Evaluation of colorimetric loop-mediated isothermal amplification assay for visual detection of Streptococcus agalactiae and Streptococcus iniae in tilapia

Strep Easy Kit; a bio-enrichment dual ICG-strip test for simultaneous detection of Streptococcus agalactiae serotypes Ia and III in fish samples

The Strep Easy Kit, a bio-enrichment dual ICG-strip test, is a diagnostic tool designed for the detection of Streptococcus agalactiae, an important pathogenic bacterium in tilapia farming. The kit can simultaneously identify two different serotypes of S. agalactiae, serotype Ia and serotype III. This capability is crucial for the collection of valuable epidemiological data and facilitates strategic planning for effective vaccine development and deployment. The Strep Easy Kit consists of two main steps: pathogen enrichment and pathogen detection. The enrichment step increases the concentration of bacteria so that the bacterial load is raised to the level reliably detectable by the subsequent ICG strip test. This is achieved by incubating the fish samples in a suitable liquid medium under specified temperature and time conditions. The second step involves the use of the dual-ICG strip test. This strip test consists of two monoclonal antibodies and one polyclonal antibody that are specific to S. agalactiae and can distinguish between S. agalactiae serotype Ia and S. agalactiae serotype III. This dual capability enables the ICG strip test to simultaneously detect both serotypes of S. agalactiae in a single test kit. The detection limit of the test kit, which consists of a dual ICG-Strip test combined with an enrichment step, is 100 CFU/mL. The kit can be used to detect S. agalactiae in both live and dead fish samples, making it versatile for various testing scenarios. The test results obtained using the Strep Easy Kit have shown a 94.4% correlation with the standard method (Thai Agricultural Standard; TAS 10453-2010), with 90.2% sensitivity and 100% specificity. Significant advantages of the Strep Easy Kit lie in its simplicity and portability, allowing farmers to perform the test by themselves and on-site. This makes it a practical and accessible tool for the tilapia farming industry.

Development of a multiplex Loop-Mediated Isothermal Amplification (LAMP) for the diagnosis of bacterial periprosthetic joint infection

BACKGROUND

Periprosthetic joint infection (PJI) is one of the most serious and debilitating complications that can occur after total joint arthroplasty. Therefore, early diagnosis and appropriate treatment are important for a good prognosis. Recently, molecular diagnostic methods have been widely used to detect the causative microorganisms of PJI sensitively and rapidly. The Multiplex Loop-Mediated Isothermal Amplification (LAMP) method eliminates the complex temperature cycling and delays caused by temperature transitions seen in polymerase chain reaction (PCR) methods, making it faster and easier to perform compared to PCR-based assays. Therefore, this study developed a multiplex LAMP assay for diagnosing bacterial PJI using LAMP technology and evaluated its analytical and clinical performance.

METHODS

We developed a multiplex LAMP assay for the detection of five bacteria: Staphylococcus aureus, Staphylococcus epidermidis, Streptococcus agalactiae, Pseudomonas aeruginosa, and Escherichia coli, frequently observed to be the causative agents of PJI. The method of analytical sensitivity and cross-reactivity were determined by spiking standard strains into the joint synovial fluid. The analytical sensitivity of the multiplex LAMP assay was compared with that of a quantitative real-time PCR (qPCR) assay. Clinical performance was evaluated using 20 joint synovial fluid samples collected from patients suspected of having bacterial PJI.

RESULTS

The analytical sensitivity of the gram-positive bacterial multiplex LAMP assay and qPCR were 105/104 CFU/mL, 103/103 CFU/mL, and 105/104 CFU/mL against S. agalactiae, S. epidermidis, and S. aureus, respectively. For P. aeruginosa and E. coli, the analytical sensitivity of the multiplex LAMP and qPCR assays were 105/104 and 106/104 CFU/mL, respectively. The multiplex LAMP assay detects target bacteria without cross-reacting with other bacteria, and exhibited 100% sensitivity and specificity in clinical performance evaluation.

