Gastric acid
The highest concentration that gastric acid reaches in the stomach is 160 mM in the canaliculi. This is about 3 million times that of arterial blood, but almost exactly isotonic with other bodily fluids. The lowest pH of the secreted acid is 0.8, but the acid is diluted in the stomach lumen to a pH between 1 and 3.
Gut flora
Due to the high acidity of the stomach, most microorganisms cannot survive there. The main bacterial inhabitants of the stomach include: "Streptococcus", "Staphylococcus", "Lactobacillus", "Peptostreptococcus", and types of yeast. "Helicobacter pylori" is a gram-negative spiral bacterium that establishes on gastric mucosa causing chronic gastritis and peptic ulcer disease and is a carcinogen for gastric cancer.