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Surviving the Stomach

The stomach acts as a decontamination chamber and its concentrated acid secretions from one of our best barriers against infections. Some factors, however, reduce the effectiveness of the stomach’s assault, thereby increasing the likelihood of a microbe’s successful passage to the intestine.
Pathogens that enter through the digestive tract survive the stomach in one of the following ways.
·         Some protozoa from protective cysts that is resistant to acid destruction. Cyst forms of Entamoeba histolytica, Giardia lamblia and Balantidium coli pass through the stomach unharmed. In the intestine the fragile trophozoites emerge and reproduce.
·         The number of organisms that survive passage through the stomach increases when large doses of a pathogen are ingested within single inoculums. For most pathogens acquired through the digestive tract, the ingested dose that ensures infections is at least 100 million to 1 billion microbes. For pathogens that are highly virulent, however only a few organisms have to arrive at the intestine to establish infection leading to disease. As few as 100 Shigella, for example, can produce severe dysentery.
·         A rapid transit through the stomach shortens the period of exposure to gastric secretions and allows contaminating organisms to escape destruction. In general fluids and semisolids are transported fastest, while meals of high fat content are held I the stomach longer and increase the likelihood that ingested pathogens will be destroyed.
·         The stomach acid may be buffered by the medium in which the microbes are transported. For example neutralization of the acid with sodium bicarbonate (antacid) can decrease the infections dose for cholera from 109 to 105 organisms, a 99.99 percent reduction. Protein in meal also decreases infectious dose by neutralizing stomach acid while occupying the protein digesting enzymes.

Some microbes that cause diseases acquired through the digestive tract do not have to survive the stomach’s acidity. They induce disease by the effects of toxins they form while growing in the contaminated food prior to ingestion.
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