CONCLUSIONS

This multiplex LAMP assay can rapidly detect five high-prevalence bacterial species causing bacterial PJI, with excellent sensitivity and specificity, in less than 1 h, and it may be useful for the early diagnosis of PJI.

Optimization and comparative analysis of LAMP and PCR techniques for the detection of leptospiral DNA in Golden Syrian hamsters

Leptospirosis is a zoonotic disease with significant public health and economic impact worldwide. Rapid and accurate diagnosis is essential for effective prevention and treatment. This study optimized a loop-mediated isothermal amplification (LAMP) assay using BFo isothermal DNA polymerase with different colorimetric indicators. LAMP was able to detect DNA from pathogenic and intermediate leptospires, while non-pathogenic leptospires and other non-leptospiral microorganisms were negative. LAMP assay combined with calcein showed a tenfold higher limit of detection (1 ng of leptospiral DNA per reaction) than LAMP combined with hydroxynaphthol blue or end-point PCR lipL32 (10 ng of DNA per reaction). Animal samples were collected from infected and non-infected Golden Syrian hamsters (Mesocricetus auratus) to evaluate and compare the performance of LAMP and PCR. These techniques showed a substantial agreement according to Cohen's kappa statistic, being both useful techniques for detecting leptospiral DNA in clinical samples. Overall, this study demonstrates that the LAMP assay is a sensitive, specific, rapid, and simple tool for the detection of leptospiral DNA. It has the potential to facilitate the diagnosis of leptospirosis, particularly in low-income regions with limited diagnosis resources.

Laboratory-controlled challenges of streptococcosis in Nile tilapia using the oral route (infected-feed) for infection

The study aimed to evaluate the oral infected-feed, intragastric-gavage, and intraperitoneal routes of the Streptococcus agalactiae infection in Nile tilapia (Oreochromis niloticus). For this purpose, 270 juveniles of Nile tilapia, with an average weight of 2 g, were distributed in 18 experimental units of 90 L, acclimatized, and raised for 55 days, until reaching 50 g (median weight). The experimental design was entirely randomized in six treatments, three of which were composed by bacterial infection routes: intraperitoneal 100 μL fish^-1 [10⁸ CFU], intragastric 100 μL fish^-1 [10⁸ CFU], feed inoculum 100 μL g feed^-1 [10⁹ CFU], and three respective control groups. Clinical signs were observed, and mortalities monitored until reaching 50% in the infected groups. Then, tissue samples from the spleen, liver, intestine, brain, and blood were collected from 20 fish per treatment for histopathological and hemato-immunological analyses. In addition, a related mortality curve was established at the end of the experimental challenge. The intraperitoneal and intragastric routes were more aggressive than the oral inoculum, causing greater brain damage, acute hemato-immunological response, and early mortality. While the orally fed inoculum, fish presented brain lesions with less intensity, and a chronic haemato-immunological response, the mortalities occurred twice as long as the other routes. The present research demonstrated that the S. agalactiae oral (feed inoculum) administration can be an innovative methodology to future experimental challenges in aquaculture research.

Reverse transcription loop-mediated isothermal amplification (RT-LAMP) combined with colorimetric gold nanoparticle (AuNP) probe assay for visual detection of tilapia lake virus (TiLV) in Nile and red hybrid tilapia

Tilapia is one of the major aquaculture species with a global economic significance. Despite a high scale of production worldwide, mortality in many tilapia cultures has recently become a problem concerned with not only intensive farming but also the prevalence of infectious pathogens. Tilapia lake virus (TiLV) has emerged as a serious single-stranded RNA disease agent that thus far has continued to cause a number of incidences across the continents. Conventional PCR-based molecular detection techniques, despite having high sensitivity for TiLV, are not best suited for the onsite identification of infected fish mainly due to their requirement of laboratory resources and extended assay turnaround time. To address this practical limitation, we have developed a novel colorimetric assay based on reverse transcription-loop-mediated isothermal amplification (RT-LAMP) and gold nanoparticle (AuNP)-labelled oligonucleotide reporter probe targeting the viral genomic segment 9 that enables the assay to be completed within an hour. This technique has been shown to be compatible with a rapid nucleic extraction method that does not demand centrifugation steps or any benchtop laboratory equipment. When validated with field-acquired tilapia samples, our RT-LAMP-AuNP assay exhibited a near-perfect agreement with the semi-nested RT-PCR assay recommended by OIE with Cohen's κ coefficient of .869, yet requiring significantly less time to perform.

