Helicobacter pylori in the oral cavity reflects handling of contaminants but not gastric infection

Possible Association of Periodontal Diseases With Helicobacter pylori Gastric Infection: A Systematic Review and Meta-Analysis

Some research has suggested that dental plaque and saliva could be reservoirs of Helicobacter pylori (H. pylori) and be capable of infecting or re-infecting the gastric mucosa after eradication, with certain studies showing a significant association between PD and gastric infection by this bacterium. An electronic search was performed in PubMed, EMBASE, and Web of Science databases with the terms “Helicobacter pylori AND periodontal diseases”; “Helicobacter pylori AND gingivitis”; “Helicobacter pylori AND chronic periodontitis”; “Helicobacter pylori AND periodontitis”; “Helicobacter pylori AND dental plaque”, to identify articles up to September 2021. The Newcastle-Ottawa scale was used to assess study quality. A meta-analysis was performed using RevMan 2020 (Cochane Collaboration) software. A total of 1,315 studies were identified and 12 were included, analyzing 226,086 patients with mean age between 10.5 and 63.4 years. The prevalence of H. pylori in the oral cavity ranged from 5.4 to 83.3%. A random-effects model was used to analyze the presence of H. pylori and subgroups were made according to the method of evaluation (PCR or RUT). Statistical significance was found in the overall analysis (p = 0.01). There is no clear evidence that H. pylori present in oral bacterial plaque causes gastric infection and vice versa.

The role of Helicobacter Pylori and laryngopharyngeal reflux in recurrent tonsillitis

OBJECTIVES

To detect Helicobacter Pylori [HP] in tonsillar tissue of recurrent tonsillitis cases and assess the possible role of Laryngopharyngeal reflux [LPR] in tonsillar HP infection.

METHODS

A prospective study was done on the cited subject in a sample size of 50 paediatric patients [Age group: 6-18 years] suffering from recurrent tonsillitis. LPR was diagnosed by Reflux Symptom index [RSI] and Reflux Finding score [RFS]. A score of more than 7 and 13 was regarded as significant for RFS and RSI respectively. Patients with both scores significant were regarded to be suffering from LPR. Tonsillar specimen after tonsillectomy were subjected to urease test, histopathology [ Modified Giemsa Staining] and culture to detect HP. A minimum of two positive tests of the mentioned three were taken as gold standard to diagnose colonization of HP. Tabulated data was statistically analysed.

RESULTS

We recorded an incidence of 9% [18 cases] for LPR in recurrent tonsillitis. No case of HP colonization of tonsils was detected in this case series, even in patients of LPR.

CONCLUSION

We conclude that tonsils are not an extra gastric reservoir of HP. In addition, there is no aetiological relationship between recurrent tonsillitis and HP. And lastly, LPR is not a significant factor for colonization of tonsils by HP.

Are the view of Helicobacter pylori colonized in the oral cavity an illusion?

Urea breath test (UBT), as a leading preferred non-invasive diagnostic technology, but may not be able to detect oral H. pylori. With negative results of UBT, the patient may have an oral infection. On the basis of the fact of success, eradication rate may increase by 21% in the 95% Cl range after the elimination of oral H. pylori, the author believes oral H. pylori does exist and the oral cavity is the second colonized site aside its primary site of the stomach. H. pylori migrated out of Africa along with its human host circa 60 000 years ago; they are not lives in stomach only. In this review article, evidence established in recent years studies with use more appropriate technology had been listed and discussed. The author considers the oral cavity is a black hole for H. pylori infection that significant effective on gastroenterology and another medical field. The role of the oral cavity as the source of H. pylori infection is so controvert in past years. It seems like a human being having a second-time face to discover H. pylori in the history.

Helicobacter pylori and oral pathology: Relationship with the gastric infection

Helicobacter pylori (H. pylori) has been found in the oral cavity and stomach, and its infection is one of the most frequent worldwide. We reviewed the literature and conducted a Topic Highlight, which identified studies reporting an association between H. pylori-infection in the oral cavity and H. pylori-positive stomach bacterium. This work was designed to determine whether H. pylori is the etiologic agent in periodontal disease, recurrent aphthous stomatitis (RAS), squamous cell carcinoma, burning and halitosis. Record selection focused on the highest quality studies and meta-analyses. We selected 48 articles reporting on the association between saliva and plaque and H. pylori-infection. In order to assess periodontal disease data, we included 12 clinical trials and 1 meta-analysis. We evaluated 13 published articles that addressed the potential association with RAS, and 6 with squamous cell carcinoma. Fourteen publications focused on our questions on burning and halitosis. There is a close relation between H. pylori infection in the oral cavity and the stomach. The mouth is the first extra-gastric reservoir. Regarding the role of H. pylori in the etiology of squamous cell carcinoma, no evidence is still available.

