Removal of inhibitory substances from human fecal specimens for detection of group A rotaviruses by reverse transcriptase and polymerase chain reactions

Isolation, purification, and characterization of a killer protein from Schwanniomyces occidentalis

The yeast Schwanniomyces occidentalis produces a killer toxin lethal to sensitive strains of Saccharomyces cerevisiae. Killer activity is lost after pepsin and papain treatment, suggesting that the toxin is a protein. We purified the killer protein and found that it was composed of two subunits with molecular masses of approximately 7.4 and 4.9 kDa, respectively, but was not detectable with periodic acid-Schiff staining. A BLAST search revealed that residues 3 to 14 of the 4.9-kDa subunit had 75% identity and 83% similarity with killer toxin K2 from S. cerevisiae at positions 271 to 283. Maximum killer activity was between pH 4.2 and 4.8. The protein was stable between pH 2.0 and 5.0 and inactivated at temperatures above 40 degrees C. The killer protein was chromosomally encoded. Mannan, but not beta-glucan or laminarin, prevented sensitive yeast cells from being killed by the killer protein, suggesting that mannan may bind to the killer protein. Identification and characterization of a killer strain of S. occidentalis may help reduce the risk of contamination by undesirable yeast strains during commercial fermentations.

NSP4 gene analysis of rotaviruses recovered from infected children with and without diarrhea

The transmembrane glycoprotein NSP4 functions as a viral enterotoxin capable of inducing diarrhea in young mice. It has been suggested that NSP4 may be a key determinant of rotavirus pathogenicity and a target for vaccine development. Twenty two G1P[6] rotaviruses from babies with and without diarrhea were comparatively analyzed along with reference strains and another 22 Taiwanese human rotaviruses of G and P combination types different from the G1P[6] type. The sequence variations in the NSP4 genes were studied by direct sequencing analysis of the amplicons of reverse transcription-PCR. Two genetic groups could be identified in this analysis. While the majority of these strains were closely related to the Wa strain, the G2 viruses were closely related to the S2 strain. Furthermore, phylogenetic analysis of the NSP4 gene among the G2 rotaviruses revealed three distinct lineages associated with DS-1, S2, and E210, respectively, as has been reported previously for the VP7 gene. However, we found no apparent correlation in the deduced amino acid sequences corresponding to the proposed enterotoxic peptide region between the rotaviruses recovered from individuals with and without diarrhea. The NSP4 gene product being a pathogenic determinant may not be a generalized phenomenon.

PCR detection of Escherichia coli O157:H7 directly from stools: evaluation of commercial extraction methods for purifying fecal DNA

Rapid identification of Escherichia coli O157:H7 is important for patient management and for prompt epidemiological investigations. We evaluated one in-house method and three commercially available kits for their ability to extract E. coli O157:H7 DNA directly from stool specimens for PCR. Of the 153 stool specimens tested, 107 were culture positive and 46 were culture negative. The sensitivities and specificities of the in-house enrichment method, IsoQuick kit, NucliSens kit, and QIAamp kit were comparable, as follows: 83 and 98%, 85 and 100%, 74 and 98%, and 86 and 100%, respectively. False-negative PCR results may be due to the presence of either inherent inhibitors or small numbers of organisms. The presence of large amounts of bacteria relative to the amount of the E. coli O157:H7 target may result in the lower sensitivities of the assays. All commercial kits were rapid and easy to use, although DNA extracted with the QIAamp kit did not require further dilution of the DNA template prior to PCR.

Colorectal cancer screening by detection of altered human DNA in stool: feasibility of a multitarget assay panel

BACKGROUND & AIMS

Assay of altered DNA exfoliated into stool represents an intriguing approach to screen for colorectal neoplasia, but multiple markers must be targeted because of genetic heterogeneity. We explored the feasibility of a stool assay panel of selected DNA alterations in discriminating subjects with colorectal neoplasia from those without.

METHODS

Freezer-archived stools were analyzed in blinded fashion from 22 patients with colorectal cancer, 11 with adenomas > or =1 cm, and 28 with endoscopically normal colons. After isolation of human DNA from stool by sequence-specific hybrid capture, assay targets included point mutations at any of 15 sites on K-ras, p53, and APC genes; Bat-26, a microsatellite instability marker; and highly amplifiable DNA.

RESULTS

Analyzable human DNA was recovered from all stools. Sensitivity was 91% (95% confidence interval, 71%-99%) for cancer and 82% (48%-98%) for adenomas > or =1 cm with a specificity of 93% (76%-99%). Excluding K-ras from the panel, sensitivities for cancer were unchanged but decreased slightly for adenomas to 73% (39%-94%), while specificity increased to 100% (88%-100%).

CONCLUSIONS

Assay of altered DNA holds promise as a stool screening approach for colorectal neoplasia. Larger clinical investigations are indicated.

Biotechnical use of polymerase chain reaction for microbiological analysis of biological samples

Since its introduction in the mid-80s, polymerase chain reaction (PCR) technology has been recognised as a rapid, sensitive and specific molecular diagnostic tool for the analysis of micro-organisms in clinical, environmental and food samples. Although this technique can be extremely effective with pure solutions of nucleic acids, it's sensitivity may be reduced dramatically when applied directly to biological samples. This review describes PCR technology as a microbial detection method, PCR inhibitors in biological samples and various sample preparation techniques that can be used to facilitate PCR detection, by either separating the micro-organisms from PCR inhibitors and/or by concentrating the micro-organisms to detectable concentrations. Parts of this review are updated and based on a doctoral thesis by Lantz [1] and on a review discussing methods to overcome PCR inhibition in foods [2].

