Potential of Bacterial Cellulose Chemisorbed with Anti-Metabolites, 3-Bromopyruvate or Sertraline, to Fight against Helicobacter pylori Lawn Biofilm

Helicobacter pylori is a bacterium known mainly of its ability to cause persistent inflammations of the human stomach, resulting in peptic ulcer diseases and gastric cancers. Continuous exposure of this bacterium to antibiotics has resulted in high detection of multidrug-resistant strains and difficulties in obtaining a therapeutic effect. The purpose of the present study was to determine the usability of bacterial cellulose (BC) chemisorbed with 3-bromopyruvate (3-BP) or sertraline (SER) to act against lawn H. pylori biofilms. The characterization of BC carriers was made using a N2 adsorption/desorption analysis, tensile strength test, and scanning electron microscopy (SEM) observations. Determination of an antimicrobial activity was performed using a modified disk-diffusion method and a self-designed method of testing antibacterial activity against biofilm microbial forms. In addition, bacterial morphology was checked by SEM. It was found that BC disks were characterized by a high cross-linking and shear/stretch resistance. Growth inhibition zones for BC disks chemisorbed with 2 mg of SER or 3-BP were equal to 26.5-27.5 mm and 27-30 mm, respectively. The viability of lawn biofilm H. pylori cells after a 4-h incubation with 2 mg SER or 3-BP chemisorbed on BC disks was ≥4 log lower, suggesting their antibacterial effect. SEM observations showed a number of morphostructural changes in H. pylori cells exposed to these substances. Concluding, SER and 3-BP chemisorbed on BC carriers presented a promising antibacterial activity against biofilm H. pylori cells in in vitro conditions.

Cryo-EM Analysis Reveals Structural Basis of Helicobacter pylori VacA Toxin Oligomerization

Helicobacter pylori colonizes the human stomach and contributes to the development of gastric cancer and peptic ulcer disease. H. pylori secretes a pore-forming toxin called vacuolating cytotoxin A (VacA), which contains two domains (p33 and p55) and assembles into oligomeric structures. Using single-particle cryo-electron microscopy, we have determined low-resolution structures of a VacA dodecamer and heptamer, as well as a 3.8-Å structure of the VacA hexamer. These analyses show that VacA p88 consists predominantly of a right-handed beta-helix that extends from the p55 domain into the p33 domain. We map the regions of p33 and p55 involved in hexamer assembly, model how interactions between protomers support heptamer formation, and identify surfaces of VacA that likely contact membrane. This work provides structural insights into the process of VacA oligomerization and identifies regions of VacA protomers that are predicted to contact the host cell surface during channel formation.

pH-dependent gating mechanism of the Helicobacter pylori urea channel revealed by cryo-EM

The urea channel of Helicobacter pylori (HpUreI) is an ideal drug target for preventing gastric cancer but incomplete understanding of its gating mechanism has hampered development of inhibitors for the eradication of H. pylori. Here, we present the cryo-EM structures of HpUreI in closed and open conformations, both at a resolution of 2.7 Å. Our hexameric structures of this small membrane protein (~21 kDa/protomer) resolve its periplasmic loops and carboxyl terminus that close and open the channel, and define a gating mechanism that is pH dependent and requires cooperativity between protomers in the hexamer. Gating is further associated with well-resolved changes in the channel-lining residues that modify the shape and length of the urea pore. Site-specific mutations in the periplasmic domain and urea pore identified key residues important for channel function. Drugs blocking the urea pore based on our structures should lead to a new strategy for H. pylori eradication.

Daphnetin: A Novel Anti-Helicobacter pylori Agent

Background: Antibiotic-resistant H. pylori was increasingly found in infected individuals, which resulted in treatment failure and required alternative therapeutic strategies. Daphnetin, a coumarin-derivative compound, has multiple pharmacological activities. Methods: The mechanism of daphnetin on H. pylori was investigated focusing on its effect on cell morphologies, transcription of genes related to virulence, adhesion, and cytotoxicity to human gastric epithelial (GES-1) cell line. Results: Daphnetin showed good activities against multidrug resistant (MDR) H. pylori clinical isolates, with minimal inhibitory concentration (MIC) values ranging from 25 to 100 μg/mL. In addition, daphnetin exposure resulted in H. pylori morphological changes. Moreover, daphnetin caused increased translocation of phosphatidylserine (PS), DNA damage, and recA expression, and RecA protein production vs. control group. Of great importance, daphnetin significantly decreased H. pylori adhesion to GES-1 cell line vs. control group, which may be related to the reduced expression of colonization related genes (e.g., babA and ureI). Conclusions: These results suggested that daphnetin has good activity against MDR H. pylori. The mechanism(s) of daphnetin against H. pylori were related to change of membrane structure, increase of DNA damage and PS translocation, and decrease of H. pylori attachment to GES-1 cells.

Anti-Helicobacter pylori Properties of the Ant-Venom Peptide Bicarinalin

The venom peptide bicarinalin, previously isolated from the ant Tetramorium bicarinatum, is an antimicrobial agent with a broad spectrum of activity. In this study, we investigate the potential of bicarinalin as a novel agent against Helicobacter pylori, which causes several gastric diseases. First, the effects of synthetic bicarinalin have been tested against Helicobacter pylori: one ATCC strain, and forty-four isolated from stomach ulcer biopsies of Peruvian patients. Then the cytoxicity of bicarinalin on human gastric cells and murine peritoneal macrophages was measured using XTT and MTT assays, respectively. Finally, the preventive effect of bicarinalin was evaluated by scanning electron microscopy using an adherence assay of H. pylori on human gastric cells treated with bicarinalin. This peptide has a potent antibacterial activity at the same magnitude as four antibiotics currently used in therapies against H. pylori. Bicarinalin also inhibited adherence of H. pylori to gastric cells with an IC50 of 0.12 μg·mL-1 and had low toxicity for human cells. Scanning electron microscopy confirmed that bicarinalin can significantly decrease the density of H. pylori on gastric cells. We conclude that Bicarinalin is a promising compound for the development of a novel and effective anti-H. pylori agent for both curative and preventive use.

Significance of dormant forms of Helicobacter pylori in ulcerogenesis

Nearly half of the global population are carriers of Helicobacter pylori (H. pylori), a Gram-negative bacterium that persists in the healthy human stomach. H. pylori can be a pathogen and causes development of peptic ulcer disease in a certain state of the macroorganism. It is well established that H. pylori infection is the main cause of chronic gastritis and peptic ulcer disease (PUD). Decontamination of the gastric mucosa with various antibiotics leads to H. pylori elimination and longer remission in this disease. However, the reasons for repeated detection of H. pylori in recurrent PUD after its successful eradication remain unclear. The reason for the redetection of H. pylori in recurrent PUD can be either reinfection or ineffective anti-Helicobacter therapy. The administration of antibacterial drugs can lead not only to the emergence of resistant strains of microorganisms, but also contribute to the conversion of H. pylori into the resting (dormant) state. The dormant forms of H. pylori have been shown to play a potential role in the development of relapses of PUD. The paper discusses morphological H. pylori forms, such as S-shaped, C-shaped, U-shaped, and coccoid ones. The authors proposes the classification of H. pylori according to its morphological forms and viability.

Anti-Helicobacter pylori Activity of Isocoumarin Paepalantine: Morphological and Molecular Docking Analysis

The Helicobacterpylori bacterium is one of the main causes of chronic gastritis, peptic ulcers, and even gastric cancer. It affects an average of half of the world population. Its difficult eradication depends upon multi-drug therapy. Since its classification as a group 1 carcinogenic by International Agency for Research on Cancer (IARC), the importance of H. pylori eradication has obtained a novel meaning. There is considerable interest in alternative therapies for the eradication of H. pylori using compounds from a wide range of natural products. In the present study, we investigated the antibacterial property of the isocoumarin paepalantine against H. pylori and it exhibited significant anti-H. pylori activity at a minimum inhibitory concentration (MIC) of 128 μg/mL and at a minimum bactericidal concentration (MBC) of 256 μg/mL. The scanning electron microscopy (SEM) revealed significant morphological changes of the bacterial cell as a response to a sub-MIC of paepalantine, suggesting a penicillin-binding protein (PBP) inhibition. Computational studies were carried out in order to study binding modes for paepalantine in PBP binding sites, exploring the active and allosteric sites. The data from the present study indicates that paepalantine exhibits significant anti-H. pylori activity, most likely by inhibiting membrane protein synthesis.

