Development of a PCR-based technique for detection of Helicobacter pylori

Virulence factor genotyping of Helicobacter pylori isolated from Costa Rican dyspeptic patients

BACKGROUND AND AIMS

Costa Rica is one of the countries with the highest incidence and mortality rates for gastric cancer. Helicobacter pylori infection rates are high in the whole country. We have previously shown that H. pylori CagA+ is significantly associated with atrophic gastritis (AG) of the antrum in a dyspeptic population. The aim of this work is to determine if other H. pylori virulence factors (vacA, dupA, oipA, iceA and babA2) are associated with atrophic gastritis (AG) or duodenal ulcer (DU).

METHODS

The presence of virulence genes in Costa Rican H. pylori isolates was analyzed by PCR in 151 cultured strains from patients with dyspeptic symptoms. Endoscopic and histopathological diagnoses were available. Odds-ratio and 95% confidence intervals for AG patients vs. non-atrophic gastritis (NAG) or DU patients vs. no duodenal ulcer (NDU) patients were calculated.

RESULTS

Amongst the studied isolates, 82% had the cagA⁺, 76.2% had the vacA s1m1, 97.0% had the oipA⁺, 21.0% had the icea1, 79.0% had the iceA2, 44.0% had the babA2⁺ and 76.0% the dupA⁺ genotypes. Infection with H pylori cagA⁺, dupA⁺, oipA⁺, iceA, babA2⁺, and vacA s1m1 genotypes was not associated with AG risk. The frequency of the dupA gene was 78.7 and 60.9% in isolates from patients with NDU and DU, respectively, and its presence was significantly associated with decreased risk of duodenal ulcer [odds-ratio: 0.33, p = 0.024, confidence interval 95% (0.11-0.85)].

CONCLUSION

H. pylori dupA genotype is inversely associated with DU risk in this population.

Analysis of culturable microbiota present in the stomach of children with gastric symptoms

Despite extensive studies on the gastric microbiota, including Helicobacter pylori and non-H. pylori, the bacterial composition in children remains unknown. In this study, we analyzed the culturable gastric bacteria in stomach biopsies from 346 children aged 1-15 years affected by gastric diseases. H. pylori and non-H. pylori were identified by specific PCR and 16S rDNA sequencing, respectively. Antibiotic susceptibilities of H. pylori and non-H. pylori were tested by the E-test and disk diffusion methods, respectively. Rapid diagnosis was also performed by H. pylori-specific PCR. Twenty-two H. pylori strains were obtained from culture, and 92 biopsies were positive by H. pylori-specific PCR. The positive rate was higher in boys (40.3%) than in girls (23.3%) (P = 0.001). Resistance rates of 22 H. pylori strains were as follows: metronidazole, 86.4%; tetracycline, 22.7%; amoxicillin, 22.7%; levofloxacin, 31.8%; clarithromycin, 36.4%. Ten isolates were multidrug-resistant. Additionally, among 366 non-H. pylori strains, 204 exhibited urease activity. Non-H. pylori resistance rates were as follows: metronidazole, 94.8%; tetracycline, 26.2%; amoxicillin, 42.6%; levofloxacin, 15.3%; clarithromycin, 46.7%. Our results showed that children with gastric disorders harbor stomach bacteria with urease activity or nitrate reductase activity. Further studies will determine the effects of non-H. pylori bacteria in gastric diseases.

Otitis Media with Effusion and Helicobacter pylori

Previous studies reported the presence of Helicobacter pylori in middle ear fluid and raised a possible causal role of this bacterium in otitis media with effusion (OME). We investigated 48 children with OME (age, 7 months to 12 years) seen in New Orleans, Louisiana, and found no evidence of H pylori presence in any middle ear fluid specimen by amplification of the 16S rRNA gene. One child had H pylori detected in a stool specimen, in accordance with the low prevalence in our population. While H pylori may be significant in other countries, these findings do not support a role for H pylori in OME in our pediatric population in the United States.

