The predominant genotype in strains that were positive for H. pylori
by PCR was the oipA
(90.8%), followed by the cagA
gene (61.6%), and the iceA
1 gene (60.2%), while the iceA
2 was amplified only in 45 strains (16%). Our results were in agreement with other studies conducted in Europe, Central and South America, and East Asia where a higher prevalence (67% or more) of the cagA
genotype was reported [22
]. In Turkey [23
], Korea and Japan, the prevalence of the iceA
1 genotype in patient with duodenal ulcer were respectively 68.8%, 69.8% and 62.5% which is similar to our study, whereas iceA
2 was prevalent in the USA and Columbia [24
]. The already mentioned similitude can be defined by the epidemiological resemblance in these countries.
For the vacA
genotype, and when considering a single combined genotype, our results showed that the vacA
s2 allele was predominant (45.6%) followed by the vacA
s1 allele (23.2%). A study in Kuwait reported that vacA
s1 and s2 types were detected in approximately equal numbers in biopsies obtained from patients of Middle-Eastern origin, while North Africans were predominantly infected with the s2 type [25
The prevalence of cagA
+ strains in Tunisian peptic ulcer and those with gastritis was similar to that shown in the study from South Africa [26
In a previous report by van Doorn et al
(19), an association was found between the iceA
1 allele and peptic ulcer disease. Other studies from Asia were suggesting that vacA
genotypes were not associated with peptic ulcer disease [27
]. These findings may reflect important geographic differences between H. pylori
strains and patients. As reported by van Doorn et al
, H. pylori
genotypes are not uniformly distributed over the world [22
]. When considering the vacA
genes, our results showed that there is a significant difference between the two studied groups (p < 0.001), but, cagA
genes were not associated with gastroduodenal diseases in our study (p > 0.05). The oipA
(HpO638) outer membrane protein expression was linked to severe inflammation and the induction of IL-8 secretion. In one Turkish study, oipA
(HpO638) gene was highly associated with peptic ulcer disease (92.9%) than with gastritis (80.9%) [28
]. In other studies, no difference in prevalence of cagA
genotypes was found between peptic ulcers and other gastroduodenal diseases [29
]. Yamaoka et al
] reported that there was no association between the iceA
status and clinical outcome in studied patients.
In our study, the oipA gene was found in 100% of gastric ulcer. Several studies failed to show a relationship between the gene status and clinical symptoms in several patient populations, this might be due to that patient selection is extremely important and the study group should be sufficiently large and diverse with respect to genotypes and clinical symptoms.
As for age, we have demonstrated that the difference between children and adults was statistically significant about the cagA
genes, but not with the vacA
genes. Regarding the distribution of gene virulent factors according to sex, no difference seen in term of cagA
gene, but the difference was statistically significant among the vacA
genes. In other reported studies, there were no significant differences in frequencies of H. pylori
virulence-associated genes, between children and adults, and the strains from men exhibited genotypes similar to those in women [30
]. Laila FN et al
] have concluded in their study that the presence of certain genotypes was not significantly associated with the age or gender of the patient.
The detection of multiple genotypes implies the presence of multiple strains in a clinical sample. Considering vacA
genes in our study, the presence of multiple H. pylori
strains in a single biopsy specimen was found respectively in 31.4% and 23.8%. Then, when comparing the genetic differences in isolates of H. pylori
from the antrum and the fundus, we determined that patients were infected with two or more strains of different cagA
, and the percentage of discordance was respectively in 9.6%, 4.6%, 8.9% and 8.5%. Consequently, if multiple genotypes are found, this is a strong indication for the presence of multiple strains. It may be speculated that more than one strain may be acquired in childhood, especially in countries with a very high prevalence of H. pylori
, but, it is not known whether multiple strains colonize simultaneously (coinfection) or at different time points (superinfection), and several studies demonstrated that coinfection or superinfection are common [32
]. The co-existence of more than one strain in the same individual may reflect the capacity of H. pylori
to evolve genetic variations during the long-term colonization from childhood [34
], and the dynamics of co-colonization by multiple strains has been studied in animal models [35
]. Since the prevalence of multiple strains colonization is clinically important in our study, there is a clear need to be considered when planning therapeutic strategies to avoid the risk of the emergence of such strains.
The present study showed that patients with peptic ulcer disease and those with gastritis were almost infected similarly by multiple strains of H. pylori. This underlines that the positive associations between H. pylori genotypes and peptic ulcer disease do not imply that patients without ulcer disease cannot be infected with high-risk H. pylori genotypes.
The combination of the distinct vacA, cagA, iceA and oipA genotypes illustrated the mosaic composition of the H. pylori genome. Strains typed as vacA s2/cagA+/iceA+/oipA+ were more prevalent than those typed as vacA s1/cagA+/iceA+/oipA+ and which are associated to severe pathologies.
In conclusion, we have examined the prevalence of vacA, cagA, iceA and oipA genotypes of H. pylori strains clinically isolated in Tunisia. No significant correlation was found between the expression of cagA and iceA genes and the two groups of studied patients, but the difference was statistically significant with the vacA and oipA genes. As for age, the difference between children and adults was statistically significant with the cagA and iceA genes, but not with oipA and vacA genes. Regarding the distribution of virulence genes to sex, the difference was statistically significant among oipA, iceA and vacA genes, but not with cagA gene.
In Tunisia, it is so possible that the high prevalence of infection with virulent factors contributes to the characteristics of H. pylori infection, but not used to discern the risk of developing serious gastroduodenal diseases in the host. Our results showed that Tunisian patients were colonized by one or more strains of H. pylori in relation of presence of vacA m1/m2 and iceA1/iceA2 in the same biopsy, than, the discordance between strains isolated from antrum and fundus was higher, and it is in favour of multicolonization.