Application of the FTA elute card coupled with visual colorimetric loop-mediated isothermal amplification for the rapid diagnosis of Streptococcus agalactiae in farmed tilapia (Oreochromis niloticus)

A method combining the FTA Elute card and visual colorimetric loop-mediated isothermal amplification (FTA-e/LAMP) was tested to diagnose Streptococcus agalactiae infections in vitro and in vivo. FTA-e/LAMP consists of two main steps: first, the FTA card is used to extract DNA and then a colorimetric loop-mediated isothermal amplification (LAMP) reaction is carried out on the extracted DNA. In vitro sensitivity was 1.9 x 10²  CFU/mL, and regarding specificity, all nine S. agalactiae strains tested positive. All Streptococcus spp. tested negative, except for S. dysgalactiae, thereby indicating the need for another set of primers to distinguish this species from S. agalactiae. To diagnose S. agalactiae infections using FTA-e/LAMP in vivo, two experimental trials on juvenile Oreochromis niloticus infected with bovine or piscine strains were carried out. Sensitivity in symptomatic fish was 100%, and 50.7% of fish without signs were positive. All negative control fish tested negative (n = 28). No bacteria were detected after 16 days post-infection (dpi). Accuracy during the first week (1-7 dpi) was 89% and decreased to 44% thereafter (10-22 dpi). FTA-e/LAMP results suggest that this method is a promising tool for early and fast diagnosis of S. agalactiae on tilapia farms.

Mechanisms and the role of probiotic Bacillus in mitigating fish pathogens in aquaculture

Diseases are natural components of the environment, and many have economic implications for aquaculture and fisheries. Aquaculture is a fast-growing industry with the aim to meet the high protein demand of the ever-increasing global population; however, the emergence of diseases is a major setback to the industry. Probiotics emerged as a better solution to curb the disease problem in aquaculture among many alternatives. Probiotic Bacillus has been proven to better combat a wide range of fish pathogens relative to other probiotics in aquaculture; therefore, understanding the various mechanisms used by Bacillus in combating diseases will help improve their mode of action hence yielding better results in their combat against pathogens in the aquaculture industry. Thus, an overview of the mechanisms (production of bacteriocins, suppression of virulence gene expression, competition for adhesion sites, production of lytic enzymes, production of antibiotics, immunostimulation, competition for nutrients and energy, and production of organic acids) used by Bacillus probiotics in mitigating fish pathogens ranging from Aeromonas, Vibrio, Streptococcus, Yersinia, Pseudomonas, Clostridium, Acinetobacter, Edwardsiella, Flavobacterium, white spot syndrome virus, and infectious hypodermal and hematopoietic necrosis virus proven to be mitigated by Bacillus have been provided.

Can histology and haematology explain inapparent Streptococcus agalactiae infections and asymptomatic mortalities on Nile tilapia farms?