Survival of Helicobacter pylori in the wastewater treatment process and the receiving river in Michigan, USA

Contaminated water may play a key role in the transmission of Helicobacter pylori, resulting in gastrointestinal diseases in humans. The wastewater treatment process is an important barrier to control the transmission of H. pylori. However, the presence and viability of H. pylori in the treatment process is not well known. In this paper, the real colony morphology of H. pylori was confirmed by two types of culture media. The survival of H. pylori through the tertiary wastewater treatment process, especially UV disinfection, and in the receiving Huron River in Ann Arbor, Michigan, was investigated by plates cultivation, regular polymerase chain reaction (PCR) assays and quantitative real-time PCR from DNA. The results demonstrated that H. pylori was not only present, but also viable in all processed wastewater samples in the Ann Arbor wastewater treatment plant (WWTP). H. pylori can be found in a higher concentration in the receiving Huron River. There are many kinds of antibiotic- and UV-resistant bacteria, including H. pylori, in the final effluent of Ann Arbor WWTP.

Development and Diagnostic Evaluation of Loop-Mediated Isothermal Amplification Using a New Gene Target for Rapid Detection of Helicobacter pylori

BACKGROUND

Helicobacter pylori cause chronic gastritis and subsequent diseases like gastric and duodenal ulcers and gastric adenocarcinoma. Current methods for detecting H. pylori have several disadvantages and it is of utmost importance to develop a simple, quick, accurate, and cost-effective diagnostic test.

OBJECTIVES

The aim of this study was to set up and evaluate a diagnostic value of loop- mediated isothermal amplification (LAMP) for detecting H. pylori.

PATIENTS AND METHODS

The analytical sensitivity values (limit of detection) of LAMP and polymerase chain reaction (PCR) were determined using serial dilutions of H. pylori DNA. Analytical specificity of the methods using new designed primers targeted ureC gene was also determined.

RESULTS

The detection limits of the LAMP and PCR assay were similar and were 10 fg of pure DNA of H. pylori, which is equal to 6 copy numbers of H. pylori genome. Analytical specificity of the tests was 100% because the tests were positive only with H. pylori DNA.

CONCLUSIONS

The analytical sensitivity of LAMP and PCR methods, using the designed primers, was 8 times more than any other reported methods. The designed methods are specific and sensitive for detection of H. pylori in different clinical and environmental samples.

The Helicobacter pylori L-form: formation and isolation in the human bile cultures in vitro and in the gallbladders of patients with biliary diseases

BACKGROUND

The Helicobacter pylori is considered the important causative agent causing biliary diseases, but the H. pylori can be isolated from very few gallbladder specimens with diseases. We studied the formation of H. pylori L-forms in bile in vitro and isolated the H. pylori L-forms from gallbladder of patients with biliary diseases.

METHODS

We inoculated the H. pylori into the human bile to induce the L-form in vitro. The gallbladder specimens were collected from patients with biliary diseases to isolate the bacterial L-forms by the nonhigh osmotic isolation technique, and the H. pylori L-forms in the L-form isolates were identified by the gene assay for the H. pylori-specific genes 16S rRNA and UreA.

RESULTS

The H. Pylori cannot be isolated from the bile-induced cultures, but the H. pylori L-form can be isolated from the H. pylori-negative bile-induced cultures. The L-form isolates of bile-induced cultures showed a positive reaction of the H. pylori-specific genes by PCR, and the coincidence ratio of the nucleotide sequences between the L-forms and the H. pylori is 99%. The isolation rate of bacteria L-form is 93.2% in the gallbladder specimens with bacteria-negative isolation culture by the nonhigh osmotic isolation technique, and the positive rate of the H. pylori-specific genes in the L-form isolates is 7.1% in the bacterial L-form-positive isolation cultures by the PCR.

CONCLUSIONS

H. pylori can be rapidly induced into the L-form in the human bile; the L-form, as the latent bacteria, can live in the host gallbladder for a long times, and they made the host became a latent carrier of the H. pylori L-form. The H. pylori L-form can be isolated by the nonhigh osmotic isolation technique, and the variant can be identified by the gene assay for the H. pylori-specific genes 16S rRNA and reA.