The Role of Helicobacter pylori in Upper Respiratory System Infections: Is it More Than Colonization?

Helicobacter pylori (HP) is recognized as a common chronic human bacterial infection and is the most common cause of gastritis. Recent studies suggest an increased HP prevalence in patients with various extra-digestive inflammatory diseases. Since many respiratory diseases are characterized by chronic inflammation as well as increased immune response, and HP may enter the nasopharyngeal cavity by gastroesophageal reflux, an association between respiratory disorders and HP infection has been suggested. Several studies discover HP in clinical samples from the patients with upper respiratory system infections. Even some of them revealed a relief after the treatment directed to HP eradication. However some studies do not support this theory and whether this association means a definite proof of a causal relationship between HP and respiratory diseases needs to be clarified. In this study, we aimed to review the reports about the role of HP in upper respiratory system infections.

Detection of helicobacter pylori in benign laryngeal lesions by polymerase chain reaction: a cross sectional study

BACKGROUND

Although Helicobacter Pylori (HP) was detected in some cases of chronic laryngitis, the results were not confirmed by polymerase chain reaction (PCR). By this time, it has not been found in laryngeal lesions by in house PCR, the most sensitive method for detecting the genome tracks. Regarding the previous results and also few numbers of studies about the presence of HP in benign laryngeal lesions, specifically by PCR, we aimed to investigate the presence of HP in benign laryngeal lesions by in-house PCR.

METHODS

The samples were taken from 55 patients with benign laryngeal lesions and frozen in -20°C. One milliliter (ml) of lysis buffer was added to 100 mg (mg) of each sample and the tube was placed in 56°C overnight. Then DNA extraction was carried out.

RESULTS

To find HP DNA, in-house PCR was performed that revealed 5 positive results among 55 patients with benign laryngeal lesions. Of them, 3 were polyp, 1 was nodule and 1 was papilloma.

CONCLUSION

Although the number of positive results was not a lot in this study, it was in contrast with previous studies which could not find any HP tracks in benign laryngeal lesions by other methods. More studies about the prevalence of HP in benign laryngeal lesions improve judging about the effect of this infection on benign laryngeal lesions.

Determination of Helicobacter pylori in patients with chronic nonspecific pharyngitis

OBJECTIVES/HYPOTHESIS

To determine if there is a relationship between Helicobacter pylori colonization in the pharynx mucous membrane and chronic nonspecific pharyngitis.

STUDY DESIGN

A prospective clinical study.

METHODS

Seventy patients with chronic pharyngitis and 20 healthy control subjects were examined with polymerase chain reaction (PCR) and culture for H. pylori colonization in the pharynx mucous membrane between March 2008 and October 2008. Patients with pharyngitis were seperated into two groups (35 patients in each) by using C-14 urea breath test, according to the presence of gastric H. pylori infection.

RESULTS

In the control group, none of the patients had H. pylori in the pharynx. In the chronic pharyngitis group, in 12 patients (34.3%) with gastric H. pylori infection and in seven patients (20%) without gastric infection, H. pylori colonization in pharynx mucosa was determined with the PCR method. In only two of chronic pharyngitis patients (5.8%), H. pylori infection was detected with culture. In the pharynx mucosa, the H. pylori infection rate was significantly higher in the chronic pharyngitis groups than in the control group (P = .002 between C-14 positive and control groups, P = .040 between C-14 negative and control groups). There was not a significant difference in H. pylori colonization in the pharynx of patients who had chronic pharyngitis with or without gastric ailments and H. pylori infection (P = .179).

CONCLUSIONS

Chronic nonspecific pharyngitis without gastric H. pylori infection is significantly related to H. pylori colonization in the pharynx, and gastric involvement increases the rate of this spread. The gold standart for detection of H. pylori infection is the PCR method.