The aim of this study was to characterise possible histopathological and haemato-immunological changes after subclinical infection by S. agalactiae S13 serotype Ib. One hundred juveniles of Nile tilapia with average weight of 45 g were distributed in ten 90 L experimental units. After the acclimation period 25 fish were euthanised, and fragments of liver, spleen and posterior mid-intestine tissue were sampled to verify the integrity of the organs and blood samples taken to check the haematological profile. Fifty animals were used to verify the optimal dosage for the challenge. The remaining 25 fish were infected with S. agalactiae S13. After 96 h, tissue fragments from the liver, spleen and posterior mid-intestine and blood samples were collected. The analyses revealed that, 96 h after contagion, S. agalactiae S13 serotype Ib caused subclinical lesions in the liver and spleen that are not commonly described as pathognomonic, in addition to haematological alterations. These results allow a better understanding of sudden recurrent mortalities in Brazilian tilapia farms, since the serotype Ib of S. agalactiae causes inapparent infections and can remain lodged in internal organs and cause irreversible lesions and haemato-immunological alterations, therefore compromising physiological functions vital for the health of fish without revealing external clinical signs in the animals.

DNA microarray analysis using a smartphone to detect the BRCA-1 gene

DNA microarrays are used to examine changes in gene expression of a large number of genes simultaneously by fluorescent labeling of complementary DNAs (cDNAs). The major bottleneck in implementing microarray technology in resource-limited settings lies in the detection instrument used for generating images of spotted oligonucleotides post-hybridization. While various methods such as a lateral flow assay have been presented to accomplish point-of-care disease detection, there is no simple and effective instrument available to gather spot images maintaining the standard microarray procedures. Nanotechnology based sensors connected with a portable smartphone readout system have the potential to be implemented in microarray technology. Here, we describe a portable fluorescence microarray based imaging system connected to a smartphone for detecting breast cancer gene expression (BRCA-1) from exon 11. This is based on the interactive binding of probe DNA to Cy3-target DNA. A paper-based microfluidics approach was used to demonstrate the DNA hybridization assay. The imaging principles of the assembled device named "FluoroZen" are similar to those of a fluorescence microscope. It uses two light spectrum filters, one to excite the fluorescent dye and the other to capture the emission spectrum. The images were acquired by using CCD cameras from FluoroZen. The smartphone integrated paper microfluidics platform presented here could be translated into clinical settings to perform point-of-care testing.

Development of a loop-mediated isothermal amplification assay for the detection and quantification of epizootic epitheliotropic disease virus (salmonid herpesvirus-3)

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A quantitative LAMP method for identification of EEDV has been developed.

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Analytical sensitivity of the qLAMP is as low as 78 pg extracted DNA from tissue.

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The method is highly specific for EEDV.

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The EEDV qLAMP method was evaluated against the qPCR method.

Epizootic Epitheliotropic Disease Virus (EEDV; Salmonid Herpesvirus-3) causes a serious disease hatchery-reared lake trout (Salvelinus namaycush), threatening restoration efforts of this species in North America. The current inability to replicate EEDV in vitro necessitates the search for a reproducible, sensitive, and specific assay that allows for its detection and quantitation in a time- and cost-effective manner. Herein, we describe a loop-mediated isothermal amplification (LAMP) assay that was developed for the quantitative detection of EEDV in infected fish tissues. The newly developed LAMP reaction was optimized in the presence of calcein, and the best results were produced using 2 mM MgCl₂, 1.8 mM dNTPs and at an incubation temperature of 67.1 °C. This method was highly specific to EEDV, as it showed no cross-reactivity with several fish viruses, including Salmonid Herpesvirus^-1, -2, -4, and -5, Infectious Pancreatic Necrosis Virus, Spring Viremia of Carp Virus, Infectious Hematopoietic Necrosis Virus, Golden Shiner Reovirus, Fathead Minnow Nidovirus, and Viral Hemorrhagic Septicemia Virus. The analytical sensitivity of the EEDV-LAMP method was estimated to be as low as 16 copies of plasmid per reaction. When infected fish tissue was used, a positive reaction could be obtained when an infected gill tissue sample that contained 430 viral copies/μg was diluted up to five orders of magnitude. The sensitivity and specificity of the newly developed LAMP assay compared to the SYBR Green qPCR assay were 84.3% and 93.3%, respectively. The quantitative LAMP for EEDV had a correlation coefficient (R² = 0.980), and did not differ significantly from the SYBR Green quantitative PCR assay (p > 0.05). Given its cost- and time-effectiveness, this quantitative LAMP assay is suitable for screening lake trout populations and for the initial diagnosis of clinical cases.

