Oxygen tension regulates reactive oxygen generation and mutation of Helicobacter pylori

High salt condition alters LPS synthesis and induces the emergence of drug resistance mutations in Helicobacter pylori

The burgeoning emergence of drug-resistant Helicobacter pylori strains poses a significant challenge to the clinical success of eradication therapies and is primarily attributed to mutations within drug-targeting genes that lead to antibiotic resistance. This study investigated the effect of high salt conditions on the occurrence of drug-resistance mutations in H. pylori. We found that high salt condition significantly amplifies the frequency of drug resistance mutations in H. pylori. This can be chiefly attributed to our discovery indicating that high salt concentration results in elevated reactive oxygen species (ROS) levels, initiating DNA damage within H. pylori. Mechanistically, high salt condition suppresses lipopolysaccharide (LPS) synthesis gene expression, inducing alterations in the LPS structure and escalating outer membrane permeability. This disruption of LPS synthesis attenuates the expression and activity of SodB, facilitates increased ROS levels, and consequently increases the drug resistance mutation frequency. Impairing LPS synthesis engenders a reduction in intracellular iron levels, leading to diminished holo-Fur activity and increased apo-Fur activity, which represses the expression of SodB directly. Our findings suggest a correlation between high salt intake and the emergence of drug resistance in the human pathogen H. pylori, implying that dietary choices affect the risk of emergence of antimicrobial resistance.IMPORTANCEDrug resistance mutations mainly contribute to the emergence of clinical antibiotic-resistant Helicobacter pylori, a bacterium linked to stomach ulcers and cancer. In this study, we explored how elevated salt conditions influence the emergence of drug resistance in H. pylori. We demonstrate that H. pylori exhibits an increased antibiotic resistance mutation frequency when exposed to a high salt environment. We observed an increase in reactive oxygen species (ROS) under high salt conditions, which can cause DNA damage and potentially lead to mutations. Moreover, our results showed that high salt condition alters the bacterium's lipopolysaccharide (LPS) synthesis, leading to a reduced expression of SodB in a Fur-dependent manner. This reduction, in turn, elevates ROS levels, culminating in a higher frequency of drug-resistance mutations. Our research underscores the critical need to consider environmental influences, such as diet and lifestyle, in managing bacterial infections and combating the growing challenge of antibiotic resistance.

Hypoxia exacerbates the malignant transformation of gastric epithelial cells induced by long-term H. pylori infection

Helicobacter pylori is a microaerophilic Gram-negative bacterium that resides in the human stomach and is classified as a class I carcinogen for gastric cancer. Numerous studies have demonstrated that H. pylori infection plays a role in regulating the function of host cells, thereby contributing to the malignant transformation of these cells. However, H. pylori infection is a chronic process, and short-term cellular experiments may not provide a comprehensive understanding of the in vivo situation, especially when considering the lower oxygen levels in the human stomach. In this study, we aimed to investigate the mechanisms underlying gastric cell dysfunction after prolonged exposure to H. pylori under hypoxic conditions. We conducted a co-culture experiment using the gastric cell line GES-1 and H. pylori for 30 generations under intermittent hypoxic conditions. By closely monitoring cell proliferation, migration, invasion, autophagy, and apoptosis, we revealed that sustained H. pylori stimulation under hypoxic conditions significantly influences the function of GES-1 cells. This stimulation induces epithelial-mesenchymal transition and contributes to the propensity for malignant transformation of gastric cells. To confirm the in vitro results, we conducted an experiment involving Mongolian gerbils infected with H. pylori for 85 weeks. All the results strongly suggest that the Nod1 receptor signaling pathway plays a crucial role in H. pylori-related apoptosis and autophagy. In summary, continuous stimulation by H. pylori affects the functioning of gastric cells through the Nod1 receptor signaling pathway, increasing the likelihood of cell carcinogenesis. The presence of hypoxic conditions further exacerbates this process.IMPORTANCEDeciphering the collaborative effects of Helicobacter pylori infection on gastric epithelial cell function is key to unraveling the development mechanisms of gastric cancer. Prior research has solely examined the outcomes of short-term H. pylori stimulation on gastric epithelial cells under aerobic conditions, neglecting the bacterium's nature as a microaerophilic organism that leads to cancer following prolonged stomach colonization. This study mimics a more genuine in vivo infection scenario by repeatedly exposing gastric epithelial cells to H. pylori under hypoxic conditions for up to 30 generations. The results show that chronic exposure to H. pylori in hypoxia substantially increases cell migration, invasion, and epithelial-mesenchymal transition, while suppressing autophagy and apoptosis. This highlights the significance of hypoxic conditions in intensifying the carcinogenic impact of H. pylori infection. By accurately replicating the in vivo gastric environment, this study enhances our comprehension of H. pylori's pathogenic mechanisms in gastric cancer.

