Biomedicine and Chemical Sciences 1(4) (2022) 278-288 Helicobacter Pylori, Infection, Virulence Factors and Treatment: A Review Amer A. Haamadia, Mohsen Hashim Risanb*, Hassan M. AboAlmaalic a College of Applied Medical Sciences, University of Kerbala, Karbala – Iraq b College of Biotechnology, University of Al- Nahrain, Baghdad – Iraq c College of Pharmacy, University of Kerbala, Karbala – Iraq A R T I C L E I N F O A B S T R A C T Article history: Gastric and ulcer peptic disease is a common disease in the community. Considering the close relationship between peptic ulcer and gastritis caused by Helicobacter pylori. The prevalence of H. pylori increased markedly with age with the maximum colonization (81.5%) occurring in adults (40-60 years). H. pylori are bacteria that can cause an infection in the stomach or duodenum (first part of the small intestine). It is the most common cause of peptic ulcer disease. H. pylori can also inflame and irritate the stomach lining (gastritis). Untreated, long- term H. pylori infection can lead to stomach cancer (rarely). H. pylori multiply in the mucus layer of the stomach lining and duodenum. The bacteria secrete an enzyme called urease that converts urea to ammonia. This ammonia protects the bacteria from stomach acid. As H. pylori multiply, it eats into stomach tissue, which leads to gastritis and/or gastric ulcer. Symptoms include dull or burning stomach pain, unplanned weight loss and bloody vomit. H-pylori- caused ulcers are commonly treated with combinations of antibiotics. Usually two antibiotics are prescribed. Among the common choices are amoxicillin, clarithromycin (Biaxin®), metronidazole (Flagyl®) and tetracycline and Proton pump inhibitor: Commonly used proton pump inhibitors include lansoprazole (Prevacid®), omeprazole (Prilosec®), pantoprazole (Protonix®), rabeprazole (Aciphex®) or esomeprazole (Nexium®) and Bismuth subsalicylate: Sometimes this drug (eg, Pepto-Bismol®) is added to the antibiotics plus proton pump inhibitor combinations mentioned above. This drug protects the stomach lining. Combination treatment is usually taken for 14 days. One newer medication, Talicia®, combines two antibiotics (rifabutin and amoxicillin) with a proton pump inhibitor (omeprazole) into a single capsule. Copyright © 2022 Biomedicine and Chemical Sciences. Published by International Research and Publishing Academy – Pakistan, Co-published by Al-Furat Al-Awsat Technical University – Iraq. This is an open access article licensed under CC BY: (https://creativecommons.org/licenses/by/4.0) Received on: August 09, 2022 Revised on: August 20, 2022 Accepted on: August 23, 2022 Published on: October 01, 2022 Keywords: Helicobacter Pylori Infection Virulence Factors and Treatment 1. Introduction 1Helicobacter is a Gram-negative bacteria possessing a characteristic helical shape. They were initially considered to be members of the genus Campylobacter, but in 1989, Goodwin et al. published sufficient reasons to justify the new genus name Helicobacter. The genus Helicobacter contains about 35 species (Goodwin et al., 1989). Al-Baldawi *Corresponding author: Mohsen Hashim Risan, College of Biotechnology, University of Al- Nahrain, Baghdad – Iraq E-mail: m_risan@yahoo.com How to cite: Haamadi, A. . A., Risan, M. H. ., & Almaali, H. M. A. (2022). Helicobacter Pylori, Infection, Virulence Factors and Treatment: A Review. Biomedicine and Chemical Sciences, 1(4), 278-288. DOI: https://doi.org/10.48112/bcs.v1i4.289 (1997) was the first who isolate this bacterium. H. pylori in Iraq infects the stomachs of more than 50% of the world’s population and has lived in such close association with modern humans since they migrated from East Africa more than 58,000 years ago (Linz et al., 2007). Before the discovery of H. pylori in the early 1980s, stomach disorders such as gastritis and peptic ulcers were ascribed to bad diet, too much coffee, or a stressful lifestyle. The disorders were treated accordingly with drugs such as antacids and proton pump inhibitors to reduce the acidity of the stomach and thus eliminate the symptoms. Bacteria were seen in the stomach as early as 1874, but these findings were ignored because nothing was believed to survive the acidic environment in the stomach. In the early 1980s, H. pylori was isolated from the antrum of patients with gastritis and ulcer disease, and later experiments fulfilled Kosh’s postulates and, importantly, antibiotic treatments got rid of the infection and the inflammation Content lists available at: https://journals.irapa.org/index.php/BCS/issue/view/15 Biomedicine and Chemical Sciences J o u r n a l h o m e p a g e : https://journals.irapa.org/index.php/BCS 37-BCS-1137-289 https://crossmark.crossref.org/dialog/?doi=10.48112/bcs.v1i4.289&domain=pdf&date_stamp=2022-10-01 https://journals.irapa.org/index.php/BCS/index https://irapa.org/ https://irapa.org/ https://en.atu.edu.iq/ https://creativecommons.org/licenses/by/4.0 mailto:m_risan@yahoo.com https://doi.org/10.48112/bcs.v1i4.289 https://journals.irapa.org/index.php/BCS/issue/view/15 https://journals.irapa.org/index.php/BCS Haamadi, Risan & AboAlmaali Biomedicine and Chemical Sciences 1(4) (2022), 278-288 279 dissapeared (Marshall & Warren, 1984). For this finding, Marshall and Warren were awarded with the Nobel Prize in Medicine and physiology in 2005. Hence, H. pylori was confirmed as the cause of gastritis and the more serious peptic ulcer diseases. In epidemiological studies, H. pylori infection was also found to correlate with gastric cancer, i.e. H. pylori is considered as an onco-pathogen. In 1994, the World Health Organization listed H. pylori infection as a carcinogen (IARC, 1994). The understanding that H. pylori infection is the causative agent of overt gastric disease opened a paradigm shift that has completely changed the treatment of stomach disorders, which are now considered as infectious diseases (Cellini et al., 2004). 2. Microbiological Characteristics of H. pylori H. pylori is a slow-growing, microaerophilic, spiral shaped multi flagellated (Lophotrichus flagella) and gram-negative bacterium, about 3 micrometers long with a diameter of about 0.5 micrometers, whose surface is coated with 12–15 nm ring-shaped aggregates of urease and heat shock protein (Figure 1). Fig. 1. Scanning electron micrograph images of H. pylori bacteria (in blue) (Abo Almaali, 2014). The urease enzyme and the heat shock protein B are located almost exclusively within the cytoplasm in the fresh log-phase cultures of H. pylori. In subcultures, urease and heat shock protein B become associated with the bacterial surface, suggesting bacterial autolysis leading to release of protein and adsorption into the bacterial surface (Mégraud & Lehours, 2007). Some of the lipopolysaccharide of the organism mimics the Lewis blood group antigens in structure. This molecular mimicry also helps in the continued existence of H. pylori in the unfavorable gastric environment. This bacterium colonizes gastric mucosa and elicits both inflammatory and immune lifelong responses, with release of various bacterial and host dependent cytotoxic substances (Figure 2). Under unfavorable circumstances it can become coccoidal, a non- culturable form with debatable viability. The bacterium is a microaerophilic and capnophilic organism, slowly growing with rigorous culture demands (Mégraud & Lehours, 2007). Fig. 2. Component of H. pylori with biological activities (Henriksson et al., 2012) Haamadi, Risan & AboAlmaali Biomedicine and Chemical Sciences 1(4) (2022), 278-288 280 3. Infection and Colonization of the Stomach H. pylori colonizes the stomach