Streptococcus agalactiae infection kills red tilapia with chronic Francisella noatunensis infection more rapidly than the fish without the infection

In this study we examined the effect that a Francisella noatunensis (Fno) infection had on hybrid red tilapia (Oreochromis niloticus × Oreochromis mossambicus) subsquently infected with Streptococcus agalactiae. A variety of hemato-immunological parameters (haematocrit, total red blood cell count, mean corpuscular volume, total white blood and differential cell counts, total plasma protein, plasma lysozyme and plasma peroxidase activities, and respiratory burst and phagocytic activities of head-kidney macrophages) were measured in hybrid red tilapia that had been previously exposed to an Fno outbreak in a tilapia grow-out farm. The head-kidneys of these apparently healthy survivors, when checked by PCR were found to be Fno-positive with hemato-immunological parameters that were similar to fish without an a priori infection. The only exception was the percentage lymphocyte count in the peripheral blood, which was slightly, but significantly, lower in the Fno-infected fish, compared to those without the infection. When experimentally infected with S. agalactiae, the Fno-infected fish died more rapidly and at a significantly higher rate than fish without the infection. During the challenge, the hemato-immunological parameters of both groups of fish were very similar, although the Fno-infected fish, challanged with S. agalactiae expressed significantly higher plasma lysozyme and peroxidase activities, and their head kidney macrophages had significantly higher respiratory burst activity compared to non-Fno-infected fish challanged with S. agalactiae. The only two parameters for which Fno-infected fish showed significantly lower expressions than that of their non-infected counterparts were haematocrit and total red blood cell count. The cause of the rapidity and higher rates of mortality observed in the Fno-infected fish when challenged with S. agalactiae is unknown; but it may be due to a reduced erythropoiesis capability within the head-kidney because of the presence of Fno.

Evaluation of PCR primers targeting the groEL gene for the specific detection of Streptococcus agalactiae in the context of aquaculture

AIMS

The aim of this study was to design a set of primers for specific detection and identification of Streptococcus agalactiae in polymerase chain reaction (PCR) that can detect a diverse range of S. agalactiae isolates from different hosts and that it is capable of discriminating between S. agalactiae and other species that are closely related or potentially present in aquaculture environments, notably Streptococcus iniae.

METHODS AND RESULTS

Primers, based on the groEL2 gene of S. agalactiae, were shown to be epidemiologically sensitive to 97 isolates of S. agalactiae, representing 11 clonal complexes derived from piscine, terrestrial and aquatic mammalian host species. The primers were tested with 10 S. iniae isolates and 22 other comparator species with no cross-reaction observed after optimization of reaction conditions. They have a high analytical sensitivity, detecting as few as 10 copies of S. agalactiae genomic DNA per reaction and are capable of detecting the target in DNA extracted from the brains of infected fish.

CONCLUSIONS

The primers proved suitable for the sensitive and specific detection of S. agalactiae from dairy-, human- and fish-related origins by PCR.

SIGNIFICANCE AND IMPACT OF THE STUDY

Due to the importance of S. agalactiae as a pathogen, many PCR primers have been published for this bacterium, designed largely for its detection in dairy and human samples, but many cross-reacting with S. iniae. The ability to differentiate between S. agalactiae and S. iniae in aquaculture derived samples is important as both infect fish, causing similar disease symptoms and are phenotypically similar, yet control strategies and zoonotic risk are species specific.

Complete Genome Sequences of Three Fish-Associated Streptococcus agalactiae Isolates

The whole-genome sequences are described here for three group B Streptococcus (GBS) (S. agalactiae) serotype Ib isolates obtained from tilapia (Oreochromis niloticus) farmed at sites in Honduras, Costa Rica, and the United States. The bacteria were isolated from the brains of fish displaying signs of streptococcosis.

