The Stomach

The pH of the gastric contents of the fasting normal human is usually less than three, which is sufficient to kill most commensal bacteria (3). However, during a meal the gastric acid is buffered, allowing bacteria ingested with food to survive at least until the pH falls, and thus permitting a transient gastric microbiota. However, where gastric acid secretion is impaired, bacteria can survive longer and even proliferate in the elevated pH conditions. Reduced gastric acid secretion (hypochlorhydria) occurs naturally with ageing (4) and is common after gastric surgery. Certain diseases such as pernicious anemia and hypogammaglobulinaemia are associated with achlorhydria, which results in the gastric pH rising to seven and above (4). This allows a diverse microbiota with up to 109 organisms per gram to establish, consisting usually of species of salivary bacteria of the genera Streptococcus, Neisseria, Staphylococcus, and Veillonella, although Bacteroides, Lactobacillus and Escherichia species are also found (4). Hypochlorhydria is also common in patients with atrophic gastritis associated with chronic Helicobacter pylori H. pylori infection.

The presence of a gastric microbiota in hypochlorhydric and achlorhydric individuals has potential toxicological sequelae since it increases the probability of xenobiotic metabolism by the bacteria, particularly since the gastric emptying time of such patients may be up to 5 hours (4). It has been suggested that the increased gastric cancer risk of achlorhydric patients is linked to increased formation of N-nitroso compounds (NOC) by their gastric microbiota (5).

Pregnancy And Childbirth

Pregnancy And Childbirth

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