Quality control and optimized procedure of hybridization capture-PCR for the identification of Mycobacterium avium subsp. paratuberculosis in faeces

Nucleic acid sequence capture techniques are used to improve both the sensitivity and specificity of PCR for the diagnosis of plant, animal and human diseases. Hybridization capture-PCR (HC-PCR) was first reported as a method for the detection of Mycobacterium avium subsp. paratuberculosis in 1995 and was successfully trialed on a small number of faecal samples from cattle with Johne's disease. A locally optimized HC-PCR method was evaluated on faeces from infected and non-infected animals. However, sample to sample cross contamination during the DNA purification step highlighted that the original format of the test was unsuitable for routine diagnostic use. Here, we report modifications and optimization of HC-PCR, particularly with respect to DNA purification from faeces, hybridization and capture steps. We also identified procedurally sensitive critical points in the test during capture and washing of magnetic beads. Southern blotting was omitted from the protocol to preserve specificity but this resulted in analytical sensitivity of 5000 organisms per 200 mg faecal sample. Nevertheless, HC-PCR detected M.paratuberculosis in pellets from infected sheep diluted at rates of up to 1 in 100 in normal faeces, suggesting that the technique should be evaluated further for low-cost diagnosis in flocks/herds using pooled samples.

Human caliciviruses in acute gastroenteritis of young children in the community

Episodes of acute gastroenteritis in prospectively followed children between 2 months and 2 years of age were examined for rotaviruses, enteric adenoviruses, astroviruses, and human caliciviruses, including both Norwalk-like viruses (NLVs) and Sapporo-like viruses (SLVs), using PCR and reverse transcription (RT)-PCR assays. A virus was identified in 60% (502/832) of all episodes and in 85% of the moderately severe or severe episodes. Human caliciviruses were as common as rotaviruses, both being detected in 29% of the cases. NLVs accounted for a 20% etiologic share of all cases; the clinical picture was a moderately severe disease with vomiting as a predominant symptom. SLVs were detected in 9% of the cases, the clinical picture being a mild diarrheal disease. Astroviruses were found in 10% and enteric adenoviruses in 6% of the cases. Diagnosis with PCR and RT-PCR methods increases the detection of all gastroenteritis viruses, particularly human caliciviruses. As a group, human caliciviruses are common causative agents of gastroenteritis in children <2 years of age in Finland, and, of these, NLVs cause more severe disease than SLVs.

Diagnosis of Enterocytozoon bieneusi by PCR in stool samples eluted from filter paper disks

We report a PCR-based assay for the detection of Enterocytozoon bieneusi. We extracted DNA from feces which had been applied to filter paper disks and evaluated four preserving solutions. Infected specimens were identified by electrophoresis of amplicons from concentrated formalin-fixed samples and unconcentrated fresh feces. Our findings demonstrate that this methodology is effective for sample collection, mailing, and diagnosis of this pathogen.

The detection of Coxiella burnetii from ovine genital swabs, milk and fecal samples by the use of a single touchdown polymerase chain reaction

The polymerase chain reaction (PCR), targeting the repetitive transposon-like region of Coxiella burnetii (Trans-PCR), was evaluated for its ability to detect directly C. burnetii in genital swabs, milk and fecal specimens of ewes. By using a combination of centrifugation step, DNA purification using Qiamp Tissue kit followed by Trans-PCR assay, the efficiency for detection of coxiella in ewes milk samples was further improved and one C. burnetii-cell could be detected in 1ml of milk. In addition, an effective, simple and rapid method to remove PCR-inhibitory substances from fecal specimens by simply diluting the DNA template to 1:100 is described, which made the detection of one microorganism per mg of sample then possible. The results obtained from seropositive ewes proved that C. burnetii could also be detected in milk and fecal samples of naturally infected animals.

The demonstration of Pasteurella multocida in the alimentary tract of chickens after experimental oral infection

A selective medium containing polymyxin B, crystal violet, thallous acetate, bacitracin and cycloheximide in 10% sheep blood dextrose starch agar, and a modified Pasteurella multocida-specific polymerase chain reaction (PCR) assay were developed for the respective isolation and detection of P. multocida from chicken alimentary tract. The selective medium and the PCR assay were highly sensitive, detecting 100 cfu from colon contents. These techniques were used to follow the localisation of an orally administered virulent P. multocida in chickens. Pasteurellae could be isolated from the crop of some birds up to 30 h, occasionally from other sites after 28 h. It was concluded that the crop was a likely site for colonisation and that infection was most likely to occur through the mucosa of the jejunum or ileum.

Rapid identification and quantification of Collinsella aerofaciens using PCR

The number and incidence of Collinsella aerofaciens in the human intestine are the highest among Gram-positive non-spore-forming bacilli. Identification of this species is very difficult and requires considerable time. A PCR-based identification system using C. aerofaciens-specific primers is described. Using this PCR method, we identified 181 C. aerofaciens-like species isolated from human feces. These 181 strains were identified using the traditional method in past studies. Results of both methods matched. The direct detection method was performed using human feces samples from seven adults. Nested PCR was applied directly to the samples and all seven samples were positive. Quantification studies were performed using LightCycler¿trade mark omitted¿. The assay uses a double-stranded DNA dye to continuously monitor product formation and in a short time is able to quantify samples to 5 log units in concentration.

Comparison of six nucleic acid extraction methods for detection of viral DNA or RNA sequences in four different non-serum specimen types

BACKGROUND

Extraction of viral nucleic acids from serum samples is widely used in diagnostic pathology tests. However, the heterogeneous nature of non-serum samples may contribute to variations in the yields of viral nucleic acids with different extraction methods and specimen types.

OBJECTIVES

Six different methods were compared for optimal extraction of viral DNA or RNA from four types of non-serum specimens.

STUDY DESIGN

The DNA viruses used were herpes simplex virus and cytomegalovirus. The RNA viruses were poliovirus, rotavirus and small round structured virus. The specimens used were from respiratory, genital, faecal and peripheral blood mononuclear cell samples. The extracted nucleic acids were amplified by PCR and detected in an enzyme immunoassay using digoxygenin-labelled amplicons.

