Association of Helicobacter pylori cagA Gene with Gastric Cancer and Peptic Ulcer in Saudi Patients
Association of Helicobacter pylori cagA Gene with Gastric Cancer and Peptic Ulcer in Saudi Patients
Journal of Microbiology and Biotechnology. 2015. Jul, 25(7): 1146-1153
Copyright © 2015, The Korean Society For Microbiology And Biotechnology
  • Received : February 03, 2015
  • Accepted : March 12, 2015
  • Published : July 28, 2015
Export by style
Cited by
About the Authors
Taisir Saber
Medical Microbiology & Immunology Department, Faculty of Medicine, Zagazig University, Egypt
Mabrouk M. Ghonaim
Medical Microbiology & Immunology Department, Faculty of Medicine, Menoufia University, Egypt
Amany R. Yousef
Clinical Pathology Department, Faculty of Medicine, Mansoura University, Egypt
Amany Khalifa
Clinical Pathology Department, Faculty of Medicine, Menoufia University, Egypt
Hesham Al Qurashi
Gastroenterology Department, King Abdul-Aziz Specialized Hospital, Taif, Saudi Arabia
Mohammad Shaqhan
Gastroenterology Department, King Abdul-Aziz Specialized Hospital, Taif, Saudi Arabia
Mohammad Samaha
Gastroenterology Department, King Abdul-Aziz Specialized Hospital, Taif, Saudi Arabia

This study was conducted to assess the relationship between occurrence of gastric cancer and peptic ulcer, and the presence of H. pylori cagA gene and anti-CagA IgG, and to estimate the value of these antibodies in detecting infection by cagA gene-positive H. pylori strains in Saudi patients. The study included 180 patients who were subjected to upper gastrointestinal endoscopy in Taif province and Western region of Saudi Arabia (60 gastric cancer, 60 peptic ulcer, and 60 with non-ulcer dyspepsia). Gastric biopsy specimens were obtained and tested for H. pylori infection by rapid urease test and culture. PCR was performed on the isolated strains and biopsy specimens for detection of the cagA gene. Blood samples were collected and tested for CagA IgG by ELISA. H. pylori infection was detected among 72.8% of patients. The cagA gene and anti-CagA IgG were found in 63.4% and 61.8% of H. pylori -infected patients, respectively. They were significantly ( p < 0.01) higher in patients with gastric cancer and peptic ulcer compared with those with non-ulcer dyspepsia. Detection of the CagA IgG was 91.6% sensitive, 89.6% specific, and 90.8% accurate compared with detection of the cagA gene. Its positive and negative predictive values were 93.8% and 86%, respectively. The study showed a significant association between the presence of the cagA gene and gastric cancer and peptic ulcer disease, and between anti-CagA IgG and the cagA gene in Saudi patients. However, a further larger study is required to confirm this finding.
Helicobacter pylori ( H. pylori ) is a clinically important pathogen that colonizes about 50% of the world’s population [4] . Although infection is found worldwide, higher rates have been reported in developing countries compared with developed areas [33] . Oral-oral or fecal-oral transmission occurs in early childhood within families, and frequently leads to lifelong persistent infection [10 , 26] .
Although infected patients may develop chronic active gastritis, most infections are asymptomatic [36 , 46] . Infection increases the risk of peptic ulcer disease (PUD), stomach adenocarcinoma, and lymphoproliferative disease of the stomach [29 , 51] . Therefore, H. pylori was classified as a class I carcinogen in humans by the World Health Organization and International Agency for Research on Cancer [50] .
The clinical outcome of H. pylori infection has been associated with bacterial virulence factors as well as host and environmental factors [32] . Two virulence factors of H. pylori , cytotoxin-associated gene A ( cagA gene) and the vacuolating cytotoxin A gene ( vacA gene), play a major role in determining the clinical outcome of H. pylori infection [9] .
The cagA gene, the first virulence factor detected in H. pylori strains, encodes a protein (CagA protein) that is associated with increased intensity of gastric inflammation and dense neutrophil infiltration [31 , 38] . In addition, the CagA protein frequently induces interleukin-8 (IL8) [23] which plays a crucial role in the inflammatory cell response to infection [13] . The cagA gene, which is not present in every H. pylori strain, is considered to be a marker for a genomic pathogenicity island ( cag -PAI) [12] . It is considered that this gene with others on the island is correlated with more severe clinical outcomes, including PUD and gastric cancer (GC) [35 , 39] .
