Helicobacter Pylori Urease Activity Research Articles

Inhibitory Effect of Partially Purified Compounds from Pomegranate Peel and Licorice Extracts on Growth and Urease Activity of Helicobacter pylori

Inhibitory Effect of Partially Purified Compounds from Pomegranate Peel and Licorice Extracts on Growth and Urease Activity of Helicobacter pylori

WITHDRAWN: Coptisine, an alkaloid from Rhizoma Coptidis, inhibits Helicobacter pylori urease activity by targeting its active site and maturation process

// Cailan Li 1, * , Ping Huang 2, * , Kambo Wong 3 , Yifei Xu 2 , Lihua Tan 1 , Hanbin Chen 4 , Qiang Lu 5 , Chaodan Luo 1 , Chunlai Tam 3 , Lixiang Zhu 2 , Ziren Su 1, 6 and Jianhui Xie 7 1 Guangdong Provincial Key Laboratory of New Drug Development and Research of Chinese Medicine, Mathematical Engineering Academy of Chinese Medicine, Guangzhou University of Chinese Medicine, Guangzhou, P. R. China 2 School of Pharmaceutical Sciences, Guangzhou University of Chinese Medicine, Guangzhou, P. R. China 3 School of Life Sciences, Center for Protein Science and Crystallography, The Chinese University of Hong Kong, Hong Kong, P. R. China 4 The First Affiliated Hospital of Chinese Medicine, Guangzhou University of Chinese Medicine, Guangzhou, P. R. China 5 Key Laboratory of Ministry of Education, Research Center of Chinese Herbal Resources and Engineering, Guangzhou University of Chinese Medicine, Guangzhou, P. R. China 6 Dongguan Mathematical Engineering Academy of Chinese Medicine, Guangzhou University of Chinese Medicine, Dongguan, P. R. China 7 Guangdong Provincial Key Laboratory of Clinical Research on Traditional Chinese Medicine Syndrome, The Second Affiliated Hospital, Guangzhou University of Chinese Medicine, Guangzhou, P. R. China * These authors have contributed equally to this work Correspondence to: Ziren Su, email: suziren@gzucm.edu.cn Jianhui Xie, email: xiejianhui888@hotmail.com Keywords: coptisine; Helicobacter pylori urease; sulfhydryl group; nickel ion; UreG Received: May 18, 2017 Accepted: January 01, 2018 Published: January 02, 2018 ABSTRACT In this study, we examined the anti- Helicobactor pylori effects of the main protoberberine-type alkaloids in Rhizoma Coptidis. Coptisine exerted varying antibacterial and bactericidal effects against three standard H. pylori strains and eleven clinical isolates, including four drug-resistant strains, with MICs ranging from 25 to 50 μg/mL and MBCs ranging from 37.5 to 125 μg/mL. Coptisine’s anti- H. pylori effects derived from specific inhibition of urease in vivo . In vitro , coptisine inactivated urease in a concentration-dependent manner through slow-binding inhibition and involved binding to the urease active site sulfhydryl group. Coptisine inhibition of H. pylori urease (HPU) was mixed type, while inhibition of jack bean urease (JBU) was non-competitive. Importantly, coptisine also inhibited HPU by binding to its nickel metallocenter. Besides, Coptisine interfered with urease maturation by inhibiting activity of prototypical urease accessory protein UreG and formation of UreG dimers and by promoting dissociation of nickel from UreG dimers. These findings demonstrate that coptisine inhibits urease activity by targeting its active site and inhibiting its maturation, thereby effectively inhibiting H. pylori . Coptisine may thus be an effective anti- H. pylori agent.

Efficient production of nanobodies against urease activity ofHelicobacter pylori in Pichia pastoris.

Helicobacter pylori is a major health problem. One of the therapeutic approaches is administration of antibody against H. pylori. The methylotrophic Pichia pastoris is a suitable host for expression of recombinant antibody fragments. The aims of this study were the expression and the evaluation of camelid nanobody in the yeast Pichia pastoris. The camelid-derived heavy-chain antibody (nanobody) against the UreC subunit of urease from H. pylori was subcloned in the pPink-HC shuttle vector and transferred into Escherichia coli TOP10. After digestion and purification, the shuttle vector was transformed in the PichiaPink expression system. The expression was evaluated in an in vitro system. The yield of the nanobody expressed in P. pastoris was estimated to be 5 mg/L as compared to 2 mg/L expressed by E. coli. The nanobody was purified and binding affinity to the UreC antigen was evaluated using ELISA. Neutralization abilities of the two nanobodies expressed in yeast and E. coli were compared. The yeast-expressed nanobody specifically detected recombinant UreC and inhibited urease activity with high efficiency. The results suggest attribution of the enhanced quality and quantity of the nanobody produced in P. pastoris to better posttranslational modification and folding in the yeast cell.