RESULTS AND CONCLUSIONS

For extraction of viral DNA, the phenol-chloroform method yielded the highest amount of DNA as judged by endpoint titration. The three methods compared for extraction of viral RNA used guanidine isothiocyanate and the QiaRNA kit was shown to yield the highest amount of viral RNA.

Use of macroporous polypropylene filter to allow identification of bacteria by PCR in human fecal samples

The detection of pathogenic bacteria directly in human fecal specimens by PCR, requires removal of PCR-inhibitory substances. To investigate whether five different macroporous filters (polypropylene, nylon, polyester, polyethylene, fluorocarbon) could retain polysaccharides, major PCR inhibitors, an in vitro model and human fecal samples were used. The in vitro model consisted of Xanthum gum solutions (3 mg/ml PBS), a bacterial polysaccharide, to which Helicobacter pylori cells were added. Fecal samples from healthy volunteers were spiked with H. pylori and Mycobacterium paratuberculosis cells. Polysaccharide concentrations were significantly reduced only by the polypropylene but not by the other filters. Accordingly, both Xanthum gum solutions and spiked fecal specimens became PCR positive only after filtration with the polypropylene filter. We conclude that this filter can be used to prepare a bacterial DNA template suitable for PCR analysis from human feces.

VP7 and VP4 genotyping of human group A rotavirus in Buenos Aires, Argentina

Specific and sensitive tests for the detection and typing of group A rotavirus strains are needed for a more comprehensive knowledge of the epidemiology of rotaviral infection. In this study 500 stool specimens taken from 1996 to 1998 from children with acute diarrhea in Buenos Aires were examined. Group A rotavirus was unequivocally demonstrated in 62% of the samples tested by enzyme-linked immunosorbent assay (ELISA) for detection of VP6 antigen, polyacrylamide gel electrophoresis of double-stranded RNA, and reverse transcription-PCR (RT-PCR) for amplification of the VP7:G (1, 062 bp) and VP4:P (876 bp) genes. Only five positive specimens were found by RT-PCR but not by ELISA. G and P typing was carried out by nested amplification of variable sequences of the VP7 and the VP4 genes with six G- and five P-type-specific primers (multiplex PCR). Results obtained by this method showed the prevalence of the following G and P types: G1, 39%; G2, 43%; G4, 4%; P[8], 16%; P[4], 71%. Unexpectedly, the G-P type combination most frequently found was G2P[4] (43%) rather than G1P[8] (12%), which is the most commonly found worldwide. Unusual strains of the type G1P[4] accounted for 14% of the total, while mixed infections with more than one type were found in 10% of the samples. Detection of fecal rotavirus-specific immunoglobulin M (IgM) and IgA antibodies in consecutive samples of two patients taken at daily intervals demonstrated that high levels of IgM and IgA antibodies were detected on day 1 after the onset of disease and that the samples remained positive for about 10 days, after which virus shedding was no longer observed. Multiplex PCR offers a sensitive and specific alternative to determine the prevalence of group A rotavirus G and P types and to identify the emergence of uncommon strains, whereas detection of fecal IgM and IgA antibodies represents a useful supplement to virus detection for the diagnosis of current or recently acquired infections.

Direct detection of Sabin poliovirus vaccine strains in stool specimens of first-dose vaccinees by a sensitive reverse transcription-PCR method

A multiplex reverse transcription-PCR method was optimized to monitor the duration of excretion of Sabin poliovirus strains in stools of vaccinees following administration of the first dose of the trivalent oral vaccine. The assay detected approximately 1 50% tissue culture infective dose of each poliovirus serotype spiked into cell culture media. Although PCR inhibitors were frequently encountered in the stool specimens, a 1:20 dilution of the extracted RNA was sufficient to obtain a positive PCR result. Analysis of 195 stool specimens collected from 26 vaccinees showed that poliovirus types 1, 2, and 3 were identified more frequently by PCR than by tissue culture isolation. The percentages of specimens positive by PCR for poliovirus types 1, 2, and 3 were 67.2, 82.6, and 53.8, respectively. In contrast, the culture method identified types 1, 2, and 3 virus in 55.4, 64.1, and 27.7% of the samples, respectively. Poliovirus type 2 excretion was detected by PCR in practically all of the oral poliovirus vaccine recipients for 4 to 8 weeks following vaccination. In contrast, excretion of type 1 and 3 viruses was more variable, with a range of 1 to 8 weeks. Shedding of type 3 virus ceased in approximately 70% of vaccinees within a week after immunization. In addition to an enhanced sensitivity for the detection of poliovirus, this PCR method permits the direct characterization of virus in stool specimens without further passage in culture, which may select for genetic variants that may not accurately reflect the virus composition in the original specimen.

Comparison of seven RNA extraction methods on stool and shellfish samples prior to hepatitis A virus amplification

When choosing an extraction method, two parameters have to be considered: recovery of the viral material and elimination or inactivation of inhibitory substances. Seven techniques for extracting hepatitis A virus (HAV) from stool and shellfish samples were compared, in order to identify the protocol most suited to both types of sample and with the best extraction yield. The protocols tested were either techniques for the recovery and purification of total RNA, such as RNAzol, PEG-CETAB, GTC-silica and Chelex, or techniques for isolating specifically HAV using a nucleotide probe or a monoclonal antibody. For stool samples, RNAzol, PEG-CETAB, and magnetic beads with antibody allowed detection of the virus in 11/12 and 12/12 of samples. For shellfish samples, three protocols allowed RNA to be extracted in 90% of cases, RNAzol, PEG-CETAB, and GTC-silica. Their rapidity and low cost make RNAzol and GTC-silica the most suitable for routine diagnostic testing. reserved.

