Real-Time Nucleic Acid Sequence-Based Amplification Assay for Detection of Hepatitis A Virus

A nucleic acid sequence-based amplification (NASBA) assay in combination with a molecular beacon was developed for the real-time detection and quantification of hepatitis A virus (HAV). A 202-bp, highly conserved 5′ noncoding region of HAV was targeted. The sensitivity of the real-time NASBA assay was tested with 10-fold dilutions of viral RNA, and a detection limit of 1 PFU was obtained. The specificity of the assay was demonstrated by testing with other environmental pathogens and indicator microorganisms, with only HAV positively identified. When combined with immunomagnetic separation, the NASBA assay successfully detected as few as 10 PFU from seeded lake water samples. Due to its isothermal nature, its speed, and its similar sensitivity compared to the real-time RT-PCR assay, this newly reported real-time NASBA method will have broad applications for the rapid detection of HAV in contaminated food or water.     

Real-time nucleic acid sequence-based amplification assay for detection of hepatitis A virus

A nucleic acid sequence-based amplification (NASBA) assay in combination with a molecular beacon was developed for the real-time detection and quantification of hepatitis A virus (HAV). A 202-bp, highly conserved 5' noncoding region of HAV was targeted. The sensitivity of the real-time NASBA assay was tested with 10-fold dilutions of viral RNA, and a detection limit of 1 PFU was obtained. The specificity of the assay was demonstrated by testing with other environmental pathogens and indicator microorganisms, with only HAV positively identified. When combined with immunomagnetic separation, the NASBA assay successfully detected as few as 10 PFU from seeded lake water samples. Due to its isothermal nature, its speed, and its similar sensitivity compared to the real-time RT-PCR assay, this newly reported real-time NASBA method will have broad applications for the rapid detection of HAV in contaminated food or water.     

Detection of Vibrio cholerae by real-time nucleic acid sequence-based amplification

A multitarget molecular beacon-based real-time nucleic acid sequence-based amplification (NASBA) assay for the specific detection of Vibrio cholerae has been developed. The genes encoding the cholera toxin (ctxA), the toxin-coregulated pilus (tcpA; colonization factor), the ctxA toxin regulator (toxR), hemolysin (hlyA), and the 60-kDa chaperonin product (groEL) were selected as target sequences for detection. The beacons for the five different genetic targets were evaluated by serial dilution of RNA from V. cholerae cells. RNase treatment of the nucleic acids eliminated all NASBA, whereas DNase treatment had no effect, showing that RNA and not DNA was amplified. The specificity of the assay was investigated by testing several isolates of V. cholerae, other Vibrio species, and Bacillus cereus, Salmonella enterica, and Escherichia coli strains. The toxR, groEL, and hlyA beacons identified all V. cholerae isolates, whereas the ctxA and tcpA beacons identified the O1 toxigenic clinical isolates. The NASBA assay detected V. cholerae at 50 CFU/ml by using the general marker groEL and tcpA that specifically indicates toxigenic strains. A correlation between cell viability and NASBA was demonstrated for the ctxA, toxR, and hlyA targets. RNA isolated from different environmental water samples spiked with V. cholerae was specifically detected by NASBA. These results indicate that NASBA can be used in the rapid detection of V. cholerae from various environmental water samples. This method has a strong potential for detecting toxigenic strains by using the tcpA and ctxA markers. The entire assay including RNA extraction and NASBA was completed within 3 h.     

Detection of infectious salmon anaemia virus by real-time nucleic acid sequence based amplification

We have developed a real-time nucleic acid sequence based amplification (NASBA) procedure for detection of infectious salmon anaemia virus (ISAV). Primers were designed to target a 124 nucleotide region of ISAV genome segment 8. Amplification products were detected in real-time with a molecular beacon (carboxyfluorescin [FAM]-labelled and methyl-red quenched) that recognised an internal region of the target amplicon. Amplification and detection were performed at 41 degrees C for 90 min in a Corbett Research Rotorgene. The real-time NASBA assay was compared to a conventional RT-PCR for ISAV detection. From a panel of 45 clinical samples, both assays detected ISAV in the same 19 samples. Based on the detection of a synthetic RNA target, the real-time NASBA procedure was approximately 100x more sensitive than conventional RT-PCR. These results suggest that real-time NASBA may represent a useful diagnostic procedure for ISAV.     

