Review

Helicobacter pylori: microbiology of a ‘slow’ bacterial infection

Helicobacter pylori (H. pylori) colonize >50% of the entire human population. Generally, H. pylori infect the human stomach in infancy when parietal cells secreting gastric acids, which reduce the survival of H. pylori, are not well matured. Once acquired, the bacterium persists for life. Thus, H. pylori infection reflects sanitary conditions during childhood. >10 studies performed in various Eastern and Western countries as well as two meta-analyses collectively indicated the H. pylori infection rate is significantly lower in patients with multiple sclerosis (MS) than in healthy controls. Thus, the bacterium might be a protective factor for MS, especially in low prevalence countries and younger generations that grew up in the low prevalence era. The protective effects of H. pylori might be explained by the hygiene hypothesis—encountering generic infection early in life facilitates development of the immunoregulatory system, which suppresses overactivity of autoimmune T cells later in life. However, no influence of common childhood infections on MS risk was reported by large MS cohort studies. Direct attenuation of autoreactive Th1 and Th17 cells by H. pylori infection was found in experimental autoimmune encephalomyelitis, an animal model of MS. These observations may underscore the direct protective effects of H. pylori on MS rather than generic infection in childhood. By contrast, several studies reported that H. pylori infection rates are significantly higher in anti-aquaporin-4 (AQP4) antibody-positive neuromyelitis optica spectrum disorder (NMOSD) than in healthy controls. H. pylori strongly activate Th17 cells via the induction of IL-23, resulting in neutrophil mobilization and activation. H. pylori neutrophil-activating protein (NAP) is a major proinflammatory protein responsible for the pathology of H. pylori-related gastric inflammatory diseases. Anti-H. pylori-NAP antibody levels were positively correlated with final EDSS scores and myeloperoxidase levels in anti-AQP4 antibody-positive NMOSD patients. Given that spinal cord lesions of NMOSD are heavily infiltrated with myeloperoxidase-positive neutrophils, H. pylori-NAP, which can be absorbed and presented to the host immune system, may exacerbate NMOSD. Thus, H. pylori infection and its proinflammatory proteins, such as NAP, may contribute to the pathology of anti-AQP4 antibody-related neural damage, by activating neutrophils. It is interesting that two representative demyelinating diseases of the central nervous system are differentially modulated by chronic H. pylori infection. The direct effects of H. pylori infection on MS and NMOSD warrant future studies.

Helicobacter pylori, a Gram-negative microaerophilic bacterium, has a helix-shaped structure. Present in the stomach of healthy individuals, asymptomatic in 50% of the world’s population, H. pylori is a unique bacterium living in an acidic environment (gastric fluid). Its role in gastric ulcers was demonstrated by B Marshall and R Warren in the 1980s (awarded the Nobel Prize in 2005). Helicobacter pylori is responsible for gastro-duodenal ulcers; chronic gastritis, gastric cancer, and adenocarcinoma. Malt gastric lymphoma and few other diseases have also been attributed to H. pylori. Infection is more prevalent in developing countries. Omeprazole (or derivatives) combined with active antibiotics have proven therapeutic efficacy and decreasing incidence in developed countries.

To determine the prevalence of Helicobacter pylori ureA and clarithromycin resistance gene 23S rRNA genotypes among H. pylori in Saudi Arabia.

A total of 100 serum and fecal samples from 70 patients and 30 healthy volunteers, from patients who presented with symptoms suggestive of gastritis or peptic ulcer disease, were taken from the main hospital in the Southern region of Saudi Arabia from September 2010 C.E. to March 2011 C.E. corresponding to Shawwal 1431 A.H. to Rabi Al-Thani 1432 A.H. We cultured the samples for H. pylori and a polymerase chain reaction was carried out to check for the presence or absence of ureA gene and clarithromycin resistance gene 23S rRNA genotypes.

Among the 70 suspected patients, the suspected bacteria isolated from the fecal samples of 60, (85.7%) were positive using the culture techniques. The presence of ureA gene and clarithromycin resistance gene 23S rRNA was determined by using the polymerase chain reaction, Among the 100 fecal specimens, 65 fecal specimens from 70% patients showed positive results to clarithromycin resistance gene 23S rRNA (sensitivity, 93%; Specificity, 100% and Accuracy, 95%), Only 60 fecal specimens were positive with ureA gene (sensitivity, 86%; Specificity, 100% and Accuracy, 90%).

23S rRNA gene was associated with clarithromycin resistance in H. pylori. There was a high prevalence of H. pylori resistance to clarithromycin in Saudi Arabia. H. pylori is a neutrophilic bacteria that has been able to colonize the human stomach by using a variety of acid-adaptive mechanisms as Urease activity that hydrolyzed the Urea producing 2 NH₃ and H₂CO₃.