Rapid and sensitive assay for detection of enterotoxigenic Bacteroides fragilis

Bacteroides fragilis is an obligatory anaerobic, gram-negative bacterium found among the normal intestinal flora of humans. Enterotoxigenic strains of B. fragilis (ETBF) have been associated with diarrheal diseases in humans and animals. The enterotoxin of ETBF induces fluid changes in ligated intestinal segments and cytotoxic response in HT29/C1 cells. By using a pair of monoclonal antibodies (MAbs; MAb C3 and MAb 4H8) specific for the lipopolysaccharide of B. fragilis, an assay based on immunomagnetic separation (IMS) in combination with PCR (IMS-PCR) was developed. After DNA extraction, a 294-bp fragment was amplified. The specificity of the IMS-PCR assay was evaluated by adding previously isolated and confirmed ETBF strains to normal fecal samples. All fecal samples to which ETBF strains were added were positive, showing a 100% specificity. The spiked fecal samples were also used for evaluation of the sensitivity of the assay. The detection limit was found to be approximately 50 CFU/g of feces. By this method 10 clinical fecal samples (5 from patients with diarrhea and 5 from healthy controls) were examined. The results of PCR were in accordance with the results of the HT29/C1 cell assay for all samples. The minimum time to retrieval of the final result by the IMS-PCR method is 36 h. The proposed IMS-PCR assay is rapid and sensitive for the direct detection of ETBF in stool samples.

Capacity of nine thermostable DNA polymerases To mediate DNA amplification in the presence of PCR-inhibiting samples

The PCR is an extremely powerful method for detecting microorganisms. However, its full potential as a rapid detection method is limited by the inhibition of the thermostable DNA polymerase from Thermus aquaticus by many components found in complex biological samples. In this study, we have compared the effects of known PCR-inhibiting samples on nine thermostable DNA polymerases. Samples of blood, cheese, feces, and meat, as well as various ions, were added to PCR mixtures containing various thermostable DNA polymerases. The nucleic acid amplification capacity of the nine polymerases, under buffer conditions recommended by the manufacturers, was evaluated by using a PCR-based detection method for Listeria monocytogenes in the presence of purified template DNA and different concentrations of PCR inhibitors. The AmpliTaq Gold and the Taq DNA polymerases from Thermus aquaticus were totally inhibited in the presence of 0.004% (vol/vol) blood in the PCR mixture, while the HotTub, Pwo, rTth, and Tfl DNA polymerases were able to amplify DNA in the presence of 20% (vol/vol) blood without reduced amplification sensitivity. The DNA polymerase from Thermotoga maritima (Ultma) was found to be the most susceptible to PCR inhibitors present in cheese, feces, and meat samples. When the inhibitory effect of K and Na ions was tested on the nine polymerases, HotTub from Thermus flavus and rTth from Thermus thermophilus were the most resistant. Thus, the PCR-inhibiting effect of various components in biological samples can, to some extent, be eliminated by the use of the appropriate thermostable DNA polymerase.

The rationale and method for constructing internal control DNA used in pertussis polymerase chain reaction

The inclusion of an appropriate internal control DNA in polymerase chain reaction (PCR) is a rapid and simple method for the detection of PCR failure. Two PCR coamplification internal control DNAs (ICD I and ICD II) with the same primer-binding sequences as the target DNA for the detection of Bordetella pertussis and Bordetella parapertussis were produced using an overlap extension technique and a PCR MIMIC construction kit, respectively. The ICD II was further evaluated in a prospective clinical study in 360 patients with a clinical diagnosis of pertussis. From 360 nasopharyngeal swabs the internal control was positive in 318 (88%) samples, but was negative in 42 (12%). After phenol-chloroform extraction an additional 10 internal controls became positive. For the detection of PCR failure, the use of internal control DNA is highly recommended for PCR-based identification of B. pertussis and B. parapertussis organisms from nasopharyngeal swabs and aspirates.

Detection of Echinococcus multilocularis in the definitive host: coprodiagnosis by PCR as an alternative to necropsy

Recently, extensions of the range of Echinococcus multilocularis in Europe and North America and drastic increases in fox populations in Europe put an increasing proportion of the human population at risk of alveolar echinococcosis. To obtain data on the local infection pressure, studies of the prevalence of the parasite in the animals that transmit the parasite, foxes, dogs, and cats, are urgently required. Such investigations, however, have been hampered by the need for necropsy of the host animal to specifically diagnose infection with the parasite. In this study, a nested PCR and an improved method for DNA extraction were developed to allow the sensitive and specific diagnosis of E. multilocularis infections directly from diluted fecal samples from foxes. The target sequence for amplification is part of the E. multilocularis mitochondrial 12S rRNA gene. The specificity of the method was 100% when it was tested against 18 isolates (metacestodes and adult worms) of 11 cestode species, including E. granulosus. The sensitivity of the method was evaluated by adding egg suspensions and individual eggs to samples of diluted feces from uninfected foxes. The presence of one egg was sufficient to give a specific signal. To confirm the PCR results, an internal probe which hybridized only with E. multilocularis amplification products but not with the DNA of other cestodes was constructed. In order to investigate the applicability of this method for epidemiological studies, 250 wild foxes from a area in southern Germany where echinococcosis is highly endemic were examined by both necropsy and PCR of rectal contents. The sensitivity correlated with the parasites' number and stage of maturity. It ranged from 100% (>1,000 gravid worms) to 70% (<10 nongravid worms). On the basis of positive PCR results for 165 foxes, the sensitivity of the traditional and widely used necropsy method was found to be not higher than 76%. We therefore present this PCR system as an alternative method for the routine diagnosis of E. multilocularis in carnivores.