The geographic origin of Helicobacter pylori isolated from Costa Rican patients

Helicobacter pylori infects a significant proportion of the world population and it is associated with pathologies which include chronic atrophic gastritis, peptic ulcer, and gastric neoplasias such as gastric adenocarcinoma and MALT lymphoma. Costa Rica has a high prevalence of the infection and an elevated incidence of gastric cancer and its associated mortality. The global population structure for H. pylori has been established using a MLST scheme. The population structure of the strains of H. pylori circulating in Costa Rica is currently unknown. We characterized the geographical origin of 24 H. pylori isolates from Costa Rican patients. We identified 142 new alleles for the genes included in the scheme and in eight of the 24 isolates from Costa Rican patients, all seven alleles sequenced were described for the first time. Twenty-one isolates from Costa Rican patients group with hpEurope strains and the remaining three isolates grouped with hspWAfrica isolates (Bayesian posterior probability values above 0.70, P = 0.05, after 2 000 000 generations). The obtained result in the MLST analysis was not unexpected and reflects the genetic composition of the Costa Rican population.

Protective efficacy of recombinant urease B and aluminum hydroxide against Helicobacter pylori infection in a mouse model

Efforts are underway for the development of an effective vaccine against Helicobacter pylori infection. We prepared recombinant full-length (568 aa) H. pylori recombinant urease B (rUreB) protein and tested it for immunogenicity and protection. BALB/c mice received either rUreB (40 μg) plus CpG (10 μg) intranasally, rUreB (50 μg) plus 3% aluminum hydroxide (50 μL) intramuscularly or rUreB (25 μg) plus Freund's adjuvant (25 μL) subcutaneously, three times (weeks 0, 2 and 6). Intranasal rUreB plus CpG was neither immunogenic nor protective; intramuscular rUreB plus aluminum hydroxide was immunogenic and modestly protective, and subcutaneous rUreB plus Freund's adjuvant was immunogenic and highly protective. The fact that protection was improved with Freund's adjuvant indicates that rUreB is a good antigen for a vaccine but that it needs a stronger adjuvant than aluminum hydroxide.

Protection against Helicobacter pylori infection by a trivalent fusion vaccine based on a fragment of urease B-UreB414

A multivalent fusion vaccine is a promising option for protection against Helicobacter pylori infection. In this study, UreB414 was identified as an antigenic fragment of urease B subunit (UreB) and it induced an antibody inhibiting urease activity. Immunization with UreB414 partially protected mice from H. pylori infection. Furthermore, a trivalent fusion vaccine was constructed by genetically linking heat shock protein A (HspA), H. pylori adhesin A (HpaA), and UreB414, resulting in recombinant HspA-HpaA-UreB414 (rHHU). Its protective effect against H. pylori infection was tested in BALB/c mice. Oral administration of rHHU significantly protected mice from H. pylori infection, which was associated with H. pylori-specific antibody production and Th1/Th2-type immune responses. The results show that a trivalent fusion vaccine efficiently combats H. pylori infection, and that an antigenic fragment of the protein can be used instead of the whole protein to construct a multivalent vaccine.

Protection against Helicobacter pylori infection in mongolian gerbil by intragastric or intramuscular administration of H. pylori multicomponent vaccine

BACKGROUND

Development of Helicobacter pylori vaccine would be a new effective strategy for prevention and treatment of H. pylori infection. Recombinant H. pylori vaccine comprising a single subunit antigen can only induce immune response with limited protection efficiency. In this study, the protective effect of H. pylori multicomponent vaccines consisting of three recombinant subunit antigens was investigated using the Mongolian gerbil model.