Characterization of Key Helicobacter pylori Regulators Identifies a Role for ArsRS in Biofilm Formation

Helicobacter pylori must be able to rapidly respond to fluctuating conditions within the stomach. Despite this need for constant adaptation, H. pylori encodes few regulatory proteins. Of the identified regulators, the ferric uptake regulator (Fur), the nickel response regulator (NikR), and the two-component acid response system (ArsRS) are each paramount to the success of this pathogen. While numerous studies have individually examined these regulatory proteins, little is known about their combined effect. Therefore, we constructed a series of isogenic mutant strains that contained all possible single, double, and triple regulatory mutations in Fur, NikR, and ArsS. A growth curve analysis revealed minor variation in growth kinetics across the strains; these were most pronounced in the triple mutant and in strains lacking ArsS. Visual analysis showed that strains lacking ArsS formed large aggregates and a biofilm-like matrix at the air-liquid interface. Biofilm quantification using crystal violet assays and visualization via scanning electron microscopy (SEM) showed that all strains lacking ArsS or containing a nonphosphorylatable form of ArsR (ArsR-D52N mutant) formed significantly more biofilm than the wild-type strain. Molecular characterization of biofilm formation showed that strains containing mutations in the ArsRS pathway displayed increased levels of cell aggregation and adherence, both of which are key to biofilm development. Furthermore, SEM analysis revealed prevalent coccoid cells and extracellular matrix formation in the ArsR-D52N, ΔnikR ΔarsS, and Δfur ΔnikR ΔarsS mutant strains, suggesting that these strains may have an exacerbated stress response that further contributes to biofilm formation. Thus, H. pylori ArsRS has a previously unrecognized role in biofilm formation.

IMPORTANCE

Despite a paucity of regulatory proteins, adaptation is key to the survival of H. pylori within the stomach. While prior studies have focused on individual regulatory proteins, such as Fur, NikR, and ArsRS, few studies have examined the combined effect of these factors. Analysis of isogenic mutant strains that contained all possible single, double, and triple regulatory mutations in Fur, NikR, and ArsS revealed a previously unrecognized role for the acid-responsive two-component system ArsRS in biofilm formation.

Growth inhibitory, bactericidal, and morphostructural effects of dehydrocostus lactone from Magnolia sieboldii Leaves on antibiotic-susceptible and -resistant strains of Helicobacter pylori

Helicobacter pylori is associated with various diseases of the upper gastrointestinal tract, such as gastric inflammation and duodenal and gastric ulcers. The aim of the study was to assess anti-H. pylori effects of the sesquiterpene lactone dehydrocostus lactone (DCL) from Magnolia sieboldii leaves, compared to commercial pure DCL, two previously known sesquiterpene lactones (costunolide and parthenolide), (-)-epigallocatechin gallate, and four antibiotics. The antibacterial activity of natural DCL toward antibiotic-susceptible H. pylori ATCC 700392 and H. pylori ATCC 700824 strains (MIC, 4.9 and 4.4 mg/L) was similar to that of commercial DCL and was more effective than costunolide, parthenolide, and EGCG. The activity of DCL was slightly lower than that of metronidazole (MIC, 1.10 and 1.07 mg/L). The antibacterial activity of DCL was virtually identical toward susceptible and resistant strains, even though resistance to amoxicillin (MIC, 11.1 mg/L for PED 503G strain), clarithromycin (49.8 mg/L for PED 3582GA strain), metronidazole (21.6 mg/L for H. pylori ATCC 43504 strain; 71.1 mg/L for 221 strain), or tetracycline (14.2 mg/L for B strain) was observed. This finding indicates that DCL and the antibiotics do not share a common mode of action. The bactericidal activity of DCL toward H. pylori ATCC 43504 was not affected by pH values examined (4.0-7.0). DCL caused considerable conversion to coccoid form (94 versus 49% at 8 and 4 mg/L of DCL for 48 h). The Western blot analysis revealed that urease subunits (UreA and UreB) of H. pylori ATCC 43504 were not affected by 10 mM of DCL, whereas UreA monomer band completely disappeared at 0.1 mM of (-)-epigallocatechin gallate. Global efforts to reduce the level of antibiotics justify further studies on M. sieboldii leaf-derived materials containing DCL as potential antibacterial products or a lead molecule for the prevention or eradication of drug-resistant H. pylori.

A new type of intrabacterial nanotransportation system for VacA in Helicobacter pylori

Helicobacter pylori possesses intrabacterial nanotransportation systems (ibNoTSs) for CagA and urease. Both systems are UreI-dependent and urea-independent, and activated by extrabacterial acid. The activation occurs/appears within 15 min after exposure to extrabacterial acid stimulation. Although it has been clarified that VacA is secreted via the type-V secretion machinery, it remains unclear how this toxin is transported toward the machinery. To clarify the intrabacterial nanotransportation system for H. pylori VacA, immunoelectron microscopic analysis was performed in this study. VacA shifted to the periphery of the bacterial cytoplasm at 30 min after the extracellular pH change, whereas CagA and urease did so within 15 min. Studies using an ureI-deletion mutant revealed that unlike CagA and urease transport, VacA transport was not UreI-dependent. VacA secretion was accelerated without an increase in the production of VacA 30 min after the exposure to extrabacterial acid. These findings indicated that H. pylori possesses a novel type of ibNoTS for VacA, which is different from that for CagA or urease, in response time and dependency of UreI.

In vitro characterization of the anti-bacterial activity of SQ109 against Helicobacter pylori

The most evident challenge to treatment of Helicobacter pylori, a bacterium responsible for gastritis, peptic ulcers and gastric cancer, is the increasing rate of resistance to all currently used therapeutic antibiotics. Thus, the development of novel therapies is urgently required. N-geranyl-N'-(2-adamantyl) ethane-1, 2-diamine (SQ109) is an ethylene diamine-based antitubercular drug that is currently in clinical trials for the treatment of tuberculosis (TB). Previous pharmacokinetic studies of SQ109 revealed that persistently high concentrations of SQ109 remain in the stomach 4 hours post oral administration in rats. This finding, combined with the need for new anti-Helicobacter therapies, prompted us to define the in vitro efficacy of SQ109 against H. pylori. Liquid broth micro-dilution was used for susceptibility studies to determine the antimicrobial activity of SQ109 against a total of 6 laboratory strains and 20 clinical isolates of H. pylori; the clinical isolates included a multi-drug resistant strain. All strains tested were susceptible to SQ109 with MIC and MBC ranges of 6-10 µM and 50-60 µM, respectively. SQ109 killing kinetics were concentration- and time-dependent. SQ109 killed H. pylori in 8-10 h at 140 µM (2MBCs) or 4-6 h at 200 µM (~3MBCs). Importantly, though the kinetics of killing were altered, SQ109 retained potent bactericidal activity against H. pylori at low pH. Additionally, SQ109 demonstrated robust thermal stability and was effective at killing slow growing or static bacteria. In fact, pretreatment of cultures with a bacteriostatic concentration of chloramphenicol (Cm) synergized the effects of typically bacteriostatic concentrations of SQ109 to the level of five-logs of bacterial killing. A molar-to-molar comparison of the efficacy of SQ109 as compared to metronidazole (MTZ), amoxicillin (AMX), rifampicin (RIF) and clarithromycin (CLR), revealed that SQ109 was superior to MTZ, AMX and RIF but not to CLR. Finally, the frequency of resistance to SQ109 was low and electron microscopy studies revealed that SQ109 interacted with bacterial inner membrane and cytoplasmic content(s). Collectively, our in vitro data demonstrate that SQ109 is an effective monotherapy against susceptible and multi-drug resistant strains of H. pylori and may be useful alone or in combination with other antibiotics for development as a new class of anti-Helicobacter drugs.