Detection of bovine torovirus in fecal specimens of calves with diarrhea from Ontario farms

Breda virus (BRV), a member of the genus Torovirus, is an established etiological agent of disease in cattle. BRV isolates have been detected in the stools of neonatal calves with diarrhea in both Iowa and Ohio and in several areas of Europe. However, this virus has been reported only once in Canada. Therefore, a study was performed to determine the extent to which bovine torovirus is present in calves with diarrhea from farms in southern Ontario. A total of 118 fecal samples from symptomatic calves and 43 control specimens from asymptomatic calves were examined by electron microscopy (EM) and reverse transcription-PCR (RT-PCR) for the presence of torovirus. Torovirus RNA was detected in 43 of the 118 diarrheic samples (36.4%) by RT-PCR with primers designed in the conserved 3' end of the torovirus genome. By EM, torovirus particles were observed in 37 of the 118 specimens (31.4%). All but one of these samples were also positive by RT-PCR. The incidence of torovirus in the asymptomatic control specimens by RT-PCR was only 11.6%. To establish the identity of the particles observed in the diarrheic specimens, five of the amplicons from samples positive by both RT-PCR and EM were cloned and sequenced. Nucleotide sequence analysis revealed that the bovine torovirus found in southern Ontario manifests between 96 and 97% sequence identity to the BRV type 1 strain found in Iowa. This study shows that bovine torovirus is a common virus in the fecal specimens of calves with diarrhea from farms in southern Ontario and thus may be an important pathogen of cattle.

Direct and rapid detection of porcine epidemic diarrhea virus by RT-PCR

To establish a practical method for detecting porcine epidemic diarrhea virus (PEDV), the use of primers derived from sequences that amplify the M protein genes of PEDV in a RT-PCR detection system was investigated. Primers were designed to amplify a 854-bp fragment by RT-PCR. This reaction was specific to the PEDV RNA but not to that of other viral genera tested. In experiments with mixtures of PEDV and either small intestine or fecal homogenates, this method could detect efficiently the PEDV RNA from samples containing very low numbers of virus (100 TCID50/sample) within 8 h. With specimens collected from swine breeding farms with the diarrhoeal disease, the PEDV RNA was detected in four intestine specimens out of 11 specimens. The result was in close agreement with the results of virus isolation and streptavidin-biotin technique for detecting PEDV and its antigens, suggesting that the RT-PCR assay would be useful method for practical application.

Detection of enterotoxigenic Bacteroides fragilis by PCR

Strains of enterotoxigenic Bacteroides fragilis (ETBF) are associated with diarrhea in young farm animals and, at least in particular settings, in children. Enterotoxin production by ETBF is currently detected by a tissue culture assay with HT-29 cells. We have developed a PCR assay based on the detection of the enterotoxin gene to identify ETBF in culture and in stool samples. Overall, 113 bacterial strains were examined, including 3 B. fragilis reference strains, 75 B. fragilis isolates (comprising 40 ETBF isolates), 20 Bacteroides spp. other than B. fragilis, and 15 strains belonging to other genera. Complete agreement was found between the results of the tissue culture assay and those of the PCR for our strains. PCR was also used to detect ETBF directly in fecal samples. Stools from two healthy volunteers were spiked with known numbers of ETBF and were processed by three different methods. A culture method, which required inoculation of the stools on selective plates and the collection of the whole bacterial growth ("sweeps"), was found to be the most sensitive. PCR performed with the plate sweeps yielded amplification products with a detection limit of 10(5) to 10(4) CFU/g of feces. By this method 18 samples of diarrheic stools (10 positive and 8 negative for ETBF) were examined. The results of the PCR were in accordance with the culture results in all cases. The proposed PCR assay represents a diagnostic tool for the rapid identification of ETBF in culture as well as in fecal samples.

Immunomagnetic separation and PCR for detection of Mycobacterium ulcerans

We have developed a technique based on the use of monodisperse magnetic beads to isolate Mycobacterium ulcerans from heterogenous mixtures, prior to PCR amplification. Using this method, we were able to detect M. ulcerans in water samples taken from Phillip Island, Australia, the site of several outbreaks of M. ulcerans disease in recent times.

Molecular diagnosis of gastrointestinal infections associated with HIV infection

Developments in medical microbiology in the past 20 years have had a profound impact on our understanding of infectious diseases and have led the way in the development of new diagnostic techniques. Molecular diagnostic techniques are generally more sensitive, specific, and rapid than conventional methods by which infectious agents are detected. For many of the opportunistic infectious agents of the gastrointestinal tract found in HIV-infected individuals, the application of molecular diagnostic techniques to the clinical laboratory is in its infancy. In this article, methods by which these techniques can be evaluated are demonstrated, and the current status and potential future application of these techniques for each gastrointestinal opportunistic pathogen are described.

Complex polysaccharides as PCR inhibitors in feces: Helicobacter pylori model

A model was developed to study inhibitors present in feces which prevent the use of PCR for the detection of Helicobacter pylori. A DNA fragment amplified with the same primers as H. pylori was used to spike samples before extraction by a modified QIAamp tissue method. Inhibitors, separated on an Ultrogel AcA44 column, were characterized. Inhibitors in feces are complex polysaccharides possibly originating from vegetable material in the diet.

Detection of swine vesicular disease virus RNA by reverse transcription-polymerase chain reaction

Two polymerase chain reaction (PCR) assays are described for the detection of swine vesicular disease virus (SVDV) RNA, a reverse transcription PCR (RT-PCR) and a reverse transcription nested PCR (RT-nPCR). Both the RT-PCR and RT-nPCR were able to detect representative members of each of seven phylogenetically distinct groups of SVDV and gave negative results with a range of porcine enteroviruses and of viruses responsible for vesicular conditions in pigs. When combined with a commercial kit for rapid RNA extraction, the RT-PCR was useful for the detection of SVDV in samples of epithelium and faeces from animals with clinical SVD. The addition of a second amplification step to create a nested PCR (RT-nPCR) increased the sensitivity of the technique for the detection of viral RNA (vRNA) in SVDV infected tissue culture fluid by a factor of approximately 1,000, for 100 TCID50 for the RT-PCR to 0.1 TCID50 for RT-nPCR. When combined with a more elaborate extraction procedure for RNA, the RT-nPCR was considerably more sensitive than virus isolation in tissue culture for detecting SVDV in nasal swabs, tissues, and faeces collected from pigs between 7 days and 176 days after infection with a recent European isolate of SVDV. However, stringent conditions are necessary for carrying out the RT-nPCR to minimise the possibility of contamination.