Sodium sulfite-driven Helicobacter pylori eradication: Unraveling oxygen dynamics through multi-omics investigation

Due to the emergence and spread of multidrug resistance in Helicobacter pylori (H. pylori), its eradication has become difficult. Sodium sulfite (SS), a widely used food additive for ensuring food safety and storage, has been recognized as an effective nonbactericidal agent for H. pylori eradication. However, the mechanism by which H. pylori adapts and eventually succumbs under low- or no-oxygen conditions remains unknown. In this study, we aimed to evaluate the anti-H. pylori effect of SS and investigated the multiomics mechanism by which SS kills H. pylori. The results demonstrated that SS effectively eradicated H. pylori both in vitro and in vivo. H. pylori responds to the oxygen changes regulated by SS, downregulates the HcpE gene, which is responsible for redox homeostasis in bacteria, decreases the activities of enzymes related to oxidative stress, and disrupts the outer membrane structure, increasing susceptibility to oxidative stress. Furthermore, SS downregulates the content of cytochrome C in the microaerobic respiratory chain, leading to a sharp decrease in ATP synthesis. Consequently, the accumulation of triglycerides (TGs) in bacteria due to oxidative stress supports anaerobic respiration, meeting their energy requirements. The multifaceted death of H. pylori caused by SS does not result in drug resistance. Thus, screening of the redox homeostasis of HcpE as a new target for H. pylori infection treatment could lead to the development of a novel approach for H. pylori eradication therapy.

The Puzzle of Coccoid Forms of Helicobacter pylori: Beyond Basic Science

Helicobacter pylori (H. pylori) may enter a non-replicative, non-culturable, low metabolically active state, the so-called coccoid form, to survive in extreme environmental conditions. Since coccoid forms are not susceptible to antibiotics, they could represent a cause of therapy failure even in the absence of antibiotic resistance, i.e., relapse within one year. Furthermore, coccoid forms may colonize and infect the gastric mucosa in animal models and induce specific antibodies in animals and humans. Their detection is hard, since they are not culturable. Techniques, such as electron microscopy, polymerase chain reaction, loop-mediated isothermal amplification, flow cytometry and metagenomics, are promising even if current evidence is limited. Among the options for the treatment, some strategies have been suggested, such as a very high proton pump inhibitor dose, high-dose dual therapy, N-acetycysteine, linolenic acid and vonoprazan. These clinical, diagnostic and therapeutic uncertainties will represent fascinating challenges in the future.

Transformation of Helicobacter pylori into Coccoid Forms as a Challenge for Research Determining Activity of Antimicrobial Substances

Morphological variability is one of the phenotypic features related to adaptation of microorganisms to stressful environmental conditions and increased tolerance to antimicrobial substances. Helicobacter pylori, a gastric mucosal pathogen, is characterized by a high heterogeneity and an ability to transform from a spiral to a coccoid form. The presence of the coccoid form is associated with the capacity to avoid immune system detection and to promote therapeutic failures. For this reason, it seems that the investigation for new, alternative methods combating H. pylori should include research of coccoid forms of this pathogen. The current review aimed at collecting information about the activity of antibacterial substances against H. pylori in the context of the morphological variability of this bacterium. The collected data was discussed in terms of the type of substances used, applied research techniques, and interpretation of results. The review was extended by a polemic on the limitations in determining the viability of coccoid H. pylori forms. Finally, recommendations which can help in future research aiming to find new compounds with a potential to eradicate H. pylori have been formulated.

The histone-like protein HU has a role in gene expression during the acid adaptation response in Helicobacter pylori

BACKGROUND

Gastritis, ulcers, and gastric malignancy have been linked to human gastric epithelial colonization by Helicobacter pylori. Characterization of the mechanisms by which H. pylori adapts to the human stomach environment is of crucial importance to understand H. pylori pathogenesis.

MATERIAL AND METHODS

In an effort to extend our knowledge of these mechanisms, we used proteomic analysis and qRT-PCR to characterize the role of the histone-like protein HU in the response of H. pylori to low pH.

RESULTS

Proteomic analysis revealed that genes involved in chemotaxis, oxidative stress, or metabolism are under control of the HU protein. Also, expression of the virulence factors Ggt and NapA is affected by the null mutation of hup gene both at neutral and acid pH, as evidenced by qRT-PCR analysis.

CONCLUSIONS

Those results showed that H. pylori gene expression is altered by shift to low pH, thus confirming that acid exposure leads to profound changes in genomic expression, and suggest that the HU protein is a regulator that may help the bacterium adapt to the acid stress. In accordance with previous reports, we found that the HU protein participates in gene expression regulation when the microorganism is exposed to acid stress. Such transcriptional regulation underlies protein accumulation in the H. pylori cell.

Helicobacter pylori and gut microbiota in multiple sclerosis versus Alzheimer's disease: 10 pitfalls of microbiome studies