Evaluation of LightCycler as a Platform for Nucleic Acid Sequence-Based Amplification (NASBA) in Real-Time Detection of Enteroviruses

The nucleic acid sequence-based amplification (NASBA) assay has been demonstrated to be more sensitive for detection of enteroviruses (EV) than RT-PCR. Many laboratories, however, do not have a dedicated instrument for the NASBA assay. This study aimed to evaluate the use of the Roche LightCycler as a platform for performing the NASBA assay for detection of EV. A diverse subgenera of EV were used to assess the specificity of the NASBA assay, including coxsackie, echovirus, poliovirus, and other enteroviruses together with related and unrelated viruses, including rhinovirus, respiratory syncytial virus, herpes simplex virus, adenovirus, influenza virus A, and cytomegalovirus. All species of EV tested were successfully detected using NASBA and no cross reactivity with other viruses was observed. Using serial dilutions of EV to assess sensitivity, the NASBA assay was compared to an in-house EV RT-PCR assay. The NASBA assay demonstrated a higher level of sensitivity. Fifty-one clinical samples positive for EV by viral culture were also evaluated. All NASBA results obtained were concordant with viral culture results. This study confirmed that the NASBA assay for the detection of EV could be readily performed on the LightCycler and easily incorporated into the workflow of a diagnostic laboratory equipped with a LightCycler, thereby eliminating the need for additional instrumentation.     

A handheld NASBA analyzer for the field detection and quantification of Karenia brevis

Blooms of Karenia brevis, the red tide forming dinoflagellate in the Gulf of Mexico, cause a myriad of ecological and economic problems for coastal communities, including massive fish and mammal mortalities, and damage to tourism and fisheries/shellfish harvesting industries. There is a need for accurate detection and prediction of K. brevis blooms, including rapid and inexpensive monitoring of both water and shellfish meats to ensure the safety of shellfish harvested for human consumption. To address this issue, we have developed a protocol for easy field extraction of cellular RNA from water samples and coupled it with a handheld nucleic acid sequence-based amplification (NASBA) sensor that amplifies and detects target mRNA specific to the rbcL gene of K. brevis. This extraction protocol is a modified version of the Qiagen RNeasy Mini Kit spin protocol and requires no specialized equipment or training. Once extracted, the RNA is amplified and detected by NASBA in an in-house designed and produced handheld sensor that provides a real-time fluorescence plotting of the amplification. Both the field RNA extraction protocol and the handheld NASBA analyzer compared favorably to laboratory-based technologies. In duplicate reactions, the amplification curves generated with the handheld detector closely mirrored the curves generated with the bench top Nuclisens EasyQ NASBA analyzer and there was no difference in the sensitivity obtained using the handheld device versus the bench top models. This extraction protocol and detection sensor will be a valuable tool for rapidly monitoring K. brevis in field environments.     

Molecular beacon probes combined with amplification by NASBA enable homogeneous, real-time detection of RNA.

Molecular beacon probes can be employed in a NASBA amplicon detection system to generate a specific fluorescent signal concomitantly with amplification. A molecular beacon, designed to hybridize within the target sequence, was introduced into NASBA reactions that amplify the genomic RNA of potato leafroll virus (PLRV). During amplification, the probe anneals to the antisense RNA amplicon generated by NASBA, producing a specific fluorescent signal that can be monitored in real-time. The assay is rapid, sensitive and specific. As RNA amplification and detection can be carried out in unopened vessels, it minimizes the risk of carry-over contaminations. Robustness has been verified on real-world samples. This homogeneous assay, called AmpliDet RNA, is a significant improvement over current detection methods for NASBA amplicons and is suitable for one-tube applications ranging from high-throughput diagnostics to in vivo studies of biological activities.     

A nucleic acid sequence-based amplification assay for real-time detection of norovirus genogroup II

AIMS: To use molecular beacon based nucleic acid sequence-based amplification (NASBA) to develop a rapid, sensitive, specific detection method for norovirus (NV) genogroupII (GII). METHODS AND RESULTS: A method to detect NV GII from environmental samples using real-time NASBA was developed. This method was routinely sensitive to 100 copies of target RNA and intermittent amplification occurred with as few as 10 copies. Quantitative estimates of viral load were possible over at least four orders of magnitude. CONCLUSIONS: The NASBA method described here is a reliable and sensitive assay for the detection of NV. This method has the potential to be linked to a handheld NASBA device that would make this real-time assay a portable and inexpensive alternative to bench-top, lab-based assays. SIGNIFICANCE AND IMPACT OF THE STUDY: The development of the real-time NASBA assay described here has resulted in a simple, rapid (<1 h), convenient testing format for NV. To our knowledge, this is the first example of a molecular beacon based NASBA assay for NV.     