Molecular biology in diagnosis and epidemiology of Helicobacter pylori: PCR for the detection and AP-PCR for characterization of patient isolates

Infection with Helicobacter pylori causes chronic active gastritis and has been associated with gastric and duodenal ulcer disease. In biopsy samples of 110 patients with clinical symptoms of active gastritis, H. pylori was detected by means of the polymerase chain reaction (PCR), using species-specific primers defining a 858 bp DNA fragment of H. pylori urease beta-subunit. Sensitivity and specificity of the PCR was compared with culture, histology and Warthin-Starry stain (WSs), detection of H. pylori urease antibodies in serum and urease testing with the Campylobacter-like organism (CLO) test. PCR yielded specific amplification products in 53 cases, whereas culture of the organisms was positive in a subset of 50 cases. Only direct detection in histological sections of biopsy specimens had a higher sensitivity, with 65 positive samples. In contrast, the CLO test was negative in eleven culture-positive and PCR-positive cases. Significant urease antibody titres were found in 39 patients with histologically confirmed diagnosis. These results placed the sensitivity of PCR between tat of the Warthin-Starry stain (WSs) and that of culture. Therefore, PCR can be proposed as a useful rapid and time-saving technique for the detection of H.pylori in gastritis. For epidemiological purposes, fingerprinting with arbitrarily chosen primers by AP-PCR was evaluated. Strain-specific patterns with up to 13 fragments were achieved with 10-nucleotide or longer primers (21-nt) with a G + C content > or = 55%. Thirty-five of 40 strains investigated by this method were distinguishable with a single primer. These results suggest a high level of DNA sequence diversity within this species with the possibility of confirming the clonality in consecutive isolates from a single individual. Alternatively, an increased in-vivo mutation rate could be responsible for DNA divergence, resulting in specific strains for each individual patient.

Use of heat release and an internal RNA standard control in reverse transcription-PCR detection of Norwalk virus from stool samples

Norwalk virus (NV) and the Norwalk-like viruses are important human pathogens that cause epidemic acute viral gastroenteritis. Current techniques used to recover NV from clinical samples involve multistep viral extraction and elution procedures with subsequent viral detection by reverse transcription-PCR (RT-PCR). In this study, a simple method using heat to recover viral RNA from 45 stool samples was compared to a conventional viral RNA extraction technique, with subsequent analysis by RT-PCR. In addition, we used an internal RNA standard for the detection of inhibitors present in processed samples. Our results indicate that the use of heat to recover NV RNA from stool samples has a sensitivity for the detection of NV RNA that is similar to the more labor-intensive, time-consuming, conventional RNA extraction technique. The use of an RNA internal standard permits the detection of inhibitors present in processed samples, allowing the identification of false negatives. The standard we developed has the advantage of allowing differential detection between wild-type viral RNA and standard using internal oligoprobe hybridization.

Rapid and effective method for preparation of fecal specimens for PCR assays

We have developed a novel method for the preparation of fecal specimens for PCR assays. Approximately 100 mg of solid stool or 200 microliters of liquid fecal sample was thoroughly suspended in 1 ml of water. Fecal debris was removed by low-speed centrifugation (2,800 x g for 2 min). The supernatant was then boiled for 10 min in a water bath and further clarified by high-speed centrifugation (12,000 x g for 5 min). Fifty microliters of the clarified supernatant was then purified by Sepharose CL-6B spin column chromatography, and a portion of the purified supernatant was used for PCR. By this method, stools containing enterotoxigenic Escherichia coli H10407 were amplified by colonization factor antigen I fimbrial gene PCR, with a sensitivity of 100 organisms per reaction. The method was also effective for processing stool specimens for Clostridium difficile toxin A and B gene PCRs. This method is rapid, effective, and simple to perform and will improve the applications of PCR to stool specimens for diagnostic purposes.

Improvement of a polymerase chain reaction assay for the detection of Echinococcus multilocularis DNA in faecal samples of foxes

A polymerase chain reaction (PCR) method was developed in order to permit a sensitive and specific identification of Echinococcus multilocularis DNA from fox faecal specimens. In an attempt to overcome problems related to the presence of endogenous PCR inhibitors in faecal extracts, we investigated a DNA extraction technique using an anion binding resin (Gene-Fizz). This simple and rapid procedure was applied to 61 faecal samples. Compared with the traditional microscopic examination, the sensitivity of PCR using Gene-Fizz was 82.3% and the specificity was 95.5%. No PCR signal was obtained for 20 Echinococcus granulosus isolates, showing that this method allowed discrimination between E. multilocularis and E. granulosus. Large-scale epidemiological surveys of fox excrements may be possible by using Gene-Fizz treatment prior to PCR amplification reactions.

Comparison of Vero cell assay and PCR as indicators of the presence of verocytotoxigenic Escherichia coli in bovine and human fecal samples

Comparisons were made between Vero cell assay (VCA) and PCR as indicators for the detection of verocytotoxigenic Escherichia coli (VTEC; also known as Shiga-like toxin-producing E. coli) and as predictors of VTEC isolation from bovine and human fecal samples. Fecal samples were collected as part of a survey on the prevalence of VTEC on dairy farms in southern Ontario (J. B. Wilson et al., J. Infect. Dis., 174:1021-1027, 1996). A total of 2,655 samples were examined by VCA and PCR, 2,153 originating from cattle and 502 originating from humans. Overall, 36.2% of the samples were positive in the VCA and 38.7% were positive by PCR. Of the VCA-positive samples screened, 41.6% yielded a VTEC isolate. For both human and bovine samples, a significant positive association between PCR result and VCA titer (P = 0.0001) was found. In addition, there was a significant positive association between the PCR result and VTEC isolation from VCA-positive samples for cattle (odds ratio = 9.1, P < 0.0001). For bovine samples positive in the VCA, VCA titer was significantly associated with the probability of obtaining a VTEC isolate. Agreement between VCA and PCR was good for both bovine and human samples (kappa = 0.69 and 0.64, respectively). The sensitivity and specificity of the PCR with respect to the VCA for bovine samples were 82.0 and 86.5%, respectively, and those for human samples were 59.3 and 98.1%, respectively. Although correlation between VCA and PCR results was not absolute, when used in conjunction, these tests complemented one another as predictors of VTEC isolation.