In contrast to the cagA gene, the vacA gene is present in nearly all H. pylori strains around the world [14] . It has been found that the presence of the cagA gene is strongly correlated with expression of the vacuolating cytotoxin activity [44] . Furthermore, it has been found that most strains possessing CagA also possess the more virulent vacuolating form of VacA [3] . Although H. pylori has a global distribution, geographical differences in the prevalence of cagA status among H. pylori isolates have been reported [2] .
The cagA genotype of H. pylori can be best identified by molecular methods, using either cultured isolates or direct gastric biopsy specimens. However, this requires invasive endoscopy. Therefore, introduction of accurate serological methods to detect specific antibodies to the H. pylori CagA protein would be more suitable for routine clinical use [20] . However, subjects infected with H. pylori strains containing the cagA gene do not always induce serum CagA antibody [45] .Moreover, it has been suggested that host immunological responses to H. pylori may vary in different populations [37] .
This study was designed to detect the prevalence of the cagA genotype in H. pylori -infected Saudi patients with upper gastrointestinal diseases and to investigate its association with severe clinical outcomes, including GC and PUD. Moreover, the study assessed the relationship between cagA genotype and the presence of serum antiCagA antibodies. To the best of our knowledge, this is the first study to examine this relationship in Saudi Arabia.
Materials and Methods
- Subjects
The study included 180 adult Saudi patients recruited from those undergoing upper gastrointestinal endoscopy because of dyspeptic complaints or possible gastric cancer in the Gastroenterology & Endoscopy units of King Abdul Aziz specialized hospital and some other hospitals in Taif province and Western region of Saudi Arabia between October 2012 and October 2014. Of these patients, 60 patients had GC (group I), 60 patients had PUD (group II), and 60 patients had non-ulcer dyspepsia (NUD) (group III). NUD patients were defined as those who have dyspepsia without endoscopic lesions of ulcers and/or malignancies [25] . Patients who received non-steroidal anti-inflammatory drugs, antacids, or antibiotics in the 2 weeks prior to examination were excluded. This study was approved by the ethical committees of the hospitals involved and each patient provided a written informed consent before participation in the study.
- Specimen Collection
Gastric biopsy specimens. After endoscopic examination, gastric biopsy specimens were obtained from the gastric antrum and examined for the presence of H. pylori by the rapid urease test; PyloriTek test kit (Serim Research Corp, USA) and culture. One antral biopsy specimen from each patient was kept in brain heart infusion (BHI) broth (Oxoid, UK) containing 20% glycerol and stored at -70℃ until DNA extraction [43] .
Blood samples. Blood samples were collected from all patients at the time of endoscopy. Sera were separated and stored at -70℃ until tested for detection of the H. pylori CagA IgG antibodies.
- H. pyloriCulture
Gastric biopsy specimens were homogenized and cultured onto H. pylori selective agar (Oxoid, UK). Incubation of the inoculated plates was performed at 37℃ for 4-7 days under microaerophilic conditions using a gas generator kit (CampGen, Oxoid, UK). H. pylori identification was based on colonial and microscopic morphology and confirmed by positive oxidase, catalase, and urease tests. The isolated H. pylori strains were preserved at -70℃ in BHI broth containing 20% glycerol until DNA extraction was performed [17 , 43] .
- DNA Extraction and PCR for Detection ofcagAGene
DNA was extracted from the isolated H. pylori strains in culture-positive cases and from gastric biopsy specimens in culture-negative H. pylori -infected patients (as indicated by a positive rapid urease test). For patients who were positive for H. pylori infection by both rapid urease and culture, DNA extraction and PCR were performed on the isolated strains and the corresponding gastric biopsy specimens. DNA extraction was performed using the QIAamp DNA mini kit (Qiagen, Hilden, Germany), as described by the manufacturer. The extracted DNA was used for detection of the cagA gene by PCR using specific primer sets (forward 5’-AAT ACA CCA ACG CCT CCA AG-3’ and reverse 5’-TTG TTG CCG CTT TTG CTC TC-3’) (Macro Gen, Korea), which were designed to amplify a 400 bp fragment from the cagA gene. PCR was carried out in a final volume of 25 µl containing 12.5 µl of Taq PCR Master Mix (Qiagen), 2 µl (0.5 µg/ µl) of template DNA, 1.0 µl (1 µM) of each primer, and 8.5 µl of PCR-grade distilled water (provided with the Taq PCR Master Mix). Amplification was performed with the following program: an initial denaturation step at 94℃ for 4 min, followed by 35 cycles, which included denaturation at 94℃ for 1 min, primer annealing at 59℃ for 1 min, and extension at 72ºC for 1 min. Finally, an extension step at 72ºC for 10 min was performed. A negative control (without template DNA) was included in each run. The PCR products were separated by electrophoresis using 2% agarose gel run in Tris acetate-EDTA (TAE) buffer and stained with ethidium bromide. The gel was visualized under ultraviolet transillumination. A molecular size marker 100 bp DNA ladder (Cleaver Scientific, UK) was used to determine the size of the bands [8 , 19] .