Inhibition of growth and urease activity of Helicobacter pylori by Korean edible seaweed extracts

Of 27 Korean seaweed species screened for potential anti- H. pylori activity, seven (25.9%) showed strong inhibitory activity based on the agar diffusion method. The strongest activity was observed for ethanol extracts from Ishige okamurae . At 1 mg/disk, the inhibition zone of I. okamurae extract was 9.0 mm, and the minimum inhibitory concentration was 12 ?g/ml based on the broth microdilution assay. Based on the free urease assay system, the 80% methanol extracts from I. okamurae had 75.4% inhibition at 0.1 mg/ml. To identify the primary active compounds, I. okamurae powders were successively fractionated according to polarity into fi ve classes of constituents including saccharides, lipids, phenolics, alkaloids, and nitrogen compounds. The I. okamurae phenolic compounds had signifi cant antimicrobial activity (12 ?g/ml minimum inhibitory concentration), while the nitrogen compound extract signifi cantly inhibited H. pylori urease activity (80.84% at 1 mg/ml). We evaluated the I. okamurae ethanol and 80% methanol extract for acute toxicity in BALB/c mice. Over the 2-week observation period, no death occurred in any mouse administered a dose of 5 g/kg body weight. These results suggest that I. okamurae extract can be used to develop therapeutic agents for chronic gastritis and peptic ulceration.

오매 추출물에 함유된 Ursolic Acid에 의한 Helicobacter pylori의 Urease 활성억제

전통식물한약재에 대한 데이터베이스, 한국식물자원에 대한 문헌 및 선행연구 결과에 근거해 선정한 6가지의 식물 한약재(연교, 소목, 형개, 황련, 소엽, 오매)의 에탄올(70%) 추출물 중에서 오매 추출물이 Helicobacter pylori의 urease 활성에 가장 강한 억제력을 나타내었다. 극성이 다른 용매를 사용한 회분식 용매추출과 칼럼 크로마토그래피를 이용한 3단계 분리공정을 통하여 오매 추출물에 함유된 유효성분을 분리 정제하였다. NMR 분석에 의해 정제된 오매 추출물에 함유된 활성성분이 ursolic acid로 확인되었다. 본 실험결과는 오매에 함유된 이 성분이 항생제를 대신하여 H. pylori 제거에 활용될 수 있음을 시사하였다. Urease activity of Helicobacter pylori was most strongly inhibited by extract of Mume Fructus among ethanol (70%, v/v) extract of 6 herbal materials selected from our previous work, database on traditional herbal materials, and literature data on Korean plant resources. Active compounds in the extract of Mume Fructus were separated by batch extraction, and further purified by chromatography in a silica gel column and an octadecyl silica gel column using solvents of different polarity. By NMR analysis of the last chromatographic fraction we identified ursolic acid as the active compound of urease inhibition. The result suggests that this component in Mume Fructus can possibly be used for the eradication of H. pylori.

A novel nanobody against urease activity of Helicobacter pylori

Helicobacter pylori infection is associated with gastritis and in some cases with gastric and duodenal ulcers, and even adenocarcinoma. Antibiotic therapy has significant limitations, such as the high cost and the emergence of antibiotic-resistant strains, generating the need for new treatments. The administration of antibody against H. pylori is a new effective therapeutic strategy. In this study, we successfully developed a single-variable domain of heavy chain antibody against recombinant UreC. A VHH phagemid library was constructed from immune camel heavy chain antibodies. The nanobodies were displayed on M13 phage. Library selection was performed against UreC recombinant protein. A specific single-variable domain of heavy chain antibody against UreC was screened in five rounds of panning. The nanobody with the highest score in the phage ELISA was selected for soluble expression. The nanobody was purified with a nickel-nitrilotriacetic acid (Ni-NTA) column and confirmed with sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and Western blotting. Affinity, specificity, and urease inhibitory properties of the nanobody were assayed. Here we showed the isolation and purification of a specific nanobody with high affinity against UreC recombinant protein that can inhibit urease activity. The isolated UreC nanobody can specifically detect and bind to UreC and inhibit urease activity. This nanobody could be a novel class of treatment measure against H. pylori infection.