MATERIALS AND METHODS

Mongolian gerbils were immunized with different formulations of three recombinant H. pylori antigens (UreB, HspA, and HpaA) with two different adjuvants (Al(OH)3, LT(R72DITH)) by intragastric (i.g.) or intramuscular (i.m.) routes. The protective effects of multicomponent vaccines were assessed after H. pylori challenge in different studies. The specific IgG antibodies in serum were monitored by ELISA, and the mRNA expressions of IL-4 and IFN-gamma in spleen tissue were detected by reverse transcribed polymerase chain reaction (RT-PCR).

RESULTS

The protective effect against H. pylori challenge in gerbils immunized with three recombinant antigens and LT(R72DITH) or Al(OH)3 was significantly higher than that in single- or double-antigen vaccine-immunized and control gerbils. Furthermore, the protective effect of the triple-antigen vaccine combined with the LT(R72DITH) adjuvant (average 86.3%) was significantly greater than that of vaccine combined with the Al(OH)3 adjuvant (average 53.4%). After the first immunization, the anti-UreB/HspA/HpaA serum IgG level in gerbils immunized with triple-antigen vaccine combined with Al(OH)3 was higher than that in gerbils immunized with the vaccine combined with LT(R72DITH). Splenic interferon (IFN)-gamma and interleukin (IL)-4 transcript levels were significantly increased in LT(R72DITH) vaccine-immunized gerbils as compared to the Al(OH)3 vaccine group. Moreover, splenic IL-4 mRNA levels were higher than IFN-gamma in gerbils immunized with triple-antigen vaccine with either LT(R72DITH) or Al(OH)3.

CONCLUSIONS

This study indicated that the recombinant multicomponent vaccine provided effective protection against H. pylori infection as compared to the single-antigen vaccine. This protective immunity would be closely associated with a predominant Th2-type response.

Development and application of a novel peptide nucleic acid probe for the specific detection of Helicobacter pylori in gastric biopsy specimens

In this work, a fluorescence in situ hybridization (FISH) method for the rapid detection of Helicobacter pylori using a novel peptide nucleic acid (PNA) probe is reported. Laboratory testing with several different bacterial species, including other Helicobacter spp., has shown that this probe is highly specific for H. pylori strains. In addition, the PNA FISH method has been successfully adapted for detection of the pathogen in paraffin-embedded gastric biopsy specimens.

Helicobacter pylori detection and antimicrobial susceptibility testing

The discovery of Helicobacter pylori in 1982 was the starting point of a revolution concerning the concepts and management of gastroduodenal diseases. It is now well accepted that the most common stomach disease, peptic ulcer disease, is an infectious disease, and all consensus conferences agree that the causative agent, H. pylori, must be treated with antibiotics. Furthermore, the concept emerged that this bacterium could be the trigger of various malignant diseases of the stomach, and it is now a model for chronic bacterial infections causing cancer. Most of the many different techniques involved in diagnosis of H. pylori infection are performed in clinical microbiology laboratories. The aim of this article is to review the current status of these methods and their application, highlighting the important progress which has been made in the past decade. Both invasive and noninvasive techniques will be reviewed.

Molecular identification of Helicobacter DNA present in human colorectal adenocarcinomas by 16S rDNA PCR amplification and pyrosequencing analysis

Seroepidemiological studies have indicated that Helicobacter pylori infection might be a possible risk factor for colorectal adenocarcinoma (CRC) development. However, limited information is available as to whether or not Helicobacter species are present in CRC tissues. In this study the presence of Helicobacter DNA in 77 CRC biopsies was investigated by means of a Helicobacter species-specific 16S rDNA PCR assay and real-time DNA pyrosequencing of the 16S rDNA variable V3 region. Pyrosequencing revealed the presence of Helicobacter DNA sequences in 21 of 77 biopsy specimens (27%). 16S rDNA sequences corresponding to H. pylori 26695 and H. pylori J99 were most commonly found. Intriguingly, one sequence belonged to Helicobacter mustelae, previously identified in ferrets. No significant correlations were found in the prevalence of Helicobacter DNA between colon and rectum tumour biopsies (P = 0.815), nor between Dukes' classes A/B and C/D (P = 0.262). 16S rDNA PCR amplification combined with pyrosequencing analysis of 16S rDNA variable V3 regions provides a powerful molecular tool to identify Helicobacter species in human biopsy specimens.