Complete Genome Sequences of Three Streptococcus agalactiae Serotype Ia Isolates Obtained from Disease Outbreaks in Nile Tilapia (Oreochromis niloticus)

This paper describes the whole-genome sequences for three Streptococcus agalactiae serotype Ia isolates. The isolates were recovered from the brains of clinically sick tilapia, Oreochromis niloticus, that were suffering from streptococcosis. One isolate was from tilapia in the United States and the other two from fish in China.

Molecular Techniques for the Detection of Organisms in Aquatic Environments, with Emphasis on Harmful Algal Bloom Species

Molecular techniques to detect organisms in aquatic ecosystems are being gradually considered as an attractive alternative to standard laboratory methods. They offer faster and more accurate means of detecting and monitoring species, with respect to their traditional homologues based on culture and microscopic counting. Molecular techniques are particularly attractive when multiple species need to be detected and/or are in very low abundance. This paper reviews molecular techniques based on whole cells, such as microscope-based enumeration and Fluorescence In-Situ Hybridization (FISH) and molecular cell-free formats, such as sandwich hybridization assay (SHA), biosensors, microarrays, quantitative polymerase chain reaction (qPCR) and real time PCR (RT-PCR). Those that combine one or several laboratory functions into a single integrated system (lab-on-a-chip) and techniques that generate a much higher throughput data, such as next-generation systems (NGS), were also reviewed. We also included some other approaches that enhance the performance of molecular techniques. For instance, nano-bioengineered probes and platforms, pre-concentration and magnetic separation systems, and solid-phase hybridization offer highly pre-concentration capabilities. Isothermal amplification and hybridization chain reaction (HCR) improve hybridization and amplification techniques. Finally, we presented a study case of field remote sensing of harmful algal blooms (HABs), the only example of real time monitoring, and close the discussion with future directions and concluding remarks.

Loop-mediated isothermal amplification assay for rapid detection of Streptococcus agalactiae (group B streptococcus) in vaginal swabs - a proof of concept study

PURPOSE

Neonatal sepsis caused by Streptococcus agalactiae [group B streptococcus (GBS)] is a life-threatening condition, which is preventable if colonized mothers are identified and given antibiotic prophylaxis during labour. Conventional culture is time consuming and unreliable, and many available non-culture diagnostics are too complex to implement routinely at point of care. Loop-mediated isothermal amplification (LAMP) is a method that, enables the rapid and specific detection of target nucleic acid sequences in clinical materials without the requirement for extensive sample preparation.

METHODOLOGY

A prototype LAMP assay targeting GBS sip gene is described.

RESULTS

The assay was 100 % specific for GBS, with a limit of detection of 14 genome copies per reaction. The clinical utility of the LAMP assay for rapid direct molecular detection of GBS was determined by testing a total of 157 vaginal swabs with minimal sample processing using a rapid lysis solution. Compared to a reference quantitative real-time PCR assay, the direct LAMP protocol had a sensitivity and specificity of 95.4 and 100 %, respectively, with positive and negative predictive values of 100 and 98.3 %, respectively. Positive and negative likelihood ratios were infinity and 0.05, respectively. The direct LAMP method required a mean time of 45 min from the receipt of a swab to generation of a confirmed result, compared to 2 h 30 min for the reference quantitative real-time PCR test.

CONCLUSION

The direct LAMP protocol described is easy to perform, facilitating rapid and accurate detection of GBS in vaginal swabs. This test has a potential for use at point of care.