- Detection ofH. pyloriCagA IgG Antibodies
Detection of H. pylori CagA IgG antibodies was performed for the H. pylori -infected patients using ELISA kits (MyBioSource, San Diego, CA, USA) according to the manufacturer’s instructions. Samples with an antibody index more than 0.9 were considered positive.
- Statistical Analysis
SPSS 16.0 software (SPSS Inc., Chicago, IL, USA) was used to analyze the data. The Chi square (x 2 ), ANOVA test, and odds ratio (OR) were determined. A P -value less than or equal to 5% was considered as significant.
Table 1 demonstrates the demographic characteristics of the studied patients. There was no significant difference regarding age, gender, locality, or socioeconomic status between the group I (GC) and group III (NUD) or between group II (PUD) and group III. H. pylori infection was diagnosed in 131 (72.8%) patients by rapid urease test and culture, where 85 patients (47.2%) were positive by rapid urease test, 6 (3.3%) patients were positive by culture, and 40 (22.2%) patients were positive by both rapid urease test and culture. Table 2 shows the H. pylori infection status among the different studied groups, where 43 (71.6%) GC patients, 46 (76.7%) PUD patients, and 42 (70%) NUD patients were infected by H. pylori .
Demographic characteristics of the studied groups.
PPT Slide
Lager Image
GC: gastric cancer. PUD: peptic ulcer disease. NUD: non-ulcer dyspepsia. aComparison between group I and group III. bComparison between group II and group III.
H. pyloriinfection among the studied groups.
PPT Slide
Lager Image
Positive infection was diagnosed by positive rapid urease test and/or culture. Negative infection was diagnosed when both rapid urease test and culture were negative. There was no significant difference regarding H. pylori status between group I and group III (P1 > 0.05) or between group II and group III (P2 > 0.05) GC: gastric cancer. PUD: peptic ulcer disease. NUD: non-ulcer dyspepsia. aComparison between group I and group III. bComparison between group II and group III.
Detection of the cagA gene in the 131 H. pylori -infected patients showed that it was positive in 83 (63.4%) patients (32 with GC, 33 with PUD, and 18 with NUD) ( Table 3 ). Fig.1 shows three positive cases for the cagA gene in agarose gel electrophoresis. The cagA gene was significantly ( p < 0.01) higher in patients with GC (74.4%) and PUD (71.7%) compared with those with NUD (42.9%). There was no significant difference between detection of the cagA gene in the isolated H. pylori strains (65.2%) and its detection directly in the corresponding biopsy specimens (63%) in culture-positive cases ( Table 4 ).
cagAgene and anti-CagA IgG status amongH. pylori-infected patients in the studied groups.
PPT Slide
Lager Image
cagA gene status was determined in the 131 H. pylori-infected patients. Sera from the 131 H. pylori-infected patients were tested for anti- CagA IgG by ELISA. GC: gastric cancer. PUD: peptic ulcer disease. NUD: non-ulcer dyspepsia. OR: Odds ratio. CI: Confidence Interval. aComparison between group I and group III. bComparison between group II and group III.
PPT Slide
Lager Image
Agarose gel electrophoresis shows 3 positive cases for cagA gene (lanes 2, 5, 7). Lane 1: 100-bp DNA marker, lane 8: negative control.
cagAgene status in the isolatedH. pyloristrains and in the corresponding biopsy specimens.
PPT Slide
Lager Image
The cagA gene was detected by PCR in the 46 isolated H. pylori strains and in the corresponding biopsy specimens.