Functional plasticity in the type IV secretion system of Helicobacter pylori

Helicobacter pylori causes clinical disease primarily in those individuals infected with a strain that carries the cytotoxin associated gene pathogenicity island (cagPAI). The cagPAI encodes a type IV secretion system (T4SS) that injects the CagA oncoprotein into epithelial cells and is required for induction of the pro-inflammatory cytokine, interleukin-8 (IL-8). CagY is an essential component of the H. pylori T4SS that has an unusual sequence structure, in which an extraordinary number of direct DNA repeats is predicted to cause rearrangements that invariably yield in-frame insertions or deletions. Here we demonstrate in murine and non-human primate models that immune-driven host selection of rearrangements in CagY is sufficient to cause gain or loss of function in the H. pylori T4SS. We propose that CagY functions as a sort of molecular switch or perhaps a rheostat that alters the function of the T4SS and “tunes” the host inflammatory response so as to maximize persistent infection.

Helicobacter pylori is a bacterium that colonizes the stomach of about half the world's population, most of whom are asymptomatic. However, some strains of H. pylori express a bacterial secretion system, a sort of molecular syringe that injects a bacterial protein inside the gastric cells and causes inflammation that can lead to peptic ulcer disease or gastric cancer. One of the essential components of the H. pylori secretion system is CagY, which is unusual because it contains a series of repetitive amino acid motifs that are encoded by a very large number of direct DNA repeats. Here we have shown that DNA recombination in cagY changes the protein motif structure and alters the function of the secretion system—turning it on or off. Using mouse and non-human primate models, we have demonstrated that CagY is a molecular switch that “tunes” the host inflammatory response, and likely contributes to persistent infection. Determining the mechanism by which CagY functions will enhance our understanding of the effects of H. pylori on human health, and could lead to novel applications for the modulation of host cell function.

Anti-Helicobacter pylori activities of natural isopentenyloxycinnamyl derivatives from Boronia pinnata

In this study we investigated the anti-Helicobacter pylori activity of four isopentenyloxycinnamyl derivatives from the Australian shrub Boronia pinnata Sm. (Rutaceae), structurally related to boropinic acid: (E)-3-(4-(3-methylbut-2-enyloxy)-3,5-dimethoxyphenyl)acrylaldehyde (1), boropinol C (2), boropinal (3) and boropinol A (4). In vitro growth of H. pylori strains 26695 and B128 was analyzed in liquid culture with increasing doses of these compounds. Bacterial morphology was visualized by scanning electron microscopy. The in vivo effects of the two most efficient molecules that reduced bacterial growth in vitro, compounds 3 and 4, were investigated on H. pylori gastric colonization in the mouse model. The presence of these compounds in the bacterial cultures led to alterations of bacterial surface and flagella. In vivo, both compounds 3 and 4 at 250 microM reduced significantly the ability of H pylori to colonize the gastric mucosa of mice, compared with untreated ones. These data indicate that these natural isopentenyloxycinnamyl derivatives related to boropinic acid can be considered as novel antibacterial agents with anti-H. pylori activity.

Docosahexaenoic acid inhibits Helicobacter pylori growth in vitro and mice gastric mucosa colonization

H. pylori drug-resistant strains and non-compliance to therapy are the major causes of H. pylori eradication failure. For some bacterial species it has been demonstrated that fatty acids have a growth inhibitory effect. Our main aim was to assess the ability of docosahexaenoic acid (DHA) to inhibit H. pylori growth both in vitro and in a mouse model. The effectiveness of standard therapy (ST) in combination with DHA on H. pylori eradication and recurrence prevention success was also investigated. The effects of DHA on H. pylori growth were analyzed in an in vitro dose-response study and n in vivo model. We analized the ability of H. pylori to colonize mice gastric mucosa following DHA, ST or a combination of both treatments. Our data demonstrate that DHA decreases H. pylori growth in vitro in a dose-dependent manner. Furthermore, DHA inhibits H. pylori gastric colonization in vivo as well as decreases mouse gastric mucosa inflammation. Addition of DHA to ST was also associated with lower H. pylori infection recurrence in the mouse model. In conclusion, DHA is an inhibitor of H. pylori growth and its ability to colonize mouse stomach. DHA treatment is also associated with a lower recurrence of H. pylori infection in combination with ST. These observations pave the way to consider DHA as an adjunct agent in H. pylori eradication treatment.

Proteomannans in biofilm of Helicobacter pylori ATCC 43504

BACKGROUND

  The human bacterial pathogen Helicobacter pylori forms biofilms. However, the constituents of the biofilm have not been extensively investigated. In this study, we analyzed the carbohydrate and protein components of biofilm formed by H. pylori strain ATCC 43504 (NCTC 11637).

MATERIALS AND METHODS

  Development of H. pylori biofilm was analyzed using scanning electron microscopy (SEM) and quantified using crystal violet staining. The extracted extracellular polysaccharide (EPS) matrix was analyzed using GC-MS and nuclear magnetic resonance (NMR) analyses. Proteomic profiles of biofilms were examined by SDS-PAGE while deletion mutants of upregulated biofilm proteins were constructed and characterized.

RESULTS

  Formation of H. pylori biofilm is time dependent as shown by crystal violet staining assay and SEM. NMR reveals the prevalence of 1,4-mannosyl linkages in both developing and mature biofilms. Proteomic analysis of the biofilm indicates the upregulation of neutrophil-activating protein A (NapA) and several stress-induced proteins. Interestingly, the isogenic mutant napA revealed a different biofilm phenotype that showed reduced aggregated colonial structure when compared to the wild type.

CONCLUSIONS

  This in vitro study shows that mannose-related proteoglycans (proteomannans) are involved in the process of H. pylori biofilm formation while the presence of upregulated NapA in the biofilm implies the potency to increase adhesiveness of H. pylori biofilm. Being a complex matrix of proteins and carbohydrates, which are probably interdependent, the H. pylori biofilm could possibly offer a protective haven for the survival of this gastric bacterial pathogen in the extragastric environments.

Helicobacter pylori impairs murine dendritic cell responses to infection

Background

Helicobacter pylori, a human pathogen associated with chronic gastritis, peptic ulcer and gastric malignancies, is generally viewed as an extracellular microorganism. Here, we show that H. pylori replicates in murine bone marrow derived-dendritic cells (BMDCs) within autophagosomes.

Methodology/Principal Findings

A 10-fold increase of CFU is found between 2 h and 6 h p.i. in H. pylori-infected BMDCs. Autophagy is induced around the bacterium and participates at late time points of infection for the clearance of intracellular H. pylori. As a consequence of infection, LC3, LAMP1 and MHC class II molecules are retained within the H. pylori-containing vacuoles and export of MHC class II molecules to cell surface is blocked. However, formalin-fixed H. pylori still maintain this inhibitory activity in BMDC derived from wild type mice, but not in from either TLR4 or TLR2-deficient mice, suggesting the involvement of H. pylori-LPS in this process. TNF-alpha, IL-6 and IL-10 expression was also modulated upon infection showing a TLR2-specific dependent IL-10 secretion. No IL-12 was detected favoring the hypothesis of a down modulation of DC functions during H. pylori infection. Furthermore, antigen-specific T cells proliferation was also impaired upon infection.