Evaluation of reverse transcription and polymerase chain reaction (RT/PCR) for the detection of rotaviruses: applications of the assay

Our aim was to evaluate the reverse transcription and polymerase chain reaction (RT/PCR) technique for the detection of rotavirus shedding by infected children as a routine diagnostic procedure, in comparison to the enzyme-linked immunosorbent assay (ELISA), electron microscopy (EM) and polyacrylamide gel electrophoresis (PAGE) of rotavirus double-stranded RNA. Two-hundred and twenty stool specimens were collected from infants and young children with diarrhoea, and 10-20% faecal suspensions were made. Several methods of rotavirus dsRNA extraction were assayed. Electrophoretic analysis of viral RNA was carried out on 10% polyacrylamide gels followed by silver staining. RT/PCR was performed using oligonucleotide primers specific for both 3' and 5' ends of the rotavirus gene encoding VP7 which are highly conserved among group A rotaviruses. Following RNA extraction with phenol-chloroform and ethanol precipitation, RT/PCR could detect rotaviral RNA in only 11 of 25 samples known to contain rotaviruses by conventional methods. The purification of RNA extracts by CF11 cellulose and the application of the RNAID method were equally effective in extracting RNA and/or removing inhibitory substances from the faecal samples. RT/PCR led to the detection of 66 positive samples from 220 specimens tested (30%), whilst 64 specimens were positive by ELISA (29%), 59 (26.8%) by PAGE and 56 (25.4%) by EM. In our study, RT/PCR was 100 times more sensitive than the ELISA test in detecting rotaviruses serially diluted in a faecal suspension. Although RT/PCR is theoretically much more sensitive than ELISA, PAGE and EM for detection of rotaviruses, great care must be taken to remove inhibitory substances from the enzymatic reactions. We do not consider that RT/PCR should replace immunoassays with high sensitivity and specificity for rotavirus testing in faecal samples, although this technique has other applications, like the search for rotavirus in different clinical specimens (sera, cerebrospinal fluid, respiratory secretions, etc.) and in environmental samples, as well as the typing of viral strains using serotype-specific primers.

A newly developed PCR assay of H. pylori in gastric biopsy, saliva, and feces. Evidence of high prevalence of H. pylori in saliva supports oral transmission

We have recently developed a new PCR assay for the detection of H. pylori. In this study, the polymerase chain reaction (PCR) assay was used to detect H. pylori in 88 gastric biopsy, 85 saliva, and 71 fecal specimens from 88 patients. H. pylori infection was confirmed in 71 of 88 patients by culture and/or histological stain of gastric biopsies. Serum IgG antibody to H. pylori was also measured and resulted in 97% sensitivity and 94% specificity. H. pylori DNA was detected by the PCR assay in gastric biopsy specimens from all 71 patients (100% sensitivity) with proven gastric H. pylori infection but not from 17 noninfected patients (100% specificity). In saliva specimens, H. pylori DNA was identified in 57 of the 68 patients (84%) with proven gastric H. pylori infection and in three of the 17 patients without gastric H. pylori infection. However, the PCR assay was only able to detect H. pylori DNA in the feces from 15 of 61 patients (25%) with proven gastric H. pylori infection and one of the 10 patients without gastric H. pylori infection. The results show that the PCR assay is reliable for detecting the presence of H. pylori in gastric biopsy and saliva specimens. The data indicate that H. pylori exists in a higher prevalence in saliva than feces and that the fecal-oral route may be an important means of transmission of this infection in developing countries but not as significant as previously suspected in the developed countries. It is likely that the oral-oral route is more prominent.

Rapid identification of Salmonella serovars in feces by specific detection of virulence genes, invA and spvC, by an enrichment broth culture-multiplex PCR combination assay

In order to make a rapid and definite diagnosis of Salmonella enteritis in children, an enrichment broth culture-multiplex PCR combination assay was devised to identify Salmonella serovars directly from fecal samples. Two pairs of oligonucleotide primers were prepared according to the sequences of the chromosomal invA and plasmid spvC genes. PCR with these two primers would produce either one amplicon (from the invA gene) or two amplicons (from the invA and spvC genes), depending on whether or not the Salmonella bacteria contained a virulence plasmid. The fecal sample was diluted 10- to 20-fold into gram-negative enrichment broth and incubated to eliminate inhibitory compounds and also to allow selective enrichment of the bacteria. One or two amplicons were obtained, the expected result if Salmonella bacteria were present. The detection limit of this PCR was about 200 bacteria per reaction mixture. The primers were specific, as no amplification products were obtained with 18 species and 22 isolates of non-Salmonella bacteria tested which could be present in the feces or cause contamination. In contrast, when 23 commonly seen Salmonella serovars (38 isolates) were tested, all were shown to carry the invA gene and seven concomitantly harbored the spvC gene of the virulence plasmid. This assay was applied to the diagnosis of Salmonella enteritis in 57 children who were suffering from mucoid and/or bloody diarrhea. Of the 57 children, 38 were PCR positive and 22 were culture positive. There were two culture-positive samples that were not detected by PCR. Thus, this PCR assay showed an efficiency of 95% (38 of 40), which is much higher than the 60% (24 of 40) by culture alone. Not only is this method more sensitive, rapid, and efficient but it will cause only an incremental increase in the cost of stool processing, since enrichment cultivation of fecal samples from diarrheal patients using gram-negative enrichment broth is a routine practice for identification in many diagnostic microbiology laboratories. This PCR method, therefore, has clinical application.