Table 3 shows that anti-CagA IgG was detected in 81(61.8%) out of 131 patients who were infected with H. pylori . They included 30 patients with GC, 33 patients with PUD, and 18 patients with NUD. It was significantly higher in patients with GC ( P1 < 0.01) and those with PUD ( P2 < 0.01) compared with those with NUD. The relation between presence of CagA IgG by ELISA and presence of the cagA gene by PCR (as a “true” test result) in the H. pylori -infected patients is demonstrated in Table 5 . The sensitivity of CagA IgG was 91.6%; the specificity was 89.6%; the positive predictive value (PPV) was 93.8%; the negative predictive value (NPV) was 86%; and the accuracy was 90.8%.
Evaluation of the role of anti-CagA IgG as a predictor for infection byH. pyloristrains carrying thecagAgene.
PPT Slide
Lager Image
The sensitivity of CagA IgG was 76/83 or 91.6%; the specificity was 43/48 or 89.6%; the positive predictive value (PPV) was 76/81 or 93.8%; the negative predictive value (NPV) was 43/50 or 86%, and the accuracy was 76+43/131 or 90.8%.
In developing countries, most persons harbor H. pylori , where the majority acquires infection during childhood. In developed countries, lower prevalence is found owing to better socioeconomic circumstances [2] .
This study showed that H. pylori infection was diagnosed in 72.8% of the studied patients. The prevalence of infection in our study is comparable to that found in a Saudi study conducted by Abo-Shadi et al. [1] , where H. pylori infection was detected in 64.7% of the gastric biopsy specimens from patients with upper gastrointestinal diseases. The prevalence found in our study lies within the wide range of H. pylori infection (50-80%) reported in Saudi Arabia [5] . In contrast, other studies conducted in some neighboring countries reported lower results, such as in an Iraqi study by Kalaf et al. [25] and a Palestinian study by Essawi et al. [19] , where the prevalence of H. pylori infection among the studied patients was 48.6% and 44%, respectively. On the other hand, 91% of the studied dyspeptic patients were positive for H. pylori in an Egyptian study by Amer et al. [2] . This variability in the prevalence among different studies may be attributed to differences in identification methods, different demographic distribution of the organism among various regions, and previous antibiotic consumption [6 , 11 , 18] .
The prevalence of cagA -positive strains of H. pylori differs in various parts of the world [2] . In this study, the cagA gene was detected in 63.4% of H. pylori -infected patients. This finding agrees with that reported in a recent study conducted in Riyadh, Saudi Arabia (61.8%) by Marie [30] . On the other hand, a higher prevalence of the cagA gene (81.7%) was recently reported in Taif, Saudi Arabia by Kadi et al. [24] ; however, the latter study was carried out on a small sample size (33 patients). Our finding is also comparable to that demonstrated in some other countries such as Tunisia [7] , Egypt [2] , Palestine [19] , and Iran [21] , where the prevalence of the cagA gene was 61.6%, 65.2%, 65.9%, and 68.7%, respectively. However, our result was different from that reported in other countries such as Russia, Turkey, Iraq, Cyprus [22 , 27 , 42] , and East to South Asian countries [15 , 16 , 47] , where the reported prevalence of the cagA gene was 85%, 78%, 39.2%, 42.5%, and 90%, respectively.
This study showed that there was a relationship between the presence of the cagA gene and clinical status, where the gene was significantly higher in patients with GC and PUD than in those with NUD. This result substantiates a role of cagA as a marker for increased virulence of H. pylori . This finding is supported by other reports from Saudi Arabia [24 , 34] , and other developing countries [2 , 25 , 41 , 42] . Moreover, studies from Europe and North America reported a significant correlation between the possession of the cagA gene and the risk of developing atrophic gastritis, PUD, and GC [35] . On the other hand, conflicting results have been reported in other countries such as Tunisia [7] , Iran [21 , 40] , China [49] , and East to South Asian countries [15 , 16 , 47] . These studies showed no significant association between cagA gene and the clinical outcome of H. pylori infection. This discrepancy between the different studies regarding the role of the cagA gene in severe clinical outcomes can be explained by the possible existence of several distinct forms of the cagA gene with an uneven geographic distribution. These differences in cagA genotypes may result in differences in virulence among cagA -positive H. pylori strains; only some forms of the cagA gene may be associated with severe gastroduodenal diseases [52] .