Detection of Helicobacter pylori in bile of cats

Lymphocytic cholangitis (LC) in cats is a biliary disease of unknown etiology. Helicobacter spp. were recently implicated in human primary sclerosing cholangitis (PSC) and primary biliary cirrhosis (PBC). Because of the similarities between PSC/PBC with LC, we hypothesized that Helicobacter spp. are involved in feline LC. A PCR with Helicobacter genus-specific 16S rRNA primers was performed on DNA isolated from feline bile samples. Four of the 15 (26%) LC samples were positive, whereas only 8/51 (16%) of non-LC samples were PCR positive (p=0.44). Sequence analysis of the amplicons revealed a 100% identity with the Helicobacter pylori specific DNA fragments. Our data suggest an etiological role of H. pylori in feline LC and that cats are a potential zoonotic reservoir.

Different Helicobacter pylori strains colonize the antral and duodenal mucosa of duodenal ulcer patients

BACKGROUND

We have investigated the possibility that the same patients may be colonized by Helicobacter pylori strains of different genotypes or phenotypes in the antrum as compared to in the duodenum. The strains were typed for DNA fingerprints, different lipopolysaccharides (LPS), and Lewis antigen expression on the O-side chains of LPS.

MATERIALS AND METHODS

Polymerase chain reaction (PCR) amplifications using primer sequences (i.e., the Enterobacterial Repetitive Intergenic Consensus [ERIC]) and randomly amplified polymorphic DNA (RAPD) elements were performed to asses chromosomal DNA diversity between H. pylori strains. The expression of different LPS types and Lewis antigens in the various H. pylori isolates were determined by whole bacterial enzyme-linked immunosorbent assays using monoclonal antibodies.

RESULTS

Duodenal ulcer patients had different H. pylori genotypes in the duodenum as compared to in the antrum as shown by ERIC-PCR (44%) and by RAPD-PCR (75%). Different DNA patterns were found among the strains that were isolated from various regions of the duodenum in 4 of 16 patients (25%) as shown by ERIC-PCR and in 8 of 16 patients (50%) as shown by RAPD-PCR. Sixty-three percent of the duodenal ulcer patients had H. pylori strains with a different Lewis antigen phenotype in the duodenum as compared to in the antrum, and 3 of 16 patients (19%) had strains with different Lewis antigens expressed by strains from different duodenal biopsies from the same patient.

CONCLUSION

The results suggest that a mixed population of different H. pylori strains with marked variation, both genotypically and phenotypically, colonize the same patient.

Identification of Helicobacter pylori and other Helicobacter species by PCR, hybridization, and partial DNA sequencing in human liver samples from patients with primary sclerosing cholangitis or primary biliary cirrhosis

Helicobacter pylori was identified in human liver tissue by PCR, hybridization, and partial DNA sequencing. Liver biopsies were obtained from patients with primary sclerosing cholangitis (n = 12), primary biliary cirrhosis (n = 12), and noncholestatic liver cirrhosis (n = 13) and (as controls) normal livers (n = 10). PCR analyses were carried out using primers for the Helicobacter genus, Helicobacter pylori (the gene encoding a species-specific 26-kDa protein and the 16S rRNA), Helicobacter bilis, Helicobacter pullorum, and Helicobacter hepaticus. Samples from patients with primary biliary cirrhosis and primary sclerosing cholangitis (11 and 9 samples, respectively) were positive by PCR with Helicobacter genus-specific primers. Of these 20 samples, 8 were positive with the 16S rRNA primer and 9 were positive with the 26-kDa protein primer of H. pylori. These nine latter samples were also positive by Southern blot hybridization for the amplified 26-kDa fragment, and four of those were verified to be H. pylori by partial 16S rDNA sequencing. None of the samples reacted with primers for H. bilis, H. pullorum, or H. hepaticus. None of the normal livers had positive results in the Helicobacter genus PCR assay, and only one patient in the noncholestatic liver cirrhosis group, a young boy who at reexamination showed histological features suggesting primary sclerosing cholangitis, had a positive result in the same assay. Helicobacter positivity was thus significantly more common in patients with cholestatic diseases (20 of 24) than in patients with noncholestatic diseases and normal controls (1 of 23) (P = <0.00001). Patients positive for Helicobacter genus had significantly higher values of alkaline phosphatases and prothrombin complex than Helicobacter-negative patients (P = 0.0001 and P = 0.0003, respectively). Among primary sclerosing cholangitis patients, Helicobacter genus PCR positivity was weakly associated with ulcerative colitis (P = 0.05). Significant differences related to blood group or HLA status were not found.

