Colorimetric Loop-mediated Isothermal Amplification Research Articles

A portable all-in-one microfluidic device with real-time colorimetric LAMP for HPV16 and HPV18 DNA point-of-care testing

Screening for high-risk human papillomavirus (HPV) infection is one of the most important preventative measures for cervical cancer. However, fast, convenient, and low-cost HPV detection remains challenging, especially in resource-limited settings. Here, we report a portable all-in-one device (PAD) for point-of-care testing (POCT) for HPV16 and HPV18 DNA in cervical swabs. The PAD was engineered to integrate modules for extraction-free sample lysis, loop-mediated isothermal amplification (LAMP) with lyophilized reagent beads, and real-time colorimetric signal sensing into a single miniaturized device, considerably shortening the sample-to-result time to 15 min. The precision liquid handling in the completely sealed microfluidic chip is achieved by a uniquely designed pressure-balanced automatic liquid flow mechanism, thereby eliminating the need for manual manipulation of liquids and thus the risk of biohazards. The PAD employs an improved real-time colorimetric LAMP (rcLAMP) assay with a limit of detection (LOD) of 1 copy/μL, enabled by enhanced assay chemistry to maximize the reaction kinetics. To validate this device for clinical application, we tested 206 clinical cervical swab samples and obtained a sensitivity of 92.1% and a specificity of 99.0%. This custom PAD enabled by microfluidic and electronic engineering techniques can be configured for the simultaneous detection of HPV16 and HPV18 or other pathogens in point-of-care applications.

Application of multiple binding sites for LAMP primers across P. falciparum genome improves detection of the parasite from whole blood samples

IntroductionMalaria remains a significant health concern, particularly in regions with widespread prevalence. As the transmission rates decrease, there is a rise in low-density infections with the causative parasite, P. falciparum, that often escape detection through standard point-of-care diagnostic tools. In-low transmission areas, even few undetected cases can trigger outbreaks, necessitating rapid and sensitive diagnostics. Loop-mediated isothermal Amplification (LAMP) stands out as a nucleic acid technique that can easily utilizes un-processed samples such of saliva, urine, and lysed whole blood templates for a sensitive detection. However, most nucleic acid tests detect genes with few copies per parasite making it difficult to detect low-density parasitaemia.MethodsWe selected Pfr364 multi-copy repeats of the P. falciparum genome as a target for amplification due to their higher copy number, ideal for rapid amplification, addressing amplification drawbacks of limited parasites DNA. We used a sequence clustering approach to design a novel set of LAMP primers, capable of binding to multiple sites. Subsequently, we developed a hydroxynaphthol blue (HNB) colorimetric LAMP assay, using genomic DNA obtained from the 3D7 strain cultivated in vitro. This assay’s performance was validated using archived clinical samples of both whole blood and matched saliva, ensuring accuracy through comparative analysis against gold standard, nested PCR, targeting the 18S RNA gene.ResultsThe HNB-LAMP assay achieved rapid amplification within 15 minutes and exhibited high sensitivity with a limit of detection of 1 parasite. Further, the LAMP assay was robust in whole blood lysed with Triton X-100 and heat-treated saliva clinical samples. Against nested PCR, the assay showed sensitivity of 100% for whole blood and 40% for saliva samples. Moreover, co-analysis with the nested PCR showed a perfect agreement between the two techniques. (K = 0.99 for whole blood, and 0.66 for saliva).ConclusionOur study presents a method for detecting P. falciparum using LAMP, which results in increased sensitivity, shorter assay times, and a simpler workflow than nucleic acid tests relying on conventional DNA extraction and additional equipment for result interpretation. These findings hold great promise for improved malaria diagnosis, especially in settings where low-density parasitaemia is prevalent and rapid and accurate malaria detection is crucial.

On-site monitoring of Escherichia coli O157:H7 in drinking water based on rapid detection of the rfbE gene at the single copy level

The sensitive and on-site detection of highly pathogenic Escherichia coli O157:H7 (E. coli O157:H7) is of great importance to ensure public health. However, conventional methods for E. coli O157:H7 detection may suffer disadvantages such as high expense and time consumption. Herein, we reported a cost-effective colorimetric platform based on loop-mediated isothermal amplification (LAMP) for ultrasensitive and rapid detection of E. coli O157:H7. In this study, a novel quantitative colorimetric LAMP assay was established by in-situ measurement of hydroxy naphthol blue (HNB) color change with a designed portable device, which was applied to the amplification of the specific rfbE gene of E. coli O157:H7. As expected, this method featured a wide linear range (100-104 copies µL−1) with excellent linear regression analysis (R2 > 0.99) and possessed a record-low detection limit of 1 copy µL−1 to lower the risk of missed detection. The proposed strategy could be employed on drinking water samples with favorable recoveries and also demonstrated potential in the analysis of complex samples. This work exhibits the promising application prospect in on-site detection without the need for expensive instrumentation and seeks to provide an original paradigm for the rapid and sensitive detection of waterborne pathogens.