In our study, we found no significant difference between PCR amplification of the cagA gene from H. pylori isolates and from the corresponding biopsy specimens in culturepositive cases. This finding was also reported in other studies and suggests that PCR may have a potential value for studying the cagA gene directly from biopsy specimens, allowing rapid identification of patients at high risk for developing PUD or GC [28 , 43] .
Based on the association of the cagA gene with severe clinical outcomes found in our study and other studies, identification of the cagA -positive H. pylori strains is of great importance for management of patients at risk for developing more severe disease. However, molecular detection of the cagA gene either in cultured strains or directly in the gastric biopsy specimens requires endoscopy, which is an invasive method. On the other hand, serology can be performed on noninvasively collected clinical samples, making it more feasible for routine clinical use and mass screening. Moreover, it provides the potential to make improvements in the management of H. pylori infection in primary care [20 , 37] .However, not all persons infected by cagA -positive H. pylori strains form anti-CagA antibodies [45] . Therefore, it was important to evaluate the reliability of anti-CagA detection as a predictor for infection by H. pylori strains carrying the cagA gene in our study. Our results found that the detection of the CagA IgG is a good indicator for infection by cagA + H. pylori strains, with an accuracy of 90.8%. Our finding is comparable to that reported in other studies [20 , 37] . In contrast, serum CagA antibody was detected in only 43.1–45.5% of Japanese subjects infected by cagA + H. pylori strains [48] .Moreover, in other East-Asian countries, a different CagA seropositivity has been reported despite almost all H. pylori possessing the cagA gene [45] . These conflicting findings may be attributed to the suggestion that host immunologic responses to H. pylori may vary in different populations [37] .
In conclusion, our study provides additional evidence for a significant association between infection by cagA gene-positive strains of H. pylori and severe clinical outcomes, including PUD and GC, in Saudi patients. Additionally, there is a good association between detection of the cagA gene by PCR and detection of the anti-CagA IgG by ELISA. However, this association needs to be confirmed by a further study that includes a large number of patients from different Saudi regions.
This work was funded by the Academic Research Center at Taif University, project number 1-434-2803. Special thanks to Dr. Laila Sh. Dorgham, Professor of community medicine, College of Applied Medical Sciences, Taif University, for her great help in statistical analysis of data.
Abo-Shadi MA , El-Shazly TA , Al-Johani MS 2013 Clinical, endoscopic, pathological and serological findings ofHelicobacter pyloriinfection in Saudi patients with upper gastrointestinal diseases. Br. J. Med. Med. Res. 3 1109 - 1124    DOI : 10.9734/BJMMR/2013/2650
Amer FA , El-Sokkary RH , Elahmady M , Gheith T , Abdelbary EH , Elnagar Y , Abdalla WM 2013 Helicobacter pylorigenotypes among patients in a university hospital in Egypt: identifying the determinant of disease severity. J. Microbiol. Infect. Dis. 3 109 - 115    DOI : 10.5799/ahinjs.02.2013.03.0092
Argent RH , Thomas RJ , Letley DP , Ritting MG , Hardie KR , Atherton JC 2008 Functional association between theHelicobacter pylorivirulence factors VacA and CagA. J. Med. Microbiol. 57 145 - 150    DOI : 10.1099/jmm.0.47465-0