Antagonistic Activities of Lactobacilli against Helicobacter pylori Growth and Infection in Human Gastric Epithelial Cells

Lactobacilli have positive effects on bowel microflora and health in humans and animals. In this study, the antagonistic activities of Lactobacillus gasseri Chen, and L. plantarum 18 were assessed by agar plate diffusion assay and tests that determined the growth and urease activity of Helicobacter pylori cocultured with lactobacilli and the adherence of H. pylori to human gastric epithelial cells in the presence of lactobacilli. The results showed that the 2 Lactobacillus strains had significant anti-H.pylori activity, and this activity may be contributed by the cell-free supernatants (CFS) of lactobacilli and live Lactobacillus strains in vitro. The antagonistic activity of the CFS against H. pylori depended on the pH and the presence of metabolites, such as organic acids and proteases. Our results also indicated that 2 Lactobacillus strains could inhibit H. pylori adherence human gastric epithelial cells. Helicobacter pylori causes chronic gastritis, peptic ulcer disease, and gastric cancer, and it infects about 50% of the world's population. Lactobacilli have been reported to have an inhibitory effect on H. pylori and can be used as probiotic to manufacture dairy products preventing H. pylori infection.

Helicobacter pylori Urease Activity is Influenced by Ferric Uptake Regulator

PurposeThe role of the Ferric Uptake Regulator (FUR) in the acid resistance of Helicobacter pylori (H. pylori) has been thought to be independent of urease. However, we demonstrated in this study that Fur influences urease activity.Materials and MethodsA fur knockout mutant of H. pylori was constructed by replacing the Fur gene with a kanamycin resistant marker gene. The wild-type H. pylori and fur mutant were compared for survival. The integrity of the inner membrane of the bacteria was evaluated by confocal microscopy using membrane-permeant and -impermeant fluorescent DNA probes. Urease activity of intact H. pylori was measured between pH 3 and 8. Real time PCR of both strains was performed for urease genes including ureI, ureE, ureF, ureG, and ureH.ResultsThe fur deletion affected the survival of H. pylori at pH 4. The urease activity curve of the intact fur mutant showed the same shape as the wild-type but was 3-fold lower than the wild-type at a pH of less than 5. Real time PCR revealed that the expression of all genes was consistently down-regulated in the fur mutant.ConclusionThe results of this study showed that fur appears to be involved in acid resistant H. pylori urease activity.

Betulinic and oleanolic acids isolated from Forsythia suspensa Vahl inhibit urease activity of Helicobacter pylori

Sixteen medicinal herbs were selected from a database on traditional herbal materials as well as literature on Korean plant resources. Then ethanol (70%, v/v) extracts of these herbs were tested for inhibition of the urease activity of Helicobacter pylori. The urease activity of H. pylori was strongly (82%) inhibited by extract of Forsythia suspensaVahl. Active compounds in extract of Forsythia suspensaVahl were first separated by batch mode solvent extraction, followed by purification by silica gel and octadecyl silica gel column chromatography using solvents of different polarity. According to NMR analysis of the last chromatographic fraction, we identified the presence of betulinic acid and oleanolic acid, which are known to have anti-inflammatory, anti-cancer, and anti-HIV viral activities.

In VitroInhibitory Effect of Flavonoids on Growth, Infection and Vacuolation ofHelicobacter pylori

Flavonoids, which are main constituents of herbal medicines, have been reported to inhibit the growth of Helicobacter pylori (HP). Therefore, to evaluate the anti-HP activity of some flavonoids (flavanols, flavones, flavonols and isoflavonoids), their effects on the growth and vacuolation of HP as well as the infective properties of HP against HeLa cells were investigated. Catechins, quercetin and naringenin weakly inhibited the growth of HP, but all tested compounds did not inhibit HP infection into KATO III cells and HP urease activity. Quercetin and naringenin inhibited HP VacA vacuolation in HeLa cells with IC (50) values of 0.046 and 0.36 mM, respectively. Quercetin also inhibited procaspase-3 activation to caspase-3 in HeLa cells induced by HP VacA toxin, which may induce cell death via the proteolytic activation of a cascade of caspases. However, quercetin did not affect Bax and Bcl-2 protein levels. Based on these findings, quercetin may improve gastric cell death by inhibiting apoptotic signaling by HP VacA toxin. Abbreviations. HP: Helicobacter pyloriBSA:bovine serum albumin ESL:enhanced chemiluminescence MIC:minimum inhibitory concentration MTT:methylthiazolyldiphenyl-tetrazolium bromide PBS:phosphate-buffered saline VacA:Vacuolating cytotoxin.