Unreliability of results of PCR detection of Helicobacter pylori in clinical or environmental samples

The aim of this study was to compare published Helicobacter pylori primer pairs for their ability to reliably detect H. pylori in gastric biopsy specimens and salivary samples. Detection limits of the 26 PCR primer pairs previously described for detection of H. pylori DNA in clinical samples were determined. Sensitivity and specificity were determined using primers with detection limits of <100 CFU/ml using 50 H. pylori-positive and -negative (by concordance by culture and histology) coded gastric biopsy specimens. These results were then confirmed with gastric biopsy specimens and saliva from patients with confirmed H. pylori status. Five of the twenty-six previously reported primer pairs (HP64-f/HP64-r, HP1/HP2, EHC-U/EHC-L, VAG-F/VAG-R, and ICT37/ICT38) had detection limits of <100 CFU/ml in the presence of gastric tissue. None had 100% specificity or sensitivity; all produced false-positive results. The HP64-f/HP64-r for ureA and HP1/HP2 for 16S rRNA individually had sensitivities and specificities of >90% with gastric biopsy specimens. No combinations of primer pairs improved the results. Using these five primer pairs, 54% of the positive saliva samples were determined to be false positive; both the HP64-f/HP64-r and the HP1/HP2 sets produced false positives with saliva. We conclude that clinicians should not rely on results using current PCR primers alone to decide the H. pylori status of an individual patient or as a basis for treatment decisions. The results of studies based on PCR identification of H. pylori in environmental samples should be viewed with caution. Possibly, specific primers sets can be identified based on the presence of multiple putative virulence factor genes.

Study on the relationship between Helicobacter pylori in the dental plaque and the occurrence of dental caries or oral hygiene index

BACKGROUND

The aims of our study were to determine the presence of Helicobacter pylori DNA in the dental plaque of Chinese children aged 3-6 years by nested polymerase chain reaction (PCR) and to investigate the relationship between this infection and the occurrence of dental caries or oral hygiene index.

METHODS

Two hundred and fourteen children from a kindergarten in Guangzhou City of China were evaluated. The children's plaques were assessed by plaque indices of Quigley-Hein. Dental plaque was analyzed using nested PCR for two sets of primers directed to the 860-bp fragment of H. pylori genomic DNA, which have been reported to be highly sensitive and specific by other researchers.

RESULTS

H. pylori was detected in dental plaque samples from 126 children, and 70 children with dental caries carried H. pylori in dental plaque. Of these children without infection, only 36 of 88 suffered dental caries. Besides, the average dental plaque index of 126 H. pylori-positive children was higher than that of 88 children without infection. In the present study, there was a significant correlation between H. pylori infection and dental caries or dental hygiene.

CONCLUSION

The oral cavity may be a reservoir for H. pylori infection in children. H. pylori in dental plaque may play a role in the occurrence of dental caries, and poor oral hygiene may represent a risk factor for H. pylori in the oral cavity.

Comparison of different methods to detect Helicobacter pylori in the dental plaque of dyspeptic patients

The aim of this study was to compare different methods of detection of Helicobacter pylori (H. pylori) in the dental plaque of dyspeptic patients. After recording the clinical indices, culture and polymerase chain reaction (PCR) methods were performed on plaque samples, while rapid urease test in addition to these tests was carried on gastric samples from 67 dyspeptic patients who attended for an upper gastrointestinal endoscopy. Forty-seven of 67 patients were H. pylori-positive in gastric biopsy material whereas the microbial dental plaque from 19 patients demonstrated H. pylori positivity detected by PCR. Among the patients, 25.4% harbored H. pylori both in the stomach and in microbial dental plaque. No significant correlations were found among the presence of H. pylori in the stomach, in plaque, and clinical variables (P > 0.05). Although oral hygiene was observed optimal and the mean of pocket depth was not found to be higher, the prevalence of H. pylori was observed to be higher in dental plaque. According to our results, PCR technique gave the highest detection rate both in gastric biopsy and in dental plaque compared to the other methods used.

Implications of oral Helicobacter pylori for the outcome of its gastric eradication therapy

BACKGROUND AND AIMS

Helicobacter pylori (H. pylori) is an important pathogen in gastritis, peptic ulcer and possibly gastric cancer, but several questions remain unanswered. Particularly how the organism is transmitted and what is the relationship between oral presence of H. pylori and the gastric infection. Accordingly, we aimed to characterize the H. pylori in oral cavity and to evaluate its relationship to gastric H. pylori infection.