Atherton J 2006 The pathogenesis ofH pylori–induced gastro-duodenal diseases. Annu. Rev. Pathol. 1 63 - 96    DOI : 10.1146/annurev.pathol.1.110304.100125
Ayoola AE , Ageely HM , Gadour MO , Pathak VP 2004 Prevalence ofHelicobacter pyloriinfection among patients with dyspepsia in South-Western Saudi Arabia. Saudi Med. J. 25 1433 - 1438
Bazzoli M , Al-Qurain A , Al-Quorain A 1999 Campylobacter pyloriin Saudi Arabia under upper gastrointestinal endoscopy. Saudi Med. J. 8 516 - 518
Ben Mansour K , Fendri C , Zribi M , Masmoudi A , Labbene M , Fillali A 2010 Prevalence ofHelicobacter pylori vacA,cagA,iceAandoipAgenotypes in Tunisian patients. Ann. Clin. Microbiol. Antimicrob. 9 10 - 16    DOI : 10.1186/1476-0711-9-10
Bindayna KM , Al Baker WA , Botta GA 2006 Detection ofHelicobacter pylori cagAgene in gastric biopsies, clinical isolates and faeces. Indian J. Med. Microbiol. 24 195 - 200
Blaser MJ , Perez-Perez GI , Kleanthous H , Cover TL , Peek RM , Chyou PH 1995 Infection withHelicobacter pyloristrains possessingcagAis associated with an increased risk of developing adenocarcinoma of the stomach. Cancer Res. 55 2111 - 2115
Brown LM 2000 Helicobacter pylori: epidemiology and routes of transmission. Epidemiol. Rev. 22 283 - 297    DOI : 10.1093/oxfordjournals.epirev.a018040
Cabrita J , Oleastro M , Matos R , Manhente A , Cabral J , Barros R 2000 Features and trends inHelicobacter pyloriantibiotic resistance in Lisbon area, Portugal 1990-1999. J. Antimicrob. Chemother. 46 1029 - 1031    DOI : 10.1093/jac/46.6.1029
Catalano M , Matteo M , Barbolla R , Jimenez Vega D , Crespo O , Leanza A 2001 Helicobacter pylori vacAgenotypes,cagAstatus andureA-Bpolymorphism in isolates recovered from an Argentine population. Diagn. Microbiol. Infect. Dis. 41 205 - 210    DOI : 10.1016/S0732-8893(01)00307-8
Censini S , Lange C , Xiang Z , Crabtree JE , Ghiara P , Borodovsky M 1996 CagA pathogenicity island ofHelicobacter pylori, encodes type I-specific and diseaseassociated virulence factors. Proc. Natl. Acad. Sci. USA 93 14648 - 14653    DOI : 10.1073/pnas.93.25.14648
Chen XJ , Yan J , Shen YF 2005 Dominant CagA/VacA genotypes and coinfection frequency ofH. pyloriin peptic ulcer or chronic gastritis patients in Zhejiang Province and correlations among different genotypes, coinfection and severity of the diseases. Chin. Med. J. Engl. 118 460 - 467
Chomvarin C , Namwat W , Chaicumpar K , Mairiang P , Sangchan A , Sripa B 2008 Prevalence ofHelicobacter pylori vacA,cagA,cagE,iceAandbabA2genotypes in dyspeptic patients. Int. J. Infect. Dis. 12 30 - 36    DOI : 10.1016/j.ijid.2007.03.012
Datta S , Chattopadhyay S , Balakrish NG , Mukhopadhyay AK , Hembram J , Berg DE 2003 Virulence genes and neutral DNA markers ofHelicobacter pyloriisolates from different ethnic communities of West Bengal, India. J. Clin. Microbiol. 41 3737 - 3743    DOI : 10.1128/JCM.41.8.3737-3743.2003
Deltenre M , Glupczynski Y , Deprez C , Nyst JF , Burette A , Labbe M 1989 The reliability of urease test, histology and culture in the diagnosis ofCampylobacter pyloriinfection. Scand. J. Gastroenterol. 160(Suppl.) 19 - 24    DOI : 10.3109/00365528909091730
Duck M , Wang Y 2001 Stool antigen assay can effectively screenHelicobacter pyloriinfection. Gastroenterology 5 98 - 103
Essawi T , Hammoudeh W , Sabri I , Sweidan W , Farraj MA 2013 Determination ofHelicobacter pylorivirulence genes in gastric biopsies by PCR. ISRN Gastroenterol. 2013 606258 -    DOI : 10.1155/2013/606258