Helicobacter pylori, gastric juice, and arterial ammonia levels in patients with cirrhosis.

Helicobacter pylori urease activity is a potential source of ammonia in the stomach of patients with cirrhosis. However, the possible role of H. pylori in the pathogenesis of hepatic encephalopathy deserves further investigations. The current study evaluates the relationship among H. pylori infection, gastric juice ammonia concentrations, and arterial ammonia levels in patients with cirrhosis. Overall, 14 patients with cirrhosis with overt hepatic encephalopathy, 19 with subclinical hepatic encephalopathy, and 13 without encephalopathy were enrolled. All patients underwent upper endoscopy, and gastric biopsy specimens were taken for H. pylori assessment (rapid urease test, histology, and culture). A gastric juice sample and an arterial blood sample were obtained for ammonia level assessment. Patients with overt encephalopathy had both higher arterial ammonia levels and a more severe hepatic impairment than the remaining patients, whereas gastric juice ammonia concentrations did not differ among the three groups. H. pylori prevalence was similar among groups. Patients with H. pylori infection had significantly higher gastric juice ammonia concentrations than those without infection (2.3 +/- 1.3 vs. 0.9 +/- 0.6 mmol/L, respectively; p = 0.003); however, no difference in arterial ammonia levels emerged between the two groups (37.7 +/- 18.6 vs. 37.6 +/- 18.8 micromol/L, respectively). No significant correlation was found between gastric juice ammonia concentrations and arterial ammonia levels. The data suggest that liver impairment remains crucial in ammonia disposal in patients with cirrhosis, whereas H. pylori infection does not seem to play a major role in the pathogenesis of hyperammonemia in these patients.

The effect of Helicobacter pylori eradication on gastric juice and blood ammonia concentrations and on visual evoked potentials in cirrhotics.

The primary source of ammonia is the gut. Ammonia can also be generated by the urease activity of Helicobacter pylori in the gastric mucosa. The aim of this study was to investigate the effect of H. pylori eradication on blood and gastric juice ammonia levels and on visual evoked potential (VEP) recordings in cirrhotic patients. Male patients with cirrhosis and H. pylori infection were prospectively evaluated. All patients were given triple regimen for eradication for 10 days. Gastroscopy together with gastric juice sampling for ammonia and mucosal sampling for H. pylori status was performed before and after therapy. Gastric juice and blood ammonia levels were measured and VEP recordings were obtained before and after treatment. Twenty-seven patients were included in the study. Patients with overt clinical hepatic encephalopathy were excluded from the study. Twenty-four out of twenty-seven patients became H. pylori-negative after the treatment. Ammonia measurements and VEP recordings were evaluated in the 24 patients in whom eradication was successful. A slight but statistically significant decrease in blood and a considerable decrease in gastric juice ammonia levels were observed after treatment [from 44.23 micromol/l to 41.6 micromol/l compared with 3234 micromol/l to 2709 micromol/l, respectively (p <.05)] in patients in whom H. pylori was eradicated. VEP recordings were abnormal in 14 out of 24 patients before the treatment. Only four of these 14 patients with abnormal recordings showed improvement. (p > .05). Helicobacter pylori eradication in cirrhotics decreases blood and gastric juice ammonia concentrations whereas it does not provide an improvement in VEP recordings.

Anti-Helicobacter pylori activity of quinolone alkaloids from Evodiae fructus.