Development of the colorimetric loop-mediated isothermal amplification technique for rapid and sensitive detection of chrysanthemum stunt viroid in chrysanthemum

Development of the colorimetric loop-mediated isothermal amplification technique for rapid and sensitive detection of chrysanthemum stunt viroid in chrysanthemum

Direct cord blood LAMP colorimetric phenol red assay for detecting α0-thalassemia (SEA deletion); the validation and post-natal screening in Thailand

Post-natal or newborn screening for thalassemia and hemoglobinopathies is useful for genetic counseling and managing thalassemia in children. We characterized thalassemia genotypes in newborns from the eastern part of Thailand. The results demonstrated a high heterogeneity of thalassemia and hemoglobinopathies with seventeen genotypes. We focused on α0- thalassemia (Southeast Asian [SEA] deletion) in this study. We developed and validated the loop-mediated isothermal amplification (LAMP) colorimetric assay for detecting α0- thalassemia (SEA deletion) using simple direct cord blood sampling compared to genomic DNA. A total of 160 cord blood samples were evaluated with the LAMP assay. The sensitivity and specificity of the LAMP colorimetric assay for α0-thalassemia (SEA deletion) using direct cord blood showed 100% (6/6 x 100) and 98.05% (151/154 x 100) whereas, genomic DNA showed 100% (6/6 x 100) and 100% (154/154 x 100), respectively. Moreover, we demonstrated other simple screening tools for α0-thalassemia with %Hb Bart’s, MCV, and MCH values and found that these parameters were not diagnostic in our samples. The direct cord blood with colorimetric LAMP assay is simple, rapid, and does not require a post-LAMP step compared to conventional PCR. These techniques could be applied in post-natal or large population screening for α0-thalassemia (SEA deletion). Finally, this could support early prevention of complications, early management, genetic counseling for α-thalassemia disease in children, or a long-term prevention and control program of severe thalassemia in Thailand.

Development of a colorimetric loop‐mediated isothermal amplification (LAMP) assay to facilitate monitoring of carbendazim‐resistant isolates of Colletotrichum truncatum based on the β‐tubulin E198A mutation

AbstractAnthracnose, a disease mainly caused by Colletotrichum truncatum, is a serious threat to vegetable soybean production worldwide. Carbendazim, a methyl‐benzimidazole carbamate fungicide, has been frequently applied to control the disease. Unfortunately, carbendazim‐resistant isolates of C. truncatum have emerged, resulting in inefficient disease control. Therefore, a rapid and simple method for monitoring the fungicide‐resistant isolates in fungal populations is essential to select the most appropriate strategy to control the disease and to handle fungicide resistance in a timely manner. In this study, we developed a colorimetric loop‐mediated isothermal amplification (LAMP) assay to detect carbendazim‐resistant isolates by using the E198A mutation in the TUB2 gene as the marker. With the optimal primers, the developed LAMP assay could detect resistant isolates after incubation for 40 min at 67°C. The results could be simply observed with the naked eye, and the assay provided 10‐fold higher sensitivity than conventional PCR. Moreover, the specificity, accuracy, and reproducibility of the generated LAMP were shown in testing with 85 C. truncatum isolates from five locations in northern Thailand. Resistant isolates carrying the F200Y mutation were not detected with the LAMP assay. Thus, the developed colorimetric LAMP assay could be used as a rapid and simple detector of certain carbendazim‐resistant isolates of C. truncatum.