and, in particular, the less acidic antrum (Figure 3). During disease progression, pH initially decreases due to hyper secretion and H. pylori might move into the first parts of the intestine, the duodenum. This region is less resistant to infection and peptic ulcer could develop. Long-term hyper secretion can cause atrophic gastritis to the mucosa and even loss of the acid producing parietal cells and higher stomach pH. Atrophy can also result in a gastric ulcer formation, which is sometimes a precursor to gastric cancer (Hidaka et al., 2001). Within the mucus layer, H. pylori is mainly confined to the 100 μm of mucus closest to the epithelial cells where pH is more neutral. Thirty percent are found within the first 5 μm and around 20% are found tightly attached to the cells (Hessey et al., 1990; Schreiber et al., 2004). The colonization of H. pylori is restricted to the superficial epithelial cells, colocalizing with the expression of the mucin MUC5AC (Hidaka et al., 2001). The strict colonization of the superficial zone might relate to the glandular mucin MUC6 that possesses terminal α1,4- GlcNAc. This structure inhibits cell wall synthesis in H. pylori thereby making these glandular regions toxic to H. pylori (Kawakubo et al., 2004). In addition to the extracellular habitat, H. pylori has also been found between cells, deeper in the tissue, and in intracellular vesicles of both cultured gastric epithelial cells and in gastric biopsies as in figure (3) (Aspholm et al., 2006; Necchi et al., 2007). These invasive bacterial cells can repopulate the extracellular environment suggesting that the intracellular lifestyle might be a way for H. pylori to escape the immune system as well as antibiotic treatment (Dubois & Borén, 2007). Fig. 3. Simplified anatomical illustration of the stomach (Henriksson et al., 2012). 4. Transmission of Helicobacter pylori H. pylori has a narrow host range and is found almost exclusively in human and some nonhuman primates. Despite hostile, the human stomach is the only identified reservoir for H. pylori. Although extensively studied, efforts to confirm the exact route of transmission have been disappointing. It has been speculated that the person-to- person spread currently appeared to be the most likely mode of transmission, especially between family members (Kivi et al., 2005; Weyermann et al., 2006). Hence, the possible routes are fecal–oral, oral– oral and gastro–oral. 5. Clinical Features Chronic H. pylori –associated gastritis such is asymptomatic but the initial acquisition of the infection cause acute gastritis with hypochlorhydria which may cause abdominal pain, nausea and vomiting that resolve within a few days. Uncomplicated peptic ulcers typically cause epigastric pain and less commonly, nausea, vomiting and weight loss, whereas some ulcers (particularly NSAID ulcers) are asymptomatic. The classically described pain of duodenal ulcer is felt as a growing or burning sensation, often with a relation to meals; occurring 1-3 hours after meals and /or at night and relieved by food. Gastric ulcer pain is instead often precipitated by food. However, symptoms are actually very poorly discriminatory for ulceration site and even for whether or not an ulcer is present. Examination usually reveals epigastric tenderness but may be normal (Parsonnet et al., 1999). 6. Virulence Factors of Helicobacter pylori The outcome of a bacterial infection is highly dependent on the prevalence and status of its virulence factors. The genetic diversity and variability of H. pylori is mirrored in the wide range of virulence factors that vary by disease, age, country and ethnicity. To be defined as an H. pylori virulence factors, the protein must be correlated with disease both in vitro and in vivo and with epidemiological disease patterns (Lu et al., 2005). Three main virulence factors of H. pylori are the cytotoxin-associated gene pathogenicity island (cagPAI), the vacuolating cytotoxin (VacA), and the outer membrane proteins (OMPs). Many of the OMPs are proposed to be involved in disease-associated mechanisms such as adherence and manipulation of the immune response. VacA and CagA are, together with BabA genes, associated with the more severe cases of gastric disease (Aljeboury et al., 2020; Haamadi et al., 2021b). Haamadi, Risan & AboAlmaali Biomedicine and Chemical Sciences 1(4) (2022), 278-288 281 6.1. CagPAI Gene The cagPAI is a pathogenicity island in the H. pylori genome and encodes numerous genes that, upon cell contact, are expressed and assembled into the needle-like type 4 secretion system (T4SS) (Rohde et al., 2003). The T4SS is evolutionarily conserved among many Gram- negatives such as Agrobacterium, Bordetella, and Legionella, but differs in different organisms in terms of what substrates are transferred. H. pylori T4SS binds the integrin β1 receptor that is located on the basal membrane and transfers the cytotoxin associated gene A (CagA) which is also encoded by the cagPAI (Kwok et al., 2007; Jiménez-Soto et al., 2009). Once inside the cell, CagA is phosphorylated on specific EPIYA motifs by host kinases, and phosphorylated CagA goes on to manipulate the cell by interacting witnumerous host cell proteins. In addition, injected non-phosphorylated CagA manipulates proliferation and immune response of host cells. Cultured epithelial cells respond by forming the characteristic “hummingbird phenotype” that is the effect of both cell scattering and elongation (Tegtmeyer et al., 2011). CagA is not considered as a virulence factor only, but it is considered an oncoprotein and is associated with development of gastric adenocarcinoma. H. pylori infections of Mongolian gerbils resulted in more gastric adenocarcinomas in a CagA- dependent manner and so did mice that were transgenic for CagA expression (Ohnishi et al., 2008). 6.2. VacA Gene Vacuolating cytotoxin A (VacA) is a multifunctional secreted cytotoxin. The vacA gene is found in all H. pylori isolates though there are differences among the alleles. The s1 allele, especially in combination with the m1 allele, is highly associated with the risk of developing peptic ulcers and gastric cancer (Palframan et al., 2012). The VacA toxin forms large vacuoles in gastric cells; however, such vacuoles are not seen in biopsies. VacA localizes to, and exerts effects on, the mitochondria where it triggers the apoptotic cascade and induces cell death by mitochondrial fission. The detailed molecular mechanisms for this, however, are not known (Palframan et al., 2012). In addition, VacA has been found to bind the integrin subunit CD18 on T-cells and suppressing their activities (Jain et al., 2011). 