**2. Characteristics of** *H. pylori*

*H. pylori* belongs to the Proteobacteria subdivision, Campylobacterales order, and Helicobacteraceae family. Helicobacter species are divided into two major lineages: the gastric Helicobacter species and the enterohepatic (nongastric) Helicobacter species [9]. *H. pylori* is a spiral, gram-negative, flagellated, microaerophilic, and facultative acidophilic bacterium [1, 5, 11, 12]. Its envelope consists of an inner (cytoplasmic) membrane, periplasm with peptidoglycan, and an outer membrane that consists of phospholipids and lipopolysaccharide [9]. This microorganism is very sensitive to drying and usual disinfectants [12]. It is transmitted via oral–oral and fecal–oral routes [5, 8, 9, 13]. Contamination of water sources is one major cause of transmission [8, 9, 14]. It is reported that 40% of samples of drinking water in Pakistan are contaminated with *H. pylori* [8]. Contamination of drinking water is also reported in 20.3% of samples in Peru. Recent transmission hypothesis has suggested that blowflies and houseflies are responsible as they feed with and breed in fecal material [14]. *H. pylori* extracts nutrients from blood and host cells [5]. The microorganism has extensive genetic diversity resulting in high mutation rates and high recombinant frequency. The virulence factors of *H. pylori* are also affected by this phenomenon and contribute to immune escape and chronic infection [2, 12]. Several methods of DNA rearrangement along with the introduction and deletion of foreign sequences are responsible for genetic diversity [9].

Some factors contributing to *H. pylori* infection are younger age, [4] low socioeconomic status, limited living space, sharing of beds, low parental education level, pollution of daily used water, and history of *H. pylori* infection in family members [4, 8, 13]. Genetic predisposition may play role in the infection of *H. pylori*. People from African and Pacific Islander ancestries have a higher risk for infection despite adjustment for other risk factors [8]. This is supported by another study which reported a higher prevalence in non-whites compared to non-Hispanic whites in the United States. Higher prevalence was even observed in Alaskan natives [10]. A diet containing less vegetables and fruits along with high consumption of fried food is increasing the risk for infection [14]. Another literature states that age and gender are not related to increased risk of infection [13]. Additionally, the effect of smoking and alcohol is uncertain on the incidence of *H. pylori* infection [13, 14].