Alteration of microbiota has been associated with intestinal, inflammatory, and neurological diseases. Abundance of "good bacteria" such as Bifidobacterium, or their products have been generally believed to be beneficial for any diseases, while "bad bacteria" such as pathogenic Helicobacter pylori are assumed to be always detrimental for hosts. However, this is not the case when we compare and contrast the association of the gut microbiota with two neurological diseases, multiple sclerosis (MS) and Alzheimer's disease (AD). Following H. pylori infection, pro-inflammatory T helper (Th)1 and Th17 immune response are initially induced to eradicate bacteria. However, H. pylori evades the host immune response by inducing Th2 cells and regulatory T cells (Tregs) that produce anti-inflammatory interleukin (IL)-10. Suppression of anti-bacterial Th1/Th17 cells by Tregs may enhance gastric H. pylori propagation, followed by a cascade reaction involving vitamin B₁₂ and folic acid malabsorption, plasma homocysteine elevation, and reactive oxygen species induction. This can damage the blood-brain barrier (BBB), leading to accumulation of amyloid-β in the brain, a hallmark of AD. On the other hand, this suppression of pro-inflammatory Th1/Th17 responses to H. pylori has protective effects on the hosts, since it prevents uncontrolled gastritis as well as suppresses the induction of encephalitogenic Th1/Th17 cells, which can mediate neuroinflammation in MS. The above scenario may explain why chronic H. pylori infection is positively associated with AD, while it is negatively associated with MS. Lastly, we list "10 pitfalls of microbiota studies", which will be useful for evaluating and designing clinical and experimental microbiota studies.

Development of genipin-crosslinked fucoidan/chitosan-N-arginine nanogels for preventing Helicobacter infection

AIM

This study aims to validate the anti-Helicobacter pylori efficacy of amoxicillin-loaded nanoparticles and nanogels with pH-responsive and site-specific drug release properties against H. pylori infection.

MATERIALS & METHODS

Genipin-crosslinked low molecular weight fucoidan/chitosan-N-arginine nanogels (FCSA) were prepared for targeted delivery of amoxicillin to the site of H. pylori infected AGS gastric epithelial cells.

RESULTS

The negatively charged nanogels (n-FCSA) adhered to H. pylori and exhibited pH-responsive drug release property to reduce cytotoxic effects in H. pylori infected AGS cells.

CONCLUSION

These in vitro findings suggest that n-FCSA nanogels are potential carriers for H. pylori specific delivery of antibacterial agents, and provide the basis for further studies on the clinical use of the nanogels.

The Impact of Oxygen on Bacterial Enteric Pathogens

Bacterial enteric pathogens are responsible for a tremendous amount of foodborne illnesses every year through the consumption of contaminated food products. During their transit from contaminated food sources to the host gastrointestinal tract, these pathogens are exposed and must adapt to fluctuating oxygen levels to successfully colonize the host and cause diseases. However, the majority of enteric infection research has been conducted under aerobic conditions. To raise awareness of the importance in understanding the impact of oxygen, or lack of oxygen, on enteric pathogenesis, we describe in this review the metabolic and physiological responses of nine bacterial enteric pathogens exposed to environments with different oxygen levels. We further discuss the effects of oxygen levels on virulence regulation to establish potential connections between metabolic adaptations and bacterial pathogenesis. While not providing an exhaustive list of all bacterial pathogens, we highlight key differences and similarities among nine facultative anaerobic and microaerobic pathogens in this review to argue for a more in-depth understanding of the diverse impact oxygen levels have on enteric pathogenesis.

Comparative Roles of the Two Helicobacter pylori Thioredoxins in Preventing Macromolecule Damage

Thioredoxins are highly conserved throughout a wide range of organisms, and they are essential for the isurvival of oxygen-sensitive cells. The gastric pathogen Helicobacter pylori uses the thioredoxin system to maintain its thiol/disulfide balance. There are two thioredoxins present in H. pylori, Trx1 and Trx2 (herein referred to as TrxA and TrxC). TrxA has been shown to be important as an electron donor for some antioxidant enzymes, but the function of TrxC remains unknown (L. M. Baker, A. Raudonikiene, P. S. Hoffman, and L. B. Poole, J Bacteriol 183:1961-1973, 2001; P. Alamuri and R. J. Maier, J Bacteriol 188:5839-5850, 2006). We demonstrate that both TrxA and TrxC are important in protecting H. pylori from oxidative stress. Individual ΔtrxA and ΔtrxC deletion mutant strains each show a greater abundance of lipid peroxides and suffer more DNA damage and more protein carbonylation than the parent. Both deletion mutants were much more sensitive to O2-mediated viability loss than the parent. Unexpectedly, the oxidative DNA damage and protein carbonylation was more severe in the ΔtrxC mutant than in the ΔtrxA mutant; it had 20-fold- and 4-fold-more carbonylated protein content than the wild type and the ΔtrxA strain, respectively, after 4 h of atmospheric O2 stress. trx transcript abundance was altered by the deletion of the heterologous trx gene. The ΔtrxC mutant lacked mouse colonization ability, while the ability to colonize mouse stomachs was significantly reduced in the ΔtrxA mutant.

A novel DNA-binding protein plays an important role in Helicobacter pylori stress tolerance and survival in the host