Conclusions/Significance

H. pylori can infect and replicate in BMDCs and thereby affects DC-mediated immune responses. The implication of this new finding is discussed for the biological life cycle of H. pylori in the host.

In vitro antibacterial and morphological effects of the urushiol component of the sap of the Korean lacquer tree (Rhus vernicifera Stokes) on Helicobacter pylori

Eradication regimens for Helicobacter pylori infection have some side effects, compliance problems, relapses, and antibiotic resistance. Therefore, alternative anti-H. pylori or supportive antimicrobial agents with fewer disadvantages are necessary for the treatment of H. pylori. We investigated the pH-(5.0, 6.0, 7.0, 8.0, 9.0, and 10.0) and concentration (0.032, 0.064, 0.128, 0.256, 0.514, and 1.024 mg/mL)-dependent antibacterial activity of crude urushiol extract from the sap of the Korean lacquer tree (Rhus vernicifera Stokes) against 3 strains (NCTC11637, 69, and 219) of H. pylori by the agar dilution method. In addition, the serial (before incubation, 3, 6, and 10 min after incubation) morphological effects of urushiol on H. pylori were examined by electron microscopy. All strains survived only within pH 6.0-9.0. The minimal inhibitory concentrations of the extract against strains ranged from 0.064 mg/mL to 0.256 mg/mL. Urushiol caused mainly separation of the membrane, vacuolization, and lysis of H. pylori. Interestingly, these changes were observed within 10 min following incubation with the 1xminimal inhibitory concentrations of urushiol. The results of this work suggest that urushiol has potential as a rapid therapeutic against H. pylori infection by disrupting the bacterial cell membrane.

[Diagnosis of Helicobacter pylori infection: comparison with gold standard]

Marshall and Warren were the first to succeed in culturing Helicobacter pylori (H. pylori) from the gastric mucosa of patients with gastritis in 1983. H. pylori is a spiral-shaped bacterium that resides in the gastric mucosa and is one of the most common infections worldwide. H. pylori infection causes gastritis and peptic ulcers and is associated with the development of gastric cancer and MALT lymphoma. Now, a variety of accurate diagnostic tests are widely available. Both invasive tests (bacterial culture, histopathology, and RUT) and non-invasive tests (UBT and serological test) are conducted for the diagnosis of H. pylori infection. This review provides a general overview of the diagnostic methods and tests the characteristics (sensitivity and specificity) for H. pylori infection.

Coccoid formation as a mechanism of species-preservation in Helicobacter pylori: an ultrastructural study

Helicobacter pylori (H. pylorii) changes from a spiral form to coccoid by the aggravation of its surrounding environment. It was believed that the coccoid H. pylori indicated to be dying or becoming dormant. However, the implication of coccoid formation, itself, has not yet been elucidated. In this study, both the ultrastructural changes and the localization of the intracellular DNA were observed during coccoid formation in H. pylori. Some coccoid forms were observed to adhere to each other during transformation from the spiral form. The DNA and Cag A in each bacterium were detected at the boundary area of the aggregate, and then mixed in one new coccoid bacterium formed from the syncytium by plural bacteria. This type of coccoid formation was thought to be a transfer phenomenon of intracellular genetic proteins into neighbor organisms. In other words, the coccoid formation of H. pylori means not only the dying or the dormant condition but also a horizontal gene transfer processes with a positive significance for species-preservation under environmental stress.

Analysis of the survival of H. pylori within a laboratory-based aquatic model system using molecular and classical techniques

Despite the significance of Helicobacter pylori infection for man, its transmission is not clearly known. The human stomach is considered the reservoir of this pathogen, and one of the accepted routes is fecal-oral, in which water acts as a vector. However, although H. pylori epidemiology associates its transmission with water, only molecular and not cultural analysis detects the bacteria in water. This study was carried out to understand these data through studying the survival of H. pylori in a laboratory water model using cultural, morphological, and molecular methods. A mineral water system spiked with H. pylori and stored at 7 +/- 1 degrees C in the dark was analyzed by different methods over a period of 3 weeks. The total number of cells observed by DAPI staining and their DNA content remained constant over this study period. In contrast, cells could no longer be cultured after 5 days. Cell viability, which was determined via the LIVE/DEAD BacLight kit, decreased up to day 14, and at day 21 all cell membranes were damaged. In addition, a gradual conversion from spiral to coccal morphology occurred from day 3 onward. However, polymerase chain reaction (PCR) technique detected H. pylori DNA at day 21 and 3 months later. A study of the cell morphology of a young colony demonstrated the coexistence of bacilli and cocci. The results of this study show that H. pylori survives in water but loses its culturability and bacillar morphology rapidly, although it remains viable for longer periods and its DNA is still detectable much later. Thus, interpreting H. pylori's behavior in water differs according to the type of analysis. Consequently, we suggest that the presence of H. pylori infective cells is overestimated by PCR, whereas, in contrast, culture techniques underestimate it. Nevertheless, H. pylori should be considered a waterborne pathogen during its viable period, independently of its shape and culturability, as its presence in water may be risky for human health.

Helicobacter pylori is invasive and it may be a facultative intracellular organism

The pathogenicity of many bacteria colonizing the gastrointestinal tract often depends on their ability to gain access to cells that are normally non-phagocytic. Helicobacter pylori colonizes the stomach of over half the world population and is the main cause of peptic ulcer disease and gastric cancer. It is generally considered to be a non-invasive pathogen present only in the lumen of the stomach and attached to gastric epithelial cells although a number of in vivo and in vitro studies have demonstrated that H. pylori is in fact invasive. In addition, H. pylori can repopulate the extracellular environment after complete elimination of extracellular bacteria with gentamicin, suggesting it may be considered a facultative intracellular bacterium. This review examines the validity of these observations and describes the evidence suggesting that the intracellular presence of H. pylori plays a role in the induction of diseases, in immune evasion, and in life-long persistence of the bacterium in the stomach of a majority of humans.

Adhesion of water stressed Helicobacter pylori to abiotic surfaces

AIM

The main aim of this work was to study and compare the adhesion of water exposed Helicobacter pylori to six different substrata and correlate any changes in morphology, physiology, ability to form aggregates and cultivability when in the planktonic or in the sessile phase.

METHODS AND RESULTS

The number of total cells adhered for different water exposure times and modifications in the cell shape were evaluated using epifluorescence and scanning electron microscopy, and physiology assessed using Syto9 and propidium iodide (PI) cellular uptake. All abiotic surfaces were rapidly colonized by H. pylori, and colonization appeared to reach a steady state after 96 h with levels ranging from 2.3 x 10(6) to 3.6 x 10(6) total cells cm(-2). Cell morphology was largely dependent on the support material, with spiral bacteria, associated with the infectious form of H. pylori, subsisting in a higher percentage on nonpolymeric substrata. Also, sessile bacteria were generally able to retain the spiral shape for longer when compared with planktonic bacteria, which became coccoid more quickly. The formation of large aggregates, which may act as a protection mechanism against the negative impact of the stressful external environmental conditions, was mostly observed on the surface of copper coupons. However, Syto9 and PI staining indicates that most of H. pylori attached to copper or SS304 have a compromised cell membrane after only 48 h. Cultivability methods were only able to detect the bacteria up to the 2 h exposure-time and at very low levels (up to 500 CFU cm(-2)).

CONCLUSIONS

The fact that the pathogen is able to adhere, retain the spiral morphology for longer and form large aggregates when attached to different plumbing materials appeared to point to pipe materials in general, and copper plumbing in particular, as a possible reservoir of virulent H. pylori in water distribution systems. However, the Syto9/PI staining results and cultivability methods indicate that the attached H. pylori cells quickly enter in a nonviable physiological state.

SIGNIFICANCE AND IMPACT OF THE STUDY

This represents the first study of H. pylori behaviour in water-exposed abiotic surfaces. It suggests that co-aggregation with the autochthonous heterotrophic consortia present in water is necessary for a longer survival of the pathogen in biofilms associated to drinking water systems.