MATERIALS AND METHODS

Out of total 100 screened for H. pylori infection female subjects (40 to 85 y), 49 patients (pts), who had positive C-urea breath test (UBT) and dyspeptic symptoms, agreed for 1 week regimen of triple anti-H. pylori therapy. The presence of H. pylori in oral cavity was assessed using bacterial culture from saliva and gingival pockets. Gastric H. pylori infection was estimated using capsulated C-urea breath test and plasma anti-H. pylori IgG and saliva IgA antibodies. In addition, plasma gastrin, ghrelin, and pepsinogen I were measured by radioimmunoassay. In selected patients, gastroscopy was additionally performed and gastric biopsy samples were taken for H. pylori random amplification of polymorphic DNA genetic profiling.

RESULTS

The triple therapy resulted in gastric H. pylori eradication in 79% pts, along with significant decrease of plasma gastrin combined with an increase in plasma ghrelin and pepsinogen I (PgI) levels and a marked alleviation of dyspeptic symptoms. In contrast to gastric effects, the eradication therapy failed to cause any changes in the presence of H. pylori in oral cavity. Moreover no relationship was observed between the presence of H. pylori in oral cavity and the gastric H. pylori eradication. In line with these findings, no relationship between gastric and oral H. pylori was found using genetic profiling by random amplification of polymorphic DNA.

CONCLUSIONS

H. pylori was detected both in the oral cavity and the stomach but oral H. pylori had no relation to gastric H. pylori and remained unaffected by eradication of gastric H. pylori.

Absence of Helicobacter pylori in the oral cavity of 10 non-dyspeptic subjects demonstrated by real-time polymerase chain reaction

Helicobacter pylori plays a significant role in gastric disease. However, the presence of this bacterium in the oral cavity remains controversial. The aim of the present study was to detect and quantify H. pylori in 29 different sites of the oral cavity in non-dyspeptic subjects by means of real-time polymerase chain reactions (PCR). Ten subjects without gastric symptoms were studied. Samples from unstimulated saliva, three sites of the tongue, oral mucosa, and 12 sites of both supragingival and subgingival plaque were collected from each subject. DNA was extracted from the oral samples and analysed for the presence of H. pylori by real-time PCR (LightCycler) using JW23/22 primers which targeted the 16S rRNA gene. DNA from H. pylori DSM 4867 was used as a positive control. Amplification efficiency for the LightCycler 2.0 runs ranged from 1.8 to 2.4. Melting curve analysis identified all the positive control capillaries, which contained H. pylori reference DNA, as a single and narrow peak at a melting temperature between 84.5 and 84.9 degrees C. All the negative control capillaries with no template control and the 29 oral samples from each subject showed either no melting peaks or broad melting peaks below 80 degrees C, which were considered as primer dimers. Therefore, H. pylori was not detected from any of the 290 oral samples. As a conclusion, H. pylori seems not to be permanently present in the oral cavity of a non-dyspeptic population.

Absence of Helicobacter pylori within the oral cavities of members of a healthy South African community

Our study aimed to evaluate the oral cavity as a reservoir from where Helicobacter pylori may be transmitted. Histology and PCR amplification were performed. Eighty-four percent of the stomach biopsies tested positive; however, H. pylori was not detected in dental samples, indicating the absence of H. pylori within the oral cavity.

Real-time quantitative PCR assay for the detection of Helicobacter pylori: no association with sudden infant death syndrome

Helicobacter pylori infection is known to be one of the most common chronic infectious diseases in humans. Recently, a hypothesis was proposed that H. pylori infection could be a frequent cause for sudden infant death syndrome (SIDS). We have investigated this postulated association by examining formalin-fixed paraffin-embedded gastric tissues of a retrospective cohort of 94 SIDS cases: The presence of H. pylori was inferred from a newly developed real-time quantitative PCR assay with SYBR Green I detection. This assay is based on the amplification of the single-copy H. pylori-specific glmM gene. Accuracy and precision were verified using a plasmid containing a 977-bp fragment of this glmM gene. The assay was very sensitive, and as few as 30 template copies per PCR reaction could be detected even in the presence of excess human DNA. The assay was validated on mucosal biopsy samples of patients with known H. pylori infections. Interfering effects due to SIDS gastric tissue were excluded. Only two (2.1%) of the SIDS samples yielded H. pylori DNA copy numbers and only beyond the lowest standard concentration. These results could be confirmed independently by immunohistochemistry using an H. pylori-specific antibody. Thus, an infection by H. pylori is very rare in cases of SIDS, and thus the postulated association of H. pylori infection and SIDS cannot be confirmed.

