Consensus RT-nested PCR detection of yellow head complex genotypes in penaeid shrimp

A consensus RT-nested (n)PCR is described that detects the six distinct genotypic variants in the yellow head virus (YHV) complex. The PCR primers targeted ORF1b gene regions more highly conserved amongst the reference strains of YHV (genotype 1) and gill-associated virus (GAV, genotype 2) and a set of 57 field isolates containing multiple representatives of each genotype. The test employed short PCR (359 bp) and nPCR (147 bp) amplicons to minimise the effects of RNA degradation. To ensure < or = 8-primer degeneracy, two primers were designed to each site, one accommodating sequence variations amongst genotype 1 isolates and the other variations amongst isolates of the other genotypes. The analytical sensitivity limits of the PCR and nPCR were estimated to be approximately 1250 and approximately 1.25 RNA copies, respectively. The superior group-specificity of the consensus RT-nPCR compared to other OIE-recommended PCR tests for YHV/GAV was demonstrated using RNA from 17 Penaeus monodon shrimp infected with representatives of each of the six genotypes. Phylogenetic analysis using the 94 nt ORF1b gene sequence spanned by the nPCR primers generated genotype assignments that were consistent with those obtained using the extended 671 nt sequence used for the initial identification of genotypes.     

A multiplex PCR for rapid and simultaneous detection of porcine circovirus type 2, porcine parvovirus,porcine pseudorabies virus,and porcine reproductive and respiratory syndrome virus in clinical specimens

A multiplex PCR (mPCR) assay was developed and evaluated for its ability to simultaneously detect multiple viral infections of swine. Specific primers were designed for each of the following four DNA or RNA viruses: porcine circovirus type 2 (PCV2), porcine parvovirus (PPV), pseudorabies virus (PRV), and porcine reproductive and respiratory syndrome virus (PRRSV). Each target produced a specific amplicon with a size of 353 bp (PCV2), 271 bp (PPV), 194 bp (PRV), or 434 bp (PRRSV). The assay was sensitive and specific in detecting each target agent in composite cell cultures and clinical specimens. Results from mPCR were confirmed by PCR for individual viruses and by virus isolation. In conclusion, the mPCR has the potential to be useful for routine molecular diagnosis and epidemiology.     

一种同时检测丙型与庚型肝炎病毒的逆转录—巢式？…

目的 庚型肝炎病毒（ＨＧＶ）与丙型肝炎病毒（ＨＣＶ）同属黄病毒科，且传播途径相似，重叠感染率高，本研究旨在建立一种同时检测ＨＧＶ与ＨＣＶ感染的方法。方法 根据ＨＣＶ与ＨＧＶ的基因序列分别选取５‘－ＵＴＲ（ＨＣＶ）与ＮＳ３（ＨＧＶ）的两套引物，在同一管内进行逆转录－巢式聚合酶锭反应，并初步应用于１５３例标本。结果 该方法能同时检出ＨＧＶ与ＨＣＶ感洒，扩增片段大小与设计相符。结论 该方法简便特异，适用     

Multiplex PCR for the detection of African cassava mosaic virus and East African cassava mosaic Cameroon virus in cassava

A multiplex PCR was developed for simultaneous detection of African cassava mosaic virus (ACMV) and East African cassava mosaic Cameroon virus (EACMCV) in cassava affected with cassava mosaic disease (CMD). One set of three primers consisting of an upstream primer common for both viruses and two down stream virus-specific primers were designed for simultaneous amplification of 368 base pair (bp) and 650 bp DNA fragments specific to the replicase gene of ACMV and EACMCV, respectively. Similarly, a second set of three primers were designed for simultaneous amplification of 540 bp and 655 bp fragments specific to the coat protein gene of EACMCV and ACMV, respectively. Primers that can amplify a 171 bp fragment of the large subunit of ribulose bisphosphate carboxylase oxygenase L were included as an internal control in these assays to determine the reliability of multiplex PCR. A simplified, cost-effective and rapid sample preparation method was adapted in place of the conventional plant DNA extraction procedure for multiplex PCR detection of ACMV and EACMCV. The method was validated using CMD-infected cassava samples obtained from farmers' fields in Nigeria. The multiplex PCR is useful for reliable assessment of the prevalence of CMBs in epidemiological studies and for crop improvement and phytosanitary programs in African countries.     