First field and laboratory evaluation of LAMP assay for malaria diagnosis in Cubal, Angola

BackgroundMalaria is a globally distributed infectious disease. According to the World Health Organization, Angola is one of the six countries that account for over half the global malaria burden in terms of both malaria cases and deaths. Diagnosis of malaria still depends on microscopic examination of thin and thick blood smears and rapid diagnostic tests (RDTs), which often lack analytical and clinical sensitivity. Molecular methods could overcome these disadvantages. The aim of this study was to evaluate, for the first time to our knowledge, the performance of a loop-mediated isothermal amplification (LAMP) for the diagnosis of malaria in an endemic area in Cubal, Angola, and to assess the reproducibility at a reference laboratory.MethodsA total of 200 blood samples from patients attended at Hospital Nossa Senhora da Paz, Cubal, Angola, were analysed for Plasmodium spp. detection by microscopy, RDTs, and LAMP. LAMP assay was easily performed in a portable heating block, and the results were visualized by a simple colour change. Subsequently, the samples were sent to a reference laboratory in Spain to be reanalysed by the same colorimetric LAMP assay and also in real-time LAMP format.ResultsIn field tests, a total of 67/200 (33.5%) blood samples were microscopy-positive for Plasmodium spp., 98/200 RDT positive, and 112/200 (56%) LAMP positive. Using microscopy as reference standard, field LAMP detected more microscopy-positive samples than RDTs (66/67; 98% vs. 62/67; 92.5%). When samples were reanalysed at a reference laboratory in Spain using both colorimetric and real-time assays, the overall reproducibility achieved 84.5%.ConclusionsThis is the first study to our knowledge in which LAMP has been clinically evaluated on blood samples in a resource-poor malaria-endemic area. The colorimetric LAMP proved to be more sensitive than microscopy and RDTs for malaria diagnosis in field conditions. Furthermore, LAMP showed an acceptable level of reproducibility in a reference laboratory. The possibility to use LAMP in a real-time format in a portable device reinforces the reliability of the assay for molecular diagnosis of malaria in resource-poor laboratories in endemic areas.Graphical

A Single-Tube Colorimetric Loop-Mediated Isothermal Amplification for Rapid Detection of SARS-CoV-2 RNA.

Since SARS-CoV-2 is a highly transmissible virus, a rapid and accurate diagnostic method is necessary to prevent virus spread. We aimed to develop and evaluate a new rapid colorimetric reverse transcription loop--mediated isothermal amplification (RT-LAMP) assay for SARS-CoV-2 detection in a single closed tube. Nasopharyngeal and throat swabs collected from at-risk individuals testing for SARS-CoV-2 were used to assess the sensitivity and specificity of a new RT-LAMP assay against a commercial qRT-PCR assay. Total RNA extracts were submitted to the RT-LAMP reaction under optimal conditions and amplified at 65 °C for 30 min using three sets of specific primers targeting the nucleocapsid gene. The reaction was detected using two different indicator dyes, hydroxynaphthol blue (HNB) and cresol red. A total of 82 samples were used for detection with HNB and 94 samples with cresol red, and results were compared with the qRT-PCR assay. The sensitivity of the RT-LAMP-based HNB assay was 92.1% and the specificity was 93.2%. The sensitivity of the RT-LAMP-based cresol red assay was 80.3%, and the specificity was 97%. This colorimetric feature makes this assay highly accessible, low-cost, and user-friendly, which can be deployed for massive scale-up and rapid diagnosis of SARS-CoV-2 infection, particularly in low-resource settings.

Loop-mediated isothermal amplification assay for screening congenital cytomegalovirus infection in newborns

Congenital cytomegalovirus (CMV) infection is a common cause of sensorineural hearing loss and neurodevelopmental impairment in newborns. However, congenital CMV infection cannot be diagnosed using samples collected more than 3 weeks after birth because testing after this time cannot distinguish between congenital infection and postnatal infection. Herein, we developed a robust loop-mediated isothermal amplification (LAMP) assay for the large-scale screening of newborns for congenital CMV infection. In contrast to conventional quantitative polymerase chain reaction (qPCR), which detects CMV within a dynamic range of 1.0 × 106 to 1.0 × 102 copies/μL, our quantitative LAMP assay (qLAMP) detects CMV within a dynamic range of 1.1 × 108 to 1.1 × 103 copies/μL. Moreover, the turnaround time for obtaining results following DNA extraction is 90 min in qPCR but only 15 min in qLamp. The colorimetric LAMP assay can also detect CMV down to 1.1 × 103 copies/μL within 30 min, irrespective of the type of heat source. Our LAMP assay can be utilized in central laboratories as an alternative to conventional qPCR for quantitative CMV detection, or for point-of-care testing in low-resource environments, such as developing countries, via colorimetric naked-eye detection.Key points• LAMP assay enables large-scale screening of newborns for congenital CMV infection.• LAMP allows colorimetric or quantitative detection of congenital CMV infection.• LAMP assay can be used as a point-of-care testing tool in low-resource environments.

