1. Introduction
Helicobacter pylori (
Hp) is one of the most important human pathogens.
Hp is a helix shaped, microaerophilic, Gram-negative bacteria. Some strains can form nonculturable coccoid form [
1,
2]. It colonizes and infects gastric epithelial cell surfaces and the overlying gastric mucin, which is a highly specialized niche [
2]. According to the World Health Organization (WHO), more than 50% of the human population is infected [
3], while over 80% of infected individuals are asymptomatic [
4].
Previous studies suggest that
Hp is genetically variable and certain genotypes may be detected only in certain populations [
5,
6]. Several virulence factors contribute to the inflammatory response towards
Hp either by altering host signaling pathways important to maintaining tissue homeostasis in epithelia cells or by differentially stimulating innate immune cells [
3,
7]. Among the different genes involved in
Hp pathogenicity,
glmM (phosphoglucosamine mutase gene) and
cagA (cytotoxin-associated gene A) virulence genes have been demonstrated to be highly sensitive predictors of several clinical outcomes [
2,
3,
8,
9,
10]. In particular, the
glmM gene is highly conserved, has a high degree of sensitivity and specificity [
11], while the
caqA gene is one of the major virulence factors in
Hp responsible for gastric pathology [
12].
Prevalence of
Hp infection varies around the world, and previous studies on obese patients have shown conflicting results: some studies have reported a higher prevalence [
13,
14,
15,
16], while others have shown a decreased prevalence when compared to the general population [
17,
18,
19].
Hp infection is considered to be limiting access to bariatric surgery [
15]. To date, there are no data about its prevalence in obese preoperative bariatric surgery patients in Estonia.
The aim of this study was to determine the prevalence of H. pylori and its virulence genes (cagA and glmM) in the obese patients going into bariatric surgery. We also aimed to reveal the relationship between Hp and clinical data.
3. Discussion
The present study revealed a remarkably high prevalence of both gastritis (96%) and Hp infection (65%) among preoperative bariatric surgery patients, the latter being confirmed by two methods, PCR and histological analysis. Hp virulence genes, caqA and glmM were associated with different forms of chronic gastritis both in the antrum and corpus. Hp was not associated with the demographic data and blood parameters of obese patients.
According to the literature, mostly serology, stool antigen assays and urea breath tests have been used for the detection of
Hp infection in obese patients [
15]. Histological investigation also has excellent sensitivity and specificity, especially when specific immunostaining is used [
15,
20]. Vanek et al. have compared serology and histology and found good accordance between the two methods [
21]. In our study, we also combined two approaches: histology and the detection of
H. pylori virulence genes such as
glmM and
cagA by the polymerase chain reaction (PCR) method.
Among the different genes involved in the pathogenicity of
Hp, the
glmM (phosphoglucosamine mutase gene) and
cagA (cytotoxin-associated gene A) virulence genes have been demonstrated to be highly sensitive predictors of severe clinical outcomes [
2,
3,
9].
CagA is the most-studied virulence factor of
Hp, which is a 120–145 kDa protein encoded on the
cag pathogenicity island (PAI) [
22]. It contains 31 potential coding regions which encodes a type IV secretion system (T4SS) through which
cagA is delivered into host cells [
23,
24,
25]. Phosphorylated or nonphosphorylated
cagA can interact with host proteins that regulate cell growth, cell motility and cell polarity altering host cell signaling. Thus,
cagA can promote cells to accumulate multiple genetic and epigenetic changes involved in gastric carcinogenesis and gastric adenocarcinoma development [
26]. Also, it is highly antigenic, inducing interleukin-8 (IL-8) secretion by gastric epithelial cells [
27]. It is one of the mechanisms involved in forming the neutrophilic infiltration of epithelium and mucous. Such pathological processes can lead to the formation of lymphoid follicles and epithelial damage of varying severity [
8,
28].
The housekeeping
glmM gene encodes a phosphoglucosamine mutase, an enzyme catalyzing the interconversion of glucosamine-6-phosphate into glucosamine-1-phosphate, which is subsequently transformed into
N-acetylglucosamine. This monosaccharide is one of the main cytoplasmic precursors of bacterial cell wall murein and outer membrane lipopolysaccharides. Consequently, the
glmM gene is essential for bacterial cell growth and assists directly with cell wall synthesis. The
glmM gene is highly conserved between strains [
29,
30]. The presence of the
glmM gene in
Hp-positive obese persons has not been described before. One of the advantages of using this gene to identify
Hp is its high sensitivity and specificity, since it has the detection rate of 10 to 100
H. pylori cells, which is significantly better than histology [
31].