Occurrence of Helicobacter pylori in dental plaque and saliva of dyspeptic patients

BACKGROUND

Helicobacter pylori infection in the stomach is associated with gastric and duodenal ulcers, gastric cancers and gastric lymphoma. The organism is transmitted by ingestion, but the oral-oral route and the fecal-oral route are also suggested. The prevalence of infection with H. pylori in developing countries, including Brazil, is higher than in developed countries.

PURPOSE

This study aimed to evaluate the role of the oral cavity as a reservoir of this species, by evaluating the occurrence of H. pylori in supragingival dental plaque and in saliva of Brazilian dyspeptic patients, whether harboring the organism or not in the stomach.

MATERIAL AND METHODS

Forty-nine patients reporting dyspeptic symptoms were subjected to oral clinical examination and collection of saliva and supragingival dental plaque samples prior to the endoscopic examination. The detection of H. pylori in oral samples was performed by PCR using 16S rRNA primers. The bacteria were detected in stomach by means of the rapid urease test.

RESULTS

Helicobacter pylori was detected in the stomach of 20 of 49 subjects reporting dyspeptic symptoms. The organism was detected in only one supragingival plaque sample, obtained from a patient positive for the urease test in the stomach and in none of the salivary samples.

CONCLUSION

Supragingival dental plaque and saliva may not be relevant reservoirs of H. pylori.

Investigation of Helicobacter pylori colonization in laryngeal neoplasia

Helicobacter pylori has been investigated in several other organ systems and localizations such as the oral cavity, but has not been investigated extensively in squamous cell carcinoma of the larynx, a region that could be directly exposed to the bacterium by the oral route or gastro-esophageal reflux. Only serological studies are available regarding the relation between H. pylori and laryngeal cancer, yielding conflicting results. To our knowledge, there is no study investigating the presence of H. pylori in laryngeal squamous cell carcinoma tissue. The purpose of this study was to investigate the presence of H. pylori in laryngeal squamous cell carcinoma tissue and to investigate the possible role of this organism in the etiopathogenesis of laryngeal cancer. Specimens from 50 patients with laryngeal cancer who underwent total or partial laryngectomy between March 1999 and December 2002 were examined by histopathological and immunohistochemical methods to detect H. pylori. The presence of H. pylori was also investigated histopathologically in 50 benign laryngeal biopsy specimens. In our study, we demonstrated that H. pylori was not present in laryngeal squamous cell carcinoma tissue or in the benign lesions. We could not find any evidence indicating that H. pylori played a role at the tissue level in the pathogenesis of laryngeal carcinoma.

Oral Helicobacter pylori: can we stomach it?

Helicobacter pylori infection is one of the most common in man. The bacterium primarily resides in the human stomach, where it plays a significant role in gastric disease. If the spread of H. pylori is to be prevented, an understanding of the transmission process is essential. The oral cavity has been proposed as a reservoir for gastric H. pylori, which has been detected by culture and PCR in both dental plaque and saliva. This review will discuss the evidence for the role of the oral cavity in the transmission of gastric H. pylori. Moreover, the difficulties encountered in addressing this topic, possible directions for future research, and the implications for the dental profession are discussed.

Ecological and immunopathological implications of oral bacteria in Helicobacter pylori-infected disease

Increasing evidence has linked colonization by Helicobacter pylori with the development of gastritis and peptic ulcer disease. H. pylori resides primarily in the gastric mucosa without invading the gastric epithelium, causing persistent mild gastric inflammation. There are many reports examining the relationship between colonization by microorganisms in the stomach and oral cavity. We found that some oral bacteria are able to trap H. pylori cells, but oral bacteria inhibit H. pylori growth in vitro. In cases where H. pylori was detected in oral cavity samples, including oral cancer surface samples, we suggested that this species had colonized the stomach and were present in the oral cavity only as a transient organism. We demonstrated that periodontopathic Campylobacter rectus strains posses proteinaceous antigens, including heat shock proteins that share antigenicity with antigens of H. pylori strains. These cross-reactive antigens between H. pylori and C. rectus may be related to the induction of immunopathological responses in periodontal tissues and the stomach. We concluded that H. pylori could not survive in the human oral cavity; however, there would be an interrelationship between periodontal disease due to C rectus and stomach diseases due to H. pylori.