6.3. BabA Gene The Blood group Antigen Binding Adhesin, BabA, mediates binding to the ABO/Leb blood group antigens. The first hint of the existence of an adhesion was provided by application of FITC-labeled H. pylori to paraffin-embedded tissue sections of human gastric mucosa and observed adherence to the foveola epithelial cells (Falk et al., 1993). Inhibition with various substrates such as human colostrum from secretors and non-secretors, antibodies, and glycoconjugates identified the receptor as the H1 and Lewis b (Leb) blood group antigens (Borén et al., 1993). H1/Leb is a terminal carbohydrate structure that defines blood group O. It is found on red blood cells and on gastro-intestinal (GI) epithelial linings such as in the stomach. Related to H1 and Leb structures are the A and B blood group antigens, but neither of these structures were identified receptors, nor did H. pylori bind the related Lea structure, demonstrating specificity for a fucose moiety (Borén et al., 1993). The cognate adhesin, Blood group Antigen Binding Adhesin (BabA), was identified by use of the re-tagging technique (Ilver et al., 1998). This technique utilizes a cross-linker attached to the receptor glycoconjugate. Binding of this receptor exposes the adhesin for cross- linking and enables detection by streptavidin-biotin via SDS- PAGE and mass spectrometry to identify the cognate adhesin. The strain used in these studies, CCUG17875, was found to contain two BabA alleles of which one is silent due to defects in the translational sequence and signal peptide (Ilver et al., 1998; Bäckström et al., 2004). This allele was called BabA1 and the allele encoding a functional BabA protein was called BabA2. Deletion of BabA2 confirmed that the BabA protein is the functional adhesin for binding to H1/Leb. During these studies, another gene was identified and called BabB. It was homologous to BabA at the 3' and 5' ends but divergent in the middle (Ilver et al., 1998). Both of these proteins were later classified as belonging to the Hop family of OMPs (Alm et al., 2000). H1 and Leb were identified as receptor structures for BabA, whereas ALeb and BLeb did not demonstrate any binding to the Peruvian isolate that was used in the original studies. When Aspholm- Hurtig et al. investigated the worldwide receptor specificity for BabA, they identified strains that, in addition to Leb/H1, could also bind the ALeb and Bleb structures. These strains were termed ‘generalists’ while those that were restricted to Leb/H1 were termed ‘specialists’ (Aspholm, et al., 2006). Interestingly, the specialist strains originated from parts of the world, such as South America, where O group is the predominant blood group. The affinity of BabA for its receptors is high, with values in the μM to nM range, though they vary substantially between clinical isolates (Aspholm et al., 2006). In addition, the affinity for H1/Leb is stronger than for ALeb or BLeb, and this could explain the higher risk of peptic ulcer disease in blood group O individuals (Aspholm et al., 2006; Anstee, 2010). In addition to the BabA-mediated attachment to the epithelial cells, BabA also interacts with the mucins MUC5AC and MUC1 (Figure 4). Clinical isolates have exceedingly diverse BabA sequences, with the highest variability in the middle domain. In addition, not all strains express BabA, and not all expressed BabA proteins are functional (Kawai et al., 2011). Thus, presence of a babA gene is not necessarily evidence of a functional BabA protein. The mechanism by which this diversity is obtained is not known. The phylogenetic analyses of the BabA variable region in different populations reveal heterogeneous selective pressures, such as escape from host immune response, receptor specificity, and affinity, that act on the protein (Aspholm, et al., 2006). During H. pylori infection studies in Rhesus macaques, mice, and gerbils, expression of BabA was frequently lost (Styer et al., 2010; Ohno et al., 2011). The loss of BabA in Rhesus macaques might be because of a higher inflammatory response to BabA-expressing adherent bacterial cells. However, it could also be because of the lower prevalence of the ABO/Leb blood group antigens in gastric mucosa during infection and hence selection against BabA-expression (Lindén et al., 2008). Haamadi, Risan & AboAlmaali Biomedicine and Chemical Sciences 1(4) (2022), 278-288 282 Fig. 4. Represented Bab gene of H. pylori (Henriksson et al., 2012) 6.4. BabA, BabB, and BabC Genes Recombination Phylogenetic analysis of the OMP C-terminal regions reveals a close genetic relationship between BabA, BabB, and BabC where BabA and BabC are most similar. Despite this similarity, only BabA has been assigned a function (Alm et al., 2000). BabA and BabB are most prevalent, and BabC is less and was recently associated with strains of European origin (Kawai et al., 2011). The three alleles are commonly found at three different loci, A, B, or C, that are in each third of the genome. The existence of three similar OMPs suggested that H. pylori utilizes them to switch antigenic appearance to avoid the immune response (Lindén et al., 2008). Indeed, after the first genome comparison between strains 26695 and J99, it was clear that BabA and BabB were found at inverted loci. In addition, 26695 have the BabC gene at the C locus, which J99 is missing (Alm et al., 1999). Comparisons of clinical isolates demonstrated that these alleles frequently recombine and switch loci to form duplicates, deletions, and chimeric genes at a frequency of about 3 × 10-6 gene conversions per cell division (Hennig et al., 2006; Amundsen et al., 2008). Interestingly, the C-terminal regions of BabA and BabB are more homologous within a genome/strain than between genomes/strains, and this suggests a concerted evolution between BabA and BabB (Pride & Blaser, 2002). No such analysis has been done for BabC, but the close relationship between these genes suggests similar results. The Leb- binding function of BabA is not affected by the loci from which it is expressed (Hennig et al., 2006). However, expression of BabA from the B or C loci could result in a gain of function because BabA could then make use of their CT-repeats for faster switching of expression (Bäckström et al., 2004; Colbeck et al., 2006). The recombination frequency is very high, and a seemingly homogeneous population from a single clone can retain a subpopulation of single clones that demonstrate an altered arrangement of the Bab genes caused by recombination (Colbeck et al., 2006). Such rearrangements can also revive lost BabA expression demonstrating that loss of a functional BabA is reversible (Bäckström et al., 2004). Recombination is also seen during experimental infections, such as in the Rhesus macaque model, where the expression of BabA is sometimes switched off by BabA-BabB recombination. 6.5. BabA Gene and Pathogenesis The pathogenic importance of an ABO/Leb-mediated attachment by BabA was demonstrated in H. pylori-infected, Leb-transgenic mice that had higher inflammatory scores compared to their non-transgenic littermates (Falk et al., 1993). This study was later confirmed in Mongolian gerbils where the animals infected with a BabA mutant had lower infiltration of inflammatory cells and a reduced cytokine response (Sugimoto et al., 2011). In 1999, Gerhard et al., (1999) updated the old Type 1 (CagA+, VacA+) and Type 2 (CagA-, VacA-) classifications of H. pylori by adding a third denominator, BabA2 (Gerhard et al., 1999). Genotypic studies demonstrated that BabA2 was correlated with cagA and the more pathogenic vacAs1 allele and was significantly associated with adenocarcinoma and better discriminated against gastritis compared to the conventional Type 1 vs. 2 definition. These results indicated that BabA expression has an important role in the disease process, and these strains were termed ‘triple-positive strains’ (Ishijima et al., 2011). Many groups tried to repeat the task of correlating babA2 with gastric disease but obtained inconclusive results (Yamaoka, 2008). Because the prevalence of BabA2 is not equivalent to expression of BabA, additional studies have investigated the correlation with BabA expression. Such studies demonstrated a correlation between BabA,CagA, and VacA, and also to more severe gastric disease such as intestinal metaplasia (Azevedo et al., 2008; Yamaoka, 2008; Odenbreit et al., 2009). Interestingly, Fujimoto et al. (2007) demonstrated a stronger correlation with duodenal ulcer and gastric cancer for strains with low levels of BabA expression than for those with high or no expression (Fujimoto et al., 2007). Evidence for the functional correlation between BabA, CagA, and VacA is now being elucidated. Adherent H. pylori are frequently found associated with the intercellular junctions where they would have immediate access for penetration of the mucosa. Such tight adherence, mediated by BabA (or other adhesins), simplifies the secretion and delivery of VacA to host cells that could trigger separation of the cellular junctions and facilitate penetration of H. pylori through the intercellular space. On the basal side, these bacteria have access to the T4SS integrin β1 receptor that is located where the bacteria can deliver CagA (Wessler & Backert, 2008). Indeed, CagA-positive bacteria are found more tightly associated with epithelial cells during infection. This hypothesis has recently been supported by Ishijima et al. who demonstrated that the BabA-Leb interaction increases T4SS-mediated induction of mRNAs for pro- Haamadi, Risan & AboAlmaali Biomedicine and Chemical Sciences 1(4) (2022), 278-288 283 inflammatory cytokines and precancerous factors in cell cultures, and stimulates intracellular levels of phosphorylated CagA (Ishijima et al., 2011). BabA, SabA, and CagA have also recently been demonstrated to share regulatory mechanism upon interaction with mucins (Skoog et al., 2012). Although not all studies were able to demonstrate a correlation between BabA, CagA, and VacA in disease progression, there is a strong indication that BabA itself can cause damage to the epithelial cells. A recent finding has suggested that BabA is involved in induction of double- strand breaks and such grave DNA damage could tilt the disease state towards more aggressive pathogenesis (Toller et al., 2011). However, it is difficult to determine if these effects are mediated by a direct binding to the receptor, or are secondary and caused by the tighter association with host cells. 6.6. SabA Gene SabA, the Sialic-acid binding adhesin, was discovered some years after BabA. Mahdavi et al., (2002) observed adherence of the CCUG17875 babA2 mutant to human gastric mucosa from a gastritis patient. The receptor was characterized to be sialyl-dimeric-Lewis x antigen (sdiLex), but more detailed analysis of the binding specificity has identified the minimal binding epitope to be NeuAcα2-3Gal with a polymorphism for the core chain (Mahdavi et al., 2002; Aspholm et al., 2006). Such sialylated antigens are expressed by inflamed tissues to recruit neutrophils and are, therefore, triggered by H. pylori infection. SabA expression is highly variable with both a PolyT tract in the promoter and CT-repeats in the coding region, and it has also recently been shown to be controlled by the acid-responsive ArsRS two component system that also regulates urease and carbonic anhydrase (Goodwin et al., 2008). Similarly to the recombination between babA and its related alleles, sabA can also recombine with its related allele sabB, and to some extent with hopQ (Talarico et al., 2012). This occurs at a frequency of 1.4 × 10 9 bp conversions per cell generation, which is lower than that seen for babA and babB recombination. 7. Treatment of H. pylori Infection The goal of H. pylori treatment is the complete elimination of the organism. Once this has been achieved, reinfection rates are low; thus, the benefit of treatment is durable. Clinically relevant H. pylori–eradication regimens must have cure rates of at least 80 percent (according to intention-to- treat analysis) without major side effects and with minimal induction of bacterial resistance. Such goals have not been achieved with antibiotics alone. Because luminal acidity influences the effectiveness of some antimicrobial agents that are active against H. pylori, antibiotics are combined with proton-pump inhibitors or ranitidine bismuth citrate (Mégraud & Lehours, 2007). So-called triple therapies, combinations of one anti secretory agent with two antimicrobial agents for 7 to 14 days, have been extensively evaluated, and several regimens have been approved by the Food and Drug Administration (FDA) (Table 1). The combination of two or more antimicrobial agents increases rates of cure and reduces the risk of selecting for resistant H. pylori. The chief antimicrobial agents used in these regimens are amoxicillin, clarithromycin, metronidazole, tetracycline, and bismuth. Primary resistance to amoxicillin and tetracycline remains uncommon, but the frequency of clarithromycin resistance is now around 10 percent in most European countries and the United States and even higher in Japan (Meyer et al., 2002). Metronidazole resistance ranges between 20 percent and 30 percent and is more frequent among women and among both men and women in the developing countries, because of the frequent use of nitroimidazoles to treat other diseases (Meyer et al., 2002). Resistance of H. pylori to macrolides is caused by point mutations in the 23S ribosomal RNA genes. Resistance to metronidazole is caused primarily by mutations in nitroreductase genes (rdxA and frxA) that interfere with the intracellular activation of nitroimidazoles (Mégraud & Lehours, 2007). 8. First-line Therapies 8.1. Proton-Pump-Inhibitor–Based Triple Therapies Following the success of initial trials of proton pump- inhibitor–based triple therapy in Italy and France, large, randomized trials confirmed the effectiveness of treatment twice daily for seven days with 20 mg of omeprazole, given either with 1 g of amoxicillin and 500 mg of clarithromycin, or with 400 mg of metronidazole and 250 mg of clarithromycin (Lind, et al., 2006; Zanten, 2009). Several comparative trials have demonstrated the equivalence of 30 mg of lansoprazole twice daily, 40 mg of pantoprazole twice daily, 20 mg of rabeprazole daily, and 20 mg of esomeprazole twice daily with omeprazole in these triple therapies, in a meta-analysis of 666 studies that included 53,228 patients, combinations of a proton-pump inhibitor, clarithromycin, and a nitroimidazole; a proton- pump inhibitor, clarithromycin, and amoxicillin; and a proton-pump inhibitor, amoxicillin. It is indicated for patients who are either allergic to or intolerant of clarithromycin or for infections with known or suspected resistance to clarithromycin. Although it is not approved by the FDA for this indication, amoxicillin has been substituted for tetracycline in patients for whom tetracycline is not recommended (Laine, et al., 2000; Misiewicz, et al., 2007). Haamadi, Risan & AboAlmaali Biomedicine and Chemical Sciences 1(4) (2022), 278-288 284 Table 1 Food and Drug Admostration - Approved treatment option for H. pylori eradication (Sebastian, and Pierre, 2002) Therapy Dose Duration Omeprazole 40 mg daily clarithromycin 500 mg daily three times and amoxicillin 1g twice daily for 10 days Omeprazole 20 mg daily clarithromycin 500 mg daily three times and amoxicillin 1g twice daily for 10 days Lansoprazole 30 mg twice daily Clarithromycin 500 mg daily three times Amoxicillin 1g twice daily for 10 days Lansoprazole 30 mg twice daily Clarithromycin 500 mg daily three times Amoxicillin 1g twice daily for 2 week Lansoprazole 30 mg twice daily Amoxicillin 1g twice daily for 2 week Esomeprazole 40 mg daily Clarithromycin 500 mg twice daily Amoxicillin 1 g twice daily for 10 days Ranitidine bismuth citrate clarithromycin 400 mg twice daily 500 mg three times daily for 2 weeks Ranitidine bismuth citrate clarithromycin 400 mg twice daily 500 mg twice daily for 2 weeks Bismuth 525 mg four times daily subsalicylate metronidazole tetracycline 250 mg four times daily 500 mg four times daily for 2 weeks In another pooled analysis, no effect of larger doses of proton-pump inhibitors was observed among the triple therapies. The duration of therapy remains controversial. In Europe, 7-day treatment is recommended, (Dore, 2000; Haamadi et al., 2021a).) Whereas in the United States, 14- day courses have been found to be better than shorter courses and are approved by the FDA. In a recent meta- analysis, 14-day treatment achieved rates of cure 7 to 9 percentage points better than 7-day treatment. Primary resistance to clarithromycin and metronidazole decreases the rates of cure by 50 percent and 37 percent, respectively. The indication for therapy, bacterial factors, patient compliance, and geographic differences can further affect rates of cure (Lee, et al., 2008). 