Figueiredo C , Quint W , Nouhan N , van den Munckhof H , Herbrink P , Scherpenisse J 2001 Assessment ofHelicobacter pylori vacAandcagAgenotypes and host serological response. J. Clin. Microbiol. 39 1339 - 1344    DOI : 10.1128/JCM.39.4.1339-1344.2001
Ghotaslou R , Milani M , Akhi MT , Nahaei MR , Hasani A , Hejazi MS , Meshkini M 2013 Diversity ofHelicobacter pylori cagAandvacAgenes and its relationship with clinical outcomes in Azerbaijan, Iran. Adv. Pharmaceut. Bull. 3 57 - 62
Hussein NR 2010 Helicobacter pyloriand gastric cancer in the Middle East: a new enigma? World J. Gastroenterol. 16 3226 - 3234    DOI : 10.3748/wjg.v16.i26.3226
Jenks PJ , Mégraud F , Labigne A 1998 Clinical outcome after infection withHelicobacter pyloridoes not appear to be reliably predicted by the presence of any of the genes of thecagpathogenicity island. Gut 43 752 - 758    DOI : 10.1136/gut.43.6.752
Kadi RH , Halawani EM , Abdelkader HS 2014 Prevalence ofH. pyloristrains harbouringcagAandiceAvirulence genes in Saudi patients with gastritis and peptic ulcer disease. Microbiol. Discov. 10 -    DOI : 10.7243/2052-6180-2-2
Kalaf EA , Al-Khafaji ZM , Yassen NY , AL-Abbudi FA , Sadwen SN 2013 Study of the cytotoxin-associated gene A (cagAgene) inHelicobacter pyloriusing gastric biopsies of Iraqi patients. Saudi J. Gastroenterol. 19 69 - 74    DOI : 10.4103/1319-3767.108474
Konno M , Fujii N , Yokota S , Sato K , Takahashi M , Sato K 2005 Five year follow-up study of mother-to-child transmission ofHelicobacter pyloriinfection detected by a random amplified polymorphic DNA fingerprinting method. J. Clin. Microbiol. 43 2246 - 2250    DOI : 10.1128/JCM.43.5.2246-2250.2005
Krashias G , Bashiardes S , Potamitou A , Potamitis GS , Christodoulou C 2013 Prevalence ofHelicobacter pyloricagAandvacAgenes in Cypriot patients. J. Infect. Dev. Ctries 7 642 - 650    DOI : 10.3855/jidc.2923
Lage AP , Godfroid E , Fauconnier A , Burette A , Butzler JP , Bollen A , Glupczynski Y 1995 Diagnosis ofHelicobacter pyloriinfection by PCR: comparison with other invasive techniques and detection ofcagAgene in gastric biopsy specimens. J. Clin. Microbiol. 33 2752 - 2756
Lamarque D , Peek RM 2003 Pathogenesis ofHelicobacter pyloriinfection. Helicobacter 8 (Suppl.l) 21 - 30    DOI : 10.1046/j.1523-5378.2003.00166.x
Marie MA 2012 Relationship betweenHelicobacter pylorivirulence genes and clinical outcomes in Saudi patients. J. Korean Med. Sci. 27 190 - 193    DOI : 10.3346/jkms.2012.27.2.190
Martins LC , Corvelo TC , Demachki S , Araujo MT , Assumpcao MB , Vilar SC 2005 Clinical and pathological importance ofvacAallele heterogeneity andcagAstatus in peptic ulcer disease in patients from North Brazil. Mem. Inst. Oswaldo Cruz 100 875 - 881    DOI : 10.1590/S0074-02762005000800009
McGee DJ , Mobley HL 2000 Pathogenesis ofHelicobacter pyloriinfection. Curr. Opin. Gastroenterol. 16 24 - 31    DOI : 10.1097/00001574-200001000-00005
Milani M , Ghotaslou R , Akhi MT , Nahaei MR , Hasani A , Somi MH 2012 The status of antimicrobial resistance ofHelicobacter pyloriin Eastern Azerbaijan, Iran: comparative study according to demographics. J. Infect. Chemother. 18 848 - 852    DOI : 10.1007/s10156-012-0425-4
Momenah AM , Tayeb MT 2007 Helicobacter pyloricagAandiceAgenotypes status and risk of peptic ulcer in Saudi patients. Saudi Med. J. 28 382 - 385
Olivares A , Buadze M , Kutubidze T , Lobjanidze M , Labauri L , Kutubidze R 2006 Prevalence ofHelicobacter pyloriin Georgian patients with dyspepsia. Helicobacter 11 81 - 85    DOI : 10.1111/j.1523-5378.2006.00367.x
Peek RM , Blaser MJ 2002 Helicobacter pyloriand gastrointestinal tract adenocarcinomas. Nat. Rev. Cancer 2 28 - 37    DOI : 10.1038/nrc703