A biologically monitored fractionation of methanol extract of the fruit of Evodia rutaecarpa led to the isolation of six quinolone alkaloids, evocarpine (1), 1-methyl-2-[(4Z,7Z)-4,7-tridecadienyl]-4(1H)-quinolone (2), 1-methyl-2-[(6Z,9Z)-6,9-pentadecadienyl]-4(1H)-quinolo ne (3), 1-methyl-2-undecyl-4(1H)-quinolone (4), dihydroevocarpine (5), 1-methyl-2-pentadecyl-4(1H)-quinolone (6). They showed potent anti-Helicobacter pylori activity with the minimum inhibitory concentration (MIC) value of 10-20 microg/ml. However, they had no effect on Helicobacter pylori urease activity at the concentration of 300 microg/ml.

Influence of pH on metabolism and urease activity of Helicobacter pylori

Background & Aims: The metabolic and urease responses of Helicobacter pylori to variations in gastric acidity are unknown. The aim of this study was to determine effects of changes of environmental pH on metabolism, urease activity, and survival of H. pylori in an unbuffered environment. Methods: Bacterial metabolism and urease activity were determined by measuring pH changes in perfused microphysiometer chambers over a pH range from 2.5 to 9.0 with or without urea and survival by restoration of metabolism at pH 7.4. Results: Glucose metabolism by acid-adapted H. pylori occurred at a perfusion pH between 3.5 and 8.6 and was highest between 7.4 and 8.2. Metabolism was irreversibly inhibited at pH <3.5 or >8.6. In the presence of 2.5 mmol/L urea, the chamber pH increased to about 6.2 during perfusion between pH 5.5 and 4.0. At pH 4.0 and below, urease activity increased several-fold without change of chamber pH. Urea in the perfusate enabled retention of metabolism after acid exposure but was toxic at pH 7.4. Conclusions: The metabolic range of acid-adapted H. pylori is between an environmental pH of 3.5 and 8.6. Extracellular pH–regulated internal urease activity allows metabolism in the pH range between 4.0 and 2.5 by maintaining periplasmic pH at 6.2. The organism is an acid-tolerant neutralophile due to internal urease activity. GASTROENTEROLOGY 1998;115:628-641

Helicobacter pylori urease activity induces gight junction injury in canine gastric mucosa monolayers

Helicobacter pylori urease activity induces gight junction injury in canine gastric mucosa monolayers

5472695 Therapeutic application of a thyme extract and in - vitro methods for inhibiting the growth and urease activity of Helicobacter pylori

5472695 Therapeutic application of a thyme extract and in - vitro methods for inhibiting the growth and urease activity of Helicobacter pylori

Replacing mass spectrometer with optical spectrometer for measuring15N abundance in detecting the Helicobacter pylori infection

Since the discovery of HP (Helicobacter pylori) and its close association with gastritis and peptic ulceration, it has been important to establish a practical method for conveniently testing HP infection. Because of the strong urease activity of HP, the urea administered orally is broken down into NH3 and CO2 by the HP urease in the patient's stomach. Then the NH3 is absorbed by the blood and excreted in the urine. The HP infection can be detected with15N — tracing method,15NH 4 + excretion test, using15N — urea as a tracer compound. Performing on the detection with a optical spectrometer made by us for measuring the15N — abundance in the urine is reported.