Development of a colloidal gold immunochromatographic strip for rapid detection of Streptococcus agalactiae in tilapia

A colloidal gold immunochromatographic strip was developed for rapid detection of Streptococcus agalactiae (S. agalactiae) infection in tilapia. The monoclonal antibodies (mAb) 4C12 and 3A9 were used to target S. agalactiae as colloidal gold-mAb conjugate and captured antibody, respectively. The colloidal gold immunochromatographic strip was assembled via routine procedures. Optimal pH and minimum antibody levels in the reaction system for gold colloidal-mAb 4C12 conjugation were pH 7.4 and 18μg/mL, respectively. Optimal concentrations of the captured antibody 3A9 and goat anti-mouse antibody were 0.6mg/mL and 2mg/mL, respectively. The sensitivity of the strip for detecting S. agalactiae was 1.5×10⁵ colony forming units (CFU). No cross-reaction was observed with other commonly encountered bacteria, including Pseudomonas fluorescens, Aeromonas hydrophila, Vibrio anguillarum and Streptococcus iniae. The assay time for S. agalactiae was less than 15min. Tilapia samples artificially infected with S. agalactiae were tested using the newly developed strip. The results indicated that blood, brain, kidney, spleen, metanephros and intestine specimens of infected fish can be used for S. agalactiae detection. The validity of the strip was maintained for 6 months at 4°C. These findings suggested that the immunochromatographic strip was effective for spot and rapid detection of S. agalactiae infected tilapia.

Detection of natural infection of infectious spleen and kidney necrosis virus in farmed tilapia by hydroxynapthol blue-loop-mediated isothermal amplification assay

AIMS

Infectious spleen and kidney necrosis virus (ISKNV) has recently been recognized as a causative agent of serious systemic disease in tilapia. Our objective was to establish a new colorimetric loop-mediated isothermal amplification (LAMP) assay with pre-addition of hydroxynapthol blue (blue-LAMP) to investigate ISKNV transmission in tilapia.

METHODS AND RESULTS

The blue-LAMP, targeting a major capsid protein gene of ISKNV, was conducted at 65°C for 45 min, allowing unaided visual detection of the pathogen based on colour change without cross-amplification of other known fish pathogens tested. Comparison of blue-LAMP and PCR assays revealed a higher detection level for blue-LAMP assay (41·33%) in a population of farmed tilapia infected with ISKNV. The investigation of ISKNV transmission pattern in farmed red tilapia using the blue-LAMP revealed a possible matroclinical form. The presence of ISKNV in the gonad samples was confirmed by in situ LAMP assay. Positive signals only appeared in ovarian follicles, and not in oocytes. Moreover, tissue tropism assay revealed that the brain was the main target organ in both farmed red tilapia (40%) and Nile tilapia (20%).

CONCLUSIONS

The developed blue-LAMP assay has the potential to be used as a viable tool for screening covert and natural infections of ISKNV in tilapia. The evidence of vertical transmission of ISKNV infection in tilapia indicates the seriousness of this disease and will require a close attention and collaboration between tilapia hatcheries and disease experts in order to find a solution.

SIGNIFICANCE AND IMPACT OF THE STUDY

The new blue-LAMP assay is a time-saving and economically viable detection tool, which allows unaided visual detection for ISKNV in tilapia, and it could be applicable for field applications. Evidence on the vertical transmission of ISKNV in farmed tilapia suggests a need for developing farm management practices to control the spread of virus in aquaculture industries.

Shewanella putrefaciens in cultured tilapia detected by a new calcein-loop-mediated isothermal amplification (Ca-LAMP) method

Shewanella putrefaciens is being increasingly isolated from a wide variety of sources and is pathogenic to many marine and freshwater fish. For better control of this pathogen, there is a need for the development of simple and inexpensive but highly specific, sensitive, and rapid detection methods suitable for application in field laboratories. Our colorogenic loop-mediated isothermal amplification (LAMP) assay combined with calcein (Ca-LAMP) for unaided visual confirmation of LAMP amplicons is a simple method for fish pathogen detection in cultured tilapia. Here, we describe the detection of S. putrefaciens using the same platform. As before, the method gave positive results (orange to green color change) in 45 min at 63°C with sensitivity 100 times higher than that of a conventional PCR assay, with no cross-amplification of other known fish bacterial pathogens tested. Using the assay with 389 samples of gonads, fertilized eggs, and fry of farmed Nile and red tilapia Oreochromis spp., 35% of samples were positive for S. putrefaciens. The highest prevalence was found in samples of gonads (55%) and fertilized eggs (55%) from adult breeding stocks, indicating that S. putrefaciens could be passed on easily to fry used for stocking production ponds. Tissue tropism assays revealed that the spleen showed the highest colonization by S. putrefaciens in naturally infected tilapia and that it would be the most suitable organ for screening and monitoring fish stocks for presence of the bacteria.