8.2. Ranitidine Bismuth Citrate–Based Therapies Ranitidine bismuth citrate in dual therapy with clarithromycin for two weeks has been approved by the FDA (Peterson, et al., 2006). Meta-analyses suggest that ranitidine bismuth citrate, with clarithromycin and amoxicillin, or with clarithromycin and a nitroimidazole, performs as well as corresponding proton-pump-inhibitor– based therapies (Rossum, 1999). Ranitidine bismuth citrate– based regimens may be less influenced by antibiotic resistance than their proton-pump-inhibitor–based counterparts (Beek & Craen, 1999). No ranitidine bismuth citrate–based triple therapy has been approved by the FDA. 8.3. Bismuth-Based Triple Therapies Bismuth in association with metronidazole and tetracycline compares well in meta-analyses with therapies based on proton-pump inhibitors or ranitidine bismuth citrate, even if the duration of treatment is reduced to seven days. This inexpensive regimen remains an important option. Metronidazole resistance negatively affects efficacy. Furazolidone, a nitrofuran derivative, has also been proposed for use in bismuth-based triple therapies. Triple therapy for two weeks, consisting of 100 mg of furazolidone four times daily, amoxicillin, and bismuth, was successful in 86 percent of cases. However, furazolidone, particularly when combined with bismuth for two weeks, is associated with substantial side effects. Standard bismuth-based therapy and its furazolidone-containing alternatives were recommended at the 1999 Latin American Consensus Conference (Coelho, León-Barúa, & Quigley, 2000). Three regimens were recommended in 1998 by U.S. Consensus Conference76: a proton-pump inhibitor, clarithromycin, and either amoxicillin or metronidazole for two weeks; ranitidine bismuth citrate,clarithromycin, and amoxicillin, metronidazole, or tetracycline for two weeks; and a proton-pump inhibitor, bismuth, metronidazole, and tetracycline for one to two weeks. The regimens recommended by the European Maastricht 2 conference are a proton pump inhibitor (or ranitidine bismuth citrate), clarithromycin, and amoxicillin or metronidazole for seven days. Because there are insufficient data for the pediatric age group, no treatment regimen for children infected with H. pylori was recommended by the European Paediatric Task Force. 9. Second-line Therapies Eradication is more difficult when a first treatment attempt has failed, usually because of either poor patient compliance or the development of antibiotic resistance. Therefore, a 10 to 14-day treatment course is advocated for second-line therapies. However, the optimal strategy for retreatment after the failure of eradication has not yet been established. Because the failure of therapy is often associated with secondary antibiotic resistance, retreatment should ideally be guided by data on susceptibility (Hojo, et al., 2001). However, such information is often unavailable, so quadruple therapies, in which a proton-pump inhibitor or an H2-receptor antagonist is added to a bismuth-based triple regimen with a high-dose metronidazole, have been suggested an optimal second-line therapy. According to a recent meta-analysis, the pooled eradication rate in 30 trials in which this strategy was tested, was 76 percent. This second-line therapy was recommended at major consensus conferences, (Lam & Talley, 1998; Bazzoli, 2001). Although it may prove disappointing, given the failure of regimens containing metronidazole (Hojo, et al., 2001). Another approach for retreatment without susceptibility testing is to prescribe a second course of proton- pump- inhibitor– based triple therapy, avoiding antimicrobial agents against which prior therapy may have induced resistance and avoiding less effective combinations, such as amoxicillin and tetracycline. If a clarithromycin-based regimen is used first, a metronidazole- based regimen should be used afterward, or vice versa. This concept is supported by pooled analysis (Hojo, et al., 2001). Nevertheless, prospective studies of Haamadi, Risan & AboAlmaali Biomedicine and Chemical Sciences 1(4) (2022), 278-288 285 consecutive combinations of triple therapies are needed. Alternative approaches to second-line proton-pump- inhibitor– based therapies have been reported recently, but mostly in abstract form. Rifabutin, given in association with amoxicillin and pantoprazole for 10 days, achieved an 86 percent rate of cure, even in patients with resistant strains (Perri et al., 2001a). In a pooled analysis of nine studies, retreatment with ranitidine bismuth citrate–based triple therapy yielded an 80 percent rate of cure (Coelho et al., 2000). Similar to the rates with quadruple therapies, and in a recent randomized trial, ranitidine bismuth citrate, clarithromycin, and tinidazole achieved an 81 percent rate of cure after the failure of triple therapies based on proton pump inhibitors (Perri et al., 2001b). In locations where ranitidine bismuth citrate is available, triple therapies based on this compound can be used for second-line treatment. 10. Conclusions Helicobacter pylori are bacteria that can cause an infection in the stomach or duodenum. It is the most common cause of peptic ulcer disease. H. pylori can also inflame and irritate the stomach lining (gastritis). Untreated, long-term H. pylori infection can lead to stomach cancer (rarely). H. pylori multiply in the mucus layer of the stomach lining and duodenum. The bacteria secrete an enzyme called urease that converts urea to ammonia. This ammonia protects the bacteria from stomach acid. As H. pylori multiply, it eats into stomach tissue, which leads to gastritis and/or gastric ulcer. Symptoms include dull or burning stomach pain, unplanned weight loss and bloody vomit. H- pylori-caused ulcers are commonly treated with combinations of antibiotics. Competing Interests The authors have declared that no competing interests exist. References Abo Almaali, H. M. M. (2014). Investigation of vacA genotypes of Helicobacter pylori from samples in Karbala Governorate (Doctoral dissertation, Ph. D. theses, genetic engineering and biotechnology, Baghdad University, Iraq). Al-Baldawi, M. R. (1997). Isolation and identification of Helicobacter pylori from patients with duodenal ulcer and studying its pathogenicity and antibiotic sensitivity, M.Sc. thesis, College of Science, Baghdad University, Iraq. Aljeboury, G. H., Risan, M. H., & Algafari, R. N. (2020). Role of VAC a and CAG a Genes in Detection and Identification of Helicobacter Pylori. Indian Journal of Public Health, 11(02), 2287. https://doi.org/10.37506/v11/i2/2020/ijphrd/1951 77 Alm, R. A., Bina, J., Andrews, B. M., Doig, P., Hancock, R. E., & Trust, T. J. (2000). Comparative genomics of Helicobacter pylori: analysis of the outer membrane protein families. Infection and immunity, 68(7), 4155- 4168. https://doi.org/10.1128/IAI.68.7.4155- 4168.2000 