Coccoid form of Helicobacter pylori as a morphological manifestation of cell adaptation to the environment

After characterization of preferred conditions for Helicobacter pylori survival in the sessile state, it was observed that the bacterium transforms from spiral to coccoid under mild circumstances, whereas under extreme ones it is unable to undergo shape modification. This strongly supports the view that transformation into the coccoid form is an active, biologically led process, switched on by the bacterium as a protection mechanism.

Intracellular, intercellular, and stromal invasion of gastric mucosa, preneoplastic lesions, and cancer by Helicobacter pylori

BACKGROUND AND AIMS

It is not clear how Helicobacter pylori, an apparently extracellular pathogen colonizing the luminal side of the gastric epithelium, invariably causes an immune-inflammatory response on the stromal side of the mucosa. Penetration of H pylori into epithelial cell lines and its interaction with immune-inflammatory cells have been documented in vitro. Several investigations also showed in vivo bacterial penetration into the epithelium up to the lamina propria; however, the identification as H pylori of the bacteria-like bodies observed in unchanged, metaplastic, or neoplastic mucosa remained sometimes questionable.

METHODS

To search for bacteria-like organisms, we used transmission electron microscopy on endoscopic biopsy specimens from 20 dyspeptic subjects and surgical specimens of neoplastic and nonneoplastic mucosa from 20 cancerous stomachs. To ascertain the H pylori nature of the organisms found, we used 6 different antibodies directed against bacterial lysates, purified vacuolating cytotoxin A, or purified cytotoxin-associated antigen A in immunogold tests. The results were compared with those of H pylori strains cultivated in vitro.

RESULTS

In nonmetaplastic gastric epithelium, cytochemically proven H pylori were detected, in the majority of cases, inside cytoplasm of epithelial cells, in intraepithelial intercellular spaces, and in underlying lamina propria, often in direct contact with immune-inflammatory cells and sometimes inside small blood vessels. Cytochemically proven H pylori were also observed inside 6 of 8 intestinal metaplasias and 9 of 20 cancers.

CONCLUSIONS

H pylori penetrates normal, metaplastic, and neoplastic gastric epithelium in vivo, intracellularly, or interstitially to cause a strong immune-inflammatory response and promote gastric carcinogenesis.

Flagellar and global gene regulation in Helicobacter pylori modulated by changes in DNA supercoiling

In Helicobacter pylori, a host-adapted bacterium with a small genome and few dedicated transcriptional regulators, promoter structure, and gene organization suggested a role for DNA topology in the transcriptional regulation of flagellar genes. H. pylori DNA supercoiling, monitored by a reporter plasmid, was relaxed by novobiocin, an inhibitor of DNA gyrase. A decrease in negative supercoiling coincided with lowered transcription of the late flagellin gene flaA. Targeted mutagenesis that either increased or decreased promoter spacer length in the flaA sigma(28) promoter lowered flaA transcript levels, expression of FlaA protein, and flagella formation. It also changed the promoter response to decreased superhelicity. Supercoiling of reporter plasmid DNA in H. pylori varied with growth phase in liquid culture. H. pylori sigma(28) promoters of various spacer length, as well as other supercoiling-sensitive genes, were differentially transcribed during the growth phases, consistent with supercoiling being associated with growth phase regulation. Genome-wide transcript analysis of wild-type H. pylori under conditions of reduced supercoiling identified flagellar, housekeeping, and virulence genes, the expression of which correlated with supercoiling change and/or growth phase. These data indicate that global supercoiling changes may help coordinate temporal (growth phase-related) regulation of flagellar biosynthesis and other cellular functions in Helicobacter.

Characterization of Helicobacter pylori lytic transglycosylases Slt and MltD

Peptidoglycan (PG) is a cell wall heteropolymer that is essential for cell integrity. PG hydrolases participate in correct assembly of the PG layer and have been shown to be required for cell division, cell daughter separation, and maintenance of bacterial morphology. In silico analysis of the Helicobacter pylori genome resulted in identification of three potential hydrolases, Slt, MltD, and AmiA. This study was aimed at determining the roles of the putative lytic transglycosylases, Slt and MltD, in H. pylori morphology, growth, and PG metabolism. Strain 26695 single mutants were constructed using a nonpolar kanamycin cassette. The slt and mltD mutants formed normal bacillary and coccoid bacteria in the exponential and stationary phases, respectively. The slt and mltD mutants had growth rates comparable to the growth rate of the parental strain. However, the mltD mutant exhibited enhanced survival in the stationary phase compared to the wild type or the slt mutant. PG was purified from exponentially growing bacteria and from bacteria in the stationary phase, and its muropeptide composition was analyzed by high-pressure liquid chromatography. This analysis revealed changes in the muropeptide composition indicating that MltD and Slt have lytic transglycosylase activities. Glycan strand analysis suggested that Slt and MltD have exo and endo types of lytic transglycosylase activity, indicating that Slt is involved mainly in PG turnover and MltD is involved mainly in rearrangement of the PG layer. In this study, we determined the distinct roles of the lytic transglycosylases Slt and MltD in PG metabolism.

Cell elongation and cell death of helicobacter pylori is modulated by the disruption of cdrA (cell division-related gene A)

The cell division-related gene A (cdrA) of Helicobacter pylori is dispensable in vivo and unique in having a repressive role on cell division and long-term survival. To clarify its role, comparisons of the wildtype HPK5 and isogenic cdrA-disrupted mutant HPKT510 were examined by ultrastructural morphology, PBP profiles, and susceptibility to beta-lactam antibiotics during long-term cultivation. Ultrastructural analyses revealed that the shorter rods of HPKT510 had a slightly wider periplasmic space between the inner and the outer membrane than those of HPK5. Cell division of HPKT510 cells was complete even under high-salt conditions in which HPK5 cells became filamentous due to inhibition of division. The filamentous HPK5 cells constructed an inner membrane without a cell wall at the presumed division site. After 4 days of cultivation (the late stationary phase), most of the HPK5 cells turned into ghosts and aggregates, while some of the HPKT510 cells remained as curved rods, which coincided with the results of cell viability. HPKT510 cells became resistant to ampicillin killing compared to HPK5 cells, although their minimum inhibitory concentrations (MICs) and PBP profiles were not significantly different. These results suggest that the cdrA product represses cell division via inhibiting cell wall synthesis at division site. During infection in both mice and humans, inactivation of cdrA eventually gains biological aspects such as increased viability, long-term survival and tolerance to antibiotics and high-salt condition, which might enhance a persistent infection.

External membrane vesicles from Helicobacter pylori induce apoptosis in gastric epithelial cells

The Helicobacter pylori infection of gastric mucosa is one of the most common infectious diseases and is associated with a variety of clinical outcomes, including peptic ulcer disease and gastric cancer. Helicobacter pylori-induced damage to gastric mucosal cells is controlled by bacterial virulence factors, which include VacA and CagA. Outer membrane vesicles are constantly shed by the bacteria and can provide an additional mechanism for pathogenicity by releasing non-secretable factors which can then interact with epithelial cells. The present report shows that external membrane vesicles are able to induce apoptosis not mediated by mitochondrial pathway in gastric (AGS) epithelial cells, as demonstrated by the lack of cytochrome c release with an activation of caspase 8 and 3. Apoptosis induced by these vesicles does not require a classic VacA+ phenotype, as a negative strain with a truncated and therefore non-secretable form of this protein can also induce cell death. These results should be taken into account in future studies of H. pylori pathogenicity in strains apparently VacA-.