Peters M , Owen RJ , Slater E , Varea R , Teare EL , Saverymuttu S 2001 Genetic diversity in theHelicobacter pylori cagpathogenicity island and effect on expression of anti-CagA serum antibody in UK patients with dyspepsia. J. Clin. Pathol. 54 219 - 223    DOI : 10.1136/jcp.54.3.219
Rizzato C , Torres J , Plummer M , Munoz N , Franceschi S , Camorlinga-Ponce M 2012 Variations inHelicobacter pyloricytotoxin-associated genes and their influence in progression to gastric cancer: implications for prevention. PLoS One 7 e29605 -    DOI : 10.1371/journal.pone.0029605
Rudi J , Rudy A , Maiwald M , Kuck D , Sieg A , Stremmel W 1999 Direct determination ofHelicobacter pylori vacAgenotypes andcagAgene in gastric biopsies and relation to gastrointestinal disease. Am. J. Gastroenterol. 94 1525 - 1531    DOI : 10.1111/j.1572-0241.1999.1138_a.x
Salehi Z , Jelodar M , Rassa M , Ahaki M , Mollasalehi H , Mashayekhi F 2009 Helicobacter pylori cagAstatus and peptic ulcer disease in Iran. Digest. Dis. Sci. 54 608 - 613    DOI : 10.1007/s10620-008-0378-8
Salih AM , Goreal A , Hussein NR , Abdullah SM , Hawrami K , Assafic M 2013 The distribution ofcagAanddupAgenes inHelicobacter pyloristrains in Kurdistan region, Northern Iraq. Ann. Saudi Med. 33 290 - 293
Saribasak H , Salih BA , Yamaoka Y , Sander E 2004 Analysis ofHelicobacter pylorigenotypes and correlation with clinical outcome in Turkey. J. Clin. Microbiol. 42 1648 - 1651    DOI : 10.1128/JCM.42.4.1648-1651.2004
Secka O , Antonio M , Tapgun M , Berg DE , Bottomley C , Thomas V 2011 PCR-based genotyping ofHelicobacter pyloriof Gambian children and adults directly from biopsy specimens and bacterial cultures. Gut Pathog. 3 5 - 11    DOI : 10.1186/1757-4749-3-5
Sharma S , Tynnyry M , Miller G 1995 Interleukin-8 response of gastric epithelial cell lines toHelicobacter pyloristimulationin vitro. Infect. Immunol. 63 1681 - 1687
Shiota S , Matsunari O , Watada M , Yamaoka Y 2010 SerumHelicobacter pyloriCagA antibody as a biomarker for gastric cancer in east-Asian countries. Future Microbiol. 5 1885 - 1893    DOI : 10.2217/fmb.10.135
Suerbaum S , Michetti P 2002 Helicobacter pyloriinfection. N. Engl. J. Med. 347 1175 - 1186    DOI : 10.1056/NEJMra020542
Tan HJ , Rizal AM , Rosmadi MY , Goh KL 2005 Distribution ofHelicobacter pylori cagA,cagEandvacAin different ethnic groups in Kuala Lumpur, Malaysia. J. Gastroenterol. Hepatol. 20 589 - 594    DOI : 10.1111/j.1440-1746.2005.03783.x
Webb P , Crabtree J , Forman D 1999 Gastric cancer, cytotoxin-associated gene A-positiveHelicobacter pylori, and serum pepsinogens: an international study. The Eurogst study group. Gastroenterology 116 269 - 276    DOI : 10.1016/S0016-5085(99)70122-8
Wei G , Chen J , Liu A , Zhang M , Liu X , Liu D 2012 Prevalence ofHelicobacter pylori vacA,cagAandiceAgenotypes and correlation with clinical outcome. Exp. Ther. Med. 4 1039 - 1044
Yamazaki S , Yamakawa A , Okuda T , Ohtani M , Suto H , Ito Y 2005 Distinct diversity ofvacA,cagA, andcagEgenes ofHelicobacter pyloriassociated with peptic ulcer in Japan. J. Clin. Microbiol. 43 3906 - 3916    DOI : 10.1128/JCM.43.8.3906-3916.2005
Yilmaz Ö , Şen N , Küpelioğlu AA , Şimşek İS 2006 Detection ofH. pyloriinfection by ELISA and western blot techniques and evaluation of anti CagA seropositivity in adult Turkish dyspeptic patients. World J. Gastroenterol. 12 5375 - 5378
Zhou J , Zhang J , Xu C , He L 2004 cagAgenotype and variants in ChineseHelicobacter pyloristrains and relationship to gastroduodenal diseases. J. Med. Microbiol. 53 231 - 235    DOI : 10.1099/jmm.0.05366-0