Development and Sensitivity Determination of 18S rRNA Gene-specific Fast Loop-mediated Isothermal Amplification (LAMP) Assay for Rapid Detection of Acanthamoeba.

Acanthamoeba, one of the free-living amoeba, has been detected in many environmental samples, mainly in water, soil and air. Acanthamoeba keratitis and granulomatous amoebic encephalitis are among the most important clinical manifestations caused by Acanthamoeba. In this study, it was aimed to determine the sensitivity of the rapid loop mediated isothermal amplification (LAMP) test designed with primers specific to Acanthamoeba 18S rRNA gene to detect more rapidly the presence of Acanthamoeba in clinical and environmental samples. Acanthamoeba strain grown in culture was diluted in 200 μL as 1x106 trophozoites and DNA was isolated, and the amount of DNA was determined by Nano-Drop Spectrophotometer. The purified DNAs were diluted from 1000 pg to 0.001 pg and used in colorimetric and fluorescence-based LAMP reactions. The LAMP reaction mixture was incubated for 60 minutes at 63 °C in a total volume of 25 μL. To determine the sensitivity of the test, positivity of Acanthamoeba genomic DNA was observed at 1, 10, 100 and 1000 pg/reaction in both colorimetric and fluorescence-based LAMP tests. The lowest analytical sensitivity of both calorimetric and fluorescent LAMP assay was determined as 1 pg/reaction. In addition, as a result of LAMP reaction applied with other parasite DNAs to evaluate the specificity of the test, no LAMP product was detected in calorimetric and 1% agarose gel electrophoresis, except for positive control, and the specificity of the test was determined as 100%. It has been demonstrated that the LAMP assay designed by targeting 18S rRNA gene of Acanthamoeba has a detection limit of 1 pg of genomic DNA. It is promising that LAMP test is more sensitive and faster than culture method, as well as simple, inexpensive and highly sensitive. For this reason, it is thought that developed test can be applied in the diagnosis of Acanthamoeba in environmental and clinical samples.

Data treatment methods for real-time colorimetric loop-mediated isothermal amplification reactions

With the SARS-CoV-2 pandemic and the need for affordable and rapid mass testing, colorimetric isothermal amplification reactions such as Loop-Mediated Isothermal Amplification (LAMP) are quickly rising in importance. The technique generates data that is similar to quantitative Polymerase Chain Reaction (qPCR), but instead of an endpoint color visualization, it is possible to construct a signal over a time curve. As the number of works using time-course analysis of isothermal reactions increases, there is a need to analyze data and standardize their related treatments quantitatively. Here, we take a step forward toward this goal by evaluating different available data treatments (curve models) for amplification curves, which allows for a cycle threshold-like parameter extraction. In this study, we uncover evidence of a double sigmoid equation as the most adequate model to describe amplification data from our remote diagnostics system and discuss possibilities for similar setups. We also demonstrate the use of multimodal Gompertz regression models. Thus, this work provides advances toward standardized and unbiased data reporting of Reverse Transcription (RT) LAMP reactions, which may facilitate and quicken assay interpretation, potentially enabling the application of machine learning techniques for further optimization and classification.

Development of colorimetric loop-mediated isothermal amplification (LAMP) assay for detecting the azoxystrobin-resistant isolates in Colletotrichum truncatum

Anthracnose, mainly caused by Colletotrichum truncatum, is a serious threat to soybean production worldwide. Azoxystrobin, a quinone outside inhibitor (QoI) fungicide, has long been frequently used in Thailand. As expected, its performance has decreased as the pathogen has developed fungicide resistance, mainly due to mutations in the target cytochrome b (cytb) gene. The substitution from glycine to alanine at codon 143 (G143A) is related to the azoxystrobin-completely resistant phenotype of C. truncatum. We thus used the G143A mutation as the reaction marker to develop a loop-mediated isothermal amplification (LAMP) method combined with hydroxynaphthol blue (HNB) for visual, simple, and rapid detection of azoxystrobin-resistant isolates of C. truncatum. Among four sets of primers designed, primer sets 1, 2, and 4 distinguished the isolate carrying the G143A mutation from wild-type isolate. Optimum conditions for the LAMP assay using primer set 4 were 63 °C for 80 min with a visible detection limit of 1 ng. Moreover, the LAMP assay was highly specific and accurate in tests of 125 isolates of C. truncatum from 13 fields in northern Thailand. This LAMP assay is highly efficient, simple, accurate for rapid field monitoring of azoxystrobin resistance in C. truncatum and implementing effective control measures.