Rapid and efficient method to eliminate substances inhibitory to the polymerase chain reaction from animal fecal samples

To detect pathogenic viruses in animal fecal specimens by polymerase chain reaction (PCR) assays, it is important to remove or inactivate PCR-inhibitory substances. Recently, it was reported that such inhibitory substances in human feces could be efficiently eliminated by a cationic surfactant, Catrimox-14 (Iowa Biotechnology, Iowa) during extraction of viral RNA. In the present report, Catrimox-14 was successfully applied to detect pathogenic viruses in fecal specimens from a variety of animals. By extraction of viral DNA in the presence of this cationic surfactant, the PCR assay could detect canine parvovirus (CPV) in all fecal specimens prepared from 13 kinds of animals, i.e., cat, chicken, cow, dog, gerbil, goat, golden hamster, horse, mouse, pig, rat, rabbit, or sheep. Pretreatment by gel-filtration or boiling failed to remove or inactivate the PCR-inhibitory substances in fecal specimens from mouse, goat, rat, and sheep.

Detection of pathogenic Yersinia enterocolitica using the multiplex polymerase chain reaction

A multiplex polymerase chain reaction (PCR) was developed to detect the presence of the ail, yst, and virF genes of Yersinia enterocolitica simultaneously, quickly and accurately. The amplified fragment sizes were 356 base-pairs (bp) for the ail gene, 134 bp for the yst gene, and 231 bp for the virF gene. The specificity of the amplified products was confirmed by hybridization with digoxigenin-labelled oligonucleotide probes. Amplification was successful whether the template was derived from a single colony of bacteria, aliquots of boiled bacterial suspensions, from DNA extracted from pure or mixed cultures or from stool specimens. Amplification of the virF gene was also achieved from strains of Y. pseudotuberculosis carrying the 70 kb plasmid but not with preparations from other related Yersinia species or from other members of the family Enterobacteriaceae. The detection limit we established was 5-10 colony forming units per millilitre (cfu/ml) and 1.0 pg of DNA.

Rapid detection of Mycobacterium avium in stool samples from AIDS patients by immunomagnetic PCR

Direct PCR detection of bacteria in clinical samples is often hindered by the presence of compounds that inhibit the PCR. To improve and accelerate the diagnosis of Mycobacterium avium-M. intracellulare complex infections, an immunomagnetic PCR (IM-PCR) assay was developed. This IM-PCR procedure combines the separation of mycobacteria by antimycobacterial monoclonal antibody coupled to magnetic beads with an M. avium-M. intracellulare complex-specific PCR protocol based on 16S rRNA gene sequences. As few as 10 M. avium bacilli were detected in spiked human stool samples, a clinical specimen usually refractory to conventional PCR analysis, by the IM-PCR method. Moreover, M. avium organisms were detected in about 24 h in 18 of 22 culture-confirmed fecal samples from AIDS patients. This IM-PCR protocol should allow for the rapid and sensitive detection of M. avium isolates in clinical specimens.

Detection of hepatitis E virus RNA in stools and serum by reverse transcription-PCR

Stools and sera collected during an experimental hepatitis E virus (HEV) infection in monkeys and collected from humans with acute HEV infections during epidemic and sporadic cases were analyzed by reverse transcription-PCR. Two methods for RNA purification were compared. Proteinase K digestion and phenolchloroform extraction were more efficient than guanidinium isothiocyanate extraction in improving the sensitivity and specificity for the detection of HEV genomes.

Comparison of four RNA extraction methods for the detection of small round structured viruses in faecal specimens

Four methods for extraction of the RNA genome of small round structured viruses (SRSVs) from faecal specimens by reverse transcription polymerase chain reaction (RT-PCR) were evaluated. The efficiency of recovery of viral RNA and removal of amplification inhibitors were compared. RNA extraction using the metal chelating agent Chelex-100 and Sephadex G200 column chromatography were the most sensitive, detecting a 10(-4) dilution of a known SRSV positive specimen. Guanidinium thiocyanate (GTC) with adsorption of viral RNA onto silica was 10-fold less sensitive. The fourth method, based on PEG precipitation followed by phenol/chloroform extraction with the addition of the detergent cetyltrimethylammonium bromide (CTAB), only detected a 1 in 10 dilution of the positive specimen. The CTAB method was 2- to 50-fold less sensitive than the GTC/silica method when dilution series of three further SRSV positive specimens were tested. Thirty-six SRSV negative faecal specimens were spiked with virus and RT-PCR performed following RNA extraction by each of the four techniques in order to assess the ability of these methods to remove amplification inhibitors. The GTC/silica method successfully removed inhibitors from all samples whereas partial or complete inhibition was observed in seven (19%) specimens following extraction by the CTAB method, 17 (47%) by the Sephadex method, and 20 (56%) by the Chelex method. We conclude that, of these four methods, the GTC/silica method is the most appropriate for the extraction of viral RNA from faecal samples prior to RT-PCR for detecting SRSVs.

PCR detection and quantitation of predominant anaerobic bacteria in human and animal fecal samples

PCR procedures based on 16S rRNA gene sequences specific for 12 anaerobic bacteria that predominate in the human intestinal tract were developed and used for quantitative detection of these species in human (adult and baby) feces and animal (rat, mouse, cat, dog, monkey, and rabbit) feces. Fusobacterium prausnitzii, Peptostreptococcus productus, and Clostridium clostridiiforme had high PCR titers (the maximum dilutions for positive PCR results ranged from 10(-3) to 10(-8)) in all of the human and animal fecal samples tested. Bacteroides thetaiotaomicron, Bacteroides vulgatus, and Eubacterium limosum also showed higher PCR titers (10(-2) to 10(-6)) in adult human feces. The other bacteria tested, including Escherichia coli, Bifidobacterium adolescentis, Bifidobacterium longum, Lactobacillus acidophilus, Eubacterium biforme, and Bacteroides distasonis, were either at low PCR titers (less than 10(-2)) or not detected by PCR. The reported PCR procedure including the fecal sample preparation method is simplified and rapid and eliminates the DNA isolation steps.