Gene-expression profiles in gastric epithelial cells stimulated with spiral and coccoid Helicobacter pylori

Human gastric epithelial immortalized GES-1 cells were infected with spiral and coccoid Helicobacter pylori. Scanning electron microscopy was used to determine the ability of the two forms of H. pylori to adhere to GES-1 cells. GES-1 cell apoptosis induced by coccoid and spiral H. pylori was analysed using flow cytometry. A cDNA microarray for 22,000 human genes was used to identify the gene-expression differences in GES-1 cells infected with the two forms of H. pylori, and the gene expression identified by the cDNA microarray was confirmed by RT-PCR. Scanning electron microscope observation showed that both coccoid and spiral bacteria can adhere to GES-1 cells. After 4 h infection, apoptosis induction was 27.4% for spiral-form infection and 10.2% for coccoid-form infection. Of 268 differentially expressed genes identified by cDNA microarray, 166 showed higher expression with the spiral H. pylori infection than with the coccoid H. pylori infection. To the best of the authors' knowledge, this is the first report that GES-1 cells infected with spiral H. pylori have higher expression of cxcl10, ccl11, ccl5, groalpha, TLR5, ATF3, fos, fosl2, gadd45a and myc. The cells infected with coccoid H. pylori had higher expression of survivin. The global profile of gene expression in GES-1 cells infected with coccoid and spiral H. pylori is described for the first time.

In vitro activity of a novel antimicrobial agent, TG44, for treatment of Helicobacter pylori infection

Due to concerns about the current therapeutic modalities for Helicobacter pylori infection, e.g., the increased emergence of drug-resistant strains and the adverse reactions of drugs currently administered, there is a need to develop an anti-H. pylori agent with higher efficacy and less toxicity. The antibacterial activity of TG44, an anti-H. pylori agent with a novel structural formula, against 54 clinical isolates of H. pylori was examined and compared with those of amoxicillin (AMX), clarithromycin (CLR), and metronidazole (MNZ). Consequently, TG44 inhibited the growth of H. pylori in an MIC range of 0.0625 to 1 microg/ml. The MIC ranges of AMX, CLR, and MNZ were 0.0078 to 8 microg/ml, 0.0156 to 64 microg/ml, and 2 to 128 microg/ml, respectively. The antibacterial activity of TG44 against AMX-, CLR-, and MNZ-resistant strains was nearly comparable to that against drug-susceptible ones. In a pH range of 3 to 7, TG44 at 3.13 to 12.5 microg/ml exhibited potent bactericidal activity against H. pylori in the stationary phase of growth as early as 1 h after treatment began, in contrast to AMX, which showed no bactericidal activity at concentrations of up to 50 microg/ml at the same time point of treatment. TG44 at 25 microg/ml exhibited no antibacterial activity against 13 strains of aerobic bacteria, suggesting that its antibacterial activity against H. pylori is potent and highly specific. The present study indicated that TG44 possesses antibacterial activity which manifests quickly and is potentially useful for eradicating not only the antibiotic-susceptible but also the antibiotic-resistant strains of H. pylori by monotherapy.

Characterization of flgK gene and FlgK protein required for H pylori Colonization-from cloning to clinical relevance

AIM: To characterize the role of flgK and its protein product in H pylori colonization.

METHODS: The PCR cloning method identified the flgK gene. An isogenic flgK mutant was constructed by gene replacement and confirmed by Southern blot analysis and PCR analysis. The recombinant FlgK protein (r-FlgK) was purified. Electron microscopy (EM) was applied to demonstrate the flagella of H pylori. An in vitro motility test was assessed in semisolid medium. The densities of H pylori colonization with either the wild-type strain or its flgK mutant were compared among BALB/c mice with or without pre-immunization with r-FlgK. The serological responses to r-FlgK were analyzed for 70 clinical patients with different densities of H pylori colonization.

RESULTS: From a duodenal ulcer strain, the flgK gene was cloned and it contained 1821 bp, with a 95.7% identity to the published sequences. No flagella were observed under EM for the mutant strain, which had a loss of motility. H pylori density was lower in the BALB/c mice inoculated by the mutant or with pre-immunization with r-FlgK compared to unimmunized mice or mice inoculated by the wild-type strain (P < 0.05). In the H pylori-infected patients, the serological responses to r-FlgK were uniformly low in titer.

CONCLUSION: FlgK encoded by flgK is important for flagella formation and H pylori motility. Deficiency in FlgK or an enhanced serological response to r-FlgK can interfere with H pylori colonization. FlgK of H pylori could be a novel target for vaccination.

Ultrastructure of Helicobacter pylori in human gastric mucosa and H. pylori-infected human gastric mucosa using transmission electron microscopy and the high-pressure freezing-freeze substitution technique

BACKGROUND

Conventional ultrastructural analyses of Helicobacter pylori and H. pylori-infected gastric mucosa by transmission electron microscopy (TEM) have limitations because of structural artifacts introduced during fixation.

METHODS

We used high-pressure freezing (HPF) followed by freeze substitution for TEM to investigate the ultrastructure of H. pylori and H. pylori-infected gastric mucosa. For HPF-freeze substitution, human gastric biopsy specimens were placed in the HPF instrument at a pressure of approximately 2,000 atm at the temperature of liquid nitrogen. Specimens were then transferred to an instrument for freeze substitution. Specimens were first placed in acetone containing 2% OsO4 at -85 degrees C. The temperature was increased to -3 degrees C, followed by embedding in Quetol 812. Ultrathin sections were double-stained by uranium acetate/lead nitrate. HPF and conventionally prepared samples were examined by TEM.

RESULTS

The H. pylori envelope was clearly seen to consist of an outer membrane, periplasmic space, and plasma membrane. The periplasmic space was filled with electron-dense materials. A peptidoglycan layer was only occasionally visible. A thick, very fine filamentous or reticular fringe corresponding to the bacterial glycocalyx was seen surrounding the H. pylori cells. At the adhesion loci of H. pylori to gastric epithelial cells, H. pylori was connected to the epithelial cells by very fine, thickly arranged filaments or more closely, with a contact zone. The epithelial cells showed indentations or pedestals.

CONCLUSIONS

The well-developed, thick bacterial glycocalyx of H. pylori appears to strongly interact with external cellular components and may play an important role in the adhesion of H. pylori to epithelial cells.

Rapid identification ofEscherichia coli andHelicobacter pylori in biological samples by capillary zone electrophoresis

The differences in surface charge of different bacteria can be exploited for their separation by capillary electrophoresis. However, this method of separation of microorganisms is beset with various drawbacks such as adhesion of bacteria to the fused silica surface or cluster formation. To overcome these phenomena we investigated the addition of poly(ethylene oxide) as a focusing agent to the running buffer and used calcium and myoinositol hexakisphosphate as specific ions that interact with the bacterial surface, changing its electrical properties and electrophoretic mobilities. In the present work, we applied CZE to identification of E. coli in infected urine (direct injection) from patients with urinary tract infections and to identification of Helicobacter pylori, which is a gram-negative bacillus responsible for one of the most common infections found in humans worldwide. Helicobacter pylori colonize the stomach and are responsible for severe diseases of the gastric tract, ranging from chronic gastric ulcer to gastric cancer.

Apoptosis and proliferation in gastric epithelium due to Helicobacter pylori: an immunohistochemical and ultrastructural study

The effect of H. pylori infection on gastric epithelial cell apoptosis and proliferation is contradictory. Using immunohistochemistry and electron microscopy, this study sought to demonstrate gastric epithelial changes (ie, apoptosis and proliferation) due to chronic H. pylori infection.

METHODS

Eighteen female 6- to 8-week old Swiss Albino mice were inoculated intragastrically with 3 doses of 10(9) CFU/mL H. pylori prepared in a Brucella Broth in 5 days. Nine others served as a control group. At the end of 28 weeks, tissue specimens from the gastric antrum were excised and examined immunohistochemically (epithelial growth factor for regeneration and Caspase-3 for apoptosis) and electron microscopically. Immunohistochemical assessment was performed using the indirect peroxidase-antiperoxidase method.