Alm, R. A., Ling, L. S. L., Moir, D. T., King, B. L., Brown, E. D., Doig, P. C., ... & Trust, T. J. (1999). Genomic- sequence comparison of two unrelated isolates of the human gastric pathogen Helicobacter pylori. Nature, 397(6715), 176-180. https://doi.org/10.1038/16495 Amundsen, S. K., Fero, J., Hansen, L. M., Cromie, G. A., Solnick, J. V., Smith, G. R., & Salama, N. R. (2008). Helicobacter pylori AddAB helicase‐nuclease and RecA promote recombination‐related DNA repair and survival during stomach colonization. Molecular microbiology, 69(4), 994-1007. https://doi.org/10.1111/j.1365- 2958.2008.06336.x Anstee, D. J. (2010). The relationship between blood groups and disease. Blood, The Journal of the American Society of Hematology, 115(23), 4635-4643. https://doi.org/10.1182/blood-2010-01-261859 Aspholm, M., Olfat, F. O., Nordén, J., Sondén, B., Lundberg, C., Sjöström, R., ... & Borén, T. (2006). SabA is the H. pylori hemagglutinin and is polymorphic in binding to sialylated glycans. PLoS pathogens, 2(10), e110. https://doi.org/10.1371/journal.ppat.0020110 Aspholm, M., Olfat, F. O., Nordén, J., Sondén, B., Lundberg, C., Sjöström, R., ... & Borén, T. (2006). SabA is the H. pylori hemagglutinin and is polymorphic in binding to sialylated glycans. PLoS pathogens, 2(10), e110. https://doi.org/10.1371/journal.ppat.0020110 Azevedo, M., Eriksson, S., Mendes, N., Serpa, J., Figueiredo, C., Resende, L. P., ... & David, L. (2008). Infection by Helicobacter pylori expressing the BabA adhesin is influenced by the secretor phenotype. The Journal of Pathology: A Journal of the Pathological Society of Great Britain and Ireland, 215(3), 308-316. https://doi.org/10.1002/path.2363 Bäckström, A., Lundberg, C., Kersulyte, D., Berg, D. E., Borén, T., & Arnqvist, A. (2004). Metastability of Helicobacter pylori bab adhesin genes and dynamics in Lewis b antigen binding. Proceedings of the National Academy of Sciences, 101(48), 16923-16928. https://doi.org/10.1073/pnas.0404817101 Bazzoli, F. (2001). Key points from the revised Maastricht Consensus Report: the impact on general practice. European Journal of Gastroenterology & Hepatology, 13, S3-7. https://europepmc.org/article/med/11686230 Beek, D. V. D., & Craen, A. D. (1999). A systematic review of Helicobacter pylori eradication therapy—the impact of antimicrobial resistance on eradication rates. Alimentary Pharmacology & Therapeutics, 13(8), 1047-1055. https://doi.org/10.1046/j.1365-2036.1999.00555.x Boren, T., Falk, P., Roth, K. A., Larson, G., & Normark, S. (1993). Attachment of Helicobacter pylori to human gastric epithelium mediated by blood group antigens. Science, 262(5141), 1892-1895. Cellini, L., Vecchio, A. D., Candia, M. D., Campli, E. D., Favaro, M., & Donelli, G. (2004). Detection of free and plankton‐associated Helicobacter pylori in seawater. Journal of Applied Microbiology, 97(2), 285-292. https://doi.org/10.1111/j.1365-2672.2004.02307.x Coelho, L. G. V., León-Barúa, R., & Quigley, E. M. (2000). Latin-American consensus conference on Helicobacter https://doi.org/10.37506/v11/i2/2020/ijphrd/195177 https://doi.org/10.37506/v11/i2/2020/ijphrd/195177 https://doi.org/10.1128/IAI.68.7.4155-4168.2000 https://doi.org/10.1128/IAI.68.7.4155-4168.2000 https://doi.org/10.1038/16495 https://doi.org/10.1111/j.1365-2958.2008.06336.x https://doi.org/10.1111/j.1365-2958.2008.06336.x https://doi.org/10.1182/blood-2010-01-261859 https://doi.org/10.1371/journal.ppat.0020110 https://doi.org/10.1371/journal.ppat.0020110 https://doi.org/10.1002/path.2363 https://doi.org/10.1073/pnas.0404817101 https://europepmc.org/article/med/11686230 https://doi.org/10.1046/j.1365-2036.1999.00555.x https://doi.org/10.1111/j.1365-2672.2004.02307.x Haamadi, Risan & AboAlmaali Biomedicine and Chemical Sciences 1(4) (2022), 278-288 286 pylori infection. The American Journal of Gastroenterology, 95(10), 2688. https://doi.org/10.1111/j.1572-0241.2000.03174.x Colbeck, J. C., Hansen, L. M., Fong, J. M., & Solnick, J. V. (2006). Genotypic profile of the outer membrane proteins BabA and BabB in clinical isolates of Helicobacter pylori. Infection and immunity, 74(7), 4375-4378. https://doi.org/10.1128/IAI.00485-06 Dore, M. P., Leandro, G., Realdi, G., Sepulveda, A. R., & Graham, D. Y. (2000). Effect of pretreatment antibiotic resistance to metronidazole and clarithromycin on outcome of Helicobacter pylori therapy. Digestive diseases and sciences, 45(1), 68-76. https://doi.org/10.1023/A:1005457226341 Dubois, A., & Borén, T. (2007). Helicobacter pylori is invasive and it may be a facultative intracellular organism. Cellular microbiology, 9(5), 1108-1116. https://doi.org/10.1111/j.1462-5822.2007.00921.x Falk, P., Roth, K. A., Boren, T., Westblom, T. U., Gordon, J. I., & Normark, S. (1993). An in vitro adherence assay reveals that Helicobacter pylori exhibits cell lineage- specific tropism in the human gastric epithelium. Proceedings of the National Academy of Sciences, 90(5), 2035-2039. https://doi.org/10.1073/pnas.90.5.2035 Fujimoto, S., Ojo, O. O., Arnqvist, A., Wu, J. Y., Odenbreit, S., Haas, R., ... & Yamaoka, Y. (2007). Helicobacter pylori BabA expression, gastric mucosal injury, and clinical outcome. Clinical Gastroenterology and Hepatology, 5(1), 49-58. https://doi.org/10.1016/j.cgh.2006.09.015 Gerhard, M., Lehn, N., Neumayer, N., Borén, T., Rad, R., Schepp, W., ... & Prinz, C. (1999). Clinical relevance of the Helicobacter pylori gene for blood-group antigen- binding adhesin. Proceedings of the National Academy of Sciences, 96(22), 12778-12783. https://doi.org/10.1073/pnas.96.22.12778 Goodwin, A. C., Weinberger, D. M., Ford, C. B., Nelson, J. C., Snider, J. D., Hall, J. D., ... & Forsyth, M. H. (2008). Expression of the Helicobacter pylori adhesin SabA is controlled via phase variation and the ArsRS signal transduction system. Microbiology, 154(8), 2231-2240. https://doi.org/10.1099/mic.0.2007/016055-0 Goodwin, C. S., Armstrong, J. A., Chilvers, T., Peters, M., Collins, M. D., Sly, L., ... & Harper, W. E. (1989). Transfer of Campylobacter pylori and Campylobacter mustelae to Helicobacter gen. nov. as Helicobacter pylori comb. nov. and Helicobacter mustelae comb. nov., respectively. International Journal of Systematic and Evolutionary Microbiology, 39(4), 397-405. https://doi.org/10.1099/00207713-39-4-397 Haamadi, A. A., Risan, M. H., AboAlmaali, H. M., Sayah, H. A., & Abbas, A. H. (2021a). Used of Probiotic Production of Saccharomyces boulardii to Eradication Triple Therapy of Helicobacter pylori Infection. Scientific Journal of Medical Research, 5(18); 40-45. Haamadi, A. A., Risan, M. H., AboAlmaali, H. M., Sayah, H. A., & Abbas, A. H. (2021b). Detection H. pylori Infection by BabA Gene From Clinical Isolate in Karbala City, Iraq. Scientific Journal of Medical Research, 5(17); 29- 35. Hennig, E. E., Allen, J. M., & Cover, T. L. (2006). Multiple chromosomal loci for the babA gene in Helicobacter pylori. Infection and immunity, 74(5), 3046-3051. https://doi.org/10.1128/IAI.74.5.3046-3051.2006 Henriksson S.; Fei Y. Y.; Schmidt A.; Bylund G.; Johansson D. X. and Lebrilla C. et al. (2012). Helicobacter pylori – Multitalented adaptation of binding properties. Analytical Chemistry Journal. 