Detection of Campylobacter jejuni added to foods by using a combined selective enrichment and nucleic acid sequence-based amplification (NASBA).

An assay to detect Campylobacter jejuni in foods that uses a short selective enrichment culture, a simple and rapid isolation procedure, NASBA amplification of RNA, and a nonradioactive in solution hybridization was studied. The presence of high numbers of indigenous flora affected the sensitivity of the assay. However, detection of C. jejuni was possible up to a ratio of indigenous flora to C. jejuni of 10,000:1. Interference by food components was eliminated by centrifugation following the enrichment step. Fourteen food samples artificially inoculated with C. jejuni (1 to 1,000 CFU/10 g) were analyzed with the NASBA assay and the conventional culture method with Campylobacter charcoal differential agar (CCDA). A few false-negative results were obtained by both NASBA (1.42%) and CCDA (2.86%) isolation. Yet the use of enrichment culture and NASBA shortened the analysis time from 6 days to 26 h. The relative simplicity and rapidity of the NASBA assay make it an attractive alternative for detection of C. jejuni in food samples.     

Detection of human enteroviruses with real-time PCR assay using TaqMan fluorescent probe

Infections with human enteroviruses are common worldwide and cause a wide range of signs and symptoms. Nowadays in current diagnostics procedures older virological methods, such virus isolation in a cell cultures and seroneutralisation assay, are replaced with molecular biology tests. The aim of the study was development of real-time PCR assay for detection of human adenoviruses. DNA isolated from MK2 cell line infected with nineteen different enterovirus strains was used for development of a qualitative real-time PCR assay using primers targeting a conserved region of the 5'UTR region and a specific TaqMan probe. The analytical sensitivity of real-time PCR assay was tested using serial dilutions of Coxackie A9 cDNA in range between 10 degrees and 10(-8). For comparison typical end-point detected RT-PCR for enterovirus detection with the same cDNA dilutions was made. The sensitivity of novel method was about ten thousand-fold higher than older one. The conclusion is that real-time PCR is very advisable in diagnostics of diseases caused with enteroviruses. The high level of sensitivity, specificity, accuracy, and rapidity provided by this assay are favorable for the use in the detection of enteroviral RNA in clinical specimens, especially from neuroinfections.     

The Development and Application of the Two Real-Time RT-PCR Assays to Detect the Pathogen of HFMD

Large-scale Hand, Foot, and Mouth Disease (HFMD) outbreaks have frequently occurred in China since 2008, affecting more than one million children and causing several hundred children deaths every year. The pathogens of HFMD are mainly human enteroviruses (HEVs). Among them, human enterovirus 71 (HEV71) and coxsackievirus A16 (CVA16) are the most common pathogens of HFMD. However, other HEVs could also cause HFMD. To rapidly detect HEV71 and CVA16, and ensure detection of all HEVs causing HFMD, two real-time hybridization probe-based RT-PCR assays were developed in this study. One is a multiplex real-time RT-PCR assay, which was developed to detect and differentiate HEV71 specifically from CVA16 directly from clinical specimens within 1–2 h, and the other is a broad-spectrum real-time RT-PCR assay, which targeted almost all HEVs. The experiments confirmed that the two assays have high sensitivity and specificity, and the sensitivity was up to 0.1 TCID₅₀/ml for detection of HEVs, HEV71, and CVA16, respectively. A total of 213 clinical specimens were simultaneously detected by three kinds of assays, including the two real-time RT-PCR assays, direct conventional RT-PCR assay, and virus isolation assay on human rhabdomyosarcoma cells (RD cells). The total positive rate of both HEV71 and CVA16 was 69.48% with real-time RT-PCR assay, 47.42% with RT-PCR assay, and 34.58% with virus isolation assay. One HFMD clinical specimen was positive for HEV, but negative for HEV71 or CVA16, which was identified as Echovirus 11 (Echo11) by virus isolation, RT-PCR, and sequencing for the VP1 gene. The two real-time RT-PCR assays had been applied in 31 provincial HFMD labs to detect the pathogens of HFMD, which has contributed to the rapid identification of the pathogens in the early stages of HFMD outbreaks, and helped to clarify the etiologic agents of HFMD in China.     