Quantitation of Helicobacter pylori in dental plaque samples by competitive polymerase chain reaction

AIM

To establish a competitive PCR (cPCR) assay for quantitation of H pylori organisms in dental plaque samples.

METHODS

The cPCR co-amplified target H pylori DNA and a known amount of internal standard template in the same tube with the same primers directed to 0.86 kb DNA of H pylori. The internal standard was a synthesised DNA bearing the same primer recognition sites at two ends and a non-homologous core sequence as the target DNA fragment. Quantitation was based on determination of the relative, not absolute, amounts of the differently sized and [32P]-dCTP labelled products derived from H pylori DNA and the competitive internal standard after gel electrophoresis separation.

RESULTS

A significant correlation between known amounts of H pylori added to dental plaque samples and the results of the cPCR was found, and a standard line was developed which allowed quantitation of H pylori in the plaque samples. cPCR was performed on supragingival plaque samples from 10 adult patients with H pylori infection in the stomach, and from five adults and six children without H pylori infection in the stomach. The ranges of H pylori numbers were 1-213 (median 25), 6-76 (10), and 4-94 (14) cells/mg of dental plaque in the three groups, respectively.

CONCLUSIONS

cPCR is useful for quantitation of H pylori in supragingival dental plaque samples; however, the number of the organisms in dental plaque samples seems very low.

Helicobacter pylori detection in human biopsies: a competitive PCR assay with internal control reveals false results

A polymerase chain reaction assay (PCR) for the diagnosis of Helicobacter pylori in human gastric biopsies was developed. To prevent false-negative results while performing PCR on human tissues, an internal control is necessary. Primer set ACT1-ACT2 which specifically amplifies a 542-bp fragment of the 16S rRNA gene of H. pylori was used. dUTP and hot-start were used to prevent false-positives from carryover of previous products and avoid non-specific extension products. A competitive internal control DNA fragment was constructed to detect the presence of inhibitors. Biopsies from 101 unselected patients with gastric symptoms were tested. PCR results were compared with results from microscopy of histological sections and conventional culturing for H. pylori. Forty-two percent of the biopsies were found to contain compounds inhibiting the PCR. The addition of the internal control assures the performance of the PCR assay and is an important quality control parameter.

An analysis of seven different methods to diagnose Helicobacter pylori infections

BACKGROUND

It has been debated which diagnostic test should be preferred for the diagnosis of Helicobacter pylori in patients with gastroduodenal diseases.

METHODS

The H. pylori infection was diagnosed prospectively in 97 untreated patients. H. pylori was diagnosed by means of tests based on five different principles: 1) culture, 2) microscopy (HLO), 3) urease activity (urea breath test (UBT) and urease test on biopsy specimens (CLO test)), 4) DNA detection (polymerase chain reaction (PCR)), and 5) IgG antibody detection (enzyme-linked immunosorbent assay (EIA) and Western blotting (WB)).

RESULTS

This study showed that two positive tests out of five tests, based on different principles, were most reliable for predicting the H. pylori infection. Most tests had specificities and predictive values for a negative result greater than 90%. The most important difference between the tests was the sensitivity and the predictive value for a positive result (PPV). WB, HLO, UBT, and PCR had sensitivities and PPV greater than 75%.