83(16): 6336–6341. Hessey, S. J., Spencer, J., Wyatt, J. I., Sobala, G., Rathbone, B. J., Axon, A. T., & Dixon, M. F. (1990). Bacterial adhesion and disease activity in Helicobacter associated chronic gastritis. Gut, 31(2), 134-138. http://dx.doi.org/10.1136/gut.31.2.134 Hidaka, E., Ota, H., Hidaka, H., Hayama, M., Matsuzawa, K., Akamatsu, T., ... & Katsuyama, T. (2001). Helicobacter pylori and two ultrastructurally distinct layers of gastric mucous cell mucins in the surface mucous gel layer. Gut, 49(4), 474-480. http://dx.doi.org/10.1136/gut.49.4.474 Hojo, M., Miwa, H., Nagahara, A., & Sato, N. (2001). Pooled analysis on the efficacy of the second-line treatment regimens for Helicobacter pylori infection. Scandinavian Journal of Gastroenterology, 36(7), 690-700. https://doi.org/10.1080/00365520116825 IARC Working Group on the Evaluation of Carcinogenic Risks to Humans, International Agency for Research on Cancer, & World Health Organization. (1994). Schistosomes, liver flukes and Helicobacter pylori (Vol. 61). International Agency for Research on Cancer. Ilver, D., Arnqvist, A., Ogren, J., Frick, I. M., Kersulyte, D., Incecik, E. T., ... & Borén, T. (1998). Helicobacter pylori adhesin binding fucosylated histo-blood group antigens revealed by retagging. Science, 279(5349), 373-377. https://doi.org/10.1126/science.279.5349.373 Ishijima, N., Suzuki, M., Ashida, H., Ichikawa, Y., Kanegae, Y., Saito, I., ... & Mimuro, H. (2011). BabA-mediated adherence is a potentiator of the Helicobacter pylori type IV secretion system activity. Journal of Biological Chemistry, 286(28), 25256-25264. https://doi.org/10.1074/jbc.M111.233601 Jain, P., Luo, Z. Q., & Blanke, S. R. (2011). Helicobacter pylori vacuolating cytotoxin A (VacA) engages the mitochondrial fission machinery to induce host cell death. Proceedings of the National Academy of Sciences, 108(38), 16032-16037. https://doi.org/10.1073/pnas.1105175108 Jiménez-Soto, L. F., Kutter, S., Sewald, X., Ertl, C., Weiss, E., Kapp, U., ... & Haas, R. (2009). Helicobacter pylori type IV secretion apparatus exploits β1 integrin in a novel RGD-independent manner. PLoS pathogens, 5(12), e1000684. https://doi.org/10.1371/journal.ppat.1000684 Kawai, M., Furuta, Y., Yahara, K., Tsuru, T., Oshima, K., Handa, N., ... & Kobayashi, I. (2011). Evolution in an oncogenic bacterial species with extreme genome plasticity: Helicobacter pyloriEast Asian genomes. BMC https://doi.org/10.1111/j.1572-0241.2000.03174.x https://doi.org/10.1128/IAI.00485-06 https://doi.org/10.1023/A:1005457226341 https://doi.org/10.1111/j.1462-5822.2007.00921.x https://doi.org/10.1073/pnas.90.5.2035 https://doi.org/10.1016/j.cgh.2006.09.015 https://doi.org/10.1073/pnas.96.22.12778 https://doi.org/10.1099/mic.0.2007/016055-0 https://doi.org/10.1099/00207713-39-4-397 https://doi.org/10.1128/IAI.74.5.3046-3051.2006 http://dx.doi.org/10.1136/gut.31.2.134 http://dx.doi.org/10.1136/gut.49.4.474 https://doi.org/10.1080/00365520116825 https://doi.org/10.1126/science.279.5349.373 https://doi.org/10.1074/jbc.M111.233601 https://doi.org/10.1073/pnas.1105175108 https://doi.org/10.1371/journal.ppat.1000684 Haamadi, Risan & AboAlmaali Biomedicine and Chemical Sciences 1(4) (2022), 278-288 287 microbiology, 11(1), 1-28. https://doi.org/10.1186/1471-2180-11-104 Kawakubo, M., Ito, Y., Okimura, Y., Kobayashi, M., Sakura, K., Kasama, S., ... & Nakayama, J. (2004). Natural antibiotic function of a human gastric mucin against Helicobacter pylori infection. Science, 305(5686), 1003-1006. https://doi.org/10.1126/science.1099250 Kivi, M., Johansson, A. L. V., Reilly, M., & Tindberg, Y. (2005). Helicobacter pylori status in family members as risk factors for infection in children. Epidemiology & Infection, 133(4), 645-652. https://doi.org/10.1017/S0950268805003900 Kwok, T., Zabler, D., Urman, S., Rohde, M., Hartig, R., Wessler, S., ... & Backert, S. (2007). Helicobacter exploits integrin for type IV secretion and kinase activation. Nature, 449(7164), 862-866. https://doi.org/10.1038/nature06187 Laine, L., Chun, D., Stein, C., El-Beblawi, I., Sharma, V., & Chandrasoma, P. (1996). The influence of size or number of biopsies on rapid urease test results: a prospective evaluation. Gastrointestinal endoscopy, 43(1), 49-53. https://doi.org/10.1016/S0016- 5107(96)70260-2 Lam, S. K., & Talley, N. J. (1998). Report of the 1997 Asia Pacific Consensus Conference on the management of Helicobacter pylori infection. Journal of Gastroenterology and Hepatology, 13(1), 1-12. https://doi.org/10.1111/j.1440- 1746.1998.tb00537.x Lee, M., Kemp, J. A., Canning, A., Egan, C., Tataronis, G., & Farraye, F. A. (1999). A randomized controlled trial of an enhanced patient compliance program for Helicobacter pylori therapy. Archives of internal medicine, 159(19), 2312-2316. https://doi.org/10.1001/archinte.159.19.2312 Lind, T., van Zanten, S. V., Unge, P., Spiller, R., Bayerdörffer, E., O'Morain, C., ... & Idström, J. P. (1996). Eradication of Helicobacter pylori using one‐week triple therapies combining omeprazole with two antimicrobials: the MACH I Study. Helicobacter, 1(3), 138-144. https://doi.org/10.1111/j.1523- 5378.1996.tb00027.x Lindén, S., Mahdavi, J., Semino-Mora, C., Olsen, C., Carlstedt, I., Borén, T., & Dubois, A. (2008). Role of ABO secretor status in mucosal innate immunity and H. pylori infection. PLoS pathogens, 4(1), e2. https://doi.org/10.1371/journal.ppat.0040002 Linz, B., Balloux, F., Moodley, Y., Manica, A., Liu, H., Roumagnac, P., ... & Achtman, M. (2007). An African origin for the intimate association between humans and Helicobacter pylori. Nature, 445(7130), 915-918. https://doi.org/10.1038/nature05562 Lu, H., Yamaoka, Y., & Graham, D. Y. (2005). Helicobacter pylori virulence factors: facts and fantasies. Current opinion in gastroenterology, 21(6), 653-659. https://doi.org/10.1097/01.mog.0000181711.04529 .d5 Mahdavi, J., Sondén, B., Hurtig, M., Olfat, F. O., Forsberg, L., Roche, N., ... & Borén, T. (2002). Helicobacter pylori SabA adhesin in persistent infection and chronic inflammation. Science, 297(5581), 573-578. https://doi.org/10.1126/science.1069076 Marshall, B., & Warren, J. R. (1984). Unidentified curved bacilli in the stomach of patients with gastritis and peptic ulceration. The lancet, 323(8390), 1311-1315. https://doi.org/10.1016/S0140-6736(84)91816-6 Mégraud, F., & Lehours, P. (2007). Helicobacter pylori detection and antimicrobial susceptibility testing. Clinical microbiology reviews, 20(2), 280-322. https://doi.org/10.1128/CMR.00033-06 Meyer, J. M., Silliman, N. P., Wang, W., Siepman, N. Y., Sugg, J. E., Morris, D., ... & Hopkins, R. J. (2002). Risk factors for Helicobacter pylori resistance in the United States: the surveillance of H. pylori antimicrobial resistance partnership (SHARP) study, 1993–1999. Annals of internal medicine, 136(1), 13-24. https://doi.org/10.7326/0003-4819-136-1- 200201010-00008 Misiewicz, J. J., Harris, A. W., Bardhan, K. D., Levi, S., O’morain, C., Cooper, B. T., ... & Lansoprazole Helicobacter Study Group. (1997). One week triple therapy for Helicobacter pylori: a multicentre comparative study. Gut, 41(6), 735-739. http://dx.doi.org/10.1136/gut.41.6.735 Necchi, V., Candusso, M. E., Tava, F., Luinetti, O., Ventura, U., Fiocca, R., ... & Solcia, E. (2007). Intracellular, intercellular, and stromal invasion of gastric mucosa, preneoplastic lesions, and cancer by Helicobacter pylori. Gastroenterology, 132(3), 1009- 1023. https://doi.org/10.1053/j.gastro.2007.01.049 Odenbreit, S., Swoboda, K., Barwig, I., Ruhl, S., Borén, T., Koletzko, S., & Haas, R. (2009). Outer membrane protein expression profile in Helicobacter pylori clinical isolates. Infection and immunity, 77(9), 3782-3790. https://doi.org/10.1128/IAI.00364-09 Ohnishi, N., Yuasa, H., Tanaka, S., Sawa, H., Miura, M., Matsui, A., ... & Hatakeyama, M. (2008). Transgenic expression of Helicobacter pylori CagA induces gastrointestinal and hematopoietic neoplasms in mouse. Proceedings of the National Academy of Sciences, 105(3), 1003-1008. https://doi.org/10.1073/pnas.0711183105 Ohno, T., Vallström, A., Rugge, M., Ota, H., Graham, D. Y., Arnqvist, A., & Yamaoka, Y. (2011). Effects