Helicobacter pylori infection is unlikely to be transmitted between partners: evidence from genotypic study in partners of infected patients

INTRODUCTION

We postulated that the oro-oral route of transmission between spouses could be an important route of transmission of Helicobacter pylori.

AIMS

To estimate the prevalence of different genotypes of H. pylori as distinguished by the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method in our local population, and to compare the genotypes of H. pylori isolated from patients and their spouses.

METHODS

Gastric biopsies were obtained from 183 dyspeptic patients during endoscopy. PCR for H. pylori was carried out using the uceC gene for amplification, and PCR products were digested further for RFLP analysis using the enzyme MboI. Spouses of H. pylori-positive index cases were screened for the infection using serological testing; if found to be positive serologically, endoscopy and gastric biopsies were performed for genotypic study of the micro-organism. For couples with indistinguishable H. pylori strain on RFLP with restriction endonuclease MboI, the process of RFLP was repeated with digestion of the PCR products using restriction endonuclease HhaI.

RESULTS

We established our PCR technique to be 89.5% sensitive and 95.5% specific. Eighty-nine subjects were found to be H. pylori positive by PCR, and eight different genotypic strains were found according to our RFLP analysis. Two genotypes accounted for 80.8% of the cases. Sixteen of 31 spouses tested serologically for H. pylori were positive. All 13 spouses who agreed to undergo endoscopy were PCR positive for H. pylori. Five couples shared indistinguishable H. pylori genotypes, but this strain was also the commonest genotype in our local population, as based on RFLP with restriction endonuclease MboI. Further RFLP on the PCR products on these five couples using restriction endonucleases HhaI showed that the H. pylori isolated from these five couples were of different strains.

CONCLUSION

The oro-oral route of transmission between spouses is unlikely to be an important mode for H. pylori infection.

Gastrointestinal problems in the handicapped child

Gastrointestinal issues are a major chronic problem in 80 to 90% of children with cerebral palsy and in children with neurodevelopmental disabilities who are at special risk of developing malnutrition because of uncoordinated swallowing, gastroesophageal reflux, and constipation. In addition to poor linear growth, there is a decrease in muscle strength and coordination, impaired cerebral function leading to decreased motivation and energy. Significant neurodevelopmental progress can be achieved with improved nutritional status. A multidisciplinary approach, with input from neurologists, gastroenterologists, nurses, occupational therapists, and dieticians, can make a major contribution to the medical wellbeing and quality of life of these children. Different neurological diseases ( eg, spinal dysraphism, syringomyelia, tethered cord syndromes) can give rise to gastrointestinal dysfunction and symptoms that may need different gastrointestinal or surgical management. The introduction of new drugs, including proton pump inhibitors and innovative endoscopic and surgical techniques in the management of gastroesophageal reflux disease and constipation also may have an impact on the treatment of neurologically handicapped children in the future.

Sites of pH regulation of the urea channel of Helicobacter pylori

Helicobacter pylori (Hp) and Streptococcus salivarius (Ss) require intrabacterial urease for acid resistance and express a urea channel, UreI. The presence of UreI was shown to increase urea permeability approximately 300-fold over that of a non-polar ureI deletion mutant. Expression of SsUreI in Xenopus oocytes increased urea uptake pH independently, whereas HpUreI shows an acidic pH dependence, half-maximal at pH 6.0. Mutagenesis of all histidines, aspartates, glutamates and the lysine in the periplasmic domain of HpUreI showed that His-123, His-131, Asp-129, Asp-140, Glu-138 and Lys-132 in the second periplasmic loop (PL2) and His-193 in the C-terminus (Ct) were important for activation of transport. With the exception of a lysine that was shown to substitute for His-193 in HpUreI, these charged amino acids are absent in SsUreI. A chimera in which PL1 of HpUreI was replaced by PL1 of SsUreI retained activity at acidic pH and gained partial activity at neutral pH. Exchange of PL2 inactivated transport, whereas exchange of Ct had no effect. Chimeras, in which either PL1 or PL2 of HpUreI replaced those of SsUreI, retained wild-type transport, but replacement of the Ct or both loops inactivated transport. PL1 appears to be important for restricting transport through HpUreI at neutral pH, whereas protonation of three histidines in PL2 and Ct and the presence of three dicarboxylic amino acids in PL2 appears to be necessary to activate HpUreI at acidic pH.