RESULTS

In the H. pylori-infected group, EGF staining in gastric epithelium was found to be decreased significantly compared to that in control group (P < 0.001). Caspase-3 reactivity was commonly observed in surface epithelial cells and glandular epithelial cells in H. pylori-infected group and totally it was statistically significant compared to Caspase-3 staining in control group (P < 0.001). Electron micrograph images demonstrated numerous apoptotic cells with condensed chromatin.

CONCLUSION

Chronic H. pylori infection of 28 weeks' duration increases apoptosis in gastric epithelium; however, increased apoptosis does not induce proliferation.

A novel mechanism of autolysis in Helicobacter pylori: possible involvement of peptidergic substances

BACKGROUND

Helicobacter pylori survival in a hostile acidic environment is known to be caused by its production of urease, which is not released by known secretion pathways. It has been proposed that H. pylori cells undergo spontaneous autolysis during cultivation and that urease becomes surface-associated only concomitant with bacterial autolysis. The aim of this study was to elucidate mechanisms by which H. pylori cells undergo autolysis during cultivation.

MATERIALS AND METHODS

Autolysis of H. pylori KZ109 cells was estimated by measuring the turbidity of the culture, by detection of cytoplasmic protein release into the culture supernatant and by scanning electron microscopic observation of H. pylori cells during cultivation. An autolysis-inducing factor (AIF) was partially purified from the culture supernatant by a partition method using ethyl acetate.

RESULTS

Bacterial turbidity of KZ109 cells was drastically decreased after late-log phase accompanying release of urease and HspB into the extracellular space. Concomitantly, cell lytic activity was detected in the culture supernatant. Scanning electron microscopic observation suggested that partially purified AIF induced cell lysis. It was also shown that the AIF is different from other autolytic enzymes or substances so far reported.

CONCLUSIONS

This study demonstrated the presence of the peptidergic autolytic substances in the culture supernatant of H. pylori KZ109 cells. The results of this study should be useful for further studies aimed at elucidation of the strategy of survival of H. pylori in the gastric environment and elucidation of the mechanisms of pathogenesis induced by H. pylori.

Intrabacterial proton-dependent CagA transport system in Helicobacter pylori

Helicobacter pylori CagA modifies the signalling of host cells and causes gastric diseases. Although CagA is injected into gastric epithelial cells through the type IV secretion machinery, it remains unclear how CagA is transported towards the machinery in the bacterial cytoplasm. In this study, it was determined that the proton-dependent intracytoplasmic transport system correlates with the priming of CagA secretion from H. pylori. The cytotoxicity of neutral-pH- and acidic-pH-treated H. pylori was examined in the AGS cell line. The amount of phosphorylated CagA in AGS cells incubated with acidic-pH- and neutral-pH-treated H. pylori was determined by enzyme immunoassay and Western blot. The production of CagA and adherence of the treated bacteria were examined by enzyme immunoassay and light microscopy, respectively. To clarify how CagA is transported towards the inner membrane of the treated bacteria, the localization of CagA was analysed by immunoelectron microscopy. The proportion of hummingbird cells in the AGS cell line rapidly increased following the inoculation of acidic-pH-treated H. pylori but increased more slowly with neutral-pH-treated H. pylori, and the phenomenon correlated with the amount of phosphorylated CagA in AGS cells. CagA was densely localized near the inner membrane in the acidic-pH-treated bacterial cytoplasm, but this localization was not observed in the neutral-pH-treated bacterial cytoplasm, suggesting that CagA shifts from the centre to the peripheral portion of the cytoplasm as a result of an extracellular decrease in pH. This phenomenon depended on the presence of UreI, a proton-dependent urea channel, but not on the presence of urea. The pH treatments did not enhance CagA production or the adherence of the bacterium to AGS cells. The authors propose that H. pylori possesses a proton-dependent intracytoplasmic transport system that probably accelerates priming for CagA injection.

Free-soluble and outer membrane vesicle-associated VacA from Helicobacter pylori: Two forms of release, a different activity

Helicobacter pylori releases VacA both as free-soluble and as outer membrane vesicle (OMV)-associated toxin. In this study, we investigated the amount of VacA released in each of the two forms and the role of each form in VacA-induced cell vacuolation in vitro. We found that: (1) free-soluble toxin accounted for about 75% of released VacA, while the remaining 25% was OMV-associated; (2) although OMV-associated VacA caused a statistically significant vacuolation, virtually all the vacuolating activity of a H. pylori broth culture filtrate was due to free-soluble VacA. While it is widely accepted that OMVs may represent an important vehicle for delivering virulence factors to the gastric mucosa, our results suggest that OMV-associated VacA could play a pathobiological role different from that of free-soluble toxin. This conclusion fits with mounting evidence that VacA exerts a large pattern of pathobiological effects among which cell vacuolation might not be the main one.

Adherence properties of Helicobacter pylori: impact on pathogenesis and adaptation to the host

The adherence of the human gastric pathogen Helicobacter pylori to the gastric mucosa is widely assumed to play a substantial role in initial colonization and long-term persistence in the human stomach. In the past, a couple of putative adhesins were identified, most of which were members of the large outer membrane protein (OMP) family of H. pylori. Among these, the BabA protein was shown to recognize the Leb antigen, which is presented as a dominant surface structure in the gastric mucosa. The SabA adhesin binds to sialylated antigens, which are up-regulated in inflamed gastric tissue. Other OMPs, such as AlpAB or HopZ were also shown to be involved in binding to gastric epithelial cells, but the corresponding receptors are unknown. The aim of this review is to summarize recent data giving new insights in binding specificities of H. pylori adhesins and their role in pathogenesis and adaptation to the host.

Bactericidal and morphological effects of NE-2001, a novel synthetic agent directed against Helicobacter pylori

The antibacterial activities of NE-2001 were tested against 24 clinical isolates of Helicobacter pylori and compared with those of amoxicillin, clarithromycin, metronidazole, and furazolidone. The MIC(50) and MIC(90) of this synthetic compound on the isolates were 8 and 16 mug/ml, respectively. This action was highly selective against Helicobacter pylori; there was a >4-fold difference between the concentration of NE-2001 required to inhibit the growth of Helicobacter pylori and that required to inhibit the growth of common aerobic and anaerobic bacteria. Exposure of Helicobacter pylori (ATCC43504) to NE-2001 at the MIC (4 mug/ml), or at a greater concentration, resulted in an extensive loss of viability. The phenomenon was also observed at pH levels between 3.0 and 7.0. When two clinical Helicobacter pylori strains were successively cultured at subinhibitory concentrations of NE-2001, no significant changes in the bactericidal effects were found. The morphological alterations of Helicobacter pylori cells (ATCC43504), exposed to NE-2001 at various concentrations for 6 h, were observed using transmission electron microcopy. The bacterium displayed features such as swelling, vacuole-like structures in the cytoplasm, and cell destruction following exposure to NE-2001. The efficacy of NE-2001 was maintained when evaluated in eight clinical isolates resistant to metronidazole and five isolates resistant to both metronidazole and clarithromycin (MIC ranging between 4 and 16 mug/ml). The above-described results suggest that NE-2001 may have the potential to be developed as a candidate agent for the treatment of Helicobacter pylori infection.