Rapid identification of the genus fonsecaea by PCR with specific oligonucleotide primers

An oligonucleotide primer set based on internal transcribed spacer regions of ribosomal DNA for PCR which gives the amplicon for only the DNA from Fonsecaea species was designed. This set yielded an amplicon with 333 bp for all strains of Fonsecaea pedrosoi and Fonsecaea compacta examined but no amplicons for related dematiaceous fungi and pathogenic yeasts. PCR using this primer set was considered to be a useful method for the rapid identification of the genus FONSECAEA:     

RT-PCR detection of yellow head virus (YHV) infection in Penaeus monodon using dried haemolymph spots

Sample collection and RNA isolation from shrimp haemolymph for RT-PCR diagnosis of yellow head virus (YHV) infections is crucial for disease control programs for cultivated shrimp in Thailand. Problems with RNA degradation arise when field samples must be collected far from the laboratory by relatively inexperienced personnel who do not have ready access to sophisticated reagents. In an attempt to solve this problem, haemolymph samples from shrimp were collected either by mixing with 10% (w/v) sodium citrate or by spotting on ISOCODE filter paper. RNA was extracted subsequently either by a rapid boiling method or by using TRI reagent and the extracts were used in a semi-quantitative, non-stop, semi-nested RT-PCR assay for YHV. Dried haemolymph spots on ISOCODE filter paper extracted with TRI reagent gave the most reliable and reproducible results. It also allowed longer periods of storage at room temperature.     

Detection and differentiation of Plum pox virus using real-time multiplex PCR with SYBR Green and melting curve analysis: a rapid method for strain typing

A real-time multiplex PCR procedure with melting curve analysis, using the green fluorescence dye SYBR Green I, was developed for rapid and reliable identification of Plum pox virus (PPV) isolates of strains D and M. Members of the different strains were identified by their distinctive melting temperatures (T(m)s); 84.3-84.43 degrees C for D isolates, and 85.34-86.11 degrees C for M isolates. The associated amplicon sizes were 114 and 380 bp, respectively. The procedure was used for detection and identification of PPV in both herbaceous and woody hosts. The Tm for members of a particular strain was very similar, with a host effect that did not hinder strain identification. Universal primers included in the study detected all isolates of PPV tested, amplifying a 74 bp fragment. The Tm of this fragment varied from 80.12 to 81.52 degrees C and may have supplementary value for PPV identification. SYBR Green-based detection was compared to detection using a hybridization LUX fluorogenic primer. Better resolution of the melting peaks was observed with SYBR Green I, than with the LUX primers, hence strain identification with SYBR Green I was more reliable. This is a simple approach to PPV strain identification with the relatively inexpensive dye SYBR Green I, and eliminates any need for electrophoretic analysis of amplicons or RFLP patterns using ethidium bromide.     

Dependence of polymerase chain reaction product inactivation protocols on amplicon length and sequence composition.

Specific diagnostic test results generated by polymerase chain reaction (PCR) depend upon control of amplicon contamination in the clinical laboratory. We compared photochemical (isopsoralen [IP]) and enzymatic (uracil N-glycosylase [UNG]) methods for their ability to prevent carryover of amplicons generated from genomic targets of five viruses. PCR products (amplicons) (herpes simplex virus, 342 bp; cytomegalovirus, 250 bp; Epstein-Barr virus, 240 bp) exposed to UV light in the presence of various concentrations of IP compound 10 (IP-10) resulted in apparent increased molecular sizes of the products, as indicated by migration patterns after gel electrophoresis, and were predictive of inactivation by the agent. For amplicons of < or = 100 bp, IP-10-induced electrophoretic shifts were related to the guanidine-cytidine (G + C) content of the PCR product; no apparent shift and no inactivation were observed for a 92-bp herpes simplex virus amplicon (G + C content, 65%), whereas the 100-bp human papillomavirus product (G + C content, 42%) showed a concentration-dependent shift (25 to 100 micrograms/ml) in electrophoretic migration and was partially inactivated. UNG effectively controlled amplicon carryover for target DNA of > or = 240 bp; however, this treatment did not inactivate the two amplicons of < or = 100 bp, regardless of the G + C content of the product. Larger products were inactivated efficiently by both methods, regardless of their G + C contents. We concluded that both IP and UNG effectively inactivated PCR amplicons but not short amplicons of < or = 100 bp. We recommend that with the adoption of PCR technology in clinical laboratories, primers should be designed to produce amplicons of at least 240 to 350 bp (depending on G + C content) and that at least one effective method of controlling carryover contamination should be incorporated into each PCR protocol.     