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.

Paper-based colorimetric loop-mediated isothermal amplification (LAMP) assay for the identification of latent Colletotrichum in harvested fruit

Paper-based analytical devices (PADs) have gained enormous attention because of their low-cost, simple fabrication, and portability. Here, we propose a paper-based device for performing reverse transcription loop-mediated isothermal amplification (RT-LAMP) with real-time simultaneous detection of C. gloeosporioides latent infections in tomatoes. RT-LAMP-based PAD platform comprises a paper substrate on which the DNA amplification reaction occurs. Among different types of tested papers, cellulose membrane (grade 4) enabled effective visualization of the amplification result. The assay was found highly selective for the latent stage of C. gloeosporioides with lower limit of detection (LOD) of 0.5 pg of total extracted RNA. The developed assay generated the results within 40 min and hence can be efficiently employed for identifying C. gloeosporioides in resource-limited settings.

Rapid detection of Salmonella enterica subsp. enterica serovar Thompson by real-time fluorescence loop-mediated isothermal amplification (LAMP) and colorimetric LAMP combined without DNA extraction in the field

Salmonella enterica subsp. enterica serovar Thompson (S. Thompson) has caused numerous international outbreaks of foodborne disease in recent years. Despite the need for methods to control and prevent these outbreaks, many researchers continue to focus on Salmonella species, and few studies have focused on S. Thompson. In this study, we developed the new loop-mediated isothermal amplification (LAMP) assay with the novel primers that targets highly specific hsdS gene for the detection of S. Thompson. The LAMP assay yielded 100% positive results for S. Thompson strains and observed no cross-reaction with 55 other strains. The sensitivity was determined to be 10 colony-forming units (CFU)/mL in pure and artificially contaminated chicken samples. The LAMP assays were further improved to develop a direct LAMP assay for on-site detection that could complete the entire process within 45 min without the need for DNA isolation. After 60 min of enrichment, artificially contaminated chicken samples (initial concentration of 3 CFU/g) were detectable by direct LAMP assay, and this assay was also effectively used for testing commercial meat samples. The proposed LAMP assay has potential applications for on-site detection of S. Thompson and for rapid tracing of contamination sources in laboratories with limited resources.

Clinical Validation of a Colorimetric Loop-Mediated Isothermal Amplification Using a Portable Device for the Rapid Detection of SARS-CoV-2.

Quick and reliable mass testing of infected people is an effective tool for the contingency of SARS-CoV-2. During the COVID-19 pandemic, Point-of-Care (POC) tests using Loop-Mediated Isothermal Amplification (LAMP) arose as a useful diagnostic tool. LAMP tests are a robust and fast alternative to Polymerase Chain Reaction (PCR), and their isothermal property allows easy incorporation into POC platforms. The main drawback of using colorimetric LAMP is the reported short-term stability of the pre-mixed reagents, as well as the relatively high rate of false-positive results. Also, low-magnitude amplification can produce a subtle color change, making it difficult to discern a positive reaction. This paper presents Hilab Molecular, a portable device that uses the Internet of Things and Artificial Intelligence to pre-analyze colorimetric data. In addition, we established manufacturing procedures to increase the stability of colorimetric RT-LAMP tests. We show that ready-to-use reactions can be stored for up to 120 days at -20 °C. Furthermore, we validated both the Hilab Molecular device and the Hilab RT-LAMP test for SARS-CoV-2 using 581 patient samples without any purification steps. We achieved a sensitivity of 92.93% and specificity of 99.42% (samples with CT ≤ 30) when compared to RT-qPCR.

The use of colorimetric loop-mediated isothermal amplification assay for naked-eye detection of bean common mosaic virus

Bean common mosaic virus (BCMV), one of the most prevalent viral diseases of common beans, has been intensively studied since its initial identification. In this paper, a one-step colorimetric reverse-transcription loop-mediated isothermal amplification (RT-LAMP) method was performed by designing oligonucleotide primers to amplify the gene encoding the coat protein of BCMV. Positive LAMP reactions were observed with the naked eye using WarmStart 2 × Master Mix from NEB, changing from pink to yellowish if the test is positive. The sensitivity of this method was similar to that of conventional PCR. The method was tested on common bean and another virus, bean common mosaic necrosis virus (BCMNV), and it was shown to specifically detect BCMV and not produce false positive from other RNAs. The RT-LAMP test was quite reliable for the diagnosis of BCMV from infected samples, and the precise, sensitive. The cost analysis showed that the development of a less expensive and efficient RT-LAMP assay for BCMV detection is an important step in expanding testing capacity and improving access to accurate testing in resource-limited settings. The test can be utilized in laboratory and in the field for the diagnosis and monitoring of BCMV, and is the first reported use of RT-LAMP for BCMV detection.