The gastric pathogen Helicobacter pylori must combat chronic acid and oxidative stress. It does so via many mechanisms, including macromolecule repair and gene regulation. Mitomycin C-sensitive clones from a transposon mutagenesis library were screened. One sensitive strain contained the insertion element at the locus of hp119, a hypothetical gene. No homologous gene exists in any (non-H. pylori) organism. Nevertheless, the predicted protein has some features characteristic of histone-like proteins, and we showed that purified HP119 protein is a DNA-binding protein. A Δhp119 strain was markedly more sensitive (viability loss) to acid or to air exposure, and these phenotypes were restored to wild-type (WT) attributes upon complementation of the mutant with the wild-type version of hp119 at a separate chromosomal locus. The mutant strain was approximately 10-fold more sensitive to macrophage-mediated killing than the parent or the complemented strain. Of 12 mice inoculated with the wild type, all contained H. pylori, whereas 5 of 12 mice contained the mutant strain; the mean colonization numbers were 158-fold less for the mutant strain. A proteomic (two-dimensional PAGE with mass spectrometric analysis) comparison between the Δhp119 mutant and the WT strain under oxidative stress conditions revealed a number of important antioxidant protein differences; SodB, Tpx, TrxR, and NapA, as well as the peptidoglycan deacetylase PgdA, were significantly less expressed in the Δhp119 mutant than in the WT strain. This study identified HP119 as a putative histone-like DNA-binding protein and showed that it plays an important role in Helicobacter pylori stress tolerance and survival in the host.

Biofilms and Helicobacter pylori: Dissemination and persistence within the environment and host

The presence of viable Helicobacter pylori (H. pylori) in the environment is considered to contribute to the levels of H. pylori found in the human population, which also aids to increase its genetic variability and its environmental adaptability and persistence. H. pylori form biofilms both within the in vitro and in vivo environment. This represents an important attribute that assists the survival of this bacterium within environments that are both hostile and adverse to proliferation. It is the aim of this paper to review the ability of H. pylori to form biofilms in vivo and in vitro and to address the inherent mechanisms considered to significantly enhance its persistence within the host and in external environments. Furthermore, the dissemination of H. pylori in the external environment and within the human body and its impact upon infection control will be discussed.

Environmental determinants of transformation efficiency in Helicobacter pylori

Helicobacter pylori uses natural competence and homologous recombination to adapt to the dynamic environment of the stomach mucosa and maintain chronic colonization. Although H. pylori competence is constitutive, its rate of transformation is variable, and little is known about factors that influence it. To examine this, we first determined the transformation efficiency of H. pylori strains under low O2 (5% O2, 7.6% CO2, 7.6% H2) and high O2 (15% O2, 2.9% CO2, 2.9% H2) conditions using DNA containing an antibiotic resistance marker. H. pylori transformation efficiency was 6- to 32-fold greater under high O2 tension, which was robust across different H. pylori strains, genetic loci, and bacterial growth phases. Since changing the O2 concentration for these initial experiments also changed the concentrations of CO2 and H2, transformations were repeated under conditions where O2, CO2, and H2 were each varied individually. The results showed that the increase in transformation efficiency under high O2 was largely due to a decrease in CO2. An increase in pH similar to that caused by low CO2 was also sufficient to increase transformation efficiency. These results have implications for the physiology of H. pylori in the gastric environment, and they provide optimized conditions for the laboratory construction of H. pylori mutants using natural transformation.

A histone-like protein of Helicobacter pylori protects DNA from stress damage and aids host colonization

Genomic DNA in a bacterial cell is folded into a compact structure called a nucleoid, and nucleoid-associated proteins are responsible for proper assembly of active higher-order genome structures. The human gastric pathogen Helicobacter pylori express a nucleoid-associated protein encoded by the hup gene, which is the homolog to the Escherichia coli histone-like protein HU. An H. pylori hup mutant strain (X47 hup:cat) showed a defect in stationary phase survival. The X47 hup:cat mutant was more sensitive to the DNA damaging agent mitomycin C, and displayed a decreased frequency of DNA recombination, indicating Hup plays a significant role in facilitating DNA recombinational repair. The X47 hup:cat mutant was also sensitive to both oxidative and acid stress, conditions that H. pylori commonly encounters in the host. The hup mutant cells survived significantly (7-fold) less upon exposure to macrophages than the wild type strain. In a mouse infection model, the hup mutant strain displayed a greatly reduced ability to colonize host stomachs. The geometric means of colonization number for the wild type and hup mutant were 6×10(5) and 1.5×10(4)CFU/g stomachs, respectively. Complementation of the hup strain by chromosomal insertion of a functional hup gene restored oxidative stress resistance, DNA transformation frequency, and mouse colonization ability to the wild type level. We directly demonstrated that the purified His-tagged H. pylori Hup protein can protect (in vitro) an H. pylori-derived DNA fragment from oxidative damage.

Mucoid Helicobacter pylori isolates with fast growth under microaerobic and aerobic conditions

BACKGROUND

Helicobacter pylori is microaerobic and turns into coccoid under aerobic conditions. In this study, two mucoid strains, A and D, were isolated from gastric biopsies which grew well on blood agar after 24-hour incubation under aerobic as well as microaerobic conditions. The aim of this study was to identify these strains and compare their growth under aerobic and microaerobic conditions with that of control H. pylori.

MATERIALS AND METHODS

The two isolates A and D were identified as H. pylori according to microscopic morphology, urease, catalase and oxidase tests. Their growth under humidified aerobic and microaerobic conditions was compared with that of control H. pylori which grew only under microaerobic conditions. They were further identified by amplification of 16S rRNA, vacA alleles, cagA and ureAB genes by PCR. Their susceptibility to current antimicrobials was also examined.

