbidity and visual detection. The sensitivity and specificity of LAMP primers was determined. Besides, We conducted both LAMP and polymerase chain reaction (PCR) for the tcdA, tcdB, cdtA, cdtB, ermB, tetM genes in 300 toxigenic C. difficile strains cultured from feces.

RESULTS

The target DNA was amplified and visualized within 60 minutes at a temperature of 62°C. A total of 26 bacterial strains were found negative for tetM, which manifested high specificity of the primers. The detection limit of LAMP was 36.1 pg/µl, which was 100-fold more sensitive than PCR. The positive rate of tetM in toxigenic C. difficile strains cultured from feces was 93.3% by both LAMP and PCR. The proportion of toxin types in those C. difficile strains was 95.7% for A+B+CDT-, 4% for A-B+CDT-, and 0.3% for A+B+CDT+, respectively.

CONCLUSIONS

This is the first study examining tetM gene in C. difficile strains cultured from feces by LAMP. Its high specificity and sensitivity, as well as visual detection, make the new assay a powerful diagnostic tool for rapid testing.

Rapid visualization and detection of Staphylococcus aureus based on loop-mediated isothermal amplification

Staphylococcus aureus is a common clinical bacterial pathogen that can cause a diverse range of infections. The establishment of a rapid and reliable assay for the early diagnosis and detection of S. aureus is of great significance. In this study, we developed a closed-tube loop-mediated isothermal amplification (LAMP) assay for the visual detection of S. aureus using the colorimetric indicator hydroxy naphthol blue (HNB). The LAMP reaction was optimized by adjusting the amplification temperature, the concentrations of Mg²⁺, dNTP, and HNB, and the incubation time. In the optimized reaction system, the specificity of LAMP for S. aureus was 100%. The results established that this method accurately identified S. aureus, with no cross-reactivity with 14 non-S. aureus strains. The limit of detection (LOD) of LAMP was 8 copies/reaction of purified plasmid DNA or 400 colony-forming units/reaction of S. aureus. Compared with conventional PCR, LAMP lowered the LOD by tenfold. Finally, 220 clinically isolated strains of S. aureus and 149 non-S. aureus strains were used to evaluate the diagnostic efficacy of LAMP (test accuracy, 99.46%). The findings indicated that LAMP is a reliable test for S. aureus and could be a promising tool for the rapid diagnosis of S. aureus infections.

On-farm colorimetric detection of Pasteurella multocida, Mannheimia haemolytica, and Histophilus somni in crude bovine nasal samples

This work modifies a loop-mediated isothermal amplification (LAMP) assay to detect the bovine respiratory disease (BRD) bacterial pathogens Pasteurella multocida, Mannheimia haemolytica, and Histophilus somni in a colorimetric format on a farm. BRD causes a significant health and economic burden worldwide that partially stems from the challenges involved in determining the pathogens causing the disease. Methods such as polymerase chain reaction (PCR) have the potential to identify the causative pathogens but require lab equipment and extensive sample processing making the process lengthy and expensive. To combat this limitation, LAMP allows accurate pathogen detection in unprocessed samples by the naked eye allowing for potentially faster and more precise diagnostics on the farm. The assay developed here offers 66.7-100% analytical sensitivity, and 100% analytical specificity (using contrived samples) while providing 60-100% concordance with PCR results when tested on five steers in a feedlot. The use of a consumer-grade water bath enabled on-farm execution by collecting a nasal swab from cattle and provided a colorimetric result within 60 min. Such an assay holds the potential to provide rapid pen-side diagnostics to cattle producers and veterinarians.

On-farm colorimetric detection of Pasteurella multocida, Mannheimia haemolytica, and Histophilus somni in crude bovine nasal samples

This work modifies a loop-mediated isothermal amplification (LAMP) assay to detect the bovine respiratory disease (BRD) bacterial pathogens Pasteurella multocida, Mannheimia haemolytica, and Histophilus somni in a colorimetric format on a farm. BRD causes a significant health and economic burden worldwide that partially stems from the challenges involved in determining the pathogens causing the disease. Methods such as polymerase chain reaction (PCR) have the potential to identify the causative pathogens but require lab equipment and extensive sample processing making the process lengthy and expensive. To combat this limitation, LAMP allows accurate pathogen detection in unprocessed samples by the naked eye allowing for potentially faster and more precise diagnostics on the farm. The assay developed here offers 66.7-100% analytical sensitivity, and 100% analytical specificity (using contrived samples) while providing 60-100% concordance with PCR results when tested on five steers in a feedlot. The use of a consumer-grade water bath enabled on-farm execution by collecting a nasal swab from cattle and provided a colorimetric result within 60 min. Such an assay holds the potential to provide rapid pen-side diagnostics to cattle producers and veterinarians.