A pangenome approach-based loop-mediated isothermal amplification assay for the specific and early detection of Bordetella pertussis

Despite widespread vaccination, Bordetella pertussis continues to cause pertussis infections worldwide, leaving infants at the highest risk of severe illness and death, while people around them are likely the main sources of infection and rapidly spread the disease. Rapid and less complex molecular testing for the specific and timely diagnosis of pertussis remains a challenge that could help to prevent the disease from worsening and prevent its transmission. We aimed to develop and validate a colorimetric loop-mediated isothermal amplification (LAMP) assay using a new target uvrD_2 informed by the pangenome for the specific and early detection of B. pertussis. Compared to that of multitarget quantitative polymerase chain reaction (multitarget qPCR) using a large clinical DNA specimen (n = 600), the diagnostic sensitivity and specificity of the uvrD_2 LAMP assay were 100.0% and 98.6%, respectively, with a 99.7% degree of agreement between the two assays. The novel colorimetric uvrD_2 LAMP assay is highly sensitive and specific for detecting B. pertussis DNA in nasopharyngeal swabs and showed similar diagnostic accuracy to complex and high-cost multitarget qPCR, but it is faster, simpler, and inexpensive, which makes it very helpful for the reliable and timely diagnosis of pertussis in primary health care and resource-limited settings.

Development of a colorimetric loop-mediated isothermal amplification diagnostic assay for deer tick virus

Deer tick virus (DTV) is an emerging pathogen in North America. This virus can cause nervous system complications such as encephalitis in humans. Further, no data are available regarding long-term effects of infection from DTV patients across variable age groups. Diagnostic tools of DTV used by government laboratories are based on RT-PCR using patient serum or ticks. This paper explores the feasibility of a colorimetric loop-mediated isothermal amplification (LAMP) assay to create a point-of-care diagnostic methodology for use in field and in primary care. LAMP consists of six primers that bind to target DNA and amplify variable length nucleotide strands that can be visualized through side reactions or via electrophoresis. First, a viable LAMP primer set, and a primer set that/ dimerizes and amplifies DNA regardless of compatibility were created in silico and validated in vitro. Then, a specific LAMP assay was developed. Our findings showed this method can be performed within 30 min and can measure with limits of detection comparable to PCR.

Differential identification of Mannheimia haemolytica genotypes 1 and 2 using colorimetric loop-mediated isothermal amplification

ObjectiveMannheimia haemolytica is the primary bacterial pathogen associated with bovine respiratory disease complex (BRDC). While M. haemolytica has been subdivided into 12 capsular serotypes (ST), ST1, ST2 and ST6 are commonly isolated from cattle. More recently, M. haemolytica strains isolated from North American cattle have been classified into genotypes 1 (ST2) and 2 (ST1 and ST6). Of the two genotypes, genotype 1 strains are frequently isolated from healthy animals whereas, genotype 2 strains are predominantly isolated from BRDC animals. However, isolation of both genotypes from pneumonic lung samples can complicate diagnosis. Therefore, the aim of this study was to develop a colorimetric loop-mediated isothermal amplification (LAMP) assay to differentiate M. haemolytica genotypes.ResultsThe genotype specificity of the LAMP was tested using purified genomic DNA from 22 M. haemolytica strains (10 genotype 1, 12 genotype 2) and strains from four related Pasteurellaceae species; Bibersteinia trehalosi, Mannheimia glucosida, Pasteurella multocida, and Histophilus somni. Genotype 1 (adhesin pseudogene B1) specific-LAMP reactions amplified DNA only from genotype 1 strains while genotype 2 (adhesin G) reactions amplified DNA only from genotype 2 strains. The overall detection sensitivity and specificity of the newly developed colorimetric LAMP assay for each genotype were 100%. The limits of detection of two LAMP assays were 1–100 target gene copies per reaction. LAMP primers designed in this study may help the differential identification of M. haemolytica genotypes 1 and 2.