Helicobacter pylori flagellar hook-filament transition is controlled by a FliK functional homolog encoded by the gene HP0906

Helicobacter pylori is a human gastric pathogen which is dependent on motility for infection. The H. pylori genome encodes a near-complete complement of flagellar proteins compared to model enteric bacteria. One of the few flagellar genes not annotated in H. pylori is that encoding FliK, a hook length control protein whose absence leads to a polyhook phenotype in Salmonella enterica. We investigated the role of the H. pylori gene HP0906 in flagellar biogenesis because of linkage to other flagellar genes, because of its transcriptional regulation pattern, and because of the properties of an ortholog in Campylobacter jejuni (N. Kamal and C. W. Penn, unpublished data). A nonpolar mutation of HP0906 in strain CCUG 17874 was generated by insertion of a chloramphenicol resistance marker. Cells of the mutant were almost completely nonmotile but produced sheathed, undulating polyhook structures at the cell pole. Expression of HP0906 in a Salmonella fliK mutant restored motility, confirming that HP0906 is the H. pylori fliK gene. Mutation of HP0906 caused a dramatic reduction in H. pylori flagellin protein production and a significant increase in production of the hook protein FlgE. The HP0906 mutant showed increased transcription of the flgE and flaB genes relative to the wild type, down-regulation of flaA transcription, and no significant change in transcription of the flagellar intermediate class genes flgM, fliD, and flhA. We conclude that the H. pylori HP0906 gene product is the hook length control protein FliK and that its function is required for turning off the sigma(54) regulon during progression of the flagellar gene expression cascade.

Antibacterial activity of highly negative charged polyoxotungstates, K27[KAs4W40O140] and K18[KSb9W21O86], and Keggin-structural polyoxotungstates against Helicobacter pylori

The antibacterial activity of polyoxometalates (PMs) against Helicobacter pylori was investigated based on determinations of minimum inhibitory concentration (MIC) and fractional inhibitory concentration (FIC), time-killing of the bacteria, bacterial morphology and PM-uptake into the bacteria cell. The result of MIC values revealed that, of 13 PMs used in this study, highly negative-charged polyoxotungstates, such as K27[KAs4W40O140] and K18[KSb9W21O86], and Keggin-structural polyoxotungstates exhibited a potent antibacterial activity with the MIC values of less than 256 microg/ml. The former was the most active, and superior to metronidazole (MTZ) against MTZ-susceptible and resistant strains and also to clarithromycin (CLR) against CLR-resistant strains. In contrast, most of polyoxomolybdates showed little antibacterial activity with the MIC values of more than 256 microg/ml. The result of FIC index values indicated that the antibacterial polyoxotungstates had partially synergistic effect in combination with MTZ and CLR but indifferent effect in combination with amoxicillin (AMX). From the results of the time-killing and scanning electron microscope images, K27[KAs4W40O140] and K18[KSb9W21O86] proved the concentration-dependent bactericidal activity with the morphological change from bacillary form to coccoid form, while Keggin-structural K5[SiV(V)W11O40] showed the bacteriostatic activity with small change of morphology to coccoid form. The fluorescent X-ray analysis demonstrated that these polyoxotungstates were taken into the bacteria cell. It is pointed out that the Keggin-structure and/or high negativity polyoxotungstates are an important factor for the antibacterial activity against H. pylori.

Lewis epitopes on outer membrane vesicles of relevance to Helicobacter pylori pathogenesis

BACKGROUND

Helicobacter pylori extrudes protein- and lipopolysaccharide-enriched outer membrane vesicles from its cell surface which have been postulated to act to deliver virulence factors to the host. Lewis antigen expression by lipopolysaccharide of H. pylori cells has been implicated in a number of pathogenic roles. The aim of this study was to further characterize the expression of lipopolysaccharide on the surface of these outer membrane vesicles and, in particular, expression of Lewis antigens and their association with antibody production in the host.

MATERIALS AND METHODS

H. pylori strains were examined for outer membrane vesicle production using transmission electron microscopy and Lewis antigen expression probed using immunoelectron microscopy. Sera from patients were analyzed for cross-reacting anti-Lewis antibodies and, subsequently, absorbed using outer membrane vesicle preparations to remove the cross-reacting antibodies.

RESULTS

The formation of outer membrane vesicles by H. pylori was observed in both in vitro and in vivo samples. Furthermore, vesicles were produced following culture in either liquid or solid medium by all strains examined. Moreover, we observed the presence of Lewis epitopes on outer membrane vesicles using immunoelectron microscopy and immunoblotting. Circulating anti-Lewis antibodies were found in the sera of gastric cancer patients but not in the sera of H. pylori-negative control subjects. Absorption of patient sera with outer membrane vesicles decreased the levels of anti-Lewis autoantibodies.

CONCLUSIONS

Our results demonstrate the ability of H. pylori to generate outer membrane vesicles bearing serologically recognizable Lewis antigens on lipopolysaccharide molecules which may contribute to the chronic immune stimulation of the host. The ability of these vesicles to absorb anti-Lewis autoantibodies indicates that they may, in part, play a role in putative autoimmune aspects of H. pylori pathogenesis.

Lack of stage-specific proteins in coccoid Helicobacter pylori cells

Helicobacter pylori exists in two distinct forms, rod shaped or coccoid, in stomachs of infected patients. Based on in vitro proteome comparisons, there are no detectable coccoid-specific proteins, which argues against the specific adaptation of coccoid Helicobacter to distinct biological functions, such as enhanced persistence or transmission to other hosts.

Morphological changes and outer membrane protein patterns in Helicobacter pylori during conversion from bacillary to coccoid form

Conversion from bacillary to fully coccoid form via an intermediate U-and V-shaped form has been described in prolonged cultures of H. pylori. This morphological transformation may be the expression of transitory adaptation to a particular environment and may play an important role in antibiotic resistance and the difficulty to eradicate the pathogen. The aim of this study was to evaluate morphological and outer membrane protein changes in H. pylori during ageing-induced conversion to coccoid morphology. We used two H. pylori strains (the reference NCTC 11639 and a fresh clinical isolate) cultivated in microaerophilic environment at 37 degrees C, monitoring their morphological and biochemical evolutions for 11 days. Microscopic examination revealed the passage from spiral to U- and V-shaped form after 5-8 days of incubation, the conversion to coccoid form and the entry into viable but non-culturable state (VBNC) between days 9 and 11. Protein pattern difference appeared at 97.4 to 45 and 30 kDa molecular weight. Biochemical tests demonstrated not only a modification of outer membrane protein profiles, but also an intra-specific variability by comparison between the two analysed strains. Our findings suggest that structural and outer membrane changes associated with coccoid transformation represent a typical response in H. pylori and may constitute a survival strategy in adverse environmental conditions.

The multiple cellular activities of the VacA cytotoxin of Helicobacter pylori

Helicobacter pylori has elaborated a unique set of virulence factors that allow it to colonize the stomach wall. These factors include urease, helicoidal shape, flagella, adhesion and pro-inflammatory molecules. Here we discuss the molecular and cellular mechanisms of action of the vacuolating cytotoxin VacA. Its activities are discussed in terms of tissue alterations which promote the release of nutrients necessary to the growth and survival of the bacterium in its nutrient-poor ecological niche. This toxin also shows some pro-inflammatory and immunosuppressive activities which may be functional to the establishment of a chronic type of inflammation.

The action of bismuth against Helicobacter pylori mimics but is not caused by intracellular iron deprivation

Helicobacter pylori is highly susceptible to bismuth, a heavy metal with antimicrobial activity linked to its effect on bacterial iron uptake. Three strains of H. pylori were analyzed for indicators of iron limitation following exposure to the MIC of colloidal bismuth subcitrate (MIC(CBS)). Similar morphologic and outer membrane changes were observed following growth in iron-limiting medium and at the MIC(CBS) that inhibited the growth of all three strains. These changes, which were also observed for iron-limited bacteria, were alleviated by the addition of iron to the cultures. H. pylori ATP levels, reduced in iron-limiting medium, were below the limits of detection in two of the three strains following exposure to bismuth. The addition of iron partially restored bacterial ATP levels in these two strains, although not to normal concentrations. In contrast, exposure of the same strains to the MIC(CBS) failed to deplete intracellular levels of iron, which were significantly reduced by culturing in iron-limiting medium. Thus, the antimicrobial effect of bismuth and of iron limitation on H. pylori may be similar. However, the respective mechanisms of intracellular action would appear to be mediated by different pathways within the cell.