RESULTS

The strains A and D produced mucoid colonies under aerobic and microaerobic conditions after 24-hour, exhibiting the typical spiral morphology of H. pylori. The results of urease, catalase and oxidase tests were positive. Sequencing of amplified products showed 99-100% homology with those of the reference H. pylori strains in GenBank. Both strains exhibited resistance to the high concentrations of antimicrobials.

CONCLUSIONS

This study reports the isolation of two mucoid strains of H. pylori with confluent growth under aerobic and microaerobic conditions. It appears that production of exopolysaccharide (EXP) could serve as a physical barrier to reduce oxygen diffusion into the bacterial cell and uptake of antibiotics. EXP protected the mucoid H. pylori isolates against stressful conditions, the result of which could be persistence of bacterial infection in the stomach.

Effect of oxidative stress during repeated ovulation on the structure and functions of the ovary, oocytes, and their mitochondria

We previously reported that superoxide generated in the ovary induces apoptosis of granulosa cells to break down follicular walls, thereby supporting ovulation in rodents, and suggested that oxidative stress underlies the mechanism of ovarian aging. To test this hypothesis, we successfully induced ovulation repeatedly in mice by sequentially administrating pregnant mare serum gonadotropin, human chorionic gonadotropin, and prostaglandin F2alpha. Kinetic analysis revealed that the number of ovulated oocytes decreased significantly with repeated cycles of ovulation with a concomitant decrease in the gene expression of mitochondrial transcription factor A and nuclear respiratory factor 1 and an increase in oocytes having abnormally distributed mitochondria. Repeated ovulation decreased the amounts of mitochondrial DNA and increased 8-hydroxydeoxyguanosine in oocytes. Cell culture analysis of the in vivo fertilized oocytes revealed that their maturation from two cells to blastocyst was inhibited significantly by repeated ovulation. All these events induced by repeated ovulation were suppressed by oral administration of L-carnitine. These results suggest that oxidative stress associated with ovulation underlies the mechanism of ovarian aging and that L-carnitine may have therapeutic potential in patients with infertility and increased incidence of aneuploidy and to suppress impaired maturation of zygotes frequently observed in childbearing at an advanced age.

Upregulation of a non-heme iron-containing ferritin with dual ferroxidase and DNA-binding activities in Helicobacter pylori under acid stress

Helicobacter pylori is a spiral Gram-negative microaerophilic bacterium. It is unique and distinctive among various bacterial pathogens for its ability to persist in the extreme acidic environment of human stomachs. To address and identify changes in the proteome of H. pylori in response to low pH, we have used a proteomic approach to study the protein expression of H. pylori under neutral (pH 7) and acidic (pH 5) conditions. Global protein-expression profiles of H. pylori under acid stress were analysed by two-dimensional polyacrylamide gel electrophoresis (2-DE) followed by liquid chromatography (LC)-nanoESI-mass spectrometry (MS)/MS and bioinformatics database analysis. Among the proteins differentially expressed under acidic condition, a non-heme iron-containing ferritin of H. pylori (HP-ferritin) was found to be consistently upregulated at pH 5 as compared to pH 7. It was also found that HP-ferritin can switch from an iron-storage protein with ferroxidase activity to a DNA-binding/protection function under in vitro conditions upon exposure to acidic environment. Prokaryotic ferritins, such as non-heme iron-binding HP-ferritin with dual functionality reported herein, may play a significant urease-independent role in the acid adaptation of H. pylori under physiological conditions in vivo.

Oxidative stress defense mechanisms to counter iron-promoted DNA damage inHelicobacter pylori

Iron, a key element in Fenton chemistry, causes oxygen-related toxicity to cells of most living organisms. Helicobacter pylori is a microaerophilic bacterium that infects human gastric mucosa and causes a series of gastric diseases. Exposure of H. pylori cells to air for 2 h elevated the level of free iron by about 4-fold as measured by electron paramagnetic resonance spectroscopy. H. pylori cells accumulated more free iron as they approached stationary phase growth, and they concomitantly suffered more DNA damage as indicated by DNA fragmentation analysis. Relationships between the intracellular free iron level, specific oxidative stress enzymes, and DNA damage were identified, and new roles for three oxidative stress-combating enzymes in H. pylori are proposed. Mutant cells defective in either catalase (KatA), in superoxide dismutase (SodB) or in alkyl hydroperoxide reductase (AhpC) were more sensitive to oxidative stress conditions; and they accumulated more free (toxic) iron; and they suffered more DNA fragmentation compared to wild type cells. A significant proportion of cells of sodB, ahpC, or katA mutant strains developed into the stress-induced coccoid form or lysed; they also contained significantly higher amounts of 8-oxo-guanine associated with their DNA, compared to wild type cells.