Previous studies have shown that the
Hp-containing
cagA gene is associated with the development of chronic active gastritis (AG) [
32], peptic ulceration [
8,
10,
33] and athrophic gastritis with an increased risk of gastric cancer [
34,
35] while the
glmM gene is associated with the development of chronic superficial gastritis as well as intestinal metaplasia (IM), gastric ulcers and gastric dysplasia, and it was less expressed in chronic gastric ulcers and atrophic gastritis [
36,
37]. Our study revealed that both genes were associated with chronic active and atrophic gastritis in the antrum and corpus, while the presence of the
glmM gene was associated with chronic active gastritis in the antrum, which is different from the data of Helaly et al. [
36]. Also, a half of the morbidly obese patients suffered from atrophic gastritis and/or metaplasia in our study, which are the main precursors of gastric cancer. According to Correa’s theory, the formation of gastric cancer is a multistep and multifactorial process where the presence of
Hp infection is one of the main factors. Gastritis begins from superficial gastritis and may progress into atrophic gastritis, metaplasia, dysplasia and gastric cancer [
36]. The majority of studies determining the prevalence of AG and IM around the world touch on the general population, but not morbidly obese patients. The prevalence of AG and IM in Estonian obese patients is quite similar to the data of Korean, Chinese and Japanese rural populations (42.7%, 63.8% and 55.5% for AG, respectively) [
37,
38,
39] while it differs from studies of German (6.0% for AG), Swedish (0.6% for AG) and US rural populations (15.0% for IM) [
40,
41,
42].
Using a combination of two tests, our study determined the prevalence of
Hp in preoperative bariatric patients in Estonia to be 64.7%. To our knowledge, this report is the first to reveal the virulence factors of
Hp among preoperative bariatric patients in Estonia, although
Hp in Estonian obese patients has been detected earlier using the serological method, with a prevalence of 51.7% [
38]. Our study did not include a non-obese control group, but previous studies have revealed the
Hp prevalence in the adult Estonian population to be 69% [
43], which is nearly similar to the present study.
Hp infection has large disparity between developed and developing countries [
39]. Although Estonia belongs to the European countries, the prevalence of
Hp infection is still quite high in comparison to other countries.
According to the previous data, the prevalence of
Hp infection in morbidly obese patients is still controversial. It has been shown to vary from 2.2% in Australia [
42] and 8.7% in Germany [
40] to 85.5% in a Saudi cohort [
41]. The increased prevalence (40.93%) of
Hp infection was found in Chinese patients with higher BMI levels in comparison with lower ones [
44]. At the same time, some studies have shown no correlation [
45,
46] or a negative correlation [
42] between obesity and the prevalence of
Hp infection. A study of the Japanese population has shown lower BMIs in patients with gastritis than in patients without gastritis [
47]. In our study we did not find an association between
Hp and BMI. The question why infected and not infected morbidly obese patients may have similar BMIs, remains to be answered. The knowledge of the pathophysiology between
Hp and obesity is limited due to the complex nature of the organism [
46]. It is possible that many factors such as geographical region and social status can play a role in the pathogenesis of
Hp infection in certain obese patients. A study by Fontana et al. [
48] demonstrated that agonist-stimulated production of interferon-γ (IFN-gamma) and macrophage chemoattractant protein-1 (MCP-1) are significantly suppressed in subjects with obesity. Weight loss completely normalizes the ability of stimulated peripheral blood mononuclear cells (PBMCs) to produce MCP-1 and IFN-gamma. Thus, obese patients have an increased risk of bacterial and viral infections [
48].
Our study did not reveal an association between
Hp and age that is in accordance with that of Helaly et al. [
34]. However, contrary data have been shown by some other studies [
45,
46] where obese patients with
Hp infection were significantly older compared to those without infection. This tendency can be related to alterations in immune system functions during human organism ageing as well as lower hygiene levels during the youth of elderly people.
We found that more than half of
Hp positive obese patients had increased hs-CRP levels in serum, which is in accordance with other data [
49]. In a study of Turkish patients it was demonstrated that serum levels of hs-CRP were significantly reduced in most
Hp positive patients after antibiotic eradication therapy [
50].
A previous animal study has demonstrated that
Hp colonization may decrease fasting blood glucose levels and improve glucose tolerance [
51]. In our study, mean glucose levels tended to be higher in
Hp positive patients, but due to the small sample size this tendency was not statistically significant.
There were a few limitations in our study. Firstly, we did not have a control group for comparison of the prevalence of Hp among the healthy population that may have considerably changed in recent years. Secondly, the current study was limited because of the small sample size (n = 68).