Gastric Microbiota Composition

Stomach is known as sterile organ as it produce acid that is not friendly for bacteria. However, the bile acid’s reflux, gastric peristalsis and mucus layer thickness thought to obstruct the colonies of bacteria in stomach. In addition, saliva contain nitrate and lactobacilli that are present in oral cavity , convert food into nitrates, in stomach they are converted into nitric oxide by gastric juice that is termed as good antimicrobial agent. Hence, due to these aspects along with some technical complexities in the sampling collection for the purpose of analysis plus deficiency of effective diagnostic kits troubled in gastric microbiota study.In 1982, Robin Warren and Barry Marshel discovered Campylobacter pyloridis that removed sterile stomach’s dogma. In 1984 the bacterium campylobacter pyloridis termed as H. pylori. H. pylori use complex bacterial mechanisms by inhabiting and colonizing the gastric mucosa and in terms damages it. Therefore, urease that is formed due to production of ammonia from urea, H. pylori hinders gastric elimination. Ammonia helps bacterium to invade the mucus layer by neutralizing acid. After invading mucus layer, bacterium inhabit epithelium and in turns activates the complex inflammatory response, therefore harms the gastric mucosa that results in chronic gastric in effected people, whereas in less than 1% results in gastric malignancies and peptic ulcer in about 10% people. Before the detection of H. pylori, in 1981, it is being reported by lancet that a huge no of acid-resistant bacterial strains in stomach are visible, some of them are Streptococcus, Neisseria and lactobacillus. But the incidence of these bacteria are not shocking because the stomach face inflammation of bacteria from mouth and also the reflux of bacteria from duodenum. 65% above phylotypes found in stomach that are described as specimen from human oral cavity. However, such bacterial species that are identified in gastric juice is temporary. These temporary bacteria forms colonies for short time period without inhabiting the gastric mucosa whereas H. pylori inhabit there. Hence, the study of gastric juice only, for the bacterial incidence is not effective, sometimes it misjudge the occurrence of bacteria in mucosal layer, whereas Firmicutes, Bacteroidetes and Actinobacteria present in gastric fluid samples, thus  in gastric mucosal samples, Firmicutes is most occurred phyla. With the advancements in culture-independent molecular methods that are based on 16S rRNA genes like FISH and dot-blot hybridization with rRNA-targeted probes, tem- perature gradient gel electrophoresis, and cloning and sequencing of rDNA have helped in the identification as well as  classification of gastrointestinal bacteria. Bik et al. very first time analyzed the gastric mucosa of 23 healthy persons by the udse of small subunit 16S rDNA clone library approach. They find 1056 non-H. pylori clones, 127 phylotypes as well as 5 dominant genera (Streptococcus, Prevotella, Rothia, Fusobacterium and Veillonella). After soime years, scientist analyzed the gastric microbiota of 10 healthy perons, by the use of cloning and sequencing 16S rRNA, and discovered 1223 non-H. pylori clones, 133 phylotypes as well as 5 dominant genera (Streptococcus, Prevotella, Neisseriae, Haemophilus and Porphyromonas).

Engstrand et al.15 in the year 2013, examined the gastric micro- biota of 13 healthy persons by pyrosequencing, iden- tifying 200 phylotypes and 5 dominant genera (Prevotella, Streptococcus, Veillonella, Rothia, Pasturellaceae), but they did not show any difference  by comparing antrum versus body.While, Delgado et al.16 investigated gastric juice and gastric biopsy samples of 12 healthy persons by culturing and pyrosequencing. He came to know that the most occurred genera were Streptococcus, Propionibacterium and Lactobacillus. These studies were based on variety of populations (African- American, Hispanic, Chinese and Europeans) thus, the gastric microbiota at both level, the phyla and genera level, was amazingly show similarity, although with a huge degree of inter-subject variability.

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