Oxidative stress-induced peptidoglycan deacetylase in Helicobacter pylori

Structural modification of peptidoglycan (PG) is one of the mechanisms that pathogenic bacteria use to evade the host innate immune system. For the noninvasive human gastric pathogen Helicobacter pylori, PG delivery to the host cells is one trigger of the immune response. H. pylori HP310 was markedly up-expressed upon cell exposure to oxidative stress. However, disruption of HP310 did not produce a phenotype distinguishable from the parent, including oxidative stress resistance characteristics. HP310 shows very weak homology to a known gene pgdA encoding PG deacetylase in Streptococcous pneumoniae. PGs from wild type H. pylori and the HP310 mutant were purified and analyzed by matrix-assisted laser desorption ionization time-of-flight and high pressure liquid chromatography. The parent strain PG is partially deacetylated, whereas several major PG-deacetylated muropeptides are absent or significantly reduced in the HP310 mutant. PG deacetylase activity was directly demonstrated by use of pure PG and HP310 protein by measuring the release of acetic acid. The Gram-negative bacterium H. pylori is highly resistant to lysozyme (up to 50 mg/ml), but the HP310 mutant is less resistant to lysozyme compared with the parent strain. Complementation of an hp310 strain with the wild type gene restored lysozyme resistance. The purified PG from the mutant is more susceptible to lysozyme (0.3 mg/ml) digestion than the wild type PG. The PG deacetylation appears to confer lysozyme resistance to escape immune detection. HP310 is representative of a new subfamily of bacterial PG deacetylases.

Repeat-based subtyping and grouping of Staphylococcus aureus from human infections and bovine mastitis using the R-domain of the clumping factor A gene

Staphylococcus aureus has become an emerging public health concern. Markers capable of differentiating separate host-specific lineages are needed for tracing strain sources. Thus, a coding variable number tandem repeat-based typing was explored in this study, based on R-domain of clumping factor A (clfA) gene. DNA from isolates and strains of human infections and bovine mastitis were amplified and sequenced. Sequences of clfA from published strains were also analyzed. Results indicate that except one with 36 copies, 44 of the 55 R-domains had repeat copies between 44 and 57, whereas the remaining 10 had 59.5 to 73 copies. Furthermore, human isolates were polymorphic, while mastitis isolates were clonal. Phylogenetic grouping assigned host-specific strains into respective clusters. The repeats were stable during passages in milk, nutrient broth, and invasion of mammary cells showing suitability for typing. Our data show that the R-domain can be useful for typing and grouping host-specific lineages. Moreover, existence of variant repeats in human strains and the dominance of a clonal motif in mastitis may imply that a specific selection has occurred in the mammary gland.

Helicobacter pylori produces unique filaments upon host contact in vitro

Helicobacter pylori exists in 2 distinct morphological states, helicoid and coccoid. Both have been observed in in vitro culture and in gastric biopsies. We visualized H. pylori during AGS cell infections using immunofluorescence microscopy. Anti-H. pylori mouse serum as well as human serum from H. pylori-positive patients recognized long, thin bacterial filaments, which formed on helicoids and more frequently on coccoids. These filaments reached lengths of 59 microm and often connected bacteria. Periodate oxidation abolished antibody recognition, suggesting that carbohydrates compose a major antigenic component of the filaments. Similar to results obtained using immunofluorescence microscopy, scanning electron microscopy imaging revealed thin filamentous structures, which were absent on uninfected cells. Both coccoid conversion and filament development increased over the time course of infection with peak filament formation at 4 h. The number of visible filaments then decreased as bacteria clustered on the apical surface of AGS cells. Since the observed filaments were clearly distinct from previously described surface structures, including flagella and the cag type IV secretion system, our results demonstrate that these filaments represent a unique, previously unrecognized, organelle.

Oxygen induces mutation in a strict anaerobe, Prevotella melaninogenica

Strict anaerobes are highly sensitive to oxygen, but the mutagenicity of oxygen in strict anaerobes has not been well understood. Prevotella melaninogenica, a strict anaerobe, is susceptible to oxygen and shows an increase in oxidative DNA damage upon exposure to oxygen. In this study, we have investigated the mutagenicity of oxygen and the types of mutations induced by oxygen. Exposure to oxygen decreased cell survival and increased the levels of 8-oxo-deoxyguanosine (8-oxodG). The frequency of rifampicin-resistant mutants was markedly increased after exposure to oxygen. After sequencing a 254-bp fragment of the rpoB gene, which encodes the beta subunit of bacterial RNA polymerase, a target molecule of rifampicin, we found that most mutants induced by oxygen had GC to TA transversions, a signature of 8-oxodG. In addition, all detected single-nucleotide changes would lead to amino acid changes that confer rifampicin resistance. These results indicate that oxygen is mutagenic in a strict anaerobe, P. melaninogenica, and its mutagenic characteristics could be analyzed with this experimental system.

Urease activity and urea gene sequencing of coccoid forms of H. pylori induced by different factors

Helicobacter pylori exists in two morphologic forms: spiral shaped and coccoid. The nonculturable coccoid forms were believed to be the morphologic manifestations of cell death for a long time. However, recent studies indicate the viability of such forms. This form of H. pylori is now suspected to play a role in the transmission of the bacteria and is partly responsible for relapse of infection after antimicrobial treatment. Urease activity of H. pylori is an important maintenance factor. Determination of urease activity and possible mutations in the DNA sequences of coccoid bacteria will hence contribute to the understanding of pathogenesis of infections, which these forms might be responsible for. In this study, our aim was to analyze the urease activity and investigate the urease gene sequences of coccoid H. pylori forms induced by different factors with respect to the spiral form. For this purpose, the urease activities of H. pylori NCTC 11637 standard strain and two clinical isolates were examined before and after transformation of the cells to coccoid forms by different methods such as exposure to amoxicillin, aerobiosis, cold starvation, and aging. The effects of these conditions on the urease gene were examined by the amplification of 411-bp ureA gene and 115-bp ureB gene regions by PCR technique and sequencing of the ureA gene. The urease activities of coccoid cells were found to be lower than those of the spiral form. ureA and ureB gene regions were amplified in all coccoid cells by PCR. Inducing the change to coccoid form by different methods was found to have no effect on the nucleotide sequence of the ureA gene. These results show that the urease gene region of coccoid H. pylori is highly protected under various mild environmental conditions.