of blood group antigen–binding adhesin expression during Helicobacter pylori infection of mongolian gerbils. Journal of Infectious Diseases, 203(5), 726-735. https://doi.org/10.1093/infdis/jiq090 Palframan, S. L., Kwok, T., & Gabriel, K. (2012). Vacuolating cytotoxin A (VacA), a key toxin for Helicobacter pylori pathogenesis. Frontiers in Cellular and Infection Microbiology, 2, 92. https://doi.org/10.3389/fcimb.2012.00092 Parsonnet, J., Shmuely, H., & Haggerty, T. (1999). Fecal and oral shedding of Helicobacter pylori from healthy infected adults. Jama, 282(23), 2240-2245. https://doi.org/10.1186/1471-2180-11-104 https://doi.org/10.1126/science.1099250 https://doi.org/10.1017/S0950268805003900 https://doi.org/10.1038/nature06187 https://doi.org/10.1016/S0016-5107(96)70260-2 https://doi.org/10.1016/S0016-5107(96)70260-2 https://doi.org/10.1111/j.1440-1746.1998.tb00537.x https://doi.org/10.1111/j.1440-1746.1998.tb00537.x https://doi.org/10.1001/archinte.159.19.2312 https://doi.org/10.1111/j.1523-5378.1996.tb00027.x https://doi.org/10.1111/j.1523-5378.1996.tb00027.x https://doi.org/10.1371/journal.ppat.0040002 https://doi.org/10.1038/nature05562 https://doi.org/10.1097/01.mog.0000181711.04529.d5 https://doi.org/10.1097/01.mog.0000181711.04529.d5 https://doi.org/10.1126/science.1069076 https://doi.org/10.1016/S0140-6736(84)91816-6 https://doi.org/10.1128/CMR.00033-06 https://doi.org/10.7326/0003-4819-136-1-200201010-00008 https://doi.org/10.7326/0003-4819-136-1-200201010-00008 http://dx.doi.org/10.1136/gut.41.6.735 https://doi.org/10.1053/j.gastro.2007.01.049 https://doi.org/10.1128/IAI.00364-09 https://doi.org/10.1073/pnas.0711183105 https://doi.org/10.1093/infdis/jiq090 https://doi.org/10.3389/fcimb.2012.00092 Haamadi, Risan & AboAlmaali Biomedicine and Chemical Sciences 1(4) (2022), 278-288 288 https://doi.org/10.1001/jama.282.23.2240 Perri, F., Festa, V., Clemente, R., Villani, M. R., Quitadamo, M., Caruso, N., ... & Andriulli, A. (2001a). Randomized study of two “rescue” therapies for Helicobacter pylori-infected patients after failure of standard triple therapies. The American Journal of Gastroenterology, 96(1), 58-62. https://doi.org/10.1016/S0002-9270(00)02245-0 Perri, F., Villani, M. R., Quitadamo, M., Annese, V., Niro, G. A., & Andriulli, A. (2001). Ranitidine bismuth citrate‐ based triple therapies after failure of the standard ‘Maastricht triple therapy’: a promising alternative to the quadruple therapy?. Alimentary pharmacology & therapeutics, 15(7), 1017-1022. https://doi.org/10.1046/j.1365-2036.2001.01002.x Peterson, W. L., Ciociola, A. A., Sykes, D. L., McSorley, D. J., & Webb, D. D. (1996). Ranitidine bismuth citrate plus clarithromycin is effective for healing duodenal ulcers, eradicating H. pylori and reducing ulcer recurrence. RBC H. pylori Study Group [see comments]. Alimentary pharmacology & therapeutics, 10(3), 251- 261. https://doi.org/10.1111/j.0953- 0673.1996.00251.x Pride, D. T., & Blaser, M. J. (2002). Concerted evolution between duplicated genetic elements in Helicobacter pylori. Journal of molecular biology, 316(3), 629-642. https://doi.org/10.1006/jmbi.2001.5311 Rohde, M., Püls, J., Buhrdorf, R., Fischer, W., & Haas, R. (2003). A novel sheathed surface organelle of the Helicobacter pylori cag type IV secretion system. Molecular microbiology, 49(1), 219-234. https://doi.org/10.1046/j.1365-2958.2003.03549.x Rossum, L. V. (1999). Evaluation of treatment regimens to cure Helicobacter pylori infection—a meta‐analysis. Alimentary pharmacology & therapeutics, 13(7), 857- 864. https://doi.org/10.1046/j.1365- 2036.1999.00542.x Schreiber, S., Konradt, M., Groll, C., Scheid, P., Hanauer, G., Werling, H. O., ... & Suerbaum, S. (2004). The spatial orientation of Helicobacter pylori in the gastric mucus. Proceedings of the National Academy of Sciences, 101(14), 5024-5029. https://doi.org/10.1073/pnas.0308386101 Skoog, E. C., Sjöling, Å., Navabi, N., Holgersson, J., Lundin, S. B., & Lindén, S. K. (2012). Human gastric mucins differently regulate Helicobacter pylori proliferation, gene expression and interactions with host cells. PloS one, 7(5), e36378. https://doi.org/10.1371/journal.pone.0036378 Styer, C. M., Hansen, L. M., Cooke, C. L., Gundersen, A. M., Choi, S. S., Berg, D. E., ... & Solnick, J. V. (2010). Expression of the BabA adhesin during experimental infection with Helicobacter pylori. Infection and Immunity, 78(4), 1593-1600. https://doi.org/10.1128/IAI.01297-09 Suerbaum, S., & Michetti, P. (2002). Helicobacter pylori infection. New England Journal of Medicine, 347(15), 1175-1186. https://doi.org/10.1056/NEJMra020542 Sugimoto, M., Ohno, T., Graham, D. Y., & Yamaoka, Y. (2011). Helicobacter pylori outer membrane proteins on gastric mucosal interleukin 6 and 11 expression in Mongolian gerbils. Journal of gastroenterology and hepatology, 26(11), 1677-1684. https://doi.org/10.1111/j.1440-1746.2011.06817.x Talarico, S., Whitefield, S. E., Fero, J., Haas, R., & Salama, N. R. (2012). Regulation of Helicobacter pylori adherence by gene conversion. Molecular microbiology, 84(6), 1050- 1061. https://doi.org/10.1111/j.1365- 2958.2012.08073.x Tegtmeyer, N., Wessler, S., & Backert, S. (2011). Role of the cag‐pathogenicity island encoded type IV secretion system in Helicobacter pylori pathogenesis. The FEBS journal, 278(8), 1190-1202. https://doi.org/10.1111/j.1742-4658.2011.08035.x Toller, I. M., Neelsen, K. J., Steger, M., Hartung, M. L., Hottiger, M. O., Stucki, M., ... & Müller, A. (2011). Carcinogenic bacterial pathogen Helicobacter pylori triggers DNA double-strand breaks and a DNA damage response in its host cells. Proceedings of the National Academy of Sciences, 108(36), 14944-14949. https://doi.org/10.1073/pnas.1100959108 Wessler, S., & Backert, S. (2008). Molecular mechanisms of epithelial-barrier disruption by Helicobacter pylori. Trends in microbiology, 16(8), 397-405. https://doi.org/10.1016/j.tim.2008.05.005 Weyermann, M., Adler, G., Brenner, H., & Rothenbacher, D. (2006). The mother as source of Helicobacter pylori infection. Epidemiology, 332-334. https://www.jstor.org/stable/20486222 Yamaoka, Y. (2008). Roles of Helicobacter pylori BabA in gastroduodenal pathogenesis. World journal of gastroenterology: WJG, 14(27), 4265. https://doi.org/10.3748%2Fwjg.14.4265 Zanten, S. V. V. (1999). The DU‐MACH study: eradication of Helicobacter pylori and ulcer healing in patients with acute duodenal ulcer using omeprazole based triple therapy. Alimentary Pharmacology & Therapeutics, 13(3), 289-295. https://doi.org/10.1046/j.1365- 2036.1999.00471.x https://doi.org/10.1001/jama.282.23.2240 https://doi.org/10.1016/S0002-9270(00)02245-0 https://doi.org/10.1046/j.1365-2036.2001.01002.x https://doi.org/10.1111/j.0953-0673.1996.00251.x https://doi.org/10.1111/j.0953-0673.1996.00251.x https://doi.org/10.1006/jmbi.2001.5311 https://doi.org/10.1046/j.1365-2958.2003.03549.x https://doi.org/10.1046/j.1365-2036.1999.00542.x https://doi.org/10.1046/j.1365-2036.1999.00542.x https://doi.org/10.1073/pnas.0308386101 https://doi.org/10.1371/journal.pone.0036378 https://doi.org/10.1128/IAI.01297-09 https://doi.org/10.1056/NEJMra020542 https://doi.org/10.1111/j.1440-1746.2011.06817.x https://doi.org/10.1111/j.1365-2958.2012.08073.x https://doi.org/10.1111/j.1365-2958.2012.08073.x https://doi.org/10.1111/j.1742-4658.2011.08035.x https://doi.org/10.1073/pnas.1100959108 https://doi.org/10.1016/j.tim.2008.05.005 https://www.jstor.org/stable/20486222 https://doi.org/10.3748%2Fwjg.14.4265 https://doi.org/10.1046/j.1365-2036.1999.00471.x https://doi.org/10.1046/j.1365-2036.1999.00471.x