A Comparison of In-House Real-Time LAMP Assays with a Commercial Assay for the Detection of Pathogenic Bacteria

Molecular detection of bacterial pathogens based on LAMP methods is a faster and simpler approach than conventional culture methods. Although different LAMP-based methods for pathogenic bacterial detection are available, a systematic comparison of these different LAMP assays has not been performed. In this paper, we compared 12 in-house real-time LAMP assays with a commercialized kit (Isothermal Master Mix) for the detection of Listeria monocytogenes, Salmonella spp, Staphylococcus aureus, Escherichia coli O157, E. coli O26, E. coli O45, E. coli O103, E. coli O111, E. coli O121, E. coli O145 and Streptococcus agalactiae. False-positive results were observed in all 12 in-house real-time LAMP assays, while all the negative controls of Isothermal Master Mix remained negative after amplification. The detection limit of Isothermal Master Mix for Listeria monocytogenes, Salmonella spp, Staphylococcus aureus, Escherichia coli O157, E. coli O26, E. coli O45, E. coli O103, E. coli O111, E. coli O121 and Streptococcus agalactiae was 1 pg, whereas the sensitivity of the commercialized kit for E. coli O145 was 100 pg. In conclusion, the 12 in-house real-time LAMP assays were impractical to use, while the commercialized kit Isothermal Master Mix was useful for the detection of most bacterial pathogens.

Colorimetric Method of Loop-Mediated Isothermal Amplification with the Pre-Addition of Calcein for Detecting Flavobacterium columnare and its Assessment in Tilapia Farms

Flavobacterium columnare, the causative agent of columnaris disease in fish, affects many economically important freshwater fish species. A colorimetric method of loop-mediated isothermal amplification with the pre-addition of calcein (LAMP-calcein) was developed and used to detect the presence of F. columnare in farmed tilapia (Nile Tilapia Oreochromis niloticus and red tilapia [Nile Tilapia × Mozambique Tilapia O. mossambicus]) and rearing water. The detection method, based on a change in color from orange to green, could be performed within 45 min at 63°C. The method was highly specific, as it had no cross-detections with 14 other bacterial species, including other fish pathogens and two Flavobacterium species. The method has a minimum detection limit of 2.2 × 10(2) F. columnare CFU; thus, it is about 10 times more sensitive than conventional PCR. With this method, F. columnare was detected in gonad, gill, and blood samples from apparently healthy tilapia broodstock as well as in samples of fertilized eggs, newly hatched fry, and rearing water. The bacteria isolated from the blood were further characterized biochemically and found to be phenotypically identical to F. columnare. The amplified products from the LAMP-calcein method had 97% homology with the DNA sequence of F. columnare.

Smartphone instrument for portable enzyme-linked immunosorbent assays

We demonstrate the utilization of a smartphone camera as a spectrometer that is capable of measuring Enzyme Linked Immunosorbent Assays (ELISA) at biologically-relevant concentrations with the aid of a custom cradle that aligns a diffraction grating and a collimating lens between a light source and the imaging sensor. Two example biomarkers are assayed using conventional ELISA protocols: IL-6, a protein used diagnostically for several types of cancer, and Ara h 1, one of the principle peanut allergens. In addition to the demonstration of limits of detection at medically-relevant concentrations, a screening of various cookies was completed to measure levels of peanut cross-contamination in local bakeries. The results demonstrate the utility of the instrument for quantitatively performing broad classes of homogeneous colorimetric assays, in which the endpoint readout is the color change of a liquid sample.