Development of a non-destructive PCR method for detection of the salivary gland hypertrophy virus (SGHV) in tsetse flies

A PCR based diagnostic method to detect salivary gland hypertrophy virus (SGHV) in tsetse flies is described. Two sets of primers GpSGHV1F/GpSGHV1R and GpSGHV2F/GpSGHV2R were selected from a virus-specific sequence. Both primer sets can detect specifically the virus in individual tsetse flies by generating an amplicon of 401 bp. Attempts were made to develop a simple and reliable non-destructive virus detection method in live flies. PCR reactions were performed on either crude or purified tsetse DNA from saliva and legs. While saliva can be an indicator for the presence of the virus in flies, the method is laborious. Crude extract from an excised middle leg resulted in a positive PCR reaction equivalent to crude extract from whole fly. However, sensitivity could be significantly increased when purified DNA was used as the template. In conclusion, PCR using a purified DNA template from a single tsetse leg represents an efficient, non-destructive method for virus diagnosis in live tsetse flies.     

Development and evaluation of a single-step duplex PCR for simultaneous detection of Fasciola hepatica and Fasciola gigantica (family Fasciolidae, class Trematoda, phylum Platyhelminthes)

A single-step multiplex PCR (here referred to as a duplex PCR) has been developed for simultaneous detection and diagnosis of Fasciola hepatica and F. gigantica. These species overlap in distribution in many countries of North and East Africa and Central and Southeast Asia and are similar in egg morphology, making identification from fecal samples difficult. Based on a comparative alignment of mitochondrial DNA (mtDNA) spanning the region of cox1-trnT-rrnL, two species-specific forward primers were designed, FHF (for F. hepatica) and FGF (for F. gigantica), and a single reverse primer, FHGR (common for both species). Conventional PCR followed by sequencing was applied using species-specific primer pairs to verify the specificity of primers and the identity of Fasciola DNA templates. Duplex PCR (using three primers) was used for testing with the DNA extracted from adult worms, miracidia, and eggs, producing amplicons of 1,031 bp for F. hepatica and 615 bp for F. gigantica. The duplex PCR failed to amplify from DNA of other common liver and intestinal trematodes, including two opisthorchiids, three heterophyids, an echinostomid, another fasciolid, and a taeniid cestode. The sensitivity assay showed that the duplex PCR limit of detection for each Fasciola species was between 0.012 ng and 0.006 ng DNA. Evaluation using DNA templates from 32 Fasciola samples (28 adults and 4 eggs) and from 25 field-collected stools of ruminants and humans revealed specific bands of the correct size and the presence of Fasciola species. This novel mtDNA duplex PCR is a sensitive and fast tool for accurate identification of Fasciola species in areas of distributional and zonal overlap.     

Universal primer quantitative fluorescent multiplex (UPQFM) PCR: a method to detect major and minor rearrangements of the low density lipoprotein receptor gene

A method based on quantitative fluorescent multiplex PCR has been developed to detect major rearrangements of the low density lipoprotein receptor gene (LDLR) which account for approximately 5% of mutations. The method involves two PCR reactions; the first (P1) amplifies the selected exons using unique primer sequences tagged with newly designed universal primers, while the second (P2) amplifies the P1 amplicons using the universal primers. One of the P2 universal primers is labelled with a fluorescent dye which is incorporated into the PCR products which are then electrophoresed on an ABI DNA sequencer. The relative amounts of the amplified peak areas are determined and compared to ratios obtained for DNA from four normal controls and known major rearrangements. The multiplex set developed is based on LDLR exons 3, 5, 8, 14, and 17 and 86% of reported major rearrangements would be detectable by this assay as well as any deletions and insertions of greater than 1 bp. The method was evaluated using DNA from 15 reported deletions and duplications which were all correctly identified. Two groups of UK patients with a clinical diagnosis of familial hypercholesterolaemia (FH) and where no mutation had been identified in LDLR or APOB (14 children and 42 adults) were screened for the presence of major LDLR rearrangements by this assay. Three major rearrangements were detected and a 4 bp duplication was identified in a fourth patient. Since it avoids the problems associated with Southern blotting, this method will be useful for detecting gene rearrangements.     