The diverse antioxidant systems of Helicobacter pylori

The gastric pathogen Helicobacter pylori induces a strong inflammatory host response, yet the bacterium maintains long-term persistence in the host. H. pylori combats oxidative stress via a battery of diverse activities, some of which are unique or newly described. In addition to using the well-studied bacterial oxidative stress resistance enzymes superoxide dismutase and catalase, H. pylori depends on a family of peroxiredoxins (alkylhydroperoxide reductase, bacterioferritin co-migratory protein and a thiol-peroxidase) that function to detoxify organic peroxides. Newly described antioxidant proteins include a soluble NADPH quinone reductase (MdaB) and an iron sequestering protein (NapA) that has dual roles - host inflammation stimulation and minimizing reactive oxygen species production within H. pylori. An H. pylori arginase attenuates host inflammation, a thioredoxin required as a reductant for many oxidative stress enzymes is also a chaperon, and some novel properties of KatA and AhpC were discovered. To repair oxidative DNA damage, H. pylori uses an endonuclease (Nth), DNA recombination pathways and a newly described type of bacterial MutS2 that specifically recognizes 8-oxoguanine. A methionine sulphoxide reductase (Msr) plays a role in reducing the overall oxidized protein content of the cell, although it specifically targets oxidized Met residues. H. pylori possess few stress regulator proteins, but the key roles of a ferric uptake regulator (Fur) and a post-transcriptional regulator CsrA in antioxidant protein expression are described. The roles of all of these antioxidant systems have been addressed by a targeted mutant analysis approach and almost all are shown to be important in host colonization. The described antioxidant systems in H. pylori are expected to be relevant to many bacterial-associated diseases, as genes for most of the enzymes carrying out the newly described roles are present in a number of pathogenic bacteria.

Lipid peroxidation as a source of oxidative damage in Helicobacter pylori: protective roles of peroxiredoxins

Oxidative stress conditions lead to enzymatic and non-enzymatic unsaturated fatty acid-initiated lipid peroxidation reactions. One exacerbating product is lipid hydroperoxide (LOOH) which itself promotes formation of several additional peroxyl radicals. Helicobacter pylori mutant strains with disruptions in genes encoding the peroxiredoxins, alkyl hydroperoxide reductase (ahpC) and the bacterioferritin comigratory protein (bcp), were more sensitive than the parent strain to oxidizing agents. These mutant strains were particularly sensitive, compared to the wild type, to killing by the unsaturated fatty acid linolenic acid but were not sensitive to the saturated fatty acid palmitic acid. A double mutant strain (ahpC bcp) accumulated more than 3-fold more lipid peroxides than the parent strain, indicating these peroxiredoxins together play a role in detoxifying lipid peroxides. The level of free iron accumulation, a signature of oxidative stress damage, was correlated specifically to organic peroxide-mediated stress by both in vivo and in vitro approaches. Free iron accumulation and concomitant destruction of [Fe-S] cluster-containing proteins (hydrogenase and aconitase) was correlated to damage mediated by exogenous t-butyl peroxide, or separately to intracellular accumulation of lipid peroxides in mutant strains. A major macromolecular target of accumulating lipid peroxides in H. pylori is DNA, as mutant analysis approaches combined with quantitative DNA fragmentation studies and specific DNA damage assessment (i.e. 8-oxoguanine formation) were used to demonstrate that such damage was especially associated with ahpC and ahpC bcp strains.

The Helicobacter pylori MutS protein confers protection from oxidative DNA damage

The human gastric pathogenic bacterium Helicobacter pylori lacks a MutSLH-like DNA mismatch repair system. Here, we have investigated the functional roles of a mutS homologue found in H. pylori, and show that it plays an important physiological role in repairing oxidative DNA damage. H. pylori mutS mutants are more sensitive than wild-type cells to oxidative stress induced by agents such as H2O2, paraquat or oxygen. Exposure of mutS cells to oxidative stress results in a significant ( approximately 10-fold) elevation of mutagenesis. Strikingly, most mutations in mutS cells under oxidative stress condition are G:C to T:A transversions, a signature of 8-oxoguanine (8-oxoG). Purified H. pylori MutS protein binds with a high specific affinity to double-stranded DNA (dsDNA) containing 8-oxoG as well as to DNA Holliday junction structures, but only weakly to dsDNA containing a G:A mismatch. Under oxidative stress conditions, mutS cells accumulate higher levels (approximately threefold) of 8-oxoG DNA lesions than wild-type cells. Finally, we observe that mutS mutant cells have reduced colonization capacity in comparison to wild-type cells in a mouse infection model.