Detection of Vibrio cholerae by Real-Time Nucleic Acid Sequence-Based Amplification

A multitarget molecular beacon-based real-time nucleic acid sequence-based amplification (NASBA) assay for the specific detection of Vibrio cholerae has been developed. The genes encoding the cholera toxin (ctxA), the toxin-coregulated pilus (tcpA; colonization factor), the ctxA toxin regulator (toxR), hemolysin (hlyA), and the 60-kDa chaperonin product (groEL) were selected as target sequences for detection. The beacons for the five different genetic targets were evaluated by serial dilution of RNA from V. cholerae cells. RNase treatment of the nucleic acids eliminated all NASBA, whereas DNase treatment had no effect, showing that RNA and not DNA was amplified. The specificity of the assay was investigated by testing several isolates of V. cholerae, other Vibrio species, and Bacillus cereus, Salmonella enterica, and Escherichia coli strains. The toxR, groEL, and hlyA beacons identified all V. cholerae isolates, whereas the ctxA and tcpA beacons identified the O1 toxigenic clinical isolates. The NASBA assay detected V. cholerae at 50 CFU/ml by using the general marker groEL and tcpA that specifically indicates toxigenic strains. A correlation between cell viability and NASBA was demonstrated for the ctxA, toxR, and hlyA targets. RNA isolated from different environmental water samples spiked with V. cholerae was specifically detected by NASBA. These results indicate that NASBA can be used in the rapid detection of V. cholerae from various environmental water samples. This method has a strong potential for detecting toxigenic strains by using the tcpA and ctxA markers. The entire assay including RNA extraction and NASBA was completed within 3 h.     

Development of conventional and real-time NASBA for the detection of Legionella species in respiratory specimens

Isothermal nucleic acid sequence-based amplification (NASBA) was applied to detect Legionella 16S rRNA. The assay was originally developed as a Legionella pneumophila conventional NASBA assay with electrochemiluminescence (ECL) detection and was subsequently adapted to a L. pneumophila real-time NASBA format and a Legionella spp. real-time NASBA using molecular beacons. L. pneumophila RNA prepared from a plasmid construct was used to assess the analytical sensitivity of the assay. The sensitivity of the NASBA assay was 10 molecules of in vitro wild type L. pneumophila RNA and 0.1-1 colony-forming units (CFU) of L. pneumophila. In spiked respiratory specimens, the sensitivity of the NASBA assays was 1-10000 CFU of L. pneumophila serotype 1 depending on the background. After dilution of the nucleic acid extract prior to amplification, 1-10 CFU of L. pneumophila serotype 1 could be detected with both detection methods. Finally, 27 respiratory specimens, well characterized by culture and PCR, collected during a L. pneumophila outbreak, were tested by conventional and real-time NASBAs. All 11 PCR positive samples were positive by conventional NASBA, 9/11 and 10/11 were positive by L. pneumophila real-time NASBA and Legionella spp. real-time NASBA, respectively.     

戊型肝炎病毒荧光定量RT-PCR快速检测技术的建立和初步应用

利用DNAMAN软件对GenBank登录的戊型肝炎病毒四个主要基因型代表株的序列进行分析, 选择其高度保守的ORF2区域设计合成引物和探针, 并用包含有扩增区域的核苷酸片段进行体外转录制备标准品cRNA。在对荧光定量RT-PCR的反应条件优化的基础上, 建立了适用于戊型肝炎病毒主要基因型检测的荧光定量RT-PCR检测技术。该检测技术可以有效检测I型和IV型戊型肝炎阳性病料, 而对猪的其它几种疫病阳性病料则为阴性结果, 证实本技术的特异性强、可靠性好。对阳性标准品的检测结果表明, 所建立的TaqMan荧光定量RT-PCR灵敏度可达2.0×101拷贝/反应, 相比于巢式RT-PCR方法, 其灵敏度高10~100倍以上。在对54份临床样品的检测中, 进一步证实了该方法快速、灵敏且重复性好, 可满足戊型肝炎病毒早期快速诊断的需要。