Multiplex PCR for distinguishing the most common phase-1 flagellar antigens of Salmonella spp

Most Salmonella serotypes alternatively express either phase-1 or phase-2 flagellar antigens, encoded by the fliC and fljB genes, respectively. Flagellar phase reversal for the identification of both flagellar antigens is not necessary at the genetic level. Variable internal regions of the fliC genes encoding the H:i, H:r, H:l,v, H:e,h, H:z(10), H:b, and H:d antigens have been sequenced; and the specific sites for each antigen in selected Salmonella serotypes have been determined. These results, together with flagellar G-complex variable internal sequences obtained by the Foodborne and Diarrheal Diseases Branch at the Centers for Disease Control and Prevention in Atlanta, GA, have been used to design a multiplex PCR to identify the G-complex antigens as well as the H:i, H:r, H:l,v, H:e,h, Hz(10), H:b, and H:d first-phase antigens. These antigens are part of the most common Salmonella serotypes possessing first-phase flagellar antigens. Salmonella enterica serotype Enteritidis is identified by adding a specific primer pair published previously. This multiplex PCR includes 13 primers. A total of 161 Salmonella strains associated with 72 different serotypes were tested. Each strain generated one first-phase-specific antigen fragment ranging from 100 to 500 bp; Salmonella serotype Enteritidis, however, generated two amplicons of 500 bp that corresponded to the G complex and a 333-bp serotype-specific amplicon, respectively. Twenty-three strains representing 19 serotypes with flagellar genes different from those targeted in this work did not generate any fragments. The method is quick, specific, and reproducible and is independent of the phase expressed by the bacteria when they are tested.     

Target for standard Thai PCR assay identical in 12 white spot syndrome virus (WSSV) types that differ in DNA multiple repeat length

A Thai PCR detection method (WSSV-232) yielding a 232 bp amplicon has been used for detection of white spot syndrome virus (WSSV) since 1996. It targets ORF 91 in the full sequence of the only Thai WSSV isolate at GenBank (AF369029). At the beginning of 2002, some Thai shrimp farmers complained that ponds stocked with WSSV-232 PCR negative post-larvae (PL) later suffered WSSV disease outbreaks. Although these outbreaks may have resulted from horizontal transmission of WSSV after stocking, it was also possible that they resulted from false negative PCR test results due to genetic changes at the PCR-assay target after the first appearance of WSSV in Thailand in 1995. Indeed, recent results have revealed at least 12 WSSV variants in Thailand that can be distinguished based on differences in DNA multiple repeat lengths in ORF 94 (GenBank AF369029). To test for variation in the WSSV-232 target sequence in ORF 91, 20 DNA extracts derived from field samples and representing 9 of the WSSV DNA multiple repeat groups were subjected to PCR amplification and sequencing using primers that generated a 403 bp amplicon covering the target for the WSSV-232 assay. An additional three repeat types were included from archived material. Analysis revealed that the 232 bp target sequence in ORF 91 was unchanged in all of the 12 types tested and that the original WSSV-232 detection system was still valid. Thus, any false negative PCR test results leading to farmer complaints would probably have arisen from small sample sizes and low sensitivity of the single-step PCR assay. If so, false negative results could be reduced by the use of nested PCR assays with larger PL sample sizes.     

Characterization of Staphylococcus aureus of cattle mastitis origin for two virulence-associated genes (coa and spa)

Bovine mastitis caused by Staphylococcus aureus is a worldwide disease of high economic significance. These organisms possess many virulence factors allowing them to evade host immune system. In the present study, 28 S. aureus isolates from milk obtained from Holstein–Friesian (H-F) crossbred and Rathi (a native breed) cattle with clinical mastitis were characterized for their two virulence-associated genes: coa and spa. All the isolates were confirmed genotypically by 23S rRNA ribotyping in which a species specific amplicon of 1,250 bp was obtained. Polymorphism was recorded in coa and spa genes. The coa gene produced one amplicon in each isolate either of 510, 600, 710 or 850 bp size with more variability observed in the Rathi isolates. The AluI restriction endonuclease generated three and five RFLP patterns with isolates from H-F crossbred and Rathi cattle, respectively. The RFLP patterns obtained from similar amplicons in isolates from two breeds did not differ. PCR amplification of the X-region for spa gene yielded amplicons of seven different sizes: 206, 243, 262, 277, 292, 306 and 339 bp with calculated number of 7, 8, 9, 10, 10, 11 and 12 bp repeats, respectively indicating presence of highly pathogenic strains. Among all the spa types, four were common to both animal groups, one was unique to H-F crossbred cattle and two were unique to Rathi cattle.