CONCLUSIONS

The non-invasive tests UBT and WB are reliable, both alone and in combination, and they are recommended for the pre-endoscopic diagnosis of H. pylori. WB is recommended as a confirmative test for antibody detection by EIA. When patients have an upper endoscopy, we recommend taking biopsy specimens for culture and histology because of the additional information obtained about susceptibility, virulence determinants, and morphology, including the degree of inflammation.

Evaluation of performances of three DNA enzyme immunoassays for detection of Helicobacter pylori PCR products from biopsy specimens

PCR is recognized as a promising method for the detection of Helicobacter pylori in gastric biopsy specimens. However, detection of PCR products by gel electrophoresis is difficult to implement in routine clinical laboratories. The aim of this study was to compare three new DNA enzyme immunoassays with the standard method in their ability to detect PCR products. The three assays were based on the amplification of a fragment of the ureC gene of H. pylori and a colorimetric hybridization assay. The first assay (GEN-ETI-K DNA enzyme immunoassay; Sorin, Sallugia, Italy) was based on the hybridization of amplified DNA with a probe bound in microtiter wells and detected with labelled anti-DNA antibody. The second assay (Pylori-prob; Biocode, Sclessin, Belgium) comprised a solid-phase sandwich hybridization system with a specific biotinylated probe being used for detection. Finally, the third assay (PCR enzyme-linked immunosorbent assay; Boehringer, Mannheim, Germany) was based on the hybridization of amplified DNA labelled with digoxigenin as a probe (used as a coating in microtiter wells) and detected with antidigoxigenin-peroxidase as conjugate. The sensitivity of the colorimetric assay was evaluated by using amplification products from PCR assays performed on several 10-fold dilutions of DNA from H. pylori CIP 101260, and the specificity was assessed with different urease-positive bacteria. Biopsy specimens from 199 patients were tested; 106 were classified as H. pylori positive, and 93 were classified as H. pylori negative by culture and/or histological examination as the "gold standard." The receiving operating characteristic curve was used to determine the best cutoff point for each assay. The detection of PCR products by colorimetric hybridization increases the sensitivity up to 100-fold compared to that with gel electrophoresis. The results are rapid (4 h) and easy to interpret and can be automated.

Corrected identity of isolates of Helicobacter pylori reference strain NCTC11637

BACKGROUND

The reference strains NCTC11637 and NCTC11638 were among the very first Helicobacters ever cultured and have been distributed through national reference culture collections to researchers throughout the world. Because H. pylori is an extremely diverse species, such reference strains are invaluable as universal standards, provided that they are identified correctly.

MATERIALS AND METHODS

H. pylori strains (previously called "NCTC11637") from three different sources and NCTC11638 were fingerprinted by the arbitrarily primed polymerase chain reaction (PCR) (also known as random amplified polymorphic DNA, or RAPD) method and further were characterized by NotI digestion and pulsed field gel electrophoresis of total genomic DNA (NotI-PFGE) and by restriction of PCR-amplified ureCD and flaA gene segments.

RESULTS

RAPD tests of two "NCTC11637" strains from different sources (CCUG17874, UA1178) indicated that they were closely related or identical to NCTC11638. Given the diversity of H. pylori strains and the high sensitivity of the RAPD method, close matches in RAPD patterns from independent clinical isolates are not expected. In contrast, the version of "NCTC11637" from the American Type Culture Collection (ATCC43504) did not match NCTC11638 in RAPD fingerprint. Concordant results were obtained by NotI-PFGE and by restriction of PCR amplified gene segments.

CONCLUSIONS

Two unrelated versions of the reference (type) H. pylori strain NCTC11637 are in general circulation and are distinguished easily by DNA fingerprinting. One matches another reference strain, NCTC11638, whereas the other is distinct from it, as expected of independent clinical isolates. Knowing which "NCTC11637" reference strain one has could be important, especially because H. pylori strains probably are diverse in phenotypic traits that are important for colonization or disease.