All the bacteria living inside you would fill a half-gallon jug; there are 10 times more bacterial cells in your body than human cells
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The infestation begins at birth: Babies ingest mouthfuls of bacteria during birthing and pick up plenty more from their mother’s skin and milk—during breast-feeding, the mammary glands become colonized with bacteria. “Our interaction with our mother is the biggest burst of microbes that we get,”
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there are estimated to be more than 500 species living at any one time in an adult intestine, the majority belong to two phyla, the Firmicutes (which include Streptococcus, Clostridium and Staphylococcus), and the Bacteroidetes (which include Flavobacterium).
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probiotics - dietary supplements containing potentially beneficial microbes - have been shown to boost immunity. Not only do gut bacteria “help protect against other disease-causing bacteria that might come from your food and water,” Huffnagle says, “they truly represent another arm of the immune system.”
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But the bacterial body has made another contribution to our humanity - genes. Soon after the Human Genome Project published its preliminary results in 2001, a group of scientists announced that a handful of human genes - the consensus today is around 40 - appear to be bacterial in origin.