Proteomic analysis of proteins expressed by Helicobacter pylori under oxidative stress

Helicobacter pylori is a spiral, slow growing gram-negative microaerophilic bacterium. It has been shown to be the etiological agent of gastroduodenal diseases, such as chronic gastritis, gastric and duodenal ulcers, and gastric cancer. To address the influence of oxidative stress and its underlying mechanisms, we have compared proliferation, urease activity and protein expression profile of H. pylori incubated under normal microaerophilic (5% O2) and aerobic stress (20% O2) conditions. Oxidative-stress cells displayed coccoid morphology and time-dependent decrease in proliferation. The urease activity was completely abrogated after 32 h. We have further compared the protein expression profiles of H. pylori under normal growing and oxidative-stress conditions by a global proteomic analysis, which includes high-resolution 2-DE followed by MALDI-TOF-MS and bioinformatic databases search/peptide-mass comparison. The results revealed that more than ten proteins were differentially expressed under oxidative stress. Most notably, the protein expression levels of urease accessory protein E (UreE, an essential metallochaperone for urease activity) and alkylhydroperoxide reductase (AhpC) with antioxidant potential are greatly decreased under stress conditions. Measurements of messenger RNA transcription level by performing RT-PCR on total mRNA also confirmed that gene expressions for these two proteins are consistently repressed under oxygen tension. These changes form a firm basis to account for the loss of urease activity and anti-oxidative ability of H. pylori after long-term exposure to reactive oxygen. Conceivably, UreE and AhpC may thus be listed as potential targets for the development of therapeutic drugs against H. pylori.

The antioxidant protein alkylhydroperoxide reductase of Helicobacter pylori switches from a peroxide reductase to a molecular chaperone function

Helicobacter pylori, an oxygen-sensitive microaerophilic bacterium, contains many antioxidant proteins, among which alkylhydroperoxide reductase (AhpC) is the most abundant. The function of AhpC is to protect H. pylori from a hyperoxidative environment by reduction of toxic organic hydroperoxides. We have found that the sequence of AhpC from H. pylori is more homologous to mammalian peroxiredoxins than to eubacterial AhpC. We have also found that the protein structure of AhpC could shift from low-molecular-weight oligomers with peroxide-reductase activity to high-molecular-weight complexes with molecular-chaperone function under oxidative stresses. Time-course study by following the quaternary structural change of AhpC in vivo revealed that this enzyme changes from low-molecular-weight oligomers under normal microaerobic conditions or short-term oxidative shock to high-molecular-weight complexes after severe long-term oxidative stress. This study revealed that AhpC of H. pylori acts as a peroxide reductase in reducing organic hydroperoxides and as a molecular chaperone for prevention of protein misfolding under oxidative stress.

DNA sequences and proteic antigens of H. pylori in cholecystic bile and tissue of patients with gallstones

BACKGROUND

Although Helicobacter pylori DNA sequences have been detected in cholecystic bile and tissue of patients with gallstones, controversial results are reported from different geographic areas.

AIM

To detect H. pylori in cholecystic bile and tissue of patients with gallstones from a previously uninvestigated geographic area, southern Italy. Detection included both the bacterial DNA and the specific antigen (H. pylori stool antigen) identified in the stools of infected patients for diagnostic purposes.

PATIENTS AND METHODS

The study enclosed 33 consecutive patients undergoing laparoscopic cholecystectomy for gallstones. DNA sequences of H. pylori were detected by polymerase chain reaction in both cholecystic bile and tissue homogenate. Moreover, we assayed H.pylori stool antigen on gall-bladder cytosolic and biliary proteins after their extraction. Bacterial presence in the stomach was assessed by urea breath test in all patients and Deltadelta13CPDB value assumed as marker of intragastric load. Fisher's exact probability and Student's t-tests were used for statistical analysis.

RESULTS

DNA sequences of H. pylori in bile were found in 51.5% and significantly correlated with its presence in cholecystic tissue homogenate (P<0.005), H. pylori stool antigen in gall-bladder (P=0.0013) and bile (P=0.04) proteins, gastric infection (P<0.01) and intragastric bacterial load (P<0.001). No correlation was found, however, with sex and age of the patients.

CONCLUSIONS

Our prevalence value of bacterial DNA in bile and gall-bladder of patients with gallstones agreed with that of the only other Italian study. The simultaneous presence of both bacterial DNA and proteic antigen suggests that the same prototype of bacterium could be located at both intestinal and cholecystic level and, therefore, the intestine represents the source of biliary contagion.

The presence of thecagpathogenicity island is associated with increased superoxide anion radical scavenging activity byHelicobacter pylori

Reactive oxygen species (ROS) generated by Helicobacter pylori infection have been suggested to be important factors in induction of gastric malignancies. Utilizing electron spin resonance spectrometry, H. pylori-dependent radical formation and hydroxyl- and superoxide-anion radical scavenging activity was investigated. In contrast to previous reports, we found that H. pylori does not produce ROS, but displays superoxide scavenging activity. This scavenging activity was increased in cag-positive H. pylori strains when compared to strains lacking an intact cag pathogenicity island, and was dependent on enzyme activity. We hypothesize that the increased scavenging activity of cag-positive H. pylori strains is an adaptation to the increased inflammatory response associated with the cag-positive genotype of H. pylori.