｀１３´Ｃ‐尿素呼気試験の第１相臨床試験（プロジェクトコード：Ｃ‐１３ＵＢＴ）

Helicobacter pylori (HP) has recently attracted attention for its involvement in the occurrence and progression of gastritis, as well as in the occurrence, worsening to intractable stage, and relapse of gastric or duodenal ulcer. However, there is no safe and simple method to accurately diagnose the presence and degree of HP infection, to evaluate the reduction in bacterial count after attempted eradication of HP, and to evaluate the success or failure of the eradication without subjecting the patient to considerable discomfort on pain. Taking advantage of the urease activity of HP to produce carbon dioxide from urea, we developed a new 13C-urea breath test (C-13UBT) that uses urea labeled with carbon 13, a stable, naturally occurring non-radioactive isotope, to detect the presence of HP infection. The present phase I study was designed to determine the safety and efficacy of the C-13UBT. Healthy volunteers ingested 100, 200, and 300 mg of 13C-urea dissolved in 100 ml of water. The subjects were placed in the sitting position in order to bring the 13C-urea into close contact with the gastric mucosa, and their expired breath was collected at designated time intervals. The subjects were divided into two groups, HP antibody titer-positive group and HP antibody titer-negative group ; the relationship between HP infection and the amount of 13C-carbon dioxide detected in the expired breath was examined. The results showed a definite difference in the amount of 13C-carbon dioxide between the HP antibody titer-positive group and the HP antibody titer-negative group at all test doses. Although a dose of 100 mg was considered to be optimal in detecting HP positive subjects in the present study, further investigation is needed to accurately determine the optimal dose and the timing for assessment. Blood biochemistry, urinalysis, observations and examinations of subjective symptoms and objective signs, and safety assessment revealed no abnormalities related to the ingestion of 13C-urea. The serum pharmacokinetic parameters of the 13C-urea were obtained by subtracting endogenous 13C-urea from the measured values. As a result, the Cmax and AUC increased dose-dependently, with the AUC0-lim (AUC until the time of final detection) and Cmax for 100, 200, and 300 mg being 22.7μg·hr/ml and 2.7μg/ml, 63.6 μg·hr/ml and 5.5μg/ml, and 83.9μg·hr/ml and 9.0μg/ml, respectively. The mean total urinary excretion of 13C-urea during the 24 hours post-ingestion was 412 mg at 100 mg, 550 mg at 200 mg, and 504 mg at 300 mg, showing an increase over the theoretical range of 150 to 300 mg which was obtained by computing the total daily urea excretion (normal laboratory test value) from the percentage of endogenous 13C-urea in the urine (about 1%). Serum levels of ammonia and blood urea nitrogen (BUN) and urinary levels of urea showed no changes dependent on the dose of 13C-urea. These results suggest that C-13UBT is a highly safe, simple, and useful test that accurately reflects the status of HP infection.

Helicobacter pylori urease inhibition by rabeprazole, a proton pump inhibitor.

We investigated the inhibitory effects of four gastric proton pump inhibitors (PPIs): rabeprazole, a novel benzimidazole PPI, omeprazole, lansoprazole and AG-2000, on the urease activity of Helicobacter pylori (H. pylori). Their 50% inhibitory concentrations (I50s) were found to be 0.29, 5.4, 9.3 and 0.3 microM respectively. Rabeprazole and omeprazole were also potent inhibitors of Jack bean and Proteus mirabilis cellular ureases. The thioether derivative of rabeprazole, one of its metabolites, had no inhibitory effect on H. pylori urease, despite being reported as a more potent inhibitor of H. pylori growth than rabeprazole. The inhibitory effect of rabeprazole was prevented completely and reversed considerably by the addition of sulfhydryl compounds, such as beta-mercaptoethanol, glutathione and dithiothreitol. Moreover, the addition of beta-mercaptoethanol recovered the urease activity inhibited by rabeprazole. From these results, we expected that rabeprazole inhibited H. pylori urease activity by forming disulfide bonds between it and the active site of the enzyme.

Pre-formed urease activity of Helicobacter pylori as determined by a viable cell count technique--clinical implications

The pre-formed urease activity of three NCTC reference strains and five clinical isolates of Helicobacter pylori was determined at room temperature (21 degrees C) and 37 degrees C by a viable cell count technique with a conventional urea slope test (Christensen's agar) as well as the commercial CLO-test. The urease activity of two gastroduodenal commensals, Proteus mirabilis and Klebsiella pneumoniae, was also tested. H. pylori strains produced positive reactions with viable cell counts of 10(6)-10(8) cfu within 30 min and with counts of 10(3)-10(6) cfu within 2 h. For some strains, smaller numbers of organisms were needed with the CLO-test than with the conventional test, and incubation of the CLO-test strips at 37 degrees C slightly decreased the number of organisms required for positive results. P. mirabilis produced a positive result on urea slopes with an initial inoculum of 10(7)-10(8) cfu at 2 h, but no positive reaction occurred for K. pneumoniae at 12 h, even with an initial inoculum of 10(11) cfu. However, both P. mirabilis and K. pneumoniae gave a positive result after incubation for 24 h with initial inocula of < 10(1) cfu and 10(3)-10(4) cfu respectively. Incubation at 37 degrees C significantly reduced the inoculum size of these organisms required for a positive result after incubation for 4 h when tested with the slopes, but not with the CLO-test. These findings indicate that H. pylori possesses much greater pre-formed urease activity than P. mirabilis and K. pneumoniae. False negative results for clinical detection of H. pylori in gastroduodenal biopsies may be due to small numbers of organisms, especially after treatment with antimicrobial agents, and false positive results may arise from gastroduodenal commensals or contaminants.